bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of implicit CFD modeling of riblets on wind turbine airfoil in transitional flow
Authors: Vimalakanthan Kisorthman , Bakhmet Iana
Published: June 2024

The study introduces a novel hybrid boundary condition, derived from existing literature, crafted for predicting the impact of riblets on airfoils in transitional flow. In contrast to models tailored for fully turbulent flow, the hybrid approach successfully captures the operational dynamics of riblets, as demonstrated through meticulous testing. The boundary condition integrates slip length and a modified specific dissipation rate (ω) boundary to encompass the entire riblet regime. Adjusting the model to match measured drag behavior enables predictions of riblet effects at higher Reynolds numbers pertinent to wind turbine blades. Validation reveals the model’s proficiency in capturing the order of magnitude in drag reduction and aligns the change in drag in the correct direction for diverse riblet heights, yet highlights discrepancies in replicating absolute drag reduction values, particularly at smaller angles of attack. This underscores the imperative for further refinement and tuning, necessitating additional experimental data at higher Reynolds numbers and across various angles of attack to ensure the model’s robust applicability across a broader spectrum of conditions.
Development of a machine learning model for wind turbine fatigue and ultimate loads based on static loads
Authors: Barlas T , Göçmen T , Riva R
Published: June 2024

A machine learning model is trained on HAWC2 time-domain aeroelastic load simulations in order to provide a load surrogate model from static rotor loads input to lifetime wind turbine design loads, to be utilized in fast design loads evaluation for design optimization. The simulations are performed on the IEA-3.4-130-RWT with a range of design variations for tip-speed-ratio, pitch-ramp settings, and blade length scaling. The surrogate model is shown to provide accurate predictions of lifetime blade and turbine ultimate and fatigue loads for design variations within the training design space.
Prediction of the friction torque of scaled blade bearings in a test rig using machine learning
Authors: Hohmann M , Blechschmidt E , Hallerberg S , Menck O
Published: June 2024

Blade bearing friction torque is a required parameter for the design of a pitch actuator, and deviations from a bearing’s initial torque can be utilized for condition monitoring of the bearing. The torque of large-scale bearings can, however, be difficult to predict due to quality fluctuations in the production of these large-scale components. Therefore, this paper employs machine learning approaches to predict the torque of a given set of bearings in a controlled test environment based on measurement data from that same set of bearings. Possible applications of the model include use for condition monitoring by checking for deviations from the bearing’s initial behavior.
Influence of wakes interaction and upstream turbulence on three tidal turbines behaviour
Authors: Dufour M-A , Pinon G , Rivoalen E , Germain G
Published: June 2024

The current study presents numerical results on three tidal turbine models (two in front, one downstream) interacting in a turbulent upstream flow. The numerical results come from a lifting-line (LL) embedded in a Lagrangian vortex particle (VP) solver: Dorothy LL-VP. The objective is to assess the extent to which this numerical tool is suited to reproduce accurately wakes interaction as well as fluctuating loads perceived by the downstream turbine. To this aim, the numerical set-up reproduces an experimental campaign led at IFREMER’s wave and current flume tank. The downstream turbine is placed at different positions to change the wakes interaction. Two upstream turbulence intensities (TI) experimentally tested are reproduced numerically using the synthetic eddy method (SEM). Favourable comparisons are obtained between numerical and experimental wakes, including velocity profiles. Preliminary results suggest that the downstream turbine performance decrease is numerically well captured. More investigations are needed on the loads fluctuations with longer computation time, and adding an angular velocity controller as well as hub modelling to Dorothy LL-VP.
Lattice Boltzmann simulation for wake interactions of aligned wind turbines using actuator line model with turbine control
Authors: Watanabe Seiya , Hu Changhong
Published: June 2024

A wind turbine wake causes a decrease in wind speed and an increase in turbulence intensity. The wind turbine wake interaction is essential for predicting the power output of a wind farm consisting of many wind turbines. This research proposes a CFD method able to reproduce wake interactions and power outputs of multiple wind turbines with high speed and accuracy. Large eddy simulations with the lattice Boltzmann method are used for fluid calculations, specifically for large-scale CFD simulations. The wind turbines are represented using an actuator line model. Optimal power generation efficiency is achieved by controlling the rotor speed and blade pitch angle. Large-scale simulations of eight aligned wind turbines are conducted using 1.75 billion grid points and 40 GPUs. We compare two cases with and without control to investigate the effect of turbine control on wake and power output. Both the instantaneous and mean streamwise velocities confirm that the turbine control reduces the wake velocity deficit of the downwind wind turbine. High-speed inflow of wind to the downstream turbines augments their power output. With implementation of turbine control, the power outputs of the downstream turbines agree well with the observation data obtained in an earlier study. The results demonstrate the importance of controlling the rotational speed and pitch angle for actuator line simulations.
Impact of 3D segment profiling on friction losses of plain bearings in wind turbines main bearings
Authors: Jakobs T , Jacobs G , Euler J , Rolink A , Röder J
Published: June 2024

