Offshore Wind Turbine Installation Research Articles

GIS-based floating offshore wind turbine installation site selection using fuzzy analytic hierarchy process in northeast Aegean Sea

The ever-increasing consumption of electrical energy due to increasing requirements arising in parallel with the developing technology forces manufactures and users to seek new and environmentally compatible energy resources. Due to it endless energy potential and continuity, wind energy, which has been used by humanity for various purposes for centuries, continues its journey, which started with windmills that transform one form of mechanical energy into another, with offshore wind energy turbines. In this study, installation site selection, which is the first step for floating offshore wind turbine installation, is carried out. First, a Fuzzy Analytic Hierarchy Process (F-AHP) is applied to obtain the weights of criteria. Transformed alternatives and criteria in a fuzzy decision matrix through triangular fuzzy numbers are used to obtain a database via a Geographic Information System (GIS). Finally, the installation site and study area are determined. This area is located in the Northeast Aegean Sea, between Çanakkale and Gökçeada, 12 km to the northeast of Gökçeada, and 12 square kilometers. The minimum distance of the area to ship routes is 3000 m, and its minimum distance to fault lines is 2000 m. The average sea depth is 110 m, and the average wind speed is 9.26 m/s (18 knots). With this potential, enough energy can be generated for settlements on Gökçeada and the coastlines.

Analysis of bubble curtain effectiveness in the coastal Virginia offshore wind turbine installation

The Coastal Virginia Offshore Wind (CVOW) consists of two turbines roughly 40 km off the coast of Virginia Beach, Virginia. Water- and seabed-borne acoustic signals from impact pile driving at CVOW were recorded during the installation of these turbines in May 2020. In-water pressure signals were measured using two vertical line arrays (VLAs) at ranges of 3 km and 7.5 km. The water depth at the wind turbines and both VLAs was about 26 m. During installation, one of the piles utilized a double bubble curtain during construction while the other pile did not. Bubble curtains are used to reduce the acoustic impacts of pile driving by creating a barrier of bubbles around the source. We found that the bubble curtains were most effective at longer ranges and at frequencies above 200 Hz. Normal modes are an efficient representation of the acoustic field in this relatively range-independent shallow water environment. The amplitudes of acoustic modes at several frequencies were used to analyze the effectiveness of bubble curtains. Energy propagating in the seabed was also measured by an array of geophones and was found to be unattenuated by the bubble screens.

Inertia load reduction for loadoff during floating offshore wind turbine installation: Release decision and ballast control

High offshore installation costs are a significant factor limiting the competitiveness of offshore wind energy. One efficient installation approach for floating offshore wind turbines is to preassemble the tower, nacelle, and rotor onshore and perform a single lifting operation to mate the superstructure with the floating foundation at the installation site. It is heavy lifting, due to the weighty payload. At the end of the mating process, a loadoff operation is conducted to transfer the preassembly to the floating foundation. It results in a sudden change in total force acting on the vessel and causes substantial acceleration and potential damage to the mechanism in the onboard nacelles. The magnitude of acceleration of the onboard nacelles can vary greatly at different release instants. In this research, a simplified two-degrees-of-freedom (DOF) (heave and pitch) model is also proposed to account for the heavy lifting process and variable ballast tanks. The sudden payload transfer is approximated using a hyperbolic tangent function to guarantee continuity and differentiability. The loadoff operation consists of the decision-making and vessel-stabilizing phases. Based on the nonlinear model predictive control method, a payload-transfer time selector and anti-pitch ballast controller have been developed to achieve optimal release time decisions and stabilize the vessel after payload release, respectively. Six-DOF simulation results show that the proposed algorithms are capable to a satisfying level of robustness of deciding the optimal payload release time instant, as well as limiting the peak and mean acceleration magnitudes of the onboard nacelles after payload release. The decision-making and control strategies may promote the sustainable energy transformation by extending the operation window and reduce the installation costs.

Contactless control of suspended loads for offshore installations: Proof of concept using magnetic interaction

Current offshore wind turbine installation and positioning methods require mechanical equipment attached on the lifted components and human intervention. The present paper studies the development of a contactless motion compensation technique by investigating a magnetically controlled pendulum. The technique involves the interaction of a magnetic pendulum with an electromagnetic actuator. Two control modes are considered: the imposition of a desired motion to the mass and the motion attenuation of a prescribed pivot excitation. The numerical model is validated and calibrated against experiments and demonstrates excellent predictive capabilities. The control exerted is effective for a broad range of excitation frequencies and amplitudes. Important parameters associated with the performance of the technique such as the separation distance of the magnets and the saturation of the controller are identified. The controllability regions for effective control depending on the characteristics of the excitation are derived. The force amplitude of the contactless actuator is comparable to currently-used active tugger line control systems, but with the additional advantage of both attractive and repulsive forces. The findings of this paper illuminate the path for the further development of a non-contact control technique which has the potential to increase the efficiency of offshore wind installations.

