Wind Turbine Platform Research Articles

Optimization Simulation of Mooring System of Floating Offshore Wind Turbine Platform Based on SPH Method

ABSTRACTIn this paper, the Smoothed Particle Hydrodynamics method is used to simulate the dynamic response of the floating offshore wind turbine mooring system in a complex marine environment by using its advantages of dealing with free surface flow and fluid–structure interaction. The single‐cable mooring system and the double‐cable mooring system are introduced into the numerical simulation model of fluid–solid coupling interaction. The first‐order irregular wave and the second‐order regular wave are used to simulate different wave conditions. The operating state of the platform in these two cases is analyzed, and the accurate data such as the velocity change of the geometric center of the platform and the change of six degrees of freedom are obtained. Using visual processing and data analysis, it is found that the optimized double‐cable mooring system structure improves the vibration reduction ability of the platform.

Multi-objective optimal control of a hybrid offshore wind turbine platform integrated with multi-float wave energy converters

Offshore floating wind turbines will play a pivotal role in achieving net-zero emissions. This study explores a hybrid platform combining an offshore floating wind turbine with wave energy converters (WECs) from an active control perspective to mitigate turbine damage risk while maximizing wave energy conversion. Initially, the control-oriented state-space modelling of the hybrid platform and the validation of the time-domain Cummins-type models of different orders are performed by the Eulerian-Lagrangian method with model linearization and downscaling. Then, a multi-objective non-causal optimal controller is introduced, balancing wave energy capture and penalizing the nacelle acceleration. When wave energy capture maximization is set as the control target, the proposed optimal controller can improve energy output by 184% as compared against a well-tuned passive damper across all peak periods tested. However this causes peak hub acceleration to increase marginally beyond the desirable limits of 3–4 m/s2 for wind turbine operation. When hub acceleration is penalized, the multi-objective optimal controller can reduce peak values below limits by between 40% and 61% with trivial loss of wave energy capture.

Investigation of motion response suppression characteristics in floating platforms equipped with novel spiral side plates

AbstractTo enhance the stability of floating wind turbine platforms, this study combines the structural characteristics of helical side plates and proposes the installation of serrated helical side plates on Spar wind turbine platforms. Based on potential flow theory, the present study employs blade element momentum theory and radiation‐diffraction theory. Upon establishing a dynamic data link library, wind‐wave coupling was implemented, and the dynamic response characteristics of platforms with different helical side plates were compared. The results indicate that in the frequency domain analysis, the platform with serrated helical side plates demonstrates reduced sensitivity to waves, with a particularly notable increase in added mass in the heave direction, suggesting excellent hydrodynamic performance. In the time domain analysis, improvements in the platform's surge and heave stability performances were observed, measuring 10.99% and 10.64%, respectively, in extreme conditions. Owing to the unique features of the serrated structure, the tension in the mooring chains on the wave‐facing side is reduced, thereby effectively lowering the fatigue load on the mooring chains.

Causality-Free Modeling and Validation of a Semisubmersible Floating Offshore Wind Turbine Platform With Tuned Mass Dampers

Causality-Free Modeling and Validation of a Semisubmersible Floating Offshore Wind Turbine Platform With Tuned Mass Dampers

Verification and validation of a coupled CFD–FEM approach with overset structured grid through free decay and regular wave tests

This paper presents a comprehensive verification and validation study applied to the hydrodynamic analysis of a semi-submersible Floating Offshore Wind Turbine (FOWT) platform. The numerical simulation is conducted using a coupled Computational Fluid Dynamics-Finite Element Method (CFD–FEM) approach. The CFD program incorporates an overset grid interpolation method, facilitating a more systematic grid refinement in the estimation of discretization uncertainties. A mooring analysis program, based on the FEM scheme, is integrated with the CFD program to simulate the dynamic responses of mooring system. The necessity of the nonlinear mooring model is demonstrated by comparing solutions with a comparative test using a linear mooring model. The verification study, based on a least-squares-based extrapolation method, quantifies the spatial and temporal discretization errors of the numerical model. The numerical solutions based on the baseline model are further validated against the model test measurements. A pitch free decay model test and a regular wave model test conducted within the OC5 project are utilized for the verification and validation study. Results from both tests demonstrate the reliability and accuracy of the coupled method.

