Semi-submersible Floating Wind Turbine Research Articles

Aerodynamic damping of a semi-submersible floating wind turbine: An analytical, numerical and experimental study

Aerodynamic damping of floating wind turbines (FWTs) plays a dominant role in suppressing the vibration of the tower and blades and the platform motions. Although much effort has been paid to investigating the aerodynamic damping of FWTs, their characteristics and influential factors have not been studied thoroughly. In the present study, the aerodynamic damping of a semi-submersible FWT is investigated by a frequency-domain analytical method and a fully coupled decay-based time-domain method, which are validated against the wave basin model tests. Effects of controller dynamics are discussed, and then the dynamic characteristics of aerodynamic damping in surge and pitch motion are addressed. It is found that the proposed analytical method can predict the aerodynamic damping with enough accuracy and extremely high efficiency compared to the time-domain numerical method. The effects of controller dynamics should be considered in the over-rated wind speed region, especially pitch motion. Controller gains can significantly affect the aerodynamic damping in pitch motion in the over-rated wind speed region. In contrast, the initial offset and wind turbulence may not be the main influential factors. The outcomes of the present study can provide insight into the aerodynamic damping and the controller design of FWTs.

Short-term prediction of hydrodynamic response of a novel semi-submersible FOWT platform under wind, current and wave loads

In the present study, the hydrodynamic response of the novel semi-submersible floating wind turbine (FOWT) platform “Three Gorges Leading (TGL)" was investigated under the actions of wind, current, and wave load and mooring recovery force. AQWA based on potential flow theory was used to establish the hydrodynamic model of the platform and calculate the hydrodynamic coefficients and frequency domain hydrodynamic response. Premised on the hydrodynamic model, the influence of environmental parameters on the hydrodynamic response of the platform was specifically analyzed, the Kriging-MOGA algorithm was used to establish an approximate prediction model for the frequency domain hydrodynamic response of the platform, and the time domain response of the platform under the predicted hazardous conditions was analyzed using FAST-AQWA (F2A) under the action of aerodynamic-hydrodynamic coupling. Findings were made that the hydrodynamic response of the platform was significantly affected by the aerodynamic load of the blades, and the novel semi-submersible platform was verified to meet the operating requirements of offshore floating wind turbines.

Numerical study of a novel hybrid system with the Wavestar wave energy converter array and a SPIC semi-submersible floating platform

To improve power generation efficiency and reduce costs in the industry of ocean renewable energy, one of the optimal strategies is the addition of wave energy converters (WECs) into the floating wind turbine. This paper proposes a novel hybrid wind-wave energy concept that comprises multiple Wavestar point absorption wave energy converters (WECs) and a SPIC semi-submersible floating wind turbine (FWT). ANSYS/AQWA software is used to perform numerical simulations based on three-dimensional potential flow theory. Three hybrid systems are designed with different numbers of Wavestar WECs, which are symmetrically arranged on the platform. Before the study, the hydrodynamic responses of the Wavestar WEC and the SPIC concept platform are simulated separately and compared with existing experimental data. After the validation of numerical models, the platform motions and the absorbed power of the WECs are investigated, which are the main factors in evaluating the performance of a hybrid system. After a series of numerical simulations, the results show that the absorbed power increase significantly with the increase in the number of the Wavestar WECs, while the platform motions also increase. It can be concluded that the wind-wave energy hybrid design needs to find a balance between the platform motions and the absorbed power of the WECs. Overall, this study can be used as a reference for the design of other novel hybrid ocean energy concepts.

Conceptualization and dynamic response of an integrated system with a semi-submersible floating wind turbine and two types of wave energy converters

Conceptualization and dynamic response of an integrated system with a semi-submersible floating wind turbine and two types of wave energy converters

An innovative method of assessing yield strength of floater hull for semi-submersible floating wind turbine in whole life period

The concepts of external and internal corrosion damage of materials have been proposed, and the improved corrosion damage models considering marine corrosion zone have been established. Then, a new method of assessing yield strength of floater hull for semi-submersible floating wind turbine considering the effect of corrosion damage in whole life period is proposed based on the equivalent design wave and structural quasi-static analysis method. Taking the OC4 floating wind turbine foundation for example, this new assessment method has been conducted. The results show that the stresses and displacements of structures will be increased under the influence of corrosion damage in whole life period and the risk of structural failure is also increased due to the corrosion damage. The structures which locate in the high stress level region will up to the yield failure critical point (yield strength margin is close to zero) by the end of service period if just considering the external corrosion damage, and these structures may fail due to yield after 18–22 years of service if considering the external and internal corrosion damage simultaneously. Therefore, the corrosion damages (especially the internal corrosion damage) have produced an important effect on the structural yield strength. In addition, the value of material factor γm = 1.1 (given by DNVGL-ST-0119) is small, and the suggested value is 1.25–1.3 for the structures in high stress level region.

