| Immersed boundary method has unique advantages in dealing with multi-body hydrodynamic problems include large deformation and sharp movement,Cut-Cell method as an extension method of immersed boundary method has been widely developed in recent years.Radial basis function Level Set Methods(abbreviated as RBF-LS method)is introduced into the Cut-Cell method to construct the dynamic interface.In the RBF-LS method,signed distanc function is approximated by radial basis function(abbreviated as RBF),spatial dispersion is avoid,thus re-initialization is unnecessary and code efficiency is improved.In addition RBF-LS method can also be easily and quickly identify the cell type of background grid.The error generated in the moving process of interface drived by RBF-LS equation is analysised.And an improved RBF-LS method,which can ensure smooth signed distance function surface of Level Set,is proposed to eliminate the error of signed distance function surface casued by cuspidal point of signed distance function surface,thereby the deformation of interface caused by signed distance function surface error.Then a local collocation point grid is introduced to inset the RBF-LS method into the Cut-Cell methed.Data exchange between local collocation point grid,background grid and interface is interpolated by RBF.Accordaning to the characteristics of RBF-LS method,a multibody cut cell parameter calculation method is proposed as well as a fast interface capture method.The main contents include:1.The derived theoretical formulas of RBF-LS method based on Gauss Basis Functions and MQ base function is demonstrated,and the error of this two kinds of RBF-LS method produced in the moving process of interface is analysised concluded that the MQ base fuction is more superior.Then collocation point grid on RBF-LS method based on MQ basis function were studied and analyzed,and an improved signed distance function RBF-LS method is proposed;2.Elaborated the implement technique of embed RBF-LS into the Cut-Cell method,include selecting and updating of collocation point grid,data exchange between different grids,computing method of Cut-Cell parameters and capturing method of the interface;3.The Cut-Cell method based on RBF-LS technique is embedded into CFD platform,classical examples is implemented to verify the reliability and effectiveness of the proposed tecniques.Finally complex nulti-body water entry problem as well as complex multi-body coupled motions of roll,sway and heave are implemented and analysed.The proposed Cut-Cell method based RBF-LS technique is an development of Cut-Cell method,which can effectively simulate hydrodynamic problems including complex multi-body moving interface,but can also be further developed to simulate hydrodynamic of fluid-structure interaction in complex multi-body movement and deformation coupling problems,even in the problems with body separate and broken. |
