bluuebunny/crossref_metadata_2025 huggingface dataset:
Chapter 35. Troilus and Briseida in the Western literature
Authors: Raya Fages Lourdes , Piqueras Yagüe Pablo
Published: June 2024

This chapter analyzes the figure of Troilus and the motif of the love triangle, consisting of him, Briseis, and Diomedes from the De excidio Troiae of Dares Phrygius to contemporary literature. We focus specifically on the medieval works that influenced the representation of these three characters and their relationship. We examine their roles in Dares’ work, in the Roman de Troie of Benoît de Sainte-Maure, in Guido delle Colonne’s Historia destructionis Troiae, in two epics of the XII and XIII centuries (De bello Troiano of Joseph of Exeter and Troilus of Albert of Stade) and in three more familiar pieces, namely Boccaccio’s Il Filostrato, Chaucer’s Troilus and Criseyde, and Shakespeare’s Troilus and Cressida, to end with a quick review of the theme from that moment until the present. The representation of the characters and their triangle was formed in the Roman de Troie following Dares, and each author who developed the story used the tradition but added his own special touches.
Bird-assisted treatment in vulnerable people: A literature review
Authors: Béguin Nathalie , Burtey Marion , Lignier Baptiste , Romo Lucia , Mazé Corinne
Published: June 2024

Animal-assisted therapy (AAT) practices have diversified following one of the earliest uses of animals in therapy, as described by Levinson (
1962
). Since the 1960s, evidence of the effectiveness of AAT can be found in the scientific literature across various populations. Different species of animals have been used for AAT, while literature reviews specific to dogs or horses can be found, there is currently no literature review that specifically focuses on bird-assisted treatments.

This study aims to conduct a comprehensive evaluation of the existing literature on bird-assisted treatments in diverse populations. We conducted a comprehensive search for the keywords “animal assisted therapy,” “animal assisted intervention,” “zootherapy,” “thérapie assistée par l’animal,” “intervention assistée par l’animal,” “zoothérapie,” “bird,” and “oiseau” in the PubMed, ScienceDirect, and PsycInfo databases, covering the period from 1975 to October 2023. A total of six articles were eligible for inclusion in our literature review, four on older individuals and two conducted within various psychiatric departments. These studies identified two distinct forms of interventions: individual and shared room cages. Irrespective of the intervention type, the primary findings demonstrated not only positive effects on depression levels and social well-being among older individuals but also favorable outcomes for psychopathological symptoms and social life among individuals with psychiatric disorders. The use of birds can be a strategy to implement AAT in institutional settings where managing larger animals or those requiring more complex care would be challenging. These results lead us to recommend bird-mediated interventions to promote well-being and reduce psychological distress among populations requiring this type of assistance.
The lower-hybrid drift instability during the evolution of Kelvin–Helmholtz instability
Authors: Yuan Huaxuanyu , Yang Yang , Wang Mingyue
Published: June 2024

The lower-hybrid drift instability (LHDI) is a pivotal phenomenon in astrophysics, playing a critical role in energy transfer, macroscopic structures, and evolutionary processes between the magnetosheath and magnetosphere. Using 2D two-fluids numerical simulation, we investigate the spatiotemporal distribution of LHDI during the evolution of Kelvin–Helmholtz instability (KHI) at Earth’s dusk-flank magnetopause. The numerical simulation results show that, during the linear phase of KHI, the LHDI, whose duration time is approximately Δt
1 ∼ 10t

A
, appears around the high-density arms. During the nonlinear phase of KHI, the LHDI appears around the KH vortexes, with a duration of about Δt
2 ∼ 5t

A
. The LHDI disappears with the decay of KH vortex.
Reflection and transmission of ultrasonic waves in a layered structure with a functionally graded porous piezoelectric base
Authors: Vashishth Anil K , Bareja Umang , Gupta Vishakha
Published: June 2024

The phenomenon of reflection and transmission of waves offers valuable insights into the internal composition and structural characteristics of materials. This study investigates the reflection and transmission of waves in functionally graded porous piezoelectric materials. These materials, distinguished by their customised electromechanical attributes and gradual property variations, present a promising avenue for optimizing performance across diverse applications, including ultrasonics. The reflection and transmission of ultrasonic waves in a novel structure, consisting of a fluid half-space (FHS) positioned above n porous piezoelectric layers, situated on top of a functionally graded porous piezoelectric half-space (FGPPHS) is studied in this paper. The material properties of FGPPHS are considered to vary along the vertical direction and and resulting equations are solved analytically and numerically. The transfer matrix method is employed to analytically determine the energy ratios and amplitude ratios for reflected and transmitted waves. Numerical computations are performed to study the impacts of frequency, gradation, angle of incidence, and porosity on the energy ratios. Furthermore, the influence of stacking of the number of porous piezoelectric layers above FGPPHS, and the choice of materials (Barium Titanate (BaTiO
3), PZT − 5H, PZT − 7H) in layers and half-space, on the energy ratios are studied. The absolute value of acoustic impedance is plotted for various angles of incidence and porosities. From the graph, it is found that the acoustic impedance can be controlled by adjusting porosity in the structure. This will be helpful in minimizing the energy loss at ceramic-medium interface and improving the mismatch of acoustic impedances at the interfaces of medical ultrasonic imaging devices or underwater sonar detectors, and NDE applications. Further, because of lower acoustic impedance, lower density and stiffness of porous piezoelectric materials, the outcomes of this study will be helpful in designing SAW devices.
An efficient pressure sensor based on environmental-friendly CNTs-graphene-PDMS film
Authors: Sadiq Hammad , Hu Hui , Huang Song , Rizwan Muhammad , Muhammad Abdullah , Nawaz Muhammad Asif , Zeeshan Muhammad
Published: June 2024

