Analysis of stiffening effects on ship vibrations

Abstract

Vibration is a subject of continual interest to naval architects, shipbuilders, marine engineers and shipowners. Its presence can ruin the reputation of a passenger ship and seriously impair the fighting efficiency of a warship. Its avoidance should be one of the aims present in any designer-s mind when engaged in planning a new ship. Vibrations experienced on board ships may be divided broadly into two classes. In the first type, the whole hull girder is thrown into a state of vibration at certain revolutions of the main engines or of some auxiliary machinery and in serious cases the movement of the hull can be clearly seen by sighting along the ship. The seriousness of such vibration depends on the revolutions at which it occurs in relation to those required to be used in service, for it is quite impracticable to run a ship in such a condition for very long without loosening rivets and causing a marked deterioration of fittings in general. Such vibration, affecting the whole hull structure, is known as resonant vibration. In the second type, isolated parts of the ship or certain fittings such as bridge structure, a mast or a panel of plating, are set in a state of vibration which, although not in general in any sense dangerous to the ship, can yet be annoying to passengers and crew. Such vibration is usually termed local vibration, its cure generally call, first for removal of the offending source and if it is not possible, then local treatment must be applied in the form of the provision of extra stiffening [...].