bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis of thiophene-isoindigo receptor small molecules and its application in photodetectors
Authors: Guan Sheng , Guo Pengzhi
Published: June 2024

Organic photodetectors (OPDs) have attracted wide attention from researchers on account of their characteristics such as easy to manufacture, low cost, lightweight, and flexible detectors. Many efforts have been made to improve the performance of OPDs. Scientists have made many efforts to improve the performance of organic photodetectors. Among them, narrow-band-gap organic photoelectric functional materials with wide spectral response exhibit application prospects in photoelectric detection. In this paper, a series of narrow-band-gap thienoisoindigo receptor small molecules were synthesized by using thienoisoindigo, and electron deficient terminal octyl cyanoacetate, 3-ethylrhodanine, and 2-(3-ethyl-4-oxothiazolidine-2-ylidene) malonitrile as receptor units, and 3-dodecylthiophene as donor unit, The photodetector with wide spectral response and high detection rate is fabricated using a Bulk Heterojunction (BHJ) structure.
Study on the microstructure and mechanical properties of W-wire/TiBe, ZrBe, and ZrTiBe alloy composites
Authors: Chu Shaochen , Wang Jinhe , Zhang Bo , Li Zhengkun , Fu Huameng , Li Hong , Zhu Zhengwang , Zhang Haifeng
Published: June 2024

The microstructure and mechanical performance of W wire/Ti70Be30, Zr65Be35, and Zr37.5Ti26Be36.5 alloy composites were investigated in this study using X-ray diffractometer, scanning electron microscopy, and mechanical universal testing machine. These composites were prepared through the melt impregnation method under optimized processing conditions. The results show that the compressive strength of the three composites is all above 2600 MPa. The Ti70Be30-W composites diffuse violently at the interface, the W-Ti phase is formed at the interface, and the cracks of the composites under the action of applied load show a stepped pattern. The Zr65Be35-W composite reacts violently at the interface, resulting in a W2Zr interfacial product, which adheres to the surface of the W filament and presents a continuous interfacial reaction layer. When subjected to external load, the crack will expand rapidly along the interfacial reactive layer. The addition of Ti in Zr37.5Ti26Be36.5-W composites effectively inhibited the W-Zr reaction, the interface reactant W2Zr disappeared, and the W-Ti interface product presented a discontinuous interfacial reaction layer on the surface of the W filament, and the material split under the action of external load, and the crack showed step-like propagation.
Hydrodynamic characterization of the surfacing attitude of the manned deep-sea submersible
Authors: Huang Jiaxin , Zhang Gangqing , Kong Weiyu
Published: June 2024

Hydrodynamic characteristics of manned deep-sea submersibles are important for optimizing design, increasing safety, and improving handling and control. To study the hydrodynamic characteristics of manned deep-sea submersibles in different surfacing attitudes, this paper carries out hydrodynamic tests on the scaled-down simplified model of “Jiaolong” submersible of 1:36. The drag, lift, and pitching moment of the manned deep-sea submersible in different surfacing attitudes are obtained by six-component sensors, and the time-averaged streamlines, turbulence kinetic energy, normal velocity and Reynolds stress distribution are obtained by photographing the wake flow field of the submersible using PIV particle image velocimetry. The results show that compared with the vertical surfacing attitude, the drag decreased by 38.2%, the lift magnitude rose by 98.9%, the pitching moment decreased by 20.8%, the vortex disappeared in the stern wake area, and the maximum turbulent kinetic energy decreased by 33.6% when surfacing at a 30° rake angle.
Characterization of mechanical properties of carbon nanotube fibers prepared by chemical vapor deposition
Authors: Li Shuping , wang Yan
Published: June 2024

A chemical vapor deposition (CVD) method for preparing carbon nanotube fibers was proposed. This method used ethanol/acetone as the carbon source, ferrocene as the catalyst and thiophene as the promoter. It used a high-temperature gas-phase flow reaction to spin out carbon tube fibers. Subsequently, the mechanical properties of carbon tube fibers prepared under different conditions (carbon source, gas flow and raw material ratio) were characterized and analyzed. The results demonstrated that the carbon fiber prepared with ethanol as the carbon source under specific synthesis conditions has good continuity and can be prepared for 3 hours in succession. In a feasible condition (Fe, S, C ratio, air flow ratio, and growth temperature), using pure acetone as the carbon source can prepare carbon nanotube fibers with fiber-specific strength > 1.5N / tex.
Energy absorption behaviour and shape change effects of 3D printed polyurethane hexagonal honeycombs
Authors: Liu Yangzuo , Wang Zelin , Tang Ziruo , Li Haotian , Xu Cheng , Ma Wuning
Published: June 2024