Dynamic Co-Simulation Analysis and Control of an IEA 15 MW Offshore Floating Semi-Submersible Wind Turbine under Taiwan Offshore-Wind-Farm Conditions of Wind and Wave

This study aims to develop dynamic co-simulation and control for analyzing the IEA 15 MW semi-submersible floating wind turbine under Taiwan offshore-wind-farm conditions of wind and wave. The IEA 15 MW wind turbine is mounted on a UMaine VolturnUS-S reference platform with a mooring system designed for a water depth of 70 m, in this study. The dynamic co-simulation combines software of SIMPACK, MATLAB/SIMULINK, AeroDyn, HydroDyn, WAMIT, and MAP++ to achieve the complex dynamic simulation of aerodynamics, hydrodynamics, mechanism dynamics and control system dynamics. In addition, this study proposes a novel power-control strategy combining fuzzy sliding-mode control with additional pitching-rate feedback. Since the motion of the floating platform, especially the pitching motion, contributes to power oscillation, the proposed novel power-control strategy with additional pitching-rate feedback can reduce the influence of the floating-platform oscillation motion, and is verified under different conditions.

Dynamic Response Analysis of Semi-Submersible Floating Wind Turbine with Different Wave Conditions

Dynamic Response Analysis of Semi-Submersible Floating Wind Turbine with Different Wave Conditions

Vibration reduction of semisubmersible floating wind turbine using optimized tuned mass and tuned inerter dampers

Over the past decade, offshore wind has positioned itself as one of the most promising renewable energy markets. While this field is currently dominated by fixed-bottom wind turbines located within a limited depth range, floating turbines are showing promise as a way to capture the more developed wind profiles available in deeper waters. Currently, the main challenge with floating offshore wind is that the systems experience larger ultimate loads compared to fixed bottom turbines. These larger loads are caused by the increased motion inherent with floating structures. This study looks to analyze the effects that traditional and inerter based structural control methods can have on reducing the motion of floating offshore wind turbines. Models are developed adding tuned mass dampers (TMD) and tuned inerter dampers (TID) into the three main columns of the semisubmersible platform. Results showed that for free decay tests, heave and pitch RMS values were reduced significantly by the addition of passive structural control. The inerter based structural control consistently outperformed traditional TMD and allowed for similar performance with significantly reduced physical mass values.

Research on Size Optimization of Wave Energy Converters Based on a Floating Wind-Wave Combined Power Generation Platform

Wind energy and wave energy often co-exist in offshore waters, which have the potential and development advantages of combined utilization. Therefore, the combined utilization of wind and waves has become a research hotspot in the field of marine renewable energy. Against this background, this study analyses a novel integrated wind-wave power generation platform combining a semi-submersible floating wind turbine foundation and a point absorber wave energy converter (WEC), with emphasis on the size optimization of the WEC. Based on the engineering toolset software ANSYS-AQWA, numerical simulation is carried out to study the influence of different point absorber sizes on the hydrodynamic characteristics and wave energy conversion efficiency of the integrated power generation platform. The well-proven CFD software STAR CCM+ is used to modify the heaving viscosity damping of the point absorber to study the influence of fluid viscosity on the response of the point absorber. Based on this, the multi-body coupled time-domain model of the integrated power generation platform is established, and the performance of the integrated power generation platform is evaluated from two aspects, including the motion characteristics and wave energy conversion efficiency, which provides an important reference for the design and optimization of the floating wind-wave power generation platform.

A particle image velocimetry investigation of the flow field close to a heave plate for models of different scales

Semi-submersible floating wind turbines are generally equipped with heave plates to introduce additional hydrodynamic damping and decrease the platform’s natural frequency. Scale effects are one of the most critical problems concerning the accuracy of model-scale experiments on these damping-augmenting devices. The current research aimed to assess the impact of the scale factor on the flow physics of oscillating circular solid plates. Forced oscillation flow visualisation model-scale experiments were performed on three geometrically similar one-leg columns of a semi-submersible platform equipped with a circular solid flat heave plate. The forced oscillation tests were performed in the range of extreme and operational Keulegan–Carpenter numbers (KCs) for two different frequencies of the heave plate’s oscillatory motion. A submersible two-dimensional (2D) three-component (3C) Stereoscopic Particle Image Velocimetry (Stereo-PIV) system was employed to measure the flow field velocity distribution. The Stereo-PIV images were obtained at four positions in the oscillation cycle. The investigation focused on detecting scale effects on the velocity and vorticity for the three models of different scales. Similarities in centre positions, shape, and contours between the three models were visualised for the measured velocity field. The computed vorticity field also revealed similarities in centre positions, shape, and contours among the three different scales. Following up on previous works focusing on the hydrodynamic forces on oscillating circular solid plates, the outcomes of this paper also confirm that, for the considered case study, the correct choice of the motion amplitude (KC) impacts the flow physics of the model tests more than the scale factor.