Given the rapid advancements in artificial intelligence, there is an escalating demand for wearable sensors. An efficient graphene-based material synthesized from the mesophase pitch of waste slurry oil was integrated into a cost-effective piezoresistive pressure sensor consisting of a conductive film made of carbon nanotubes (CNTs), graphene, and Polydimethylsiloxane (PDMS). A simple fabrication approach has been suggested to infuse PDMS with CNTs-graphene, resulting in a pressure sensor exhibiting superior conductivity, enhanced sensitivity, and quick responsiveness to diverse pressure variations. Moreover, films containing varying percentages of graphene were compared. Scanning electron microscopy was utilized to examine the surface and structural characteristics of the CNTs-graphene-PDMS film, alongside studying the pressure sensor's sensing capabilities. Various applications were examined for both the individual sensor and the array of sensors. The findings demonstrate the successful detection of diverse human motions, Morse code recognition, and effective discernment of various pressures by the fabricated pressure sensor, indicating its potential for applications in smart devices, robotics, and wearable sensors.
Rumor spreading and control in both homogeneous and heterogeneous networks with guidance mechanism
Authors: Wu Yanting , Liu Shijie , Li Xiaohan , Zhao Donghua , Liu Maoxing , Sun Yongzheng
Published: June 2024

In this paper, we study the influence of authoritative institutions on rumor propagation and establish an IHSQR model, where Q represents the guided individuals. We consider the homogeneous and heterogeneous network models, respectively. By analyzing the conditions for the global asymptotically stable of equilibria in these models, we show their behavior under various scenarios. For the homogeneous network model, a case study of the Haze rumor is given, which verifies the effectiveness of the model. For the heterogeneous network model, we introduce optimal control to determine the minimum guidance strength and cost. The results show that the guiding role has a significant impact on rumor spread. Specifically, the stronger the guiding role, the smaller the size of rumor spreading. Therefore, to control the spread of rumors, authoritative institutions can play an important guiding role in managing and mitigating rumor propagation.
Conditions and benefits of X-point radiation for the island divertor
Authors: Feng Y. , Winters V. , Zhang D. , Geiger J. , Gao Y. , Reiter D. , Helander P. , Beidler C.D. , Endler M. , Gradic D. , Jakubowski M. , König R. , Kremeyer T. , Krychowiak M. , Naujoks D. , Otte M. , Perseo V. , Reimold F. , Schlisio G. ,   the W7-X Team
Published: June 2024

We present a method to geometrically quantify the three magnetic island chains with the poloidal mode numbersm= 4, 5, and 6 (referred to in this paper as high-iota, standard, and low-iota islands, respectively), on which the W7-X divertor relies. The focus is on a comparative study of their detachment performance using a series of models of different physical and geometrical complexity, ranging from one- to three-dimensional (1D to 3D). In particular, it aims to identify the key physical elements behind the correlation between impurity radiation and island geometry and the associated detachment stability. Assuming intrinsic carbon as a radiator, we scan the three island chains with the EMC3-Eirene code based on otherwise identical code inputs. We find that the three islands behave differently in the radiation distribution, in the development of the radiation zones during detachment, and in the ‘radiation costs’, defined as the product of impurity and electron density near the last closed flux surface. While the radiation costs for the iota = 5/4 and 5/5 island chains linearly increase with the total radiation, the low-iota island with iota = 5/6 shows a bifurcation behavior in the sense that the radiation costs initially increase and then decrease when the total radiation exceeds a critical level. Consistent with the numerical trends, stable detachment, which is experimentally easy and robust to achieve with the standard iota = 5/5 island chain, remains an experimental challenge with the low-iota configuration. Dedicated numerical experiments show that the recycling neutrals and the ratio of parallel to perpendicular heat transport, which depends closely on the field line pitch, play a significant role in the formation and evolution of the radiation layer. A deeper understanding of the underlying physics relies on simpler models that explain why and how flux expansion can reduce the radiation costs. From these insights, we derive the conditions in which detached plasmas can benefit from the expansion of flux surfaces around the X-point. We show and explain why the current divertor design limits the actual capability of the high-iota configuration and propose solutions. The work is presented within a theoretical/numerical framework but cites relevant experimental evidence to emphasize its practical significance.
Thermal conductivity of Al/AlN interpenetrating phase composites with different preform porosity
Authors: Yan Xiao , Zhao Chunzhi , Sasaki Gen
Published: June 2024