Assessing areas suitable for offshore wind energy considering potential risk to breeding seabirds in northern Japan

Offshore wind energy is expected to play a major role in realizing carbon neutrality. However, the installation of offshore wind turbines is of concern for breeding seabirds. Identifying areas with low potential risk for breeding seabirds in Japan is urgently needed. This study identified technically and legally potential areas for wind energy development that are suitable for breeding seabirds by integrating risk assessment models through a spatial approach using Geographic Information System (GIS). While many studies and the government have assessed the potential areas for offshore wind energy in northern Japan, this study shows that most of these legally potential areas overlap with major concern areas for breeding seabirds. Currently, Japanese rules do not sufficiently consider the risk to seabirds when zoning areas for installing offshore wind energy system. The results imply that the risk to breeding seabirds should be carefully examined when zoning areas for local offshore wind energy installations. The approach developed in this study is expected to aid in clearly identifying areas suitable for the installation of offshore wind turbines and minimize the impacts on breeding seabirds. It provides a balance between the expansion of offshore wind energy and conservation biology.

Adaptive dynamic positioning control of an offshore wind turbine installation vessel subjected to thruster dynamics and input constraints

This paper suggests an adaptive positioning control method for a DP-equipped offshore wind turbine installation vessel. The method combines a finite-time disturbance observer (FTDO) with adaptive command filtered backstepping (CFB) to handle issues related to thruster dynamics, input saturation, model parameter uncertainties, and unknown environmental disturbances. By analyzing the environmental loads acting on the pile legs, a mathematical model for the installation vessel is established. To counteract the unknown disturbance actively, a FTDO is utilized. Additionally, an auxiliary dynamic system (ADS) is used to mitigate the thruster input saturation issue. Then an adaptive positioning controller is designed based on the FTDO and ADS, and Lyapunov stability theory is used to prove that all signals in the control system remain uniformly ultimately bounded. Numerical simulations are conducted to verify the effectiveness of the proposed control approaches.

Research on process safety of offshore wind turbines installation: A theoretical model and empirical evidence

As the world energy problem becomes more and more prominent, offshore wind farms have made remarkable progress in the last few years. With the advent of the rush to install offshore wind turbines around the world, offshore wind turbine (OWT) installation accidents have gradually increased. The process safety associated with offshore wind turbine installations has been a growing concern in offshore wind industry. To address this issue, this study aims to identify the factors affecting offshore wind turbine installation process safety, and to evaluate the correlations among these factors. The study involved an investigation into the causes and procedures of accidents that occurred during offshore wind turbine installation, leading to the development of customized safety factors. A questionnaire survey was developed and administered by a team of offshore wind industry professionals, including scholars, managers, and workers, and the data collected was analyzed using a theoretical model based on structural equation modeling. The results show that environment and weather condition, organization and management, and OWT installation technology have a significant impact on OWT installation technology. Furthermore, OWT installation technology has the largest total effect on the process safety of OWT installation.

Extended reality-based choice experiment to assess the impact of offshore wind turbines in historic center: The case of Manfredonia

This paper proposes a novel four-step methodology to achieve an extended-reality-based choice experiment in historic and touristic centers. The study exploits the case of Manfredonia (a seaside town in southern Italy) to apply the new approach and investigates public attitudes and preferences towards the installation of offshore wind turbines in the area. The novelty of the proposed work is twofold: i) for the first time, a structured methodological approach is defined for the development of a hybrid extended-reality-based choice experiment; ii) the perception of the visual impact of offshore wind turbines is assessed in a touristic and historic city in southern Italy exploiting the proposed approach. Our findings underscore the importance of continuously monitoring public perceptions to maintain and promote support for sustainable energy solutions, particularly in relation to the perception of wind energy's visual impact. In particular, 65% of respondents express their worries about wind power plants impact on the landscape. Moreover, the positive coefficient of the visual impact (0.011) suggests a positive utility of respondents from a higher off-shore turbines' density and a marginal willingness to accept a compensation of about 13€ for the visual impact and of about 33€ for the distance from the shore. In this context the use of extended reality technology in choice experiment scenarios significantly improves the results and enhances the understanding of the landscape impact of offshore wind farms.

