Recently, problems such as a coupled vibration of engine structure and engine room (a part of a ship's hull) are tending increase as ships' hulls and engines become larger.
In order to make clear the vibratory characteristics of engine structures and engine rooms, and to obtain an analytical method of their coupled vibration, the authors have carried out some fullscale vibration measurements by means of a vibration generator attached on the cylinder cover of the engine. And the following results were derived from the investigation.
(1) Three types of vibration pattern of the engine structure, H-type, X-type and x-type, could be excited by one vibration generator.
(2) The measurements, which made under the condition of foundation bolts, tie bolts and oil doors altered from the standard, showed that their frictional resistance affected on the vibration amplitude of engine structure, especially on the X-type of vibration.
Oil doors greatly contributed to the strength of the engine structure in transverse and longitudinal direction.
(3) There were many natural frequencies seen in H-type and X-type vibration of the engine structure because of its coupling effects with the engine room vibration. The natural frequencies had a tendency to decrease as the exciting force of the vibration generator increased. The latter facts showed that the vibration of engine structure was a king of non-linear, and this was caused by sliding of parts in the engine structure.
(4) The resonant frequencies of the engine structure at trial running could be estimated from the results obtained by the vibration generator tests.

View full abstract