Study On AUV Hydrodynamic Optimization And Motion Performance Near Free Surface

With the development of science and technology,and the growth of population,the demand for nature resources,both type and amount,has been continually increasing.more and more countries are paying attention to ocean resources exploitation,that leads to territorial disputes in the sea fiercer than ever before.Countries all over the world are putting lots of manpower and material resources to develop detecting or mining equipments and naval facilities.Autonomous Underwater Vehicles(AUVs)have their irreplaceable advantages in ocean resources detecting and development.Researchers are working on AUVs with good maneuverability and endurance,which largely relies on the help of Computational Fluid Dynamics(CFD).This dissertation looks into CFD simulation accuracy,main hull shape and attachment arrangement optimization,and hydrodynamic performance of AUV in smooth sea and wave sea.The content as follows:Basic CFD knowledge was firstly introduced,a cavity case was simulated to prove the practicability of CFD/EFD combination approach by Data Assimilation(DA)method and shortcoming were detected.Adaptive Simulated Annealing(ASA)was put into original method to improve the robustness and accuracy.Three direct route drag calculation methods of revolution bodies were introduced.Advantages and disadvantages were summarized by comparison.2D CFD method,standard wall function and self adaptive mesh strategy were specially presented for its good time performance and accuracy on revolution body drag calculation.The effect on total body drag was studied when length or fullness of nose or tail changed separately.A platform was established to optimize AUV main hull shapes when revolution body adopted.The platform was proved to be of high calculation precision,high work efficiency and application wide.CFD simulation results were compared with experiment data to validate the accuracy.validated method was conducted to study drag and moment variation when different size attachment was arranged at different position.An optimization method combining Kriging approximate model and Multi-Island Genetic Algorithm(MIGA)was developed to reduce direct route drag of AUVs by changing attachments arrangement.Volume Of Fluid(VOF)and overset mesh technologies were adopted to calculate drag,lift and moment variations when AUV sailing near free surface with zero or specific attack angle.Direct towing test,Oblique towing test,sway test and yaw test at several depth near free surface were all simulated to study force and moment changes with depth variation.Hydrodynamic coefficients from model test were adopted to study static stability,dynamic stability and turning quality variations as depth changed.The potential flow theory was conducted to carry out time domain analyses of AUV force and moment variations at different depth or speed in head or oblique waves,Maximum bearing amplitude when AUV sailing at particular depth was then calculated.Force variation and motion response of AUV sailing in irregular waves were studied in time domain,Higher order wave force affects to AUV moment posture was specially researched.Also force variation and motion response of AUV floating in regular or irregular waves were labored.First order wave force effect to AUV in short time period and higher order wave force effect to AUV in long time range were specially studied.