bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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.
Reference dynamic power cable of floating offshore wind turbine for thermal and simple fatigue evaluation
Authors: Abrahamsen A B , Faria B R , Lund R S , Verelst D R , Roques J , Hochet M , Dykes K 
Published: June 2024

Abstract
With the increased interest in floating offshore wind turbines, there is an increased focus on evaluating the lifetime of the auxiliary systems, such as the mooring lines and the dynamic power cables, because these systems are in-mature compared to bottom-mounted offshore wind farms. This paper proposes a conceptual reference dynamic power cable suitable for the 15 MW NREL reference turbine mounted on the UMaine floater installed at 82 m water depth. This provides a basis for discussing the life evaluation of dynamic cables obtained from aeroelastic simulation of the floating offshore wind turbine platform exposed to the environmental conditions of the South Brittany site in France. An electromagnetic-thermal finite element simulation is used to determine the current capacity of the cable and aeroelastic simulations are used for a simple assessment of the main failure modes as maximum cable tension, minimum bending radius and fatigue damage accumulation.
Dynamic Thermal Behavior of Natural Ester Liquid-Filled Transformer for Offshore Wind Turbine in Cold Climate
Authors: Al-Abadi A , Gamil A 
Published: June 2024

Abstract
The current study presents a dynamic thermal model (DTM) which accounts for variation of liquid properties with temperature to predict the development of temperature pattern of the entire transformer for offshore wind application during energizing process. The DTM is benchmarked against dynamic heat run test which is applied on a natural ester filled transformer designed for offshore wind application. The transformer is equipped with fiber-optic sensors (FOS) to observe the temperature distribution of the winding and the liquid during heating up and cooling down processes. The investigations involve in-depth analysis of the thermal behavior of the winding and liquid at different locations to give physical interpretation of the dynamic thermal response of different transformer components during dynamic loading. The results are further validated with transient computational fluid dynamics (CFD) simulations. Eventually, the study gives guidelines and recommendations of dynamic loading of transformer filled with natural ester in cold climate.
Experiments on Interaction between Six Vertical-Axis Wind Turbines in Pairs or Trios
Authors: Jodai Yoshifumi , Tokuda Haruki , Hara Yutaka 
Published: June 2024

Abstract
The interaction between six closely placed vertical-axis wind turbines (VAWTs) in a parallel-pair arrangement (layout 1), a staggered-pair arrangement (layout 2) and a parallel-trio arrangement (layout 3) were investigated. Six miniature wind turbine models were used in the wind tunnel experiments. The rotor gap g
1 within each turbine pair or trio is set fixed values. In the layout 1, three paired turbines are in line perpendicular to the main stream. In the layout 2, two paired turbines are in line perpendicular to the main stream on a front rail and remaining paired turbines are on a rear rail. In the layout 3, two trios of turbines are in line perpendicular to the main stream. Increases in the averaged turbine power up to 106% of the single turbine power PSI
with the decrease in an inter-cluster gap g
2, have been demonstrated in the layout 1. The power of a downstream central turbine pair significantly decreases with increasing a streamwise spacing s in the layout 2. In the layout 3, the averaged turbine power reaches 0.95PSI
for Case A. Reducing an inter-cluster interval (g
2 or s) improves a wind-farm performance in a unit footprint area in all the layouts tested.
Numerical Investigation of Atmospheric Boundary Layer Control in Wind Farms with Multirotor Systems
Authors: Martins Flavio A. C. , Ferreira Carlos S. , Van Zuijlen Alexander 
Published: June 2024

Abstract
This study investigates the near-wake aerodynamics of actuator disks (multirotor devices) paired with lift-generating devices (rotor-sized wings, dubbed ABL-control devices). These rotor-sized wings generate vortical structures that enhance the vertical momentum flux from above the atmospheric boundary layer (ABL) into the wind farm, aiding wake recovery. Using three-dimensional actuator surface models based on Momentum theory, the study employs steady-state Reynolds-averaged Navier–Stokes computations in OpenFOAM to address the current proof-of-concept model. The numerical results of this paper are validated with a comparison against the experimental results of a scaled multirotor device in a wind tunnel. The performance of the ABL-controlling devices is evaluated through the wind farm’s total pressure and vertical momentum flux. Results indicate that ABL-control significantly accelerates wake recovery, with designs featuring two or four ABL-control devices achieving 95% total pressure recovery at x/D ≈ 5, one order of magnitude shorter than the baseline setup without ABL-control.
Validation of the structural response of a 70kW VAWT
Authors: Malcolm DJ , Ajala-Inyang O 
Published: June 2024

