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Hofwing, M., Strömberg, N. & Tapankov, M. (2011). Optimal Polynomial Regression Models by using a Genetic Algorithm. In: Y. Tsompanakis & B.H.V. Topping (Ed.), Proceedings of the Second International Conference on Soft Computing Technology in Civil, Structural and Environmental Engineering: . Paper presented at The Second International Conference on Soft Computing Technology in Civil, Structural and Environmental Engineering Conference, 6-9 September, Chania, Crete, Greece. Stirlingshire: Civil-Comp Press, Article ID 39.
Öppna denna publikation i ny flik eller fönster >>Optimal Polynomial Regression Models by using a Genetic Algorithm
2011 (Engelska)Ingår i: Proceedings of the Second International Conference on Soft Computing Technology in Civil, Structural and Environmental Engineering / [ed] Y. Tsompanakis & B.H.V. Topping, Stirlingshire: Civil-Comp Press , 2011, artikel-id 39Konferensbidrag, Publicerat paper (Övrigt vetenskapligt)
Abstract [en]

Different regression models are commonly used to approximate the behavior of an unknown response in a given design domain. The regression models are usually obtained from a design of experiments, the corresponding responses and the constitution of the regression model. In this work a new approach is proposed, where the constituents of a polynomial regression model are of arbitrary order. A genetic algorithm is used to find the optimal terms to be included in the so-called optimal polynomial regression model. The objective for the genetic algorithm is to minimize the sum of squared errors of the predicted responses. In practice the genetic algorithm generates an optimal set of exponents of the design variables for the specified number of terms in the regression model, where each term is a product of a regression coefficient and the design variables. Several example problems are presented to show the performance and accuracy of the optimal polynomial regression model. Results show an improved performance for optimal polynomial regression models compared to traditional regression models.

Ort, förlag, år, upplaga, sidor
Stirlingshire: Civil-Comp Press, 2011
Serie
Civil-Comp Proceedings, E-ISSN 1759-3433 ; 97
Nyckelord
Polynomial regression model, Metamodeling, Design of experiments (DoE)
Nationell ämneskategori
Maskinteknik
Identifikatorer
urn:nbn:se:liu:diva-72350 (URN)10.4203/ccp.97.39 (DOI)
Konferens
The Second International Conference on Soft Computing Technology in Civil, Structural and Environmental Engineering Conference, 6-9 September, Chania, Crete, Greece
Projekt
MERA
Tillgänglig från: 2011-11-25 Skapad: 2011-11-25 Senast uppdaterad: 2019-12-29Bibliografiskt granskad
Hofwing, M. & Strömberg, N. (2009). Robustness of residual stresses in castings and an improved process window. In: Proceedings of the 35th Design Automation Conference, August 30-September 2, San Diego, USA 2009: . Paper presented at The 35th Design Automation Conference, August 30-September 2, San Diego, USA (pp. 1081-1091). The American Society of Mechanical Engineers, Article ID DETC2009-86454.
Öppna denna publikation i ny flik eller fönster >>Robustness of residual stresses in castings and an improved process window
2009 (Engelska)Ingår i: Proceedings of the 35th Design Automation Conference, August 30-September 2, San Diego, USA 2009, The American Society of Mechanical Engineers , 2009, s. 1081-1091, artikel-id DETC2009-86454Konferensbidrag, Publicerat paper (Refereegranskat)
Abstract [en]

In this work the robustness of residual stresses in finite element simulations with respect to deviations in mechanical parameters in castings is evaluated. Young's modulus, the thermal expansion coefficient and the hardening are the studied parameters. A 2D finite element model of a stress lattice is used. The robustness is evaluated by comparing purely finite element based Monte Carlo simulations and Monte Carlo simulations based on linear and quadratic response surfaces. Young's modulus, the thermal expansion coefficient and the hardening are assumed to be normal distributed with a standard deviation that is 10% of their nominal value at different temperatures. In this work an improved process window is also suggested to show the robustness graphically. By using this window it is concluded that least robustness is obtained for high hardening values in combination to deviations in Young's modulus and the thermal expansion coefficient. It is also concluded that quadratic response surface based Monte Carlo simulations substitute finite element based Monte Carlo simulations satisfactory. Furthermore, the standard deviation of the responses are evaluated analytically by using the Gauss formula, and are compared to results from Monte Carlo simulations. The analytical solutions are accurate as long as the Gauss formula is not utilized close to a stationary point.

