Analytical And Experimental Investigation On Hydrodynamic Characteristics Of Porous Disc

With the development and utilization of marine resources,the research on the interaction mechanism between marine engineering facilities and waves in the ocean also needs to be deepened and developed continuously.As an important energy dissipating component,porous plate can be applied to marine structures such as breakwaters and floating platforms.A lot of research has been conducted on the hydrodynamic properties of submerged porous plates,but the hydrodynamic properties of porous plates near the free surface need to be studied in depth.Theoretical and experimental methods were used to study the hydrodynamic characteristics of porous discs and their influence on wave loads for the problem of wave load suppression on offshore structures.The influence of porous disc opening ratio,draft and water depth on its added mass,damping coefficient and wave exciting forces was investigated;the trend of reflection coefficient and transmission coefficient of the porous disc to incident waves was analyzed,and the nonlinear hydrodynamic properties of the porous disc near the free surface are of interest.Firstly,a semi-analytical model of the submerged porous disc based on the linear potential flow theory was established,the velocity potential decompositions method was applied to avoid solving the complex dispersion equation;the unknown coefficients of velocity potential in each region of the analytical model through the pressure and velocity continuity conditions was solved,;the expressions of added mass,damping coefficient and wave exciting forces of the submerged porous disc were given;the computational procedure verifies the accuracy of the analytical model of the submerged porous disc established in this paper by convergence verification and comparison with published results.Then,based on the analytical model established in the previous section,the theoretical analysis of the hydrodynamic characteristics of the submerged porous disc was carried out.The influence of wave parameters and geometric parameters of the porous disc on the hydrodynamic characteristics of the submerged disc was investigated;the influence of the real and imaginary parts of the porous effect parameter G on the wave exciting forces of the submerged porous disc was investigated.For the porous effect parameter G,the wave exciting forces decreases as it increases in both the real and imaginary parts;when the draft or the opening ratio is small,there is a negative additional mass.Finally,the physical model experiment method was used to investigate the force problem and wave energy decay law of the porous disc model near the free surface considering different opening ratio,draft and wave frequency.By analyzing the force-time curve of the disc model and its frequency spectrum,it was found that the disc model is not only influenced by the firstorder wave force,but also the second-order or even higher-order wave force dominates in some experiment conditions where wave breaking occurs;the draft of the porous disc is also an important factor influencing the flow field: when the model is at the lower part near the free surface,the wave gathering phenomenon is generated at the upper part of the disc model;when the model is at the upper part near the free surface,the phenomenon of wave-wrapped gas compression breaking will occur in the lower part of the disc.