Model tests of a 10 MW semi-submersible floating wind turbine under waves and wind using hybrid method to integrate the rotor thrust and moments

Abstract. This paper describes the results of a wave tank test campaign of a 1/49 scaled SATH 10 MW floating platform. The software-in-the-loop (SiL) hybrid method was used to include the wind turbine thrust and the in-plane rotor moments. Experimental results are compared with a numerical model developed in OpenFAST of the floating wind turbine. The tank test campaign was carried out in the scaled model tested at the deep ocean basin from the Lir National Ocean Test Facility at Cork, Ireland. This floating substructure design was adapted by Saitec to support the 10 MW wind turbine within the ARCWIND project (Adaptation and Implementation of Floating Wind Energy Conversion Technology for the Atlantic Region) with the aim of withstanding the environmental conditions of the European Atlantic Area region. CENER provided the wind turbine controller specially designed for the SATH 10 MW configuration. A description of the experimental setup, force actuator configuration and the numeric aerodynamic parameters is provided in this work. The most relevant experimental results under wind and wave loading are shown in time series and frequency domain. The influence of the submerged geometry variations in the pitch natural frequency is discussed. The paper shows the simulation of a case with rated wind speed, where the tilted geometry for the computation of the hydrostatic and hydrodynamic properties of the submerged substructure is considered. This case provides a better agreement of the pitch natural frequency with the experiments than an equivalent simulation using the undisplaced geometry mesh for the computation of the hydrodynamic and hydrostatic properties.

Experimental investigation on the dynamic response of an innovative semi-submersible floating wind turbine with aquaculture cages

Floating offshore wind turbines integrating with other functional devices can not only produce green electricity but also realize three-dimensional utilization of ocean space. Therefore, an innovative concept of semi-submersible floating wind turbine with aquaculture cages is proposed here. Correspondingly, its dynamical behaviors are required to be examined and investigated while various oceanic conditions are considered, including but not limited to an irregular wave condition and combined wind and wave conditions. Hence, a series of model tests in 1:40 scale is carried out in Shanghai Jiao Tong University Ocean Engineering Basin. Firstly, the scaling law and experimental setup are interpreted in detail. Calibrations of the wind generator and wave makers are carefully performed to ensure the accuracy and reliability of model tests. Then the dynamic responses of the new floating wind-aquaculture platform (FWAP) are studied experimentally, including the periods, damping, motions, accelerations and tower top loads. The results show that the existence of nets mainly has a damping effect on the dynamics of the new FWAP under different sea states. The motions, accelerations and tower top loads can be significantly increased when the FWAP undergoes 50-year extreme sea state. When the new FWAP is subjected to combined wind and wave, more complicated dynamic responses can be detected due to the rotation of wind turbine. The results can serve as a reference basis for the improvement of the new FWAP.

Numerical study on passive structural control of semi-submersible floating wind turbine considering non-collinear wind and waves

Floating offshore wind turbines have great potential in the deep-sea regions and they often suffer from the combined action of wind and waves, which affects the safety of wind turbines and the stability of power generation. At present, the tuned mass dampers installed in the wind turbine nacelles are widely used to control the vibration of wind turbine structures, but their mass are relatively small and have limited effectiveness on the large motion of floating offshore wind turbines. Moreover, the motion control of floating offshore wind turbines is mostly considered under the condition that the wind and waves are collinear while the non-collinear condition has been rarely investigated. Therefore, the tuned mass damper system installed in the nacelle and the platform of semi-submersible floating offshore wind turbine is studied through numerical methods in this research, and the non-collinear wind and waves conditions are considered. The results show that the high-frequency tuned mass damper installed in the nacelle is effective to reduce the response of tower but has little effect on the platform. The low-frequency tuned mass damper works well to control the response of tower and platform no matter it is installed in the nacelle or in the platform. For the irregular wave, the effect of tuned mass damper is not obvious and the large-mass one even increases the response. For the non-collinear wind and wave, the tuned mass dampers installed in the nacelle and platform at the same time have the best effect to reduce the response of wind turbine for various wind-wave angles.