Nonlinear analysis of horizontal bearing capacity of large-diameter rigid piles based on double conical strain wedge model

Large-diameter rigid piles are commonly employed in offshore wind turbine installations. A double conical strain wedge (DCSW) model is proposed in this paper to simulate the large-diameter rigid pile-soil interaction and determine the lateral subgrade reaction. A nonlinear analysis method is developed to predict horizontal response for large-diameter rigid piles installed in layered cohesionless soil, which can account for the effect of vertical side shear stress, pile end bending moment, and shear force. The rationality of the DCSW model is then verified by comparing its predictions with the experimental and theoretical results of existing studies. Subsequently, the new DCSW method is applied to investigate the horizontal bearing characteristics of the large-diameter rigid piles. The results reveal the presence of a rotation point situated at a depth range of (0.66–0.76) Lb (Lb is the burial depth of the pile). Additionally, the resisting bending moment caused by the vertical side shear stress between the pile-soil interface is able to enhance the horizontal bearing capacity of the pile.

Influence of Horizontal Loading in Changing the Ultimate Uplift Bearing Capacity of Monopile Foundation of Offshore Wind Turbine

Throughout their lifespan, monopile foundations supporting offshore wind turbines inevitably experience horizontal loads from waves, winds, and currents, resulting in cumulative deformation. It has been believed that deformation caused by horizontal loading weakens the interaction between the pile and the soil, leading to a reduction in the ultimate uplift bearing capacity of the pile foundation. However, there is a scarcity of literature investigating this issue, particularly regarding monopiles used in offshore wind turbine installations. Therefore, this study aims to explore the impact of horizontal cyclic loads on the ultimate uplift bearing capacity of monopile, focusing on the pile–soil interaction. To achieve this, a series of 1 g model tests were conducted on a rigid model pile embedded in silt with varying relative compaction. The test results indicate that the ultimate uplift bearing capacity of the pile is significantly diminished after experiencing horizontal cyclic loading, and the extent of reduction is closely linked to the amplitude of the horizontal deformation. A semi-empirical model is developed to predict the ultimate uplift bearing capacity of the pile foundation following horizontal cyclic loading. The key findings of this study are as follows: (1) The earth pressure in the active zone gradually decreases with an increasing number of cycles, while the earth pressure in the passive zone experiences a slight increase under horizontal cyclic loading. (2) The position of the pile rotation center under horizontal cyclic loading is approximately 0.84 times the depth at which the pile is buried, and this relationship appears to be independent of soil density and cyclic load ratio. (3) The variation of earth pressure corresponding to the horizontal deformation of the pile in the active zone can be divided into three phases: a rapid decline phase, a slow decline phase, and a stable phase. (4) The reduction in the ultimate uplift capacity is influenced by the cyclic ratio and number of cycles but does not appear to have a significant relationship with soil density.

Fatigue assessment of flange connections in offshore wind turbines under the initial flatness divergence

Bolted ring flange connections are widely utilized in offshore wind turbines to connect steel tubular segments. After the massive production and installation of offshore wind turbines in the past decade, flatness divergence is regarded as one of the most important initial imperfections for the fatigue design of flange connections. Offshore wind turbines are subjected to wind, wave, and current loads. This initial imperfection may alter the structural response and accelerate the fatigue crack growth. This paper aims to analyse the impact of the initial flatness divergence on the structural response of flange connections and evaluate its consequences on fatigue damage. Two different offshore wind turbines with fixed foundations and floating foundations are modelled to simulate their global responses to environmental loads. Based on a superposition method, local finite-element models of flange connections are established with three types of flatness divergence. Using the same bolt pretension and external loads from global modelling, the impact of these geometric imperfections is further examined by comparing the structural responses of flanges under different radial and peripheral opening lengths. Then, the fatigue assessments on flange connections in both fixed wind turbines and floating wind turbines are conducted, and the impacts of initial flatness divergence on these two different wind turbines are analysed.

Effects of structural flexibility on the dynamic responses of low-height lifting mechanism for offshore wind turbine installation

Installation complexities are one of the major challenges in the floating offshore wind turbine (OWT) industry. The modern concept introduced by the SFI-MOVE project is an effort to overcome the complexities by utilizing a low-height lifting mechanism. It is common to idealize a crane in the lifting mechanism as a rigid body since the structural deflections are smaller than the responses introduced by the other system components. However, structural flexibility can play an essential role in demanding offshore operations with smaller acceptable tolerances. In this study, lifting cranes are modeled using the finite element method and simplified by implementing equivalent 3D beam elements. Dynamic analysis is performed for various environmental conditions, and the responses of the crane structure and the OWT are calculated for each load case. This research reveals that crane structure flexibility influences the relative motion between a floating spar buoy and an OWT during mating operations. Crane structural flexibility contributes significantly to the OWT rotations. In addition, the response deviation between using rigid and flexible cranes increases as the excitation force increases. Therefore, it is recommended to consider the crane structural flexibility in the calculation when strict installation tolerances are needed.

