Research Of An Underwater Robot And Dynamic Characteristic For Nuclear Power Station Pool

As the energy crisis and the environment pollution problem are becoming increasingly serious,human beings are urged to explore new energy.Nuclear energy,as a clean and efficient new energy,has come into view.Over the past few decades,thousands of nuclear power stations were built all over the world.After the Fukushima nuclear accident in Japan,all countries in the world were paid attention to nuclear safe issue.The nuclear power pool considered as a core component of a nuclear power station was damaged,which can easily lead to nuclear accidents.In the past the nuclear power pool was repaired by man,which was not only inefficient,but also easy to cause harm to the operators.Therefore,it is of great practical significance to design an underwater robot which can weld walls in emergency,and inspect in routine replacing manual operation and research related technology.An omni-directional movement underwater robot system which includes a control subsystem,a mechanical body subsystem and a cable collection subsystem are designed for welding in emergency and inspecting in routine.The mechanical body subsystem considered as a core has an open frame structure,which can carry a weld device fixed on the 3 DOFs moving mechanism and an observation equipment.The robot can realize an all-directional movement to address in the underwater multi-obstacle environment by eight thrusters arranged on the body.Moreover,the robot can position on the bottom or wall of the nuclear pool to carry out an accurate inspection or welding by the thrust of the top thruster.In addition,the position of the 3 DOFs operating mechanism is adjusted to reduce the influence of the restoring force and the restoring moment on the body,which can help the body turn over.When the robot is attached on the wall,the observation device or the gun can track the target or weld by adjusting the position of 3 DOFs operating mechanism.The tail cable on the robot is used for signal transmission,as well as power supply for the body and operation devices,which can meet the need of underwater welding for large current supply.The controller design and maneuverability of an underwater robot are based on the dynamic model.In order to establish an accurate dynamic model the main disturbance factors of the robot are analyzed in depth.The body is always suspended in the water resulting in decreasing the stability.Therefore,the hydrodynamic force and the cable force become the main disturbance factors affecting the control precision and the stability.In order to accurately reveal the hydrodynamic characteristics of the robot in the process of movement,especially during the turn process,a hydrodynamic model is established for the robot applied in the nuclear pool.The model includes not only the hydrodynamic factors of a wide area,also the wall hydrodynamic factors caused by the wall block.A direct motion experiment,an oblique motion experiment,a planar motion mechanism experiment and a cantilever motion experiment are virtually simulated by CFD to solve the related hydrodynamic coefficients.Then a simulation calculation of a near wall hydrodynamic force is presented and the hydrodynamic force is obtained when the robot moves near the wall.The cable on the tail cause an obvious disturbance to the movement and location of a robot,hence the mechanical properties of the cable on the tail of the robot are analyzed.According to the particularity of the nuclear pool environment the three-dimensional mechanical model of the cable under steady and dynamic motion are respectively established by the cable microelement method.The steady and dynamic mechanical properties of each point of the cable on the tail of the robot are obtained by numerical simulation.The force changes of the connection point between the winch and the cable are obtained,which can provide the reference data for the controller design of a winch.Then the motion simulation of a robot with the cable and without the cable is respectively carried out,the effect of a cable on a robot can be analyzed by comparing.According to the previous design the prototype of an underwater robot system is developed,and a performance measurement experiment is carried out in an indoor pool,which verifies the indexes of the design of an underwater robot system.The hydrodynamics experiment of the robot is carried out on basis of a test system built in a circulating water tank.The hydrodynamic coefficients and the near wall hydrodynamic characteristic parameters in the dynamic model are obtained by experiments,which can prove the reliability of the CFD simulation by comparing.The experiment of the mechanical characteristic of the cable is carried out by a test device built and a selt-made test model in a circulating water tank,and the steady mechanical properties and dynamic mechanical characteristics of the cable under different flow velocities can be obtained.The authenticity of the three-dimensional cable force model and numerical simulation method is verified by comparing the results of the experimental results and numerical calculation.