Establishing a fully coupled CFD analysis tool for floating offshore wind turbines

An accurate study of a floating offshore wind turbine (FOWT) system requires 16 interdisciplinary knowledge about wind turbine aerodynamics, floating platform 17 hydrodynamics and mooring line dynamics, as well as interaction between these 18 discipline areas. Computational Fluid Dynamics (CFD) provides a new means of 19 analysing a fully coupled fluid-structure interaction (FSI) system in a detailed manner. 20 In this paper, a numerical tool based on the open source CFD toolbox OpenFOAM for 21 application to FOWTs will be described. Various benchmark cases are first modelled 22 to demonstrate the capability of the tool. The OC4 DeepCWind semi-submersible 23 FOWT model is then investigated under different operating conditions. 24 With this tool, the effects of the dynamic motions of the floating platform on the wind 25 turbine aerodynamic performance and the impact of the wind turbine aerodynamics 26 on the behaviour of the floating platform and on the mooring system responses are 27 examined. The present results provide quantitative information of three-dimensional 28 FSI that may complement related experimental studies. In addition, CFD modelling 29 enables the detailed quantitative analysis of the wind turbine flow field, the pressure 30 distribution along blades and their effects on the wind turbine aerodynamics and the 31 hydrodynamics of the floating structure, which is difficult to carry out experimentally

A validated BEM model to analyse hydrodynamic loading on tidal stream turbines blades

This is the author accepted manuscript. The final version is available from the link in this record.AWTEC 2016: 3rd Asian Wave and Tidal Energy Conference, 24-28 October 2016, SingaporeThis paper details a Blade Element Momentum (BEM) model for a 3 bladed, horizontal axis Tidal Stream Turbine (TST). The code capabilities are tested and validated by applying a range of different turbine parameters and operating conditions, where results are compared to numerous datasets. The model shows excellent agreement to performance and thrust measurements for 3 of the 4 datasets. Compared to other BEM models improved correlations are seen at higher rotational speeds. The fourth case shows over predictions of up to 30% in power at peak operating speed. In this case, CFD studies show better correlation due to the ability to capture detailed flow features around the blade as well as free surface effects, however require 3 to 4 orders of magnitude greater computational cost. Steady, non-uniform inflow functionality is incorporated into the model, where distributions of thrust and torque along the blade as well as cyclic loads are determined. These show the potential of the model to be used in combination with tools such as stress and fatigue analyses to improve the blade design process.This research is carried out as part of the Industrial Doctoral Centre for Offshore Renewable Energy (IDCORE) programme, funded by the Energy Technology partnership and the RCUK Energy programme (Grant number EP/J500847/1), in collaboration with EDF R&D

Blade-explicit fluid structure interaction of a ducted high-solidity tidal turbine

This work elaborates a computational fluid dynamic (CFD) model utilised in the investigation of the structural performance concerning a ducted high-solidity tidal turbine in aligned and yawed inlet flows. Analysing the hydrodynamic performance at aligned flows portrayed the distinctive power curve at which energy is transferred via the fluid-structure interaction. At distinct bearing angles with the axis of the turbine, variations in the blade-interaction due to the presence of the duct was acknowledged within a limited angular range at distinct tip-speed ratio values. As a result of the hydrodynamic analysis, a structural investigation of the blades was discretely evaluated in an effort to acknowledge fluid-structure phenomena

Analysing fibre composite designs for high-solidity ducted tidal turbine blades

This study elaborates a one-way fluid-structure interaction numerical model utilised in investigating the structural mechanics concerning the rotor blades comprising a ducted high-solidity tidal turbine. Coupling hydrodynamic outcomes as structural inputs in effort of acknowledging the most applicable setup, distinct designs are investigated, solid blades and cored blades, implementing fibre-reinforced composite materials, analysed within criteria related to blade axial deformation, induced radial strains, and rotor specific mass

An investigation of the effects of wind-induced inclination on floating wind turbine dynamics: heave plate excursion

International audienc

Investigation of focused wave impact on floating platform for offshore floating wind turbine : a CFD study