In this investigation, the thermal conductive (TC) properties of the Al/AlN interpenetrating phase composites (IPCs) with varying preform porosity at different temperatures (20°C to 200°C) were studied. The TC values obtained through experimentation were compared to predictions generated by analytical models. IPCs with higher preform porosity exhibit higher TC. The TC of IPCs exhibits an inverse temperature dependence. Theoretical models accurately predict the thermal conductivity of IPCs with high preform porosity.
Experimental study on the influence of welding structure details of TC4 titanium alloy under thermo-vibration coupling environment on vibration fatigue life
Authors: Liu Jianghua , Zhao Zicheng , Wang Bin , Wang Cunxian , Lv Jinfeng , Wen Yongshuai , Zhao Nan , Li Liyuan
Published: June 2024

The widespread application of titanium alloy materials in aerospace structural design makes them susceptible to thermo-vibration coupling fatigue failure in harsh vibration and thermal environments. Vibration fatigue issues significantly affect the safety and operational reliability of aircraft. In order to obtain optimal design details for titanium alloy welding structures under thermo-vibration coupling conditions, experimental specimens with different structural details of TC4 titanium alloy welding structures were designed to simulate actual structural designs. The structural details included skin with U-shaped supports at different angles, skin with L-shaped supports, and skin with T-shaped supports. A thermo-vibration coupling vibration fatigue test system was established, and vibration fatigue tests were conducted at a temperature of 150°C. All structural fatigue crack failures occurred at the welds. The experimental results were statistically analysed, and using the Chauvinet criterion, abnormal data points were removed. The influence of structural details on vibration fatigue life was determined through F-tests. It was found that for the skin with a U-shaped support structure, a support angle of 90° resulted in a longer vibration fatigue life. When comparing skin with T-shaped support and skin with L-shaped support structures, the T-shaped support structure exhibited a longer vibration fatigue life. Among the three structural types, the skin with a T-shaped support structure has the longest vibration fatigue life. These experimental conclusions serve as important references for the design of thin-walled structures in aircraft structural design.
Influence and mechanism of titanium doping on the electrochromic performance of nickel oxide nanofilm
Authors: Zhang Zuosheng , Zhang Yong , Shen Die
Published: June 2024

This research investigates the preparation and electrochromic performance of titanium-doped nickel oxide nanofilms. Through chemical bath deposition, nickel oxide doped with various ratios of titanium (NiO) films was successfully synthesized. The study extensively analyzes the structural features and properties of these films using such characterization techniques as X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy, among others. The experimental findings highlight that moderate titanium doping (0.3%) notably enhances the porous structure and crystalline properties of NiO films, leading to improved optical modulation (88%), coloring efficiency (CE up to 42.6 cm2/C), and cycle stability (maintaining 61% optical modulation after 500 cycles). However, excessive titanium doping tends to diminish the electrochromic response time. These results underscore the significant impact of titanium doping on the electrochromic performance of NiO films, providing essential insights for their potential applications in smart windows, displays, and related fields.
Finite element simulation analysis of vibration transmission characteristics of double shell based on ANSYS
Authors: Chen Zhe , Ding Chao , Liu Zhen , Sun Shilin
Published: June 2024

Ship noise contains a large number of low-frequency line spectrum features. It is difficult to distinguish where they come from and even more difficult to identify the ship’s target types using the line spectrum. Therefore, research on ship targets’ vibration transmission characteristics and radiation noise is of great importance for underwater target recognition. From the perspective of underwater acoustic target recognition, this article establishes a simplified finite element model of the double shell using ANSYS, calculates the displacement response of the double shell under harmonic loads, and conducts modal analysis, harmonic response analysis, and transient dynamic analysis, which verifies the consistency of vibration between the inner shell and outer shell. Marine experimental data show that the low-frequency line spectrum of ship noise is related to the vibration frequency of ship main engines. It may be caused by diesel engine vibration transmitted through ship hull vibration and can be used as an auxiliary feature for underwater acoustic target recognition.
Internal flow field changes and cavitation characteristics research of the high-pressure axial plunger pump
Authors: Zheng Xiaofeng , Zhou Kai
Published: June 2024

High pressure axial piston pumps have the characteristics of high power density, small volume and high integration degree and are used in coal machinery, construction machinery and other industrial fields. However, the cavitation impact of the oil flow field inside the pump directly affects the performance and stability of the plunger pump. Once the fault occurs, it will cause the equipment to stop, threatening the life of the current personnel. Taking the axial piston pump as the research object, this paper conducts a numerical simulation analysis of part of the basin model in the piston pump, discusses the fluid characteristics and cavitation mechanism in the piston pump, and provides a theoretical reference for the design and application of high pressure pumps.
Honeycomb structure design of automotive crash box
Authors: Jia Tang , Hui Guo , Shuang Huang
Published: June 2024

