Research On Hydrodynamic Performance Of A Submerged Tidal Energy Device With A Single Mooring Line And Prototype Development

With the depletion of conventional energy sources such as oil and natural gas,green and pollution-free renewable energy sources have gradually attracted the attention of scientific researchers and have made great progress.Tidal current energy,as a kind of marine renewable energy,has attracted extensive attention due to its periodicity,predictability and high energy density.Tidal energy devices with different structural forms emerge one after another.However,the high costs of installation,offshore construction,maintenance and maintenance greatly limit the commercialization process of the devices.Therefore,this paper proposes a new type of the submerged tidal energy device.The device can realize lifting and sinking motion by injecting or removing seawater into the seabed base,thus reducing the cost of offshore construction,equipment maintenance and maintenance;The main body of the submerged tidal energy device is suspended 10?20m below the surface of sea water,which has the advantages of strong concealment and no influence of ocean extreme weather such as wind and waves.It can provide electric energy for ocean islands and offshore instruments.This paper proposes a structural layout of submerged tidal energy device according to the characteristics of tidal current.The buoyancy body is located at the top of the device,a pair of contra-rotating diffuser-augmented tidal turbines(DATTs)set aside of the buoyancy body.This structural layout increases the relative height between floating center and gravity center of the device,and further enhances the stability of the device in pitching motion.As the core component of absorbing and converting tidal current energy,DATTs use counter-rotating form to offset the extra torque generated by the rotation of tidal current turbines and enhance the stability of the device.The no-load start technology is adopted in nacelle to reduce the start-up inflow speed and increase the working efficiency of the device.The floating body provides buoyancy for the whole device,so that it can suspend and work in seawater;The cross tail located at the tail of the floating body provides restoring moment when the device is yawing,thus ensuring the flow adaptability of the device.In addition,this paper analyzes the advantages of this structural arrangement in the pitching and rolling movements of power generation devices from the perspective of force analysis.According to the attitude of the device in calm water and the designed inflow velocity,a method for selecting the connection point position is proposed and verified in model test and prototype sea test.DATT's hydrodynamic performance not only affects the working attitude of the device,but also affects the efficiency of the whole system.Tidal currents in terms of ebb and flood tides are approximately bidirectional,this paper modifies the NACA foil to form bidirectional BDA airfoil,and calculates its hydrodynamic performance.The bidirectional turbine is designed based on the bidirectional foils by using the blade element momentum(BEM)theory,and its hydrodynamic performance is analyzed by means of numerical simulations and model tests.The results show that the bidirectional turbine has almost the same energy conversion capability in both of the tidal current directions.After a diffuser is installed on the turbine's periphery,the hydrodynamic performance of the DATT is evaluated by numerical simulations and model tests.The hydrodynamic performance of the bidirectional turbine is compared with the DATT,and the design scheme of the submerged tidal energy device is determined.The distance between DATTs and the height position of floating bodies relative to DATTs will affect DATT's hydrodynamic performance.Therefore,3D models of the DATTs and the submerged tidal energy devices with different sizes are respectively constructed.In the form of numerical simulation,the influences of side-by-side diffuser spacing and the height position of floating bodies relative to conduit turbines on the flow performance and hydrodynamic performance of DATT are analyzed,and the relative positions between side-by-side DATTs and floating body are determined to guide the development of the submerged tidal energy device's model and prototype.A 1:5^thscaled submerged tidal energy device model is developed,and model tests are carried out in a circulating water tank to test the device's attitude and power generation performance.The research shows that the whole device model can basically maintain a positive floating attitude under calm water and designed condition.A prototype of the 1:1^thscaled submerged tidal energy device is developed and tested.Through the onshore tests,while verifying the data acquisition accuracy of the turbine controller,the power generation efficiency of the generators and the stability of the control system are tested.The sea trial is to verify the rotary performance of the device under the action of forward and reverse tidal currents in the real marine environment.The sea trial test results show that the device has tidal current direction adaptability,can realize autonomous changing directions following the change of tidal current direction,and has good stability in pitching and rolling movementsIn conclusion,this paper explores the development of a submerged tidal energy device.The working attitude and power generation performance of the device are analyzed and studied in the form of numerical simulations,model tests and prototype sea trials,which provides certain data support for the development of the submerged tidal energy device in China..