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  • 101.
    Koernig, Andreas
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics.
    Andersson, Nicke
    Linköping University, Department of Management and Engineering, Solid Mechanics.
    Thermo-mechanical fatigue crack propagation in a single-crystal turbine blade2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Simulation of crack growth in the internal cooling system of a blade in a Siemens gas turbine has been studied by inserting and propagating cracks at appropriate locations. The softwares used are ABAQUS and FRANC3D, where the latter supports finite element meshing of a crack and calculation of the stress intensities along the crack front based on the results from an external finite element program. The blade is subjected to thermo-mechanical fatigue and the cracks are grown subjected to in-phase loading conditions.

     

    The material of the blade is STAL15SX, a nickel-base single-crystal superalloy. The <001> crystalline direction is aligned with the loading direction of the blade, while the secondary crystalline directions are varied to examine how it affects the thermo-mechanical crack propagation fatigue life of the blade.

     

    The finite element model is set up using a submodeling technique to reduce the computational time for the simulations. Investigations to validate the submodeling technique are conducted.

     

    From the work it can be concluded that a crack located at a critical location in the cooling lattice reach above the crack propagation target life. Cracks located at noncritical locations have crack propagation lives of a factor 5.2 times the life of the critical crack.

  • 102.
    Korolija, Alexandra
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    FE modeling of bolted joints in structures2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This paper presents the development of a finite element method for modeling fastener joints in aircraft structures. By using connector element in commercial software Abaqus, the finite element method can handle multi-bolt joints and secondary bending. The plates in the joints are modeled with shell elements or solid elements.

    First, a pre-study with linear elastic analyses is performed. The study is focused on the influence of using different connector element stiffness predicted by semi-empirical flexibility equations from the aircraft industry. The influence of using a surface coupling tool is also investigated, and proved to work well for solid models and not so well for shell models, according to a comparison with a benchmark model.

    Second, also in the pre-study, an elasto-plastic analysis and a damage analysis are performed. The elasto-plastic analysis is compared to experiment, but the damage analysis is not compared to any experiment. The damage analysis is only performed to gain more knowledge of the method of modeling finite element damage behavior.

    Finally, the best working FE method developed in the pre-study is used in an analysis of an I-beam with multi-bolt structure and compared to experiments to prove the abilities with the method. One global and one local model of the I-beam structure are used in the analysis, and with the advantage that force-displacement characteristic are taken from the experiment of the local model and assigned as a constitutive behavior to connector elements in the analysis of the global model.

  • 103.
    Kozlov, Vladimir
    et al.
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, Faculty of Science & Engineering.
    Nazarov, S. A.
    St Petersburg State Univ, Russia; Peter Great St Petersburg State Polytech Univ, Russia; Inst Problems Mech Engn RAS, Russia.
    Waves and Radiation Conditions in a Cuspidal Sharpening of Elastic Bodies2018In: Journal of elasticity, ISSN 0374-3535, E-ISSN 1573-2681, Vol. 132, no 1, p. 103-140Article in journal (Refereed)
    Abstract [en]

    Elastic bodies with cuspidal singularities at the surface are known to support wave processes in a finite volume which lead to absorption of elastic and acoustic oscillations (this effect is recognized in the engineering literature as Vibration Black Holes). With a simple argument we will give the complete description of the phenomenon of wave propagation towards the tip of a three-dimensional cusp and provide a formulation of the Mandelstam (energy) radiation conditions based on the calculation of the Umov-Poynting vector of energy transfer. Outside thresholds, in particular, above the lower bound of the continuous spectrum, these conditions coincide with ones due to the traditional Sommerfeld principle but also work at the threshold frequencies where the latter principle cannot indicate the direction of wave propagation. The energy radiation conditions supply the problem with a Fredholm operator of index zero so that a solution is determined up to a trapped mode with a finite elastic energy and exists provided the external loading is orthogonal to these modes. An example of a symmetric cuspidal body is presented which supports an infinite sequence of eigenfrequencies embedded into the continuous spectrum and the corresponding trapped modes with the exponential decay at the cusp tip. We also determine (unitary and symmetric) scattering matrices of two types and derive a criterion for the existence of a trapped mode with the power-low behavior near the tip.

  • 104.
    Krantz, Dino
    Linköping University, Department of Management and Engineering, Fluid and Mechatronic Systems.
    Methodology and vibrational analysis for measurements on a VTOL RAPS2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In this thesis a methodology for measuring vibrations has been produced andinvestigated for APID 60, a rotorcraft in a Vertical Take-off and landing remotelypiloted aircraft system (VTOL RPAS). A comparative study was carried out forthe purpose of identifying the methodology with respect to design modificationscommon to the APID 60. The pilot-study identified experimental modal analysis(EMA) as a feasible part of the methodology for experimentally extracting themodal parameters of a structure. The EMA was performed on the main frameof the APID 60 where an impact hammer test was chosen as the technique forextracting the response data. As a comparison a point mass was added to thestructure to alter the dynamic properties and the test was repeated.The results from the EMA was compared with a modal analysis performednumerically with a calculation software. Comparison of the results from EMAwith the modal analysis performed numerically indicates consistency. This confirmsa good reliability of the methodology produced. However, the structure onwhich the test were preformed is simple in terms of constant structural properties.Further work should therefore investigate whether this methodology of measuringvibrations could be successfully applied to a structure with higher complexity.

  • 105.
    Krishnasamy, Ezhilmathi
    Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Hybrid CPU-GPU Parallel Simulations of 3D Front Propagation2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This master thesis studies GPU-enabled parallel implementations of the 3D Parallel Marching Method (PMM). 3D PMM is aimed at solving the non-linear static Jacobi-Hamilton equations, which has real world applications such as in the study of geological foldings, where each layer of the Earth’s crust is considered as a front propagating over time. Using the parallel computer architectures, fast simulationscan be achieved, leading to less time consumption, quicker understanding of the inner Earth and enables early exploration of oil and gas reserves. Currently 3D PMM is implemented in shared memory architecture using OpenMP Application Programming Interface (API) and the MINT programming model, which translates C code into Compute Unified Device Architecture (CUDA) code for a single Graphical Process Unit (GPU). Parallel architectures have seen rapid growth in recent years, especially GPUs, allowing us to do faster simulations. In this thesis work, a new parallel implementation for 3D PMM has been done to exploit multicore CPU architectures as well as single and multiple GPUs. In a multiple GPU implementation, 3D data isdecomposed into 1D data for each GPU. CUDA streams are used to overlap the computation and communication within the single GPU. Part of the decomposed 3D volume data is kept in the respective GPU to avoid complete data transfer between the GPUs over a number of iterations. In total, there are two kinds of datatransfers that are involved while doing computation in the multiple GPUs: boundary value data transfer and decomposed 3D volume data transfer. The decomposed 3D volume data transfer is optimized between the multiple GPUs by using the peer to peer memory transfer in CUDA. The speedup is shown and compared between shared memory CPUs (E5-2660, 16cores), single GPU (GTX-590, C2050 and K20m) and multiple GPUs. Hand coded CUDA has shown slightly better performance than the Mint translated CUDA, and the multiple GPU implementation showed promising speedup compared to shared memory multicore CPUs and single GPU implementations.

  • 106.
    Krus, Petter
    et al.
    Linköping University, Department of Management and Engineering, Fluid and Mechatronic Systems. Linköping University, Faculty of Science & Engineering.
    Ericson, LiselottLinköping University, Department of Management and Engineering, Fluid and Mechatronic Systems. Linköping University, Faculty of Science & Engineering.Sethson, MagnusLinköping University, Department of Management and Engineering, Fluid and Mechatronic Systems. Linköping University, Faculty of Science & Engineering.
    Proceedings of 15:th Scandinavian International Conference on Fluid Power, June 7-9, 2017, Linköping, Sweden2017Conference proceedings (editor) (Refereed)
    Abstract [en]

    SICFP2017

    This is the proceedings of the 15th Scandinavian International Conference on Fluid Power held at Linköping University in Sweden on 7-9 June 2017. The theme of the conference was “Fluid Power in the Digital Age”. The contributions are well aligned with this theme, and are indeed reflecting the great developments. We are very grateful to the effort put in by the authors to produce such high quality papers, and also to those taking time to review papers to further enhance the quality. The contributions clearly shows that the fluid power industry, and academia, have both challenges as well as opportunities in keeping up with the evolving capabilities provided by the digitalization. It was with great joy to see old and new colleagues and friends attending our conference and the division of Fluid and mechatronic systems, at Linköping University. The conference is a bi-annual event, with alternating localization between Linköping in Sweden and Tampere in Finland. The process of hosting such an event is a great effort for our organization and I would like to thank all those involved in organizing this conference, and wish good luck with the next one to our Finnish colleagues. Thank you!

    Prof. Petter Krus

    Head of Division

    Fluid and Mechatronic Systems

    Review Process

    Each author attending the conference days had the opportunity to select from three different ways of presenting their contribution. Firstly, a reviewed process with at least two international reviewers of each contribution. The process resulted in most cases with feedback from the reviewers with comments spanning everything between diagram legends to scientific methods. Some proposed papers where rejected upon recommendations from reviewers. Secondly contributions where also presented in industry sessions where the review process where internal only by the staff of the division. A third extended abstract presentation format where also presented during the conference.

    This proceedings contain all presented contributions from the reviewed papers in the first section and thereafter the non-reviewed papers in second section. All reviewed papers are marked in the footer by the acceptance date.

  • 107.
    Landin, Tore
    et al.
    Linköping University, Department of Management and Engineering, Machine Design.
    Nilsson, Jesper
    Linköping University, Department of Management and Engineering, Machine Design.
    Förbättring av sidostabilitet på såbill2019Independent thesis Basic level (university diploma), 10,5 credits / 16 HE creditsStudent thesis
    Abstract [en]

    This report presents the work on improving the lateral stability of the seed coulters of Väderstad seed drill model Spirit. The work lasted ten weeks and was carried out at Väderstad AB spring 2019. The basic problem was analyzed with a number of different methods, and tests were carried out both in the field and in the test rig. With the results from these, it was found that the suspension of the seed coulters allowed both torsional and lateral movements at low loads. 

     The work started with a root cause analysis which was then used to produce a requirement specification. This was then used to develop concepts. After evaluation, the best concepts were selected, analyzed, modeled and calculated. When the concepts were deemed to be sufficiently functional, several manufacturing analyses were made to assess the suitability for serial production. 

     Three concepts were developed. One is a final concept that can be mounted directly on existing machines in the form of injection-molded plastic blocks on the seed coulters. One is a concept for future year models were flanges are mounted on the fall of the seed coulters. This concept is available in two parts, either in the form of a welded steel profile or as part of a sand cast reconstruction of the seed coulters. The third and final concept is a reconstruction of the machine's seed coulters with a spring to control the bill pressure. In addition, a method for evaluating the side stability of the seed coulters has been developed. 

     The reason for the Nordic model's problems is that the seed coulters tend to track the grooves of the fertilizer carriers. This can be solved by having the seed coulters support each other in the lateral direction. 

     As a continued work, a more thorough examination of the sand cast flange concept is recommended. This is in line with Väderstad's philosophy of making built to last products. 

  • 108.
    Lantz, Jonas
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    On Aortic Blood Flow Simulations: Scale-Resolved Image-Based CFD2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis focuses on modeling and simulation of the blood flow in the aorta, the largest artery in the human body. It is an accepted fact that abnormal biological and mechanical interactions between the blood flow and the vessel wall are involved in the genesis and progression of cardiovascular diseases. The transport of low-density lipoprotein into the wall has been linked to the initiation of atherosclerosis. The mechanical forces acting on the wall can impede the endothelial cell layer function, which normally acts as a barrier to harmful substances. The wall shear stress (WSS) affects endothelial cell function, and is a direct consequence of the flow field; steady laminar flows are generally considered atheroprotective, while the unsteady turbulent flow could contribute to atherogenesis. Quantification of regions with abnormal wall shear stress is therefore vital in order to understand the initiation and progression of atherosclerosis.However, flow forces such as WSS cannot today be measured with significant accuracy using present clinical measurement techniques. Instead, researches rely on image-based computational modeling and simulation. With the aid of advanced mathematical models it is possible to simulate the blood flow, vessel dynamics, and even biochemical reactions, enabling information and insights that are currently unavailable through other techniques. During the cardiac cycle, the normally laminar aortic blood flow can become unstable and undergo transition to turbulence, at least in pathological cases such as coarctation of the aorta where the vessel is locally narrowed. The coarctation results in the formation of a jet with a high velocity, which will create the transition to turbulent flow. The high velocity will also increase the forces on the vessel wall. Turbulence is generally very difficult to model, requiring advanced mathematical models in order to resolve the flow features. As the flow is highly dependent on geometry, patient-specific representations of the in vivo arterial walls are needed, in order to perform an accurate and reliable simulation. Scale-resolving flow simulations were used to compute the WSS on the aortic wall and resolve the turbulent scales in the complex flow field. In addition to WSS, the turbulent flow before and after surgical intervention in an aortic coarctation was assessed. Numerical results were compared to state-of-the-art magnetic resonance imaging measurements. The results agreed very well, suggesting that that the measurement technique is reliable and could be used as a complement to standard clinical procedures when evaluating the outcome of an intervention.The work described in the thesis deals with patient-specific flows, and is, when possible, validated with experimental measurements. The results provide new insights to turbulent aortic flows, and show that image-based computational modeling and simulation are now ready for clinical practice.

