Offshore Wind Turbine Aerodynamic Performance And Novel Floating System

As the global climate deterioration, environmental pollution and the shortage problem of conventional energy are more and more serious, many countries are trying to find out the clean renewable substitutable energy. Wind energy resource, which is of both the most mature technology and the most promising commercial prospect, are being paid more and more attentions. In particular, the exploitation of the offshore wind energy resource, which has advantages of higher wind speed, lower turbulent intensity, less limitation of noise level, land saving, etc., has been becoming an important researcher direction of the future wind energy exploitation.In this work, at the background of the exploitation and the development of offshore wind energy, based on numerical simulation and theoretical analysis, combing with available experimental model tests and field observation data, the problems of offshore wind energy assessment, aerodynamic performance of 2D airfoils and 3D blade of large offshore wind turbine, offshore wind turbine impaced by ship and future deep-water floating system have been systematically studied. The main contents can be summarized as follows:1 In the view of the situation of such limited distribution of weather observation stations, particularly in coastal zones, the sophisticated non-hydrostatic Mesoscale meteorology MM5 Model has been applied to high-resolution numerical simulation of wind fields in Dalian coastal zone during year 2000, based on the reanalysis data from National centers for Environmental Prediction (NECP) year 2000, vegetation-land-use data from U.S. Geological Survey (USGS) and observation data from the four weather stations in Dalian. The annual average wind speed, the annual available wind hours, the available wind energy density and other important wind resource information have been qualitatively and quantitatively obtained for Dalian about different heights.2 Numerical simulations for the pneumatic characteristics of the large wind turbine popular two-dimensional airfoils have been done, based on Navier-Stokes equations and k-? SST turbulence model. Considering influence of the dynamic stall, which happens in the large angle of attack, the related parameters of the turbulence model has been properly modified. Moreover, the effect of blade surface dust accumulation has been taken into consideration. The lift coefficients and the drag coefficients of wind turbine airfoil have been computed under different roughness areas, roughness locations and roughness heights. Consequently, the mechanisms of the surface roughness effect for the airfoil pneumatic characteristics have been clarified. In addition, the 2D and 3D aerodynamic interference effect between wind turbine blade and tower has been studied, and the perturbation of the force acting on the tower under the blade rotational effect was clearly clarified. Finally, based on the natural typhoon real time history, the aeroelastic response of the airfoil can be calculated by embedding structural dynamics Newmark-? codes into the CFD solver, and the nonlinear interaction between the airfoil vibration and the unsteady flow can be successfully studied by taking advantage of the sliding mesh technique for the simulation of the airfoil's dynamic responses. As a result, three kinds of nonlinear stall-induced vibration have been considered: pitching oscillation, flap-wise oscillation and flap-pitching coupled oscillation.3 Numerical simulations of the three-dimensional aerodynamic performance for the NREL 5MW offshore wind turbine blades have been done by using advanced sliding mesh technique, based on Navier-Stocks equations and RNG k-? turbulence model, which is very suitable for the rotational fluid flow. The variations of the rotor output power for the 5MW OWT according to different inlet wind speeds and different rotor rotational speeds have been studied. Furthermore, the distribution characters of wind field in the wake of OWT have been investigated.4 The dynamic process of the collision between a typical 3MW offshore wind turbine with monopile foundation and a simplified 2000t-class ship, has been studied by the famous LS-DYNA explicit code. What's more, from the design idea of sacrificing unimportant structrures for saving the main structure of OWT, a new conceptual steel sphere shell-circular ring aluminum foam pad crashworthy device for OWT was proposed. As a result, the good performance of the new device has been verified from both views of theoretical analysis and numerical results.5 Two new conceptual offshore floating wind turbine systems with the Tension legs-Mooring lines were proposed, which were based on the National Renewable Energy Laboratory 5MW offshore wind turbine model. Taking the coupled effect of dynamic response of the top wind turbine, tower support structure and lower mooring system into consideration, the time domain analysis with the couple effect of wind, wave and current, has been done for the two offshore floating platforms: the single-OWT system and the multi-OWT system. What's more, based on new single-OWT design, 1/60 scaled model tests under typical sea cases have been done in advanced wind-wave tunnel of Harbin Institute of Technology. The test results between new Tension legs-Mooring lines system model and pure Tension legs model have been systematically compared. As a result, the performance of the new combined Tension legs-Mooring lines system has been verified in views of theoretical analysis, numerical results and scaled model tests.