Offshore Wind Energy Industry Research Articles

Use of drones in offshore wind farm inspections

Abstract: With the increase in global investments in offshore wind energy and the rapid implementation of wind technologies in hazardous deep water environments, operational inspection of wind turbines and related infrastructure plays an important role in the safe and efficient operation of offshore wind farms. In recent years, much attention has been paid to the use of unmanned aerial vehicles (UAVs) and remotely piloted unmanned aerial vehicles (RPAs) commonly referred to as "drones" for remote inspection of renewable energy infrastructure, i.e. photovoltaic farms and onshore wind farms. Drones have significant potential also in in offshore wind energy. Inspection with drones allows for to reduce not only the number of flight operations (involvement of aircraft and flight crews) and the transport of personnel carrying out the maintenance and repair of offshore wind turbines. With drones is possible carry the equipment transported for hazardous inspection work. The involvement of UAVs also reduces the plant downtime needed to detect faults and collect diagnostic information from the entire wind farm. The benefits of inspection technology in the offshore wind energy industry based on drones are confirmed by the previous tests, and the prospect of offshore energy development encourages further work with the use of UAVs. At the same time, it should be borne in mind that any unexpected failure of the drone system during its mission may interrupt control works (during inspections), and thus reduce the electricity generated by wind turbines. The article presents the potential of drones in the process of inspecting wind farms, including offshore wind farms, presents examples of UAV models used for inspections, indicates methods of conducting inspections with the use of drones and highlights a significant reduction in the costs of the operation of offshore wind farms as a result of limiting the use of manned aviation (helicopters and flight crews) and the elimination of the risk associated with the involvement of personnel to perform inspections of wind farms at sea. The potential of unmanned floating platforms as part of cooperation with UAV in the process of inspecting offshore wind farms was also indicated. Keywords: wind energy, offshore, drones, wind farms, drone inspections, maritime inspections, marine aviation, offshore, offshore wind energy, safety air operations, risk analysis

Development of high-precision wind, wave and current forecast system for offshore wind energy industry in Taiwan: a two-stage method of numerical simulation and AI correction

ABSTRACT At the Changhwa Fuhai wind farm, the high-resolution numerical models for wind, wave and current simulations are crucial to provide daily forecasts as a decision-support system for Taiwan’s offshore wind energy industry. In this study, the two-stage method, consisting of numerical simulation and deep-learning correction based on the observed data at Fuhai wind farm site, is implemented to further improve the meteorological and marine forecast accuracy. The recurrent neural network-long short-term memory (RNN-LSTM) model is adopted in the deep learning analytics. Currently, this system is capable of daily providing the next 4-day wind field forecast and the next 7-day wave and current field forecast. Through the testing, it is found that the error correction of wind simulations can reduce root mean square error (RMSE) by up to 36.7%. Furthermore, through adopting the SQL and HBase hybrid database system, a wide range of historical data as well as daily forecast data can be quickly queried and displayed on the web interface to provide important decision support to the relevant wind power companies in scheduling offshore construction plans, forecasting wind energy production, and arranging wind turbines’ shutdown and maintenance sequence.

Dynamics of a Y-shaped semi-submersible floating wind turbine: a comparison of concrete and steel support structures

ABSTRACT Concrete semi-submersible floating wind turbines (FWTs) have generated increasing interest in the offshore wind energy industry due to their superiority over steel structures in aspects of construction and maintenance. However, the influence of construction materials on the dynamics of FWTs was scarcely studied before. The dynamics of two FWTs, mounted on a concrete and a steel Y-shaped semi-submersible platform respectively, are investigated by means of 1:60 scale combined wind and wave model tests and coupled multi-body simulations. The results indicate that the steel structure with a lower centre of gravity exhibits advantages in platform pitch motion alleviation. The steel structure is also subjected to lower pitch-induced tower base loads and nacelle acceleration than its concrete counterpart. However, an opposite trend is found in the wave-frequency responses, leading to an insignificant difference of tower base loads and nacelle acceleration between the two structures. ABBREVIATIONS: FWTs: Floating wind turbines; CoG: Centre of gravity; CoB: Centre of buoyancy; LCP3: Lightweight prestressed concrete platform; HSP3: High-strength steel platform; WTWF: Wind tunnel and wave flume joint laboratory; ROC: Rated operational condition; JONSWAP; Joint North Sea Wave Observation Projection; RAO: Response amplitude operator; BEM: Blade element momentum theory; DOF: Degree of freedom; GDW: Generalised dynamic wake theory; PSD: Power spectral density; QTF: Quadratic transfer function