    List of papers
    1. Quantifying Turbulent Wall Shear Stress in a Stenosed Pipe Using Large Eddy Simulation
    Open this publication in new window or tab >>Quantifying Turbulent Wall Shear Stress in a Stenosed Pipe Using Large Eddy Simulation
    2010 (English)In: Journal of Biomechanical Engineering, ISSN 0148-0731, E-ISSN 1528-8951, Vol. 132, no 6Article in journal (Refereed) Published
    Abstract [en]

    Large eddy simulation was applied for flow of Re = 2000 in a stenosed pipe in order to undertake a thorough investigation of the wall shear stress (WSS) in turbulent flow. A decomposition of the WSS into time averaged and fluctuating components is proposed. It was concluded that a scale resolving technique is required to completely describe the WSS pattern in a subject specific vessel model, since the poststenotic region was dominated by large axial and circumferential fluctuations. Three poststenotic regions of different WSS characteristics were identified. The recirculation zone was subject to a time averaged WSS in the retrograde direction and large fluctuations. After reattachment there was an ante grade shear and smaller fluctuations than in the recirculation zone. At the reattachment the fluctuations were the largest, but no direction dominated over time. Due to symmetry the circumferential time average was always zero. Thus, in a blood vessel, the axial fluctuations would affect endothelial cells in a stretched state, whereas the circumferential fluctuations would act in a relaxed direction.

    Place, publisher, year, edition, pages
    American Society Mechanical Engineers, 2010
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-58347 (URN)10.1115/1.4001075 (DOI)000278965500002 ()
    Available from: 2010-08-13 Created: 2010-08-11 Last updated: 2017-12-12
    2. Quantifying turbulent wall shear stress in a subject specific human aorta using large eddy simulation
    Open this publication in new window or tab >>Quantifying turbulent wall shear stress in a subject specific human aorta using large eddy simulation
    2012 (English)In: Medical Engineering and Physics, ISSN 1350-4533, E-ISSN 1873-4030, Vol. 34, no 8, p. 1139-1148Article in journal (Refereed) Published
    Abstract [en]

    In this study, large-eddy simulation (LES) is employed to calculate the disturbed flow field and the wall shear stress (WSS) in a subject specific human aorta. Velocity and geometry measurements using magnetic resonance imaging (MRI) are taken as input to the model to provide accurate boundary conditions and to assure the physiological relevance. In total, 50 consecutive cardiac cycles were simulated from which a phase average was computed to get a statistically reliable result. A decomposition similar to Reynolds decomposition is introduced, where the WSS signal is divided into a pulsating part (due to the mass flow rate) and a fluctuating part (originating from the disturbed flow). Oscillatory shear index (OSI) is plotted against time-averaged WSS in a novel way, and locations on the aortic wall where elevated values existed could easily be found. In general, high and oscillating WSS values were found in the vicinity of the branches in the aortic arch, while low and oscillating WSS were present in the inner curvature of the descending aorta. The decomposition of WSS into a pulsating and a fluctuating part increases the understanding of how WSS affects the aortic wall, which enables both qualitative and quantitative comparisons.

    Place, publisher, year, edition, pages
    Elsevier, 2012
    Keywords
    Human aorta, Atherosclerosis, Wall shear stress, Computational fluid dynamics, Scale resolving turbulence model, Reynolds decomposition
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-84887 (URN)10.1016/j.medengphy.2011.12.002 (DOI)000309028800016 ()
    Note

    Funding Agencies|Swedish research council|VR 2007-4085VR 2010-4282|National Supercomputer Centre (NSC)|SNIC022/09-11|

    Available from: 2012-11-01 Created: 2012-10-26 Last updated: 2017-12-07
    3. Wall shear stress in a subject specific human aorta - Influence of fluid-structure interaction
    Open this publication in new window or tab >>Wall shear stress in a subject specific human aorta - Influence of fluid-structure interaction
    2011 (English)In: International Journal of Applied Mechanics, ISSN 1758-8251, Vol. 3, no 4, p. 759-778Article in journal (Refereed) Published
    Abstract [en]

    Vascular wall shear stress (WSS) has been correlated to the development of atherosclerosis in arteries. As WSS depends on the blood flow dynamics, it is sensitive to pulsatile effects and local changes in geometry. The aim of this study is therefore to investigate if the effect of wall motion changes the WSS or if a rigid wall assumption is sufficient. Magnetic resonance imaging (MRI) was used to acquire subject specific geometry and flow rates in a human aorta, which were used as inputs in numerical models. Both rigid wall models and fluid-structure interaction (FSI) models were considered, and used to calculate the WSS on the aortic wall. A physiological range of different wall stiffnesses in the FSI simulations was used in order to investigate its effect on the flow dynamics. MRI measurements of velocity in the descending aorta were used as validation of the numerical models, and good agreement was achieved. It was found that the influence of wall motion was low on time-averaged WSS and oscillating shear index, but when regarding instantaneous WSS values the e.ect from the wall motion was clearly visible. Therefore, if instantaneous WSS is to be investigated, a FSI simulation should be considered.

    Place, publisher, year, edition, pages
    World Scientific Publishing, 2011
    Keywords
    computational fluid dynamics; wall deformation; windkessel model; pressure wave; magnetic resonance imaging
    National Category
    Applied Mechanics
    Identifiers
    urn:nbn:se:liu:diva-71720 (URN)10.1142/S1758825111001226 (DOI)000299096300006 ()
    Note
    funding agencies|Swedish research council| VR 2007-4085 VR 2010-4282 |National Supercomputer Center (NSC)| SNIC022/09-11 |CMIV||Available from: 2011-11-02 Created: 2011-11-02 Last updated: 2016-03-14
    4. Large eddy simulation of LDL surface concentration in a subject specific human aorta
    Open this publication in new window or tab >>Large eddy simulation of LDL surface concentration in a subject specific human aorta
    2012 (English)In: Journal of Biomechanics, ISSN 0021-9290, E-ISSN 1873-2380, Vol. 45, no 3, p. 537-542Article in journal (Refereed) Published
    Abstract [en]

    The development of atherosclerosis is correlated to the accumulation of lipids in the arterial wall, which, in turn, may be caused by the build-up of low-density lipoproteins (LDL) on the arterial surface. The goal of this study was to model blood flow within a subject specific human aorta, and to study how the LDL surface concentration changed during a cardiac cycle. With measured velocity profiles as boundary conditions, a scale-resolving technique (large eddy simulation, LES) was used to compute the pulsatile blood flow that was in the transitional regime. The relationship between wall shear stress (WSS) and LDL surface concentration was investigated, and it was found that the accumulation of LDL correlated well with WSS. In general, regions of low WSS corresponded to regions of increased LDL concentration and vice versa. The instantaneous LDL values changed significantly during a cardiac cycle; during systole the surface concentration was low due to increased convective fluid transport, while in diastole there was an increased accumulation of LDL on the surface. Therefore, the near-wall velocity was investigated at four representative locations, and it was concluded that in regions with disturbed flow the LDL concentration had significant temporal changes, indicating that LDL accumulation is sensitive to not only the WSS but also near-wall flow.

    Place, publisher, year, edition, pages
    Elsevier, 2012
    Keywords
    Low-density lipoprotein, Wall shear stress, Disturbed flow, Atherosclerosis
    National Category
    Fluid Mechanics and Acoustics
    Identifiers
    urn:nbn:se:liu:diva-72895 (URN)10.1016/j.jbiomech.2011.11.039 (DOI)000300863600019 ()
    Note
    funding agencies|Swedish Research Council| VR 2007-4085 VR 2010-4282 |National Supercomputer Centre (NSC)| SNIC022/09-11 |CMIV||Available from: 2011-12-09 Created: 2011-12-09 Last updated: 2017-12-08
  • 109.
    Lantz, Jonas
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology.
    Ebbers, Tino
    Linköping University, Center for Medical Image Science and Visualization (CMIV). Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart and Medicine Center, Department of Clinical Physiology in Linköping.
    A new method for obtaining high-resolution velocity data from magnetic resonance imaging?2013Conference paper (Other academic)
  • 110.
    Lantz, Jonas
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Ebbers, Tino
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology. Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Health Sciences. Linköping University, Center for Medical Image Science and Visualization (CMIV).
    Engvall, Jan
    Linköping University, Center for Medical Image Science and Visualization (CMIV). Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart and Medicine Center, Department of Clinical Physiology in Linköping.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Numerical and experimental assessment of turbulent kinetic energy in an aortic coarctation2013In: Journal of Biomechanics, ISSN 0021-9290, E-ISSN 1873-2380, Vol. 46, no 11, p. 1851-1858Article in journal (Refereed)
    Abstract [en]

    The turbulent blood flow through an aortic coarctation in a 63-year old female patient was studied experimentally using magnetic resonance imaging (MRI), and numerically using computational fluid dynamics (CFD), before and after catheter intervention. Turbulent kinetic energy (TKE) was computed in the numerical model using large eddy simulation and compared with direct in vivo MRI measurements. Despite the two totally different methods to obtain TKE values, both quantitative and qualitative results agreed very well. The results showed that even though both blood flow rate and Reynolds number increased after intervention, total turbulent kinetic energy levels decreased in the coarctation. Therefore, the use of the Reynolds number alone as a measure of turbulence in cardiovascular flows should be used with caution. Furthermore, the change in flow field and kinetic energy were assessed, and it was found that before intervention a jet formed in the throat of the coarctation, which impacted the arterial wall just downstream the constriction. After intervention the jet was significantly weaker and broke up almost immediately, presumably resulting in less stress on the wall. As there was a good agreement between measurements and numerical results (the increase and decrease of integrated TKE matched measurements almost perfectly while peak values differed by approximately 1 mJ), the CFD results confirmed the MRI measurements while at the same time providing high-resolution details about the flow. Thus, this preliminary study indicates that MR-based TKE measurements might be useful as a diagnostic tool when evaluating intervention outcome, while the detailed numerical results might be useful for further understanding of the flow for treatment planning.

