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Distributed System Simulation Methods: For Model-Based Product Development
Linköping University, Department of Management and Engineering, Fluid and Mechatronic Systems. Linköping University, Faculty of Science & Engineering.
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. , 118 p.
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: urn:nbn:se:liu:diva-122754DOI: 10.3384/diss.diva-122754ISBN: 978-91-7685-875-2 (print)OAI: oai:DiVA.org:liu-122754DiVA: diva2:872653
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
List of papers
1. Multi-Threaded Distributed System Simulations Using the Transmission Line Element Method
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, 921-930 p.Article 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
Keyword
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
2. Improved Scheduling Techniques for Parallel Distributed-Solver System Simulation
Open this publication in new window or tab >>Improved Scheduling Techniques for Parallel Distributed-Solver System Simulation
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Shortening simulation time is an important step towards efficient simulation-based product development. A long-used method is to exploit physically motivated time delays to split up the model into distributed solvers. In this way, the use of a centralized sequential solver can be circumvented. For maximum simulation performance, however, an efficient scheduling technique is also required. Four task scheduling methods for distributed-solver simulations has been implemented and evaluated. Experiments indicate that the best choice largely depend on model size, load distribution and granularity. Lock-based barrier synchronization provides the highest speed-up for small models. A fork-join implementation, with implicit synchronization and work-stealing scheduling, works better for models with a large total workload. It is common that workload and load distribution of a simulation model varies during execution depending on the current state of the simulation. Three of the implemented schedulers support dynamic load balancing during execution. Results show that task-stealing is the most efficient method for the specific test model. A possible continuation of this work is an automatic selection of the best scheduling technique based on knowledge about model properties and available computer resources.

Keyword
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-122749 (URN)
Available from: 2015-11-19 Created: 2015-11-19 Last updated: 2015-11-19
3. Multi-Threaded Real-Time Simulations of Fluid Power Systems Using Transmission Line Elements
Open this publication in new window or tab >>Multi-Threaded Real-Time Simulations of Fluid Power Systems Using Transmission Line Elements
2012 (English)Conference paper, Published paper (Refereed)
Abstract [en]

The demand for large-scale real-time simulations of fluid power systems is in-creasing, due to growing demands for added functionality. Real-time simulationscan be used in for example hardware-in-the-loop experiments and embeddedcontrol systems. In order to achieve real-time performance, it is often necessaryto use small or simplified models, reducing the usefulness and accuracy of theresults. This article proposes the use of transmission line modelling (TLM) forexploiting multi-core hardware in real-time and embedded systems. The charac-teristics of the TLM method are analysed to identify difficulties and possibilities.A method for how to parallelise TLM models is then presented. Subsequently, aprogramming interface for implementing the parallel models in the target systemsis introduced. Practical experiments show that the approach works and that themethod is applicable. So far, however, it has required great effort on the part ofthe engineer, both when it comes to programming, compiling and importing themodel into the target environments, although some attempts to automate the pro-cedure have been successful, reducing the level of complexity.

Keyword
Real-time simulation, Distributed modelling, Transmission line mod- elling, Parallel simulation, Multi-core, Model fidelity
National Category
Fluid Mechanics and Acoustics Other Mechanical Engineering
Identifiers
urn:nbn:se:liu:diva-76377 (URN)
Conference
8th International Fluid Power Conference, March 26-28, 2012, Dresden, Germany
Available from: 2012-04-05 Created: 2012-04-05 Last updated: 2015-11-19Bibliographically approved
4. Full Vehicle Simulation of Forwarder with Semi Active Suspension using Co-simulation
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
Keyword
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: 2016-05-12Bibliographically approved
5. An Explicit Method for Decoupled Distributed Solvers in an Equation-Based Modelling Language
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, 57-64 p.Conference 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
Keyword
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
6. Tool-Independent Distributed Simulations Using Transmission Line Elements And The Functional Mock-up Interface
Open this publication in new window or tab >>Tool-Independent Distributed Simulations Using Transmission Line Elements And The Functional Mock-up Interface
2013 (English)Conference paper, Published paper (Refereed)
Abstract [en]

This paper describes how models from different simulation tools can be connected and simulated on different processors by using the Functional Mockup Interface (FMI) and the transmission line element method (TLM). Interconnectivity between programs makes it possible to model each part of a complex system with the best suited tool, which will shorten the modelling time and increase the accuracy of the results. Because the system will be naturally partitioned, it is possible to identify weak links and replace them with transmission line elements, thereby introducing a controlled time delay. This makes the different parts of the system naturally independent, making it possible to simulate large aggregated system models with good performance on multi-core processors. The proposed method is demonstrated on an example model. A suggestion of an XML extension to the FMI standard for describing TLM ports is also presented.

Keyword
Functional Mockup Interface (FMI), Functional Mockup Unit (FMU), Transmission Line Element Method (TLM), Parallelism, Co-Simulation
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-99870 (URN)
Conference
53rd SIMS conference on Simulation and Modelling, October 4-6, Reykjavik, Iceland
Available from: 2013-10-22 Created: 2013-10-22 Last updated: 2015-11-19Bibliographically approved
7. Parallel Implementations of the Complex-RF Algorithm
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, 1558-1572 p.Article 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
Keyword
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
8. Job-Scheduling of Distributed Simulation-Based Optimization with Support for Multi-Level Parallelism
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, 187-197 p.Conference 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 (print), 1650-3740 (online) ; 119
Keyword
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: 2016-09-14Bibliographically approved

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