Wind power is a crucial technology in transitioning to a carbon-free energy future. To increase the economic competitiveness, the levelized cost of electricity of wind power needs to be further reduced. A critical factor contributing to maintenance expenses is the failure of main rolling bearings. Replacing these rolling bearings in the case of damages is a costly procedure as it necessitates dismantling the wind turbine drivetrain. Unlike conventional rolling bearings, segmented plain bearings allow for the up-tower replacement of individual faulty segments, significantly reducing downtime and maintenance costs. The FlexPad plain bearing concept specifically addresses the need for an easy-to-maintain main bearing for wind turbines. While the current FlexPad design guideline focuses on global geometrical parameters disregarding a detailed segment profile optimization, literature suggests that a 3D-profile on the segments can enhance bearing performance by reducing frictional losses. However, the investigations conducted in literature were limited to stationary thrust bearings. The FlexPad bearing's inherent flexibility and conical shape preclude direct application of the findings in literature. Therefore, a coupled elastohydrodynamic-multi-body simulation model was developed to account for the bearing's flexibility while investigating different 3D-profiles. This study quantifies the impact 3D-profiles on friction power, solid contact, and maximum hydrodynamic pressure, demonstrating the advantages. The best 3D-profiles achieve a decrease in friction power of 18.3% with an increase of the maximum hydrodynamic pressure of just 4.9%.
On the influence of rotor nacelle assembly modelling on the computed eigenfrequencies of offshore wind turbines
Authors: Reinhardt T , Sastre Jurado C , Weijtjens W , Devriendt C
Published: June 2024

Motivated by the mismatch of measured and computed eigenfrequencies for the second tower mode of offshore wind turbines as well as previous studies examining the influence of including flexible blades in structural models, the need to extend the current integrated model to include flexible blades became apparent. A basic modelling approach which takes the blades as beam elements was implemented in an in-house finite element model of offshore wind turbines and benchmarked for the NREL 5 MW reference turbine with OpenFast. Moreover, the modelling approach was benchmarked with measurements that were obtained during the installation of a Belgian offshore wind turbine. The inclusion of flexible blades is shown to have a significant influence on the second tower mode and is able to reduce the mismatch between measurements and computations. Furthermore, the capability of the inclusion of flexible blades to model the effects of additional parameters is presented. Overall, the need to extend the rotor nacelle modelling in structural models of offshore wind turbines beyond a lumped mass approach is demonstrated.
Comparative analysis of rolling contact fatigue life in a wind turbine pitch bearing with different modeling approaches
Authors: Rezaei Ashkan , Schleich Florian , Menck Oliver , Grassmann Matthis , Bartschat Arne , Nejad Amir R.
Published: June 2024

The load calculation for wind turbines usually does not take pitch bearings into account, and the pitch-bearing internal load distribution is calculated in a decoupled process. In the current study, a coupled wind turbine load simulation considering the pitch bearings is proposed. Internal pitch-bearing load distribution and roller contact fatigue life are compared to a decoupled approach using a high-fidelity finite-element model. Internal pitch-bearing load distribution can be an essential variable in almost all major pitch-bearing failures. Furthermore, rolling contact fatigue is one of the major types of pitch-bearing failure that can represent the bearing service life. The results show that the flexibility of the surroundings has an effect on the contact forces. As a result, the finite element model-based life calculation of the NREL 5 MW turbine predicts a longer rolling contact fatigue life for the bearing than the multi-body system-based one. For the IWT7.5, sample load cases indicate that this behavior is different, leading to the conclusion that the life of the bearing is significantly affected by the stiffness of the bearing and its surrounding components.
Leveraging Vision Transformers for Detecting Porosity in Wind Energy Composites
Authors: Khan AW , Balzani C
Published: June 2024

The structural robustness and operational efficiency of wind turbine rotor blades are crucial for the overall effectiveness of wind energy systems, often constructed with fiber-reinforced polymers (FRPs) and adhesives. However, porosity within these materials poses a significant threat, weakening structural strength and effectiveness. Air pockets lead to stress concentration points, reducing load-carrying capacity and elevating the risk of blade failure, especially under dynamic wind loads. Manual detection of these air pockets is laborious, necessitating automated inspection techniques. Advanced imaging technologies, such as computed tomography (CT) scanning and deep learning, hold promise for identifying and quantifying porosity in FRPs and adhesives, reducing labor while enhancing accuracy. The study introduces a transformer-based model for porosity detection, departing from convolution-based methods, emphasizing the incorporation of global context throughout the network. Leveraging Vision Transformer (ViT) framework advances, the model is applied to porosity segmentation in wind energy blades, showing promising results with limited datasets. The prospect of using larger datasets suggests potential for a versatile solution in segmenting porosity or voids in various wind energy blade composites, including adhesives.
Numerical simulation of stabilisation of floating wind with submerged hydrofoil
Authors: Wang Junxian , Yang Liang , Xing Jingru , Yang Jianhui
Published: June 2024