  • 111.
    Lantz, Jonas
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Ebbers, Tino
    Linköping University, Center for Medical Image Science and Visualization, CMIV. Linköping University, Department of Medical and Health Sciences, Physiology. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart and Medicine Centre, Department of Clinical Physiology UHL.
    Engvall, Jan
    Linköping University, Center for Medical Image Science and Visualization, CMIV. Linköping University, Department of Medical and Health Sciences, Clinical Physiology. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart and Medicine Centre, Department of Clinical Physiology UHL.
    Karlsson, Matts
    Linköping University, Center for Medical Image Science and Visualization, CMIV. Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Validation of Turbulent Kinetic Energy in an Aortic Coarctation Before and After Intervention – MRI vs. CFD2013In: J Cardiovasc Magn Reson. 2013; 15(Suppl 1): E46, 2013Conference paper (Other academic)
  • 112.
    Lantz, Jonas
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Ebbers, Tino
    Linköping University, Center for Medical Image Science and Visualization, CMIV. Linköping University, Department of Medical and Health Sciences, Clinical Physiology. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart and Medicine Centre, Department of Clinical Physiology UHL.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Quantifying Turbulent Kinetic Energy in an Aortic Coarctation with Large Eddy Simulation and Magnetic Resonance Imaging2012Conference paper (Refereed)
  • 113.
    Lantz, Jonas
    et al.
    Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Medicine and Health Sciences. Linköping University, Center for Medical Image Science and Visualization (CMIV).
    Henriksson, Lilian
    Linköping University, Center for Medical Image Science and Visualization (CMIV). Region Östergötland, Center for Diagnostics, Department of Radiology in Linköping.
    Persson, Anders
    Linköping University, Center for Medical Image Science and Visualization (CMIV). Linköping University, Department of Medical and Health Sciences, Division of Radiological Sciences. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Center for Diagnostics, Department of Radiology in Linköping.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering. Linköping University, Center for Medical Image Science and Visualization (CMIV).
    Ebbers, Tino
    Linköping University, Center for Medical Image Science and Visualization (CMIV). Linköping University, Department of Medical and Health Sciences, Division of Cardiovascular Medicine. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Heart and Medicine Center, Department of Clinical Physiology in Linköping.
    Importance Of Including Papillary Muscles And Trabeculae In Cardiac Flow Simulations2016In: Proceedings of the 2016 Summer Biomechanics, Bioengineering and Biotransport Conference, Organizing Committee for the 2016 Summer Biomechanics, Bioengineering and Biotransport , 2016Conference paper (Other academic)
  • 114.
    Lantz, Jonas
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Resolving flow and mass transport in a healthy subject-specific aorta using large eddy simulation2012In: Journal of Cardiovascular Magnetic Resonance 2012, 14(Suppl 1), 2012Conference paper (Refereed)
  • 115.
    Lantz, Jonas
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Resolving Low-Density Lipoprotein (LDL) on the Human Aortic Surface Using Large Eddy Simulation2011In: 64th Annual Meeting of the APS Division of Fluid Dynamics, 2011Conference paper (Refereed)
  • 116.
    Lantz, Jonas
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Renner, Johan
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Wall shear stress in a subject specific human aorta - Influence of fluid-structure interaction2011In: International Journal of Applied Mechanics, ISSN 1758-8251, Vol. 3, no 4, p. 759-778Article in journal (Refereed)
    Abstract [en]

    Vascular wall shear stress (WSS) has been correlated to the development of atherosclerosis in arteries. As WSS depends on the blood flow dynamics, it is sensitive to pulsatile effects and local changes in geometry. The aim of this study is therefore to investigate if the effect of wall motion changes the WSS or if a rigid wall assumption is sufficient. Magnetic resonance imaging (MRI) was used to acquire subject specific geometry and flow rates in a human aorta, which were used as inputs in numerical models. Both rigid wall models and fluid-structure interaction (FSI) models were considered, and used to calculate the WSS on the aortic wall. A physiological range of different wall stiffnesses in the FSI simulations was used in order to investigate its effect on the flow dynamics. MRI measurements of velocity in the descending aorta were used as validation of the numerical models, and good agreement was achieved. It was found that the influence of wall motion was low on time-averaged WSS and oscillating shear index, but when regarding instantaneous WSS values the e.ect from the wall motion was clearly visible. Therefore, if instantaneous WSS is to be investigated, a FSI simulation should be considered.

  • 117.
    Larsson, Rikard
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    On Material Modelling of High Strength Steel Sheets2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The work done in this thesis aims at developing and improving material models for use in industrial applications.

    The mechanical behaviour of three advanced high strength steel grades, Docol 600DP, Docol 1200M and HyTens 1000, has been experimentally investigated under various types of deformation, and material models of their behaviour have been developed. The origins of all these material models are experimental findings from physical tests on the materials.

    Sheet metal forming is an important industrial process and is used to produce a wide range of products. The continuously increasing demand on the weight to performance ratio of many products promotes the use of advanced high strength steel. In order to take full advantage of such steel, most product development is done by means of computer aided engineering, CAE. In advanced product development, the use of simulation based design, SBD, is continuously increasing. With SBD, the functionality of a product, as well as its manufacturing process, can be analysed and optimised with a minimum of physical prototype testing. Accurate numerical tools are absolutely necessary with this methodology, and the model of the material behaviour is one important aspect of such tools.

    This thesis consists of an introduction followed by five appended papers. In the first paper, the dual phase Docol 600DP steel and the martensitic Docol 1200M steel were subjected to deformations, both under linear and non-linear strain paths. Plastic anisotropy and hardening were evaluated and modelled using both virgin materials, i.e. as received, and materials which were pre-strained in various material directions.

    In the second paper, the austenitic stainless steel HyTens 1000 was subjected to deformations under various proportional strain paths and strain rates. It was experimentally shown that this material is sensitive both to dynamic and static strain ageing. A constitutive model accounting for these effects was developed, calibrated, implemented in a Finite Element software and, finally, validated on physical test data.

    The third paper concerns the material dispersions in batches of Docol 600DP. A material model was calibrated to a number of material batches of the same steel grade. The paper provides a statistical analysis of the resulting material parameters.

    The fourth paper deals with a simple modelling of distortional hardening. This type of hardening is able to represent the variation of plastic anisotropy during deformation. This is not the case with a regular isotropic hardening, where the anisotropy is fixed during deformation.

    The strain rate effect is an important phenomenon, which often needs to be considered in a material model. In the fifth paper, the strain rate effects in Docol 600DP are investigated and modelled. Furthermore, the strain rate effect on strain localisation is discussed.

    List of papers
    1. A study of high strength steels undergoing non-linear strain paths—Experiments and modelling
    Open this publication in new window or tab >>A study of high strength steels undergoing non-linear strain paths—Experiments and modelling
    2011 (English)In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 211, no 1, p. 121-131Article in journal (Refereed) Published
    Abstract [en]

    This paper presents an evaluation of the constitutive behaviour, including plastic anisotropy and mixed isotropic-kinematic hardening of two high strength steels, Docol 600DP and Docol 1200M, during strain path changes. A series of tensile and shear tests was performed on both virgin and pre-strained materials. The initial anisotropy and work hardening parameters were obtained from tensile tests, shear tests and a bulge test of the virgin material, whereas the kinematic hardening parameters were identified by comparing numerical predictions to experimental results related to the pre-strained materials. Numerical predictions using the obtained parameters agree well with the experimental results, both in the case of proportional, and under non-proportional strain paths.

    Place, publisher, year, edition, pages
    Elsevier, 2011
    Keywords
    Non-linear strain paths, Plastic anisotropy, Mixed isotropic-kinematic hardening, Shear test
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-60772 (URN)10.1016/j.jmatprotec.2010.09.004 (DOI)
    Available from: 2010-12-01 Created: 2010-10-26 Last updated: 2017-12-12
    2. On the modelling of strain ageing in a metastable austenitic stainless steel
    Open this publication in new window or tab >>On the modelling of strain ageing in a metastable austenitic stainless steel
    2012 (English)In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 212, no 1, p. 46-58Article in journal (Refereed) Published
    Abstract [en]

    The plastic hardening of metastable austenitic stainless steel is partly governed by martensitic transformation, the occurrence of serrated plastic flow, and plastic strain ageing phenomena. In this paper an elasto-viscoplastic material model with isotropic distortional plastic hardening is developed. The model accounts for static and dynamic strain ageing as well as the martensitic transformation. An experimental programme has been conducted in order to fit the model parameters to an austenitic stainless steel within the EN 1.4310 standard. The identification of the dynamic strain ageing was based on so called jump tests, where a sudden strain rate increase was shown to result in an instantaneous positive strain rate sensitivity followed by negative steady state strain rate sensitivity. Furthermore, the static strain ageing was identified by unloading tensile test specimens at specified plastic strains and then reloading these specimens after different periods of time. The observed material behaviour in the test situations can be predicted by the developed model. Lastly, the model was validated by predicting the force-displacement relation of the material in a shear test: the prediction agrees well with experimental results.

    Place, publisher, year, edition, pages
    Elsevier, 2012
    Keywords
    Plastic anisotropy; Isotropic-distortional hardening; Portevin-Le Chatelier effect; Dynamic strain ageing; Static strain ageing; Martensitic transformation
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-73731 (URN)10.1016/j.jmatprotec.2011.08.003 (DOI)000297893000008 ()
    Available from: 2012-01-12 Created: 2012-01-12 Last updated: 2017-12-08
    3. An evaluation of the statistics of steel material model parameters
    Open this publication in new window or tab >>An evaluation of the statistics of steel material model parameters
    2012 (English)In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 212, no 6, p. 1288-1297Article in journal (Refereed) Published
    Abstract [en]

    In robustness studies, variations of material properties are often represented by simple assumptions, such as scaling of stress-strain relations, often due to lack of knowledge or deeper understanding of the material physics and the material model applied. By performing material characterisation tests on several batches of a DP600 steel and fitting a phenomenological material model to each batch, this paper studies the dispersion of material model parameters, as well as correlations between both experimental and model parameters. It is concluded that some of the charcterisation tests may be omitted in the future, due to correlations found between parameters. The results may also be applied in a robustness study by inversely using the retrieved statistics to generate reasonable new sets of material model parameters. The methodology presented may be adopted for any other type of material characterisation process.

    Place, publisher, year, edition, pages
    Elsevier, 2012
    Keywords
    Robustness studies, material model parameter variations, dual phase steel
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-70193 (URN)10.1016/j.jmatprotec.2012.01.016 (DOI)000303176900008 ()
    Note
    funding agencies|SFS ProViking project Super Light Steel Structures||Available from: 2011-08-24 Created: 2011-08-24 Last updated: 2017-12-08Bibliographically approved
    4. On isotropic-distortional hardening
    Open this publication in new window or tab >>On isotropic-distortional hardening
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    Isotropic-distortional hardening allows for individual stress-plastic strain relations in different straining directions. Such hardening can be obtained by allowing the parameters in the effective stress function to depend on anisotropy functions of the equivalent plastic strain. A methodology to calibrate these anisotropy functions is proposed in this work, and is demonstrated on an austenitic strainless steel. A high exponent eight parameter effective stress function for plane stress states is utilised. The anisotropy functions are calibrated by the use of experimental data from uniaxial tensile test data in three material directions and a balanced biaxial test. The plastic anisotropy is assumed to vary piecewise linearly with respect to the equivalent plastic strain, and it is evaluated at a finite number of plastic strains. Thus, it is correctly represented at each level of plastic strain included in the evaluation, even if large increments in plastic strain are used in the calibration. It was found that there are at least two sets of anisotropy functions which satisfy the conditions in the calibration procedure. The resulting uniaxial stress-strain relations from the two sets of anisotropy functions in four additional straining directions, not included in the calibration set, were compared to the corresponding experimental data. From this validation, one of the anisotropy function sets could be discarded, whereas the other one gave a good prediction of the stress-strain relations in all the four additional directions.

    Keywords
    Plastic anisotropy, distortional hardening
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-81920 (URN)
    Available from: 2012-09-25 Created: 2012-09-25 Last updated: 2012-09-25Bibliographically approved
    5. Strain rate effects in a high strength dual phase steel
    Open this publication in new window or tab >>Strain rate effects in a high strength dual phase steel
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    This work focuses on strain rate effects in a high strength dual phase steel, DP600. Attention is given to the mathematical formulation of the strain rate sensitivity, and to its influence on the strain at localisation. Both an experimental and a numerical study are presented. In the experimental study, uniaxial and notched tensile tests, as well as shear tests were conducted at various loading rates. Furthermore, strain rate jump tests were conducted in order to further investigate the strain rate sensitivity. It is clearly shown that the material has a positive strain rate sensitivity, and that a multiplicative contribution to the flow stress is a better approximation than an additive one. A material model including a non-linear plastic hardening, a high exponent yield surface, a thermal softening effect and a variety of multiplicative strain rate sensitivity functions is presented and calibrated. This material model is used in finite element simulations of the mechanical tests. The predicted results are in good agreement with the experimental findings. The stabilising effect of the strain rate sensitivity is shown to be important whenever strain localisation becomes an issue in finite element simulations. It is also shown that the strain rate sensitivity index depends on the plastic strain rate, which thus is the case also for the stabilising effect. From a supplementary study, it is concluded that the assumed thermal softening will affect the onset of localisation.

    Keywords
    Strain rate, dual phase steel, plastic instability, notched tensile test, shear test
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-81921 (URN)
    Available from: 2012-09-25 Created: 2012-09-25 Last updated: 2012-09-25Bibliographically approved
  • 118.
    Le Tran, Minh
    Linköping University, Department of Electrical Engineering, Automatic Control.
    Rigid-Body Modelling of Forklift Masts and Mast Sway Simulations2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Reach truck masts are subjected to oscillations, which have significant impacts on the dynamics of the entire vehicle. Mast oscillations can cause undesirable outcomes in extreme situations and therefore it is desirable to be able to predict these outcomes before they occur. A forklift manufacturer in Mjölby initiated a thesis with the intention to obtain a model that can simulate mast sway for situations where oscillations occur. The objective of the thesis was to create a model of Triplex masts and find dependencies between model parameters and variables such as fork height and load.

