| 1. |
- Andersson, Christian, et al.
(author)
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Efficient Predictor for Co-Simulation with Multistep Sub-System Solvers
- 2016
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Reports (other academic/artistic)abstract
- An industrial model of a dynamic system is usually not just a set of differential equations. External inputs acting on the system are common, such as an external force acting on a body or wind pressing on a car. Update of these inputs needs to be handled by the numerical solver in an efficient way.In dynamical simulation, multistep methods are commonly used. A multistep method uses the solution history in order to predict the future solution. When an input is changed, the history is no longer a good approximation for the future solution which may result in order reductions and simulation failure.In this paper, a modification of the predictor is presented. Modifying the predictor, instead of restarting the method, results in an increased performance of the method. The cost of the modification must be weighed with the cost of restarting the method. Experiments show that the benefit of modifying the predictor outweighs the cost of a restart.
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| 2. |
- Andersson, Christian, et al.
(author)
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PyFMI: A Python Package for Simulation of Coupled Dynamic Models with the Functional Mock-up Interface
- 2016
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Reports (other academic/artistic)abstract
- With the advent of the Functional Mock-up Interface (FMI) standard, exchanging dynamic models between modeling and simulation tools has been greatly simplified. At the core of it, FMI is a standardized and unified model execution interface for dynamic models. FMI has gained widespread adoption among users and numerous commercial and open source tools implement support for the standard. In this article, the Python package PyFMI is introduced. PyFMI supports loading and execution of models compliant with the FMI standard, called Functional Mock-up Units (FMUs). It includes a master algorithm for simulation of coupled FMUs together with connections to both Assimulo, for simulation of single FMUs, and to SciPy, for performing parameter estimation. Accessing models compliant with FMI in Python, which is an open and accessible scripting language, is intended to further spread the standard and also promote and facilitate future development of the standard. This is due to Python being a convenient language for experimentation and prototyping of numerical algorithms. PyFMI is also demonstrated on a number of problems that highlights its viability for solving industrial grade simulation problems with FMUs.
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| 3. |
- Eich, Edda, et al.
(author)
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Stabilization and projection methods for multibody dynamics
- 1990
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Reports (other academic/artistic)abstract
- In recent years, there has been growing interest in stabilized index reduction techniques for differential-algebraic equations (DAE) of multibody dynamics. A number of the proposals which incorporate the idea of a projection onto the constraint manifold are discussed. The methods are divided into classes based on whether the projection is performed on the residuals of the discretized DAE or on the numerical solution itself, and demonstrate relationships between the methods of each class
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| 4. |
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| 5. |
- Führer, Claus, et al.
(author)
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Computing with Python
- 2013
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Book (other academic/artistic)abstract
- Description: Python® is a free open-source language and environment that has great potential in scientific computing. Computing with Python presents the programming language in close connection wit mathematical applications. The approach of the book is concept based rather than a systematic introduction to the language. It is written for a mathematical readership and is aimed at students with a mathematical background. Computing with Python can be used as a course book for absolute beginners on Python with guidance and support from a teacher. It is also suitable as a self study book for more advanced students with some programming knowledge and an interest in mathematical or scientific disciplines. The book integrates programming with mathematics and gives a systematic treatment of Python’s capabilities with application to scientific computing.
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| 6. |
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| 7. |
- Maghdid, Dara, et al.
(author)
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A Study on Variation Technique in Courses on Scientific Computing
- 2014
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Reports (other academic/artistic)abstract
- The background of this study is a project aiming at assessing the quality of teaching and learning in scientific computing in different cultural settings. This, we hope will lead us to constructing standards, which can provide outcomes of comparable quality in scientific computing in different countries and societies. Specifically we want to gain insight which quality benchmarks are suitable for the project. The tool we use in teaching is a set of variation techniques. The presented pilot study aims at the examination of the role variation theory for the quality of elementary courses in scientific computing. Earlier studies by others confirmed that variation theory offers a comprehensive set of variables characterizing teaching, well described and easy to follow and measure and which can result in improving teaching. The main data for this investigation was collected via interviewing students.
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| 8. |
- Nakhimovski, Iakov, 1976-
(author)
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Contributions to the Modeling and Simulation of Mechanical Systems with Detailed Contact Analyses
- 2006
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Doctoral thesis (other academic/artistic)abstract
- The motivation for this thesis was the need for further development of multibody dynamics simulation packages focused on detailed contact analysis. The thesis makes contributions in three different areas:Part I summarizes the equations, algorithms and design decisions necessary for dynamics simulation of flexible bodies with moving contacts. The assumed general shape function approach is presented. Additionally, the described technique enables studies of the residual stress release during grinding of flexible bodies. The proposed set of mode shapes was also successfully applied for modeling of heat flow.Part II is motivated by the need to reduce the computation time. The availability of the new cost-efficient multiprocessor computers triggered the development of the presented hybrid parallelization framework. The framework is designed to be easily portable and can be implemented without any system level coding or compiler modifications.Part III is motivated by the need for inter-operation with other simulation tools. A co-simulation framework based on the Transmission Line Modeling (TLM) technology was developed. The framework enables integration of several different simulation components into a single time-domain simulation. The framework has been used for connecting MSC.ADAMS and SKF BEAST simulation models.Throughout the thesis the approach was to present a practitioner roadmap. The detailed description of the theoretical results relevant for a real software implementation is put in focus. The software design decisions are discussed and the results of real industrial simulations are presented.This work has been supported by SKF, SSF/ProViking, ECSEL, KK-stiftelsen.
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| 9. |
- Strömgren, Magnus
(author)
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Some PDAE aspects of the numerical simulation of a CO2 heat pump
- 2006
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Licentiate thesis (other academic/artistic)abstract
- We consider network modelling and numerical simulation of a simple CO2 heat pump consisting of a compressor, a valve and two heat exchangers. In a first step we investigate analytical and numerical properties of the heat exchanger model. The heat exchanger model is derived from the Euler equations under the assumption that the velocity of the refridgerant flow is small compared to the local speed of sound. While the Euler equations form a hyperbolic system, the character of the new system, called The zero Mach number limit of the Euler equations, is unclear. The lack of a time derivative in the momentum equation makes the heat exchanger model by itself a PDAE system. We analyse a frozen-coefficient linearisation of the heat exchanger model by transformation to a canonical form. The canonical form reveales that the system is equivalent to a hyperbolic equation and a parabolic block. The parabolic block is equivalent to a parabolic equation and an algebraic-differential relation, similar to the system that results when the heat equation ut = uxx + f is written as a first order system. We prove a stability estimate suggesting that the solution is more sensitive to perturbations, especially in time-dependent boundary conditions, than is indicated by previous results. Furthermore, we consider semidiscretisation of the linearised heat exchanger model. In a method of lines approach using collocation at the gridpoints, we suggest that it is possible to use a simple first order difference scheme taking into account the direction of the flow and the boundary conditions. We show that using this difference scheme, the solution to the semidiscrete equations satisfies a discrete analogue to the stability estimate in the continuous case. The results of the linear analysis is verified in numerical experiments with the nonlinear heat exchanger model.
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