The crash box can protect the safety of passengers when a car collides. Due to its excellent mechanical properties, honeycomb structure can be applied to automotive crash boxes. Two kinds of crash boxes made of regular hexagonal honeycomb structure and re-entrant hexagonal honeycomb are designed. The research results indicate that, compared to the crash box made of hexagonal honeycombs, the crash boxes made of re-entrant hexagonal honeycombs have superior energy absorption ability. Furthermore, the influence of different structural parameters on the energy absorption performance (EAP) of the crash box made of re-entrant hexagonal honeycombs is analyzed. It is found that the total energy absorption and peak force increase with the increase of thickness and concave angle. The research in this article provides certain reference significance for the design of honeycomb structure crash boxes.
Surface-enhanced raman scattering properties of Au@TiO2 plasma exciton array structures
Authors: Wang Xinxin , Hui Kezhen , Liu Jiaming , Huang Jinghui , Xu Jianchun , Guo Limin , Wang Xiaohui
Published: June 2024

Surface Enhanced Raman Scattering (SERS) is an ultrasensitive spectroscopic analysis technique widely used for molecular detection. SERS is characterized by rapid analysis, trace detection, ultra-high sensitivity, non-destructive, etc., and can analyze the concentration, composition, and structure of the detected substances. It has a significant potential for application in many fields, such as biomedicine, trace detection, food safety, and environmental protection. However, fabrication of homogeneous, stable, and ultrasensitive SERS substrates remains a challenge for the practical application of SERS technology. Precious metals and semiconductors have been proven attractive and versatile for SERS detection. In this work, three-dimensional Au@TiO2 substrates were prepared using a facile strategy, and two different types of Raman probe molecules were used to demonstrate the versatility of the design. Using 4-MBA as the probe molecule, the enhancement factor of the TiO2 substrate could reach 1.52×104, and the detection limit was as low as 10-16 M. The results indicate that the Au@TiO2 substrate is simple to prepare, inexpensive, and serves as an excellent SERS substrate structure. 4-MBA and R6G dual probe molecules demonstrate the universality of the Au@TiO2 nanocavity array structure. In the meantime, the results of the simulations match the experimental results. It also demonstrates that the three-dimensional Au@TiO2 has the potential to be an excellent SERS substrate.
Investigation of a modified IEA 15MW wind turbine including a winglet with a new mid-fidelity acoustic toolchain
Authors: Seelemeyer Philipp , Appel Christina
Published: June 2024

This paper presents the applicability of a new hybrid tool chain for wind turbine rotor turbulent boundary-layer trailing-edge noise (TBL-TEN) to complex rotor geometries. The research introduces a rapid, high-fidelity 2D CFD/CAA method, which enables the assessment of innovative low-noise profile designs concerning TBL-TEN, coupled with a mid-fidelity extrapolation technique for the 3D analysis, aiming to minimize computational time essential for design processes. This procedure is applied here to compare the changes in performance, load distribution and noise reduction if a winglet is added to a large-scale wind turbine, using the example of the IEA Wind TCP Task 47 15-MW-reference turbine [12]. In the first step, a 3D CFD calculation of the entire turbine is performed in order to derive the local flow parameters and thus the input variables for the 2D CAA. These results for the 2D TEN are then extrapolated for the entire turbine using the fast summation and extrapolation method TAP (Turbine acoustic prediction) [1]. As only data for the TEN is included here, only this noise source for the winglet can be analyzed. For a more complete comparison, a 3D scale-resolving simulation was set up for a static wind tunnel situation in order to be able to qualitatively classify the tip/vortex interaction noise that was not recorded by the procedure mentioned above.
Improved RANS methodology to account for flow separation on rough blades
Authors: Gutiérrez R , Aranguren P , Zamponi R
Published: June 2024

The RANS inaccuracy in predicting flow separation becomes relevant in thick-modern blades, especially once they get dirt or eroded. The literature has tackled the problem by modifying the coefficient a
1 in the k − ω − SST turbulence model without considering its dependency on the adverse pressure gradient condition. This study aims to assess the mentioned dependency by estimating a
1 per blade side and angle of attack. Pressure-coefficient measurements for 18 %, 25 %, and 30 % thick airfoils in clean-inflow conditions at a Reynolds number based on chord of 3 × 106 are considered in the estimation. Hence, a unique variation of a
1 is obtained per each airfoil, justifying the need to adapt a
1 locally within the OpenFOAM code. This modification considerably improves the flow separation prediction with respect to the standard a
1 value and the fb
method. As a result, the CL
error is reduced by 8 %, whereas a certain CD
error remains for all the RANS solutions. Finally, an aeroelastic model of a 4.5 MW wind turbine reveals that the non-corrected RANS solution causes an overshoot of power and loads near rated power, whereas the corrected RANS replicates the shape of the power and loads curves. Consequently, the suggested methodology can be used to search for the required a
1 relation to local flow conditions.
Improvements to the Blade Element Momentum Formulation of OpenFAST for Skewed Inflows
Authors: Branlard E. , Jonkman J. , Lee B. , Jonkman B. , Singh M. , Mayda E. , Dixon K.
Published: June 2024