Socio-economic impact of a 200 MW floating wind farm in Gran Canaria

This research analyses the economic impact of a 200 MW offshore floating wind farm in an isolated tourist-led region as the Canary Islands in terms of regional and national gross value added (GVA) and employment. After analysing the value chain of the offshore wind energy industry, the impact of the regional and national economy has been estimated using an input/output model. The main aim is to evaluate this impact in comparison to more industrialized region and to bottom-fixed offshore wind farms. The value chain analysis shows that the floating offshore wind capabilities in Spain are very high. Two different scenarios have been developed to take into account transfers of the value-chain between the regional and the national level. It is concluded that similar level of investment in the Canary Islands and in Mainland-Spain will lead to different impacts in the economy due to their different economic structures. The highly tourism-led Canarian economy, characterised by a marginal industrial sector and overdeveloped services one, will lead to an overall lower GVA and, at the same time, to a higher employment demand. Several indicators have been deployed using the results of this research that show the impact in tourist-led economies and also of floating versus bottom-fixed offshore wind farms. The GVA generated through the whole project is high, reaching 680 million euros at national level, which includes a regional contribution of 365 to 245 million euros, showing the high impact of the project in the national and local economy.

Assessment of hurricane generated loads on offshore wind farms; a closer look at most extreme historical hurricanes in New England

We simulated and assessed the environmental forces including wave and wind loads generated by the most extreme historical hurricanes in the US northeast within the proposed offshore/planned wind farms: Hurricane Carol in 1954, and 1938 New England hurricane. Offshore wind energy industry is on the verge of rapid growth off the US east coast. Development of wind energy projects in this area requires a comprehensive assessment of hurricane risks in planning and operation stages. In this study, we used an ocean modeling system (COAWST: Coupled Ocean Atmosphere Wave Sediment Transport) to better understand and characterize hurricane-generated loads within the planned wind farm sites offshore Rhode Island and Massachusetts. The COAWST model was first validated using observed data and then applied to hurricanes with return periods of around 500-year (recommended by IEC 61400-3-1). Hurricane Carol and 1938 hurricane were simulated using a parametric model which generated the peak wind speeds of 49 m/s and 45 m/s, spatially averaged over the area, that led to significant wave heights of 11.90 m and 9.80 m, respectively. .Spatial variability of the wind and wave loads within the proposed sites were assessed. Further, the effects of these variabilities on the structural response of a typical monopile were demonstrated using the OpenFAST Model. Results showed up to 60% spatial variability of hurricane loads in the leased areas. Results demonstrated the need of using advanced ocean modeling systems for planning and operation of wind farms as opposed to traditional statistical methods such as measure and correlate for site characterization.

Wind Farm Support Vessel Extreme Roll Assessment While Docking in the Bohai Sea

Robust prediction of extreme motions during wind farm support vessel (WFSV) operation is an important safety concern that requires further extensive research as offshore wind energy industry sector widens. In particular, it is important to study the safety of operation in random sea conditions during WFSV docking against the wind tower, while workers are able to get on the tower. Docking is performed by thrusting vessel fender against wind tower (an alternative docking way by hinging is not studied here). In this paper, the finite element software AQWA has been used to analyze vessel response due to hydrodynamic wave loads, acting on a specific maintenance ship under actual sea conditions. Excessive roll may occur during certain sea conditions, especially in the beam sea, posing a risk to the crew transfer operation. The Bohai Sea is the area of diverse industrial activities such as offshore oil production, wave and wind power generation, etc. This paper advocates a novel method for estimating extreme roll statistics, based on Monte Carlo simulations (or measurements). The ACER (averaged conditional exceedance rate) method and its modification are presented in brief detail in Appendix. The proposed methodology provides an accurate extreme value prediction, utilizing available data efficiently. In this study the estimated return level values, obtained by ACER method, are compared with the corresponding return level values obtained by Gumbel method. Based on the overall performance of the proposed method, it is concluded that the ACER method can provide more robust and accurate prediction of the extreme vessel roll. The described approach may be well used at the vessel design stage, while defining optimal boat parameters would minimize potential roll.