Honeycombs have been used in a wide range of repeatable energy-absorbing elements due to their light weight and high energy absorption capacity. In the engineering environment, honeycombs will produce a shape change effect and rebound under multiple loading and unloading, so it is of great importance to investigate the energy-absorbing properties of honeycombs under the shape change effect for the application of honeycombs. In this study, the deformation process and energy absorption properties of 3D printed honeycombs under multiple loading were obtained through multiple quasi-static compression tests. On this basis, the coupling between shape change effects and honeycomb energy absorption is revealed. It is shown that the number of compressions does not affect the four-stage force-displacement curve characteristics of the honeycombs, but only the energy absorption efficiency of the honeycombs. There is an inverse relationship between the resilience of honeycombs and the energy absorption capacity of honeycombs, and the change of honeycomb stiffness under repeated compression is the direct cause of this relationship. The research results provide a reference for the application of honeycombs in the field of repetitive energy absorption.
Numerical simulation of blood flow in coronary bifurcation
Authors: Liu Changshuo , Xu Xingming
Published: June 2024

A numerical simulation of blood flow in a Y-shaped coronary artery was executed by constructing ideal geometric models. The influences of bifurcation angle, the initial velocity of inlet blood flow, and the diameter ratio of bifurcated vessels on the blood flow velocity field, wall shear stress, wall pressure, etc. were analyzed. The blood velocity at the bifurcation of the blood vessel was slower, while the wall shear stress and wall pressure value were higher. The wall shear stress and wall pressure increased with the increase of blood flow velocity at the entrance. Greater bifurcation angle led to higher wall shear stress. With the increase of the diameter ratio of the two branches, the maximum value of the shear stress became smaller. The probability of thrombosis formation increases as the diameter ratio increases. The numerical results showed that the bifurcation of the blood vessel is the optimal place to form the thrombosis.
Effect of finned configuration of circular tube based on fluid-structure coupling on hydrogen flow characteristics
Authors: Wu Xunliang , Shao Mingxue , Cai Kaiyuan , Li Xiaoliang , Feng Songjiang
Published: June 2024

Nuclear thermal propulsion has the characteristics of high specific impulse, large thrust, green and efficient, and is the primary choice of manned deep space exploration propulsion system. Because the circulating flow of propellant hydrogen in the internal pipeline of the engine is always affected by the harsh environment of high temperature and high pressure, it is very important to study the flow characteristics of hydrogen in the pipeline, the heat exchange characteristics of hydrogen and pipeline and the deformation characteristics of pipeline under heat stress. In this paper, the flow phenomena of hot hydrogen in round tubes in a laminar flow state were analyzed by numerical simulation with COMSOL Mulitiphisics6.0, and the fluid-structure coupling between hot hydrogen fluid and pipe was investigated by a multi-physics field. It is concluded that the smoother the inner wall of the pipeline is, the smaller the hydrogen flow velocity is, the smaller the surface pressure of the pipe wall is, and the smaller the fluid extrusion and impact deformation of the pipe in the typical pipe with the inner fin is. It inspires studying the application of hot hydrogen flow and pipeline configuration in nuclear thermal rocket engines, including improving heat transfer energy and uniformity.
Study on manufacturing process and load-bearing capacity of innovative GFRP composite sandwich panels with connecting grooves
Authors: Du Yanpin , Qi Yujun
Published: June 2024

Composite sandwich panels have been widely utilized in various fields, including civil engineering, wind turbine blades, and transportation engineering, due to their lightweight, high strength, corrosion resistance, and exceptional thermal and damping properties. This paper introduces a novel wood-core composite sandwich panel produced through pultrusion. It features connection grooves designed to fulfill lateral connection requirements. The production of this innovative composite sandwich panel has been completed. The bending load-bearing capacity of this panel is comprehensively studied through theoretical analysis, and a modeling approach utilizing the general finite element software ANSYS is introduced. Ultimately, the efficacy of both theoretical methods and finite element simulations is verified through rigorous experiments. The research findings presented in this paper are highly significant for optimizing the design and manufacturing of composite sandwich panels, ultimately enhancing their utilization in rail transit vehicles and other industries.
Sub-nanosecond magnetic vortex reversal induced by localized resonant strain field in doped nanomagnets
Authors: Cui Huanqing , Yang Xiaokuo , Zhang Mingliang , Wei Bo , Xia Yongshun , Dou Shuqing
Published: June 2024

The strain-induced magnetic vortex dynamics in nanomagnets with ring-shaped impurities are investigated by means of micromagnetic simulations. It is found that the type and location of impurities can modulate the strain-stimulated spin wave spectrum of the magnetic vortex. Compared with pure nanomagnets without doping, the scattering impurities make the eigenfrequency of nanomagnets higher, while the pinning impurities lead to lower eigenfrequency. Moreover, the spin wave oscillation amplitude in a doped nanomagnet is strengthened by the gradient of exchange energy at the interface between the impurity ring and nanomagnet. The magnetic vortex polarity in a nanomagnet with specific doping schemes can be reversed in a sub-nanosecond scale by a localized resonant strain signal. Besides the switching efficiency improvement, the threshold stress of sub-nanosecond polarity reversal in nanomagnets with specific doping schemes is also reduced compared to the counterpart of nanomagnets without impurities. These results indicate that doping engineering of nanomagnets is a significant method to achieve straintronic devices with higher operating frequency and lower energy consumption.
Design and research on ultra-high pressure sealing structure based on tight plug ring
Authors: Li Guiyuan , Li Jiaxing , Wu Yong , Liu Haoxuan , Niu Tianhong , Zhang Long
Published: June 2024