A Positive Position Feedback controller for vibration control of wind turbines

Wind energy has become one of the most important energy sources in the last decades. Most of this type of energy comes from turbines installed onshore though there has been a paradigm shift in this field with the installation of offshore wind turbines, anchored to the seabed or floating ones. Both offshore and onshore technologies have a set of associate problems which sometimes can compromise the turbine integrity, such as environmental disturbances or harmful vibrations. Most of these vibrations and loads are actively compensated in commercial wind turbines through strategies which can modify the turbine power reference to reduce the tower and blades oscillations, at the expense of compromising efficiency. In this work, a new type of control vibration for wind turbines based on piezoelectricity is proposed. A closed loop control is developed from the sensing of the tower vibrations, followed by an in-house designed Positive Position Feedback (PPF) controller, and with a control signal applied to the piezoelectric transducers working as actuators. To design the PPF controller, a simplified wind turbine model is created in COMSOL Multiphysics. A state-space model is obtained, parametrized, validated and used for the tuning of the PPF controller presented in this paper. Simulation results show that with a set of piezoelectric transducers located along the turbine tower, significant reduction of the tower vibrations can be achieved.

Global Trends and Characteristics of Offshore Wind Farm Research over the Past Three Decades: A Bibliometric Analysis

Offshore wind power is a valuable renewable energy source. However, the development of offshore wind farms is facing many challenges, including understanding their impacts on ecosystems and society, as well as knowledge gaps in research. In this study, a bibliometric analysis was performed with the aim of providing a comprehensive understanding of current global progress in offshore wind farm research. Three stages of development were considered for the analysis and comparison of research characteristics and outcomes. Based on the total number of scientific publications and the international collaboration ratio (ICR), Europe has been leading research in and the development of offshore wind power since the early 1990s. However, a fast-growing period of offshore wind farm development occurred after 2000, during which Europe and Asia in particular showed increases in ICR. The installation of offshore wind turbines may have non-negligible adverse impacts on marine ecosystems, especially in ecologically vulnerable regions or developing countries. Research and relevant studies should be integrated to investigate and reduce the ecological and environmental damage that results from offshore wind farm development. This paper presents a systematic evaluation of the global developmental trends in offshore wind farm research, which could help to characterize and guide future trends within this field.

Assessment of allowable sea states for offshore wind turbine blade installation using time-domain numerical models and considering weather forecast uncertainty

Installation of offshore wind turbines, particularly blades, is challenging and should be executed within the allowable limit of sea states to ensure the safety and the efficiency of installation. During the execution phase where weather forecast will be used in the decision-making process, uncertainty in weather forecast is an important issue required to be dealt with. The purpose of this paper is to assess allowable sea states for offshore blade installation, with emphasis on both considering weather forecast uncertainty and using time-domain numerical models for installation response analysis. The general procedure is presented, which includes generation of the response-based alpha-factor αR (that is a reduction indicator reflecting weather forecast uncertainty) in the planning phase based on time-domain modelling and analysis of blade installation, and assessment of corresponding allowable sea states in the execution phase. Single blade installation by a semi-submersible crane vessel at the North Sea center is studied in this paper, and two typical limiting response parameters, namely the blade root radial motion and velocity, are considered. The αR factors correspond to these two limiting parameters are first generated respectively, based on the forecast uncertainty quantification of sea states, the quantitative assessment of system dynamic responses and the estimation of their characteristic values through probabilistic analysis. The characteristic values of the responses that correspond to a certain exceedance probability (10−2 or 10−4) could be generated with and without the consideration of the weather forecast uncertainty. Finally, the allowable sea states with and without the weather forecast uncertainty are obtained when the characteristic value reaches the allowable response limit. These could be further used to identify overall workable weather windows for the offshore blade installation and support operation decision-making. Results indicate that there is a significant difference between the allowable sea states with and without considering weather forecast uncertainty. As the forecast lead time increases, the allowable sea states gradually decrease. Hence, it is necessary to apply αR to involve and quantify the effect of weather forecast uncertainties on operations. Moreover, since time-domain simulations are used for dynamic response analysis of the installation system, the effect of statistical uncertainty related to the use of a limited number of simulations to derive the characteristic response values is also investigated and is found small.

