Noise and Engineering Design

T. Priede
1968 Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences  
I ntroduction T he paper presents a short account of various investigations carried out on the basic mechanism of noise produced by machines involving solid structures. T he emitted noise of the m achine is generally due to bending vibration of either the outer or inner surfaces or both. In vehicles, for example, consideration of both the internal and external surfaces is of im portance : vibrations of the internal surfaces produce noise inside the cab or car saloon and this affects the driver
more » ... affects the driver and passengers, while the external surfaces produce the noise which affects the community. T he vibrations which produce excessive noise are very seldom detrim ental to the opera tion or the life of the machine. In m any cases a noisier m achine is more efficient and often has a greater life expectancy. A typical example is the comparison of the noise produced by a petrol and a diesel engine. The diesel engine operates at higher peak cylinder pressures and higher rates of pressure rise resulting from combustion. These factors are the prim ary causes of considerably greater noise. T he diesel engine, however, is not only the most efficient prime mover, but also, because of its compactness, its life is several times th at of a petrol engine. Operational life of over 200000 miles without appreciable m aintenance is not uncommon. There are m any aspects of present-day machine design trends which follow general economic considerations, but which result in greater emitted noise. In transport, every effort is made to reduce the weight of the vehicle for the same load carrying capacity, examples of this are air cooling, the use of light-weight materials and higher operational speeds. Similar trends can be easily recognized in the production industry. In general, the improvement in efficiency and economy of the machines results in higher levels of noise. This trend imposes greater difficulties on effective noise control. Thus in every case a clear understanding of the machine design, its operation and environment, is required; only then will worthwhile reductions of noise be achieved within the economic framework. . M echanism of generation of vibration and noise in machines W hen considering a simple single degree of freedom vibratory system there are two factors which determine vibration am plitude: (a the characteristics of the force, and (b) the characteristics of the vibratory system. The emitted noise, however, will also depend on the size of the vibratory system in relation to the frequency of vibration. For machines, which are generally very complex structures and which are set into vibration by numerous exciting forces of complex nature, the same basic principles apply. It could be stated that machine noise is determined by the form, the m agnitude and the 57-2
doi:10.1098/rsta.1968.0030 fatcat:4pi3kcv7rbazpo7s7t3zfkxede