Three-Dimensional Fluid-Solid Coupling Numerical Method For Simulating Debris Flow Dynamic Impact On The Engineering Structures

The catastrophic impact posed by debris flow is one of the main causes of the destruction of the engineering structures.Traditional methods mainly simplified the impact force of debris flow as static process and a single-point impact problem,which cannot present the uncertainties and random features of the impact process of debris flow process,as well as the nonlinear evolution of engineering structure failure.As such,a threedimensional numerical model,describing fluid-solid process of debris flow impacting structures will be a beneficial solution for explaining the dynamic evolution of debris flow impact and failure process of engineering structure.In this context,this dissertation,supported by the National Key R&D Program(2018YFC1505401-2)and the National Natural Science Foundation of China(52078493),aims to propose a three-Dimensional fluid-solid coupling numerical method for simulating debris flow Dynamic impact on the engineering structures,considering the theories of finite element method(FEM)and discrete element method(DEM),in particular the three-dimensional smooth fluid particle dynamics(SPH)with debrisflow rheology.The proposed method is supposed to benefit the hazard mitigation against debris flows.The main research contents of the paper are as follows:(1)For the problem of small strain response of the engineering structure under the debris-flow impact,a three-dimensional FEM-SPH fluid-solid coupling method,using Johnson’s contact surface algorithm,is used.The spatial distribution of pressure and its temporal dynamic variation are obtained using the proposed FEM-SPH method.The applicability of the three-dimensional FEM-SPH coupling model is discussed with respect to the ability in catchment scope,the contact deformation mechanism and the numerical calculation efficiency.(2)Based on the SPH numerical simulation results of the debris flow dynamic process,a dimensionality reduction conversion algorithm that simplifies the three-dimensional impact process into a two-dimensional contact surface effect of the structure is proposed,using the procedure of three-dimensional fluid particle search,fixed contact domain judgment,and coordinate system conversion.The proposed method is able to the rapidly calculate and analyze of the dynamic impact force of the debris flow on the engineering structure surface.The 2018 Yabakei debris flow case in Japan is then selected to verify the proposed method.(3)For the large deformation failure problem of the engineering structure failing under the impact of the debris flow,a three-dimensional DEM-SPH fluid-solid coupling numerical model using an improved nonlinear parallel bonding model is constructed.A published flume experimental test is selected as benchmark test to verify the proposed method.It is shown that the proposed method can effectively analyze the two-phase contact problem in fluid-solid coupling process and well describes in the large deformation failure of structure under the impact of the debris flow.(4)The 2010 Yohutagawa debris flow event in Japan is final selected as a case study to verify the effectiveness of the proposed fluid-solid coupling numerical method for debris flow dynamic impact on the structures.The complex flow velocities and dynamic impact process on the sabo dam is analyzed.The analysis results support the applicability and rationality of the proposed numerical method.