1975-02-01

Modes of Engine Structure Vibration as a Source of Noise 750833

This paper presents the results of recent investigations carried out at I.S.V.R. into the mechanism of structurally radiated noise.The overall modal characteristics of a simplified engine structure have been analysed theoretically using finite element programs developed at I.S.V.R. and a comparison is made with experimental results obtained on an equivalent physical model cast in one piece to minimise damping. These results have given an important new insight into the vibration behaviour of a typical engine block casting.The mechanism whereby the modes of vibration of a typical engine structure are excited by the forces in each cylinder is analysed in conjunction with experimental results obtained by a novel static deflection technique. Also presented are the results of a study into the optimum way of isolating a light panel from block induced vibration.The acoustic power radiated by representative modes of engine vibration through the acoustically important frequency range is discussed and some results of directivity tests are also given.

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