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Multi-Threaded Real-Time Simulations of Fluid Power Systems Using Transmission Line Elements
Linköping University, Department of Management and Engineering, Fluid and Mechatronic Systems. Linköping University, The Institute of Technology.
Linköping University, Department of Management and Engineering, Fluid and Mechatronic Systems. Linköping University, The Institute of Technology.
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.

Place, publisher, year, edition, pages
2012.
Keyword [en]
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: urn:nbn:se:liu:diva-76377OAI: oai:DiVA.org:liu-76377DiVA: diva2:514165
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
In thesis
1. Multi-Threaded Distributed System Simulations: Using Bi-Lateral Delay Lines
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. 56 p.
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
2. Distributed System Simulation Methods: For Model-Based Product Development
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. 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: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

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