Numerical Simulation Of Self-Propulsion Submerged Body Moving In The Stratified Fluid

Due to the heat radiation from sun and thermohaline circulation,there are a wide range of pycnoclines in the ocean.When a submerged body moving near the pycnocline,internal waves will be generated because of volume effect and turbulent wake effect.The characteristics of the internal wave are wide range,long duration and can modulate with the microscale waves and capillary waves in the free surface.These changed internal waves can be detected by Synthetic Aperture Radar(SAR).In order to investigate the traits of wakes produced by the Suboff moving in the linearly stratified fluid,this dissertation proposes a numerical method to simulate the self-propulsion Suboff moving in the linearly stratified fluid.This method can more accurately simulate the motion of the underwater vessel,and more comprehensively analyze its hydrodynamic and motion performance.Moreover,a detailed investigation of wakes will be taken.Firstly,before considering the complex situation,taking Suboff as the research object,using Reynolds Average Navier-Stokes methods and SST k-ω model,calculate the resistance of different velocity Suboff in the homogeneous fluid.Then,this paper analyzes the distribution law of the axial velocity during the calculation and compare the results with the experimental data which shows the feasibility and accuracy of the method.The next step is to use the same method to predict the open water curve of the submarine propeller INSEAN E1619.The results of numerical simulation are shown a great agreement with the experimental data.Besides,this paper also investigates the vortex structure downstream the propeller which lays an excellent foundation for analyzing the wakes of Suboff moving in the linearly stratified fluid.Based on the above research,the simulation of self-propulsion Suboff moving in the homogeneous fluid is conducted.The slippery mesh is used to achieve the rotation of the propeller,and the PI controller applies to control the rotation speed of the propeller.By judging the difference between the thrust of the propeller and the resistance of the Suboff,it is easy to find the "self-propulsion point" of a given speed Suboff.In addition,the self-propelled factors of the Suboff are calculated,and this paper focuses on analyzing the propeller tip vortex structure and the distribution law of the near flow field in the homogeneous fluid.Finally,a numerical model of linearly stratified fluid which based on the thermal density current model is established.By using the same numerical method which applies in the homogeneous fluid,the self-propulsion Suboff moving in the linearly stratified fluid is simulated.The results show that the PI controller used in this dissertation has a huge advantage,since the resistance of Suboff changes every time in the linearly stratified fluid,the speed of propeller could be adjusted at any time.Moreover,the self-propulsion point can be found faster than other methods which means that the application of PI controller can improve the efficiency of calculation.The velocity distribution characteristics and the vortex structure in the downstream of hull are compared with the homogenous situation at the self-propulsion state,and the influence of density stratification on the near flow field has been investigated.