Study On The Key Technologies Of Hydrokinetic Current Turbines Designed For Underwater Moored Platforms

Underwater Moored Platforms(UMPs)are a class of ocean platforms that are anchored to the seabead via cables.UMPs have a wide range military and civil applications,such as military defense and underwater monitoring.Currently,most UMPs are battery-powered and because of their finite energy supply and the uninterrupted consuming of energy by the onboard electronic devices,stored energy limitations typically limit the duration of their installed operation.Extending the operational life of UMPs can significantly reduce the cost for missions where a sustained presence is require,because of the high costs associated with retrieving,repowering,and redeploying remote systems.This thesis aims at investigating the underwater energy supply of UMPs.Two types of hydrokinetic current turbines(HCTs)for UMPs are designed to convert the energy stored in currents and supply power for the UMPs.Based on a literature review of the present theories and technologies of HCTs,this paper studied the two HCTs with a combined theoretical,numerical and experimental method.The design of the design of the HCTs,the hydrodynamic performance of the turbine and the coupled motion performance of the UMP are studied with efforts.The main contents and innovations of this study are summarized as follows:(1)Design of the HCTs for UMPs.Firstly,the technical index for the HCTs are proposed considering the motion particularity of the UMPs.According to the technical index,two different HCTs are designed-a horizontal HCT(HHCT)and a vertical HCT(VHCT).The blade of the turbine is optimized for low-velicty situations.The magnetic coupling device is used to tranfer the torque of the turbine,a magnetic simulation is performed to predict the torque and thrust performance of the magnetic coupling device.(2)Computational fluid dynamics(CFD)analysis of the VHCT.The numerical simulation was based on the time-averaged Reynolds Navier-Stokes equation.The CFD modeling procedures of the VHCT is described in detail.A verification and validation study is performed to prove the the mesh density,simulation time step and turbulence models.The structure parameters,blade arc angle and open angle,on the performance of the turbine is studied and illustrated with the aid of the flow field visualization technology.The wake of the turbines are also compared.(3)Computational fluid dynamics(CFD)analysis of the HHCT.Steady simulations are firstly carried out to investigate the hydrodynmic performance of 5 different blades,with the aim of finding out the one with the highest coefficient of power.Then comprehensive transient CFD simulations are performed on the turbine,where the effect of the UMP is considered as well.The effect of tip speed ratio,the position of the turbine,yaw angle and turbulence intensity on the hydrodynamic performance and the wake of the turbines are studied.(4)Dynamic modeling and motion simulation of the UMP system.Firstly a three-dimensional rigid mathematical model of the UMP is produced based on the Newton-Euler method.Then the dynamic model of the cable is built based on the concentrated mass method.The models for the UMP and the cable are then combined using the coupling conditions of the motion and velocity.Based on the model of the UMP system,the effect of the net buoyancy,the position of the gravity center,the length of the cable,the positon of the turbine and the velocity of the inflow on the motion characteristics of the system is studied.