Potential environmental effects of deepwater floating offshore wind energy facilities

Over the last few decades, the offshore wind energy industry has expanded its scope from turbines mounted on foundations driven into the seafloor and standing in less than 60 m of water, to floating turbines moored in 120 m of water, to prospecting the development of floating turbines moored in ~1,000 m of water. Since there are few prototype turbines and mooring systems of these deepwater, floating offshore wind energy facilities (OWFs) currently deployed, their effects on the marine environment are speculative. Using the available scientific literature concerning appropriate analogs, including fixed-bottom OWFs, land-based wind energy facilities, wave and tidal energy devices, and oil and gas platforms, we conducted a qualitative systematic review to estimate the potential environmental effects of deepwater, floating OWFs during operation, as well as potential mitigation measures to address some of the effects. We evaluated six categories of potential effects: changes to atmospheric and oceanic dynamics due to energy removal and modifications, electromagnetic field effects on marine species from power cables, habitat alterations to benthic and pelagic fish and invertebrate communities, underwater noise effects on marine species, structural impediments to wildlife, and changes to water quality. Our synthesis of 89 articles selected for the review suggests that many of these potential effects could be mitigated to pose a low risk to the marine environment if developers adopt appropriate mitigation strategies and best-practice protocols. This review takes the necessary first steps in summarizing the available information on the potential environmental effects of deepwater, floating OWFs and can serve as a reference document for marine scientists and engineers, the energy industry, permitting agencies and regulators of the energy industry, project developers, and concerned stakeholders such as coastal residents, conservationists, and fisheries.

Mitigating occupational health and safety risks in the proposed Australian offshore wind energy industry: lessons from the safety case regime

The offshore wind energy industry is growing at an encouraging rate, and Australia is seeking to commence offshore wind development. Although there is research on the planning and environmental risks, there is limited research addressing health and safety risks. Some scholars argue the two industries are different, while others support the application of offshore petroleum safety to wind. This article analyses whether the industries have many similarities, and whether the safety case provides the most robust safety regulatory framework for both industries, concluding that Australia’s approach is a solid foundation for safety in the developing wind industry.

Soil parameters for offshore wind farm foundation design: A case study of Zhuanghe wind farm

The Zhuanghe wind farm is under development offshore China. The site investigation campaign was completed in 2019. Both monopiles and suction buckets are considered as foundation types, and they are presently in the design phase. Soil testing was carried out at both the HDEC and the NGI laboratories. Soil parameters obtained from the laboratory tests are interpreted and discussed in this paper. Important soil parameters for foundation design, such as static and cyclic shear strengths, shear modulus and thixotropy from the tests on the Zhuanghe soil are compared with available databases in the literature, and soil parameters for foundation design are recommended. The purpose of this study is to provide a realistic reference for research and practice in the offshore wind energy industry offshore China where very few advanced tests for windfarm development are available. • Details of soil conditions and soil parameters for an actual wind farm location offshore China is provided. • Representative soil parameters that can be used for foundation design at the Zhuanghe offshore wind farm site is recommended • Static strength is evaluated based on both laboratory tests and in situ CPTU tests, and a reasonable cone factor is suggested • Shear modulus and thixotropy are recommended based on laboratory tests and discussed according to available database in the literature.

Influence of extended potential-to-functional failure intervals through condition monitoring systems on offshore wind turbine availability

Condition monitoring systems are deployed in various industries for decades contributing to optimizing operational performance and maintenance efforts. Several publications address this potential for application in the offshore wind energy industry; however, none attempts to quantify the impact that longer warning times ahead of a failure would have on asset availability. The aim of this paper is to bridge this gap by considering particularly the access restrictions for offshore operations through a probabilistic model which simulates existence of different condition monitoring systems on offshore wind turbines in the time domain. Results of this study quantify the positive impact that a longer warning time of potential-to-functional failure (P-F interval) has on availability, highlighting that variation of maintenance strategy through transformation of unplanned activities into planned interventions that can be conducted during a suitable weather window ahead of a component failure can lead to reduced operation and maintenance (O&M) costs.

