Study On The Flow Regimes And Dynamics Performance Of Heteromorphic Coarse-grain In Pipeline Transportation

Dredging technology is widely used in the construction of port and waterway,water conservancy construction,dredging of environmental protection,landfilling,submarine tunnel excavation and deep sea mining.The transportation of excavated materials is a vital part of dredging construction.The way of pumping solid-liquid mixed slurry by pipeline is the most common transportation method in dredging engineering due to its high efficiency and environmental friendliness.The flow regime of particles in the pipeline and the dynamic characteristics under the corresponding flow regime affect the safety and high efficiency of the material transportation.Especially the complex dredged materials such as the heteromorphic particles have also been the research hotspot.Based on this,the CFD-DEM coupling calculation method is used in this paper to study the flow characteristics,pipeline section concentration distribution and particle dynamics of various different shapes of granular mud in horizontal pipelines.The main research contents of this paper are as follows:(1)In this paper,a slurry in which fine particles mixed with water are regarded as continuous phase,and coarse particles carried in the slurry are regarded as discrete phases.The computational fluid dynamics(CFD)method is used to solve the flow field,and the discrete element method(DEM)is used to calculate the motion force of the particle system.The two models transmit the mass,momentum and energy with a certain model to establish the CFD-DEM coupling calculation model.The simulation results are compared with the experimental data in the literature,and the key parameters in the model are determined to verify the accuracy of the coupled model.(2)CFD-DEM model is performed to simulate the flow regime of mud(seawatersand)in horizontal straight pipe,the critical velocity of flow transition is obtained according to DHLLDV framework respectively for spherical particles,square-shaped particles and line-shaped particles in pipeline.The mud is subjected to threedimensional simulation to analyze the influence of the conveying speed and particle shape on the mud flow regime and the state change process.(3)Based on the above analysis of the flow characteristics,the distribution of the volume fraction of the fully developed section in the pipeline on the cross section,the variation of the interaction force and the settlement velocity of the particles at different positions are investigated,and consideration of the influence of particle shape and flow state on related dynamic characteristics are considered comprehensively from both micro and macro aspects;the fluidity stability within the tube and its effect on mud flow is analyzed at the same time;(4)In order to further close to the actual working conditions,the three different shapes of the particles in the above study were uniformly mixed,and the flow characteristics of the mixed slurry in the pipeline and the dynamic characteristics such as inter-particle force,particle number and velocity distribution were analyzed,and the influence of shape on relevant parameters is obtained.Based on this,the regulation strategies explored to ensure construction safety and improve transportation efficiency.