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Braun, Robert
Publications (10 of 18) Show all publications
Hällqvist, R., Schminder, J., Eek, M., Braun, R., Gårdhagen, R. & Krus, P. (2018). NOVEL FMI AND TLM-BASED DESKTOP SIMULATOR FORDETAILED STUDIES OF THERMAL PILOT COMFORT. In: ICAS congress proceeding: . Paper presented at 31st Congress of the International Council of the Aeronautical Sciences,Belo Horizonte, Brazil, September 9-14, 2018. International Council of the Aeronautical Sciences, Article ID ICAS2018_0203.
Open this publication in new window or tab >>NOVEL FMI AND TLM-BASED DESKTOP SIMULATOR FORDETAILED STUDIES OF THERMAL PILOT COMFORT
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2018 (English)In: ICAS congress proceeding, International Council of the Aeronautical Sciences , 2018, article id ICAS2018_0203Conference paper, Published paper (Other academic)
Abstract [en]

Modelling and Simulation is key in aircraft systemdevelopment. This paper presents a novel,multi-purpose, desktop simulator that can beused for detailed studies of the overall performanceof coupled sub-systems, preliminary controldesign, and multidisciplinary optimization.Here, interoperability between industrially relevanttools for model development and simulationis established via the Functional MockupInterface (FMI) and System Structure andParametrization (SSP) standards. Robust anddistributed simulation is enabled via the TransmissionLine element Method (TLM). The advantagesof the presented simulator are demonstratedvia an industrially relevant use-case wheresimulations of pilot thermal comfort are coupledto Environmental Control System (ECS) steadystateand transient performance.

Place, publisher, year, edition, pages
International Council of the Aeronautical Sciences, 2018
Keywords
OMSimulator; FMI; TLM; Pilot Thermal Comfort; Modelling and Simulation
National Category
Applied Mechanics Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:liu:diva-152897 (URN)978-3-932182-88-4 (ISBN)
Conference
31st Congress of the International Council of the Aeronautical Sciences,Belo Horizonte, Brazil, September 9-14, 2018
Available from: 2018-11-27 Created: 2018-11-27 Last updated: 2018-11-27
Hällqvist, R., Braun, R. & Krus, P. (2017). Early Insights on FMI-based Co-Simulation of Aircraft Vehicle Systems. In: Petter Krus, Liselott Eriksson and Magnus Sethson (Ed.), Proceedings of 15:th Scandinavian International Conference on Fluid Power, June 7-9, 2017, Linköping, Sweden: . Paper presented at 15:th Scandinavian International Conference on Fluid Power, June 7-9, 2017, Linköping, Sweden (pp. 262-270). Linköping: Linköping University Electronic Press, 144
Open this publication in new window or tab >>Early Insights on FMI-based Co-Simulation of Aircraft Vehicle Systems
2017 (English)In: Proceedings of 15:th Scandinavian International Conference on Fluid Power, June 7-9, 2017, Linköping, Sweden / [ed] Petter Krus, Liselott Eriksson and Magnus Sethson, Linköping: Linköping University Electronic Press, 2017, Vol. 144, p. 262-270Conference paper, Oral presentation only (Other academic)
Abstract [en]

