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Mechatronic Modeling and Simulation Using Bond Graphs by Shuvra Das | PDF Free Download.
Shuvra Das is a professor of mechanical engineering at the University of Detroit Mercy. He received his undergraduate degree from the Indian Institute of Technology in Kharagpur, India in 1985. Both his master’s and doctoral degrees in engineering mechanics are from Iowa State University.
Dr. Das’s research and teaching interests include engineering mechanics, computational mechanics using finite and boundary element methods, modeling and simulation, inverse problems, mechatronics, condition-based health monitoring of engineering systems, etc.
He has written over 50 conference and journal publications and has received several awards including the best teacher award from the North Central section of ASEE in 2002 and the Junior Achievement Award at the University of Detroit Mercy.
Many years ago when I was an undergraduate student of mechanical engineering at the Indian Institute of Technology, Kharagpur, India, Professor Amalendu Mukherjee was our teacher for a course on systems and controls.
Probably a year or two before this, he had come across an intriguing technique for systems modeling called bond graphs.
He was very excited about it and was quickly becoming an expert in this area. The great teacher that he was, he got equally excited about teaching this technique to as many of his students as possible.
Our class was, therefore, one of the first in the institute to learn about bond graphs and the joy of bond graphing. I cannot say that bond graphing was a joy to everyone in the class. There were probably three broad opinions in the class about bond graphs.
Some did not care; to them, this was just another one in a list of courses that they had to take. A second group just did not get it! But by far the largest group was the one that felt an increased level of excitement as they learned something that was logical, easy once you got the basics, and powerful.
In retrospect, probably the excitement was more because of a great teacher’s ability to convey the material than the material itself.
Nevertheless, many of us were bitten by the bond graphing bug. In pursuing advanced studies, I was taken away from the systems modeling world because of other academic interests. But many years later, I had the opportunity to develop and teach courses in the area of mechatronics.
Even when I first learned about bond graphs, the unifying nature of the topic appealed to me a lot. That was when I first realized that mechanics, circuits, and hydraulics are not so far apart from each other as they have been thought to be.
If one starts looking at the forest rather than the trees, a very unifying theme emerges. Naturally, for the multidisciplinary area of mechatronics, I felt that bond graph-based modeling would be an ideal fit.
Once I reviewed what had happened in bond graphing since I had first been excited by it, I found that I was not the only one making the connection between bond graphs and mechatronics. Many established researchers in the field had already connected those dots.
Karnopp, Rosenberg, and Margolis (2006) modified their text and its title to reflect this connection. Others, such as Hrovat et al. (2000), Margolis and Shim (2001), DeSilva (2005), Brown (2001), have been making significant contributions to mechatronics research and were using bond graphs as the modeling tool.
When we first learned about bond graphs in our course on systems and controls, we came away with the idea that the technique was rather exciting, but we were unsure about its practical use.
Most of us thought that perhaps only about a handful of excited researchers, such as Professor Mukherjee, were going to use it. In the many years that have passed since my undergraduate days, several software tools have come to the market.
20Sim, CAMP-G, AMESIM, and Professor Mukherjee’s very own SYMBOLS 2000 are now all commercial tools, which means people are using them to solve real problems.
Why are bond graphs well suited for mechatronic systems? Engineering system modeling has always been multidisciplinary in nature. A review of any of the classical texts in system modeling, such as Ogata (2003), reveals this fact.
In the mechatronic systems world, it is more so the case. In traditional approaches to modeling multidisciplinary systems, the governing equations are derived from a combination of Newton’s laws, Kirchoff’s laws, Bernoulli's equations, and other fundamental governing equations in different domains of knowledge.
I have always seen that students have a difficult time dealing with the application of these laws in the derivation of system equations, especially since they almost always have some level of mastery in their own discipline but lack confidence in disciplines that are not theirs.
While students struggle with deriving the governing equations for a variety of systems, texts using this traditional approach quickly move to solutions of these equations in time and frequency domains, their meanings, different ways the solutions can be plotted, the information these plots convey, etc.
This leads to a situation where even at the end of a course, many students are not confident in developing the equations to model a new system that they encounter.
Bond graphing has three advantages in comparison to the traditional approach. First, it utilizes the similarities that exist between all disciplines so that students learn to see the engineering system as a whole and not in terms of its separate pieces.
This is the characteristic we try to teach in a systems course. Second, basic components from different disciplines and their behaviors are categorized under a few generalized elements. So, for example, students are not thinking of capacitances and springs as two different entities, but as the same generalized entity.
Third, the bond graph is a visual representation of the system from which derivation of the governing equations is algorithmic.
Therefore, it can be automated. As a result of this, students are not struggling with and losing confidence at the early stage of the learning process; they are able to more easily transition to a stage where they can learn about the behavior of systems, interpretation of data, etc.
While users of the bond graph methodology claim that it is the “greatest thing since sliced bread,” people who have not used it before finding it confusing and formidable.
Bond graph users sometimes lament about why more people don’t “see it their way.” I believe it should be the job of bond graph enthusiasts to educate others and introduce them to this technique.
Through this text, I have attempted to do exactly that. My motivation in writing this book is to help students, especially first-time users, get familiar with the technique and develop confidence in using it.
If an introductory mechatronics course is the first course in a mechatronics sequence, this text is intended to be for the second course in that sequence.
It is assumed that students have some idea about mechtronics systems, its different components, and have had some hands-on experience with some of them prior to learning how to model mechatronic systems.
The structure of this book and the handling of different topics have been done with this goal in mind. I have purposely stayed away from elaborate mathematical derivations and proofs. There are many texts that address that information.
I have tried to deal with the method from the perspective of a modeler who is seeking results. Key concepts are uncovered slowly with a lot of rudimentary examples at the early stage so that readers can develop some confidence in their ability to use the method.
In the second half of the book, when readers have potentially learned how to develop bond graph models, I have included simulation results for most of the examples that are part of the text. This ensures that readers can model, simulate, and practice as they progress through the chapters.
Although the models can be simulated using any software tool that can handle bond graphs, 20Sim has been used for all the simulation work in this text.
A free version of 20Sim can be downloaded from the software Web site. I would strongly encourage readers to model the examples in this text for themselves. There is no better way to learn than to try things out for oneself.
This book is not a result of many years of research on this topic. Rather, it is a result of several years of teaching this topic.
Hence, I have tried to focus on the student who is learning this topic for the first time. If students benefit from this work it will be the biggest reward for me.
Also, I consider this text as a “work in progress.” Already I feel that other topics could have been added to make the book more comprehensive.
But I will be realistic about goals and deadlines and hold those back for some future publication.
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