A new ultra-high pressure sealing structure was designed based on the sealing requirements of ultra-high pressure vessels, using a tight plug ring. The finite element method was used for simulation analysis. The results show that the contact pressure on the sealing surface of the tight plug ring is linear with the vessel pressure, which is always greater than the vessel pressure. To further verify its sealing performance, a semi-closed bomb test device was designed based on the principle of the semi-closed bomb, which can generate a pressure of 300 MPa. The test pressure exceeded 300 MPa multiple times, but no gas leakage was observed. The comprehensive research results indicate that the sealing structure has good performance and can meet the sealing requirements of 300 MPa ultra-high pressure.
Efficient geometric parametrization of blades cross-sections by means of B-splines
Authors: Llamazares G , San Miguel U , Plaza A
Published: June 2024

Optimization and enhancement of rotor blade design are critical to improving the productivity of the wind energy industry. Airfoil geometry is a key factor that makes airfoil design and optimization a common task for aerodynamicists. Ensuring proper airfoil parametrization is essential. It serves as the first step in aerodynamic optimization, where the efficiency is directly related to the geometric complexity. This research presents a cost-effective and robust method for fitting airfoils using B-splines. We take into account factors such as computational cost, resource requirements, and accuracy. In this work, we present a method for minimizing the geometric distances between target points and a B-spline curve. We streamline the fitting process, create a computational Python package, and explore different approaches, objective functions, algorithms, and error tolerance settings. The work concludes that it is highly recommended to use an iterative fitting process, to adequately represent common airfoils with B-splines. Moreover, the accuracy and the computational cost can be managed subject to the minimization algorithm used, and the technique utilized for the objective cost calculation. The fitting procedure we develop in this study gives the smallest number of variables capable of accurately representing a desired airfoil.
Computational investigation of the effect of the trailing edge thickness on the wind turbine performance
Authors: Echenique Daniel , Puertolas Aitor Plaza , Amo Rubén Gutierrez
Published: June 2024

Trailing edge (TE) thickness is a manufacturing constraint in blade design, especially for airfoils with a sharp TE. To achieve a specific TE thickness, blade geometry is often modified during the design process, typically in the outer zone of the blade where the airfoil’s TE is thinner. This area has a significant impact on energy production and loads. Quantifying the effect of TE thickness modifications is crucial for making informed design decisions.

Therefore, this study quantifies and compares the impact of linear and polynomial geometry modifications on airfoil aerodynamics and turbine performance. Xfoil and OpenFAST were used to calculate these performance variations in the well-known NREL 5 MW wind turbine. The TE thickness of the model was modified to meet various manufacturing constraints, ranging from no restriction to a limit of 12mm TE thickness.

In terms of the aerodynamic behavior of the airfoils, the maximum efficiency of airfoils with low relative thickness decreases as the TE thickness increases. Annual Energy Production shows a reduction of up to 0.42% for the worst case, while blade root loads increase by up to 20%. For low relative thickness airfoils, the linear method has proven to be a better option with less impact on performance.
Partitioned time couplings of an aero-mechanical wind turbine problem.
Authors: Guern Caroline Le , Blondel Frédéric , Pfister Jean-Lou , Guy Nicolas , Bergmann Michel
Published: June 2024

Wind turbine developments have led to more powerful offshore rotor systems, creating complex aero-hydro-servo-elastic behaviors that require numerical analysis. A mutliphysics problem can be modelled using several approaches: a “monolithic” method where the systems are considered as a unique block or a “partitioned coupling” where the different domains are solved sequentially. The latter is the retained technique for this work in which different solvers are related to distinct equations that require independent time discretisations. The focus is set on coupling a wind turbine’s mechanical solver with an aerodynamic code, the latter being modelled through an inviscid vortex method and the structural aspect using a finite element method. The study aims to present the implementation process and comparison of different time integration coupling schemes within a large wind turbine simulation framework where aeroelastic effects are studied on the IEA 15MW wind turbine. A ”Conventional Serial Staggered” (CSS) scheme is used as a reference coupling technique, allowing independent time integration while limiting coupling to a single time step. Alternatively, a resembling “subcycling” architecture is proposed and implemented to remedy cases with different temporal discretisations and reduce computational costs of CSS when using the inviscid vortex method.
Numerical analysis of static and dynamic wind turbine airfoil characteristics in transonic flow
Authors: Vitulano M C , De Tavernier D , De Stefano G , Von Terzi D
Published: June 2024

