Research On Hydrodynamic And Motion Stability Of Net Cavitation Jet Cleaning Robot For Marine Ranching

In recent years,China has made great efforts to develop Marine ranching equipment,but faced with the problem of a large number of Marine organisms attached to the net of Marine ranching.If the Marine organisms attached to the net are not cleaned regularly,the fluidity of sea water will be reduced,the water resistance of ranching will be increased,which will affect the structural safety and is not conducive to fish farming.Regular replacement of net and manual cleaning can greatly increase the cost,and intelligent underwater cleaning robot can solve this practical problem instead of manual.Because the ocean environment is complicated and accompanied by the interference of waves,the working surface of the robot is net,so it has practical value to develop a robot with excellent hydrodynamic characteristics,motion stability and cleaning effect.In this paper,a new type of net cavitation jet cleaning robot for Marine ranching is proposed and taken as the research object.The robot uses cavitation jet to clean net,crawler walking and thrust propeller adsorption.The lightweight design is considered in the structural design,and non-metallic materials are used on the premise of satisfying the structural strength.This structure enables the robot to accurately adjust its underwater posture and walk more flexibly on the net.First of all,the robot need to have enough power to maintain the cleaning work underwater.This requires the robot to move with as little water resistance as possible and make the propeller more efficient.In this paper,based on computational fluid dynamics(CFD)method,the hydrodynamic characteristics of robot and propeller are numerically simulated by STAR CCM+ software,the relationship curves of propeller speed and thrust,torque and open water characteristic curves are calculated.By simplifying the robot model,establish the underwater control equation,select the appropriate turbulence model,and divide the robot into the trimmed mesh and the polyhedral mesh according to the propeller movement and non-movement,the curves of flow resistance and net pressure are obtained under different flow attack speeds and different propeller speeds.According to the different parts of the robot to meet the flow,determine the suitable situation for the robot to work.Then,the cavitation performance of the nozzle in the cleaning mechanism was studied.Based on cleaning mechanism of cavitation jet,the axial vapor phase volume fraction and velocity curve of the nozzle outlet were obtained by Fluent simulation analysis when the diameter of the nozzle contraction section and the outlet diffusion angle were different under submerged conditions.The influence of cavitation jet from nozzle on robot motion stability is analyzed.Finally,based on the hydrodynamic characteristics of the robot,the dynamics model of the robot is established and the motion stability of the robot is simulated by combining the designed depth controller and attitude controller,to ensure that the designed controller meets the stability of the robot in the case of underwater disturbance.At the same time,the working trajectory of the robot is designed,and the tracking effect meets the requirements under the mediation of the motion controller.Through the overall performance experiment of the robot,it is verified that the robot has good stability in underwater straight and turn cleaning operations and its cleaning ability reaches the industry standard.