    The thesis was conducted modelling the mast with a rigid multibody approach where torsion springs and dampers were used between mast parts to simulate mast elasticity. Clearance at the connections were considered and included in the model. The obtained model constitutes of 8 parameters that could be tuned to attain different oscillation characteristics. Parametric optimisation was carried out to find optimal sets of parameters for compliance with sway measurement tests with different load and fork height cases. 

    The thesis has resulted in a model that is able to simulate mast sway with different oscillation characteristics depending on model parameters. Performed parametric optimisation resulted in parameters that reveal useful information about how model parameters depend on load and fork height. The method used for obtaining optimal parameters can likewise be applied to other mast models in order to gain insight into model parameters as functions of load and fork height.

  • 119.
    Leidermark, Daniel
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Crystal plasticity and crack initiation in a single-crystal nickel-base superalloy: Modelling, evaluation and appliations2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this dissertation the work done in the projects KME-410/502 will be presented.The overall objective in these projects is to evaluate and develop tools for designingagainst fatigue in single-crystal nickel-base superalloys in gas turbines. Experimentshave been done on single-crystal nickel-base superalloy specimens in order toinvestigate the mechanical and fatigue behaviour of the material. The constitutivebehaviour has been modelled and veried by FE-simulations of the experiments.Furthermore, the microstructural degradation during long-time ageing has been investigatedwith respect to the material's yield limit. The eect has been includedin the constitutive model by lowering the resulting yield limit. Moreover, the fatiguecrack initiation of a component has been analysed and modelled by using acritical plane approach in combination with a critical distance method. Finally, asan application, the derived single-crystal model was applied to all the individualgrains in a coarse grained specimen to predict the dispersion in fatigue crack initiationlife depending on random grain distributions.

    This thesis is divided into three parts. In the rst part the theoretical framework,based upon continuum mechanics, crystal plasticity, the critical plane approachand the critical distance method, is derived. This framework is then used in thesecond part, which consists of six included papers. Finally, in the third part, detailsof the used numerical procedures are presented.

    List of papers
    1. Room temperature yield behaviour of a single-crystal nickel-base superalloy with tension/compression asymmetry
    Open this publication in new window or tab >>Room temperature yield behaviour of a single-crystal nickel-base superalloy with tension/compression asymmetry
    Show others...
    2009 (English)In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 47, no 2, p. 366-372Article in journal (Refereed) Published
    Abstract [en]

    The constitutive behaviour at room temperature of a single-crystal nickel-base superalloy is presented in a new model. This model is based on crystal plasticity and takes Schmid- as well as non-Schmid stresses, elastic anisotropy and tension/compression asymmetry into account. By comparison with uniaxial tensile and compressive tests, the model is shown to reproduce the real behaviour well, including the tension/compression asymmetry. The model also shows that typically encountered deviations in orientations ofcastings have a non-negligible influence on stiffness and yield limit, which must be taken into account for industrial applications.

    Keywords
    Tension/compression asymmetry, Single-crystal superalloy, Crystal plasticity, Yield surface
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-50547 (URN)10.1016/j.commatsci.2009.08.012 (DOI)
    Available from: 2009-10-12 Created: 2009-10-12 Last updated: 2017-12-12
    2. Tension/Compression asymmetry of a single-crystal superalloy in virgin and degraded condition
    Open this publication in new window or tab >>Tension/Compression asymmetry of a single-crystal superalloy in virgin and degraded condition
    Show others...
    2010 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 58, no 15, p. 4986-4997Article in journal (Refereed) Published
    Abstract [en]

    The mechanical behaviour at room temperature of a single-crystal superalloy exposed to long term ageing at elevated temperature has been investigated, a topic important for the material’s resistance to thermal-mechanical fatigue. Specimens with several different crystallographic orientations were plastically deformed in either tension or compression before and after the long term furnace exposure. While the thermally activated degradation of the microstructure causes a reduction in yield limit of up to 25% for specimens initially deformed in the |001 and |011| directions, none or only moderate reduction was seen for specimens initially deformed along the |111| direction. This can be explained by the strong correlation between yield limit reduction and the amount of γ coarsening. By introducing an isotropic degradation function in a newly developed crystal plasticity model, the constitutive behaviour of both virgin and degraded materials has been described with good agreement with the experimental results.

    Place, publisher, year, edition, pages
    Elsevier, 2010
    Keywords
    Deformation mechanisms, Rafting/Coarsening, Tension/compression asymmetry, Single-crystal superalloy
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-56590 (URN)10.1016/j.actamat.2010.05.032 (DOI)000280570500008 ()
    Available from: 2010-05-25 Created: 2010-05-25 Last updated: 2017-12-12
    3. Fatigue crack initiation in a notched single-crystal superalloy component
    Open this publication in new window or tab >>Fatigue crack initiation in a notched single-crystal superalloy component
    Show others...
    2010 (English)In: Procedia Engineering, ISSN 1877-7058, E-ISSN 1877-7058, Vol. 2, no 1, p. 1067-1075Article in journal (Refereed) Published
    Abstract [en]

    In this paper, the fatigue crack initiation in notched single-crystal test specimens of material MD2 is investigated and analysed. A critical plane approach is adopted, in which the total strain ranges on the discrete slip planes are evaluated. Furthermore, a Coffin-Manson type of expression is used to describe the number of cycles to fatigue crack initiation. This relation is determined from a set of smooth test specimens loaded uniaxially in the [001], [011] and directions at 500 °C with Rε=−1. The numerical procedure is then applied to a series of experiments, in which notched single-crystal test specimens were exposed to uniaxial cyclic loading in the [001] direction at 500 °C with Rε=0.

    Place, publisher, year, edition, pages
    Elsevier, 2010
    Keywords
    Fatigue initiation; Low cycle fatigue; Critical plane approach; Single-crystal superalloy
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-56588 (URN)10.1016/j.proeng.2010.03.115 (DOI)
    Available from: 2010-05-25 Created: 2010-05-25 Last updated: 2017-12-12Bibliographically approved
    4. A combined critical plane and critical distance approach for predicting fatigue crack initiation in notched single-crystal superalloy components
    Open this publication in new window or tab >>A combined critical plane and critical distance approach for predicting fatigue crack initiation in notched single-crystal superalloy components
    2011 (English)In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 33, no 10, p. 1351-1359Article in journal (Refereed) Published
    Abstract [en]

    The fatigue crack initiation in notched single-crystal components of material MD2 is investigated and analysed. A critical plane approach in combination with a critical distance method has been adopted, in which the total shear strain ranges on the discrete crystallographic slip planes are evaluated. To determine the critical distance two approaches were evaluated, a mean value approach and a cycle dependent approach. Furthermore, a Coffin-Manson type of expression (derived from the results of a set of 12 smooth specimens) is used to predict the number of cycles to fatigue crack initiation. The numerical procedure is applied to a series of experiments, in which notched single-crystal components were exposed to uniaxial cyclic loading in the nominal [001] crystal direction at 500 degrees C with R(epsilon) = 0. A good correlation between the experimental results and the simulated results was found.

    Place, publisher, year, edition, pages
    Elsevier, 2011
    Keywords
    Single-crystal superalloy; Fatigue crack initiation; Critical plane approach; Notch correction; Critical distance theory
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-69763 (URN)10.1016/j.ijfatigue.2011.05.009 (DOI)000292795100002 ()
    Available from: 2011-08-10 Created: 2011-08-08 Last updated: 2017-12-08Bibliographically approved
    5. Evaluation of Fatigue Crack Initiation in a Notched Single-crystal Superalloy Component
    Open this publication in new window or tab >>Evaluation of Fatigue Crack Initiation in a Notched Single-crystal Superalloy Component
    Show others...
    2011 (English)In: Procedia Engineering, ISSN 1877-7058, E-ISSN 1877-7058, Vol. 10, p. 619-624Article in journal (Refereed) Published
    Abstract [en]

    The fatigue crack initiation in a notched single-crystal nickel-base superalloy component at 500 °C was investigated and analysed. A critical plane approach in combination with a critical distance method has been adopted, in which the total shear strain ranges on the discrete slip planes are evaluated. Furthermore, a Coffin-Manson type of expression is used to predict the number of cycles to fatigue crack initiation. The experimental test specimens were studied by microscopy to determine on which crystallographic plane the fatigue initiation occurred. A good correlation between the experimental results and the simulated results were found.

    Place, publisher, year, edition, pages
    Elsevier, 2011
    Keywords
    single-crystal superalloy, fatigue crack initiation, critical plane approach, notch correction, critical distance theory
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-70548 (URN)10.1016/j.proeng.2011.04.103 (DOI)
    Available from: 2011-09-12 Created: 2011-09-12 Last updated: 2017-12-08
    6. The effect of random grain distributions on fatigue crack initiation in a notched coarse grained superalloy specimen
    Open this publication in new window or tab >>The effect of random grain distributions on fatigue crack initiation in a notched coarse grained superalloy specimen
    Show others...
    2012 (English)In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 51, no 1, p. 273-280Article in journal (Refereed) Published
    Abstract [en]

    Coarse grained superalloys are of large interest in high temperature applications, and can be found in e.g.gas turbine components, where great care must be given with respect to high temperature fatigue. Due tothe large grain size, the material behaviour at e.g. sharp notches cannot be considered homogeneous. As aconsequence, the fatigue behaviour is likely to expose a large variation. In order to numerically investigatethis variation, a Monte Carlo analysis has been carried out by 100 FE-simulations of notched specimens,where placements and orientations of the grains were randomised. Furthermore, each grain wasmodelled as a unique single-crystal, displaying both anisotropic elastic and plastic behaviour and tension/compression asymmetry. The effect of randomness was investigated by the obtained dispersion infatigue crack initiation life. It was concluded that the fatigue life behaviour of coarse grained nickel-basesuperalloys may show a considerable variation, which cannot be captured by one single deterministicanalysis based on data for a homogenised material. Furthermore, the dispersion is of such a magnitudethat it needs to be taken into account in industrial applications where highly stressed coarse grainedmaterials are used.

    Place, publisher, year, edition, pages
    Elsevier, 2012
    Keywords
    Coarse grained superalloy, Fatigue crack initiation, Critical plane approach, Crystal plasticity, Monte Carlo analysis
    National Category
    Applied Mechanics
    Identifiers
    urn:nbn:se:liu:diva-72092 (URN)10.1016/j.commatsci.2011.07.054 (DOI)000296214300034 ()
    Note
    Funding agencies|Swedish Research Council| 60628701 |Siemens Industrial Turbomachinery AB in Sweden||Swedish Energy Agency via the Research Consortium of Materials Technology for Thermal Energy Processes| KME-502 |National Supercomputer Centre in Linkoping, Sweden||Available from: 2011-11-16 Created: 2011-11-16 Last updated: 2017-12-08Bibliographically approved
  • 120.
    Leidermark, Daniel
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Aspenberg, David
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Gustafsson, David
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Simonsson, Kjell
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    The effect of random grain distributions on fatigue crack initiation in a notched coarse grained superalloy specimen2012In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 51, no 1, p. 273-280Article in journal (Refereed)
    Abstract [en]

    Coarse grained superalloys are of large interest in high temperature applications, and can be found in e.g.gas turbine components, where great care must be given with respect to high temperature fatigue. Due tothe large grain size, the material behaviour at e.g. sharp notches cannot be considered homogeneous. As aconsequence, the fatigue behaviour is likely to expose a large variation. In order to numerically investigatethis variation, a Monte Carlo analysis has been carried out by 100 FE-simulations of notched specimens,where placements and orientations of the grains were randomised. Furthermore, each grain wasmodelled as a unique single-crystal, displaying both anisotropic elastic and plastic behaviour and tension/compression asymmetry. The effect of randomness was investigated by the obtained dispersion infatigue crack initiation life. It was concluded that the fatigue life behaviour of coarse grained nickel-basesuperalloys may show a considerable variation, which cannot be captured by one single deterministicanalysis based on data for a homogenised material. Furthermore, the dispersion is of such a magnitudethat it needs to be taken into account in industrial applications where highly stressed coarse grainedmaterials are used.