Design and stability analysis of a new six-floater oscillating water column-based floating offshore wind turbine platform

The operational efficiency and lifespan of Floating Offshore Wind Turbines (FOWTs) are adversely impacted by the inherent platform motions and undesired vibrations induced by wind and wave loads. To effectively address these effects, the control of specific structural motions is of utmost importance, with platform pitch and yaw identified as the primary Degrees Of Freedom (DOF) that require attention. This study proposes a novel utilization of Oscillating Water Columns (OWCs) as a reliable and viable solution to mitigate platform pitch and yaw motions, thereby significantly enhancing the efficiency and reducing fatigue in wind turbines. This article aims to evaluate the impact resulting from integrating OWCs within each discrete floater of a Six-Floater platform. By considering different combinations of OWCs, a comprehensive analysis of the Response Amplitude Operators (RAOs) associated with pitch and yaw motions is presented. The primary objective is to identify the most efficient arrangements of OWCs and determine suitable combinations that effectively stabilize platform pitch and yaw motions. The empirical results substantiate that specific OWC configurations exhibit notable dampening effects on both pitch and yaw motions, particularly within specific wave frequency intervals. Consequently, it can be inferred that the integration and adequate operation of OWCs facilitate a substantial improvement in the stabilization of multi-floater platforms.

Fault-Tolerant Control of Floating Wind Turbine With Switched Adaptive Sliding Mode Controller

The fast-growing development of floating wind turbines demands control systems capable of both reducing output power fluctuations and fault-tolerant function. In this paper, we propose an adaptive switched sliding mode controller to enhance the performance of floating wind turbine systems in the presence of environmental uncertainties and actuator faults. A control-oriented switched linear model for floating wind turbines is introduced, considering the average dwell time. Based on the proposed controller, a full-order state observer and an adaptive law compensate for the debilitated control outputs resulting from detecting errors, disturbances, and faults. The control parameters are derived by solving stability theorems, which are proved by the Lyapunov stability theory, linear matrix inequality technique, and average dwell time technique. The proposed model and controller are validated on the NREL 5MW wind turbine and spar-buoy platform using the high-fidelity fatigue, aerodynamics, structures, and turbulence (FAST) code. The performance of the proposed controller is compared with an optimal gain-scheduling proportional-integral controller under different wind-wave combined conditions. The results show that the proposed controller improves the power quality and attenuates mechanical loads of floating wind turbine under healthy and faulty conditions. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Note to Practitioners</i> —Floating wind turbines have drawn significant interest in renewable energy. When operating in the ocean far from shore, it is of great importance for floating wind turbines to have fault-tolerance capabilities for achieving stable power quality when faults occur in one or more components. A challenging problem is how to mitigate the fault effects on the wind turbine system. This paper proposes an adaptive fault-tolerant control strategy in the case of actuator fault occurrence in floating wind turbines.

Real-time hybrid test method for floating wind turbines: Focusing on the aerodynamic load identification

Since the development of floating wind turbine (FWT) shows a rapid trend towards larger capacity and larger rotor size, the traditional full-model basin test method has encountered limits. Especially the balance between the wind generation system (WGS) size and scale ratio of the model FWT system. Under such circumstances, the hybrid model test method provides the possibility to improve the FWT model test. In the hybrid model test method, the original physical model system is divided into physical subsystem and numerical subsystem, and the data acquisition and process module between the 2 subsystems plays an important role. In this paper, a framework of real-time hybrid test (RTHT) system is setup firstly, which combines physical model wind turbine and motion platform. The damping modification to the corresponding numerical code is applied to improve the motion calculation accuracy. Delay implementation is employed to avoid motion divergence. Then a simulation loop is setup in numerical environment to study the identification of aerodynamic load. The influence of identification accuracy to the RTHT result is analyzed. Lastly, the dual-accelerometer method of aerodynamic load identification is employed in the proposed RTHT system. Decay tests and irregular wave only tests are carried out to validate the aerodynamic load identification method. The capability and potential of the RTHT method of floating wind turbine model test is preliminary proved in the work of this paper.

