The Effect of Loading Conditions on Ship Vibration Characteristics

선박(船舶)의 적화상태(積貨狀態)가 선체진동(船體振動) 특성(特性)에 미치는 영향

The loading condition, of a ship, especially a multi-purpose cargo carrier, in service, is often changed. Then, the prediction of natural frequency changes is necessary to provide measures for prevention of ship vibrations. In this paper a simplified method for the above purpose is presented. The bases of the method are analytical solutions for the lateral vibrations of uniform Timoshenko beams carrying a concentrated mass and the Dunkerley's formula. In this method a ship in the standard ballast condition is reduced to a uniform Timoshenko beam having same system parameters as those of the midship section. To investigate the validity of the proposed method, numerical calculations are carried out for a 46,000 DWT bulk carrier and compared with detailed calculations based on the finite difference method. Even in cases those the cargoes in a hold, length of which is about 13% of the ship's length, are reduced to a concentrated mass, the proposed method gives results of several percent differences from the detailed calculations up to the six-noded mode.