Numerical Modeling Of Wave-Induced Ship Motions

An important function of the port is reducing the ship motions and minimizingthe wave-induced loads so as to handle cargoes conveniently. Now, in domestic andinternational design norms, there are mainly two expressions for the equilibriumstandard of a berthed ship: one is the acceptable wave height in front of the quays, theother is the amplitude of ship motions. However, ship motions are closely related towave period, height and ship properties. Consequently, it is very irrational toseparately take wave height or oscillation amplitude as the equilibrium standard. Thetraditional method to study this question is physical modeling. But physical model isonly suitable to be conducted in the determine process owing to its great expensive.So, the numerical modeling is an appropriate tool to provide necessary data for thechoice of port plans in the initial design stage. This paper employs the improved slice theory-STF method and Simple GreenFunction method, which is used to solve 2-dimension radiate potential function, toestablish the differential equations of ship motion in harbor. Furthermore, a computerprogram based on the above theories is developed. Different from the former works,this paper not only takes account of the boundary condition of open basin, but alsodiscusses the case of solid wharf. Moreover, the paper introduces the formulas ofnonlinearrolldamping improving the original method. Comparisons between computed values and other references or experimental dataare presented in this paper. The agreement is good. At the same time, the effect ofwave direction and period to the ship motions is discussed in this paper. The result from the paper indicates that if a designer knows the geometricdescription, the weight distribution and sea conditions, he can predict the ship motionsand wave-induced forces in harbor with reasonable accuracy, which is very helpful forthe choosing of port plans.