Parameter Optimization Of Seabed Hydraulic Jet Trenching Machine

Seabed hydraulic jet trenching machine is a type of specialty facility for pipeline laying and burial.Researches show that there are many problems in developing and designing jet trenching machines.The most important problem is:there is no basis for selecting jetting parameters.The selection of jetting parameters entirely depends on the designers' experience and there is even no related national standard for reference.Thus,whether the jetting parameters are suitable is not known,and the soil-breaking ability of water jet cannot be fully understood.This thesis puts forward study and optimization of nozzle structure parameters and soil-breaking process parameters,both of which significantly affect the soil-breaking performance of water jet.The influence of nozzle inner structure on flow velocity-increasing efficiency is studied by using numerical simulation and orthogonal test method,and then improved structure parameters are obtained.Also,the influence of related process parameters on soil-breaking performance is studied.Numerical simulation and dimensionless analysis are both conducted in order to determine the relationship between jetting parameters and soil-breaking performance.Effective standoff distance and optimized jetting angle are obtained.Research in this thesis mainly draws the following conclusions:(1) The number of numerical simulations and the quantity of data to be processed can be greatly reduced by using orthogonal test method.And it can totally achieve the effect of full-scale numerical simulations.Lots of time and cost can be saved,too.This application is of great guiding significance for the future design of numerical simulations.(2) The influence of nozzle inner structure to outlet performance is studied through numerical simulation.In the condition of certain diameters,the key influential factors to the nozzle efficiency are the length of the nozzle shrinking section and the degree of the nozzle diffusing angle,followed by the length of the nozzle diffusing section.According to the results of numerical simulation,the nozzle inner structure is modified for better,and the nozzle performance is then improved.(3) According to dimensionless analysis of the data from several numerical experiments, as well as the theory of soil-breaking critical pressure,an equation about the relationship between soil-breaking critical pressure and jetting standoff is obtained.Using this equation in some certain conditions,soil-breaking critical standoff is determined.That is,soil-breaking of water jet can be effective when the standoff is below 140mm.(4) With sets of fixed standoff,total pressures on the wall are analyzed in different degrees of the jetting angle.The best degree of the jetting angle is determined.That is,the max pressure on the wall appears when the angle between jetting direction and the wall is 75 degrees.It proves that the soil-breaking effective is not the best with a vertical jetting on the wall.