Modelling and Simulation is extensively used for aircraft vehicle system development at Saab Aeronautics in Linköping, Sweden. There is an increased desire to simulate interacting sub-systems together in order to reveal, and get an understanding of, the present cross-coupling effects early on in the development cycle of aircraft vehicle systems. The co-simulation methods implemented at Saab require a significant amount of manual effort, resulting in scarcely updated simulation models, and challenges associated with simulation model scalability, etc. The Functional Mock-up Interface (FMI) standard is identified as a possible enabler for efficient and standardized export and co-simulation of simulation models developed in a wide variety of tools. However, the ability to export industrially relevant models in a standardized way is merely the first step in simulating the targeted coupled sub-systems. Selecting a platform for efficient simulation of the system under investigation is the next step. Here, a strategy for adapting coupled Modelica models of aircraft vehicle systems to TLM-based simulation is presented. An industry-grade application example is developed, implementing this strategy, to be used for preliminary investigation and evaluation of a cosimulation framework supporting the Transmission Line element Method (TLM). This application example comprises a prototype of a small-scale aircraft vehicle systems simulator. Examples of aircraft vehicle systems are environmental control systems, fuel systems, and hydraulic systems. The tightly coupled models included in the application example are developed in Dymola, OpenModelica, and Matlab/Simulink. The application example is implemented in the commercial modelling tool Dymola to provide a reference for a TLM-based master simulation tool, supporting both FMI and TLM. The TLM-based master simulation tool TLMSimulator is investigated in terms of model import according to the FMI standard with respect to a specified set of industrial needs and requirements.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2017
Series
Linköping Electronic Conference Proceedings, ISSN 1650-3686, E-ISSN 1650-3740 ; 144
Keywords
FMI, TLM, Modelica, Aircraft Vehicle Systems
National Category
Aerospace Engineering
Identifiers
urn:nbn:se:liu:diva-142400 (URN)10.3384/ecp17144262 (DOI)9789176853696 (ISBN)
Conference
15:th Scandinavian International Conference on Fluid Power, June 7-9, 2017, Linköping, Sweden
Projects
OpenCPS
Available from: 2017-10-30 Created: 2017-10-30 Last updated: 2019-05-08Bibliographically approved
Braun, R. & Krus, P. (2017). Parallel Implementations of the Complex-RF Algorithm. Engineering optimization (Print), 49(9), 1558-1572
Open this publication in new window or tab >>Parallel Implementations of the Complex-RF Algorithm
2017 (English)In: Engineering optimization (Print), ISSN 0305-215X, E-ISSN 1029-0273, Vol. 49, no 9, p. 1558-1572Article in journal (Refereed) Published
Abstract [en]

Even though direct-search optimization methods are more difficult to parallelize than population-based methods, there are many unexploited opportunities. Five methods for parallelizing the Complex-RF methods have been implemented and evaluated. Three methods are based on the unchanged original algorithm, while two require modifications. The methods have been tested on two test function and one real simulation model. An analysis of the algorithm has been performed. This provides a basis for parametrization of the parallel methods. Without changing the original algorithm, speed-up of 2.5-3 is achieved. With allowing modifications, a speed-up of up to 5 is obtained without significantly reducing the probability of finding the global minimum. Speed-up does not scale linear to the number of threads. When more threads are added, parallelization efficiency decreases. However, a comparison with a particle swarm method shows that Complex-RF performs better regardless of the number of threads, due to its fast convergence rate.

Place, publisher, year, edition, pages
Taylor & Francis, 2017
Keywords
Parallel optimization, direct-search, simplex, Complex-RF
National Category
Electrical Engineering, Electronic Engineering, Information Engineering Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:liu:diva-122751 (URN)10.1080/0305215X.2016.1260712 (DOI)000404810100006 ()
Note

The prevuous status of this article was Manuscript.

Available from: 2015-11-19 Created: 2015-11-19 Last updated: 2017-08-09Bibliographically approved
Braun, R., Hällqvist, R. & Fritzson, D. (2017). TLM-Based Asynchronous Co-simulation with the Functional Mockup Interface. In: Bernhard Schweizer (Ed.), Proceedings of the IUTAM Symposium on Solver-Coupling and Co-Simulation, Darmstadt, Germany, September 18-20, 2017: . Paper presented at IUTAM Symposium on Solver-Coupling and Co-Simulation. Switzerland
Open this publication in new window or tab >>TLM-Based Asynchronous Co-simulation with the Functional Mockup Interface
2017 (English)In: Proceedings of the IUTAM Symposium on Solver-Coupling and Co-Simulation, Darmstadt, Germany, September 18-20, 2017 / [ed] Bernhard Schweizer, Switzerland, 2017Conference paper, Published paper (Refereed)
Abstract [en]

Numerical stability is a key aspect in co-simulation of physical systems. Decoupling a system into independent sub-models will introduce time delays on interface variables. By utilizing physical time delays for decoupling, affecting the numerical stability can be avoided. This requires interpolation, to allow solvers to request input variables for the time slot where they are needed. The FMI for co-simulation standard does not support fine-grained interpolation using interpolation tables. Here, various modifications to the FMI standard are suggested for improved handling of interpolation. Mechanical and thermodynamic models are used to demonstrate the need for interpolation, as well as to provide an industrial context. It is shown that the suggested improvements are able to stabilize the otherwise unstable connections.

