Research On Implicit Interface Modeling Method

Modeling and simulating the motion and deformation of interface has always been the focus and difficulty in computationalfluidmechanics(CFD)field.In the field of ship and naval architecture,the sampling points used in the modeling are usually obtained by ship-lines or discrete points of computational grid.Efficiently and accurately modeling interface with scattered points has become a research focus.This paper is focus on the implicit reconstruction and track of scattered points.Based on the radial basis function(RBF)and standard level set method,an efficient RBF implicit interface reconstruction and track technique is proposed to reconstruct and track the free surface and ship hull.The outlines of this paper are as follows:First,implicit interface modeling and tracking method at home and abroad is reviewed.The feature and problem of interface modeling methods are summarized.Improved RBF method and level set method are proposed.Second,the theory and technique strategy of traditional RBF implicit interface reconstruction method is elaborated.An efficient RBF interface reconstruction method is proposed to improve the computational efficiency of large full rank matrix.Controlling points in the solution are decreased to improve computational efficiency.The computational domain is partitioned as multiple local domains by partitions of unity and splicing techniques.RBF implicit interface reconstruction method is applied to all the local domains to obtain the body surfaces.The local surfaces are integrated by smoothing splicing functions to obtain smoothing closed surface.Large matrix is decomposed into several small matrixes to further improve efficiency of interface reconstructing.Third,based on the efficient RBF implicit interface reconstruction technique,a partitioned level set implicit interface tracking technique is proposed to improve the mass non-conservation problem of standard level set method.In the standard level set method,numerical error would occur in the numerical solution of partial differential equations.Distance signed function are redistributed by a re-initialization step to correct interface position,leading to mass non-conservation.In this paper,an efficient RBF is proposed to re-express the level set distance signed function.Partial differential equations are transformed into ordinary differential equations by separating spatial variables and time variables.Therefore,the solution of Partial differential equations is transformed into the interpolation problem and the solution of weight coefficients of RBF.Mass non-conservation problem encountered in the re-initialization step is avoided.Last,implicit interface modeling and tracking method is programmed in Fortran 90.Several test cases are simulated to validate present method by comparing with RBF method and standard level set method.The results show that present method can improve the accuracy and efficiency of interface reconstruction and mass conservation problem.Besides,present method is applied to the reconstruction of Wigley and KCS hull,the tracking of linear wave and second order stokes wave.Good results are obtained which validates the capability of present method for interface modeling and moving boundary tracking.Present study paves the way for the interface representation in the field of ship and naval architecture.