vibration problems in machines diagnosis and resolution pdf

The understanding of vibration signals from turbo-machinery is an important feature of many  industries. It forms the basis of condition monitoringand is of crucial importance in the rapid diagnosis and rectification of faults. The field calls for a variety of skills ranging from instrumentation expertise to mathematical manipulation and signal processing. The focus is on gaining a physical understanding of the processes giving rise to vibration signals. This may be viewed as a process of seeking to infer internal conditions from (sometimes limited) external measured data.

This often requires some form of mathematical model, and the approach
taken is to use some basic finite element analysis to study system behaviour.
These methods were first applied to rotating machinery several decades ago, but with progress in computing and the advent of packages such as MATLAB®, the ease with which the concepts may be applied has dramatically improved. It is now a relatively straightforward matter to examine proposed design changes – in effect, to perform numerical experiments.

The material in this book stems both from my experiences in the industry and, in more recent years, of teaching and research in academia. Inevitably, my own experiences have, to some degree, influenced my choice of examples. In my various posts, I have had fruitful interactions with many people who have significantly enhanced my perception of problems in machinery.
There are too many people involved to thank individually, but I must mention three. Professor Mike Friswell and I have worked together closely for 20 years, and I acknowledge innumerable helpful and illuminating discussions. I also thank Professor John Penny for his help with proofreading and a
number of helpful suggestions on the structure of the text.

Both of these people were my co-authors, together with Professor Seamus Garvey, of the book
I refer to in many places which gives a more complete discussion of rotor
dynamics. My deepest thanks go to my wife, Rita: Not only has she given me
grammatical advice, but has also helped maintain my sanity throughout the
final months of preparing this text.

The general field of condition monitoring has received substantial attention
over the last few decades and it is worth reflecting on the state of the topic,
because, although it has always been practised at some level, the manner in
which condition is assessed is constantly under review in the light of recent
developments in understanding.

In assessing the condition of a piece of equipment, the operator gathers data such as vibration, operating temperature, noise, performance and electrical parameters where appropriate. At one time, the comparison with normal condition was achieved largely on the basis of staff experience, but
the general trend has been towards a more precise quantified approach.

This has been required by revised patterns of working and increasing
plant complexity, but it is, in essence, the same operation. A fundamental
question arises of how one can ‘codify’ the knowledge of an experienced
engineer and focus the knowledge on a specific area of plant. This presents
indeed a challenge which has shown significant progress in recent years,
although the issue cannot be regarded as completely resolved.

Important progress has been made in computational modelling (both finite element
analysis (FEA) and computational fluid dynamics (CFD)), artificial neural
networks (ANNs), statistical approaches, expert systems and identification
methods. All of these have a role to play in assessing the condition of a piece
of equipment and their role will be outlined in subsequent chapters. First of
all however, the general field of condition monitoring, as applied to rotating
machines, is reviewed.