Research On The Modeling And Mechanism Of Liquid-solid 2-phase-flow Of Cutting System For Cutter Suction Dredgers

In the construction of the golden channel of inland river and marine artificial islands,the cutter suction dredger has become the main equipment for its stable,energy-saving and efficient advantages.The cutting system of the cutter suction dredger involves not only soil cutting and slurry formation but also cooperation with slurry transmission system,so it is particularly important in the suction system.In the actual dredging construction,the mechanism of underwater cutting and slurry formation is so complicated as to be deeply discovered.With the support of China Science and Technology Foundation Program,Research on the Modeling and Mechanism of Liquid-solid 2-Phase-Flow of Cutting System for Cutter Suction Dredgers(No.51679178),this dissertation studies the cutting system for cutter suction dredger,and DPM model and Two fluid model are adopted to simulate the liquid-solid 2-phase-flow of the cutting system,the relationship between the operating parameters and the suction efficiency,the change of the suctioned particles' size distribution are studied,the movement mechanism of sand particles and the slurry formation process are discussed,and based on the similarity principle a comprehensive dredging simulation experiment platform is designed and developed,simulation experiments a variety of operating parameters are carried out,the slurry concentration characteristics on external flow field are studied by means of high-speed photography,and the results of model experiment and numerical simulation are compared and analyzed.The main research work is as follows:(1)The analytical model of cutting system is established and the relative analysis methods are introduced.The two major systems of soil engineering classification,the classification standards of dredging soil in China and the main physical properties of the soil are studied,the main components of the cutting system and the electrical characteristics of the main electrical driving devices are analyzed,and the operating parameters of the cutting system are studied.Based on the two-dimensional cutting theory,the 3D cutting force calculation model of the cutter tooth is established,and the coordinate transformation model on teeth holder,cutting system and the dredger,the motion model,the cutting force calculation model and the dynamics model for the cutting system are set up considering the motion characteristics of the cutting system.The engineering turbulence model and the liquid-solid two-phase flow simulation method are studied.It provides original basis for the design of the comprehensive simulation experiment platform,the experimental scheme design and the boundary conditions setting in CFD simulation.(2)The DPM simulation model of liquid-solid two-phase flow in cutting system is established,the relationship between suction efficiency,particle size distribution change and operating parameters is simulated and analyzed.In the numerical simulation the standard k-? model and the Realizable k-? model are used respectively to simulate liquid phase,Rosin-Rammler distribution model describes the particle size distribution,the multiphase flow model adopts the discrete phase model(DPM),the cutter rotation motion is simulated by the Multi-reference Frame(MRF)and the finite volume method based on unstructured meshes is also applied to solve the CFD equations.The characteristics of the liquid-solid two-phase-flow under different operating parameters are simulated.The velocity vector field,pressure distribution and turbulent kinetic energy distribution under the two turbulence models and the moving trajectory of solid particles are studied.The liquid velocity vector field,pressure distribution,turbulent kinetic energy distribution and solid particle motion trajectory are analyzed.The relationship between the suction efficiency,the change of the particle size distribution and the operating parameters,and the sand particle moving mechanism are studied and discussed.(3)By two-fluid model,dynamic mesh and sliding mesh technology,the dynamic process of fluid in a rotating cycle is simulated and analyzed,and the timevarying characteristics of volume fraction of liquid-solid two-phase and velocity of sand particles are discussed.The liquid-solid two-phase-flow of cutting system and its complicated evolution process are numerically dynamically simulated by the EulerEuler two fluid model,the standard k-? model,the sliding meshing method and dynamic meshing method which simulate the cutter rotating and swing movement.Through numerical calculation results,the change of the two phases' volume fraction in cross section plane,vertical section plane,vertical plane and external contour of cutter in and around the cutting system under typical operating parameters is analyzed.The 2 phases' velocities and their changing on the centerline of suction mouth and inner and outer circumferential sampling points above the backring are calculated and analyzed.The slurry formation process and its developing trend are explored.(4)Based on the theory of similarity,the prototype and experimental model of a certain dredger cutting system are analyzed,and a small-scale comprehensive dredging simulation platform is developed.According to the dimensional analysis method Buckingham ? of similarity theory is applied to deduce the similarity criterion of liquid-solid two-phase-flow of the prototype and model of the cutting system,the relationship between prototype and model is setup,and then the similarity ratio of the operating parameters and the relative parameters of the liquid and solid phases for the model and the prototype are determined.On the premise of satisfying the flow similarity referring to the main technical performance parameters of cutting system of prototype cutter suction dredger,a small-size indoor comprehensive dredging simulation experiment platform is developed with the functions of complex soil cutting test,matching optimization of cutting-discharging system,automatic control of dredging operation,data acquisition and monitoring,underwater flow field observation and high-speed photograph.(5)Dredging simulation experiments with a variety of typical operating parameters are carried out,the experiment data and part simulation results are compared and analyzed,which verifies the correctness of the theoretical research.On dredging simulation comprehensive experimental platform,dredging simulation experiments under various operating parameters are carried out,the experiment results are recorded,the high speed photography system records the dredging scenarios,and data analysis and digital image processing are also conducted.The experimental data verifies the relationship between the operating parameters and the suction efficiency,the change of the suctioned particles' size distribution.Based on the digital image processing technology the slurry concentration distribution of the fluid solid two phase flow in and around the cutting system is studied,the characteristics of slurry concentration distribution in the slurry spillage area in undercut and overcut modes are revealed,and the liquid-solid two-phase concentration distribution outside the cutting system in undercut and overcut modes is quantified.