6-DOF Motion Simulation Of Autonomous Underwater Vehicles Considering The Influence Of Lateral Flow

Autonomous underwater vehicle(AUV) is an intellectualized platform which can be used in research activities such as exploration, detection, anti-torpedo in complicated ocean environment. It can meet the requirements of scientific research, military and commercial demands. Ocean environment is always shifting and there exists ocean current, pycnocline(thermocline, halocline), wave. These ocean parameters will cause great impact on the motion performance of AUV. It is of great importance in researching the motion performance of AUV under lateral flow when it moves straight. In this thesis, the motion performance of AUV with various hull appendages was investigated to provide theoretical guidance for design of hull shape and appendages. So, the 6 degree of freedom(6-DOF) simulation method was proposed based on dynamic mesh in computational fluid dynamics(CFD) software FLUENT. Achievements of the thesis are as follows.Straight moving of AUV without ocean current was researched using the proposed 6-DOF numerical simulation method. Geometry model of AUV was built in Solidworks, tetrahedron mesh was divided in ICEM. In the method, the mesh files were introduced in FLUENT code to conduct finite element analysis, then mass of AUV was attributed through loading user defined function(UDF) in the FLUENT. The stable motion of AUV was finally realized by setting rational distance of gravity and buoyancy center.The motion performance of AUV and characteristics viscous flow field were studied in the lateral flow disturbances. Combined RANS equation with standard k-? turbulence model, unsteady viscous flow field around the AUV and position and attitude of the AUV were calculated in the lateral flow disturbances. The motion characteristics of the AUV were simulated in various lateral flow velocities and directions. The influences of lateral flow on motion performance of AUV were discussed through analyzing trajectory of center of gravity and attitude angle of the AUV, fluid force and moment, velocity and pressure filed around the AUV.Motion performance, position and attitude of the AUV with various layout of hull shapes, such as layout and shape of tail fins, distance between gravity center and buoyancy center, were investigated in the lateral flow disturbances. Results show that the AUV with X 45?- tail fins can keep better motion performance than the one with X 90?- tail fins do. The AUV behaves well when L/ L?=0.0736, where L?is the distance from the root of end of the tail fins to the tail end of the AUV, L is the length of AUV. AUV with too small tail fins will performs bad motion stability with strong rolling and pitching. Distance between gravity center and buoyancy center will also strongly affect the motion performance of the AUV. So, it's the reason why the distance between gravity center and buoyancy center is the key factor for hull shape design. Achievements of the present study can provide theoretical reference for design of the structure and control system of the AUV.