Study On The Global Vibratian Added Water Mass Of Trimaran

As a ship type with good capability,the high-speed trimaran has been attracting the world's attention. Because of its particular type, good capability and tactical performance, the high-speed trimaran will be widely applicated in the fields of warship and civil ship, and even be thought to be aircraft carrier. As well as ordinary ships, when they sail in the water,harmful vibration may occur due to all kinds of drive.To prevent the generation of harmful vibration, the global vibration performance of high-speed trimaran must be calculated in the course of ship design, so that reasonable scheme and necessary measures can be taken to prevent the harmful vibration.The global vibration added water mass of ternate-cylinders have been analyzed by finite element software ANSYS in this paper, and used in the study of global vibration modal analysis of trimaran.The main work is as follows:1) Verify the feasibility of this method.First, the added water mass of single-cylinder is analyzed by this method. The result shows that the added water mass we calculate is less than the result of theoretic calculation. Because theoretical added water mass is used by potential theory that the cylinder is though to be a rigid body, but in ANSYS the material is steel, so the result is less than the theoretical calculation.Then, the added water mass of dual-cylinder is analyzed by this method. According to the results it is obtained:the added water mass of dual-cylinder is influented by the distance between the cylinders. When the distance between the cylinders increase, the added water mass discrease,and tends to be value when the distance increase to a certain value. This is consistent with the experiments done by Weng Changjian. In contrast, horizontal vibration added water mass increases when the distance ldiscrease.2) The ternate-cylinder added water mass. According to the results it is obtained: added water mass of ternate-cylinders is influented by the size of side body and the distanse between main body and side body, the added water mass of vertical vibration increase when the size of the body increase or the distance decrease. Horizontal vibration added water mass is in the contrast. The two factors influence coefficient curve is given based on the result.3) For the preliminary designed high-speed trimaran, dry and wet modalities have been calculated in the paper. Because the added water mass only influence the frequency,but not the free vibration shape, the first four overall vibration shapes have been obtained by dry modality calculation.