This study performed an aerodynamic characterization of the FFA-W3-211 wind turbine tip airfoil in transonic flow using Unsteady Reynolds-Averaged Navier-Stokes (URANS) simulations, for both steady and dynamic operational conditions. First, the boundary between subsonic and supersonic flow in static conditions was identified, depending on the angle of attack, the approach flow Mach number, and the Reynolds number. The analysis points out that higher Reynolds numbers promote the occurrence of local supersonic flow. Thereafter, to investigate the dynamic behavior in the transonic flow regime, a sinusoidal pitching motion with representative values was imposed. A hysteresis, similar to but distinct from dynamic stall, was observed for entering and leaving the supersonic and subsonic regions. Elevated reduced frequencies widened the hysteresis loop, resulting in increased normal forces on the airfoil. The study indicated that an increase in reduced frequency leads to an earlier onset of transonic flow. In conclusion, the risk of transonic flow occurring during normal operation of the next generation wind turbines predicted in earlier studies could be corroborated. Moreover, dynamic effects and Reynolds number dependencies can be significant.
CFD investigation of flatback airfoils and swallow tail for wind turbine blades
Authors: Solombrino C , Ravishankara A Koodly , Özdemir H , Venner C H
Published: June 2024

Modern wind turbines use longer blades to improve annual energy production. Longer blades require thicker airfoils for structural integrity. Thicker airfoils are susceptible to issues like erosion, abrupt stalls, and early boundary layer transition, leading to increased drag and decreased lift, affecting overall performance. Flatback airfoils offer structural and aerodynamic advantages, being stiffer, less sensitive to surface roughness. However, this comes with a drag penalty, mainly due to the increase in base drag. Swallow tail add-on has been proposed to overcome these challenges. URANS simulations are used to analyze the aerodynamic performance of the different airfoils and hybrid RANS/LES simulations are used to study the flow features in more detail. The swallow tail airfoil was found to maintain many of the advantages of the flatback airfoils while reducing the drag penalty.
Numerical investigation of vortex induced vibrations on cylinders
Authors: Vlastos D , Riziotis V A , Papadakis G , Manolas D I , Chaviaropoulos P K
Published: June 2024

The paper addresses Vortex Induced Vibrations (VIV) caused by tower vortex shedding through LES simulations of a wind tunnel experiment. A high-fidelity (HiFi), Fluid Structure Interaction (FSI) framework for aeroelastic analysis of 3D flexible cylinders is established, based on the open-source Computational Fluid Dynamics (CFD) code OpenFOAM and the coupling library preCICE. In the present study, the FSI framework is employed with the aim to replicate a low Reynolds (Re=26000) forced vibrations wind tunnel experiment of a circular cross-section rigid cylinder. The paper compares predictions of the aerodynamic damping of the oscillating cylinder for different oscillation frequencies within the lock-in range and amplitudes against experimental results. While the model consistently predicts the lock-in range of frequencies and the trends in the variation of the aerodynamic damping with the oscillation amplitude, it falls short of accurately capturing the maximum value of the aerodynamic damping at the onset of lock-in.
Hierarchical sensitivity study on the aeroelastic stability of the IEA 15 MW reference wind turbine
Authors: Verdonck Hendrik , Hach Oliver
Published: June 2024

Increased rotor size and blade flexibility are leading to new stability characteristics for current and future wind turbines. Numerical aeroelastic models are an essential tool to understand these new mechanisms and to design next-generation wind turbines suitably. A comprehensive understanding of how model input parameters influence the stability analysis will enhance the confidence in these simulations. This article presents a study on the sensitivity of uncertain parameters on aeroelastic stability predictions of the IEA 15 MW turbine model in HAWCStab2. It uses a hierarchical approach to handle the large number of investigated model parameters. Relevant uncertainties are identified through one-at-a-time and elementary effects analyses first. The remaining parameters are fed into a variance-based uncertainty quantification (UQ), that employs polynomial chaos expansion representations as surrogates for a full nonlinear description of the sensitivities. A robust post-processing of the stability analysis results is the main challenge of the presented methodology, but it is shown how the UQ process can still be used to explore the parameter space effectively. The presented study shows that the structural blade properties have the highest sensitivity and that a set of relatively small parameter variations can lead to unstable behavior of the reference model.
Machine Learning Based Predictions of Airfoil Aerodynamic Coefficients for Reynolds Number Extrapolations
Authors: Özgören Ahmet Can , Acar Deniz Alper , Kamrak Recep , Eriş Görkem Mahir , Özdemir Yasin , Uzol Nilay Sezer , Uzol Oğuz
Published: June 2024

This study investigates the application of various machine learning (ML) algorithms for predicting two critical aerodynamic coefficients, i.e. the maximum lift coefficient (C

l max
) and the minimum drag coefficient (C

d min
), for wind turbine airfoils at any given Reynolds number. We propose to use clustering techniques to group similar airfoil shapes and use the created partitions to predict unseen airfoil properties utilizing their similarity. Here, we also represent airfoils in the PARSEC low dimensional space, rather than high dimensional airfoil points space, to remedy the small number of training data. For this purpose, an extended experimental airfoil database is created and used for training models based on five different ML algorithms. We observe that the Decision Tree Ensemble (DTE), Random Forest (RF) and multi-layer perceptron (MLP) models emerge as the most effective predictors for C

l max
and C

d min
. Testing these two ML models on three additional airfoil cases not included in the training database shows that the C

l max
prediction performance is generally reasonable, with error levels being around 5% on average. In contrast, the prediction error levels for C

d min
are usually higher, with an average of around 15%.
Study of surface roughness on flow past a wind turbine tower section
Authors: VimalKumar Shyam , De Tavernier Delphine , Von Terzi Dominic , Belloli Marco , Viré Axelle
Published: June 2024