This research focuses on the optimal design and method of attaching a submerged hydrofoil to an offshore platform to enhance stabilisation. The flapping hydrofoil, exhibiting a hybrid motion combining heave and pitch, is engineered to convert incoming wave energy. It generates a distinctive wake that effectively counteracts incoming waves, thereby reducing wave impact. In this study, a NACA0030-type hydrofoil was strategically positioned between two columns of the platform model. Comprehensive analyses were conducted to evaluate the free-floating platform’s response to regular waves, with a focus on the attached hydrofoil. The results indicate that the hydrofoil significantly reduces the surge motion and drifting speed of the platform, affirming its effectiveness in enhancing stabilisation.
A Hybrid Testing Framework for Wind Turbine Mechanical Components
Authors: Nordtorp F. , Baş E. E. , Gomes C. , Abbiati G.
Published: June 2024

As wind turbines continue to increase in size, hybrid testing is emerging as a key-enabling solution for experimental assessment of their large mechanical components. Hybrid testing is conducted using a hybrid model which combines physically tested and numerically simulated components. In this work, the Kane method is proposed to formulate the equation of motion for the hybrid model of a wind turbine rotor system where one single blade is physically tested. The Kane method allows for formulating the equation of motion of multi-body-dynamic models efficiently and, therefore, it is widely used in state-of-art simulation software. The hybrid model of the rotor is successfully implemented on a single-degree-of-freedom test bench with a cantilever steel beam serving as the physical substructure. The performance of the implemented hybrid model is assessed through a comparison with a pure numerical simulation of the same system. The main finding of the study emphasizes the efficiency of incorporating physically measured restoring force as model parameters while formulating the equation of motion of a hybrid model.
Enhancing CFD-based design of wind turbine blades
Authors: Aa Madsen M H , Zahle F , Sørensen N N , Bottasso C L
Published: June 2024

CFD-based shape design is a state-of-the-art approach in wind energy that can lead to novel shape features. High computation costs have, however, until now hindered a widespread use of the approach. To address this issue, this work investigates two ways to enhance a CFD-based design framework, using a shape study of wind turbine blade tips as a test case. First, a quantification of the speed-up factor (× 3.6) achieved through so-called tailored meshes is presented. Then, a comparison of mesh adaptation strategies is given, further speeding up the procedure (× 2.3). The combined speed-up factor reaches above 8, showing that CFD-based shape design procedures may indeed be accelerated using tailored meshes and a correct mesh adaptation strategy.
Modelling of Wind Turbines as Porous Disks for Wind Farm Flow Studies
Authors: Catania M. , Pomaranzi G. , Fontanella A. , Zasso A.
Published: June 2024

This study explores the use of porous disks as a modeling approach for wind turbines in both wind tunnel experiments and computational fluid dynamics (CFD) simulations. Experimental testing is conducted on a 0.2m diameter disk made of wired mesh, measuring its wake for several yaw angles. The experiment is recreated in a CFD environment based on the porous-medium approach. The CFD model is validated against part of the measurements and it is used to further investigate the disk wake. Results indicate the porous disk wake resembles that of a wind turbine, especially at a downstream distance of four diameters, and the CFD model effectively captures the disk behavior. Discrepancies between experiment and CFD appear further downstream mainly due to the wake recovery process being only partially captured by the CFD model. When the disk has a yaw angle the wake is displaced laterally, but less than in a widely-accepted deflection model, and this could be due to the lack of wake curling.
A stably-stratified atmospheric inflow assimilated to measured mean profiles interacting with a wind park
Authors: Wrba Linus , Bührend Lukas , Englberger Antonia , Dörnbrack Andreas , Wildmann Norman
Published: June 2024

In this paper, a simulation chain is presented. This method comprises the precursor large-eddy simulation (LES) of a stably-stratified atmospheric boundary layer (ABL), the assimilation of the simulated mean velocities to measured wind profiles, and finally a simulation of the generated turbulent ABL flow passing through two wind turbines in a row. The high-resolved precursor simulation with a horizontal grid spacing of 3 m accounts for the characteristic turbulence of the stably-stratified ABL. Using an assimilation technique, the horizontal velocities are adapted accurately to the measured mean wind profiles for the WiValdi wind farm site at Krummendeich. The wakes of two wind turbines in a row with the assimilated inflow is successfully computed. With the simulation chain presented, it is possible to generate realistic atmospheric inflows for wind-turbine simulations with manageable computational effort.
Nacelle modeling considerations for wind turbines using large-eddy simulations
Authors: Amaral R , Houtin-Mongrolle F , Von Terzi D , Viré A
Published: June 2024