In this work, we modify the blade element momentum algorithm of OpenFAST to improve its predictions under large skewed inflow conditions. We use the well-known Glauert’s skew correction and introduce continuous extension of the model for high-thrust conditions. We present the rationale behind Glauert’s empirical model and discuss the different conventions possible for the axial induction factor. We verify the model against the higher-fidelity lifting-line vortex method and blade-resolved computational fluid dynamics, and we observe that the new implementation enhances the accuracy and reliability of OpenFAST’s aerodynamic modeling capabilities in conditions involving large skew angles. For the parametric studies run using the different codes, we find that the power changes with the skew angle as cos1.7(θ
skew) and the thrust as cos0.65(θ
skew). An analysis of the azimuthal variation of the induced velocities in the rotor plane reveals that current redistribution models used in blade element momentum codes may need to be refined.
A directivity correction for accurate semi-empirical wind turbine noise prediction
Authors: Saldaña O , Rautmann C , Plaza A
Published: June 2024

Public acceptance of wind farms is a significant challenge in the development of wind energy. The acoustic impact generated by wind turbines is a common concern among local residents. The primary noise source in wind turbines is generated by aerodynamics. Atmospheric turbulence reaching the blade leading edge or turbulent boundary layer passing the trailing edge produce the main aeroacoustic sources. The noise generated by these mechanisms is commonly predicted by means of semi-empirical models, which do not demonstrate great reliability when compared to acoustic measurements. This paper presents a correction to the directivity of airfoil noise radiation, resulting in improved sound pressure levels on the ground plane surrounding a wind turbine. This improvement is achieved without requiring any additional computational effort. The sound pressure levels perceived on the ground plane are known to have asymmetrical shape. Maximum noise levels correspond to observers directly in the upwind and downwind locations, whereas the minimum levels belong to the positions close to the rotor plane. Said asymmetrical shape is not represented in the semi-empirical models. The proposed correction takes into consideration the airfoil thickness in the radiation directivity equations, resulting in the expected asymmetrical shape of noise footprints on the ground plane around a wind turbine. The correction was found to not affect the accuracy of the spectrum predicted by the semi-empirical models when compared to dedicated field measurements under the standard IEC 61400-11 procedure. When implementing the proposed correction, the virtual NREL 5 MW wind turbine’s published noise footprints, which were originally calculated using computationally expensive methods, are accurately reproduced.
Numerical investigation of effects of riblets on wind turbine performance
Authors: Tubije J M , Jin Yaqing , Leonardi Stefano
Published: June 2024

In this study, systematically designed wind tunnel experiments were conducted to characterize the aerodynamic performance of a DU91-W2-250 airfoil with a riblet film. To quantify the impact of the riblet film on wind turbine performance, experimental results were used as input data for numerical simulations. Large-eddy simulations were conducted for the smooth and modified airfoils under uniform and turbulent inflow conditions. For the turbulent inflow simulations, staggered cubes were introduced upstream of the wind turbine to generate velocity fluctuations in the flow. Results from the numerical simulations show that improvements in the aerodynamic performance of the airfoil with riblets enhance the aerodynamic torque that drives the wind turbine, thereby increasing the power output. The improvement in the power coefficient with the use of the riblet film is higher for turbulent incoming wind compared to uniform flow conditions.
An innovative segmented blade concept with a partial pitch control for large wind turbine systems
Authors: Kim Taeseong , Hou Lio Alan Wai , Lee Gyeong Han , Choi Dong Kuk , Lee Soo Yong
Published: June 2024

This study investigates the feasibility of a segmented blade with a partial pitch concept. Three different cases were considered where the pitch bearing is positioned at 33%R, 50%R and 66%R, respectively. The PI controller is used with different controller gains corresponding to the blade design. Wind step case and DLC1.1 are applied to analyse its performances. From the wind step case, general controller behaviours and wind turbine responses are investigated. From DLC1.1, the statistics and ultimate loads are studied. From this study, it could be concluded that the segmented blade with a partial pitch could benefit to maintain power without increasing extra loads too much.
How does the blade element momentum method see swept or prebent blades?
Authors: Li Ang , Gaunaa Mac , Pirrung Georg Raimund , Lønbæk Kenneth
Published: June 2024

