Floating Wind Turbine Platform Research Articles

Exploring Motion Stability of a Novel Semi-Submersible Platform for Offshore Wind Turbines

The stability of offshore floating wind turbine foundation platforms is a fundamental requirement for the efficiency and safety of wind power generation systems. This paper proposes a novel small-diameter float-type semi-submersible platform to improve system stability. To evaluate the superior motion stability of the proposed floating platform, a comprehensive frequency–domain response analysis and experimental study were conducted in comparison with the OC4-DeepCwind platform developed by the National Renewable Energy Laboratory (NREL). The respective comparison of the frequency–domain response analysis and the experimental results demonstrated that the proposed floating wind turbine platform shows better hydrodynamic characteristics and resonance avoidance capability. This not only reduces the Response Amplitude Operators (RAOs), but also enhances the system stability, namely, effectively avoiding the regions of concentrated wave loading and low-frequency ranges. Furthermore, the proposed small-diameter semi-submersible platform has the potential to reduce manufacturing costs, providing valuable insights for the manufacturing of offshore floating wind turbine systems.

Hydrodynamic response analysis of a hybrid TLP and heaving-buoy wave energy converter with PTO damping

In the present study, the numerical investigation is performed to analyse the hydrodynamic performance of circular and concentric arrangements of cone-cylinder-type heaving point absorber wave energy converter (WEC) around a Frustum Tension-Leg Platform (FTLP) based on potential flow theory. The responses of the single FTLP and the FTLP-WEC hybrid system are analysed for the rated wind speed of a 5 MW wind turbine to observe the influence of the WECs on wind power absorption of wind turbines supported on FTLP. The presence of the FTLP floating wind turbine platform and other WECs affects the hydrodynamic coefficients of the WEC. The influence of the hybrid system on the hydrodynamic coefficients is analysed on determining the ratio of the hydrodynamic coefficients for a single WEC system to those for a hybrid system. Further, the study analyses the instantaneous wave power absorption for the WECs arranged around the FTLP in a circular and concentric pattern. The hydraulic power take-off for the hybrid system with two different control strategies is then discussed to improve the wave power absorption of the WECs. The study observed higher wave power absorption of the WECs with the influence of the PTO system. The mean interaction factor and the capture width ratio of the hybrid system are further studied to understand the influence of array arrangement for the WECs. The hybrid system is noted to have favourable dynamic responses for different environmental factors and contributes positively in increasing power output.

A Novel Semi-Spar Floating Wind Turbine Platform Applied for Intermediate Water Depth

For the exploitation of offshore wind resources in areas with intermediate water depths, a novel semi-spar floating foundation is introduced to combine the superiority of the conventional semisubmersible and spar-type floater. It consists of an upper floater and a hanging weight, which are connected through 12 suspension ropes. Such a floating foundation can be wet-towed as a semisubmersible floater, which features a large waterplane moment of inertia to increase stability and reduce transportation costs. After being anchored on site, it behaves as a spar floater with moderate draft and superior hydrodynamic characteristics. The stability of the proposed semi-spar platform during wet towage is analyzed. Afterward, a fully coupled aero-hydro-servo-elastic simulation is conducted to evaluate its hydrodynamic responses in comparison with the responses of the well-acknowledged OC3-spar and OC4-semisubmersible platforms. Then, the ultimate strength of the mooring lines and suspension ropes under extreme conditions was numerically investigated, as well as the relationship between the ropes’ tension and wave direction. Eventually, a cost-effectiveness analysis is conducted in terms of power generation and steel mass. The results demonstrate that the proposed semi-spar design meets the safety criteria in transportation and exhibits a smaller response in surge and pitch motions. In addition, the ultimate strength of mooring lines and suspension ropes satisfies the safety requirements, and simulation reveals that the lateral suspension ropes parallel to the propagation direction are sensitive to the environmental conditions of winds and waves. This study confirms that the newly proposed floating wind turbine exhibits excellent hydrodynamic and power generation performance, which is of great significance for the sustainability of the energy and electricity industry.