Ort, förlag, år, upplaga, sidor
The American Society of Mechanical Engineers, 2009
Nyckelord
Robustness, Finite element method, Monte Carlo, Response surface, Casting, Process window
Nationell ämneskategori
Maskinteknik
Identifikatorer
urn:nbn:se:liu:diva-72349 (URN)10.1115/DETC2009-86454 (DOI)
Konferens
The 35th Design Automation Conference, August 30-September 2, San Diego, USA
Projekt
MERA
Tillgänglig från: 2009-06-15 Skapad: 2011-11-25 Senast uppdaterad: 2019-12-29Bibliografiskt granskad
Strömberg, N. & Klarbring, A. (2009). Topology Optimization of Structures with Contact Constraints by using  a Smooth Formulation and Nested Approach. In: 8th World Congress on Structural and Multidisciplinary Optimization June 1-5 2009, Lisbon, Portugal. Lissabon, Portugal
Öppna denna publikation i ny flik eller fönster >>Topology Optimization of Structures with Contact Constraints by using  a Smooth Formulation and Nested Approach
2009 (Engelska)Ingår i: 8th World Congress on Structural and Multidisciplinary Optimization June 1-5 2009, Lisbon, Portugal, Lissabon, Portugal, 2009Konferensbidrag, Publicerat paper (Refereegranskat)
Ort, förlag, år, upplaga, sidor
Lissabon, Portugal: , 2009
Nationell ämneskategori
Teknik och teknologier
Identifikatorer
urn:nbn:se:liu:diva-21031 (URN)
Tillgänglig från: 2009-09-28 Skapad: 2009-09-28 Senast uppdaterad: 2017-05-15
Strömberg, N. & Klarbring, A. (2008). Minimization of Compliance of a Linear Elastic Structure with Contact Constraints by using Sequential Linear Programming and Newton's method. In: Proceedings of the 7th International ASMO-UK/ISSMO International Conference on Engineering Design Optimization (pp. 379-386).
Öppna denna publikation i ny flik eller fönster >>Minimization of Compliance of a Linear Elastic Structure with Contact Constraints by using Sequential Linear Programming and Newton's method
2008 (Engelska)Ingår i: Proceedings of the 7th International ASMO-UK/ISSMO International Conference on Engineering Design Optimization, 2008, s. 379-386Konferensbidrag, Publicerat paper (Refereegranskat)
Nationell ämneskategori
Teknik och teknologier
Identifikatorer
urn:nbn:se:liu:diva-50782 (URN)
Tillgänglig från: 2009-10-14 Skapad: 2009-10-14 Senast uppdaterad: 2017-05-15
Hofwing, M. & Strömberg, N. (2008). Simulation of residual stresses in stamping dies. In: Nader Asnafi (Ed.), Proceedings of the IDDRG 2008 Conference : Best in class stamping, 16-18 June 2008, Olofström, Sweden: . Paper presented at IDDRG 2008, Best in class stamping, 16-18 June 2008, Olofström, Sweden (pp. 765-776). Olofström: Industriellt utvecklingscentrum i Olofström AB
Öppna denna publikation i ny flik eller fönster >>Simulation of residual stresses in stamping dies
2008 (Engelska)Ingår i: Proceedings of the IDDRG 2008 Conference : Best in class stamping, 16-18 June 2008, Olofström, Sweden / [ed] Nader Asnafi, Olofström: Industriellt utvecklingscentrum i Olofström AB , 2008, s. 765-776Konferensbidrag, Publicerat paper (Refereegranskat)
Abstract [en]

In the past stamping dies have in principle been designed by rules of thumb and intuition. As the sheet metals in the vehicle industry have got increased mechanical properties in recent years the demands on the stamping dies have increased. For instance increase in stiffness is desirable in order to better control spring-back. The most simple way to satisfy this new demand would be to make the stamping dies even more heavy in order to be able to handle the new sheet metals. Since there are restrictions of the weight of the stamping dies in the stamping machines and since the overhead cranes usually have reached the limit of what they can handle, this is not a desirable solution. Another approach, in order to increase the stiffness without increasing the weight is to use topology optimization. Recently in a master thesis at Volvo Car Corporation a conceptual design of a stamping die has been done by topology optimization. In that work no consideration is taken to the fact that the stamping die is casted. Casting implies that residual stresses possibly are produced during the solidification and cooling process. The residual stresses might affect the fatigue life and the risk of failure of the stamping die.