Two setups are used to investigate differences between modeling a wind turbine nacelle by means of an actuator-line model (ALM) and a wall-model (WM) using large-eddy simulations. One advantage of the ALM is that it requires a lower mesh refinement, making it less computationally costly. In the first setup, the nacelle is in standalone configuration and the ALM results show a much lower turbulence intensity and a significantly slower wake recovery when compared to the WM cases. In the second setup, the nacelle is in a rotor-nacelle assembly configuration and many variations of the ALM are tested in order to match the results from the experiment addressed in the OC6 task phase III. Contrary to previous findings that the nacelle might affect the turbine loads, this study shows that the improved match with the experiment stems from the increased mesh refinement in the nacelle region rather than the actual presence of the nacelle. Nevertheless, the wake profiles in the near-wake show a very good agreement between the ALM and WM, regardless of the refinement in the nacelle region. These cases also show a higher wake deficit than not using any nacelle at all.
Behavior and mechanisms of Doppler wind lidar error in complex terrain: stable flow case study at Perdigão
Authors: Black A , Lundquist J K , Montavon C , Robey R
Published: June 2024

A numerical experiment is carried out investigating the magnitude of biases in ground-based lidar measurements in complex flow conditions. Biases assessed include those arising from flow curvature and from the interaction of turbulence with the wind field reconstruction (WFR) algorithms used by a WindCube lidars and anemometers. RANS-CFD and WRF-LES simulations were performed for the Perdig˜ao Field Experiment site for a range of atmospheric conditions. Virtual anemometer and lidar data were generated for four locations: two near exposed ridge tops and two in low-speed regions in the valley. The LES data at these four locations show that the scalar inflation terms (the relation between scalar and vector averaged wind speed) for virtual lidar and virtual cups agree very well with predictions using perturbation theory. While the lidar errors vary greatly with location and height, the contribution from the flow curvature tends to be larger than the differences arising from scalar inflation. For one lidar/mast pair near the ridge top, comparisons between simulations and measurements are carried out for a resonant mountain wave event on June 14th, 2017, and for the whole duration of the Perdig˜ao campaign for winds perpendicular to the ridges. The lidar error during the mountain wave, a period of strong stability and low inversion height, is significantly larger than the campaign average. The sensitivity of the lidar error to atmospheric stability is confirmed by the RANS simulations, which suggests strong sensitivity of flow curvature error to stability conditions and to the shape of the wind speed profile near the top of the boundary layer.
Evaluation of wind turbine blades’ rain-induced leading edge erosion using rainfall measurements at offshore, coastal and onshore locations in the Netherlands
Authors: Caboni Marco , Slot Henk M. , Bergman Gerben , Wouters Dennis A. J. , Van Der Mijle Meijer Harald J.
Published: June 2024

The impingement of rain drops on wind turbine blades determines leading edge erosion (LEE) which is a factor driving high maintenance costs. In order to better quantify rain-induced LEE, we carried out detailed rainfall measurements, by means of disdrometers, in conjunction with wind speed measurements. Measurements were performed at three different Dutch sites, encompassing an offshore, a coastal and an onshore location. Based on rainfall and wind speed measurements, and assuming a virtual 15 MW wind turbine, we estimated the blade’s LEE using a fatigue-based model. Developed by means of different published rotating arm erosion data, our fatigue model relates the measured rainfall characteristics to the LEE incubation period, here assumed as the leading edge protection (LEP) system’s end of life. Assuming a polyurethane LEP system, results indicate that the blades’ incubation period is around 3.9 years at the offshore location, 6.6 years at the coastal location and 8.3 years at the onshore location. These results are connected to the higher wind speeds during rainfalls, and higher occurrences of very intense rainy events which, according to the measurements, progressively occur at the onshore, coastal and offshore locations.
Research updates on filter units for secondary stabilisation of offshore wind farm power cables
Authors: Pistani Fabrizio , Griffits Terry , An Hongwei , Tong Feifei , Draper Scott
Published: June 2024

This paper presents an experimental and numerical campaign that was carried out to improve the understanding of the performances of filter units, or rock bags, when used as mean of secondary stabilisation for subsea power cables in offshore wind farms. The main parameters of influence are discussed. The capabilities of the experimental facility are presented as well as the experimental approach with a description of the cases tested. The numerical models are also described. Finally some of the findings about the main mechanisms of instability are presented.
Design of a Floating Vertical Axis Wind Turbine for Wind-Wave Basin Experiments
Authors: Hossain Md Sanower , Escalera Mendoza Alejandra Stefania , Ahsan Faraz , Todd Griffith D. , Brownstein Ian , Strom Ben , Frye Alex
Published: June 2024

This paper presents the design and manufacturing of two novel small floating Darrieus vertical axis wind turbines (VAWT) developed for a wind-wave basin test campaign. As with typical designs, the rotor design needed to satisfy the traditional structural safety requirements (such as strain, deflection, resonant-free dynamics) from design standards along with other manufacturing and assembly constraints. In addition, for this particular design, some special conditions are present as the facility (the wind-wave basin itself) and use of existing Floating Offshore-wind and Controls Advanced Laboratory (FOCAL) semi-submersible floating platform (originally designed for HAWT test) imposed an additional set of design requirements including wind speed and size constraints, and specific, target overturning moments and rotor mass. Addressing all these constraints (facility, existing hull, structural safety, and manufacturing) presented a challenging design task in this case, thus the focus of this paper is presenting the design approach and results leading to final designs satisfying all these competing requirements. Using the presented design process, two Darrieus troposkein-shaped vertical axis wind turbines (two-bladed and three-bladed versions) were designed and manufactured, after ensuring compliance with all the design requirements. The presented study can aid researchers interested in developing similar floating turbine test campaigns.
A dynamic-simulation based workability and accessibility combined method for systematic analysis of floating wind operations
Authors: Moreno Carlos Pérez , Lange Johannes , Snedker Thor , Bayati Ilmas
Published: June 2024

