Research On Hydrodynamic Performance Of Under-actuated AUV Sailing Near Water Surface

Marine resources are attracting more and more attention from the human beings who are continuously seeking new resources. In the process of exploring the rich marine resources, AUV is a kind of important auxiliary detection tools, especially the torpedo shaped under-actuated AUV, it has neat appearance and simple structure, it plays an important role in the process of searching the marine resource. Good AUV hydrodynamic performance is the key to accurately search for the underwater resources, at present most research for its hydrodynamic performance is being in deep water, there is a little hydrodynamic performance research in near surface, and under-actuated AUV hydrodynamic performance is easily affected by free liquid surface when sailing near surface. Its hydrodynamic performance is much different from when sailing in deep water. It has a certain theoretical value and engineering significance on the research about the near surface hydrodynamic performance.In recent years, with the development of computer technology, optimization of grid technology and the improvement of solver’s precision, more and more people are using the theory of CFD numerical simulation method to study the hydrodynamic performance of AUV. It is based on the theory of CFD in this paper, it simulates the movement of under-actuated AUV near surface with the fluent software, then it calculates the hydrodynamic coefficients of under-actuated AUV when it is sailing near surface and analyzes its hydrodynamic performance.Firstly, this paper analyzes the hydrodynamic performance when under-actuated AUV is direct sailing near surface in different depth and different speed, then it analyzes the hydrodynamic performance when under-actuated AUV oblique towing near surface in different attack angle or drift angle, calculates the resistance and moment under each working condition, the curve of resistance and moment varies with depth and speed is given. By analyzing the specific values, speed and stress contours, it summarizes change amplitude and change reasons for force and moment.Secondly, this paper numerically simulates the heaving motion, pitching motion, swaying motion and yawing motion in the near surface of the under-actuated AUV, it calculates the resistance and moment when it is pitching, heaving, yawing and swaying in different frequency, through the certain software curve fitting, the hydrodynamic coefficients are obtained after dimensionless, then it gains the rules of hydrodynamic coefficient varies with frequency.Finally, it analyzes the line’s effect on the resistance performance of under-actuated AUV. By comparing the resistance coefficient of saucer-shaped AUV, torpedo-shaped AUV, streamlined AUV and ellipsoid-shaped AUV when they are sailing in the same conditions, then it lists which one is better in resistance performance.