# Vibration Problems in Machines: Diagnosis and Resolution, 2nd Ed.

**1 PURPOSE**

As the author notes, turbomachinery is an important feature of many industries. The book discusses both monitoring and diagnostics in rotating systems. It does provide a good overview of turbomachinery and the analysis of issues made apparent by vibration. The best role for this text is to serve as a primer for those familiar with the principles of shaft vibration that want to use this knowledge to prevent and understand turbomachine operational and performance problems.

**2 SUMMARY**

The book seems intended to be a textbook. There are problems at the end of each chapter, solutions at the end, and MATLAB solutions available online. The book provides a good overview of the basic principles of shaft vibration but does not deal with any of the topics in typical academic detail. The strength of this book is in describing turbomachine operational characteristics and the vibrancy impact of normal and abnormal operations.

For those familiar with shaft vibrations, Chapter 5 forward will be the most valuable. These chapters describe common operational issues and present the means to model such phenomena. While describing the modeling approach, the author utilized actual data or described simple examples. The result is a good discussion of turbomachine problems and their vibrational effects. Whether for the reader who wants to model such phenomena or for that who wishes to understand measured data, the later chapters provide a useful guide.

**3 MEDIUM**

Chapter 1: Introduction

This is a broad introduction to rotating turbomachinery from monitoring to analysis to diagnostics. The author also

provides a summary of the content and topics of the following chapters.

Chapter 2: Data Presentation

This chapter attempts to cover the entire area of turbomachinery signal analysis and data presentation in 40 pages.

Clearly, this is not possible. The presentation does a comprehensive high-level discussion of the predominant data analysis and presentation techniques. The discussion is specific to the techniques used for turbomachinery. For those

familiar with vibration analysis, but not the specific practices applied to turbomachinery, this could be a good introduction. Due to the brief treatment, this chapter presents the basic premise of the analysis methods and the type of inferences that can be drawn from the results. There are no detailed examples or discussions of actual machine issues.

At the end of the chapter, the author provides some perspective on the data analysis considering the presence of noise and error in the measurements being collected. My favorite phrase from the book is the author’s note quoting Irons (1987), “Computing is for understanding, not numbers.”

Chapter 3: Modeling and Analysis

Somewhere between an introduction to modeling and a discussion of specific turbomachinery cases, this chapter touches on the basic concepts of modeling and turbomachinery vibration. The basic concepts of finite element analysis (FEA) are presented at a high level. As the author notes, this is far from a comprehensive description of FEA.

In a similar vein, the turbomachinery discussion introduces important concepts in rotating shaft vibration. Some simple examples of shaft dynamics are presented to illustrate the basics.

Chapter 4: Faults in Machines (1)

The author begins with a discussion of flexible and rigid shafts and systems. There is a discussion of shaft imbalance and multiple techniques for balancing shafts. This segment includes several basic problems with numerical examples. In the final segment, there is a discussion of recent advancements. The author refers the reader to later chapters for more information on these topics.

This chapter is more an introduction of fundamental concepts than an explanation of turbomachinery faults. The exception is the discussion of balancing which is more complete with examples.

Chapter 5: Faults in Machines (2)

This is the second segment treating machine faults. The treatment of more realistic problems seems to be where the author is focused. This treatment is more practical with a basic modeling foundation. The effect is to provide a good understanding for the reader of the problems and at least an introduction to possible modeling approaches.

There is a discussion of the sources of misalignment in terms of practical machine arrangements and shaft support. The major types of issues discussed include flexible and solid couplings, the shaft catenary, and the excitations due to couplings.

In the cracked rotors section, the author presents a means to model such problems and discusses the implications. Under torsional excitation, the author discusses the effects of different types of turbomachines including, pumps, turbines, and generators. He also provides the foundation of the impact of gear sets on torsional excitation.

The instability segment discusses oil-whirl and oil-whip in bearings and the impact on shaft vibration. This is followed by a discussion of synchronous and asynchronous excitation.