  • 121.
    Leidermark, Daniel
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    COMPARATIVE ANALYSIS OF STRESS RELAXATION AND CREEP IN A SINGLE-CRYSTAL SUPERALLOY2016In: PROCEEDINGS OF THE ASME TURBO EXPO: TURBINE TECHNICAL CONFERENCE AND EXPOSITION, 2016, VOL 7A, AMER SOC MECHANICAL ENGINEERS , 2016, no UNSP V07AT28A005Conference paper (Refereed)
    Abstract [en]

    The creep response of the single-crystal nickel-base super alloy MD2 has been investigated in this study. A set of constant load creep experiments was performed loaded in the nominal [001], [011] and [111] crystal orientations. A crystal plasticity. - creep relaxation model, based on thermomechanical fatigue stress relaxation tests, was benchmarked to simulate the creep behaviour. The responses from the model were then compared to the results obtained during the creep tests. From the comparison it could observed that a trend for the [001] crystal orientation is present. A relative creep response between the simulations and experiments could be observed for the different stress levels. At high and increasing stress levels the relative relation is increasing. Under a certain stress level the relative relation is instead increasing for decreasing stress levels. This relative relation arises from the stress relaxation evaluation process, in which the creep parameters are defined, presumably due to the high stress relaxation that is present in the initial time frame. No trend was seen for the [011] and [111] crystal orientations. A discrepancy between the simulations and experiments was still obtained, also related to the high stress relaxation of the initial time frame.

  • 122.
    Leskovec, Martin
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    Method Development for Heat Transfer Predictions in Channel Flows: An efficient CFD approach for ribbed stationary channels2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Gas turbines are today used in numerous industrial and aeronautical applications. To increase the specific power output and efficiency, a high turbine inlet gas temperature is desired. The high temperature leads to the need of cooling critical components in the hot gas path. Siemens Industrial Turbomachinery AB, SIT AB, in Finspång manufactures gas turbines where the internal cooling of critical components is done through serpentine channels. To utilize the cooling air as efficiently as possible, vortex creating objects are placed inside the channel which result in higher heat transfer. To compute the heat transfer in the channel, correlation based approaches that will give a uniform value for an entire channel are often used.

    This thesis contains two parts. First, investigating how an automated CAE process can be developed that is able to be incorporated into the SIT AB CAE process of today and with a future vision of a, basically, "one-click-CFD" approach for non-generic geometries. Secondly, how CFD simulations for predicting heat transfer levels inside the cooling channels with high accuracy and that captures local features of heat transfer can be performed.

    The suggested CAE approach involves the CAD-tool NX for geometry creation and for managing an entire CFD project the ANSYS software Workbench, combined with ANSYS Meshing for generation of computational grid, CFX-pre and CFX for pre-processing and solving and CFD-post for post-processing. This approach is suggested for generic geometries due to the simplicity in incorporating it into existing CAE processes. For the future vision of non-generic geometries, the inhouse developed project manager Concept is suggested. It allows for customized coupling between a broader range of available software tools.

    To validate the CFX model and to investigate how the CFD calculations should be performed, two cases were set up, one where the CFD model and the inhouse code was compared to experimental data of a generic geometry and one where the CFD model and the inhouse code were compared at engine-like conditions. The results for the experimental case resulted in heat transfer coefficients from the CFD model that were 30% off from experimental data, and the inhouse code maximum deviation was 10%. Compared to previous numerical studies this was considered to be of acceptable accuracy, and the location of data extraction points were considered to cause the deviation in the CFD model. For the engine-like case both CFD and inhouse code predicted the heat transfer level as expected. The simulations were performed in steady state mode on automatically generated meshes with the SST-Reattachment turbulence model. The Reynolds number varied from 10 000 to 80 000 and the meshes were around 4-10M elements in size.

  • 123.
    Lind, Malin
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    Josefsson, Karl Johan
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    A CFD Method for Simulation of Gas-Liquid Flow in Cooling Systems: An Eulerian-Eulerian Approach2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    When designing modern engines it is important to construct a cooling system that cools the engine structure efficiently. Within the cooling system there is always a certain amount of air which can accumulate and form air pockets in critical areas, such as the water jacket, which can lead to wall degradation. A Computational Fluid Dynamics (CFD) method in STAR-CCM+ from CD-adapco, was derived at Volvo Cars in order to study the accumulation of air bubbles in the water jacket. The method was derived by investigating and evaluating already existing methods. The method initially considered as the best suited was the Eulerian-Eulerian approach. The method was validated against three simpler geometries where experimental data was available. The Eulerian-Eulerian approach treats both phases, liquid and gas, as continuous phases. The idea with the method is to solve the Navier-Stokes equation, the continuity equation and the energy equation for both phases using the Eulerian approach, therefore called Eulerian-Eulerian. The interaction between the two phases was important to model properly which was done by including several interaction models within STAR-CCM+. By tuning different coefficients, which were investigated by a thorough parameter study, the method resembled the experimental data in a satisfying way. The best suited mesh for these simpler geometries was a directed mesh. However, the mesh in the water jacket was automatically generated by STAR-CCM+ and the simpler cases were therefore validated with an automated mesh as well. To capture the experimental data the convection scheme for volume fraction had to be of second order when simulating with automated mesh. This resulted in convergence issues when implementing the method on the water jacket. Instead first order convection scheme, which did not present as satisfying results as second order, had to be implemented. Simulations of the water jacket were performed with two different velocities, that were 10 m/s and 19 m/s, and different flow split ratios for the three outlets. Air with volume fraction 0.1 was injected at the inlet during the first 0.5 s followed by 0.5-1.1 s of further simulation without injecting air. Increased velocity resulted in increased flow through of gas, whereas no big difference could be seen between the different outlet flow split ratios. At two different zones lower pressure was found which resulted in gas holdup. To be able to validate the results from the water jacket, experiments would be necessary to perform in order to provide experimental data for comparison. Velocity profiles from the derived two-phase method resemble the velocity profiles from the one-phase simulation from Volvo, which indicated that the two-phase method did not affect the solution in a remarkable way. Granted that the zones of lower pressure and gas holdup normally coincides, the pressure field from the one-phase simulation could be directly studied, which would lower the computational costs significantly.

  • 124.
    Lindberg, David
    Linköping University, Department of Management and Engineering. Linköping University, The Institute of Technology.
    MSC Adams modelling of mechanical system in A400M Crew Entrance Door2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Saab Aerostructures has developed the Crew Entrance Door (CED) for Airbus A400M. Airbus has decided some different load cases for which the Crew Entrance Door must be built to withstand without something breaking down.

    The door is maneuvered by a mechanical system and the load cases are essential for the sizing of the components in the mechanical system. Saab has previously used MS Excel to analytically calculate resulting forces in the mechanical system due to external and/or internal loads in the different load cases. This report describes how the mechanical system for A400M Crew Entrance Door instead can be modeled and solved numerically with the computer program MSC Adams/View.

    Creating a model of a mechanical system in MSC Adams/View proved to be easy and fairly quick. The benefit of working with MSC Adams instead of MS Excel is that it is quicker and more user friendly.

    The major differences when comparing results were believed to be an effect of comparing results from a kinematic model with results from a dynamic model. Therefore it is in the Authors opinion that the analytical method to calculate resulting forces with MS Excel can be replaced by numerical calculations with MSC Adams/View. However, apart from calculating reaction forces there are additional post-simulation calculations for which it is perhaps more beneficial to use MS Excel. To do these post-simulation calculations in MS Excel it is easy to use exported results from MSC Adams.

    If Saab Aerostructures decide to start working with MSC Adams/View and if Saab wants geometry to be imported to the model, then an advise from the Author is to have a software installed which can convert step-files (*.stp or *.step) to the MSC Adams preferred file format Parasolid (*.xmt_txt or *.x_t). The software should also be able to repair geometry which will greatly increase mass accuracy.

  • 125.
    Lindbom, Erik
    Linköping University, Department of Management and Engineering, Machine Design.
    Anordning för rengöring avkomponent i mjölkningsrobot: Framtagning av lösning för förbättrad rengöring avspentvättkopp för att motverka bakterietillväxt2017Independent thesis Basic level (degree of Bachelor), 10,5 credits / 16 HE creditsStudent thesis
    Abstract [en]

    This report describes how to make the VMS teat cleaning cup clean itself properly.The purpose is to create a sulotion that make sure the whole cup gets washedduring normal cleaning. The solution should be compatible with earlier versionsof the VMS and will be tested to see if the amount of bacteria decreases.

  • 126.
    Linder, Jonas
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, Faculty of Science & Engineering.
    Indirect System Identification for Unknown Input Problems: With Applications to Ships2017Doctoral thesis, monograph (Other academic)
    Abstract [en]

    System identification is used in engineering sciences to build mathematical models from data. A common issue in system identification problems is that the true inputs to the system are not fully known. In this thesis, existing approaches to unknown input problems are classified and some of their properties are analyzed.

     A new indirect framework is proposed to treat system identification problems with unknown inputs. The effects of the unknown inputs are assumed to be measured through possibly unknown dynamics. Furthermore, the measurements may also be dependent on other known or measured inputs and can in these cases be called indirect input measurements. Typically, these indirect input measurements can arise when a subsystem of a larger system is of interest and only a limited set of sensors is available. Two examples are when it is desired to estimate parts of a mechanical system or parts of a dynamic network without full knowledge of the signals in the system. The input measurements can be used to eliminate the unknown inputs from a mathematical model of the system through algebraic manipulations. The resulting indirect model structure only depends on known and measured signals and can be used to estimate the desired dynamics or properties. The effects of using the input measurements are analyzed in terms of identifiability, consistency and variance properties. It is shown that cancelation of shared dynamics can occur and that the resulting estimation problem is similar to errors-in-variables and closed-loop estimation problems because of the noisy inputs used in the model. In fact, the indirect framework unifies a number of already existing system identification problems that are contained as special cases.

    For completeness, an instrumental variable method is proposed as one possibility for estimating the indirect model. It is shown that multiple datasets can be used to overcome certain identifiability issues and two approaches, the multi-stage and the joint identification approach, are suggested to utilize multiple datasets for estimation of models. Furthermore, the benefits of using the indirect model in filtering and for control synthesis are briefly discussed. 

    To show the applicability, the framework is applied to the roll dynamics of a ship for tracking of the loading conditions. The roll dynamics is very sensitive to changes in these conditions and a worst-case scenario is that the ship will capsize.  It is assumed that only motion measurements from an inertial measurement unit (IMU) together with measurements of the rudder angle are available. The true inputs are thus not available, but the measurements from the IMU can be used to form an indirect model from a well-established ship model. It is shown that only a subset of the unknown parameters can be estimated simultaneously. Data was collected in experiments with a scale ship model in a basin and the joint identification approach was selected for this application due to the properties of the model. The approach was applied to the collected data and gave promising results.

  • 127.
    Lindström, Stefan B
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Föreläsningar i mekanik: statik och dynamik2019Book (Other academic)
    Abstract [sv]

    Föreläsningar i mekanik: statik och dynamik är lämplig för grundkurser i mekanik på civilingenjörsprogram. Den ger en koncis och formell beskrivning av mekanikens teoretiska ramverk. Ett särdrag hos denna lärobok är terorins tydliga indelning i postulat, definitioner och satser med rigorösa härledningar. Läsaren finner stöd i rikliga illustrationer och en korsreferens för varje härledningssteg. För att stärka studenternas duglighet i problemlösning understryks vikten av korrekt utförda friläggningsdiagram.

  • 128.
    Lindström, Stefan B
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Lectures on engineering mechanics: statics and dynamics2019Book (Other academic)
    Abstract [en]

    Lectures on Engineering Mechanics: Statics and Dynamics is suitable for Bachelor's level education at schools of engineering with an academic profile. It gives a concise and formal account of the theoretical framework of elementary Engineering Mechanics.

    A distinguishing feature of this textbook is that its content is consistently structured into postulates, definitions and theorems, with rigorous derivations. The reader finds support in a wealth of illustrations and a cross-reference for each deduction. This textbook underscores the importance of properly drawn free-body diagrams to enhance the problem-solving skills of students.