The flow around wind turbine towers usually reaches very high Reynolds numbers greater than a million. Understanding the flow around the towers under these conditions is crucial, as it may lead to vibrations due to the vortices formed. Investigating aerodynamic characteristics at such high Reynolds numbers, both numerically and experimentally, is challenging. The current study validates such an experimental study, where a rough surface is employed to increase the effective Reynolds numbers and accelerate the laminar-turbulent transition in the boundary layer. Unsteady Reynolds-Averaged Navier-Stokes (RANS) simulations are carried out using OpenFOAM for a Reynolds number range of 1.36·105 to 6.8·105. The constant (a
1) used to calculate the eddy viscosity is varied to simulate the flow separation during adverse pressure gradients. A force partitioning method is implemented in OpenFOAM and various force contributions are analysed for this Reynolds number range. It is seen that the RANS simulations overpredict the aerodynamic characteristics and the extent of flow separation unless the value of a
1 is varied as a function of the Reynolds number. Furthermore, it is observed that the only force contributor is the vorticity-induced force, as the simulations are performed for a fixed cylinder.
Norm-Optimal Iterative Learning Control for Wind Turbines During Grid Faults
Authors: Spijkerman D. , Navalkar S.T. , Solberg B. , Mulders S.P.
Published: June 2024

Due to the increasing share of (offshore) wind turbines, more stringent requirements on power quality have been established. Importantly, the low-voltage ride-through grid requirement states that a wind turbine must remain connected to the electrical grid after a short intermittent grid fault. In the industry mainly gain-scheduled PID-controllers are used to mitigate the effects of grid faults on turbine operation, whereas more advanced solutions have been proposed in the literature such as model predictive control or multiple parallel PI-controllers. Remarkably, all controller implementations mentioned earlier are based on feedback control, where no feedforward strategies have been discussed in the literature. However, feedforward control could improve grid fault recovery performance by exploiting the relatively known fault characteristics by virtue of the specification in the Transmission System Operator requirements. Therefore, for the first time, a norm-optimal Iterative Learning Control (NO-ILC) algorithm is presented that solves these issues by learning the feedforward signal that optimally mitigates the effects of a grid fault. The NO-ILC algorithm applies model-free learning based on iterations, in which the framework of NO-ILC has been extended to include explicit input constraints. The goal of the NO-ILC is to reduce a (quadratic) cost function on specific input and output channels whilst conforming to specific input constraints by solving an optimisation problem, with, for this study blade pitch and rotor speed as respective input and output channels. It is shown that the NO-ILC algorithm can yield improved performance on a high-fidelity model, with a 45% decrease in the cost function used by NO-ILC compared to the nominal feedback control. The optimised feedforward signals resulting from NO-ILC can be used as an analysis tool to closer match the nominal grid fault feedback controllers response with that of NO-ILC, or directly applied as a library that can supplement the feedback controllers output during a grid fault.
UNICO: an open-source controller optimized for stall-regulated wind turbines
Authors: Cioni Stefano , Papi Francesco , Cocchi Emanuele , Bianchini Alessandro
Published: June 2024

Stall regulation turbines still represent the preferred solution for small wind turbines. In stall-controlled rotors the controller plays a key role but, differently from pitch-based ones, no open-source controller was available to date. The study presents the UNICO (UNIfi research COntroller) controller, which has been specifically developed for variable speed stall-regulated turbines. The controller has been developed in MATLAB® Simulink® and a dynamic link library (.dll) has been generated, which can be coupled with common simulation codes such as OpenFAST and QBlade using a Bladed-style interface. UNICO includes features that are specifically tailored to variable-speed stall-regulated turbines. For below-rated conditions, the controller employs either the commonly used k-ω2 law or a tracking of the optimal tip speed ratio. For above-rated conditions, a PI controller is used to track a user-imposed reference speed. The reference speed is set to decrease linearly with wind speed, providing a safety margin for turbine operation at higher wind speeds. UNICO has been tested on a 50-kW stall-regulated reference turbine. Preliminary results show how the proposed controller can achieve better overall performance in comparison to the simplified control laws implemented in state-of-the-art codes. Additionally, the rotor speed can be controlled in above-rated conditions, providing an increased run away safety margin.
Model predictive control of wakes for wind farm power tracking
Authors: Sterle Arnold , Hans Christian A. , Raisch Jörg
Published: June 2024