This work aims at providing a new methodology to assess combined workability and accessibility (W&A) of a floating offshore wind turbine, that is, the capability to transfer technicians to perform maintenance work. The proposed approach accounts for site-specific met-ocean conditions and industry-typical W&A limits by virtue of significant wave height, peak wave period, and wave heading, in contrast to only considering wave height, as currently done to take operation and maintenance decisions. A multi-body model of the VolturnUS-S 15 MW floating platform with a Service Operation Vessel (SOV) is used to compute the accessibility based on time-domain simulations and motion-compensated gangway limits. An iterative algorithm is implemented to find the maximum accessible wave height for each period and wave heading. Then, based on the limiting accessibility, single-body hydro-aero-elastic simulations are used to compute the nacelle accelerations, in order to estimate workability. The accessibility is hereby found to be the most limiting factor, with significant changes depending on the peak wave period and wave heading.
Investigating North Sea Precipitation Variability: Implications for Offshore Wind Energy Siting and Condition Assessments
Authors: Ivanova Tsvetelina , Porchetta Sara , Buckingham Sophia , Helsen Jan , Van Beeck Jeroen , Munters Wim
Published: June 2024

Rain-driven wind turbine blade erosion, particularly in offshore locations, has been observed as early as within 5 to 7 years of turbine operation, which is below the lifetime expectancy design age of 20 to 25 year. Due to the harsh atmospheric conditions offshore, the preservation of wind turbine blade integrity has become a fundamental necessity. To address this challenge, we compare precipitation maps from two distinct sources (satellite data and a reanalysis product) over 12 years in the region of the North Sea, and we pursue insights into local weather patterns through temporal analysis. This integrated approach enhances the understanding of offshore conditions by focusing on precipitation and wind speed data analysis in time and space. This enables more efficient wind farm planning, operation and maintenance, as well as wind farm siting via informed decisions that account for the risk of rain-driven blade erosion and allow for mitigation measures.
Cost optimization of dynamic cable lazy wave configurations for floating offshore wind turbines
Authors: Syed Huzaifa , Muggiasca Sara
Published: June 2024

This research aims to design a low-cost dynamic cable lazy wave configuration at different curvature factors by adopting an integrated approach to optimally size the length of different sections of the dynamic cable accounting for maximum allowable tension, maximum allowable curvature, minimum allowable sag position and maximum allowable hog position. The research explores trade-offs associated with the increase in costs as curvature factor decreases. The configuration is subjected to Near, Far and No offset scenarios to analyse the impact on costs and its performance. The assessment includes determining configuration costs and optimal lengths at different curvature factors for each scenario. Observations reveal that the hang-off point consistently experiences the highest curvature across the arc length in all configurations and scenarios. Optimal configurations for Far scenario outperform configurations designed for No offset scenario when subjected to the remaining two scenarios. Optimal configurations of Near scenario failed to adhere to the maximum allowable curvature limit when subjected to Far and No offset scenarios. The study highlights the sensitivity of the curvature factor to the ratio of lengths of each section in the configuration. These results indicate that a configuration designed for Far offset is more likely to perform well under all scenarios due to its unique section length ratios. The results also portray the possibility of a fit configuration with lower number of buoyancy modules.
Reduced-order modelling of floating offshore wind turbine: Aero-hydro-elastic stability analysis
Authors: Meng Fanzhong , Lio Alan W.H. , Riva Riccardo
Published: June 2024

A reduced-order aero-hydro-elastic analysis tool for performing the stability analysis on floating offshore wind turbines is presented. In this work, a high-order non-linear aero-elastic model initially developed for onshore wind turbines is extended by utilizing a super-element body, which models the floating platform, the mooring system and the hydrodynamic contributions. The turbine structure is modelled by a Finite beam Element Method, and the aerodynamic loads are modelled by the Blade Element Momentum method coupled with a Beddoes-Leishman type dynamic stall model in a state-space formulation. The linearization is performed around steady state equilibrium at any given mean wind speeds, rotor speeds and collective blade pitch angles utilizing Coleman transformation to remove the periodic terms. The order reduction is based on two projections to reduce the number of structural states and aerodynamic states separately using the structural modal project matrix and the aerodynamic shape functions. Concurrently, we investigate the effect of unsteady aerodynamic states on the stability analysis of a floating wind turbine. The results show the low-order aero-hydro-elastic model expands the scope of numerical tools available for conducting structural modal analysis and aero-hydro-elastic stability analysis on floating wind turbines.
Techno-Economic Analysis Incorporating Intelligent Operation and Maintenance Management: A Case Study of An Integrated Offshore Wind and Hydrogen Energy System
Authors: Li Honglin , Li Mingxin , Carroll James , Zhang Jie
Published: June 2024

