Study On The Calculation Of Wave-induced Load In Longitudinal Strength Analysis Of Ship With Small Block Coefficient

In the process of strength assessment of ship structures,wave-induced load,that means to say,additional wave bending moment and shear force has always been the main components of ship hull external load,which draw attention of ship structure engineers.For conventional ship type,some ship hull longitudinal strength calculation methods for wave-induced load are proposed by classification society rules.For irregular ship form,the direct calculation method is generally used to estimate the wave-induced load.In particular,is to use the linear method based on frequency-domain and spectrum analysis for long-term predication.This calculation method may make relatively accurate forecasts on wave-induced load of ship with large block coefficient and straight broadside similar to large container ship.But for high speed ship with small block coefficient and large bow flare,sailing in the actual process.The wave dynamic effect and the full shape change under sharp movement have significant effects on wave transient character,so large error will occur when linear method based on frequency-domain is applied to ships with small block coefficient.In view of these problems,two kinds of ship type,one with large flare and small block coefficient and the other with straight broadside are set as research object in this paper,using different methods to calculate the additional wave load of them.The main work and conclusions are following:a)Research combed the commonly used methods in the whole assessment of longitudinal strength and the development process of the wave-induced load computational method,and then compared the linear method based on frequency-domain and nonlinear method based on time-domain.b)A ship with large flare and small block coefficient and the other with straight broadside and large block coefficient are established as research object.Four present regulations were used to calculate their wave additional load.It is found the specification tend to think that,the former one has a greater wave-induced moment in sagging condition and smaller result in hogging condition than the later one.c)Based on the theory of Trochoid wave,the above two models' wave load were calculated by FEM,and the analysis find that wave additional load in sagging condition is greater than that in hogging condition.In addition,ship with straight broadside and large block coefficient tends to have a higher wave-induced load in hogging condition,worthy of attention after superimposed on hydrostatic load.d)Hydrodynamics numerical method was used to calculate wave-induced load of two models.Results shows that the design wave method based on frequency-domain linear algorithm,without considering the dynamic effect of waves,has a certain deviation in solving wave-induced loads of ship with small block coefficient and large flare.In addition,through the comparison based on the standard formula and finite element calculation,based on the theory of the Trochoid wave and wave-induced load based on the hydrodynamic numerical algorithm of the calculation results,the wave-induced loads at mid-section of two models were analyzed.It turns out the hogging additional wave moment given by frequency-domain linear algorithm tend to be on conservative side.