Place, publisher, year, edition, pages
Switzerland: , 2017
Series
IUTAM Bookseries, E-ISSN 1875-3493 ; 35
Keywords
Co-simulation, FMI, TLM, Numerical stability
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:liu:diva-157342 (URN)10.1007/978-3-030-14883-6_2 (DOI)978-3-030-14882-9 (ISBN)978-3-030-14883-6 (ISBN)
Conference
IUTAM Symposium on Solver-Coupling and Co-Simulation
Available from: 2019-06-10 Created: 2019-06-10 Last updated: 2019-06-10
Braun, R., Ericson, L. & Krus, P. (2016). Full Vehicle Simulation of Forwarder with Semi Active Suspension using Co-simulation. In: : . Paper presented at ASME/BATH 2015 Symposium on Fluid Power and Motion Control, October 12-14, 2015, Chicago, USA. ASME Press
Open this publication in new window or tab >>Full Vehicle Simulation of Forwarder with Semi Active Suspension using Co-simulation
2016 (English)Conference paper, Published paper (Refereed)
Abstract [en]

A major concern in the forest industry is impact on the soil caused by forest machines during harvesting. A six-wheel pendulum arm forwarder is being developed. The new forwarder aims at reducing soil damage by an even pressure distribution and smooth torque control and thereby also improving the working environment. The suspension contains pendulum arms on each wheel controlled by a hydraulic load sensing system in combination with accumulator.

A natural approach is to model each part of a system in the bestsuited software. In this case, the hydraulic system is modelled in the Hopsan simulation tool, while the vehicle mechanics is modelled in Adams. To understand the whole system it is necessary to simulate all subsystems together. An open standard for this is the Functional Mock-up Interface. This makes it possible to investigate the interaction between the hydraulic system and the multi-body mechanic model.

This paper describes how different simulation tools can be combined to support the development process. The technique is applied to the forwarder’s pendulum suspension. Controllers for height and soil force are optimized to minimize soil damage and maximize comfort for the operator.

Place, publisher, year, edition, pages
ASME Press, 2016
Keywords
System simulation, distributed solvers, parallelism, scheduling, transmission line element method
National Category
Electrical Engineering, Electronic Engineering, Information Engineering Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:liu:diva-122750 (URN)10.1115/FPMC2015-9588 (DOI)000373970500047 ()
Conference
ASME/BATH 2015 Symposium on Fluid Power and Motion Control, October 12-14, 2015, Chicago, USA
Available from: 2015-11-19 Created: 2015-11-19 Last updated: 2017-12-20Bibliographically approved
Braun, R. & Krus, P. (2016). Multi-Threaded Distributed System Simulations Using the Transmission Line Element Method. Simulation (San Diego, Calif.), 92(10), 921-930
Open this publication in new window or tab >>Multi-Threaded Distributed System Simulations Using the Transmission Line Element Method
2016 (English)In: Simulation (San Diego, Calif.), ISSN 0037-5497, E-ISSN 1741-3133, Vol. 92, no 10, p. 921-930Article in journal (Other academic) Published
Abstract [en]

By introducing physically motivated time delays, simulation models can be partitioned into decoupled independent sub-models. This enables parallel simulations on multi-core processors. An automatic algorithm is used for partitioning and running distributed system simulations. Methods for sorting and distributing components for good load balancing have been developed. Mathematical correctness during simulation is maintained by a busy-waiting thread synchronization algorithm. Independence between sub-models is achieved by using the transmission line element method. In contrast to the more commonly used centralized solvers, this method uses distributed solvers with physically motivated time delays, making simulations inherently parallel. Results show that simulation speed increases almost proportionally to the number of processor cores in the case of large models. However, overhead time costs mean that models need to be over a certain size to benefit from parallelization.

Place, publisher, year, edition, pages
Sage Publications, 2016
Keywords
Distributed Solvers, Parallelism, Problem Partitioning, Transmission Line Modelling, System Simulation
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-88024 (URN)10.1177/0037549716667243 (DOI)000385704300004 ()
Note

When first pubished online the status of this article was Manuscript.

Funding agencies: ProViking research School; Swedish Foundation for Strategic Research (SSF)

Available from: 2013-01-29 Created: 2013-01-29 Last updated: 2017-12-06Bibliographically approved
Braun, R. (2015). Distributed System Simulation Methods: For Model-Based Product Development. (Doctoral dissertation). Linköping: Linköping University Electronic Press
Open this publication in new window or tab >>Distributed System Simulation Methods: For Model-Based Product Development
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Distributed system simulation can increase performance, re-usability and modularity in model-based product development. This thesis investigates four aspects of distributed simulation: multi-threaded simulations, simulation tool coupling, distributed equation solvers and parallel optimization algorithms.

