Methods For Ship Local Slamming Loads And Structural Response Calculation

Local slamming loads and structural response is a key problem in the design of ship structure,and it is also a hot issue in this field at present.In order to reasonably design ship local structures which are frequently subjected to slamming loads and also to increase the discourse power of our country during the enactment of clauses about ship slamming in the common rule of the International Association of Classification Societies(IACS),some research work were carried out in this paper.Taking into account the complexity of ship slamming,the 2D slamming problem was firstly discussed and water entry of wedge and curved sections was studied.Through analyzing the Modified Logvinovich Model(MLM)that could be applied in water entry of the wedge,a semi analytical model was proposed,which has modified the unreasonable negative pressure and pressure distribution in MLM model and was adequate for flow separation.Based on the semi analytical model,a new method for predicting maximum pressure coefficients was presented,which could consider the effect of the change of deadrise.The applicability of the semi analytical model to the analysis of water entry of wedge and curve sections was verified by comparing results of the semi analytical model and the commercial software LS-DYNAConsidering the elasticity of actual structures,a hydroelastic method was presented to analyze water entry of a complex wedge grillage and a numerical program was also developed.Comparing results of the hydroelastic program and LS-DYNA during solving water entry of a panel beam model,the damping term of the hydroelastic program was proved unreasonable and a damping correction factor was introduced to improve the program.For a panel beam model and a complex wedge grillage,calculation results of the improved hydroelastic program and LS-DYNA were compared and the correctness of hydroelastic method was verified.The experiment investigation of water entry of 2D and 3D models was carried out.Through analyzing test data,test results showed good stability.Through comparing results of the experiment and LS-DYNA for the 2D model,the numerical analysis method of this paper by using LS-DYNA was verified.The test technology for the 3D model was introduced and based on the test data,a fast calculation method to predict maximum pressure coefficients of the bow flare zone was proposed.The study on the method of predicting the ship local slamming loads was carried out.Base on the three-dimensional linear frequency domain theory and three-dimensional nonlinear time domain theory,the relative motion between the ship and the wave was calculated.Through the probability analysis of the vertical impact velocity in the short design sea state,the vertical design impact velocity was obtained.Combining the vertical impact velocity and maximum slamming pressure coefficients,the design slamming pressure which just considered the vertical motion was achieved.Synthesizing the three-dimensional linear frequency domain theory,probabilistic analysis method,the result of the drop test and LR rule,a more rational calculation method of pressure load design was proposed.The research of local structural response under the slamming loads was carried out and an assessment method which could be applied in real ships was given.Through introducing an equivalent static coefficient,the relationship between the dynamic response and the static response of local structure was established.According to water entry of an elastic wedge grillage,the influence of impact velocities,angles of deadrise,boundary conditions and mesh density on the equivalent static coefficient was analyzed.Using the relevant conclusions obtained from the analysis of the elastic grillage,it was advised to calculate the equivalent static coefficient of different positions through analyzing water entry of the local structure and then the yield and buckling assessments of real ship structures were achieved.Through the study on water entry of rigid sections,water entry of elastic wedge grillages,experiments of water entry,the prediction of local slamming loads in the wave and local structural responses under slamming loads,a direct calculation method that could be used to assess the local slamming strength of a real ship was established,which would be helpful to the rational design of the ship structure.