Most existing research related to a semi-submersible offshore floating platform focuses on the wave-structure interaction under either a regular or irregular wave condition. In order to numerically model the irregular wave impact on a semi-submersible platform hydrodynamic response with a low computational cost, in this study, a focused wave is utilized. The platform under this consideration is the DeepCwind semi-submersible platform. A high fidelity CFD numerical solver based on solving Navier-Stokes equations is adopted to estimate the dynamic response and the hydrodynamic loading of the platform. The focused wave is firstly generated based on a first order irregular wave theory in a numerical wave tank and validated against the linear wave theory results. Next, for CFD coding validation, the surface elevation of a fixed FPSO model associated with a focused wave is calculated and compared with the benchmark results. At last, the dynamic responses of the platform are numerically simulated under various focused wave parameters, and the results are compared with those obtained from an in-house potential flow theory tool at Électricité de France (EDF). It is found that the predicted CFD surge motion responses are close to those achieved with the second order potential theory while differ from the results obtained using linear potential theory. As to the pitch motion, differences are observed between two results, due to the different methods used for second order loads and viscous effects calculation. Turning to the results under different wave parameters, the surge and heave motion responses increase as the wave period goes up. However, the pitch motion is not affected significantly by varying wave periods. It may be due to the fact that the low-frequency effects have limited impact on the pitch motion. The strong nonlinearity at extremely large wave amplitude will be the task in our near future study

A Validated BEM Model to Analyse Hydrodynamic Loading on Tidal Stream Turbine Blades

This paper details a Blade Element Momentum (BEM) model for a 3 bladed, horizontal axis Tidal Stream Turbine (TST). The code capabilities are rigorously tested by applying a range of different turbine parameters and operating conditions, where results are compared to numerous validation datasets. The model shows excellent agreement to performance and thrust measurements from 3 of the 4 datasets, where improved correlations are seen at high rotational speeds to other BEM models. The exception case shows over predictions of up to 30% in power at peak operating speed. In this case, CFD studies show better correlation due to the ability to capture detailed flow features around the blade as well as free surface effects, however require 3 to 4 orders of magnitude greater computational cost. Steady, non-uniform inflow functionality is incorporated into the model, where distributions of thrust and torque along the blade as well as cyclic loads are determined. These show the potential of the model to be used in combination with tools such as stress and fatigue analyses to improve the blade design process. This paper details the validation of an efficient BEM model through experimental results and additional CFD analysis, as well as demonstrating its application for detailed analysis of hydrodynamic loading to be used in blade designs. Keywords— Tidal Stream Turbine (TST), Blade Element Momentum (BEM), performance modelling, non-uniform inflow, blade cyclic loading, hydrodynamic loadin

A numerical performance analysis of a ducted high-solidity tidal turbine

This study puts forward an investigation into the hydrodynamic performance concerning a ducted, high-solidity tidal turbine utilising blade-resolved computational fluid dynamics. The model achieves similarity values of over 0.96 with experimentation data regarding a three-bladed horizontal-axis tidal turbine in validation of three distinct parameters: power & torque coefficient, thrust coefficient, and wake velocity profiles. Accordingly, the model was employed for the analysis of a ducted, high-solidity turbine in axially-aligned flows at distinct free-stream velocities. The resultant hydrodynamic performance characteristics portrayed a peak power coefficient of 0.34, with a thrust coefficient of 0.97, at a nominal tip-speed ratio of 1.75. Coefficient trend agreement was attained between the numerical model and experimentation data established in literature and blade-element momentum theory; the model furthers the analysis by elaborating the temporal hydrodynamic features induced by the fluid-structure interaction in specification to the wake formation velocity profiles, pressure distribution along the blades and duct, mass flow rate, and vortex shedding effects to establish the characteristic flow physics of the tidal turbine

The dynamic response of floating offshore wind turbine platform in wave-current condition

In this paper, the fluid–structure interaction of floating offshore wind turbine (FOWT) platforms under complex ocean conditions is investigated using OpenFOAM and in-house developed models. Two types of FOWT platform, i.e., a semi-submersible platform and a barge platform, are studied for their dynamic responses to either wave or current. The results reveal that a semi-submersible platform exhibits larger cross-flow motion and lock-in phenomenon, while a barge platform experiences smaller motion with no significant lock-in within the velocity range examined. The combined wave–current conditions are further studied for the semi-submersible platform, with different angles between wave and current, the current speeds, and wave parameters. Unlike other investigations focusing on colinear wave–current interaction, in which the waves usually mitigate vortex-induced motion (VIM); here, we find that waves might lead to an enhanced VIM with a large angle between current and wave. The evaluation on the interaction effect factor shows that the largest wave height in the lock-in region does not lead to the most dangerous scenario, herein, the largest platform motion. Instead, a smaller wave height with a large wave period can induce even larger motion