In this study, a comprehensive examination of wind-hydrogen energy systems is conducted through detailed techno-economic analysis and sensitivity analysis. The primary emphasis is on optimizing operation and maintenance (O&M) strategies and understanding the impacts of market dynamics. Utilizing Monte Carlo simulations, we first identify the optimal intelligent O&M plan, leading to significant reductions in annual O&M costs ($39.9/MW) and downtime (6.59 days per turbine) compared to conventional methods. The incorporation of prognostics and health management (PHM) further demonstrate a notable impact, leading to a 9.9% reduction in O&M costs and a 10.7% decrease in downtime. In the broader context, these outcomes translate into reductions in the O&M expenditures, total lifecycle costs of the system, Levelized Cost of Hydrogen (LCOH) and Levelized Cost of Energy (LCOE) by 3.9%, 0.75%, 2.4%, and 1.8%, respectively, highlighting the economic benefits of intelligent O&M strategies. The extensive sensitivity analysis, encompassing 54 scenarios, delves into the effects of maintenance strategies, hydrogen prices, wind energy share, and subsidies, revealing nuanced insights into cost savings and operational efficiencies. Notably, intelligent maintenance and favorable hydrogen subsidies effectively reduce LCOH, while the interplay between wind energy share and hydrogen pricing influences system profitability and efficiency, underscoring the complex dynamics at play in optimizing renewable energy systems.
Incorporation of floater rotation and displacement in a static wind farm simulator
Authors: Riva Riccardo , Pedersen Mads M. , Pirrung Georg , Bredmose Henrik , Feng Ju
Published: June 2024

Thanks to the development of several wake models, recent years have seen a huge development of static wind farm simulators. As new wind farms are planned for deep waters, there is a need to extend these tools to account for the floater rotation and displacement. In this work, we have addressed this task by selecting a reduced set of environmental conditions and generating a database from medium-fidelity simulations, whose computational cost has been reduced by developing a new static solver. Then, we trained neural networks and embedded them in PyWake via a model-agnostic interface. Finally, the wake deflection due to rotor tilt has been modeled by extending a state-of-the-art model. The results indicate that the rotor can move downwind by up to 10% of the diameter and rotate in tilt by 3° at rated wind speed.
Exploring memory mechanisms for friction fatigue in vibratory pile driving
Authors: Tsetas Athanasios , Tsouvalas Apostolos , Metrikine Andrei
Published: June 2024

This paper studies the mechanism that leads to the reduction of frictional soil reaction forces during pile driving, termed friction fatigue. We focus on axial vibratory driving, an environmentally friendly monopile installation method, and examine two friction fatigue formulations, i.e. a penetration-based and a cyclic memory mechanism. Friction fatigue plays a pivotal role in pile drivability and post-installation bearing capacity for piles installed via axial vibratory driving. Through numerical analyses and validation against field data from onshore experiments, the efficacy of these memory mechanisms is assessed. The results reveal that the proposed cyclic memory mechanism provides consistently more accurate predictions than the corresponding penetration-based approach, offering a promising option for modelling friction fatigue in vibratory driving. This study advances our understanding of friction fatigue in the context of vibratory driving for offshore monopile installation, emphasizing the need for further numerical and experimental works in this topic.
Spatial Optimization for Energy Island Location and Cable Routing Considering Offshore Zoning
Authors: Verikios G. , Janssen F. , Satish A. , Liu Y
Published: June 2024

The energy hub concept presents a compelling opportunity to channel electricity from offshore wind farms to the grid, facilitating cross-border energy trading and conversion. However, one of the main challenges lies in the strategic identification of a suitable energy island location and the establishment of an interconnected cable routing path. Part of the complexity arises from the need to navigate offshore zoning regulations and accommodate various spatial uses within the offshore area. This paper exhibits a case study to explore the spatial optimization for a potential offshore energy hub in the North Sea. It aims at finding out an optimal spatial configuration of the offshore energy hub, such that the island location and the associated cable routing do not infringe upon keep-out zones while strategically positioning the hub closer to high-capacity wind farms. To achieve this goal, detailed geographical data incorporating offshore zoning information is leveraged for spatial optimization. The Dijkstra’s algorithm is then applied to identify the optimal island location and cable routing path. The effectiveness of this spatial optimization methodology is demonstrated through a case study involving offshore wind farm sites in the North Sea. Given the real geographical data, simulation results underscore the efficacy of the Dijkstra’s algorithm in determining the optimal energy hub layout. In particular, an optimal spatial design is achieved, based on cable lengths, asset capacities, offshore zoning and island/platform location for a potential offshore energy hub in the North Sea while ensuring compliance with keep-out zoning regulations.
Corrosion fatigue analysis of NREL’s 15-MW offshore wind turbine with time-varying stress concentration factors
Authors: McAuliffe James , Baisthakur Shubham , Broderick Brian , Fitzgerald Breiffni
Published: June 2024

