Numerical Analysis Of The Drag Force Of An Offshore Backfilling Plough And Optimization Of Plough Body Structure

In the exploitation of offshore oil and gas resources,offshore pipelines are mainly used to transport oil and natural gas.The movement of ocean currents,offshore geological activities and human fishery production will damage the offshore pipelines to different degrees and lead to oil and gas leakage,which will not only bring serious economic losses,but also lead to Marine environmental pollution.In order to ensure the stability of offshore pipelines and protect them from external forces,the common protection method for offshore pipelines is to dig trenches and backfill and bury them.At present,the trench excavation and backfilling equipment technology of offshore pipeline is mainly monopolized by European and American countries.With the rapid development of offshore oil and gas resources in China,it is of great theoretical and practical significance to study the backfilling technology of offshore pipelines.The backfill of offshore pipeline is mainly completed by offshore backfilling plough.This paper puts forward the overall structure scheme of the offshore backfilling plough,and completes the design of the offshore backfilling plough,including guide and support front slipper,walking and adjusting device,backfilling device,plough body structure and offshore balanced hydraulic system,etc.By analyzing and comparing different adjustment schemes of front slipper,the ground mode of guiding and supporting integrated front slipper is determined.The parameters of main body and hydraulic components of backfilling plough are determined.The three-dimensional structure model of the backfilling plough was established,and the motion analysis was carried out to ensure that the moving parts of the plough body did not interfere with each other.The numerical simulation method of total drag force of backfilling plough is studied.The coordinate system for solving the offshore backfilling plough drag force,the cable coordinate system and the offshore backfilling plough coordinate system are established.The mutual transformation matrix between coordinate systems,the motion equation of the tow cable,the motion equation of the offshore backfilling plough and the boundary conditions are established.The motion equations of the tow cable under the Ablow and Schechter model and the backfilling plough under the Abkoeitz model are established.By coupling method,with the coupling between the upper and the end points of the towline and the corresponding connecting parts,the boundary conditions of offshore backfilling plough towing force were determined.The dimensionality reduction method is proposed to solve the case.Through the analysis of too many unknowns in the equation,the transformation of the equation is completed,the three-dimensional problem is transformed into the two-dimensional one,and the theoretical solution to the drag force is obtained.Based on the fluid-solid coupling theory,the structure optimization model of offshore backfilling plough was established.Using functional extremum theory,the flow curve model of backfilling plough body was established to obtain the brachistochrone curve.Aiming at the application of 2d curve in 3D space,three-dimensional flow curve is materialized,different flow curve analysis models are established,and the conclusion that optimization curve is also applicable in 3D structure is drawn.Based on the analysis of the effect of offshore soil and water flow during the plough body's working process,the multiphase turbulence model was established as the basic analysis model.By analyzing the interaction between soil and water,volume fraction,interphase exchange coefficient,solid shear stress,particle temperature and other parameters,the influencing factors of 3d simulation were determined.The boundary conditions of velocity inlet and pressure outlet are determined by using D-P model to analyze the adaptability of boundary conditions for soil properties applicable to offshore operation simulation.Considering the influence of working environment and the convergence of solution,the boundary conditions of wall are determined as non-sliding wall.By comparing the actual working speed of the equipment with the speed of sound,the model algorithm based on pressure is determined.By using UG and ANSYS to exchange data,the simulation proves that the optimal flow curve in 2D state is also applicable in 3D state.Put forward the optimization scheme of hole on the plow body,to open a hole on the plough body,compares and analyses the five hole openings are drawn to plough on both ends between the hole and the plough body,and the influence of the relationship between the structure size,studied the opening after the formation of the force,the influence of the spinning force to plow body according to the hole on the plow at both ends of the presence of fluid pressure,flow around the back pressure is lower than other parts of the pressure,the characteristics of vortex theory,the establishment of a Newtonian fluid vortex differential equation,through the simulation,has been clear about the 5 hole model can effectively reduce the plough body working resistance,realize the optimization of the mechanical structure,Finally,the structural scheme of opening 5 holes in the fender is determined.The overall plan of the onshore experiment of backfilling plough was completed,and the experimental site with a certain degree of match between the onshore experimental soil and the offshore soil was selected.The onshore experiment method was put forward,the prototype of the offshore backfilling plough was developed,and the adjustment of slipper and drag force of the backfilling plough were completed.The experimental data were collected from different data parameter modules in the experiment,and the experimental data were analyzed.The results verified the rationality of backfilling plough design parameters,and the first-hand data were collected for further experiments of offshore backfilling plough.Through the analysis of experimental data,it is concluded that the overall drag force of the curved plough body is 21%less than that of the straight plough body in the terrestrial environment,which is consistent with the trend of the theoretical analysis data and proves the accuracy of the theoretical analysis.A method for estimating the towing force in offshore experiments is proposed,and the optimum towing distance is determined,which provides reference data for offshore experiments.