Study On Hydrodynamic Performance Of Underwater Manipulator

With the continuous exploration and development of the sea,underwater manipulators were widely used for underwater acquisition,marine exploration and maintenance of underwater equipment.In contrast to land-based manipulators,underwater manipulators have to overcome not only their own gravity and payload,but also the hydrodynamic forces and moments caused by the water environment,which undoubtedly makes precise control of the underwater manipulator more difficult.To address these issues,this paper conducts a study on the hydrodynamics of underwater manipulators based on computational fluid dynamics to investigate the influence of the current environment and the posture of the underwater manipulator on the hydrodynamics of the underwater manipulator.The main research of this paper is as follows:Firstly,simulations of the underwater manipulator model were carried out to investigate the effect of the current velocity and the posture of the underwater manipulator on the hydrodynamic coefficients(Drag coefficient C_D,Lift coefficient C_L,Moment coefficient C_M)pressure coefficient Cp and Strouhal number St,considering only the top winding current.The results indicated that the velocity of the flow increases the hydrodynamic coefficient as well as St within a certain range,but when the velocity increases to the point where the Reynolds number is in the supercritical range,the hydrodynamic coefficients and St will no longer change significantly.When the postures of the underwater manipulator are symmetrical about the axis or origin,it has the same distribution of hydrodynamic and surface pressure coefficients.It was also found in the study that a semi-circular leading edge reduces the magnitude of the hydrodynamic coefficients compared to a right-angled leading edge and also makes the trailing section more susceptible to a kamado vortex.Afterwards,the effect of lateral and end winding on the underwater manipulator was integrated and a numerical simulation of the three-dimensional model of the underwater manipulator was carried out.The results showed that lateral and end-face bypasses exist simultaneously and influence each other as the fluid flows through the underwater arm.Lateral bypass is the main way in which fluids pass through the underwater manipulator,but the axial flow of fluid at the end face can have an effect on vortex shedding near the end face.As the underwater manipulator is turned,the axial flow of fluid at the end face develops across the entire arm section so that there is no more vortex shedding in the wake field across the arm section.By analyzing the hydrodynamic coefficients of the underwater manipulator in different postures,it can be found that when the underwater manipulator posture is symmetrical about the axis or origin,it has nearly the same distribution of hydrodynamic and surface pressure coefficients.Finally,the bidirectional fluid-structure coupling is calculated for the underwater manipulator and the results were compared with the absence of coupling.By analyzing the hydrodynamic coefficients of the underwater manipulator at different flow velocities,it can be seen that when the Reynolds number is in the range of 6×10~3≤Re≤3×10~4,the hydrodynamic coefficients are gradually smaller as the velocity of the water increases,while St is gradually increasing.Analysis of the results with and without fluid-structure coupling reveals that the deformation of the structure due to fluid action results in a shorter axial flow distance of the fluid at the end face and an increase in the number of vortices at the tip.This deformation also leads to a reduction in the hydrodynamic coefficients of the underwater manipulator and the reduction in the hydrodynamic coefficients increases as the amount of deformation increases.