Performance-based target reliability analysis of offshore wind turbine mooring lines subjected to the wind and wave

Reliability assessment is a crucial aspect of the design and operation of structures, particularly in balancing safety and cost considerations. This paper introduces a novel method for evaluating the performance-based target reliability of floating wind turbine platforms in offshore environments. The method focuses on the platform's motion modes and wave frequencies, which significantly influence the system's structural integrity and performance. An improved limit state function is proposed to enhance the accuracy of reliability calculations, specifically for steady-state conditions. The platform's six degrees of freedom motions are carefully analyzed to investigate their dependence on wave frequencies. By considering the time response of these motions and accounting for uncertainties in wave characteristics, wave impact directions, and wind effects, a comprehensive reliability analysis is conducted to assess the stability modes of the platform. This paper introduces the term 'Reliability Performance-Based' (RPB) analysis as a new concept to evaluate the system's reliability at a given performance level. Furthermore, an optimal target reliability index is defined to address the economic aspect of the design process. The proposed methodology's PEB analysis focuses on capturing uncertainties in wave characteristics and wind effects on floating wind turbine platforms. This includes a detailed examination of wave and wind-induced loads and their propagation through the system concerning its performance level. Statistical models were integrated to quantify these uncertainties, applying Monte Carlo simulations to assess their effects on the platform's reliability. This approach allows for a nuanced understanding of the interactions between environmental factors and structural responses, enhancing the precision of our reliability assessments. It enables the consideration of economic efficiency alongside safety, ensuring a balanced approach to the design and operation of the floating wind turbine platform. By providing a comprehensive reliability assessment framework, it aids in the optimization of design and decision-making processes for floating wind turbine platforms.

Reference dynamic power cable of floating offshore wind turbine for thermal and simple fatigue evaluation

With the increased interest in floating offshore wind turbines, there is an increased focus on evaluating the lifetime of the auxiliary systems, such as the mooring lines and the dynamic power cables, because these systems are in-mature compared to bottom-mounted offshore wind farms. This paper proposes a conceptual reference dynamic power cable suitable for the 15 MW NREL reference turbine mounted on the UMaine floater installed at 82 m water depth. This provides a basis for discussing the life evaluation of dynamic cables obtained from aeroelastic simulation of the floating offshore wind turbine platform exposed to the environmental conditions of the South Brittany site in France. An electromagnetic-thermal finite element simulation is used to determine the current capacity of the cable and aeroelastic simulations are used for a simple assessment of the main failure modes as maximum cable tension, minimum bending radius and fatigue damage accumulation.

Control Co-Design Studies for a 22 MW Semisubmersible Floating Wind Turbine Platform

We present a control co-design software framework that can be used to optimize floating wind turbines and their controllers. Because this framework has many options for design variables, constraints, and merit figures, along with modeling fidelity levels, we seek to demonstrate best practices for using the tool while designing a floating platform for the new 22 MW offshore reference wind turbine developed within the International Energy Agency Wind Technology Commercialization Programme 55 on Reference Wind Turbines and Farms. During these studies, we evaluate the use of different simulation fidelity levels, the effect of using different load cases for controller tuning, and the difference between sequential and simultaneous control co-design solutions. Based on these efforts, we suggest using an algorithm that performs an initial search of the design space before optimization. We find that solving smaller optimization problems, in a sequential manner, leads to more reliable outcomes in fewer iterations than larger, simultaneous control co-design solutions. However a simultaneous CCD solution produces a platform with a 2% lower mass than the sequential CCD outcome.

Probabilistic Prediction of Floating Offshore Wind Turbine Platform Motions via Uncertainty Quantification and Information Integration

The accurate prediction of short-term platform motions in a real environment is crucial for the safe design, operation, and maintenance of floating offshore wind turbines (FOWTs). Numerical simulations of motions are typically associated with high uncertainties due to abstracted theoretical models, empirical parameters, initial environment parameters, etc. Therefore, it is necessary to integrate other sources of information associated with less uncertainty, e.g., monitoring data, for accurate predictions. In this paper, we propose a probabilistic prediction based on the Bayesian approach that logically integrates motion monitoring data with simulated motion predictions of FOWTs, considering uncertainties in the environment model, structural properties, motion prediction method, monitoring data, etc. The approach consists of constructing a prior probability density function (PDF) of a random variable (which characterizes the largest value of the initial motion response) via numerical simulations and a likelihood function based on platform motion monitoring data and deriving a posterior PDF of the random variable by Bayesian updating. Then, posterior distributions of short-term extreme motion responses are derived using the posterior PDF of the random variable, representing lower uncertainty and improved accuracy. A Metropolis–Hastings algorithm is adopted to obtain PDFs of complex probability distributions. The effectiveness of the approach is demonstrated on a real FOWT platform in Scotland. The proposed probabilistic prediction approach results in posterior distributions of short-term extreme platform motions associated with less uncertainty and higher accuracy, which is attributed to integrating prior knowledge with monitoring data.