Nonlinear Destructive Interaction between Wind and Wave Loads Acting on the Substructure of the Offshore Wind Energy Converter: A Numerical Study

Even though the offshore wind industry’s growth potential is immense, the offshore wind industry is still suffering from problems, such as the large initial capital requirements. Many factors are involved, and among these, the extra costs incurred by the conservative design of offshore wind energy converters can be quickly addressed at the design stage by accounting for the nonlinear destructive interaction between wind and wave loads. Even when waves approach offshore wind energy converters collinearly with the wind, waves and wind do not always make the offshore wind energy converter’s substructure deformed. These environmental loads can intermittently exert a force of resistance against deformation due to the nonlinear destructive interaction between wind and wave loads. Hence, the nonlinear destructive interaction between wave and wind loads deserves much more attention. Otherwise, a very conservative design of offshore wind energy converters will hamper the offshore wind energy industry’s development, which is already suffering from enormous initial capital expenditures. In this rationale, this study numerically simulates a 5 MW offshore wind energy converter’s structural behavior subject to wind and random waves using the dynamic structural model developed to examine the nonlinear destructive interaction between wind and wave loads. Numerical results show that the randomly fluctuating water surface as the wind blows would restrict the offshore wind energy converter’s substructure’s deflection. Nonuniform growth of the atmospheric boundary layer due to the wavy motions at the water surface as the wind blows results in a series of hairpin vortices, which lead to the development of a large eddy out of hairpin vortices swirling in the direction opposite to the incoming wind near the atmospheric boundary layer. As a result, the vertical profile of the longitudinal wind velocity is modified; the subsequent energy loss drastically weakens the wind velocity, which consequently leads to the smaller deflection of the substructure of the offshore wind energy converter by 50% when compared with that in the case of wind with gusts over a calm sea.

Wind science and engineering: Solutions and new Certificate of Approvals proposed for offshore wind turbine installation

Wind conditions are the most critical concerns during offshore wind turbine installation. Unfavorable wind can cause safety issues and a long time waiting, resulting in project delay and huge costs. Offshore wind energy industry utilizes weather forecast reports, however, many times the reports are found inconsistent, particularly in wind speed. The decision for installation work is then hard to make. The present paper provides a solution, by using the concept of time lag in Cross-Correlation and Pearson Correlation Coefficient, to analyze the similarity degree of the two reports, as well as to predict the next opening of weather window and the periodicity of the window. Not only aligning the reports, but also precisely judging of wind types are critical. The paper introduces a new view, in simulating four wind models, and defines their wind characteristics by Fourier Transform in frequency domain, to identify wind types in the anemometer measured data. The results show wind types in the anemometer data are identified. In whole paper, the industrial standard Certificate of Approvals are considered. Moreover, two new Certificate of Approvals specific to the above situations are proposed, for the industry’s reference during offshore wind turbine installation. The purpose of this paper is to assist scientific/engineering frame works and the decision making for offshore wind, in the way of establishing new Certificate of Approvals. All inputs in the present paper are random or measured by author’s personal devices to avoid the infringement of intellectual properties and patents.

A p–y Model for Large Diameter Monopiles in Sands Subjected to Lateral Loading under Static and Long-Term Cyclic Conditions

The design of large diameter monopiles subjected to cyclic lateral loading is of interest in many applications, such as, for example, in the offshore wind energy industry. Engineering design methods to estimate the deflection of these structures are required for this purpose. In the present work, a p–y model for large diameter monopiles subjected to lateral loading is proposed. The model considers a pile in cohesionless soil subjected to static and long-term cyclic loading. Its formulation features the consideration of nonlinear relations for the ultimate soil resistance pu and the initial subgrade modulus Epy0 among the soil depth and a cyclic factor that accounts for the effect of the soil density and loading amplitude. A relation is also proposed to account for a base shear force at the tip of the monopile. The proposed relations were employed and solved under the beam on nonlinear Winkler foundation (BNWF) approach and were adjusted to simulate a number of three-dimensional (3D) finite-element (FE) models accurately, accounting for variations on pile geometry, soil properties, and loading conditions. In the end, the performance of the proposed relations was evaluated through the comparison with a field test and a centrifuge test.