Abstract
This paper describes a project for predicting and measuring the structural response of a 70 kW vertical axis wind turbine (VAWT), while offering insights for optimizing efficiency and ensuring longevity. We employ the traditional frequency response approach and model the turbine behavior using its stationary modal shapes. Results for three key sensor locations – lower central mast bending, upper blade flapwise bending, and central horizontal arm out-of-plane bending – reveal that the codes accurately predict the critical resonance and capture the dominant harmonic amplitudes. In addition, it is shown how a statistical treatment of the steady state solution can lead to predictions of the fatigue cycle distribution enabling accurate life predictions. The program demonstrates the potential to significantly improve the design and operation of VAWT using simple, steady state, simulation codes for capturing VAWT aerodynamics. The model demonstrates sufficient accuracy while offering computational efficiency compared to more complex models.
Lift-Induced Wake Re-Energization for a VAWT-Based Multi-Rotor System
Authors: Broertjes T J , Bensason D , Sciacchitano A , Ferreira C 
Published: June 2024

Abstract
This study explores the performance and near-wake dynamics of a VAWT-based Multi-Rotor System in both its original configuration and in the presence of external lift-generating devices, specifically employed for wake control operations. The wake of a scaled VAWT-based MRS was measured in a wind tunnel using Particle Tracking Velocimetry. Lift-generating devices, including a 3-element cascading wing on top and a single-element wing in the middle of the MRS, were used to enhance wake control and deflection. Measurements in the near-wake revealed notable differences between configurations with and without these devices. Without them, the wake remained concentrated in the actuator surface’s projected downstream area, with minimal crossflow diffusion. Conversely, the configuration with lift-generating devices exhibited significant wake deformation, including axial expansion and lateral contraction, promoting streamwise momentum recovery. As a result, increased power recovery was found downstream of such a system compared to the clean MRS. These findings underscore the potential of such systems, particularly when equipped with lift-generating devices, to manipulate wake dynamics and enhance wind farm efficiency, thereby advancing innovative wind energy solutions.
Experimental study of the impact of blade-tip mounted rotors on the X-Rotor vertical-axis wind turbine
Authors: Bensason David , Sciacchitano Andrea , Ferreira Carlos 
Published: June 2024

Abstract
The Horizon 2020 European Commission-funded project - X-ROTOR - proposes a radical rethink of the traditional vertical-axis wind turbine geometry. The X-Rotor vertical axis wind turbine relies on blade-tip mounted rotors, referred to as secondary rotors, for power generation and takeoff. This study examines the aerodynamic effects of secondary rotors on a scaled X-Rotor model’s loading in an open-jet wind tunnel. Particle image velocimetry measurements are taken at two cross-stream planes within the volume of rotation of a scaled turbine model at two phase-locked positions. The measurements are compared with cases without secondary rotors present to understand the local impact of the blade-tip mounted devices on the wake and vortex strengths. The results indicate an accelerated turbulent diffusion of the trailing tip-vortex of the X-Rotor, and the subsequent local in-plane velocity gradients induced by the trailing tip-vortex are diminished. These insights and experimental database contribute to the development and validation of numerical models of the X-Rotor with blade-tip mounted rotors.
NREL 15-kW: An Advanced Horizontal-Axis Reference Turbine for Distributed Wind
Authors: Gupta A , Bortolotti P , Summerville B 
Published: June 2024

Abstract
Distributed wind energy can play a significant role in the renewable energy landscape. A recent study conducted by the National Renewable Energy Laboratory (NREL) identified the lack of availability and utilization of reference wind turbine models as a major hindrance in the development of the distributed wind energy technology sector, even though such models are widely used in offshore and land-based wind research. Therefore, NREL is developing three reference wind turbine architectures, also called archetypes, for distributed wind energy applications. This paper describes the detailed design and modeling of the first of the three reference turbine archetypes, called the NREL 15-kW turbine. It is a passive-yaw, upwind turbine with a rated power of 15 kW.
Using intrusive approaches as a step towards accounting for stochasticity in wind turbine design
Authors: Branlard E. , Frontin C. , Maack J. , Laird D. 
Published: June 2024

Abstract
Current wind turbine design methods require tens of thousands of time-domain simulations and use different random seeds to account for the stochasticity of the environmental conditions. The account of stochasticity is nonintrusive because the sampling method calls a deterministic model multiple times without changing its underlying equations. In this work, we investigate and demonstrate using simple proof of concepts how intrusive approaches can be used to directly account for stochasticity in the equations representing a mechanical system. Our long term goal is to apply such methodology to the design of wind turbines without requiring an excessive number of simulations. Intrusive methods manipulate stochastic variables directly to provide the probability density functions (PDFs) of the states and outputs at any time as functions of the PDFs of the inputs. We illustrate how different methods can be used with a reduced-order model of a wind turbine with one degree of freedom and for linear and nonlinear models. We discuss how the methods can be extended and what it will take to apply them to a level of fidelity similar to current state-of-the-art wind turbine design tools.
Power Density Analysis of Wind Turbine Main Bearing Units by Holistic Optimization of Material, Manufacturing and Design of the Main Shaft
Authors: Hollas Christian , Jacobs Georg , Züch Vitali , Röder Julian , Reinisch Niklas , Gouverneur Moritz , Bailly David , Babashahi Maryam , Gramlich Alexander 
Published: June 2024