In this paper, a model predictive control scheme for wind farms is presented. Our approach considers wake dynamics including their influence on local wind conditions and allows the tracking of a given power reference. In detail, a Gaussian wake model is used in combination with observation points that carry wind condition information. This allows the estimation of the rotor effective wind speeds at downstream turbines, based on which we deduce their power output. Through different approximation methods, the associated finite horizon nonlinear optimization problem is reformulated in a mixed-integer quadratically-constrained quadratic program fashion. By solving the reformulated problem online, optimal yaw angles and axial induction factors are found. Closed-loop simulations indicate good power tracking capabilities over a wide range of power setpoints while distributing wind turbine infeed evenly among all units. Additionally, the simulation results underline real time capabilities of our approach.
Development of a novel method for the correction of the nacelle wind speed in stall-controlled wind turbines
Authors: Vivas Larisa , Papi Francesco , Papatsiros Vasilis , Maudhuit Olivier , Bianchini Alessandro
Published: June 2024

Accurate estimation of the oncoming wind is key to ensure an accurate control of any wind turbine. The wind speed is commonly measured with an anemometer located on the nacelle; hence, the measurement is influenced by the rotor and the nacelle itself and needs to be corrected so as not to incur inaccurate energy yield assessments. This study introduces an innovative method for correcting the nacelle wind speed in stall-controlled wind turbines. The development of the method has benefitted from the unique possibility of exploiting two datasets containing 10-minute averaged wind data from two identical EUNICE EW16 wind turbines and a meteorological mast located at the same site. The innovative method is systematically compared with the Nacelle Transfer Function outlined in the IEC 61400-12-2, serving as a benchmark for evaluation. The high accuracy and simplicity of the proposed method make it particularly suitable for the optimization of wind turbine performance in industrial applications. Moreover, an accurate estimation of the incoming wind speed can enable innovative control techniques, such as those based on Tip-Speed-Ratio (TSR) tracking. This is addressed in the study through simulations by comparing a TSR-Tracking strategy with the most common k-ω2 strategy. The study demonstrated that the TSR-Tracking strategy could be adopted in stall-controlled wind turbines if an accurate estimation of the free-stream wind speed is available.
Evaluation of LES-based time-decoupled model-predictive control in different wind farm layouts
Authors: Janssens Nick , Meyers Johan
Published: June 2024

Very recently, Janssens and Meyers (Wind Energy Sci., vol. 9, 65–95, 2024) proposed a time-decoupled model-predictive control (TD-MPC) framework for wind farm power optimization using a control model based on coarse-grid large-eddy simulation (LES). In a receding-horizon fashion, by computing the controls for the next time window based on a prediction of the flow (so ahead of time), they achieved (almost) real-time computational speed. The current paper further explores the potential of this approach in the context of dynamic yaw control, under the assumption of exact state knowledge. To that end, the LES-based, TD-MPC framework is validated on a reference wind farm for three different wind directions, for which we observe gains ranging from 4 (for staggered configurations) to 42% (for aligned configurations w.r.t. the wind direction). The LES-based controller always outperforms a Betz optimal controller and a static (wake model based) yaw controller at near real-time speed. An analysis of the yaw angles reveals that the framework is very effective in steering the wakes away from downstream turbines in upstream and downstream regions, synchronized to the turbulent inflow. By comparing the performance of the LES-based controllers (based on the actuator disc turbine model) against a reference simulation that uses a more accurate actuator sector model, we illustrate the robustness of the approach in the presence of the additional model error.
Active control of yaw drift of single-point moored wind turbines
Authors: Dos Santos C R , Stenbro R , Stieng L E , Hanseen-Bauer Ø W , Wendt F , Psichogios N , Aardal A B
Published: June 2024

Single-point moored floating wind turbines can benefit from the self-alignment of the structure with the prevailing wind direction. However, to be successful, the effects of yaw-drift must be mitigated using effective control strategies during power production. In this work, we investigate sources contributing to yaw drift and propose active control solutions to the problem. The analyses utilize the IEA 15 MW wind turbine mounted on a single-point moored floating foundation. Aero-hydro-servo-elastic simulations using the software 3DFloat are performed under various conditions of wind, waves and current. The results indicate that yaw drift can be actively controlled using nacelle-yaw actuation techniques and individual pitch control of the blades. These approaches effectively align the rotor with the wind direction, increasing the robustness of single-point wind turbines by ensuring increased power production, and maintaining the structural life.
A control-oriented load surrogate model based on sector-averaged inflow quantities: capturing damage for unwaked, waked, wake-steering and curtailed wind turbines
Authors: Guilloré A , Campagnolo F , Bottasso C L
Published: June 2024

This paper presents a novel approach to constructing a load surrogate model. The surrogate estimates the damage equivalent loads (DELs) of a wind turbine of a given type regardless of its position within a wind farm, and under various farm control actions. The model relies solely on local inflow quantities (sector-averaged wind speeds and turbulence intensities) and local control parameters (rotor speed, pitch angle, and yaw misalignment). Despite its highly simplified representation of the complex behavior of the turbulent wind field, wake effects, and controller dynamics, these quantities prove sufficient to characterize DELs. The paper demonstrates the training of this load model within a simulation environment. Validation results using a different wind farm configuration indicate that the surrogate can accurately predict fatigue loads for both unwaked and waked turbines, encompassing scenarios of wake steering and induction control.
Impact of wake steering on loads of downstream wind turbines at an above-rated condition
Authors: Thedin R , Kreeft J , Barter G , Jonkman J , Shaler K
Published: June 2024

