Wave Interaction With Perforated Caisson Sitting On A Rubble-Mound Foundation

A perforated caisson sitting on a rubble-mound foundation consisted of a perforated front wall,a solid rear wall,a wave-absorbing chamber between them and the rubble-mond foundation.This kind of structure was widly used in engineering pracice because it can effectively reduce the reflected waves and the wave forces.However,considering the mechanism was complicated,most of the researches by now,on the basis that perforated caisson was set on the impermeable seabed,simplified the structure.Thus,studying wave interaction with perforated caisson sitting on a permeable rubble bed was not only the supplement to the academic research but also a need for engineering practice.Different from previous researches with a single method,in present research,model experiments,numerical simulations and analytical solution were proposed to study this issue.By comparing the results given by these three methods,diverse and accurate tools were developed as well as practical researches and theoretical analysis been proposed.Investigating wave interaction with perforated caisson sitting on a permeable rubble bed of different heights experimentally,an adaptive differential evolution with optional external archive based SVR model(JADE-SVR model)was established for experimental data analysis.Comparing to the traditional multiple regression analysis,it was found out that JADE-SVR model was more advanced in accuracy and generalization performance when describe the relationship between the wave reflection coefficient,wave forces and their influencing factors.The model was promising in engineering practice.A numerical model based on the Volume-averaged/Reynolds averaged Navier-Stokes(VARANS)equations were established.In addition,the three-step finite element method was applied to solve VARANS equations numerically,and the CLEAR-VOF method was applied to capture the free fluid surface.Considering wave motion on the permeable seabed,a new calibration method was proposed to determine the artificial coefficients occurred in that model.The resistance-type porosity model was verified by several testing cases and then used to simulate wave interactions with perforated caisson sitting on a rubble-mound foundation.The porosity model gave reliable results and can be adopted in engineering practice.The validated numerical model was then used for extension research.It was found that,by irregular waves,when the wave-absorbing chamber width grows,the reflection coefficient and the horizontal wave force acting on the perforated caisson sitting on the rubble-mound foundation tend to decrease(?)increase(?)decrease and oscillate periodically.the reflection coefficient tended to decrease and then increase with increasingε_r.The reflection coefficient reached its minimum value as aboutε_r=0.2.A mathematical model based on eigenfunction expansion method was developed to investigate wave interaction with partially perforated caisson sitting on a rubble bed.By using this new mathematical model,wave reflection coefficients,wave forces action on each wall of the caisson,the total horizontal and vertical wave forces and their phase decay were discussed in detail as the relative wave-absorbing chamber width,the perforated rate and characterization parameters of the rubble bed varied.