Hydrostatic stability and hydrodynamics of a floating wind turbine platform integrated with oscillating water columns: A design study

One of the challenges in the installation of Floating Wind Turbines (FWTs) is the occurrence of undesired resonant motions under environmental conditions, which adversely impact their lifespan, maintenance cost, components stress, and electrical performance. This article addresses this challenge by proposing a novel design for the substructure of semisubmersible FWTs, aimed at mitigating the undesired oscillations and improving sustainability. The design concept involves integrating Oscillation Water Columns (OWCs) within the FWT’s substructure, focusing on a specific type of semisubmersible FWT called WINDMOOR. The chambers have been incorporated into the columns, allowing water to enter and compress/decompress the air inside them. The main objective of this article is to demonstrate the feasibility of integrating OWCs into a semi-submersible platform-type FWT. To accomplish this, the adjustment of ballast inside the substructure is performed, followed by evaluations of the system’s intact hydrostatic stability and hydrodynamic performance. Sensitivity analysis has also been conducted to assess the impact of the chamber size on system performance. The results indicate that a chamber size of 4.5 m satisfies the criteria for intact hydrostatic stability without requiring changes to the substructure dimensions. However, increasing the chamber size negatively affects system stability. Furthermore, the hydrodynamic analysis employing Response Amplitude Operators (RAOs) illustrates the effectiveness of integrating OWCs to enhance the stability of this novel hybrid system. This integration results in increased damping effects, which contribute to the reduction of resonant motions in the system’s modes, particularly heave, roll, and pitch. Throughout the article, comprehensive comparisons have been conducted between the WINDMOOR FWT and the proposed hybrid semisubmersible FWT-OWCs system. These comparisons have been performed at every step, including the redesign of the substructure, adjustment of ballast, hydrostatic stability analysis, and hydrodynamic analysis.

Effect of the multi-segment mooring system failure on the dynamic motions of the floating platform

The mooring system can effectively reduce the dynamic response of floating wind turbine platforms (FOWT), especially in extreme environmental conditions. Investigating mooring line failure is crucial for ensuring safety in FOWT operations. MSM-BMW is the multi-segment mooring (MSM) arrangement of the catenary and taut lines, consisting of the buoy multi-clump weight (BMW) that is proposed as a new concept to reduce platform hydrodynamic response. The aim of this study is to assess the performance of FOWTs in both intact and mooring system failure scenarios for two mooring systems: OC4-DeepCwind, representing the primary configuration, and MSM-BMW, representing a hybrid mooring system. The boundary element method (BEM) has been used in the time domain under irregular wave conditions in different wave directions. To simulate mooring line failure, a specific mooring line was intentionally detached from the floating platform at a predetermined time. The hydrodynamic platform responses, mooring line tensions and their statistical responses were checked. Based on the result the BMW concept presents a better performance in both intact and failure modes in comparison primary mooring system (OC4) that significantly reduces platform offset.

Design, local structural stress, and global dynamic response analysis of a steel semi-submersible hull for a 10-MW floating wind turbine

Platforms for floating wind turbines cannot be designed using conventional procedures like other offshore constructions. The design of floating wind turbine platforms must consider the significant nonlinearity of the fully coupled aero-hydro-servo-elastic dynamics, which necessitates a time-domain load transfer for structural stress analysis. This article presents and verifies an effective yet practical design method for floating wind turbine platforms, which can provide reasonable internal stress for design checks. A robust design process is proposed. Following the proposed method and procedure of a 10-MW wind turbine, a steel semi-submersible platform is developed with the criterion for the steel platform’s design checks, intact stability analysis, natural period analysis, and buckling analysis executed. A tangible concept is established, along with fully coupled numerical models of the 10-MW wind turbines supported on the steel structure. The dynamic behavior of the steel platform is evaluated by accessing and comparing the dynamic performances of the concrete- and steel-support wind turbine numerical models. The key findings and conclusions from the steel platform’s design and numerical study are summarized below. In addition, future design and analysis ideas are proposed, expanding the engineering practice and research on floating wind turbine platforms.

Performance of a hybrid TLP floating wind turbine combined with arrays of heaving point absorbers

In the present study, the hydrodynamic performance of circular and concentric arrangements of cone-cylinder-type heaving point absorbers around a Submerged Tension-Leg Platform (STLP) is analysed using the numerical model in the frequency domain based on the potential flow theory. The presence of the Wave Energy Converters (WECs) around the STLP floating wind turbine platform affects the hydrodynamic performance of the hybrid floating platform. So to illustrate the effects of WECs on the platform, the ratio of hydrodynamic coefficients for a single WEC system to that for a hybrid system is analysed. An array of heaving point absorbers is placed in circular and concentric patterns to understand the performance of heaving point absorbers in the absorption of wave energy. The cone-cylinder type heaving point absorber is selected for the present study as they yield more power as compared to other shaped point absorbers. The study compares the wave power absorption of each point absorber around the platform for irregular wave conditions of the North Sea. The effect of incoming waves is illustrated by analysing four different wave heading angles. To quantify the performance of the WECs in an array, the q-factor and coefficient of variation are studied for each array at different sea states. The study suggested the best possible arrangement pattern for wave power absorption and power uniformity among the floaters in the array. The study performed will be helpful in the design and analysis of the possible arrangement of point absorbers around the floating wind turbine platform for wave power absorption.