Study on Characteristics and Optimal Layout of Components in Shallow Water Mooring System of Floating Wind Turbine

Offshore wind energy resources far exceed those on land. However, the increase in water depth of the continental shelf in China’s sea area slows down as the distance from the shore increases. In view of the characteristics of China’s sea, how to optimize the design of mooring systems to adapt to the water depth conditions in China’s waters and to resist the harsh sea conditions is one of the major problems encountered in the development of floating wind turbines. In this paper, the 5MW-OC4 semi-submersible floating wind turbine is taken as the research object, and the frequency domain and time domain calculation of the floating wind turbine are carried out by using SESAM software under the water depth of 40 m in the Bohai Sea. By comparing the motion response and tension of catenary and tension mooring floating wind turbine. The mooring system is optimized by combining the buoy and clump weight. The results show that the catenary mooring mode is more suitable for the floating wind turbine under shallow water conditions. Mooring accessories used in combination have the same effect on the overall response of the floating wind turbine as changing the same mooring parameters when used alone, but the effect of changing the mooring parameters on the performance optimization of the mooring system is more obvious when used in combination, and a reasonable combination of accessories can significantly change the overall characteristics of the floating system and affect the safety and cost of the system.

Optimization design of multiple tuned mass dampers for semi-submersible floating wind turbine

Compared with spar-buoy and tension-leg platform floating offshore wind turbines (FOWTs), the flexibilities in operating water depth promote generalized applications of semi-submersible FOWT. In this study, a passive structural control strategy of a tuned mass damper (TMD) design method for a semi-submersible FOWT was implemented to mitigate FOWT responses under combined winds and waves. A reduced coupled model of a semi-submersible FOWT with TMDs mounted in the nacelle and platform was established based on D'Alembert's principle. Sequentially, the parameters of the reduced coupled model were estimated using the Leven-Marquardt (LM) algorithm, and the simulation accuracy was validated by comparison with the related fully coupled model in OpenFAST. To minimize the standard deviation of tower-top displacement, the design of the TMD was optimized by genetic algorithm (GA) based on the reduced coupled model, and three different TMD configurations were proposed. Furthermore, the effectiveness of the optimized TMDs was evaluated based on a fully coupled model in OpenFAST under typical sea states. The optimized nacelle and platform TMDs could effectively suppress the tower fundamental and platform pitch frequencies, respectively. Moreover, improved mitigation effects were observed using the optimized multiple TMDs, which comprise local dampers installed in the nacelle and platform.

Effect of the multi-segment mooring system by buoy and clump weights on the dynamic motions of the floating platform

In this paper, two hybrid mooring system is proposed to improve the performance of the dynamic motions of the floating platform. The concepts are a multi-segment arrangement of the catenary and taut mooring lines, including buoy and clump weight. Two mooring concepts named MSM-BSW and MSM-BMW were designed for a 5 MW OC4-DeepCwind semi-submersible floating wind turbine. These models' mooring forces and platform response were compared to the main model (OC4) under regular and irregular wave conditions. The dynamic response of the platform is performed utilizing both Morrison theory and three-dimensional radiation/diffraction theory based on the boundary element method (BEM) in ANSYS-AQWA software. Adding buoy, increase the horizontal mooring line angle at the fairlead, resultantly on one hand's mooring stiffness in surge and pitch increased so the MSM-BSW model could reduce surge and pitch motions. On the other hand, the buoy can reduce the mooring suspended weight, leading to an increase in the heave platform response. In the case of MSM-BMW, more clump weights increased the mooring line stiffness in the heave direction. In regular and irregular wave conditions, numerical results indicate that the change of natural periods in both MSM-BSW and MSM-BMW case studies leads to the low-frequency resonance having a significant difference from OC4. In contrast, the wave frequency resonance of the three concepts is similar.

Effects of atmospheric stability on the structural response of a 12 MW semisubmersible floating wind turbine

AbstractGlobal dynamic response models used for the design of wind turbines are largely based on neutral stability, which is not representative of real atmospheric conditions. Offshore wind farms, for example, have been seen to experience predominantly unstable conditions, especially at lower wind speeds. In the current work, we use four wind generation models under stable, neutral and unstable atmospheric stability conditions to study the low‐frequency content of the global responses of a semisubmersible floating wind turbine (FWT). To represent the wind fields, we use the Kaimal Spectrum and Exponential Coherence Model (Kaimal), the Mann Spectral Tensor Model (Mann), a point measurement based model (TIMESR) and large‐eddy simulation (LES). At the low‐frequency range, both atmospheric stability and the turbulence wind model significantly affect the response of the FWT. In all the cases studied throughout this paper, the structural response under unstable conditions is higher than under stable or neutral conditions. The TIMESR and the Kaimal models fitted to the FINO‐1 offshore meteorological mast measurements show more similar responses than the Mann model; surge and pitch are higher for the TIMESR and Kaimal models, and yaw is lower. When fitted to LES, TIMESR and Kaimal predict surge and pitch responses closer to LES, but they underestimate the responses related to yaw, opposite to what the Mann model does. The responses are directly related to turbulence intensity and coherence, which are affected by atmospheric stability. Therefore, based on the analyses carried out through this study, the structural analysis of FWT should account for the effect of atmospheric stability.

