chapter  1
18 Pages

Vibration Engineering

Vibration is the repetitive, periodic, or oscillatory response of a mechanical system. The rate of vibration cycles is termed ‘‘frequency.’’ Repetitive motions that are without aberrations and are regular and occur at relatively low frequencies are commonly called ‘‘oscillations’’ whereas any repetitive motion, even at high frequencies, with low amplitudes and having irregular and random behavior falls into the general class of vibration. Nevertheless, the terms vibration and oscillation are often used interchangeably, as is done in this book. Vibrations can occur naturally in an engineering systems and will be representative of

their free and natural dynamic behavior. Vibrations also may be forced onto a system through some form of excitation. The excitation forces may be either generated internally within the dynamic system or imparted on the system through an external source. When the frequency of the forcing excitation coincides with that of the natural motion, the system will respond more vigorously with increased amplitude. This condition is known as ‘‘resonance,’’ and the associated frequency is called the ‘‘resonant frequency.’’ Vibrations can be ‘‘good’’ or ‘‘bad,’’ the former serving a useful purpose and the latter having unpleasant or harmful effects. For many engineering systems, operation at a resonance would be undesirable and could be destructive. It is important to study human’s responses to vibrations. Suppression or elimination of bad vibrations and generation of desired forms and levels of good vibration are the general goals of vibration engineering. This book deals with the analysis, observation, and modification of vibrations in engineer-

ing systems. Applications of vibration are found in many branches of engineering such as aeronautics and aerospace, civil, manufacturing, mechanical, mechatronics, and even electrical and electronics. Usually, an analytical or computer model is needed to analyze the vibrations in an engineering system. Models are also useful for the design and development of an engineering systems for good performance with respect to vibrations. Monitoring and testing of vibrations and experimentation are also important in the design, implementation, maintenance, and repair of engineering systems. As all these topics of study are important in the field of vibration engineering, this book will cover, as pertinent, the following:

2. Analysis

3. Design

4. Experimentation

5. Control

In particular, practical applications and design considerations related to modifying the vibrational behavior of mechanical devices and structures will be studied. This knowledge will be useful in the practice of vibration regardless of the application area or the branch of engineering; for example, in the analysis, design, construction, operation, and maintenance of complex structures such as the U.S. Space Shuttle and the International Space Station (Figure 1.1). It can be seen in Figure 1.1 that long and flexible components, which would be prone to complex ‘‘modes’’ of vibration, are present. The structural design should take this into consideration. Also, functional and servicing devices such as robotic manipulators (e.g., Canadarm) can give rise to vibration interactions, which must be controlled for accurate performance. The approach used in this book is to introduce analysis, computer techniques, and practical applications of vibrations in the very beginning, along with experimental techniques, and then integrate the applications and design considerations into fundamentals and analytical methods throughout the text.