  • 129.
    Lindström, Stefan
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Stålhand, Jonas
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Klarbring, Anders
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Modeling of the mechanobiological adaptation in muscular arteries2017In: European journal of mechanics. A, Solids, ISSN 0997-7538, E-ISSN 1873-7285, Vol. 64, p. 165-177Article in journal (Refereed)
    Abstract [en]

    The growth and remodeling of arteries, as controlled by the local stress state and the sensory input from the endothelial cells of the artery wall, is given a novel theoretical framework incorporating the active behavior of vascular smooth muscle. We show that local sensory input maps uniquely to the ratio between a target arterial wall cross-section area corresponding to homeostatic conditions and the current arterial wall area. A growth law is formulated by taking the production rates of individual constituents of the arterial wall to be functions of this target-to-current wall area ratio. We find that a minimum active stress response of vascular smooth muscle is necessary to achieve stable adaptation of the artery wall to dynamic flow conditions. With a sufficient active stress alteration in response to stretch, stable growth toward a homeostatic state can be observed for finite step changes or ramp changes in the transmural pressure or the flow rate. (C) 2017 Elsevier Masson SAS. All rights reserved.

  • 130.
    Llamas, Xavier
    et al.
    Linköping University, Department of Electrical Engineering, Vehicular Systems. Linköping University, Faculty of Science & Engineering.
    Eriksson, Lars
    Linköping University, Department of Electrical Engineering, Vehicular Systems. Linköping University, Faculty of Science & Engineering.
    Parameterizing Compact and Extensible Compressor Models Using Orthogonal Distance Minimization2017In: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 139, no 1, p. 012601-1-012601-10, article id GTP-15-1569Article in journal (Refereed)
    Abstract [en]

    A complete and compact control-oriented compressor model consisting of a mass flow submodel and an efficiency submodel is described. The final application of the model is a complete two-stroke mean value engine model (MVEM) which requires simulating the compressor operating at the low-flow and low-pressure ratio area. The model is based on previous research done for automotive-size compressors, and it is shown to be general enough to adapt well to the characteristics of the marine-size compressors. A physics-based efficiency model allows, together with the mass flow model, extrapolating to low-pressure ratios. The complexity of the model makes its parameterization a difficult task; hence, a method to efficiently estimate the 19 model parameters is proposed. The method computes analytic model gradients and uses them to minimize the orthogonal distances between the modeled speed lines (SpLs) and the measured points. The results of the parameter estimation are tested against nine different standard marine-size maps showing good agreement with the measured data. Furthermore, the results also show the importance of estimating the parameters of the mass flow and efficiency submodels at the same time to obtain an accurate model. The extrapolation capabilities to low-load regions are also tested using low-load measurements from an automotive-size compressor. It is shown that the model follows the measured efficiency trend down to low loads.

  • 131.
    Lokharu, Evgeniy
    Linköping University, Department of Mathematics, Mathematics and Applied Mathematics. Linköping University, Faculty of Science & Engineering.
    Small-amplitude steady water waves with vorticity2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The problem of describing two-dimensional traveling water waves is considered. The water region is of finite depth and the interface between the region and the air is given by the graph of a function. We assume the flow to be incompressible and neglect the effects of surface tension. However we assume the flow to be rotational so that the vorticity distribution is a given function depending on the values of the stream function of the flow. The presence of vorticity increases the complexity of the problem and also leads to a wider class of solutions.

    First we study unidirectional waves with vorticity and verify the Benjamin-Lighthill conjecture for flows whose Bernoulli constant is close to the critical one. For this purpose it is shown that every wave, whose slope is bounded by a fixed constant, is either a Stokes or a solitary wave. It is proved that the whole set of these waves is uniquely parametrised (up to translation) by the flow force which varies between its values for the supercritical and subcritical shear flows of constant depth. We also study large-amplitude unidirectional waves for which we prove bounds for the free-surface profile and for Bernoulli’s constant.

    Second, we consider small-amplitude waves over flows with counter currents. Such flows admit layers, where the fluid flows in different directions. In this case we prove that the initial nonlinear free-boundary problem can be reduced to a finite-dimensional Hamiltonian system with a stable equilibrium point corresponding to a uniform stream. As an application of this result, we prove the existence of non-symmetric wave profiles. Furthermore, using a different method, we prove the existence of periodic waves with an arbitrary number of crests per period.

    List of papers
    1. On bounds and non-existence in the problem of steady waves with vorticity
    Open this publication in new window or tab >>On bounds and non-existence in the problem of steady waves with vorticity
    2015 (English)In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 765, no R1Article in journal (Refereed) Published
    Abstract [en]

    For the problem describing steady gravity waves with vorticity on a two-dimensional unidirectional flow of finite depth the following results are obtained. (i) Bounds are found for the free-surface profile and for Bernoullis constant. (ii) If only one parallel shear flow exists for a given value of Bernoullis constant, then there are no wave solutions provided the vorticity distribution is subject to a certain condition.

    Place, publisher, year, edition, pages
    Cambridge University Press (CUP): STM Journals, 2015
    Keywords
    surface gravity waves; waves/free-surface flows
    National Category
    Mathematics
    Identifiers
    urn:nbn:se:liu:diva-114417 (URN)10.1017/jfm.2014.747 (DOI)000348130700001 ()
    Note

    Funding Agencies|Swedish Research Council; G.S. Magnusons Foundation of the Royal Swedish Academy of Sciences; Linkoping University

    Available from: 2015-03-02 Created: 2015-02-20 Last updated: 2017-12-04
  • 132.
    Loukil, Mohamed
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering. RISE SICOMP, Broderna Ugglas Gata,Hus 208B, S-58188 Linkoping, Sweden.
    Varna, Janis
    Lulea Univ Technol, Sweden.
    Crack face sliding displacement (CSD) as an input in exact GLOB-LOC expressions for in-plane elastic constants of symmetric damaged laminates2019In: International journal of damage mechanics, ISSN 1056-7895, E-ISSN 1530-7921, article id UNSP 1056789519866000Article in journal (Refereed)
    Abstract [en]

    The crack opening and crack sliding displacements of both faces of an intralaminar crack are the main parameters defining the significance of each crack in laminate stiffness degradation, according to the previously published GLOB-LOC approach for symmetric laminates with an arbitrary number of cracks in all plies. In the exact stiffness expressions of this approach, the crack density is always multiplied by crack opening displacement and crack sliding displacement. The dependence of crack opening displacement on geometrical and elastic parameters of adjacent plies was studied previously and described by simple fitting functions. The crack sliding displacement has been analyzed for low-crack densities only and the proposed finite element method-based fitting expressions are oversimplified not including the out-of-plane ply stiffness effects. Based on finite element method analysis, more accurate expressions for so-called non-interactive cracks are suggested in the presented article. For the first time the shear stress perturbations are analyzed and interaction functions are presented with the feature that they always lead to slightly conservative predictions. The presented simple fitting functions, when used in the GLOB-LOC model, give predictions that are in a good agreement with finite element method results and with experimental data for laminates with damaged off-axis plies in cases when crack face sliding is of importance. The significance of including crack sliding displacement in stiffness predictions is demonstrated.

  • 133.
    Lund Ohlsson, Marie
    et al.
    Mid Sweden University, Sundsvall, Sweden.
    Laaksonen, Marko S.
    Mid Sweden University, Östersund.Sweden.
    Holmberg, Joakim
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Evaulation of two sitting positions in Cross-Country Sit-Skiing2016In: Abstract book of the 7th International Congress on Science and skiing, 2016Conference paper (Other academic)
    Abstract [en]

    INTRODUCTION In cross-country sit-skiing (CCSS) athletes with reduced trunk control mainly sit with their knees higher than the hips (KH) to increase trunk stability. To improve the spine curvature by reducing kyphosis a new sitting position was created where the knees are lower than the hips by help of a forward trunk support (KL). The aim of this study was to evaluate the new KL position and compare it to KH in terms of physiological and biomechanical measurements as well as musculoskeletal simulations. METHODS Five abled-bodied female cross-country skiers (62.6±8.1kg, 1.67±0.05m) performed two sets of tests; one in each sitting position on a skiing ergometer (ThoraxTrainer A/S, Denmark). Each test comprised a 30s all-out test (AO), an incremental submaximal test (4 to 6 x 3 min, SUB1-SUB6) and a maximal time-trial test of 3 min (MAX). During SUB and MAX external power and kinematics were measured. Metabolic rates (MR) were calculated from oxygen consumption and lactate concentrations. The AnyBody Modelling system (AMS 6.0, Anybody Technology A/S, Denmark) were used to simulate full-body musculoskeletal models over 4 poling cycles of SUB2, SUB4 and MAX. From the simulations muscular metabolic rate (mMR) and musculo-skeletal efficiency (ME) were computed (Holmberg et al., 2013). RESULTS &amp; DISCUSSION The performance (W/kg) was higher in KH (p &lt; 0.01) in both AO (24%) and MAX (32%). KL had more flexed knee, more extended hip and less kyphosis in trunk, while KH had larger range of motion (ROM) in hip and larger flexion and ROM in spine at SUB4 and MAX. Gross efficiency (GE) was higher in KH than KL. The total MR and ratio of anaerobic MR to total MR were higher in KL at SUB3 and SUB4. Simulations showed that 4 subjects had higher ME in KH for both SUB4 and MAX, though no statistical significance were observed. mMR were higher for KL at SUB2 and SUB4 but it was higher for KH at MAX. The ratio of mMR in body parts to total mMR showed higher ratio for KL in arm-shoulders (6.7-9.1%) and higher ratio for KH in trunk (3.7-4.6%) and hip-legs (3.0-4.6%). CONCLUSION The physiological results were comparable to others (Lajunen, 2014 &amp; Verellen et al, 2012) and the simulation results were novel by showing how the motion of the trunk contributes to the total metabolic rate. KH position showed higher performance and GE while the KL position indicated higher mMR for arm-shoulders, and had also higher anaerobic MR. Therefore the KH position is favorable for abled-bodied athletes because KL limits trunk motion. REFERENCES Holmberg, L. J. et al. (2013). Comput Methods Biomech Biomed Engin, 16(9), 987-992. Lajunen, K. (2014). Effect of sitting posture on sit-skiing economy. Bachelor’s thesis, University of Jyväskylä.Verellen, J. et al. (2012). Eur J Appl Physiol, 112(3), 983-989.

  • 134.
    Lundström, Erik
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Overload effects on the fatigue crack propagation behaviour in Inconel 7182012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In this master thesis, work done in the TURBO POWER project High temperature fatigue crack propagation in nickel-based superalloys during spring 2012 will be presented. The overall objective of this project is to develop and evaluate tools for designing against fatigue in gas turbine applications, with special focus on the crack propagation in the nickel-based superalloy Inconel 718. Experiments have been performed to study the effect of initial overloads, and it has been shown that even for small initial overloads a significant reduction of the crack growth rate is received. Furthermore, FE simulations have been carried out in order to describe the local stress state in front of the crack tip since it is believed to control, at least partly the diffusion of oxygen into the crack tip and thus also the hold time crack growth behaviour of the material. Finally, an evaluation method for the stresses is presented, where the results are averaged over an identifiable process/damaged zone in front of the crack tip.

  • 135.
    Lundvall, Fredrik
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics.
    Larsson, Niklas
    Linköping University, Department of Management and Engineering, Solid Mechanics.
    Stelkroppsanalyser på trafiksystemet Actibump: Kraftfördelning och utvecklingsförslag av Actibumps konstruktion2019Independent thesis Basic level (degree of Bachelor), 10,5 credits / 16 HE creditsStudent thesis
    Abstract [en]

    To optimize traffic flow with safe speeds, Edeva AB has developed the traffic system Actibump. The system provides a feedback for drivers if they drive too fast by folding a hatch that creates an inverted bump. Drivers who keep allowed speed can pass Actibump without the hatch folding down.

    When vehicles drive over Actibump in folded position, forces spread in its construction and the company wants a greater understanding of how these forces are distributed. The task was to create a model for how forces are transferred from the contact point of a tire to components concerned and to find any improvements on the construction to reduce the stress. The focus of the work was the driving chain and the hinge joint of the hatch.

    The workflow was divided into two parts where the work began with making simplified 2D calculations to get an overall view of the force distribution. Then 3D simulations were made in Creo Mechanism, the results of which could be compared to the 2D calculations. The simulations in Creo Mechanism became the final result.

    The result shows that the component called the cradle caused larger forces than necessary in the driving chain and in the hinges of the hatch. With the 3D simulations as a reference, an ideation for the cradle resulted in four different concepts. These concepts were subjected to the same simulations as for the original cradle and one of these was chosen based on results and producibility.