Over the last twenty years, significant development in wind turbine technologies has led to a dramatic increase in the scale of wind turbines with many now beginning to be installed in offshore locations. Consequently, modern multi-megawatt offshore wind turbines are exposed to increased cyclic loading in addition to an increased risk of corrosion attack. The combination of these two factors may result in wind turbine support structures becoming increasingly vulnerable to fatigue corrosion. The objective of this work is to investigate the impact of material thinning in fatigue-prone areas with respect to fatigue loading and ultimately to examine the potential repercussions on the lifespan of wind turbine support structures. To achieve this, a composite model is constructed coupling results from a multi-body structural dynamic model with time-varying Stress Concentration Factors (SCF) obtained from a finite element model (FEM) of NREL’s 15-MW monopile-based offshore wind turbine. The nonlinear aeroelastic multi-body dynamic model of the wind turbine is used to generate stress time histories for a set of environmental conditions based on the operational conditions of the wind turbine. The finite element model of the wind turbine is then used to identify fatigue-vulnerable regions in the wind turbine support structure and calculate SCFs for these specific areas. The integration of SCFs into the fatigue calculations reduced the lifespan of the turbine tower by a factor of 4, demonstrating the importance of precisely modelling such local stress concentrations for effective fatigue analysis. A novelty of this work arises in the ability of the finite element model to update the SCFs of the fatigue-prone areas over time as corrosion-induced wastage alters the substructure’s geometry, thereby inducing a global redistribution of stresses. A fatigue analysis is carried out availing of the SCFs which vary annually in addition to the stress-time histories produced by the multi-body dynamic model. The results illustrate that the phenomenon of corrosion thinning induced an 8.9% reduction in the fatigue life of the wind turbine tower, thus emphasising the significant importance of proactive maintenance strategies to mitigate the impact of corrosion.
Development of a numerical model for floating Vertical Axis Wind Turbines
Authors: Ghigo Alberto , Sirigu Massimo , Collu Maurizio , Bracco Giovanni
Published: June 2024

Vertical Axis Wind Turbines (VAWTs), which are primarily used in small-scale applications, such as in remote or urban areas, could be particularly promising for floating offshore wind projects, where they offer benefits like increased stability, lower maintenance costs, and the potential for closer spacing due to lesser aerodynamic wake effects. However, to be competitive with floating HAWTs, scaling up VAWTs size is an urgent necessity to facilitate large-scale industrialization. To achieve this goal, the development of tools capable of assessing VAWT performance in challenging offshore environments is crucial. This work aims to introduce a time domain model of a floating VAWT, developed within the Matlab-Simscape environment. The model comprises a floating platform, a wind turbine, and a mooring system. The aerodynamics is simulated using the Double Multiple Stream Tube method, which relies on Blade Element Momentum (BEM) theory. Hydrodynamics is modelled using WEC-Sim, a Simscape library developed by NREL and SANDIA. Among the main advantages of the model are the flexibility and low computational time. The article presents a case study involving a semi-sub foundation, the OC4-DeepCwind, supporting a Darrieus H-rotor VAWT. The results obtained are compared with those from QBlade Ocean, an open-source tool developed by TU Berlin, demonstrating a good agreement between the two codes.
Influence of wave spreading on offshore wind turbine design: IEA 15-MW scenario
Authors: Ryan Gerard V. , McAdam Ross A. , Adcock Thomas A. A.
Published: June 2024

Offshore ocean waves are directionally spread, whereby the propagation of energy travels in different directions. Despite this multi-directionality, the use of 3-dimensional wave models for loading on fixed offshore wind turbines has been limited. This is partially due to the common assumption that uni-directional sea-states are conservative within a design philosophy. This may not always be true given that in operating conditions the amount of aerodynamic damping in the side-side direction is much lower than the fore-aft direction. This paper aims to address this issue by providing the influence of wave spreading on various offshore wind turbine design scenarios: fatigue, ultimate and service limit state design. This study demonstrates that wave spreading indeed results in more fatigue damage for operating load cases. Despite this, the overall fatigue and ultimate limit state utilisation is still reduced when a wave spreading is adopted.
Hydrodynamic Response of Semi-Submersible FOWT Floaters: A Numerical Investigation of Wave and Mooring Parameter Dependencies
Authors: Mian H H , Siddiqui M S , Stoevesandt B , Ullah H , Machot F A
Published: June 2024