Wake steering strategies often seek to gain power at the expense of increased fatigue loads. Here, we investigate the feasibility of applying wake steering at an above-rated condition. In such a condition, the farm is operating at rated power, and thus, increased power output is not the goal. Instead, wake steering is considered in the context of load reduction. We perform a sweep of wind directions and yaw misalignment angles, ranging from negative to positive values. This approach allows us to obtain trends and identify asymmetries in turbine response for symmetric scenarios. We use a wind farm consisting of five aligned IEA Wind 15-MW reference wind turbines, and analyze trends related to the blade-root, low-speed shaft, and tower-base moments, both in terms of standard deviation and damage equivalent loads. We show that for any given fixed wind direction, the turbines can be yawed such that the fatigue loads are reduced. Reductions of up to 5% (depending on the component) in terms of standard deviation and damage equivalent loads can be achieved by negatively yawing the turbine. A negative yaw misalignment has shown to be the direction of larger improvements. Such results contrast those found for below-rated conditions, where a positive yaw misalignment is typically preferred. However, since load reduction is not uniform across all component loads, more study and consideration is required before operational recommendations can be made.
Uncertainty quantification of wind turbine fatigue lifetime predictions through binning
Authors: Sadeghi N. , Noppe N. , Morato P. G. , Weijtjens W. , Devriendt C.
Published: June 2024

Aging wind energy assets demand the development of methods able to effectively support informed decision-making. These needs have inspired the use of data-driven methodologies, which offer valuable insights to wind turbine owners and/or operators. Many approaches can be found in the literature for extrapolating fatigue damage measurements to estimate the lifetime of wind turbines. In some cases, resampling approaches are proposed to compute the confidence levels associated with the generated projections, yet a standardized framework has not been adopted. Most reported studies identify the relationship between short-term damage and long-term Environmental and Operational Conditions (EOCs) by mainly rendering mean lifetime predictions and their associated confidence levels, whereas additional predicted lifetime statistical information is usually overlooked. In this work, we showcase the importance of properly accounting for the variability in lifetime predictions, describe how to summarize binned damages using statistical estimators and investigate bootstrapping variants for computing the confidence levels in the generated damage estimators.
Data-driven forecasting of FOWT dynamics and load time series using lidar inflow measurements
Authors: Gräfe Moritz , Pettas Vasilis , Cheng Po Wen
Published: June 2024

This study focuses on forecasting the fairlead tension and floater dynamics time series of floating offshore wind turbines (FOWTs) using a data-driven approach that incorporates onboard sensor measurements and lidar inflow data. Sensors on FOWTs can provide data on turbine dynamics, such as rotational and translational movements, and load metrics like mooring line loads. However, these sensors are limited to current state measurements and do not provide future signal projections. In this research, we investigate a data-driven forecasting methodology using a simulated dataset. This dataset encompasses FOWT responses to diverse environmental conditions and the associated lidar measurements. Utilizing a Long Short-Term Memory (LSTM) sequence-to-sequence model, this study forecasts the time series of fairlead tension, surge, and pitch for forecasting horizons of 20, 40, and 60 seconds, considering lidar ranges from 100m to 500m. The performance of these forecasting models is benchmarked against a simple persistence model. The results indicate that incorporating lidar inflow measurements significantly improves the forecasts of fairlead tensions and platform motions. The enhancement for pitch motion forecasts is observed across all forecasting horizons. For fairlead tension and surge motion, the enhancement is observed for the longer horizons of 40s and 60s. These findings underscore the value of lidar data in accurate forecasting and emphasize the need to account for the interplay between lidar range, wind speed, and forecasting horizon to achieve optimal forecast accuracy.
Boosting field data using synthetic SCADA datasets for wind turbine condition monitoring
Authors: Milani Ali Eftekhari , Zappalá Donatella , Castellani Francesco , Watson Simon
Published: June 2024

State-of-the-art Deep Learning (DL) methods based on Supervisory Control and Data Acquisition (SCADA) system data for the detection and prognosis of wind turbine faults require large amounts of failure data for successful training and generalisation, which are generally not available. This limitation prevents benefiting from the superior performance of these methods, especially in SCADA-based failure prognosis. Data augmentation approaches have been proposed in the literature for generating failure data instances within a SCADA sequence to reduce the imbalance between healthy and faulty state data points, which is relevant to fault detection tasks. However, the successful implementation of DL-based failure prognosis methods requires the availability of multiple run-to-failure SCADA sequences. This paper proposes a data-driven method for generating synthetic run-to-failure SCADA sequences with custom operational and environmental conditions and progression of degradation. An Artificial Neural Network (ANN) is trained with signals that represent these factors to reconstruct the SCADA signals. Then, it is used to generate synthetic SCADA datasets based on data available from a wind turbine that experienced a gearbox failure. Synthetic data sets generated are evaluated on the basis of the similarity of their signal distributions, the temporal dynamics within each signal, and the temporal dynamics among different SCADA signals with those in similar field datasets. The results show that the generated synthetic datasets are consistent with their field counterparts, with a comparatively lower diversity in their dynamic behaviour in time.
Optimal tuning of individual pitch control using economic goal-oriented objectives
Authors: Aktan H D , Bottasso C L
Published: June 2024

