Preface

This is a book about experimental modal analysis. Yes.there are other text books on this subject but this one is different. Other books have deep theoretical developments that researchers and PhDs all relish but do not get to the core of what is needed, from a practical standpoint, to provide practitioners with the critical information needed to perform the day to day modal test and develop a model from measured data.

This book is really written for the novice, manager, engineer and technician; the novice that may come in any shape or form.

• the newbie to modal testing and needs basics to get started
• the engineer that has not been involved in experimental dynamic testing
• the research/graduate student who has a need to make measurements and no one to guide them
• the engineer in a small company that gets tasked to perform modal tests
• the engineer promoted to fill the shoes of a well-seasoned modal test engineer who moves to management or retires
• the manager who needs to understand basics to properly secure funding to support important projects
• the engineer that needs to write test plans, conduct tests and extract useful information from data acquired
• the technician who needs to acquire data that is useful for development of a model
• for all to understand what each needs to do in order to be able to provide a model that can be used to evaluate systems, understand dynamic characteristics and solve complicated structural dynamic problems

While this book is not written to impress those well versed in modal analysis, many of the theoretical oriented folks will find very useful practical information regarding modal tests if they have never actually worked in a lab environment and have only developed theoretical approaches to solve these problems. But this text is also good for the graduate students who have research that has a need for experimental structural dynamic models to be developed but the PhD candidate is not focused on experimental modal analysis directly and his advisor is not familiar either - but there is a need for the PhD student to make meaningful measurements but not get bogged down with the intricate details of experimental modal analysis.

This book is also useful as a textbook for an undergraduate course to introduce very basic concepts necessary to perform an experimental modal test - possibly as a laboratory related class or as an addition to a vibrations class or for a graduate class on structural dynamics. This book definitely has sufficient material to be used as a first introduction to experimental modal analysis as an upper level undergraduate class or beginning graduate level class.

This book is meant to focus on the practical aspects of experimental modal analysis. Only limited theory is presented in the text in order to illustrate or expound upon certain methodologies of experimental modal testing that have their roots in the underlying theory. In many cases, the theory (or final equation of a long derivation) is just presented; this text is not about developing the details of the theory but rather applying the theory to solve real problems. There are an abundance of good textbooks in the area of vibrations but very few contain even a small piece of the content of this book. There are some textbooks on experimental modal analysis but most concentrate on the theoretical side of modal analysis assuming the implementation of a real test is easy and straightforward.

Back in the late 1990s, the Society for Experimental Mechanics had a series in Experimental Techniques magazine entitled "Modal Space - Back to Basics" - that series published for 17 continuous years. The series addressed very simple problems commonly encountered by experimental modal analysis testers. The articles were never more than 2 pages and had a variety of experimental modal analysis topics addressed. But the material was scattered from one article to the next and they were just intended to be "snip-its" of information that resulted from years and years of teaching industry modal seminars, teaching in-house modal seminars and many, many emails received over 20 or more years working in this area. This book is about pulling all that information together and providing a more complete treatment of that material.

So this text is laid out in two parts - the first part is more of the traditional theory related to analytical and experimental modal analysis whereas the second part is about the practical issues related to experimental modal tests followed by appendices with additional useful information. Chapter 1 is a very simple overview of the entire experimental modal test to set the stage for the entire text; this is extremely useful to the new folks starting into modal analysis. Chapter 2 through 5 have some of the cornerstones of basic information. Chapter 2 has all the pertinent theory summarized related to single degree of freedom systems to multiple degree of freedom systems with equations presented in the physical domain, modal domain, Laplace domain and the frequency domain. Chapter 3 presents a good summary of all the pertinent digital signal processing techniques that are needed for the acquisition of measured data; sampling issues to frequency data to noise are all addressed here. Chapter 4 presents the most common excitation techniques used for modal testing today - impact and shaker excitation. Chapter 5 contains some of the rudimentary information necessary for modal parameter estimation. Chapter 6 through 9 have a more practical side of the material. Chapter 6 is related to the issues related to setting up a test from start to finish. Chapter 7 has many examples related to impact testing which is the most widely used excitation technique for traditional experimental modal tests. Chapter 8 further discusses shaker excitation techniques and issues related to running these types of tests as well as multiple input multiple output testing. Chapter 9 provides some very practical insights into the reduction of the data collected using different modal parameter estimation approaches. Chapter 10 and 11 have a variety of different issues related to modal testing that are difficult to place in one of the previous chapters because they span more than one topic or were just not appropriate for a particular chapter. There are several appendices that have some very simple analytical models that help to show the math in action. A few more appendices have a scattering of broad information that may be useful to the modal test engineer. And a few final chapters have some data sets that have been used for modal parameter estimation with results for the user to try to decompose with their own software used in their lab; the data sets are available in universal file format on the book webpage so that they can be downloaded and processed and compared to the users results.

Finally, there are the thanks to so many that have crossed paths during my time spent in this modal community. I started working in the mid-seventies and early on came across John O'Callahan and G. Dudley Shepard up at then the University of Lowell (the former Lowell Tech). John, analytical and Dudley, experimental - they were a pair that started modal at the University of Massachusetts Lowell in the Modal Analysis and Controls Laboratory. I worked with John in many different ways - as a consultant, a mentor and advisor, and as a colleague. His analytical roots were strong and deep and I learned much from him. From the late 80's to the end of the century, there were many experimental modal analysis seminars that were taught with Chuck Van Karsen; these seminars were often referred to as the Chuck and Pete show. Many commented how the material taught was so complementary to each other and that the lectures should always be arranged the same way because they were so well orchestrated; the reality was that we would pick straws at the start of each and every seminar and we never taught the same sections of the seminar each time - so much for complementary material. I hope that Chuck learned as much from me as I learned from him - those years teaching seminars reinforces the need for this book. Phillip Cornwell at Rose Hulman is one of the best teachers that I have run across in my years as an educator in this field. Phil has provided very useful comments in the development of this book.

Over the many years at the University of Massachusetts Lowell in the former Modal Analysis and Controls Laboratory and the current Structural Dynamics and Acoustic Systems Laboratory, I have been blessed with a wide number of excellent students in my research lab and their research efforts. All of them have made significant contributions to the research performed. While it is impossible to name all of them, they certainly know their contributions scattered throughout this book. But there are several that need special mention due to extra support and effort that is far beyond over and above. PawanPingle has been very helpful in looking at this book and giving a different perspective on things to address. Louis Thibault and Tim Marinone were always available to support some of the special items that were requested to illustrate a point or two. Sergio Obando had many test runs of which data is used in this book. Julie Harvie also provided useful feedback for the book as well as had many tests performed...