  • 136.
    Lång, Marcus
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    CFD-Method for 3D Aerodynamic Adjoint Simulations: For External Automotive Aerodynamics2019Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Today’s rules and regulations regarding emissions from combustion vehicles are very strict and the travel range per tank and/or charge, especially for electric vehicles, is a crucial factor which will always be considered by the customers. Hence, automotive manufacturers strive to boost fuel and battery economy. This can, to a great extent, be done by improving the aerodynamics of the vehicle for lower drag. The conventional CFD process for aerodynamic development is relatively time consuming and there is rarely enough timeor resources to find the optimal design in all regions of the vehicle. Hence, the adjoint solver was investigated to make the aerodynamic development process more efficient by providing sensitivities of the geometry with respect to drag force.

    The adjoint solver was investigated both through a literature review as well as by performing CFD and adjoint simulations. The CFD and adjoint simulations were performed using Fluent 2019 R1 and the realizable k-ε turbulence model. It was found that it is important to monitor surface sensitivities during the solution in addition to the adjoint residuals to assess convergence of the adjoint simulation. It is also recommended to analyse regions of high residuals in the domain to ensure that they are far away from the surface(s) of interest. Investigations regarding different stabilization schemes as well different meshes for the adjoint solver were performed.

    It was concluded that the residual minimization scheme (RMS) is the preferred stabilization scheme. It was found that a coarser mesh can be used to reduce localized transient behaviour if the adjoint solver has trouble converging. It was found that a simplified model of a fully detailed car geometry is necessary to reduce the complexity and the resolution of the mesh to be able to use the RMS and to avoid local instabilities. A proposed CFD and adjoint procedure with guidelines and recommendation was developed.

  • 137.
    Lönn, David
    Linköping University, Department of Management and Engineering. Linköping University, The Institute of Technology.
    Robust design: Accounting for uncertainties in engineering2008Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis concerns optimization of structures considering various uncertainties. The overall objective is to find methods to create solutions that are optimal both in the sense of handling the typical load case and minimising the variability of the response, i.e. robust optimal designs.

    Traditionally optimized structures may show a tendency of being sensitive to small perturbations in the design or loading conditions, which of course are inevitable. To create robust designs, it is necessary to account for all conceivable variations (or at least the influencing ones) in the design process.

    The thesis is divided in two parts. The first part serves as a theoretical background to the second part, the two appended articles. This first part includes the concept of robust design, basic statistics, optimization theory and meta modelling.

    The first appended paper is an application of existing methods on a large industrial example problem. A sensitivity analysis is performed on a Scania truck cab subjected to impact loading in order to identify the most influencing variables on the crash responses.

    The second paper presents a new method that may be used in robust optimizations, that is, optimizations that account for variations and uncertainties. The method is demonstrated on both an analytical example and a Finite Element example of an aluminium extrusion subjected to axial crushing.

    List of papers
    1. Finite element based robustness study of a truck cab subjected to impact loading
    Open this publication in new window or tab >>Finite element based robustness study of a truck cab subjected to impact loading
    2009 (English)In: International Journal of Crashworthiness, ISSN 1358-8265, E-ISSN 1754-2111, Vol. 14, no 2, p. 111-124Article in journal (Refereed) Published
    Abstract [en]

    Optimised designs have a tendency of being sensitive to variations. It is therefore of great importance to analyse this sensitivity to assure that a design is robust, i.e. sufficiently insensitive to variations. To analyse robustness, variations are introduced in model parameters and their influences on simulation responses are studied. This is usually achieved using the Monte Carlo method. Though, due to the large number of simulations needed, the Monte Carlo method is very costly for problems requiring a long computing time. Therefore, in this work a meta model-based Monte Carlo method is used to evaluate the robustness of a vehicle structure. That is, the Monte Carlo analysis is performed on a surface approximation of the true response, over the domain of interest. The methodology used is to first identify the variables that influence the response the most, referred to as a screening, using simple linear response surfaces. This is followed by a more detailed sensitivity analysis using only the identified variables and a quadratic response surface, thereby incorporating second order effects. A truck cab model exposed to a pendulum impact load is used as an evaluation of this method, and the important variables and their influence on the response are identified. The effect of including results from forming simulations is also evaluated using the truck cab model. Variations are introduced before forming simulations, thereby taking forming effects into account in the sensitivity analysis. The method was found to be a good tool to identify important dispersion variables and to give an approximate result of the total dispersion, all with a reasonable amount of simulations.

    Place, publisher, year, edition, pages
    Taylor & Francis, 2009
    Keywords
    Monte Carlo, meta model, robust design, response surface method, sensitivity analysis, robustness
    National Category
    Applied Mechanics
    Identifiers
    urn:nbn:se:liu:diva-15474 (URN)10.1080/13588260802412992 (DOI)
    Projects
    ROBDES
    Note
    On the day of the defence date the status of this article was: Accepted.Available from: 2008-11-11 Created: 2008-11-11 Last updated: 2017-12-14Bibliographically approved
    2. An approach to robust optimization of impact problems using random samples and meta-modelling
    Open this publication in new window or tab >>An approach to robust optimization of impact problems using random samples and meta-modelling
    2010 (English)In: International Journal of Impact Engineering, ISSN 0734-743X, E-ISSN 1879-3509, Vol. 37, no 6, p. 723-734Article in journal (Refereed) Published
    Abstract [en]

    Conventionally optimized structures may show a tendency to be sensitive to variations, for instance in geometry and loading conditions. To avoid this, research has been carried out in the field of robust optimization where variations are taken into account in the optimization process. The overall objective is to create solutions that are optimal both in the sense of mean performance and minimum variability. This work presents an alternative approach to robust optimization, where the robustness of each design is assessed through multiple sampling of the stochastic variables at each design point. Meta-models for the robust optimization are created for both the mean value and the standard deviation of the response. Furthermore, the method is demonstrated on an analytical example and an example of an aluminium extrusion with quadratic cross-section subjected to axial crushing. It works well for the chosen examples and it is concluded that the method is especially well suited for problems with a large number of random variables, since the computational cost is essentially independent of the number of random variables. In addition, the presented approach makes it possible to take into consideration variations that cannot be described with a variable. This is demonstrated in this work by random geometrical perturbations described with the use of Gaussian random fields.

    Keywords
    Robust optimisation, geometric imperfections, meta model, robustness
    National Category
    Applied Mechanics
    Identifiers
    urn:nbn:se:liu:diva-15478 (URN)10.1016/j.ijimpeng.2009.07.002 (DOI)
    Projects
    ROBDES
    Note
    Tidigare titel: Robust optimisation methodology using random samples and meta modelling Available from: 2008-11-11 Created: 2008-11-11 Last updated: 2017-12-14Bibliographically approved
  • 138.
    Lönn, David
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics . Linköping University, The Institute of Technology.
    Fyllingen, Ørjan
    Norwegian University of Science and Technology, Trondheim.
    Nilsson, Larsgunnar
    Linköping University, Department of Management and Engineering, Solid Mechanics . Linköping University, The Institute of Technology.
    An approach to robust optimization of impact problems using random samples and meta-modelling2010In: International Journal of Impact Engineering, ISSN 0734-743X, E-ISSN 1879-3509, Vol. 37, no 6, p. 723-734Article in journal (Refereed)
    Abstract [en]

    Conventionally optimized structures may show a tendency to be sensitive to variations, for instance in geometry and loading conditions. To avoid this, research has been carried out in the field of robust optimization where variations are taken into account in the optimization process. The overall objective is to create solutions that are optimal both in the sense of mean performance and minimum variability. This work presents an alternative approach to robust optimization, where the robustness of each design is assessed through multiple sampling of the stochastic variables at each design point. Meta-models for the robust optimization are created for both the mean value and the standard deviation of the response. Furthermore, the method is demonstrated on an analytical example and an example of an aluminium extrusion with quadratic cross-section subjected to axial crushing. It works well for the chosen examples and it is concluded that the method is especially well suited for problems with a large number of random variables, since the computational cost is essentially independent of the number of random variables. In addition, the presented approach makes it possible to take into consideration variations that cannot be described with a variable. This is demonstrated in this work by random geometrical perturbations described with the use of Gaussian random fields.

  • 139.
    Lönn, David
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Öman, Michael
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Nilsson, Larsgunnar
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Simonsson, Kjell
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Finite element based robustness study of a truck cab subjected to impact loading2009In: International Journal of Crashworthiness, ISSN 1358-8265, E-ISSN 1754-2111, Vol. 14, no 2, p. 111-124Article in journal (Refereed)
    Abstract [en]

    Optimised designs have a tendency of being sensitive to variations. It is therefore of great importance to analyse this sensitivity to assure that a design is robust, i.e. sufficiently insensitive to variations. To analyse robustness, variations are introduced in model parameters and their influences on simulation responses are studied. This is usually achieved using the Monte Carlo method. Though, due to the large number of simulations needed, the Monte Carlo method is very costly for problems requiring a long computing time. Therefore, in this work a meta model-based Monte Carlo method is used to evaluate the robustness of a vehicle structure. That is, the Monte Carlo analysis is performed on a surface approximation of the true response, over the domain of interest. The methodology used is to first identify the variables that influence the response the most, referred to as a screening, using simple linear response surfaces. This is followed by a more detailed sensitivity analysis using only the identified variables and a quadratic response surface, thereby incorporating second order effects. A truck cab model exposed to a pendulum impact load is used as an evaluation of this method, and the important variables and their influence on the response are identified. The effect of including results from forming simulations is also evaluated using the truck cab model. Variations are introduced before forming simulations, thereby taking forming effects into account in the sensitivity analysis. The method was found to be a good tool to identify important dispersion variables and to give an approximate result of the total dispersion, all with a reasonable amount of simulations.

  • 140.
    Lönning, Jonathan
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    Experimental Investigation of Fuel Mixing Concepts for 3rd Generation DLE Burners: Evaluation Through Water Rig and Atmospheric Combustion Rig Measurements2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    New Siemens burner concepts thought to produce a more homogeneous air/fuel mix-ture and a better distribution of the fuel over the burner cross section have been evaluated. A homogeneous air/fuel mixture is known to produce the lowest levels of emitted oxides of nitrogen (NOx) which is a main objective for Siemens Industrial Turbomachinery AB (SIT). It is desired that a burner concept can be found which further reduces the amount of emitted NOx but at the same time maintains a moderate pressure drop.

    A water rig was used in in order to evaluate the mixing performance of the new concepts. A video camera, a laser and a fluorescent substance, simulating fuel, was used to record movies of the burner mixing tube cross section. The movies were post processed in Matlab using in-house scripts where intensity and RMSD fields were obtained. These fields were used to compare the fuel mixing ability of totally 21 new burner concepts to the burner concept currently applied in the SGT-800.

    The water rig experiments have shown that a more homogeneous air/fuel mixture, compared to the reference burner, is possible to achieve with 11 out of the 21 tested concepts. The water rig has shown a repeatability within 5%.

    The water rig results obtained from a test with the reference burner were also compared to CFD simulation results. The water rig showed good agreement to the CFD simulation when comparing the trends of the fuel mixing ability.

    Two of the newly developed concepts were also tested in the Atmospheric Combustion Rig (ACR) at SIT to evaluate the pressure drop and emitted NOx in atmospheric conditions. One of these concepts showed a deterioration of the fuel mixing performance based on the water rig experiments while the other showed an improvement. The expectations of these concepts in terms of emitted NOx were therefore a significant deterioration and improvement, respectively. The results showed that both concepts performed quite similar with a moderate reduction of emitted NOx. The unexpected results have been derived to the pressure dependence of NOx, burner to burner differences from manufacturing and the small amount of available measurement points. The measured pressure drop over the burners reached unacceptable levels and the design of the new concepts therefore needs further improvements.

  • 141.
    Lövgren, Sebastian
    et al.
    Linköping University, Department of Management and Engineering, Machine Design.
    Norberg, Emil
    Linköping University, Department of Management and Engineering, Mechanics.
    Topology Optimization of Vehicle Body Structure for Improved Ride & Handling2011Independent thesis Advanced level (degree of Master (One Year)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Ride and handling are important areas for safety and improved vehicle control during driving. To meet the demands on ride and handling a number of measures can be taken. This master thesis work has focused on the early design phase. At the early phases of design, the level of details is low and the design freedom is big. By introducing a tool to support the early vehicle body design, the potential of finding more efficient structures increases. In this study, topology optimization of a vehicle front structure has been performed using OptiStruct by Altair Engineering. The objective has been to find the optimal topology of beams and rods to achieve high stiffness of the front structure for improved ride and handling. Based on topology optimization a proposal for a beam layout in the front structure area has been identified. A vital part of the project has been to describe how to use topology optimization as a tool in the design process. During the project different approaches has been studied to come from a large design space to a low weight architecture based on a beam-like structure. The different approaches will be described and our experience and recommendations will be presented. Also the general result of a topology-optimized architecture for vehicle body stiffness will be presented.

