On Impact Force Of Berthing Ship And Moored Ship Under The Action Of Waves

In port engineering, the impact on a berthing structure of a ship is a destructive load, especially to the large-scale open port. The accurate calculation on the berthing impact of the ship is of great importance to the rational designing port and the safe operation of the port. If a simple and accurate calculation method can resolve this problem, the physical model experimentation would not necessarily operate. So the project cost could reduce by saving investment. An existing formula for calculating the impact of the ship has been given in the"Load Code for Harbour Engineering"in China in 1998. But some port engineers found the values of berthing impact calculated by this formula were not accurate enough, while they designed large-scale open ports. In this paper, a revising suggestion for the formula of the Code is advanced through research. For the large-scale open port, sometimes the berthing impact caused by moored/berthed ship under wave action is larger than that by ship during berthing operation. First, the berthing impact caused by moored/berthed ship under wave action is researched in this paper. A mathematical model on the motion of a berthing ship in the frequency domain is established, and analyzed by potential flow theory of Fluid Mechanics. The numerical method is adopted in the solution procedure. The added mass, radiation damping, exciting force and berthing impact are computed. Then applying Cummins's method, the numerical results in time domain are obtained by the Fourier transform of the radiation damping. The results in time domain are not depended on the frequency of the wave. In this paper, the added mass in time domain is transformed to added mass coefficient as the date for future.For series of ships in different berthing conditions, the added mass coefficients are obtained by the numerical method. Combining other test dates with these, the major influence factors (ship beam, draft, water depth) on the added mass coefficients are found and the mathematical relation between them are determined by dimensional analysis as well. A new formula for added mass coefficient has been established by the multivariate regressive analysis with MATLAB.When the values calculated by the present formula are compared with test dates, it is improved that the present formula is applicable for the ship during berthing operation. Only the added mass coefficient is the most important part of revising works for the impact calculation. Other which needed revising parts is modified on the base of much reference as well. After much calculating by the new formulas, it is testified that the result precision can be insured.