The blade element momentum (BEM) method is among the mostly used engineering aerodynamic models for wind turbine rotors. Even though the BEM method is strictly only applicable to straight blades forming a planar rotor, it is in practice used for load calculation and design optimization of blades with relatively large sweep, prebend or coning. The present work aims to answer the question: How does the BEM method see swept or prebent blades? The blade element part of the method can be adapted for swept or prebent blades by projecting the velocity and loads between the 2-D airfoil section and the 3-D blade geometry under the cross-flow principle. However, momentum theory considers the 3-D wake and the induction of a planar actuator disc with straight blades. There could be significant differences between the results calculated from different implementations of the BEM method, while the details of the implementations are often omitted in the literature. In the present work, a consistent implementation including the definition of airfoil section alignments and the coordinate systems is provided. It is shown that for a given circulation distribution, the BEM method will predict approximately the same local aerodynamic loads for non-straight blades as if the blades were straight and the rotor was planar. This means using the BEM method to perform aerodynamic optimization of modern rotors with curved blades and/or rotors that are not planar can only have little meaningful result. In order to model the impact of the wake geometry on the induction, more advanced models that take into account the wake geometry on the induction are necessary.
An aeroelastic coupling of an actuator sector model with OpenFAST in atmospheric flows
Authors: Mohammadi Mohammad Mehdi , Chanprasert Warit , Olivares-Espinosa Hugo , Ivanell Stefan
Published: June 2024

This study presents an implementation of an aeroelastically coupled actuator sector model with OpenFAST in a neutral atmospheric boundary layer flow for a 15 MW reference turbine. Three structural cases with different levels of fidelity are considered. In addition, the results from an aeroelastic actuator line model are used for comparison. The results of the structural cases show the significance of including the torsional deflections and structural nonlinearities to accurately calculate the blade loads as it reduces the power and flapwise damage equivalent load values considerably. In terms of the wake flow, there are differences in the near wake between the considered structural cases. Despite this, further downstream the differences become non-significant. In addition, the results from the actuator sector model are in agreement with those obtained from the actuator line model while using the actuator sector model offers a reduction of around 55% to 80% in the computational time depending on the used structural solver.
Moving control surfaces in a geometry-resolved CFD model of an airborne wind energy system
Authors: Pynaert Niels , Haas Thomas , Wauters Jolan , Crevecoeur Guillaume , Degroote Joris
Published: June 2024

Properly understanding the unsteady interaction of the wind with the aircraft is critical to develop reliable airborne wind energy (AWE) systems. High-fidelity simulation tools are needed to accurately predict these interactions, providing insights into the design and operation of efficient and safe AWE systems. In this work, we present a computational fluid dynamics (CFD) framework of an airborne wind system which resolves all lifting surfaces and includes moving control surfaces. This work considers a reference multi-megawatt ground-gen pumping system. To simulate complex fluid flow problems, with large rigid-body motion and deflecting control surfaces using CFD, we opt for the Chimera/overset technique. The goal of this contribution is to demonstrate the effect of the control surfaces in the CFD framework. This work is a major milestone in the ongoing development of high-fidelity aero-servo-elastic simulation models for airborne wind energy systems.
Numerical investigation of vortex-induced forces on a wind turbine tower segment at very high Reynolds numbers
Authors: Ebstrup K , Sørensen N N , Bertagnolio F , Grinderslev C , Horcas S G
Published: June 2024

The vortex-induced forces on an extruded cylinder with a span of two diameters representative of a finite segment of a non-tapered wind turbine tower at a very high Reynolds number (Re = 8.0×106) are numerically investigated using an incompressible Navier-Stokes flow solver with an Improved Delayed Detached Eddy Simulation (IDDES) turbulence model and correlation-based boundary layer transition modelling. The solution shows spanwise correlated structured vortex shedding with the Strouhal number St = 0.48. The boundary layer transition is found to occur at θ
transition = 70
◦
, and boundary layer separation is found to occur at θ
separation = 120
◦
. Results from the grid dependency study strongly imply that when using IDDES, the Strouhal number converges to higher values than previously reported by the literature as the grid is refined, with results ranging from St ∼ 0.44 using a grid with 4.2 × 106 cells, to St = 0.48 for the finest considered grid with 33 × 106 cells. This behaviour is not seen for URANS, where St = 0.33 for the finest grid.
Aerodynamic and Structural Assessment of Floating Wind Turbine Rotor Under Varying Tilt Angle
Authors: Mian H H , Siddiqui M S , Franchina N , Kouaissah O , Wang G , Nygaard T A
Published: June 2024

