- Email: [email protected]
Machinery noise and diagnostics
Mechanical Systems and Signal Processing (1988) 2(3), 305-307
B O O K REVIEW R. H. Lyon, Machinery Noise and Diagnostics, £35. Butterworths, 1987. ISBN 0 409 90101 6 The book presents a practical insight into acoustic signal analysis of noise and vibration emitted from machines. In this context two categories are of interest, namely, reduction of noise and vibrations and diagnostics. The introductory part of the book shows the usefulness of the two subjects in various applications of mechanical engineering. Later on the author systematically develops a design discipline, based on long practical experience. This design discipline links basic theory, accumulated experience and solutions to sound and vibration problems. Using basic formulae and physical understanding, with the addition of necessary analysis, a sound methodology is built, presenting fundamental design principles which every consultant on machinery noise should acquire. The profound interpretation of the relations between the parameters of the problem, which are given in terms of input/output acoustic signals focus on what is really important. Indeed, Professor Lyon has published a long series of papers and reports and his book is based on a seminar on machinery noise and diagnostics he organised and ran. The book therefore looks like a summary of the subject and is convenient to read and comprises a systematic review of the chain: sources--transmission---criteria--solution/diagnostics. In the following part of the book the author describes typical noise and vibration sources, including various types of imbalance, impact, shafts, gear meshes, crank-slider mechanisms, magnetic forces, combustion and turbulent boundary layer. The interaction between excitation and structure is explained, and especially the contact force at high frequencies. At this early stage, the author illustrates diagnostic elements and solutions to noise and vibration problems, in spite of the fact that specific problems are dealt with, generality is not lost. The next chapter discusses structural responses to dynamic excitation. The various kinds of elastic waves that usually propagate in such structures are characterised, demonstrating the mechanical radiation through various machinery elements. Essential terms such as mobility, damping, modal density, transfer function, modal response of a finite structure, reciprocity and many others are defined. Simple elements, which include straight beams and plates are used to illustrate the application of these definitions. More complicated machinery parts are then analysed. The author provides details about the response of a machine imbalance forces, transmission of forces and an isolator of a flexible system. The systems also include high-rise buildings and ship structures and the same methods may be used for other types of systems as well. The fourth chapter presents mobility as a means of design for structural changes, in order to reduce the magnitude of vibration. A very good correlation between experiment and theory is observed in this case, even for complicated machine parts. A method for the definition of the most dominant path of sound and vibration transmission is also included. The author recommends the combination of experimental results with theoretical models as a very efficient approach, which yields in turn improved predictions. Flanking of vibration from the element on which the source acts to the other parts of the machine, via the structural junctions, is a major item in this chapter. Here joint mobilities and coupling loss factors are used for the formulation. The influence of the modal densities 3O5 0888-3270/88/030305+03 $03.00/0 © 1988 AcademicPress Limited
306
BOOK REVIEW
on the coupling is used later in the chapter for a description of the SEA method, about which the author has written another book. The applicability and efficacy of this method is demonstrated using an example of combined structural elements of a ship. The fifth chapter uses the description and explanation of methods from the previous chapters for the estimation and reduction of structural vibration. It is concerned with sound radiated by machines, where radiation efficiency is applied as a primary measure. The substantial difference in radiation under and above the critical frequency is taken into account. Following his methodology, the author begins his description with the simple case of a pulsating sphere, and then he goes on with other elementary sources--a piston loaded by vertical force and torsion, radiation through an exit of a muzzle blast and the radiation caused by a collision of solid bodies. Complicated problems, such as identifying the power of a weak source within an intense sound field, is done by applying the reciprocity principle. Description of the most important factors in sound radiation from machine elements summarises this chapter and the acoustic treatment of noisy machines. The sixth chapter begins the series of chapters, which deal with diagnostics. This chapter deals with the simplest kind of diagnostics, which is based on the energy content of the signal. The method determines the changes in the signal power due to faults in the machine. Deficiencies of the method are mentioned, especially in locating the fault. The demonstrations include rotating machines, gear meshes, ball bearing with race defects, horizontal centrifuge, diesel engine and a valve. The diagnostics include identification of modulations due to faults, analysis of peaks in the power spectrum of noise transmitted through machine parts and separating the "low time" part of the output time function, by windowing, in order to distinguish the effect of the source from the effect of the path. Modal analysis is used in order to identify