Hydrodynamic Investigation on Floating Offshore Wind Turbine Platform Integrated with Porous Shell

As the siting of wind turbines increasingly transitions from shallow water to offshore deep-water locations, improving the platform stability of floating offshore wind turbines is becoming a growing concern. By coupling a porous shell commonly used in traditional marine structures, with a FOWT (floating wind turbine platform), a new spar-buoy with a porous shell was designed. A numerical model investigating the coupling effect of the aero-hydro-mooring system is developed, and the results of the motion response are compared with the OC3-Hywind spar. The motion response of the two platforms was simulated in the time-domain with the incident wave period varied in the range of 5~22 s. The exciting wave force with added mass and radiation damping of the spar with the porous shell is compared with the OC3-Hywind spar. The results demonstrate that the motion response amplitude of the spar with the porous shell decreases in all three main motion freedoms (i.e., surge, heave and pitch, etc.), among which the heave motions are most significantly attenuated. The study shows that the coupling of porous shells with a floating platform to achieve the reduced motion responses is feasible and can be an innovative structure for the development of deep-sea offshore floating wind turbines.

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 and Experimental Study on an Anti-Oscillation Device for the DeepCwind Floating Semi-Submersible Turbine Platform

The DeepCwind floating wind turbine platform has become one of the most successful structures for accommercial floating wind farms, and the stability of it is crucial for survivability. Hence, this paper studies an anti-oscillation device with the purpose of reducing the heave and surge effects of the platform. The influence of various chamfered perforations at different sizes of the anti-heave device on the floating platform was further studied by numerical and experimental methods. Furthermore, through an analysis of the surge and heave of the pedestal with anti-heave devices with different chamfered perforations under different wave heights and wave periods, the effects on the hydrodynamic performance of the pedestal were studied. Physical experiments were conducted on a pedestal with anti-heave devices with chamfered perforations under the working conditions of different wave heights and wave periods to verify the reliability of the numerical simulation. The results show that the anti-heave effect of the anti-oscillation device is obvious under the small wave period and large wave height. Under the working conditions of different wave heights and wave periods, different perforated chamfers have different effects on reducing the oscillation of the pedestal, and its effect does not change linearly with an increasing chamfer. Under most working conditions, the anti-heave effect of the 35° chamfered perforated model was found to be the most obvious.

Design of Variable Pitch Control Method for Floating Wind Turbine

Because of the randomness of wind speed and the nonlinearity of the dynamic equation of variable pitch control, it is difficult to establish an accurate dynamic equation of variable pitch of floating fan. In view of this situation, this paper takes the 5 MW floating wind turbine of the NREL (National Renewable Energy Laboratory) as the research object, establishes the dynamic equation under the basic control of FAST, uses the L-M (nonlinear least square method) to identify the dynamic parameters of the system and obtains the dynamic model of the floating fan under variable pitch stability control. Compared with the output of FAST in the same case, the accuracy of the control model is verified; the FAST base pitch control adopts PI control, but the effect of FAST base control is relatively poor. This paper proposes a disturbance-adaptive pitch control method based on fractional PID feedback; the results show that compared with the FAST base pitch control, the control method is more suitable for variable pitch control of a floating wind turbine. The generating power is more stable, the overshoot of generating power is smaller and the fluctuation of wind speed is smaller. Except for surge and heave, the fluctuation of the other four degrees of the freedom of the floating wind turbine platform is reduced, making it more suitable for the variable pitch control of the floating wind turbine.