Load Reduction of Semi-Submersible Floating Wind Turbines by Integrating Heaving-Type Wave Energy Converters with Bang-Bang Control

Floating offshore wind turbines (FOWTs) are subject to intensive structural loads due to the extra degrees of freedom (DOF) of the floating platform, which may shorten the fatigue lifetime of critical wind turbine structures. Integrating wave energy converters (WECs) into FOWTs could potentially help improve both overall energy capture and platform dynamic responses and, thus, is expected to reduce the levelized cost of energy (LCOE). In this work, a novel hybrid wind-wave energy platform consisting of a semi-submersible FOWT and three heaving-type WECs is proposed, and the feasibility of reducing FOWT dynamic responses and fatigue loads by integrating heaving-type WECs with different PTO control schemes is investigated. More specifically, the aero-hydro-servo-elastic-mooring coupled numerical model is established, and a preliminary study is performed to evaluate the dynamic responses and power production of the hybrid platform under various environmental conditions. Particularly, the two kinds of PTO control strategies have been comparatively studied, which have shown that the active bang-bang control could effectively suppress the platform heave and pitch motion by up to 34.6 % and 17.1%, respectively. Moreover, the tower-base fatigue damage equivalent load (DEL) has been reduced by up to 11.21%, and the system power production could be increased by almost 6%. Therefore, it is shown that integrating heaving-type wave energy converters with bang-bang control is able to effectively reduce the dynamic responses and fatigue loads of semi-submersible FOWT while absorbing additional wave energy at the same time.

Impact of pitch actuator fault on 10-MW semi-submersible floating wind turbine

The pitch actuator of the offshore wind turbine has a high failure rate, and this fault will lead to aerodynamic imbalance on the floating system, especially when the 10 MW wind turbine is applied. In this paper, the impact of actuator faults on the floating platform motion and turbine structure is investigated. The 10-MW OO-Star semi-submersible platform is used as the reference structure. The fault discussed in this study involved one blade seizing, followed by an emergency shutdown. Coupled non-linear aero-hydro-servo-elastic simulations were carried out in the time domain using OpenFAST. The platform motions and structural loads caused by the fault were compared with the normal operating conditions. The effects of the pitch rate at the initial fault on the loads of the critical components are presented. The results revealed that imbalanced loads due to blade seizing can lead to particularly large excitations of the dynamic responses of the wind turbine. The maximum lateral nacelle acceleration is increased by 27.9%. In addition, the parametric study on the effects of the pitch rate for feathering blade was carried out. It was found that the pitch rate of 8 deg/s is favorable to alleviate the structural loads.

Wind–Wave Coupling Effect on the Dynamic Response of a Combined Wind–Wave Energy Converter

There is a huge energy demand from offshore renewable energy resources. To maximize the use of various renewable energy sources, a combined floating energy system consisting of different types of energy devices is an ideal option to reduce the levelized cost of energy (LCOE) by sharing the infrastructure of the platform and enhancing the power production capacity. This study proposed a combined concept of energy systems by combing a heave-type wave energy converter (WEC) with a semisubmersible floating wind turbine. In order to investigate the power performance and dynamic response of the combined concept, coupled aero-hydro-servo-elastic analysis was carried out using the open-source code F2A, which is based on the coupling of the FAST and AQWA tools by integrating all the possible environmental loadings (e.g., aerodynamic, hydrodynamic). Numerical results obtained by AQWA are used to verify the accuracy of the coupled model in F2A in predicting dynamic responses of the combined system. The main hydrodynamic characteristics of the combined system under typical operational conditions were examined, and the calculated responses (motions, mooring line tension and produced wave power) are discussed. Additionally, the effect of aerodynamic damping on the dynamic response of the combined system was examined and presented. Moreover, a second fully coupled analysis model was developed, and its response predictions were compared with the predictions of the model developed with F2A in order for the differences of the calculated responses resulted by the different modeling techniques to be discussed and explained. Finally, the survivability of the combined concept has been examined for different possible proposed survival modes.