Predicting the aerodynamic performance of floating offshore wind turbines (FOWTs) proves challenging due to platform motion induced by waves. The effect of wind and waves results in a six-degree-of-freedom motion of the platform, directly influencing turbine performance. Understanding the impact of specific degrees of freedom (DOF) motions on aerodynamics and structural response is crucial for effective wind turbine design. This research examines the impact of rotor tilt on both aerodynamic performance and structural response. The investigation employs computational fluid dynamics (CFD) analysis and mapping aerodynamic loads onto the finite element (FE) mesh for structural analysis. The study employs a comprehensive 3D simulation, utilizing the moving reference frame (MRF) method for the NREL 5 MW reference wind turbine CFD simulations. It explores different rotor tilt angles (5°, 10°, 15°, and 20°) encountered by offshore structures during their operation and examines their impact on aerodynamic performance. Predicted aerodynamic loads were mapped onto the blade FE mesh using the radial basis function (RBF) interpolation technique and solved using the open-source FE solver CalculiX. The analysis shows that the turbine performance is relatively unaffected up to a tilt angle of 10°. However, further increase in rotor tilt angle adversely impacts turbine performance, leading to notable reductions in thrust and power output. The fluid-structure coupled analysis provided insights into the deformations and stresses experienced by the turbine blade, indicating a notable increase in flap-wise displacement for larger tilt angles, while edge-wise displacement is not as significantly affected. The maximum stress location on the blade generally correlates well with actual observations.
Floating wind turbine stability and time response analysis with rotating modes
Authors: Pamfil Bogdan , Bredmose Henrik , Kim Taeseong
Published: June 2024

The periodic azimuthal time dependence of a linearized simple floating wind turbine model with four degrees of freedom is dealt with by developing a particular procedure that enables a stability analysis calculation and reduces computational efforts to calculate time responses. We apply Hill’s method for the aeroelastic stability analysis by generating a constant state-space hyper-matrix that takes into account the periodic azimuthal dependence of the system. It is used to compute precisely the time domain response and to solve an overall eigenvalue problem where natural frequency and modal damping are determined through the eigenvalues. For a varying rotational speed with a fixed air density, eigenfrequencies from Hill’s method are displayed on a Campbell diagram that is based on a waterfall plot of the frequencies obtained by decay tests peaks using the time domain model. Through the modal analysis as well, an investigation of the impact of aerodynamic damping is done following the same procedures by rather fixing the rotational speed and varying air density. In the end, a forcing moment of the platform pitch motion is added to analyze the accuracy of fast time response calculations compared to the time domain model benchmark results.
Multi-fidelity, steady-state aeroelastic modelling of a 22-megawatt wind turbine
Authors: Zahle Frederik , Li Ang , Lønbæk Kenneth , Sørensen Niels N. , Riva Riccardo
Published: June 2024

In this work we present multi-fidelity steady-state aeroelastic framework that leverages the state-of-the-art simulation tool HAWC2 for the structural model, and a variety of aerodynamic models, comprising of the low fidelity blade element momentum (BEM) method, the medium fidelity blade element vortex cylinder (BEVC) method and the coupled near wake and vortex cylinder method, and finally the high-fidelity CFD solver EllipSys3D. The aeroelastic framework is part of AESOpt, an aerostructural framework for design of wind turbine blades. The different aerodynamic models are applied to compute the aeroelastic steady state of the newly designed IEA 22 MW Reference Wind Turbine. The results show a very good agreement between the medium- and high-fidelity aerodynamic models with a maximum of 2.7% difference between the high-fidelity aeroelastic response and that of the lower fidelities.
Edgewise Structural Damping of a 2.8-MW Land-Based Wind Turbine Rotor Blade
Authors: Chetan Mayank , Bortolotti Pietro
Published: June 2024

Modern wind turbines push the predictive capabilities of state-of-the-art aero-servo-elastic tools. The existing limitations hide across the numerical tool chain and can result in serious issues, such as missing aeroelastic instabilities during the design phase. Structural damping is an input that is usually hard to estimate, but also has a major impact on the turbine behavior. In this paper, we discuss an experiment that aims to accurately quantify the structural damping characterizing the edgewise modes of modern wind turbine blades. The experiment is carried out on a 2.8-MW land-based wind turbine and features a fast yaw actuation that induces an edgewise motion on one of the three blades. The Covariant-subspace system identification (Cov-SSI) method is then used to post-process the blade root moment to estimate the short-term edgewise structural damping. Despite limitations of the Cov-SSI method, which consistently under-predicts the absolute values of damping, we observe that structural damping decreases across the first three blade edgewise modes, which is different from the stiffness-proportional damping model that assumes that structural damping increases with the modes. This paper argues that a stiffness-proportional damping model, which is implemented in most aeroelastic tools, is therefore not conservative and might hide aeroelastic instabilities that can instead appear in the field.
Mitigating blade erosion damage through nowcast-driven erosion-safe mode control
Authors: Barfknecht N , Imhoff R , Von Terzi D
Published: June 2024

The erosion-safe mode (ESM) is a novel mitigation strategy that reduces rainfall-induced erosion damage by lowering the tip-speed of the turbine during precipitation events. The ESM requires accurate information about future expected rainfall for its control. In current research, it is debated what method or source should be used to this end. This study explores the effectiveness of driving the ESM using a state-of-the-art weather-radar-based probabilistic rainfall nowcast provided by the Royal Netherlands Meteorological Institute (KNMI). The performance of the nowcast is assessed for various lead times with an impingement-based damage model for three sample sites in the Netherlands and for two distinct ESM strategies. The results show that the quality of the nowcast degrades with increasing lead times, where the 5- and 15-minute lead times exhibit sufficiently good accuracy and response time for adjusting turbine speeds. Overall, the results highlight that the probabilistic information in the nowcast can be employed to improve the efficiency and viability of the ESM.
Optimization of curtailment intervals of wind turbines through assessment of measured loads during start-up and shutdown events
Authors: Ziegler Lisa , Schulze Andreas , Henning Michael
Published: June 2024

