Study On DEM-based Coupled Numerical Methods For The Flow Systems Of Water And Soil

Flow systems of water and soil widely exists in the geological engineering,geotechnical engineering and hydraulic engineering,for example,the systems of dam foundation-hydraulic structures,water loss and soil erosion processes,the processes of sand production from oil wells and sudden surge problems of foundation pit,the basic principles involved particle movements and interactions between particles of particle-scale as well as fluid flow and fluid-particle interactions of microscale or mesoscale.At present,it is difficult to deeply understand the microscomic mechanism of the above systems by using physical experiments and numerical analysis methods based on Euler-Euler（E-E）model.Discrete Element Method（DEM）uses particle units to model the solid phase and reflects the real particle-particle interaction through contact models as well as can couple with a variety of fluid numerical analysis methods（such as CFD-DEM,LBM-DEM,etc.）,providing an effective numerical tool for understanding the above microscomic mechanism.However,the existing DEM-based coupled numerical analysis methods are often limited by the number of particles,problem dimensions and the implementation of dual commercial or dual open source models,which limit their applications in the numerical analysis of water and soil flow systems.In view of the above problems,the paper innovatively developed a new implementation model OpenFOAM-PFC^3D of CFD-DEM coupling method and applied it to the numerical simulations and microscomic characteristic research of common flow systems of water and soil in practical engineering.Based on the above works,the following research results are obtained:（1）Based on the Euler-Lagrangian（E-L）model,following the Tsuji’s coarse grid fluid-particle coupling numerical analysis systems,using Anderson and Jackson’s concept of local average of the continuity equation and Navier-Stokes（N–S）equation,the innovative development of the CFD-DEM coupling numerical analysis method is a new type of implementation model OpenFOAM-PFC^3D,and describes in detail the control equations of the model,the pressure and velocity coupling equation algorithms,the basic principle and programming details.（2）An applicable benchmark problem validation system of CFD-DEM coupling method in practical engineering was established.Based on the commonly used four typical problems,namely,a single spherical particle sedimentation in static water,Darcy’s law,repose angle characteristics study of spherical particle piles and one dimensional consolidation,the proposed new implementation model was validated comprehensively.By comparing the numerical solution and analytical solution,we determined that the relative errors were within the acceptable range,and proved the implementation model in applicability and accuracy of such problems.（3）The proposed novel numerical model was used numerically to research the stability problem of hydraulic structures pipling flow.We established a thress-dimensional numerical considering water-base-hydraulic structure coupling as well as detailedly introduced the modeling ideas of rigid-like structure and coupling relationship between three.The characteristics of fluid flow,response of hydraulic structure and response of solid phase were studied under the condition of different water level difference.The development law of piping flow in hydraulic structures wase revealed from the microscomic-scale.（4）The proposed novel numerical model was used numerically to study the common soil erosion problems.A three-dimensional numerical model of particle flow erosion was established.Among them,the particle piles included two kinds of conditions,namely,monosized particles and polydispersed particles.The microscomic flow response of particles affected by fluid erosion under different conditions was studied.The effects of particle size,particle size distribution and pipe inclination angles on particle erosion characteristics were revealed.