| Among the causes of marine platform accidents over the years,one of the most crucial factor is the slamming effect of waves.In order to ensure the safe and long-term work of the marine platform at sea,it is necessary to systematically study the cause and mechanism of the wave slamming load.Taking 981 Semi-submersible Drilling Unit as an example,the slamming load on platforms in North Atlantic wave conditions was analyzed based on DNVGL Guidance.Slamming loads on plates,circular cylinders and Semi-submersible platforms were comprehensively simulated in the paper.Based on the slamming load,two methods of static analysis and transient dynamic analysis were used to evaluate the structural strength of semisubmersible platform.The main contents of this paper were as follows:1.The model of fluid field in actual size was built,and then,the third-order Stokes wave theory is adopted in the paper according to DNVGL Guidance.Based on the Finite Volume method of CFD,a corresponding three dimensional numerical wave tank was built by the FLUENT.By using two methods,the open channel wave and the boundary velocity wave,a stable wave field was obtained,and the numerical solution of the obtained waveform is in agreement with the theoretical one.2.The fluid-field models of two-dimensional flat structure and three-dimensional cylindrical structure were built respectively.Numerical simulations were made on the wave slamming response of the slab and the cylinder which were fixed.The calculation results showed that the wave slamming load were periodic and impulsive.Meanwhile,the load cycle and the wave cycle were consistent.3.Constructing the fluid-field model of semi-submersible platform,the slamming response of the platform was numerically simulated by moving grid technology to realize the movement of the platform in two degrees of freedom of heave and pitch.Compared to the threedimensional platform structure being fixed,the slamming pressure appeared double peaks whose value was smaller when the platform moved by two degrees of heave and pitch.4.Considering the slamming load,two methods based on static analysis and transient dynamic analysis are used to check the local strength of semi-submersible platform.The calculation shows that the response of the platform column under transient dynamic analysis is almost three times that of the static analysis.Therefore,the transient dynamic analysis method is more predictive of the structural weakness. |