Dynamic response analysis of floating wind turbine platform in local fatigue of mooring

The moorings of the Floating Wind Turbine (FWT) platforms, long term suffering from the coupling loads of wind, waves and currents, are especially prone to structural fatigue. The purpose of this study is to mine effective information from the dynamic response of the FWT platform to achieve early damage detection for mooring health conditions. However, high nonlinearity of the FWT platform dynamic response, that is caused by the complexity of the working environment, hinders the accuracy of fatigue analysis and damage detection, Therefore, in this study, motivated by the accuracy of the chaotic features in quantifying nonlinearities and reliability of the convolutional neural network for feature extraction, an intelligent damage detection model, named Convolutional Neural Network-t-distribution Stochastic Neighbor Embedding (CNN-t-SNE), is proposed to automatically detect the damage magnitude of the moorings. Through analyzing the dynamics of FWT platform mooring from structure creep to failure, it is found that the yaw response is the most sensitive to structural damage. To examine the reliability of the proposed CNN-t-SNE method, the Lyapunov exponent and chaotic attractor quantify the nonlinearity of the features in the neural networks to indicate that the nonlinearity of the features decreases as the neural network layer deepens.

Study on the Shape of Appendage for the Reduction of Motion of Floating Wind Turbine Platforms

Study on the Shape of Appendage for the Reduction of Motion of Floating Wind Turbine Platforms

Mooring System Transport and Installation Logistics for a Floating Offshore Wind Farm in Lannion, France

This study addresses the planning procedures for the installation of the mooring systems that support the floating offshore wind turbines in a wind farm. It considers the logistics of the installation process and discusses the important role of the weather windows in the planning of those operations at a preliminary stage of the project. The case study is based on a wind farm array of 47 Telwind floating wind turbine platforms, to be located in Lannion (France), with a potential of 470 MW. The study includes the transport and logistics requirements of different mooring components, such as chains, connectors and drag anchors; the description of the installation operations considering the typology of vessels that are necessary in these manoeuvres; as well as the planning and costs associated with the transport and installation. Given the diversity of elements and operations involved in the installation procedure, it is demonstrated that the research results of duration and costs of this type of operations are only possible to obtain using a simulation tool.

Coupled dynamic response analysis of multi-column floating offshore wind turbine with low center of gravity

To realize the application of the floating offshore wind turbine (FOWT) from deep to relatively shallow waters, a new concept of multi-column floating wind turbine platform with low center of gravity (CG) is designed and validated. The multi-column low CG platform is designed to support a 6MW wind turbine class and operated at a water depth of 50m in the South China Sea. The frequency domain software WADAM and time domain software NREL-FAST are used to simulate coupled dynamic responses of the floating wind turbine system with second-order wave loads considering. The dynamic behaviors of multi-column low CG FOWT system under normal operation and parked conditions are presented. The influence of second-order wave force on the motion responses of the multi-column platform, fore-aft force and moment of the tower base and mooring force are researched respectively. The results demonstrate that the coupled dynamic responses at rated operating condition and extreme condition meet the normal operating requirements and extreme survival requirements of FOWT system in the shallow water (50m) of South China Sea. In addition, it is found that, the wave frequency response gradually replaces the second-order low frequency response as the main influencing factor of the coupled dynamic response of the FOWT system with the increasing severity of the sea states. However, in general, the magnitude of second-order low frequency response increases with the increasing severity of the design load case. Thus, in the subsequent design of the shallow water FOWT system, the second-order effects should be paid enough attention.

Açık Kaynaklı Panel Yöntemi Kodlarının Ticari Kod ile Karşılaştırılması ve Değerlendirilmesi

This work provides a benchmark study regarding the open-source panel method codes of two floating wind turbine platforms. HAMS, NEMOH, and WAMIT are compared in terms of their results, computational performance, user-friendliness, and, flexibility. WAMIT’s data is sourced from previous publications for the OC3 Hywind Spar and OC4 DeepCWind Semisubmersible. These reference values are compared to NEMOH and HAMS for the main parameters representing the movement of the structure: wave excitation forces, added mass values, and potential damping. Both of the open source panel method codes were quite successful in the concept of a simple one-piece spar float rather than a multibody semi-submersible in terms of NRMS values. Overall, the most close results were obtained from the surge for added mass, and the most unfavorable results were from radiation damping in the heave. NEMOH brings ineligible results for pitch on both platforms. Neglecting the pitch axis results of NEMOH, both codes showed parallel and reasonably close results to WAMIT. The study aims to help researchers to choose a free open-source alternative to a validated commercial code.

