Numerical Simulation Of Viscous Hydrodynamics Of Unmanned Underwater Glider

Unmanned underwater glider, which takes advantage of the strengths of buoy and autonomous underwater vehicle technology, is a kind of ideal platform used to measure marine environment parameters and is concerned extensively. The growing diversity and complexity of underwater tasks put forward higher requirements for improving the maneuverability of underwater glider. Realization of most motions like dive, recovering and turning are as prerequisite of accurately predicting the viscous hydrodynamic coefficients, which will directly affect the accuracy of the hydrodynamic model. In addition, there are large amount of viscous hydrodynamic coefficients are harder and more complex to be determined than the inertial ones do. So how to determine viscous hydrodynamic coefficients is the most difficult and basic work of maneuverability prediction. In this paper, in order to meet requirements of projects of hybrid-driven underwater glider and numerical model test platform, numerical simulation method of predicting viscous hydrodynamic coefficients of unmanned underwater glider was investigated based on computational fluid dynamics(CFD) to obtain various viscous hydrodynamic coefficients of unmanned underwater glider quickly and accurately. Achievements of this thesis will provide theoretical basis and guidance for optimal design of hydrodynamic shape, establishment of motion model, maneuverability prediction and motion simulation of unmanned underwater glider. Achievements are as follows:Followed by introduction of numerical simulation theory of viscous flow, numerical simulation of straight motion of the unmanned underwater glider was conducted under different navigation speeds to obtain the drag coefficient. Variation of drag coefficient under different Reynolds numbers was also analyzed.Then nonlinear viscous hydrodynamic model of unmanned underwater glider was built and the towing test was numerically simulated in horizontal and vertical planes. According to the established nonlinear hydrodynamic model, cubic spline curving fitting and regression analysis method were used to determine the damping derivatives and corresponding nonlinear hydrodynamic coefficients. The influences of different data processing methods on the results were analyzed and discussed.Added momentum source method, in which the added momentum source term was coupled into the N-S equations through user defined function(UDF) in FLUENT code, was proposed to numerically simulate the rotating arm test in the horizontal plane. Aimed to REMUS AUV as a case study, the proposed momentum source method was compared with SRF method by using standard k-w and SST k-w turbulent model respectively. The lateral force and yaw moment at different rotating radius are predicted. By comparing computational results with experiment results, it showed that the added momentum source method with standard k-w turbulent model had comparative results with the experiment results, and errors between of simulations and tests could meet the requirements of engineering prediction.Based on the proposed added momentum source method and focused on the unmanned underwater glider developed by Tianjin University, rotating arm test in both horizontal and vertical planes were numerically simulated. The first order rotary derivatives of the unmanned underwater glider were obtained. The regression analysis was applied to determine the nonlinear hydrodynamic coefficients caused by the angular velocity.