Abstract
Given the continuous increases in wind turbine (WT) rated power and size, the nacelle weight and logistic handling costs increases significantly. To support heavier nacelles, stronger towers are needed which again increases material costs, so a need for nacelle power density increase arises. One solution to this problem is to increase the power density of the cast or forged WT main shaft. The power density in cast main shafts is limited by the low tensile strength of cast iron. High tensile strength steels, which theoretically increase power density, are used in state-of-the-art forged main shafts. However, their inner shaft diameter is kept small to reduce drilling costs. Since the loads of WT main shafts are dominated by the bending moments of the rotors, a high section modulus corresponds to a high power density. Material near the centre of the shaft therefore decreases the shaft power density. Hollow forging combines high tensile strength steel with a variable inner shaft diameter, enabling shaft designs with increased power density. Additionally, the use of air-hardening ductile (AHD) steel eliminates the need for costly heat treatment if the wall thickness is thin enough. The paper presents a holistic system model for the predesign of main bearing units (MBU) considering various materials and manufacturing methods. The model enables a feasibility assessment of hollow forged main shafts by comparing the resulting MBU weights across a wide range of WT power ratings. The MBU is selected instead of solely analysing the main shaft to account for the bearing and bearing housing weights, which depend on the main shaft geometry. The results show increased MBU power density of up to 23% for hollow forged shafts compared to forged shafts of the same material. Furthermore, when the shaft is hollow forged from AHD steel, the increase is even greater, up to 52%.
Floaters upscaling for multi-megawatt floating wind turbines
Authors: Di Carlo S , Fontanella A , Bontumasi S , Pietro F Di , Ambrosini S , Muggiasca S , Belloli M 
Published: June 2024

Abstract
The floating wind industry requires wind turbines with increasing power ratings, which will require bigger platforms. However, few floater concepts are publicly available for numerical simulation of future wind turbines. To overcome this limit, this work proposes a fast and straightforward upscaling methodology to upscale already available floating platforms to greater wind turbine power ratings. The methodology does not aim to optimize the floater design, but it can generate realistic floater data for preliminary numerical simulations. The methodology is applied here to four floaters: a semisubmersible, a barge, a TLP and a spar. The platforms are upscaled for a 15 MW wind turbine and a specific deployment site. The upscaling methodology is adapted for each floater since some differences arise from one platform to the other. Whenever possible a comparison with already existing 15 MW substructures is proposed and commented.
How do technological choices affect the economic and environmental performance of offshore wind farms?
Authors: Kainz S , Guilloré A , Bottasso C L 
Published: June 2024

Abstract
The ongoing energy transition towards fully sustainable energy systems requires designing wind farms looking beyond the sole levelized cost of energy, in order to concurrently ensure not only the economic profitability but also the environmental friendliness of future plants. Within this new approach to design, it becomes necessary to understand the effects that various possible technological choices have on both the economic and the environmental performance of wind farms. This study presents a framework designed to support these coupled economic-environmental assessments. The capabilities of the code are showcased by analysing the impact of different choices in terms of support structure type, specific power, tower height, powertrain type, and array and export voltage level for an exemplary offshore farm, chosen here as the IEA Wind 740-10-MW Reference Offshore Wind Plant with irregular layout. While the effects of many technological choices on the cost of energy are already well understood by industry, the present analysis shows that — at least in this specific case — climate change impacts are mainly driven by steel production, due to the massive amount of required material, but also, interestingly, by vessel activities. A low specific power, tall towers, and a high export cable voltage appear to offer the greatest potential for the concurrent improvement of the environmental and economic performance of the plant.
The Petiole of the Miriti Palm: A sustainable material for wind turbine blades?
Authors: Gomes I. Dos S. , Vaz J. R. P. , Wong J. C. H. , Wood D. H. 
Published: June 2024

Abstract
The Miriti Palm (Mauritia flexuosa) grows abundantly in the Amazon Region of Brazil. The petiole (PMP) that supports the leaves, has a density of about one-half of Balsa wood (BW), which is used in the manufacture of wind turbine blades. A further possible advantage of PMP is that harvesting does not kill the palm tree, in contrast to the harvesting of BW. Because the mechanical properties of PMP have not been measured, we determined the shear and tensile properties of 16 samples of PMP and BW to allow a preliminary assessment of PMP as a possible material for blades. The absolute shear and tensile strengths for BW are higher, but specific properties (normalized by the density) are similar and can favour PMP. Direct substitution of BW by PMP would reduce the weight of a typical large blade by around 2%.