Numerical Simulation Of Water Entry Process Using OpenFOAM

With the rapid growth of marine resources,the deep-sea cranes are a kind of important marine engineering equipment,whose engineering simulation and control strategy design have received the widespread attention of many scholars.When the crane hoisting the payload into the wave,the crucial problem is that the extreme hydrodynamic force on the payload surface would cause a series of nonlinear movements of the payload at the water entry stage.The nonlinear movements of the payload can entail the danger of collisions of the payload with the ship or other objects and the cable breaks,which can threaten the safety of equipment and personnel.A numerical method is urgently needed to analyze the change of hydrodynamic force on the payload when the payload is hoisted by a crane.Compared with costly and complex physical experiments,an open-source computational fluid dynamics software,OpenFOAM,and the overset mesh technology are used to develop a multi-region-based numerical wave tank(NWT)that is used to simulate the water entry of a payload hoisted by a crane.The hydrodynamic force on the wedge is analyzed emphatically when the asymmetric wedge enters the regular wave.The main research contents are as follows:Firstly,numerical results of water entry of a symmetric/asymmetric wedge into the calm water are presented and compare with the literature data to validate the NWT model.The influence of gravity on pressure distribution and free surface are analyzed in the simulation of the water entry problem.At the same time,the relationship between horizontal velocity and hydrodynamic force on the wedge surface is analyzed.Secondly,the numerical wave tank considers the sixDoFRigidBodyMotion-solver which can decouple the mutual dependence of the hydrodynamic force and the body acceleration.Then the free-falling water entry of wedges is studied by using a numerical wave tank.Considering the rotating motion,the data of the inclined wedge falling into the calm water are calculated.The results obtained by NWT are compared with the published experimental data,which verifies the accuracy of the numerical wave tank to simulate the payload free-falling water entry problem.Finally,basing on the simulations of wedge entering into calm water,the wave entry problems are also calculated.For simulating the water entry of a wedge into a wave,the solidBody-solver,one of the dynamic mesh solvers in OpenFOAM,is modified in this paper.The new solidBody-solver can hold the wedge still until the several cycle waves are generated,and then drive the wedge into the wave at the desired locations(wave peak,wave trough,cross point with the still water level).Aiming at safe hoisting operation of crane vessels,wave-entry of wedges that have finite volumes in the whole duration of entering wave from touching the water surface to submerging into the wave is studied.Detailed results of the free surface and the pressure distribution are provided to analyze the influence of wave parameters,entry velocities,and entry locations on the hydrodynamic force of symmetric/asymmetric wedges that have finite volumes.The results of the water entry simulation provide helpful guidance to the design of the control system of the ship crane during offshore operations.The numerical wave tank will also continue to be developed for validation analysis of crane control systems.