Study On Pressure Instability In Moving Particle Semi-implicit Method

The Moving Particle Semi-implicit method is a meshless particle method for in-compressible fluid,it is widely applied in various field including nuclear engineering field,marine engineering field,mechanical engineering field and bioengineering field etc.The Moving Particle Semi-implicit method has been developed greatly in the past twenty years and has achieved remarkable results in different fields.Compared to very mature and perfect grid method,there are still many defects in the Moving Particle Semi-implicit method method.This is the root cause of its inability to scale up business.In this paper,the pressure oscillation problem of moving particle semi-implicit method is studied systematically.The existing free surface detection schemes in the Moving Particle Semi-implicit method are compared and analyzed.According to the characteristics of its free surface recognition,it is classified into volumetric method and geometric method.And it is found that there are two kinds of defects in the existing free surface recognition schemes:the internal particles are misjudged as free surface particles and free surface particles cannot be accurately identified.In view of the above defects,a novel free surface recognition scheme based on global scanning is proposed in this paper.By simulating the problem of liquid drop impingement and wet dam breaking problem,results showed that the free surface identification scheme based on global scanning on the free surface of the particles has a high recognition accuracy,and free surface accurately identify plays an important role in stability calculation of the pressure field.In the study of pressure oscillation,the mechanism of pressure oscillation in tradi-tional MPS method is studiedd firstly.Through the one-dimensional simplified model,the relationship between the change of the position relation and the change of fluid state is ana-lyzed.Then the mechanism of pressure oscillation in two-dimensional case is proposed.The impact of collision model and kernel function on pressure oscillation in traditional MPS method is studied.Then in view of the factors that influence the pressure oscillation by using fixed pressure coefficient matrix of the discrete format,high precision source term,kernel function,free surface identification scheme based on global scanning and imperfec-tion of particle interpolation correction,a kind of modified Moving Particle Semi-implicit method is proposed.Through the verification of dam break model,static water model and droplet deformation model,it is found that the improved free particle semi-implicit method can effectively suppress the pressure oscillation.In the end,the Moving Particle Semi-implicit method has been studied in three di-mensions.According to the two-dimensional global scanning free recognition scheme,we propose a global scanning free recognition scheme for the three-dimensional sit-uation.Through verification and calculation of static model and dynamic dam break model,the results show that the three-dimensional global scanning free surface recog-nition scheme has high surface particle identification precision.On the basis of the two-dimensional modified moving particle semi-implicit scheme,we propose a three-dimensional modified moving particle semi-implicit scheme.Through the verification and calculation of the 3d dam break model,the results show that the three-dimension modified moving particle semi-implicit method can effectively suppress the pressure oscillation.