Multi-threaded simulation makes it possible to split up the workload over several processing units. This reduces simulation time, which can save both time and money during the product development cycle. The transmission line element method (TLM) is used to decouple models to independent sub-models.

Different simulation tools are suitable for different problems. Tool coupling makes it possible to use the best suited tool for simulating each part of the whole product. Models from different tools can then be coupled into one aggregated simulation model. An emerging standard for tool coupling is the Functional Mock-up Interface (FMI). It is investigated how this can be used in conjunction with TLM.

Equation-based object-oriented languages (EOOs) are becoming increasing popular. A logical approach is to let the equation solvers maintain the same structure that was used in the modelling process. Methods for achieving this using TLM and FMI are implemented and evaluated.

In addition to parallel simulations, it is also possible to use parallel optimization algorithms. This introduces parallelism on several levels. For this reason, an algorithm for profile-based multi-level scheduling is proposed.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2015. p. 118
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1732
National Category
Electrical Engineering, Electronic Engineering, Information Engineering Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:liu:diva-122754 (URN)10.3384/diss.diva-122754 (DOI)978-91-7685-875-2 (ISBN)
Public defence
2015-12-18, ACAS, A-huset, Campus Valla, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2015-11-19 Created: 2015-11-19 Last updated: 2016-10-31Bibliographically approved
Nordin, P., Braun, R. & Krus, P. (2015). Job-Scheduling of Distributed Simulation-Based Optimization with Support for Multi-Level Parallelism. In: Proceedings of the 56th Conference on Simulation and Modelling (SIMS 56): October, 7-9, 2015, Linköping University, Sweden. Paper presented at The 56th Conference on Simulation and Modelling (SIMS 56), “Modelling, Simulation and Optimization”, Linköping, Sweden, 7-9 October 2015 (pp. 187-197). Linköping: Linköping University Electronic Press
Open this publication in new window or tab >>Job-Scheduling of Distributed Simulation-Based Optimization with Support for Multi-Level Parallelism
2015 (English)In: Proceedings of the 56th Conference on Simulation and Modelling (SIMS 56): October, 7-9, 2015, Linköping University, Sweden, Linköping: Linköping University Electronic Press, 2015, p. 187-197Conference paper, Published paper (Refereed)
Abstract [en]

In many organizations, the utilization of available computer power is very low. If it could be harnessed for parallel simulation and optimization, valuable time could be saved. A framework monitoring available computer resources and running distributed simulations is proposed. Users build their models locally, and then let a job scheduler determine how the simulation work should be divided among remote computers providing simulation services. Typical applications include sensitivity analysis, co-simulation and design optimization. The latter is used to demonstrate the framework. Optimizations can be parallelized either across the algorithm or across the model. An algorithm for finding the optimal distribution of the different levels of parallelism is proposed. An initial implementation of the framework, using the Hopsan simulation tool, is presented. Three parallel optimization algorithms have been used to verify the method and a thorough examination of their parallel speed-up is included.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2015
Series
Linköping Electronic Conference Proceedings, ISSN 1650-3686, E-ISSN 1650-3740 ; 119
Keywords
Job-scheduling, parallelism, distributed simulation, optimization
National Category
Electrical Engineering, Electronic Engineering, Information Engineering Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:liu:diva-122752 (URN)10.3384/ecp15119187 (DOI)9789176859001 (ISBN)
Conference
The 56th Conference on Simulation and Modelling (SIMS 56), “Modelling, Simulation and Optimization”, Linköping, Sweden, 7-9 October 2015
Available from: 2015-11-19 Created: 2015-11-19 Last updated: 2018-02-02Bibliographically approved
Braun, R. & Krus, P. (2014). An Explicit Method for Decoupled Distributed Solvers in an Equation-Based Modelling Language. In: David Broman & Peter Pepper (Ed.), Proceedings of the 6th International Workshop on Equation-Based Object-Oriented Modeling Languages and Tools: . Paper presented at 6th International Workshop on Equation-Based Object-Oriented Modeling Languages and Tools, Berlin, October 10, 2014 (pp. 57-64). New York: Association for Computing Machinery (ACM)
Open this publication in new window or tab >>An Explicit Method for Decoupled Distributed Solvers in an Equation-Based Modelling Language
2014 (English)In: Proceedings of the 6th International Workshop on Equation-Based Object-Oriented Modeling Languages and Tools / [ed] David Broman & Peter Pepper, New York: Association for Computing Machinery (ACM), 2014, p. 57-64Conference paper, Published paper (Refereed)
Abstract [en]