Extreme loads analysis of a site-specific semi-submersible type wind turbine

ABSTRACT As a vital key part of the modern offshore wind energy industry, floating offshore wind turbines (FOWT) are built to generate green renewable energy. Robust prediction of extreme loads during FOWT operation is an important safety concern. In this paper, the FAST code has been used to analyse offshore wind turbine internal bending moments due to environmental hydrodynamic wave loads, acting on a specific FOWT under actual local sea conditions. This paper advocates a computationally efficient Monte Carlo based methodology for estimating extreme load or response statistics, based on simulations or measurements. For this purpose, the averaged conditional exceedance rate (ACER) method is proposed. The described approach may be well used at the design stage, while defining optimal wind turbine parameters that would minimise potential FOWT mechanical damage due to excessive environmental loadings.

A Metocean Reference Station for Offshore Wind Energy Research in the U.S.

There is an acute need for a long-term metocean reference site that will aid the near-term development of the offshore wind energy industry in the United States. High quality, multi-year observations of the wind resource at hub height in areas relevant to offshore wind energy are a requirement for reducing uncertainties in wind resource assessment, improving the fidelity of numerical models, assimilated products of the resource, and forecasts of near-term operational conditions and wind energy power production. Yet, few long-term data sets exist over the U.S. outer continental shelf that can provide accurate guidance for developers, turbine manufacturers, and utility operators. Thus, there is a critical need for robust, long-term data collection at a site having conditions representative of wind energy development areas. Additionally, an efficient and effective location for validating existing measurement systems and testing and verifying the accuracy of new sensors will play a key role in reducing uncertainty of estimates of the wind resource and reducing the cost and risk associated with offshore development.

A Simulation of Non-Simultaneous Ice Crushing Force for Wind Turbine Towers with Large Slopes

When the offshore wind energy industry attempts to develop in cold regions, ice load becomes the main technological challenge for offshore wind turbine foundation design. Dynamic ice loads acting on wind turbine foundations should be calculated in a reasonable way. The scope of this study is to present a numerical model that considers the non-simultaneous ice crushing failure acting on the vertical structure of a wind turbine’s foundation. The local ice crushing force at the contact surface between the ice sheet and structure is calculated. The boundary of the ice sheet is updated at each time step based on the indentation length of the ice sheet according to its structure. Ice loads are validated against two model tests with three different structure models developed by other researchers. The time series of the ice forces derived from the simulation and model tests are compared. The proposed numerical model can capture the main trends of ice–wind turbine foundation interaction. The simulation results agree well with measured data from the model tests in terms of maximum ice force, which is a key factor for wind turbine design. The proposed model will be helpful for assisting the initial design of wind turbine foundations in cold regions.

A systematic Failure Mode Effects and Criticality Analysis for offshore wind turbine systems towards integrated condition based maintenance strategies

Condition-based maintenance is applied in various industries to monitor and control critical assets and to optimize maintenance efforts. Its applicability to the offshore wind energy industry has been considered for almost 20 years and has resulted in the development and implementation of solutions that have contributed to lower cost of maintenance and increased asset availability. However, there is currently no public domain guidance available that provides the information required to (i) prioritize systems for which condition monitoring would generate highest value and to (ii) understand the parameters that need to be monitored by a specific system from failure cause to failure mode. Both items are addressed in this paper, providing a clearly structured, risk-based assessment methodology and corresponding results for state-of-the-art offshore wind turbines. A total of 337 failure modes have been identified and analysed by experts representing approximately 70% of the European offshore wind market to assess potential benefits of condition monitoring systems. Results may be used to target the development of condition monitoring systems focusing on critical systems and to find optimal O&M strategies by understanding failure paths of main offshore wind turbine systems resulting in a lower cost of energy and a more optimal risk-return balance.