Numerical simulation and experimental study on perforated heave plate of a DeepCwind floating wind turbine platform

ABSTRACT In this study, the heave plate of a DeepCwind floating wind turbine platform with a capacity of 5 MW was used as the research object. The influence of the perforated chamfer on the hydrodynamic performance of the heave plate was studied through physical experiments and numerical simulations. Vertical force amplitudes, additional mass coefficients, and damping coefficients were obtained for heave plates with different types of perforations. The results of the numerical simulations and physical experiments revealed that hydrodynamic coefficients changed consistently. During the same period, the damping and additional mass coefficients of the heave plate gradually decreased and increased with an increase in the motion amplitude, respectively. When comparing with different perforation angles, the coefficients initially decrease and then increase with an increase in the perforation angle. In the case of a large perforation angle, the coefficients were higher than those of the conventional heave plate without perforations.

Hydrodynamic coefficients from forced and decay heave motion tests of a scaled model of a column of a floating wind turbine equipped with a heave plate

This paper describes the results of an experimental campaign aimed at the determination of heave hydrodynamic coefficients for a column of a floating wind turbine platform, equipped with a solid heave plate. The tests are carried out with an experimental system that allows performing both heave forced oscillation tests and heave decay tests. A specific characteristic of the system is the reduced mechanical friction, thanks to the use of air bushings. A series of forced oscillation and decay experiments have been carried out with such a model, and the hydrodynamic coefficients obtained in both types of tests are compared. Results show correlation between both methods if the mean of the peaks of the decay process is chosen to represent its Keulegan–Carpenter number (KC), with a fair matching of the results in the KC range where both methods are applicable. With the objective of conducting an uncertainty assessment which can be relevant for the full-scale extrapolation of results, non-dimensional added mass and damping coefficients are proposed. They incorporate the primitive relevant variables and are shown to lead to a notable collapse of the various results in the form of curves with small differences among them. With these coefficients, an uncertainty assessment is carried out, propagating to those coefficients the uncertainties of the primitive variables in place. Such non-dimensional coefficients are useful to develop simple models to estimate the dimensional ones to be used in numerical simulations of the full scale system. The estimated uncertainties can serve to define design safety margins for the values of such coefficients.

Review on Dynamics of Offshore Floating Wind Turbine Platforms

This paper presents a literature review of the dynamics of offshore floating wind turbine platforms. When moving further offshore, there is an increase in the capacity of wind power. Generating power from renewable resources is enhanced through the extraction of wind energy from an offshore deep-water wind resource. Mounting the turbine on a platform that is not stable brings another difficulty to wind turbine modeling. There is a need to introduce platforms that are more effective to capture this energy, because of the complex dynamics and control of these platforms. This paper highlights the historical developments and progresses in the design of different types of offshore floating wind turbine platforms needed for harvesting the energy from offshore winds. The relative advantages and disadvantages of the platform types with the design challenges are discussed. The major types of floating platforms included in this study are tension leg platform (TLP) type, spar type, and semisubmersible type. This study reviews the previous work on the dynamics of the floating platforms for a single turbine and multiple turbines under various operating environmental conditions. The numerical methods to analyze the aerodynamics of the wind turbine and hydrodynamics of floating platforms are discussed in this paper. This paper also investigates the performance of analytical wake loss models of Jensen, Larsen, and Frandsen that can provide guidelines for using these wake models in future applications. There are still a lot of challenges that need to be addressed to study the accurate behavior of floating platforms operating under combined wind–wave environmental conditions. With the current technological advancements, the offshore floating multi-turbine platform can be a potential solution to harness the abundant offshore wind resource. Based on this literature review, recommendations for future work are suggested.

A low-fidelity dynamic wind farm model for simulating time-varying wind conditions and floating platform motion

This paper introduces a dynamic parametric wind farm model that is capable of simulating floating wind turbine platform motion coupled with wake transport under time-varying wind conditions. The simulator is named FOWFSim-Dyn as it is a dynamic extension of the previously developed steady-state Floating Offshore Wind Farm Simulator (FOWFSim). One-dimensional momentum conservation is used to model dynamic propagation of wake centerline locations and average velocities, while momentum recovery is approximated with the assumption of a constant temporal wake expansion rate. Platform dynamics are captured by treating a floating offshore wind farm as a distribution of particles that are subject to aerodynamic, hydrodynamic, and mooring line forces. The finite difference method is used to discretize the momentum conservation equations to yield a nonlinear state-space model. FOWFSim-Dyn is validated against steady-state experimental wind tunnel data obtained from the literature along with simulation results acquired from FAST. The model is shown to possess a satisfactory level of fidelity for engineering applications. Finally, dynamic simulations are conducted to ensure that time-varying predictions match physical expectations and intuition.