In this work the residual stress state after casting is analyzed for the original stamping die as well as the optimized stamping die from the master thesis discussed above. The analyses are performed using an uncoupled approach, where one thermal analysis is followed by a quasi-static elasto-plastic analysis. The thermal analysis simulates the solidification and cooling during the casting process, while the quasi-static elasto-plastic analysis uses the temperature history, obtained from the thermal analysis, in order to build up residual stresses. The thermal analysis includes the release of latent heat. Furthermore, the material properties included in the heat equation (density, conductivity, specific heat) are given as temperature dependent properties for the mould as well as the casting. In the quasi-static elasto-plastic analysis the plasticity is described by the von Mises yield surface in combination with isotropic hardening and the mechanical properties (thermal expansion coefficient, Young's modulus, yield stress, hardening parameter, Poisson's ratio) are given as temperature dependent properties. The simulations show high levels of residual stresses.

 

Ort, förlag, år, upplaga, sidor
Olofström: Industriellt utvecklingscentrum i Olofström AB, 2008
Nationell ämneskategori
Maskinteknik
Identifikatorer
urn:nbn:se:liu:diva-72348 (URN)978-91-633-2948-7 (ISBN)
Konferens
IDDRG 2008, Best in class stamping, 16-18 June 2008, Olofström, Sweden
Tillgänglig från: 2009-06-15 Skapad: 2011-11-25 Senast uppdaterad: 2019-12-29Bibliografiskt granskad
Gustafsson, E. & Strömberg, N. (2007). Successive Response Surface Methodology by using Neural Networks. In: Proceedings of 7th World Congress on Structural and Multidisciplinary Optimization, Seoul, Korea: .
Öppna denna publikation i ny flik eller fönster >>Successive Response Surface Methodology by using Neural Networks
2007 (Engelska)Ingår i: Proceedings of 7th World Congress on Structural and Multidisciplinary Optimization, Seoul, Korea, 2007Konferensbidrag, Publicerat paper (Övrigt vetenskapligt)
Nationell ämneskategori
Teknik och teknologier
Identifikatorer
urn:nbn:se:liu:diva-12736 (URN)
Tillgänglig från: 2007-11-07 Skapad: 2007-11-07
Lundvall, O., Strömberg, N. & Klarbring, A. (2004). A flexible multi-body approach for frictional contact in spur gears. Journal of Sound and Vibration, 278(3), 479-499
Öppna denna publikation i ny flik eller fönster >>A flexible multi-body approach for frictional contact in spur gears
2004 (Engelska)Ingår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, Vol. 278, nr 3, s. 479-499Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

In the present paper, a large rotational approach for dynamic contact problems with friction is proposed. The approach is used for modelling a spur gear pair with shafts and bearings. The model is obtained by superposing small displacement elasticity on rigid-body motions, and postulating tribological laws on the gear flanks. The finite element method is used to model the elastic properties of the gear pair. Shafts and bearings are represented by linear springs. The tribological laws of the contact interface are Signorini's contact law and Coulomb's law of friction. An important feature of the approach is that the difficulties of impacting mass nodes are avoided. The governing equations of the model are numerically treated by use of the augmented Lagrangian approach. In such manner the geometry of the gear flanks are well represented in the numerical simulations. It is possible to study accurately the consequences of different types of profile modifications as well as flank errors. In this work, the dynamic transmission error is studied. For instance, it turns out that the effect from profile modification is less significant for the transmission error when frictional effects are included.

Nationell ämneskategori
Teknik och teknologier
Identifikatorer
urn:nbn:se:liu:diva-22562 (URN)10.1016/j.jsv.2003.10.057 (DOI)1828 (Lokalt ID)1828 (Arkivnummer)1828 (OAI)
Tillgänglig från: 2009-10-07 Skapad: 2009-10-07 Senast uppdaterad: 2017-12-13
Strömberg, N. (2003). A method for structural dynamic contact problems with friction and wear. International Journal for Numerical Methods in Engineering, 58(15), 2371-2385
Öppna denna publikation i ny flik eller fönster >>A method for structural dynamic contact problems with friction and wear
2003 (Engelska)Ingår i: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 58, nr 15, s. 2371-2385Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

A method for structural dynamic contact problems with friction and wear is suggested. The method is obtained by including wear in the non-smooth contact dynamics method of Moreau. A comparison of the method to the discrete energy-momentum method of Simo and Tarnow is also outlined briefly. The fully discrete equations are treated using the augmented Lagrangian approach, where a non-smooth Newton method is used as the equation solver. Two two-dimensional examples are solved by the method. It is investigated how solutions of contact, friction and wear are influenced by inertia. It is shown that the quasi-static assumption might be questionable for solving contact problems with friction and wear. © 2003 John Wiley and Sons, Ltd.

