| In the seabed excavation operation,the excavating device of the grab dredger directly acts on the seabed mud,and the excavation resistance and excavation process are directly related to the physical and mechanical characteristics of the mud,the structure and working mode of the excavating device.The above factors will directly affect the accuracy of construction operations,so marine excavation is a research topic involving multidisciplinary geotechnical,marine engineering and mechanical engineering.The research of this subject is based on the original theory of seabed mud and rock excavation,and the theoretical analysis,numerical simulation and experimental research of grab and excavated mud as a systematic dynamic process.It is expected to make a breakthrough in the theoretical research of seabed excavation operations.Mainly completed the following research work:1)A method based on the ellipsoid distribution failure density factor is applied to the critical state of material particles.For the Mohr stress circle of the material particles,the yield or invalid criterion of the critical state of the material particles is proposed.Based on the Mohr invalid theory of materials,the relationship between internal friction angle,cohesion and principal stress of shear strength parameters is derived.Through in-depth analysis of the micromechanical mechanism of the triaxial loading simulation experiment,the material particle triaxial simulation test is designed in detail.The influence of various parameters on the peak value of stress difference and the location of the invalid point in the stress-strain curve is searched.Based on the determination of the mesoscopic parameters of the discrete elements of the material particles,the calibration of the parameters of the sea-bed mud discrete element model is carried out.The influence law of the microscopic parameters of the mudstone is added,and the mesoscopic parameters of the debris are obtained.2)A method of unit integration for solving the equilibrium state analysis of material boundary is proposed.The mechanical model of the digging material in the two-dimensional and three-dimensional state is analyzed,and the mechanical characteristic parameters of the corresponding material are obtained.The Rankine theory is used to quantitatively analyze the shear invalid of the material layer under ideal conditions,and the shape and location of the invalid surface under the action of back active and forward passive pressure are determined respectively.A mathematical model for the grabbing resistance of the grab lateral invalid factor and the excavation speed is established.Based on the combined trapezoidal method,the grabbing resistance is discretized,and the mathematical function relationship between the digging force of the grab and the material parameters is obtained.At the same time,the determination of the grab mining curve and the analysis of the flat excavation trajectory are carried out,and the excavation trajectory curve of the grab is obtained.3)The dynamics of discrete element coupled multibody systems and the method of discrete element coupling computational fluid dynamics are proposed.Based on the above method,the process of grabbing the material is simulated.The discipline of the excavation resistance of the ordinary excavation and the excavation process and the force variation of the wire rope(opening and closing rope and supporting rope)with time are studied.The excavation trajectory of ordinary excavation and flat digging is analyzed.Based on the fuzzy neural network,the simulation analysis of the flat digging accuracy of the grab is carried out.The variation discipline of the simulation data curve of the related research is completely consistent with the theoretical calculation of the excavated material.The correctness of the material-grab mining theoretical model is verified.Meanwhile,it provides a theoretical basis for the excavation test of the grab.4)A test method for detecting the load of the winding torque of the opening and closing rope and the supporting rope into the opening and closing rope and the supporting rope is designed.The preliminary test of the ordinary excavation and flat digging test on the plane of the grab test platform is carried out.The load of the grab supporting rope and the open and close rope is obtained,and the excavation trajectory when the grab is used to excavate the sediment.The mud and water stone test of the grab dredger is analyzed,and the force load of the measured opening and closing rope and the supporting rope is obtained.Based on the relationship between the force of the wire rope and the numerical model of the excavation resistance,the force of the wire rope is further transformed into the excavation resistance.In the flat digging test of the grab dredger,the flat digging test of the single bucket and the multi-bucket is carried out,and the reasonable grabping accuracy of the grab is obtained.The above test verifies the correctness of the simulation results of the grab excavation material process.In summary,this paper aims to study the mechanical mechanism of grabbing materials.Based on the analysis of the microscopic properties of the material particles,a macroscopic mechanical model of the grab-material interaction is established.At the same time,the key technology of grabbing and digging is studied.In the numerical simulation of the excavation materials,a method based on discrete element method and multi-body system dynamics and computational fluid dynamics is proposed.The simulation data provides theoretical support for experimental research.Based on the experimental research on the excavation materials,a comprehensive and in-depth analysis of the excavation process of the grab is carried out.The relevant test results verify the correctness of theoretical analysis and numerical simulation. |
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