Numerical Investigation of the Structural Behavior of an Innovative Offshore Floating Darrieus-Type Wind Turbines with Three-Stage Rotors

The vertical axis wind turbine (VAWT) design has several advantages for offshore wind turbine installation. The VAWT provides omnidirectional wind power, and its mechanical rotating mechanisms can be installed near sea level. In this paper, the selection of a suitable composite material for floating H-Darrieus-type wind turbines with three-stage rotors and its properties are discussed. The centrifugal forces acting on the composite blades are compared to the values of these forces evaluated on the aluminum blades. Abaqus software is used for numerical simulations. The selection of appropriate laminations used to model the composite materials is discussed. The optimum combination of selected layers is determined to reduce the values of maximum bending stresses and displacements, resulting in a high strength-to-weight ratio. In the post-processor, a path is taken at the location of the application of the maximum load on the blade and the values of the displacements and stresses along this path are determined. These maximum values are compared to the unidirectional strength of the selected composite material to ensure a safe design.

The current opportunities and challenges for offshore wind in the United States

Over the past decade, offshore wind installations have expanded dramatically in Europe and China, increasing renewable energy presence in these markets. However, the United States lags in offshore wind development despite significant coastline and wind resource availability. Each coast of the United States possesses unique opportunities and challenges to installation due to variations in bathymethry and weather patterns. This paper reviews the planning and installation challenges of offshore wind turbines in the United States by incorporating lessons learned from offshore wind plants already in place in other countries. The goal of this paper is to provide a review of offshore wind turbine installation methods by highlighting challenges unique to this form of renewable energy in the United States.

Tuning of passive TMD for floating offshore wind turbine using linear matrix inequalities

Over the last several years, the number of offshore wind turbine installations has increased exponentially. A change from shallow to deep marine waters will be seen in future installations. As we move further away from the shore, the loading on the floating offshore wind turbine (FOWT) system increases. This higher load may have a negative impact on the wind turbine's efficiency. It may also lead to power fluctuations, large tower displacements and increased fatigue loads. In order to circumvent these effects, passive secondary devices are installed. A tuned mass damper (TMD) is one such device that may be utilized for load mitigation. In this paper, an efficient method is presented for the design of TMD for FOWT. The design problem is posed as feedback response control problem for the plant represented by the FOWT-TMD system. The design objective is to evaluate the static controller such that the response of the FOWT is minimized. The controller gains correspond to the TMD properties. The TMD parameters are obtained using iterative LMI, which uses a combination of convex and metaheuristic optimization. The proposed TMD is found to be useful in lowering the FOWT response. The methods described in this paper can be utilized to determine the best TMD configuration.

Three-dimensional computational fluid dynamic analysis of a large-scale vertical axis wind turbine

The vertical axis wind turbine (VAWT) configuration has many advantages for an offshore wind turbine Installation. In this paper, the three dimensional (3D) computational fluid dynamics analysis of a large-scale 5 MW VAWT is conducted. At the optimum tip-speed ratio (TSR), the VAWT maximum inline force was 75% larger than the maximum lateral force. It was found the dynamic stall effects cause the VAWT flow field to become increasingly asymmetrical at the mid-span plane, when the TSR is reduced. The attachment of end plates to the blade tips, resulted in a performance improvement during the upwind phase with the average blade torque coefficient in this range being increased by 4.71%. Conversely, during the blade downwind phase a reduction in performance was found due to the increase in drag from the end plates and the average blade torque coefficient in this phase was reduced by 23.1%.

A procedure to redesign a comparable blade structure of a two-bladed turbine based on a three-bladed reference

Two-bladed turbines might be an alternative for future offshore wind turbine installations due to the promising opportunity to be more economical compared to three-bladed turbines. Looking at the rotor blades, two-bladed turbines with a comparable design either rotate 22.5% faster or have up to 50% increased chord lengths. The latter result in a significantly higher second moment of area, which enables rotor mass savings and thus fewer costs while withstanding ~50 % higher flapwise loads per blade. Unfortunately, such a design could also cause buckling issues. Increasing the design tip speed reduces stability issues but lowers the rotor mass savings. Consequently, the challenging task is to find an optimal compromise between preventing buckling and saving rotor mass, and thus to ensure a fair comparison of two- and three-bladed turbines’ blades. To overcome this challenge, a procedure for redesigning a comparable blade structure is introduced. The procedure is exemplarily demonstrated for large 20 MW offshore wind turbines. Compared to the three-bladed reference, the overall rotor mass reduction of the two-bladed turbine is 13.5 % for the most beneficial compromise detected. Simultaneously, the blades showing good accordance with the reference concerning static stresses and buckling characteristics under their respective loads.