Individual pitch control (IPC) is a method developed to cope with fatigue loads, which works by actively changing the pitch angles of each blade based on feedback. While beneficial for fatigue damage, the use of IPC leads to some reduction in yield and an increase in pitch activity, which can influence operation and maintenance (O&M) costs. Tuning of the IPC parameters plays a significant role, as different settings could result in different trade-offs among lifetime, yield, and O&M costs. In this paper, an optimal parameter tuning method for IPC for existing turbines is proposed. The effects of IPC on competing objectives, i.e. energy production, pitch system wear, and fatigue life are utilized to maximize the long-term profit based on given constraints. The proposed approach is demonstrated in a simplified scenario, where the tower is the only critical component that requires damage reduction to achieve a target lifetime. The performance of the proposed approach is compared to a standard tuning that targets load reductions in terms of d- and q-axis components. Results indicate that the proposed optimal tuning approach provides IPC gains that meet the desired lifetime of the component, and that improve profit compared to the standard approach.
Erosion-safe operation using double deep Q-learning
Authors: Visbech Jens , Göçmen Tuhfe , Réthoré Pierre-Elouan , Hasager Charlotte Bay
Published: June 2024

Leading edge erosion on wind turbine blades can reduce aerodynamic efficiency and cause increased maintenance costs, potentially impacting the overall economic viability. Erosion-safe operation is the concept of reducing the blade tip speed during periods of heavy rain, thereby significantly reducing the erosion development and progression. This study explores the application of reinforcement learning, namely using a double deep Q-network, to implement erosion-safe operation. The proposed methodology involves learning a policy for tip speed control that maximizes revenue over a specific period of time. We demonstrate the concept based on 5 years of simulation of the DTU 10MW reference turbine and mesoscale weather simulation from Horns Rev. The trained model was found to increase the cumulative revenue by 1.6 % compared to not using erosion-safe operation. The model was able to effectively adapt to varying weather conditions and stochastic damage progression. Based on 10,000 random simulations, the trained model outperforms two baseline models in more than 98 % of the simulations.
Analysis and evaluation of two reference LiDAR-assisted control designs for wind turbines
Authors: Steinmann Perez Cedric D. , Lio Alan W.H. , Meng Fanzhong
Published: June 2024

LiDAR-assisted wind turbine control holds promise in reducing structural loads and enhancing rotor speed regulation. However, a research gap exists in the practicality and limitations of commercially available fixed-beam LiDARs for large turbines and evaluating commonly employed LiDAR-assisted feedforward approaches. This study addresses these gaps by examining the implications of utilizing fixed-beam LiDARs in two wind turbine sizes and two reference LiDAR-assisted control strategies. A comprehensive evaluation considers coherence variations, uncertainties related to inaccurate pitch angle mapping with the upcoming wind speed, and their combined impact on load reduction. Numerical simulations reveal that an excessively low cut-off frequency in the low-pass filter can compromise preview time compensation. This is problematic in larger turbines, where coherence with limited LiDAR beams is inferior compared to smaller wind turbines, which deteriorates the effectiveness of the LiDAR-assisted control. Among the reference LiDAR-assisted control methods, the evaluation indicates the Schlipf approach has greater load reduction independence, while Bossanyi’s approach, which uses measurement of current blade pitch, yields positive results with fine-tuned baseline controllers. However, allowing baseline controller-induced frequencies to propagate into the controller may increase system excitation at certain frequencies due to the use of the actual pitch angle for feedforward pitch rate calculation.
Controller design for the X-Rotor offshore wind turbine concept
Authors: Recalde-Camacho L , Leithead W , Morgan L , Kazemi Amiri A
Published: June 2024

This paper explores the design of a full envelope speed controller to operate the X-Rotor Offshore Wind Turbine. The X-Rotor is a heavily modified V-rotor vertical axis wind turbine, in which the primary rotor has conventional blades angled both up and down from the ends of a relatively short and stiff cross-arm. The upper half employs full span blade pitching for speed regulation and the lower half is aimed at reducing overturning moments on the main bearing and provides power take-off through compact secondary horizontal axis turbines mounted at the tip of the lower blades. The operational strategy is somewhat similar to that of a variable speed pitch regulated horizontal axis wind turbine, however it differs in the following aspects: the way aerodynamic torque is balanced across the operating envelope, the adjustment of equilibrium operating points at below rated operation, the relationship of aerodynamic torque on the primary rotor to pitch angle, and the operation of the secondary rotors to increase energy capture. These aspects increase the complexity of the control strategy but also ease the controller requirements. The developed controller is tested on a turbine model with sufficient complexity to model the essential dynamic properties of the turbine concept.