Nyckelord
Augmented Lagrangian and Newton's method, Contact, Dynamics, Friction, Wave
Nationell ämneskategori
Teknik och teknologier
Identifikatorer
urn:nbn:se:liu:diva-46351 (URN)10.1002/nme.858 (DOI)
Tillgänglig från: 2009-10-11 Skapad: 2009-10-11 Senast uppdaterad: 2017-12-13
Ireman, P., Klarbring, A. & Strömberg, N. (2003). A model of damage coupled to wear. International Journal of Solids and Structures, 40(12), 2957-2974
Öppna denna publikation i ny flik eller fönster >>A model of damage coupled to wear
2003 (Engelska)Ingår i: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 40, nr 12, s. 2957-2974Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The present paper presents a model of damage coupled to wear. The damage model is based on a continuum model including the gradient of the damage variable. Such a model is non-local in the sense that the evolution of damage is governed by a boundary-value problem instead of a local evolution law. Thereby, the well-known mesh-dependency observed for local damage models is removed. Another feature is that the boundary conditions can be used to introduce couplings between bulk damage and processes at the boundary. In this work such a coupling is suggested between bulk damage and wear at the contact interface. The model is regarded as a first attempt to formulate a continuum damage model for studying crack initiation in fretting fatigue. The model is given within a thermodynamic framework, where it is assured that the principles of thermodynamics are satisfied. Furthermore, two variational formulations of the full initial boundary value problem, serving as starting points for finite element discretization, are presented. Finally, preliminary numerical results for a simple one-dimensional example are presented and discussed. It is qualitatively shown how the evolution of damage may influence the wear behaviour and how damage may be initiated by the wear process. © 2003 Elsevier Science Ltd. All rights reserved.

Nyckelord
Contact, Continuum thermodynamics, Damage, Fretting, Friction, Gradient of damage, Internal variables, Wear
Nationell ämneskategori
Teknik och teknologier
Identifikatorer
urn:nbn:se:liu:diva-46608 (URN)10.1016/S0020-7683(03)00121-5 (DOI)
Tillgänglig från: 2009-10-11 Skapad: 2009-10-11 Senast uppdaterad: 2017-12-13
Ireman, P., Klarbring, A. & Strömberg, N. (2002). Finite element algorithms for thermoelastic wear problems. European journal of mechanics. A, Solids, 21(3), 423-440
Öppna denna publikation i ny flik eller fönster >>Finite element algorithms for thermoelastic wear problems
2002 (Engelska)Ingår i: European journal of mechanics. A, Solids, ISSN 0997-7538, E-ISSN 1873-7285, Vol. 21, nr 3, s. 423-440Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

In the present paper three algorithms are applied to a finite element model of two thermoelastic bodies in frictional wearing contact. All three algorithms utilize a modification of a Newton method for B-differentiable equations as non-linear equation solver. In the first algorithm the fully-coupled system of thermomechanical equations is solved directly using the modified method, while in the other two algorithms the equation system is decoupled in one mechanical part and another thermal part which are solved using an iterative strategy of Gauss-Seidel type. The two iterative algorithms differ in which order the parts are solved. The numerical performance of the algorithms are investigated for two two-dimensional examples. Based on these numerical results, the behaviour of the model is also discussed. It is found that the iterative approach where the thermal subproblem is solved first is slightly more efficient for both examples. Furthermore, it is shown numerically how the predicted wear gap is influenced by the bulk properties of the contacting bodies, in particular how it is influenced by thermal dilatation. © 2002 Éditions scientifiques et médicales Elsevier SAS. All rights reserved.

Nyckelord
Friction, Numerical methods, Pang's Newton method, Semi-smooth equations, Thermomechanical contact, Wear
Nationell ämneskategori
Teknik och teknologier
Identifikatorer
urn:nbn:se:liu:diva-46843 (URN)10.1016/S0997-7538(02)01208-1 (DOI)
Tillgänglig från: 2009-10-11 Skapad: 2009-10-11 Senast uppdaterad: 2017-12-13
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