Design And Experimental Verification Of Jetting Arm Of Submarine Jet Trencher

Submarine pipelines and cables are usually buried by submarine trencher to achieve the purpose of protection.Submarine jet trencher is usually used for the construction of sediment with low shear strength.The jetting arm is an important component of the jet trencher,which distributes the water flow in the pipeline and eject the water in high speed to act on the seabed sediment to achieve the purpose of trenching.Aiming at the sediment conditions and trenching requirements in Bengal sea,this paper studies and designs a jetting arm for a submarine jet trencher.Firstly,the sediment scouring process of submerged jet is simulated by using the sediment scouring model based on the theory of sediment movement,and the influence of some factors on the scouring is analyzed.The results show that the model can well simulate the sediment scouring of submerged jet.The scouring process is fast at first,then slow,and finally reach a stable equilibrium state.The depth and width of the pit increase linearly with the increase of jet outlet velocity and the increase of nozzle diameter.When the nozzle scours while it's moving,it will transport suspended sediment backwards,filling the trench to a certain extent.When there are two nozzles scouring,the change of the distance between the two nozzles will change the shape of the pit.When the distance is small,the maximum pit depth is larger than that of the single nozzle.When the distance is large,it is the same as that of the single nozzle.The use of a pair nozzles can effectively increase the width of the pit,but if the distance between the two nozzles is too large,there is a bulge in the middle of the pit.Then,according to the basic working principle of jetting arm of submarine jet trencher,based on the simulation of sediment scouring of multiple pairs of nozzles,the reasonable number and diameter of nozzles are determined.According to the results of numerical simulation of sediment scouring,the jetting arm is designed,and three main pipe types of the jetting arm are numerically simulated,and the flow field and outlet velocity characteristics are analyzed.Finally,a model test is designed based on the gravity similarity theory;the test pool is designed and established;the jetting arm is made;the trencher model used in the test is introduced;the measuring equipment is introduced,and the model test is carried out to verify the designed jetting arm.The test results show that the designed jetting arm can meet the trenching requirements,verifying the feasibility of using numerical simulation to design the jetting arm of submarine jet trencher.