The work under review is devoted to the problem of the vibration of linear mechanical systems research.
Discomfort resulting from close association with vibrating mechanical systems is common experience: damage to components arising from oscillating stresses is common knowledge. Prime examples of delinquent systems cover the range from diesel-engined marine propulsion systems through building frames and transformer cores, panels of aircraft, turbo-alternator shafts, gas turbine rotors to gyroscopic instruments.
It is also well known that vibratory phenomena may be utilised in specially designed systems, for example to convey material, to drive foundation piles, or to filter out unwanted frequencies in electronic circuits.
Minimisations of discomfort and damage, and optimisation of systems which utilise vibration, are desirable goals: to achieve them it is necessary for engineers to understand how modifications to a system affect its oscillatory behaviour.
In the present trend towards more and more specialization, engineers in this field appear to concentrate either on experimental techniques associated with the development of equipment to a trouble-free state, or on theoretical techniques associated with technical design problems. Both occupations require a basic understanding of the theory of mechanical vibration; the former in order that the experimental results may be interpreted and changes in system parameters made in the correct direction; the latter as a basis for the for the development and use of methods for predicting the response of real systems, which generally are more complicated than necessary for a basic understanding.
As a field of study, vibration theory has wider application than indicated above. Oscillatory phenomena arise in many other areas of human activity, one of the most recent to become prominent being the control of management systems; fortunately much of the underlying eigenvalue theory is common. Therefore, although developed in this book in relation to the oscillations of mechanical systems, in studying the subject one has the satisfaction of learning a basic subject of relevance to a wide range of disciplines.
Essentially engineering in the use of a combination of art and science to solve problems which arise in harnessing the forces of nature on behalf of mankind. As an example of part of the art, successful engineers are assumed to have an instinct for correct proportions.
Special attention is paid in the article to the methods of scientific research. The increasingly used scientific approach to the discovery of knowledge may be expressed in terms of four steps:
1) define the problem, or refine its definition;
2) model the relevant aspects of the real world situation, usually mathematically;
3) use the model to discover its relevant behaviour;
4) check the validity of the model by comparing this behaviour with that of the real system, and return to (1) continuing the sequence as often as necessary.
That is, in scientific discovery the model is continually refined until eventually it predicts, without exception, the behaviour of the real system.
Engineering design involves steps similar to the three, but instead of step four the results of step three must be interpreted in a design. Model refinement, if it is necessaiy, arises at the development stage and may result in costly hardware modifications. Hence, problem-solving is an engineering design environment involves a considerable knowledge of the state of the art in that particular field of application at the problem definition and modeling stages, if previous
errors are to be avoided. Design involves a compromise between many conflicting requirements, hence interpreting the model results is also an art.
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