  • 142.
    Magnusson, Emelie
    Linköping University, Department of Management and Engineering, Mechanics.
    FE analysis and design of the mechanical connection in an osseointegrated prosthesis system2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In this master thesis the connection between the two major parts of an osseointegrated prosthesis system for lower limb amputees has been investigated by finite element (FE) analysis. The prosthesis system is developed by Integrum and the current design consists of a fixture, which is integrated in the residual bone, an abutment that penetrates the skin and an abutment screw that holds the parts together. The connection between the fixture and the abutment has a hexagonal section and a press-fit section that together form the connection. Due to wear and fracture problems it is desired to improve the connection. A tapered connection could be an alternative and three different taper angles, the effect of the length of the taper and the smoothness of the outer edge of a tapered fixture have been investigated. The results show that the taper has potential to function well and that a longer connection will give lower stresses in the system, but further investigations are needed.

  • 143.
    Martinsson, Joel
    et al.
    Linköping University, Department of Electrical Engineering. Linköping University, Faculty of Science & Engineering.
    Liu, Bin
    ABB Corp Research, Sweden.
    Controlled Start Transmission Hydraulic Clutch Disc Temperature Modelling and Applications2016In: 2016 IEEE INTERNATIONAL CONFERENCE ON MECHATRONICS AND AUTOMATION, IEEE , 2016, p. 1209-1214Conference paper (Refereed)
    Abstract [en]

    Controlled Start Transmissions can be described as a mechanical transmission combined with a hydraulic clutch for controlled torque output. CSTs are commonly used to start up heavy loads for example mining conveyors and produces heat during startup. Models for CST clutch heat generation together with thermal behavior has been developed and investigated. This includes a temperature model together with a kinetic model of the gearbox and a torque model of the clutch. Validation of separate model components and sensitivity analysis of parameters are conducted. The developed models are then compared by analyzing measurements and simulations to investigate generated heat during regular usage.

  • 144.
    Moverare, Johan
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Odén, Magnus
    Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials . Linköping University, The Institute of Technology.
    Influence of Microstresses on Anisotropic High Cycle Fatigue Behaviour of Duplex Stainless Steels2002In: Proc. 8th International Fatigue Congress, 2002, p. 541-548Conference paper (Other academic)
  • 145.
    Moverare, Johan
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Sato, Atsushi
    University of Birmingham.
    Hasselqvist, Magnus
    Siemens Industrial Turbomachinery AB.
    Karlsson, Fredrik
    Siemens Industrial Turbomachinery AB.
    Reed, R.C.
    University of Birmingham.
    A New Single Crystal Superalloy for Power Generation Applications:  2011In: Proceeding of the 8th International Charles Parsons TurbineConference 2011, 2011, p. G2-2-Conference paper (Refereed)
    Abstract [en]

    A newly developed single crystal superalloy (known as STAL15) is described which is suitable for use in first stage blades of highly efficient industrial gas turbines (IGTs). With 15 wt% Cr and 4.55 wt% Al, the alloy combines good corrosion and oxidation resistance with sufficient creep and fatigue performance. Thus a novel and useful balance of environmental and mechanical properties is displayed. In this paper, the details of the development project are described. The new alloy is shown to be an alumina (Al2O3) former; the mechanisms behind the Al2O3-formation process are studied and the effects arising from changes in the chemical composition have been modelled. In addition, the mechanical properties in terms of creep and fatigue resistance are evaluated together with the alloy stability during long term (up to 10,000 hours) exposure. For such applications, the new alloy is superior to existing nickel-based single crystal superalloys designed for aero engine applications and which are optimized for very high creep resistance; experience has shown that they are not ideal for use in IGTs of the type used for power generation or mechanical drive, due to their low corrosion resistance. The main reason for this is that IGTs are exposed to more harsh conditions in terms of air quality through the turbine and significantly longer time between overhaul/inspection. Traditionally this has been handled by use of polycrystalline alloys such as IN792 and IN738LC or the single crystal alloy PWA1484; unfortunately these do not form a protective Al2O3 layer and hence display limited resistance to environmental degradation. The new alloy does not display this weakness and is therefore highly optimised for IGT applications.

  • 146.
    Munjulury, Raghu Chaitanya
    et al.
    Linköping University, Department of Management and Engineering, Fluid and Mechatronic Systems. Linköping University, Faculty of Science & Engineering.
    Martins Abdalla, Alvaro
    USP, São Carlos, Brazil.
    Staack, Ingo
    Linköping University, Department of Management and Engineering, Fluid and Mechatronic Systems. Linköping University, Faculty of Science & Engineering.
    Krus, Petter
    Linköping University, Department of Management and Engineering, Fluid and Mechatronic Systems. Linköping University, Faculty of Science & Engineering.
    Knowledge-based future combat aircraft optimization2016In: 30th Congress of the International Council of the AeronauticalSciences (ICAS 2016), Bonn: International Council of Aeronautical Sciences (ICAS) , 2016, Vol. 1, p. 273-280Conference paper (Refereed)
    Abstract [en]

    Future combat aircraft inherently conceal all the components internally essentially for stealth reasons. The geometry is optimized for subsonic and supersonic flight area distribution and the components and payload to be fitted inside the aircraft. The basic requirements to accomplish are fuel consumption, mission profile, and military performance. Analytical methods comprise of a quick aerodynamic and structural optimization. The result obtained is then compared with multi-fidelity aero-structural analysis

  • 147.
    Naronikar, Aditya
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics.
    Riström, Anton
    Luleå University of Technology, Luleå.
    CFD and Experimental Study of Refuelling and Venting a Fuel System2019Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In 1999, California Air Resources Board (CARB) implemented a regulation that required all gasoline cars sold in California be fitted with an Onboard Refueling Vapor Recovery System (ORVR). The ORVR system is designed to prevent Volatile Organic Compounds (VOCs) from escaping into the atmosphere during refuelling by storing the gas vapours in a carbon canister. Due to the complex nature of the fuel system, making design changes could have large implications on the ORVR performance of the vehicle. It is therefore desirable to develop a CFD model that can predict the effects of design changes, thereby reducing the need to perform physical tests on each design iteration. This master thesis project was performed at the Fuel Systems department at Volvo Cars in order to help reduce project lead times and product development costs by incorporating CFD as a part of the fuel system development cycle. The CFD results obtained were validated through experimental tests that were also performed as part of this project.

    In this master thesis project, a CFD model was developed to simulate the refuelling of gasoline for a California specification Volvo XC90 with an OPW-11B pump pistol. The model was set up in STAR-CCM+ using the Eulerian Volume of Fluid model for multiphase flow, the RANS realizable k-epsilon turbulence model and the two layer all y+ wall treatment. The effects of the carbon canister were modelled as a porous baffle interface in the simulations where viscous and inertial resistances of the porous media were adjusted to obtain a desired pressure drop across the canister. This method proved to be a suitable simplification for this study. The effects of evaporation as well as a chemical adsorption model for the carbon canister have been excluded from the project due to time limitations.

    It was found that the CFD simulations were in good agreement with the experimental results, especially with respect to capturing the overall behaviour of the fuel system during refuelling. It was found that resolving the flow spatially (and temporally) in the filler pipe was a crucial part in ensuring solver stability. A pressure difference between experiment and simulation was also observed as a consequence of excluding evaporation from the CFD model.

    After the CFD model had been verified and validated, changes to different parts of the fuel system were investigated to observe their effects on ORVR performance. These included changing the recirculation line diameter, changing the carbon canister properties and changing the angle of how the pump pistol was inserted into the capless unit. It was found that the recirculation line diameter is a very sensitive design parameter and increasing the diameter would result in fuel vapour leaking back out into the atmosphere. Similarly, increasing the back pressure by swapping to a different carbon canister would result in the leakage of fuel vapour. On the other hand, insignificant changes in system behaviour were observed when the fuel pistol angle was changed.

  • 148.
    Nazari, Amir
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics.
    Nourozi, Behrouz
    Linköping University, Department of Management and Engineering, Solid Mechanics.
    Behavioral Analysis of Volvo Cars Instrument Panel During Airbag Deployment2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Airbags are a passive safety technology, required to function with zero failure rate. Advances in Computer Aided Engineering have allowed vehicle manufacturers to predict material and system behavior in the event of a crash. The sudden and rapid nature of a vehicle frontal crash, together with strict requirements put on safety make this a sensitive task. This thesis focuses on the front passenger airbag deployment and the instrument panel’s response. Various airbag modelling techniques are studied and presented in this document.

    This work is part of a larger-scale attempt to model a generic-sled that is physically representative of a real vehicle. Various component tests are to be performed in the sled environment, as opposed to a real vehicle, to save costs. Various modules are added to the sled once their behavior is verified by testing and in simulations. Software are advanced enough to identify location and magnitude of stress concentrations that develop during crash.

    LS-DYNA is used for explicit finite element simulations of the instrument panel (IP) in question with different airbag models. Verification has been achieved by design of experiment (DOE); with tests conducted to capture both the movements of the airbag housing and IP movements in response. These movements are broken down in various phases, facilitating implementation in the sled environment.

    Simplifications are made both to the computer models as well as the physical testing environment. The effects of these simplifications are quantified and discussed. Theoretical background is provided where fit while assumptions are justified wherever made. DYNAmore recommendations regarding costeffective calculations as well as result verification are followed.

    The obtained results show that the FE models replicate the real event with acceptable precision. The findings in this work can, by minor tweaks, be implemented on other IP models in the Volvo Cars range, leading to cost-saving solutions. This thesis provides the necessary information for sled implementations as well as future improvement suggestions.

  • 149.
    Nezhadali, Vaheed
    Linköping University, Department of Management and Engineering, Machine Design.
    Multi-objective optimization of Industrial robots2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Industrial robots are the most widely manufactured and utilized type of robots in industries. Improving the design process of industrial robots would lead to further developments in robotics industries. Consequently, other dependant industries would be benefited. Therefore, there is an effort to make the design process more and more efficient and reliable. The design of industrial robots requires studies in various fields. Engineering softwares are the tools which facilitate and accelerate the robot design processes such as dynamic simulation, structural analysis, optimization, control and so forth. Therefore, designing a framework to automate the robot design process such that different tools interact automatically would be beneficial. In this thesis, the goal is to investigate the feasibility of integrating tools from different domains such as geometry modeling, dynamic simulation, finite element analysis and optimization in order to obtain an industrial robot design and optimization framework. Meanwhile, Meta modeling is used to replace the time consuming design steps. In the optimization step, various optimization algorithms are compared based on their performance and the best suited algorithm is selected. As a result, it is shown that the objectives are achievable in a sense that finite element analysis can be efficiently integrated with the other tools and the results can be optimized during the design process. A holistic framework which can be used for design of robots with several degrees of freedom is introduced at the end.

  • 150.
    Ngaruye, Innocent
    et al.
    Linköping University, Department of Mathematics, Mathematical Statistics . Linköping University, Faculty of Science & Engineering.
    Nzabanita, Joseph
    Department of Mathematics, University of Rwanda.
    von Rosen, Dietrich
    Linköping University, Department of Mathematics, Mathematical Statistics . Linköping University, Faculty of Science & Engineering.
    Singull, Martin
    Linköping University, Department of Mathematics, Mathematical Statistics . Linköping University, Faculty of Science & Engineering.
    Small Area Estimation under a Multivariate Linear Model for Repeated measures Data2017In: Communications in Statistics - Theory and Methods, ISSN 0361-0926, E-ISSN 1532-415X, Vol. 46, no 21, p. 10835-10850Article in journal (Refereed)
    Abstract [en]

    In this article, Small Area Estimation under a Multivariate Linear model for repeated measures data is considered. The proposed model aims to get a model which borrows strength both across small areas and over time. The model accounts for repeated surveys, grouped response units and random effects variations. Estimation of model parameters is discussed within a likelihood based approach. Prediction of random effects, small area means across time points and per group units are derived. A parametric bootstrap method is proposed for estimating the mean squared error of the predicted small area means. Results are supported by a simulation study.

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