Internship Final Paper

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Final Report on Internship Program
American University of Beirut

A Comparison of Two Approaches of Handling Contacts in Rigid Multibody Dynamics

Abstract

This paper is based on my work completed during an eight-week internship at the University of Wisconsin-Madison. My work was to contribute to a research program aimed at using new software that handles contacts in rigid multibody dynamics much faster than the traditional dynamic simulation software used. This new approach seems to be promising and the long run goals of this research program is to be able to simulate very complex models using this software package which will make much faster simulation and therefore a lot of time is saved, more data is obtained, and therefore designs are improved. The first parts of my work was to get familiar with this new software, called Chrono::Engine and try to run some demo tutorials, as well as trying to understand the code and the approach that was used into handling contacts. Then I had to get familiar with one of the most famous simulation software packages used in the market, ADAMS/View (Automatic Dynamic Analysis of Mechanical Systems) and run the simulation of a very complex hydraulic excavator model after thoroughly investigating the model then to monitor some variables and note down the results.

The second part of my work was to run a same model in Chrono::Engine and ADAMS/View that has many contacts and compare the CPU time that each of the software needs in order to complete the simulation of the model. This experiment was aimed at looking into the speed of the simulation and to investigate how efficient and powerful is Chrono::Engine. After results are obtained, we were able to make a quick conclusion that calls for future work in this domain, in order to be able to handle and simulate very complex models with many contact forces. Table of Contents

1. Introduction………………………………………………….4 2. Review of Software………………………………………….5 3. Numerical Experiments………………………………………7 4. Numerical Results……………………………………………15 5. Conclusion…………………………………………………...19 6. Achievements…………………………………………………19 Appendix: Published Paper: Madsen, Pechdimaljian, Negrut

1. Introduction

As we all acknowledge, time is so valuable and any approach that saves time is appreciated and encouraged to use. The more contacts we find in a model, the longer CPU time it takes to simulate it. Models like a hydraulic excavator for example, takes about 10 hours to simulate it crossing a pot hole, as will be shown in later sections. In design industries, testing and simulating are essential in order to monitor the behavior of a system under mechanical disturbances like bumps or pot holes. If one wishes to test the behavior of a tank model, at least 100 simulations are needed, that makes about 1000 hours of simulation, which is not time efficient at all. It is essential to come up with an approach that saves time and handles contacts at least 100 times faster. This approach was developed in software called Chrono::Engine. Our work here is to test its efficiency in terms of accuracy of results and more importantly, the CPU time to complete a single run of the model.

2. Review of both software

2.1 ADAMS

The ADAMS/View program is a 3-D interactive environment in which the parametric properties of the mechanical system are defined. Constraints between individual parts can be applied so that the resulting motion of the system mocks that of its physical counterpart. Forces, torques and motions can be applied so the system moves in a particular fashion. It is also possible to implement control systems. The user only needs to define the parametric data; the equations of motion are automatically applied when the finalized model is...
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