The Modelica language offers an intuitive way to create object-oriented models. This makes it natural also to use an object-oriented solver, where each sub-model solves its own equations. Doing so is possible only if sub-models can be made independent from the rest of the model. One way to achieve this is to use distributed solvers by separating sub-models with transmission line elements. This offers robust and predictable simulations, simplified model debugging and natural parallelism. It also makes it possible to use different time steps and solver algorithms in different parts of the model to achieve an optimal trade-off between performance and accuracy. The suggested method has been implemented in the Hopsan simulation environment. Different modelling techniques for taking advantage of the distributed solver approach are explained. Finally, three example models are used to demonstrate the method.

Place, publisher, year, edition, pages
New York: Association for Computing Machinery (ACM), 2014
Keywords
distributed solvers, transmission line element method, Modelica, model generation
National Category
Computer Systems
Identifiers
urn:nbn:se:liu:diva-111478 (URN)10.1145/2666202.2666212 (DOI)978-1-4503-2953-8 (ISBN)
Conference
6th International Workshop on Equation-Based Object-Oriented Modeling Languages and Tools, Berlin, October 10, 2014
Projects
HiPO
Funder
Swedish Foundation for Strategic Research
Available from: 2014-10-17 Created: 2014-10-17 Last updated: 2015-11-19Bibliographically approved
Braun, R. (2013). Multi-Threaded Distributed System Simulations: Using Bi-Lateral Delay Lines. (Licentiate dissertation). Linköping: Linköping University Electronic Press
Open this publication in new window or tab >>Multi-Threaded Distributed System Simulations: Using Bi-Lateral Delay Lines
2013 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

As the speed increase of single-core processors keeps declining, it is important to adapt simulation software to take advantage of multi-core technology. There is a great need for simulating large-scale systems with good performance. This makes it possible to investigate how different parts of a system work together, without the need for expensive physical prototypes. For this to be useful, however, the simulations cannot take too long, because this would delay the design process. Some uses of simulation also put very high demands on simulation performance, such as real-time simulations, design optimization or Monte Carlo-based sensitivity analysis. Being able to quickly simulate large-scale models can save much time and money.

The power required to cool a processor is proportional to the processor speed squared. It is therefore no longer profitable to keep increasing the speed. This is commonly referred to as the "power wall". Manufacturers of processors have instead begun to focus on building multi-core processors consisting of several cores working in parallel. Adapting program code to multi-core architectures constitutes a major challenge for software developers.

Traditional simulation software uses centralized equation-system solvers, which by nature are hard to make parallel. By instead using distributed solvers, equations from different parts of the model can be solved simultaneously. For this to be effective, it is important to minimize overheadcosts and to make sure that the workload is evenly distributed over the processor cores.

Dividing an equation system into several parts and solving them separately means that time delays will be introduced between the parts. If these occur in the right locations, this can be physically correct, since it also takes some time for information to propagate in physical systems. The transmission line  element method (TLM) constitutes an effective method for separating system models by introducing impedances between components, causing physically motivated time delays.

Contributions in this thesis include parts of the development of the new generation of the Hopsan simulation tool, with support for TLM and distributed solvers. An automatic algorithm for partitioning models has been developed. A multi-threaded simulation algorithm using barrier synchronization has also been implemented.

Measurements of simulation time confirm that the simulation time is decreased almost proportionally to the number of processor cores for large models. The decrease, however, is reduced if the cores are divided on different processors. This was expected, due to the communication delay for processors communicating over shared memory. Experiments on real-time systems with four cores show that a four times as large model can be simulated without losing real-time performance.

The division into distributed solvers constitutes a sort of natural cosimulation. A future project could be to use this as a platform for linking different simulation tools together and simulating them with high performance. This would make it possible to model each part of the system in the most suitable tool, and then connect all parts into one large model.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2013. p. 56
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1576
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-88025 (URN)LIU-TEK-LIC-2013:10 (Local ID)978-91-7519-694-7 (ISBN)LIU-TEK-LIC-2013:10 (Archive number)LIU-TEK-LIC-2013:10 (OAI)
Presentation
2013-02-08, A34, Hus A, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2013-01-29 Created: 2013-01-29 Last updated: 2016-10-31Bibliographically approved
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