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.

Scaling considerations and optimal control for an offshore wind powered direct air capture system

The optimal design and operation of an offshore wind powered direct air capture (DAC) system is complex owing to the intermittent energy supply and the modularity of the units. A solid amine DAC process involves multiple individual units which undergo periodic loading to capture carbon dioxide (CO2) from ambient air, followed by regeneration to produce pure CO2 for utilisation or sequestration. The modular nature of a solid DAC process is exploited in this study to investigate the optimal design and coordinated operation of multiple DAC units mounted on a single 15 MW offshore wind turbine platform, with battery energy storage for additional short term power buffering. Important design parameters considered include the number of independently controllable units, the cyclic capacity of each unit (proportional to the amount of adsorbent) and the battery capacity and maximum power ratings. The design study results highlighted the diminishing returns to the CO2 capture rate with scaling, with a full design optimisation based upon cost estimations left for future work as the technology matures. It was found the optimal configuration was 14 DAC units, each with a cyclic capacity of 2000 kg CO2 , giving a total annual capture rate of 45 600 ton yr−1 and a wind utilisation factor of 96.6%. Furthermore, it was found that a rules-based control strategy based on high and low loading limits was competitive with a machine learning based controller and outperformed a model predictive control scheme.

Dynamic responses of a semi-submersible wind turbine platform subjected to focused waves with viscous effects

Dynamic responses of a semi-submersible wind turbine platform subjected to focused waves with viscous effects

Effects of ballast transfer on modeling and dynamic responses of a 15MW semi-submersible floating wind turbine

The total ballast accounts for more than 60% of displacement for large-megawatt floating wind turbines (FWT), including fixed and adjustable ballast. Properly using and controlling the variable ballast is attractive to optimize the dynamic performance but is not well studied yet. This study aims to demonstrate and quantify the effects of ballast transfer on the dynamic behavior and performance of FWTs. A 15 MW semi-submersible FWT equipped with an appropriate ballast transfer system is modeled and numerically analyzed. A hydrostatic model is first established to calculate inertial and hydrostatic properties of the FWT during the ballast transfer. Fully coupled time-domain simulations with and without ballast transfer are then carried out to predict the wind turbine performance, platform motion, and structural responses under various environmental conditions. The results indicate that ballast transfer can change the hydrostatic and hydrodynamic properties of the FWT, with an increase of approximately 3.5% in pitch hydrostatic stiffness. In addition, the ballast transfer can increase the average power generation, reduce platform pitch and roll motions, and significantly decrease the hub thrust and the tower base bending moment. The insights obtained serve as a foundation for the development of active ballast systems and the optimization of FWT operation.

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.

Study of the Hydrodynamic Characteristics of Anti-Heave Devices of Wind Turbine Platforms at Different Water Depths

Abstract This paper focuses on the effect of water depth on the hydrodynamics of floating offshore wind turbines with open-hole anti-heave devices. The three-floating-body wind turbine platform is used as the primary research object in this paper. The effect of water depth on the reduction of the heave motion of a floating platform with anti-heave devices is systematically investigated through a series of experiments and numerical simulations. The results show high agreement between the test results and simulations, with larger values of heave motion in deep water. A wind turbine platform with anti-heave devices can effectively reduce the lifting and sinking motions when the wave period is large.

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.

Simplified Strength Assessment for Preliminary Structural Design of Floating Offshore Wind Turbine Semi-Submersible Platform

The study aims to develop a simplified strength assessment method for the preliminary structural design of a semi-submersible floating offshore wind turbine platform. The method includes load cases with extreme wave load effects and a load case dominated by wind load. The extreme load effects due to waves are achieved using the design waves. Seven characteristic responses of the semi-submersible platform due to waves are chosen. The design waves for the extreme characteristic responses are all from extreme wave conditions where the significant wave heights are close to the one for a return period of 100 years. The extreme load effects dominated by wind loads are approximated using the modified environmental contour method. The load effects are the tower base shear force and bending moment. The two load effects are correlated, and a linear equation can approximate the relationship between their extreme values. The finite element analysis results show that the frame design of the bottom of the outer column is essential for structural strength. The wave load can also result in significant stress in the area close to the tower base.