Chapter 6: Rotor-Stator Interaction

As the author notes, this chapter marks the transition from shaft dynamics to machine effectiveness. Rotor-stator interaction is discussed via the working fluid and through direct interaction. The author moves from basic examples and brief discussions of modeling principles to actual machine characteristics. For those familiar with vibrations or shaft dynamics, this is the first segment to really relate the basic principles to working machines.

The interaction through the bearings segment begins with the classic journal bearing phenomena and develops the basic equations for this case. There is also a discussion of rolling element bearings and their characteristics. The final segment in this section provides a brief introduction to other types of bearings.

In the interaction via the working fluid section, the author focuses on pump bushes and seals. Most of this section is devoted to pumps and the effects of the fluid and points of interaction. The interaction through direct stator contact is limited to a few specific cases. These include the Newkirk effect, collision and recoil, and the Morton effect.

Chapter 7: Machine Identification

The stated intent of this chapter is to present the latest developments and techniques in turbomachinery vibration. The current state of the modeling segment discusses techniques to align modes with actual performance. Under Primary Components, the discussion is divided into:

• The rotating elements

• The bearings and other interaction between rotor

and stator

• The stator and its supporting structure

The author notes that the accuracy of shaft models is quite high. The complexity of modeling bearings is highlighted. It is noted that bearings uniquely may contribute to stability or instability at different speeds. Inaccuracies and the difficulties in modeling as-built support structures are discussed in this segment. There is a discussion of these limitations and the errors that result.

The problems with system identification common to many built-up structures are discussed in the System

Identification section. Matrix inversion and the resulting errors and limitations are discussed along with regularization to minimize these effects. The use of least squares and the problems of ill-conditioned matrices are also discussed. The use of Kalman filters for modal analysis is discussed, and a more detailed presentation on Kalman filtering is provided.

Chapter 8: Some Further Analysis Methods

Under Standard Approaches, it is noted that critical plant systems require monitors in three categories:

• Detection of a fault

• Diagnosis and localization of a fault

• Corrections or mitigation of the effects of a fault

Major sections of this chapter are devoted to artificial neural networks and singular value decomposition. In the Useful Techniques segment, the discussion touches on:

• Hilbert transforms

• Time-frequency and Wigner-Ville analyses

• Wavelet analysis

• Cepstrum

• Empirical mode decomposition

Chapter 9: Case Studies

This chapter presents five case studies of actual turbomachine issues. The first is a crack on an alternator rotor. A detailed history of the operation and monitoring of the turbine-alternator train is presented. This is a good illustrative example. This is followed by discussions of modal testing of a cracked rotor, gearbox problems on a boiler feed pump, vibrations of a centrifugal pump, and low-pressure turbine instabilities. The first example is best illustrated with actual data.

Chapter 10: Overview and Outlook

This chapter discusses a number of possible future solutions and improvements in the field. In most cases, only a paragraph or two is devoted to the topic. One of the longer discussions is on progress in modeling. Current and future capabilities are discussed with practical observations on the potential of some of the techniques. Another topic with a lengthier discussion is shaft modification. Here, the author discusses the potential to respond to faults or to avoid operational issues by modifying the system. Various means to make modifications to shaft dynamics are discussed.

Solutions to Problems

Solutions to the problems at the end of each chapter are presented. While there is some discussion of the methods to be used, these are substantially the final results with minimal explanations. They are not complete solutions to any but the simplest problems.

**4 RECOMMENDATIONS**

With the understanding that this is not a comprehensive text in turbomachine vibration, I would recommend this text for those who want to model actual machine vibration or interpret the measured data from machines. It treats several real-world machine issues and provides a high description of what to expect and how to model such cases. To fully utilize this material, one should have a sound understanding of shaft vibration, vibrations, and turbomachine fundamentals.

*James K. Thompson, Ph.D., PE, INCE Bd CertJKT EnterprisesJKT.JKTEnterprises@outlook.com*