unwanted normal shapes, e.g. bending modes in a longitudinal vibration of a rod. The application of inverse filters for the source and the path is presented and the chapter is concluded by the analysis of uncertainty in sound transmission and the statistics of the transfer function. Signal phase diagnostics are presented in the seventh chapter. The aim is mostly a reliable reconstruction of input signal out of the output measurements and definition of faults along the path of propagation of vibration. Hence, the shape of the signal, which is strongly influenced by the phase function, becomes very important. The techniques used for the phase diagnostics are: inverse filters, cepstral analysis and windowing within the frequency domain, for example, cepstral analysis allows the identification of late arrivals of signals. The development of this complicated technique is done by gradual improvements and sophistication which finally result in clear and unique consequences. The author extends the one-dimensional investigation to the case of phase in two dimensions. He supports his claims by experimental tests and phase variance analysis for various structural systems. It should be mentioned here that cepstral analysis and Hilbert transforms used in this chapter are at the frontiers of acoustic diagnostics of machinery. Future trends in acoustic diagnostics are discussed in chapter 8. These methods are bound to allow diagnostics and wave form reconstruction in complicated situations, such as simultaneous excitation by several sources. A general scheme of computerised sets for diagnostics which may include subroutines for a variety of applications is illustrated. Finally, the use of orthonormal functions for the description of various signals is suggested: Laguerre functions for impulse and step functions, Hermitian functions for the description of phase and log magnitude, and Beranek functions which are involved with Hilbert transforms of Hermite functions.
BOOK REVIEW
307
At the end of the book there are three appendices which include the relevant mathematics, criteria for noise and vibration of machines, definition of transfer functions and measured data. The book, in general, uses basic principles for the physical interpretation of machine responses to dynamic sources. This background allows engineering recommendations concerning noise and vibration control and diagnostics. Since the author uses the most important factors for constructing design and control methods, the number of principles to be remembered is not large, but their knowledge is a powerful device in this context. Hence, the book is recommended both for the expert and the beginner, it is an inexhaustible source of motivation in studying the applicative constituents of acoustics in mechanical engineering, and the possibility of diagnostics based on measurements of sound wave transmission through the structure and in its vicinity. G. ROSENHOUSE
Israel Institute of Technology, Haifa
B O O K REVIEW R. H. Lyon, Machinery Noise and Diagnostics, £35. Butterworths, 1987. ISBN 0 409 90101 6 The book presents a practical insight into acoustic signal analysis of noise and vibration emitted from machines. In this context two categories are of interest, namely, reduction of noise and vibrations and diagnostics. The introductory part of the book shows the usefulness of the two subjects in various applications of mechanical engineering. Later on the author systematically develops a design discipline, based on long practical experience. This design discipline links basic theory, accumulated experience and solutions to sound and vibration problems. Using basic formulae and physical understanding, with the addition of necessary analysis, a sound methodology is built, presenting fundamental design principles which every consultant on machinery noise should acquire. The profound interpretation of the relations between the parameters of the problem, which are given in terms of input/output acoustic signals focus on what is really important. Indeed, Professor Lyon has published a long series of papers and reports and his book is based on a seminar on machinery noise and diagnostics he organised and ran. The book therefore looks like a summary of the subject and is convenient to read and comprises a systematic review of the chain: sources--transmission---criteria--solution/diagnostics. In the following part of the book the author describes typical noise and vibration sources, including various types of imbalance, impact, shafts, gear meshes, crank-slider mechanisms, magnetic forces, combustion and turbulent boundary layer. The interaction between excitation and structure is explained, and especially the contact force at high frequencies. At this early stage, the author illustrates diagnostic elements and solutions to noise and vibration problems, in spite of the fact that specific problems are dealt with, generality is not lost. The next chapter discusses structural responses to dynamic excitation. The various kinds of elastic waves that usually propagate in such structures are characterised, demonstrating the mechanical radiation through various machinery elements. Essential terms such as mobility, damping, modal density, transfer function, modal response of a finite structure, reciprocity and many others are defined. Simple elements, which include straight beams and plates are used to illustrate the application of these definitions. More complicated machinery parts are then analysed. The author provides details about the response of a machine imbalance forces, transmission of forces and an isolator of a flexible system. The systems also include high-rise buildings and ship structures and the same methods may be used for other types of systems as well. The fourth chapter presents mobility as a means of design for structural changes, in order to reduce the magnitude of vibration. A very good correlation between experiment and theory is observed in this case, even for complicated machine parts. A method for the definition of the most dominant path of sound and vibration transmission is also included. The author recommends the combination of experimental results with theoretical models as a very efficient approach, which yields in turn improved predictions. Flanking of vibration from the element on which the source acts to the other parts of the machine, via the structural junctions, is a major item in this chapter. Here joint mobilities and coupling loss factors are used for the formulation. The influence of the modal densities 3O5 0888-3270/88/030305+03 $03.00/0 © 1988 AcademicPress Limited