Floating wind turbines have enormous potential in harnessing high wind speeds in deep ocean locations. Compared with bottom-fixed technology, the latter is limited by the depth to which it can be installed. These turbines are designed to be deployed in deep waters and rely on specialized floaters such as spar buoys, semi-submersibles, and tension leg platforms to provide structural support. These floaters are tethered to the seabed using mooring lines, which regulate their movements and maintain stability. However, the existing literature lacks in-depth studies that comprehensively analyze how waves and mooring lines impact the motion of a semi-submersible floater. To address this gap, computational fluid dynamics (CFD) simulations are conducted using the overset methodology to replicate the actual loads experienced by semi-submersible floaters accurately. The study accurately predicts the six degrees of freedom (DOF) of the platform’s motion. The mooring lines are modeled using static or moving boundaries, and their interaction with the floater surface has been modeled using contact forces. The approach can simulate the impact of waves and mooring lines on the floater’s motion. The study uses the specifications depicted in the OC5 semi-submersible platform with mooring in test conditions and compares it with available experimental data to validate the numerical model. Once validated, the model is used to explore the hydrodynamic behavior of the floating structure across a range of waves characterized by varying amplitudes, periods, and directions. Similarly, in the case of the mooring lines, variations in critical parameters such as stiffness, pre-tension, and free length are introduced. This systematic manipulation of parameters enables a comprehensive investigation into their respective impacts on the dynamic response and motion of the floating platform.
Surrogate-assisted optimization of floating wind turbine substructure
Authors: Baudino Bessone M , Singh D , Kalimeris T , Bachynski-Polić E , Viré A
Published: June 2024

This paper presents a surrogate-assisted optimisation approach to speed up the substructure analysis in the preliminary design phase. The approach consists of replacing the radiation-diffraction analysis in a frequency domain analysis model for floating wind turbines with a data-driven surrogate model predicting the hydrodynamic coefficients for parameterised substructure geometries. This procedure is compared with the reference approach of estimating the hydrodynamic coefficients via radiation-diffraction analysis. A representative use case of assessing the trade-off between minimising the capital cost and reducing the wave-induced nacelle acceleration standard deviation for a semi-submersible substructure is presented. The accuracy of the surrogate model is found to increase significantly up to training datasets consisting of 400 designs and less noticeably afterwards. For a dataset consisting of 400 designs, the mean error on the prediction of the hydrodynamic coefficients and the error at one standard deviation from the mean are generally below 7% and 10%, respectively. For the same dataset size, the mean error on the most probable maximum wave-induced pitch over a 3h storm period is below 17%, while the error at one standard deviation from the mean is lower than 27%. The same values for the most probable maximum nacelle acceleration are under 7% and 12%, respectively. The surrogate model can capture the trade-off between the two objective functions, and the optimal designs identified with the surrogate model generally follow the same trend as those obtained with the reference model. However, relying on the surrogate model for performing the analysis of the substructure introduces local minima in the objective function that cause a discrepancy between the optimal designs identified with the surrogate model and those identified with the reference model.
Assessing the impacts of wakes on floating wind farms with shared anchors
Authors: Coughlan Katherine , Mahfouz Mohammad Youssef , Lozon Ericka , Arwade Sanjay
Published: June 2024

This paper examines wake effects for floating wind farms with shared anchors. Three 20-turbine farms are examined: a grid-formation baseline with no shared anchors, a farm based on 3-line anchors, and a farm based on 6-line anchors, governed by a wind turbine spacing of 8 rotor diameters. The IEA 15 MW reference turbine on the UMaine semisubmersible platform was used with a taut mooring system in deep- water depths representative of U.S. west coast lease areas. A steady-state wake model showed that, when evaluating a sweep of wind headings, the baseline design had the lowest wake losses, with a value of 11.7 %, followed by the 6-line at 12.9% and the 3-line at 13.8%. Dynamic simulations were run in FAST.Farm to analyse the effects of wakes on mean anchor loads for wind headings that showed significant wake losses. The baseline farm showed the largest anchor load reductions due to wake effects (up to 16%), followed by the 3-line farm (up to 8%), and the 6-line farm, which showed relatively consistent load magnitudes on the 6-line anchors across all headings.
Coupled modeling of wake steering and platform offsets for floating wind arrays
Authors: Lozon Ericka , Hall Matthew , Mahfouz Mohammad Youssef
Published: June 2024

Wake effects are a key challenge in the design and analysis of wind farms. For floating wind farms, the platforms offset under the aerodynamic loading of the turbine and are constrained by mooring systems that can vary significantly in allowable offsets. When considering wake steering, the crosswind offset of the turbine can counteract the lateral deflection of the wake. This work presents a tool to efficiently model the coupled impacts of wake steering and platform offsets for floating wind farms. The tool relies on the frequency-domain wind farm model RAFT and the steady-state wake model FLORIS. A verification with FAST.Farm is presented, then the tool is applied to a simple two-turbine case study. A range of mooring systems with increasing platform offsets and varied yaw misalignment angles are considered while comparing the impact on turbine power. Additional sensitivities to turbine spacing and mooring system orientation are explored. The results show that there is a least-optimal watch circle width for downwind turbine power production that varies with yaw misalignment angle and turbine spacing. Additionally, the turbine offsets under yaw-misaligned conditions vary significantly depending on mooring system orientation relative to the rotor plane, which in turn impacts the optimal misalignment angle. These results highlight the importance of including floating platform offsets and mooring systems in the evaluation of wake steering strategies for floating wind arrays.