There is an increasing amount of curtailment of wind parks due to grid overload or negative market prices. Operators need to also account for the effect of curtailment on component loads, wear, and lifetime. This paper investigates curtailment leading to turbine shutdown. A novel methodology to optimize the length of curtailment intervals based on load neutrality is introduced. Measurement data from the structural health monitoring system of an onshore and an offshore wind turbine are used to quantify effects of curtailment on loads and wear of tower, blade, and pitch system. Shutdown and start-up events increase loads on the tower and pitch system. Blades benefit from lower edgewise loads and reduced erosion. Results show that load neutrality for the tower is reached on average after 63 min of idling for the onshore and after 200 min for the offshore wind turbine evaluated (not generalizable). An optimal curtailment strategy shall use flexible time intervals but ensure load neutrality on yearly average. This can serve as a simple and valuable guideline for wind farm operators to evaluate the criticality of curtailment times in terms of asset fatigue life. Future research shall investigate curtailment strategies that also include deration of power output.
A Virtual Actuator for Advanced Individual Pitch Control (IPC)
Authors: Hovgaard T. G. , Caponetti F. , Grunnet J. D.
Published: June 2024

We present a virtual actuator concept for wind turbine control, wherein rotor force and moment references from various controllers are optimally combined to compute individual blade pitch angles. The approach aims to minimize pitch bearing wear, too. The combined references can come from known control algorithms such as speed regulation, tilt-yaw control, tower dampening and helical wake control [3]. We formulate this as an optimization problem which we solve in an MPC fashion, however, instead of the usual prediction horizon over time, we use a discretized azimuth map as our finite horizon. Serving as a unified interface for all control features utilizing individual pitching, the virtual actuator replaces the plethora of multi-blade transformations and gain-scheduling functions in traditional IPC with one coherent function. Users can directly prioritize features and input constraints on actuators and structural loads. Notably, upstream control algorithms provide rotor force or moment references rather than pitch references. Simulations showcase the virtual actuator’s ability to compute intricate pitch trajectories, surpassing the capabilities of conventional IPC methods. Our method yields novel individual pitching which optimally merges conflicting IPC objectives while minimizing actuator wear.
Automatic Detection and Intensity Classification of Pitch Misalignment of Wind Turbine Blades: a Learning-based Approach
Authors: Milani Sabrina , Leoni Jessica , Cacciola Stefano , Croce Alessandro , Tanelli Mara
Published: June 2024

In recent years, monitoring wind turbine operations, especially in offshore and remote installations, has become crucial. System failures, challenging assessments, and costly maintenance operations are notable concerns. Blade pitch misalignment poses one of the most significant threats, being a leading cause of downtime and energy production reduction. Traditional assessments through frequent inspections are resource-intensive and time-consuming; still they are frequently required as turbines lack routine implementation of effective automatic detection systems.

To address this, our study introduces a novel machine learning-based method for autonomous pitch misalignment recognition, which relies on signals measured by a limited set of sensors, already integrated into modern wind turbines. From those signals, frequency domain features derived by harmonic analysis are extracted, ensuring robust detection also in turbulent wind conditions.

This innovative method lays the groundwork for early and precise wind turbine diagnostics, promoting the shift from time-based to condition-based inspections. This transition aims to reduce maintenance costs and unexpected downtime, ultimately enhancing energy production.
Enhanced Modeling of Joint Yaw and Axial Induction Control Using Blade Element Momentum Methods
Authors: Liew Jaime , Heck Kirby , Howland Michael F.
Published: June 2024

Wind turbine control via concurrent yaw misalignment and axial induction control has demonstrated potential for improving wind farm power output and mitigating structural loads. However, the complex aerodynamic interplay between these two effects requires deeper investigation. This study presents a modified blade element momentum (BEM) model that matches rotor-averaged quantities to an actuator disk model of yawed rotor induction, enabling analysis of joint yaw-induction control using realistic turbine control inputs. The BEM approach reveals that common torque control strategies such as K − Ω2 exhibit sub-optimal performance under yawed conditions. Notably, the power-yaw and thrust-yaw sensitivities vary significantly depending on the chosen control strategy, contrary to common modeling assumptions. In the context of wind farm control, employing induction control which minimizes the thrust coefficient proves most effective at reducing wake strength for a given power output across all yaw angles. Results indicate that while yaw control deflects wakes effectively, induction control more directly influences wake velocity magnitude, underscoring their complementary effects. This study advances a fundamental understanding of turbine aerodynamic responses in yawed operation and sets the stage for modeling joint yaw and induction control in wind farms.