Semi-submersible Floating Wind Turbine Research Articles

AK-MDAmax: Maximum fatigue damage assessment of wind turbine towers considering multi-location with an active learning approach

Lifetime fatigue damage prediction plays a key factor in wind turbine structure’s reliability assessment. However, the damage estimation of wind turbines requires thousands of simulations and significant computational costs. To address this problem, this paper proposes an efficient active learning Kriging named AK-MDAmax for estimating the maximum fatigue damage of wind turbine towers with less computational cost. The proposed AK-MDAmax approach is based on the previous AK-DA approach. Kriging models are used to estimate the fatigue damage of wind turbine towers at different wind-wave conditions. An efficient active learning approach is developed to assess multi-location maximum cumulative fatigue damage. One 15MW Semi-submersible floating wind turbine model from the IEA project is used to demonstrate the efficiency of the proposed approach. Results indicate the proposed approach can efficiently and accurately estimate wind turbine towers’ maximum cumulative fatigue damage. The AK-MDAmax approach requires less than 3% of the computational effort compared with the typical simulation approach, and the related absolute error is less than 1%. The AK-MDAmax approach could be useful for designers to optimize wind turbine structures and reduce design time and costs.

Coupled dynamic and power generation characteristics of a hybrid system consisting of a semi-submersible wind turbine and an array of heaving wave energy converters

A wind-wave hybrid system consisting of a semi-submersible floating wind turbine and an array of heaving wave energy converters (HWECs) provides a solution for co-located marine renewable energy extraction. The knowledge of the coupled dynamic and power features of the hybrid system is important to the design and operation but is poorly understood. This study proposes a comprehensive numerical model that can tackle the full couplings by bridging the aerodynamic module of OpenFAST and the hydrodynamic simulator WAFDUT through an in-house code based on multi-body dynamics. The coupled dynamic and power generation characteristics of the hybrid system are investigated, with an emphasis on the influence of the HWECs on the wind-induced motion, mooring tension, and wind power generation of the turbine. Results show that the HWECs do not produce negative effects on the wind-induced surge, heave, and pitch motions. The HWECs can slightly reduce the mooring tension and slightly improve wind power generation. The array of HWECs can generate over 500 kW wave power in the waves with periods of 6 s–10 s, which can be a qualified supplement to wind power. The findings offer useful knowledge about the key properties of the hybrid system for practical use.

Conceptual design, parameter optimization and performance investigation of a 10MW semi-submersible floating wind turbine in shallow water

There is lacking of floating wind turbine supporting large wind turbine, i.e. 10 MW, aiming at shallow water applications. In this paper, a 10 MW semi-submersible floating wind turbine named OUCwind is proposed for shallow water, and a scale optimization procedure is proposed during the preliminary design stage. It offers an engineering-practical method to determine the main parameters of a new-proposed floater, and critical floater characteristics, such as floater stability, natural period, platform mass etc. are chosen as important design criteria. The hydrodynamic performance with different scale parameters are investigated and it is found that enlarging distance between columns is a cost-effective way to get better stability and hydrodynamic performance. The structural performance of the new-designed OUCwind floater are compared with other two well-known braceless 10 MW platforms, 10 MW-CSC, and OO-star. From the frequency-domain analysis results, the surge linear transfer function, mean drift force and quadratic transfer function near the surge natural frequency of OUCwind is relatively small compared with other two platforms. In the time domain, the new-designed OUCwind also performs better in surge motion and mooring line tension response compared with 10 MW-CSC and OO-star, especially under extreme condition. Nevertheless, for the heave and pitch motions, the wave-frequency response of the OUCwind platform is relatively large under extreme load conditions.

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.