Dynamic and structural performances of offshore floating wind turbines in turbulent wind flow

A realistic turbulent wind field differs from a steady uniform one, in terms of the wind shear, the turbulence intensity and the coherence structure. Although it has been clear that an offshore floating wind turbine will behave differently in the turbulent wind, the individual effect of the above three items are not investigated sufficiently until now. The primary objective of the present research is to investigate in details how the wind shear, the turbulence intensity and the coherence influence the dynamic and structural responses of offshore floating wind turbines. Aero-hydro-servo-elastic coupled simulation of a semi-submersible floating wind turbine is run in time-domain. The wind shear has a limited effect on the global responses of the floating wind turbine although its influence on each individual blade is considerable. Comparatively, the floating wind turbine is quite sensitive to the turbulence intensity. In a wind field with high turbulence intensity, the platform motions become more violent and the structural loads are increased substantially. The proper orthogonal decomposition method is used to investigate the coherence quantitatively. A partial coherence structure helps to reduce the flow variation seen by the rotor and thereby beneficial to the safety of the floating wind turbine

Unsteady aerodynamics of offshore floating wind turbines using free vortex wake model

Among the offshore floating wind turbine software packs, the blade element momentum theory (BEM) and generalized dynamic wake (GDW) model are widely used. A free vortex wake model has been coupled to FAST v7 to do a comparative dynamic analysis between using the BEM theory and GDW method on offshore floating wind turbine. The verification test on the free-wake model has been performed according to the NREL VI experiment in steady and yaw conditions. To analyze the unsteady aerodynamics of floating wind turbine, the OC3 spar type wind turbine has been used to do simulations. The global performances on both the rotor and the platform and their interactions are shown and discussed

Floating wind turbine system

A floating wind turbine system with a tower structure that includes at least one stability arm extending therefrom and that is anchored to the sea floor with a rotatable position retention device that facilitates deep water installations. Variable buoyancy for the wind turbine system is provided by buoyancy chambers that are integral to the tower itself as well as the stability arm. Pumps are included for adjusting the buoyancy as an aid in system transport, installation, repair and removal. The wind turbine rotor is located downwind of the tower structure to allow the wind turbine to follow the wind direction without an active yaw drive system. The support tower and stability arm structure is designed to balance tension in the tether with buoyancy, gravity and wind forces in such a way that the top of the support tower leans downwind, providing a large clearance between the support tower and the rotor blade tips. This large clearance facilitates the use of articulated rotor hubs to reduced damaging structural dynamic loads. Major components of the turbine can be assembled at the shore and transported to an offshore installation site

Experimental study of a TLP offshore floating wind turbine

Tank testing in a wind and wave environment is a key part of the design process for the development of an offshore floating wind turbine. The current paper describes an extensive experiment campaign carried out at the Kelvin Hydrodynamics Laboratory at the University of Strathclyde to determine the hydrodynamic performance of the Iberdrola TLPWIND offshore floating wind turbine with the NREL 5MW reference turbine over a range of environmental conditions. Tests were carried out for 70m water depth and the deployment area selected as off Aberdeen, North Sea. The campaign included free oscillation tests, tests in regular waves and irregular waves, and additionally examined failure and accidental load cases

EFFECT OF THE ROTATING BLADES ON THE STABILITY OF FLOATING WIND TURBINE

ABSTRACT: The objectives of the proposed study is to study the effect of rotating blades on the stability of floating wind turbine. The rotating blades or can be called as gyromotion effect had resulted in various of effect towards the stability of floating wind turbine such as that can be seen with human eyes are pitch, yaw, surge, roll, sway and heave, the paper will briefly summarise the background of floating wind turbine and the methodology used to analyse and compute the effect of rotating blade or gyromotion towards the stability of floating wind turbine by using a simulation software which is Star CCM that can simulate the real life time event in order to analyse the effect of the rotating motion towards the stability of the structure. The data used in the study will be from previous researches that have been made

Non-linear dynamic analysis of the response of moored floating structures

© 2016 Elsevier Ltd. The complexity of the dynamic response of offshore marine structures requires advanced simulations tools for the accurate assessment of the seakeeping behaviour of these devices. The aim of this work is to present a new time-domain model for solving the dynamics of moored floating marine devices, specifically offshore wind turbines, subjected to non-linear environmental loads. The paper first introduces the formulation of the second-order wave radiation-diffraction solver, designed for calculating the wave-floater interaction. Then, the solver of the mooring dynamics, based on a non-linear Finite Element Method (FEM) approach, is presented. Next, the procedure developed for coupling the floater dynamics model with the mooring model is described. Some validation examples of the developed models, and comparisons among different mooring approaches, are presented. Finally, a study of the OC3 floating wind turbine concept is performed to analyze the influence of the mooring model in the dynamics of the platform and the tension in the mooring lines. The work comes to the conclusion that the coupling of a dynamic mooring model along with a second-order wave radiation-diffraction solver can offer realistic predictions of the floating wind turbine performance.Postprint (published version

Dynamic response and power production of an integrated offshore renewable energy system

This study investigates the dynamics and energy production of a new offshore floating renewable energy system, which integrates an offshore floating wind turbine (OFWT), a wave energy converter (WEC) and two tidal turbines. The hybrid concept is proposed to enhance the energy production through the combination of the three types of renewable energy systems. Simulation results show that the combined concept achieves a synergy between the floating wind turbine, the wave energy converter and the tidal turbines. Compared with a single floating wind turbine, the combined concept undertakes reduced surge and pitch motions. The overall power production increases by approximately 15%

Towing of Floating Wind Turbine Systems

Towing is an important marine operation and floating wind turbines are the new way forward in our ever-expanding need for energy. In offshore floating wind turbine installation process, transport is an important phase. Presently, the turbines are assembled on shore and then towed to the installation spot one at a time. In this thesis, the theory behind the towing operation, modelling and simulation of various towing scenarios are carried out and the mathematical basis of the analysis is studied. It discusses previous research work that has been published in similar operations. The modeling and simulation has two different scenarios. In the first scenario is to find the optimum tow-point for the towing operation. It was found that it varies slightly with sea state but closer to center of buoyancy is optimal. In the second scenario, the simulation aims to find the scope of towing multiple turbines during a single tow-operation. In the process line tension was checked for a single turbine at different towing speeds. It was found that it is unfeasible to tow multiple turbines

Progress on the experimental set-up for the testing of a floating offshore wind turbine scaled model in a field site

This document describes design and realization of a small-scale field experiment on a 1:30 model of spar floating support structure for offshore wind turbines. The aim of the experiment is to investigate the dynamic behaviour of the floating wind turbine under extreme wave and parked rotor conditions. The experiment has been going on in the Natural Ocean Engineering Laboratory of Reggio Calabria (Italy). In this article, all the stages of the experimental activity are presented, and some results are shown in terms of motions and response amplitude operators. Finally, a comparison with corresponding results obtained using ANSYS AQWA software package is shown, and conclusions are drawn. The presented experimental set-up seems promising to test offshore floating structures for marine renewable energy at a relatively large scale in the Natural Ocean Engineering Laboratory field site