Study On The Added Water Mass Calculation Method Of SWATH Ship

When the natural frequency of ship’s global vibration is proximity or coincidence with frequency of ship’s main motivation, the resonance will occur and cause unnecessary harm, so the natural frequency of ship’s global vibration is predicted in early stage of ship design. The outboard water has very important effect on ship vibration, so it is necessary to take into account the added water mass in the prediction process.SWATH (Small Waterplane Area Twin Hull) ship has many advantages compared with monohull ship, but also because of its unique hull form, many calculation formulas of added water mass cannot be used to estimate added water mass of SWATH ship, which has an effect on the prediction of natural frequency of SWATH ship, so it is very necessary to carry on the thorough research to the calculation method of added water mass of SWATH ship.The fluid structure coupling vibration is a complicated problem, which involves fluid dynamic and structural dynamic. Under normal circumstances, it is difficult to get the analytical solution, only the numerical solution can be used to calculate, In the second chapter, detailedly explained and derived FEM (finite element method) and BEM (boundary element method) for solving the problem of fluid structure coupling vibration of ship, and compared two methods with a simple model of SWATH ship.In the third chapter, using two-dimensional BEM program and present calculation formula of added water mass, studied on the influence of different section shapes on the added water mass. On this basis, taking the simple model of SWATH ship as the research object, studied on the influence of different demihull spacing on the added water mass. Based on the two aspects, proposed the calculation method of added water mass of SWATH ship.In the fourth chapter, established a three-dimensional finite element model of a SWATH testing ship and calculated its wet modal by BEM and calculation method presented in this paper, verified the feasibility of calculation method of added mass water presented in this paper by comparing results. Then the reliability of numerical simulation is verified by comparing the experimental result.