306
BOOK REVIEW
on the coupling is used later in the chapter for a description of the SEA method, about which the author has written another book. The applicability and efficacy of this method is demonstrated using an example of combined structural elements of a ship. The fifth chapter uses the description and explanation of methods from the previous chapters for the estimation and reduction of structural vibration. It is concerned with sound radiated by machines, where radiation efficiency is applied as a primary measure. The substantial difference in radiation under and above the critical frequency is taken into account. Following his methodology, the author begins his description with the simple case of a pulsating sphere, and then he goes on with other elementary sources--a piston loaded by vertical force and torsion, radiation through an exit of a muzzle blast and the radiation caused by a collision of solid bodies. Complicated problems, such as identifying the power of a weak source within an intense sound field, is done by applying the reciprocity principle. Description of the most important factors in sound radiation from machine elements summarises this chapter and the acoustic treatment of noisy machines. The sixth chapter begins the series of chapters, which deal with diagnostics. This chapter deals with the simplest kind of diagnostics, which is based on the energy content of the signal. The method determines the changes in the signal power due to faults in the machine. Deficiencies of the method are mentioned, especially in locating the fault. The demonstrations include rotating machines, gear meshes, ball bearing with race defects, horizontal centrifuge, diesel engine and a valve. The diagnostics include identification of modulations due to faults, analysis of peaks in the power spectrum of noise transmitted through machine parts and separating the "low time" part of the output time function, by windowing, in order to distinguish the effect of the source from the effect of the path. Modal analysis is used in order to identify unwanted normal shapes, e.g. bending modes in a longitudinal vibration of a rod. The application of inverse filters for the source and the path is presented and the chapter is concluded by the analysis of uncertainty in sound transmission and the statistics of the transfer function. Signal phase diagnostics are presented in the seventh chapter. The aim is mostly a reliable reconstruction of input signal out of the output measurements and definition of faults along the path of propagation of vibration. Hence, the shape of the signal, which is strongly influenced by the phase function, becomes very important. The techniques used for the phase diagnostics are: inverse filters, cepstral analysis and windowing within the frequency domain, for example, cepstral analysis allows the identification of late arrivals of signals. The development of this complicated technique is done by gradual improvements and sophistication which finally result in clear and unique consequences. The author extends the one-dimensional investigation to the case of phase in two dimensions. He supports his claims by experimental tests and phase variance analysis for various structural systems. It should be mentioned here that cepstral analysis and Hilbert transforms used in this chapter are at the frontiers of acoustic diagnostics of machinery. Future trends in acoustic diagnostics are discussed in chapter 8. These methods are bound to allow diagnostics and wave form reconstruction in complicated situations, such as simultaneous excitation by several sources. A general scheme of computerised sets for diagnostics which may include subroutines for a variety of applications is illustrated. Finally, the use of orthonormal functions for the description of various signals is suggested: Laguerre functions for impulse and step functions, Hermitian functions for the description of phase and log magnitude, and Beranek functions which are involved with Hilbert transforms of Hermite functions.
BOOK REVIEW
307
At the end of the book there are three appendices which include the relevant mathematics, criteria for noise and vibration of machines, definition of transfer functions and measured data. The book, in general, uses basic principles for the physical interpretation of machine responses to dynamic sources. This background allows engineering recommendations concerning noise and vibration control and diagnostics. Since the author uses the most important factors for constructing design and control methods, the number of principles to be remembered is not large, but their knowledge is a powerful device in this context. Hence, the book is recommended both for the expert and the beginner, it is an inexhaustible source of motivation in studying the applicative constituents of acoustics in mechanical engineering, and the possibility of diagnostics based on measurements of sound wave transmission through the structure and in its vicinity. G. ROSENHOUSE
Israel Institute of Technology, Haifa