Impact of model uncertainties on the fatigue reliability of offshore wind turbines

The impact of environmental load uncertainties on the spatial fatigue reliability of offshore wind turbine foundations is discussed and exemplified. Design procedures are utilizing overall or partial safety factors to include different model- and statistical uncertainties. Uncertainties in the final design are related to decisions taken during the design process, such as; load models, analysis methods and statistical descriptions. Furthermore, to benefit from more elaborate methods, strategies to account for reduced uncertainties by increased knowledge must be adopted. This is especially important for the offshore wind energy industry, where the aim is to produce renewable energy at a competitive cost level. The challenges and consequences of using a detailed design basis are exemplified and discussed through structural reliability analyses. Epistemic load effect uncertainties related to the foundation fatigue will be presented for a detailed wind directional model, wind-wave misalignment, and a second order wave load model. It will be shown that all of these represent important uncertainties to consider during the fatigue design of an offshore wind farm.

Sea Breeze Sensitivity to Coastal Upwelling and Synoptic Flow Using Lagrangian Methods

AbstractSea breezes occur nearly daily in the U.S. Mid‐Atlantic summer during high electricity demand periods, and thus have important implications for the burgeoning U.S. offshore wind energy industry. The sea breeze's offshore component is poorly understood and ill defined relative to its onshore counterpart. Here a new Lagrangian method not yet readily used to study the sea breeze, relative dispersion, was validated and applied to a validated Weather Research and Forecasting model in the U.S. Mid‐Atlantic. This Lagrangian method is used to characterize the onshore convergent and offshore divergent sea breeze extents and intensities, and test their sensitivities to both atmospheric synoptic flow and oceanic coastal upwelling, another common summer season regional phenomenon. It was found that offshore‐directed synoptic flow impacted the sea breeze onshore extent more than offshore extent, and that coastal upwelling did not significantly impact sea breeze onshore or offshore extent for these carefully selected case studies. Upwelling, however, produced an earlier sea breeze onset (~5 hr), and a shallower, sharper, and more intense offshore/onshore sea breeze during strong offshore synoptic flow, consistent with past studies. The offshore side of the sea breeze cell—with stronger intensity during upwelling—crossed the New Jersey Wind Energy Area at ~1900 UTC, regardless of synoptic wind or upwelling conditions. Results overall are consistent with dynamic linear sea breeze theory. Uncertain projected trends in coastal upwelling/sea breezes in a warming world highlight the importance of continued study of coastal air‐sea interactions for improved offshore wind energy assessment and prediction.

Evaluating and Improving NWP Forecast Models for the Future: How the Needs of Offshore Wind Energy Can Point the Way

AbstractTo advance the understanding of meteorological processes in offshore coastal regions, the spatial variability of wind profiles must be characterized and uncertainties (errors) in NWP model wind forecasts quantified. These gaps are especially critical for the new offshore wind energy industry, where wind profile measurements in the marine atmospheric layer spanned by wind turbine rotor blades, generally 50–200 m above mean sea level (MSL), have been largely unavailable. Here, high-quality wind profile measurements were available every 15 min from the National Oceanic and Atmospheric Administration/Earth System Research Laboratory (NOAA/ESRL)’s high-resolution Doppler lidar (HRDL) during a monthlong research cruise in the Gulf of Maine for the 2004 New England Air Quality Study. These measurements were compared with retrospective NWP model wind forecasts over the area using two NOAA forecast-modeling systems [North American Mesoscale Forecast System (NAM) and Rapid Refresh (RAP)]. HRDL profile measurements quantified model errors, including their dependence on height above sea level, diurnal cycle, and forecast lead time. Typical model wind speed errors were ∼2.5 m s−1, and vector-wind errors were ∼4 m s−1. Short-term forecast errors were larger near the surface—30% larger below 100 m than above and largest for several hours after local midnight (biased low). Longer-term, 12-h forecasts had the largest errors after local sunset (biased high). At more than 3-h lead times, predictions from finer-resolution models exhibited larger errors. Horizontal variability of winds, measured as the ship traversed the Gulf of Maine, was significant and raised questions about whether modeled fields, which appeared smooth in comparison, were capturing this variability. If not, horizontal arrays of high-quality, vertical-profiling devices will be required for wind energy resource assessment offshore. Such measurement arrays are also needed to improve NWP models.