Research On The Dynamic Of Deep-sea Sediments With The Characteristics Of Nonlinear Gradient Modulus

The study of mining system is the main research direction of deep sea mineral resources development.Specifically,the deep-sea mining collector plays an important part in the mining system,influencing the mining efficiency.The deep-sea sediments are usually heterogeneous due to overburden pressure.When the deep-sea mining collector experiments in a static state,the deep-sea mining collector vibration can easily cause excessive deformation of the deep-sea sediments,resulting in sink of the mining collector.Once it happened,soil deformation significantly decreases the stability and efficiency of the mining collector.On the other hand,ground pressure is an important technical index of the pedrail mining collector,which directly influences the walking stability of the mining collector.During the running experiment,the gravity of the deep-sea mining collector often deviates from the geometric center,which causes the ground pressure of the pedrail to be unevenly distributed.Compared with the previous dynamic response of soil under uniform load,the result is different.Aiming at the problem of soil deformation caused by the vibration of the mining collector and the problem of eccentricity for the walking mining collector,this study analyzed the dynamic response of the deep-sea sediments,which can provide a theoretical rationale for improving the walking efficiency of the mining collector.The main research results in this paper are as follows:1.In this paper,experiments were conducted to confirm the heterogeneity of deep-sea sediments,and to reveal the relationship that the elastic modulus increases nonlinearly with depth.After that,by predigesting the mining collector vibration to in-situ harmonic load,the wave equations were built for solving the dynamic response of deep-sea sediments with nonlinear modulus to mining collector loading.The heterogeneous medium was degenerated into a homogeneous medium,and the solution of the equations was verified by Cagniard-de Hoop method.After this verification,further discussion was conducted on the effects of changing vibration frequency or loading amplitude on the mechanical response of deep-sea sediments.The results indicate that the soil deformation was increased but later decreased with the increase of vibration frequency,and soil deformation increases increased with increasing loading amplitude.2.The dynamic response of heterogeneous deep-sea sediments under moving non-uniform load was determined analytically.The heterogeneity of deep-sea sediments is associated with elastic modulus increasing nonlinearly with depth.The ground pressure of the mining collector with longitudinal eccentricity was assumed as trapezoidal distribution.The complex Fourier series method was conducted to expand the soil displacement and the formula of ground pressure at an arbitrary point of the pedrail grounding section.Thus,the governing partial differential equations(PDEs)of soil motion were simplified to ordinary differential equations(ODEs).The analytical solution of the ODEs was solved by the method of Frobenius.After verifying the approximate analytical solution by means of comparisons with the finite element software ABAQUS simulated results for the special cases of homogeneity,this approximate analytical solution was utilized to assess the effect of heterogeneity,eccentricity,and pedrail length on the response of deep-sea sediments.