bluuebunny/crossref_metadata_2025 huggingface dataset:
Changes in above- versus belowground biomass distribution in permafrost regions in response to climate warming
Authors: Yun Hanbo , Ciais Philippe , Zhu Qing , Chen Deliang , Zohner Constantin M. , Tang Jing , Qu Yang , Zhou Hao , Schimel Joshua , Zhu Peng , Shao Ming , Christensen Jens Hesselbjerg , Wu Qingbai , Chen Anping , Elberling Bo
Published: June 2024

Permafrost regions contain approximately half of the carbon stored in land ecosystems and have warmed at least twice as much as any other biome. This warming has influenced vegetation activity, leading to changes in plant composition, physiology, and biomass storage in aboveground and belowground components, ultimately impacting ecosystem carbon balance. Yet, little is known about the causes and magnitude of long-term changes in the above- to belowground biomass ratio of plants (η). Here, we analyzed η values using 3,013 plots and 26,337 species-specific measurements across eight sites on the Tibetan Plateau from 1995 to 2021. Our analysis revealed distinct temporal trends in η for three vegetation types: a 17% increase in alpine wetlands, and a decrease of 26% and 48% in alpine meadows and alpine steppes, respectively. These trends were primarily driven by temperature-induced growth preferences rather than shifts in plant species composition. Our findings indicate that in wetter ecosystems, climate warming promotes aboveground plant growth, while in drier ecosystems, such as alpine meadows and alpine steppes, plants allocate more biomass belowground. Furthermore, we observed a threefold strengthening of the warming effect on η over the past 27 y. Soil moisture was found to modulate the sensitivity of η to soil temperature in alpine meadows and alpine steppes, but not in alpine wetlands. Our results contribute to a better understanding of the processes driving the response of biomass distribution to climate warming, which is crucial for predicting the future carbon trajectory of permafrost ecosystems and climate feedback.
Chapter 8. Ireland, Scotland, Wales
Authors: Moran Pádraic
Published: June 2024

This chapter examines the historical significance of the Latin language in Ireland, Scotland, and Wales during the medieval period. It provides a historical overview of the linguistic and cultural connections between these regions, surveying the arrival of Latin literary culture and the subsequent development of native Latin scholarship, most notably in the fields of grammar, computistics, biblical exegesis, and hagiography. The chapter also gives a summary account of the characteristic features of Hiberno-Latin in particular, with regard to phonology and orthography, vocabulary, morphology, syntax, and stylistics.
Chapter 11. Chronological and regional layers - Poland
Authors: Wójcik Rafal
Published: June 2024

The paper presents a brief review of Latin literature in Poland from its origins (the second half of the tenth century) until 1543 (the year traditionally considered the end of the Middle Ages in Poland). The study points especially to chronicles from the early medieval period, as well as to so called late Middle Ages in Poland, ca. 1440–1543.
Chapter 26. Latin traditions in medieval cartography
Authors: Gautier Dalché Patrick
Published: June 2024

The tradition of medieval maps is studied, mainly that of the mappae mundi, representations of the oecumene or the terrestrial sphere. These images, diagrammatic or offering topographical details, originate from the educational tradition of Antiquity. They are found in great numbers in manuscripts, but also in monumental ensembles (religious buildings or palaces). They were constantly reworked according to the interests of their authors and the functions they attributed to them. Their functions are varied: knowledge of the places they depict is a prerequisite for allegorical exegesis; in monasteries, they serve as a support for spiritual practices; sovereignty is justified by domination over a world they represent; military expeditions are planned thanks to the geopolitical vision they provide.
Chapter 29. Gendering authorship
Authors: Ferrante Joan
Published: June 2024

This contribution reviews the roles of women in medieval Latin literature (history, poetry and religious texts), as composers of texts and as inspirers or provokers of men’s texts. It also notes texts that are no longer extant but whose existence and sometimes quality is known because they are referred to in the works of men who received them.
Chapter 39. Hamlet
Authors: Giovampaola Chiara della
Published: June 2024

This chapter focuses on Hamlet. The starting point is the Latin account of Saxo Grammaticus, dated to the thirteen century, and the endpoint is Shakespeare’s play. It investigates the relation between the two in terms of similarities and differences regarding the plot and the main characters. The chapter reserves special attention to the theme of pretended madness. Moreover, in comparing the two versions, it aims to track Hamlet’s origins in the Nordic and Roman tradition and the mutations which occurred from Saxo to Shakespeare. It also attempts to explain the reasons for Hamlet’s fortune in Medieval and Modern literature.
Sonic Hedgehog activates prostaglandin signaling to stabilize primary cilium length
Authors: Ansari Shariq S. , Dillard Miriam E. , Zhang Yan , Austria Mary Ashley , Boatwright Naoko , Shelton Elaine L. , Stewart Daniel P. , Johnson Amanda , Wang Christina E. , Young Brandon M. , Rankovic Zoran , Hansen Baranda S. , Pruett-Miller Shondra M. , Carisey Alexandre F. , Schuetz John D. , Robinson Camenzind G. , Ogden Stacey K.
Published: June 2024

Sonic Hedgehog (SHH) is a driver of embryonic patterning that, when corrupted, triggers developmental disorders and cancers. SHH effector responses are organized through primary cilia (PC) that grow and retract with the cell cycle and in response to extracellular cues. Disruption of PC homeostasis corrupts SHH regulation, placing significant pressure on the pathway to maintain ciliary fitness. Mechanisms by which ciliary robustness is ensured in SHH-stimulated cells are not yet known. Herein, we reveal a crosstalk circuit induced by SHH activation of Phospholipase A2α that drives ciliary E-type prostanoid receptor 4 (EP4) signaling to ensure PC function and stabilize ciliary length. We demonstrate that blockade of SHH-EP4 crosstalk destabilizes PC cyclic AMP (cAMP) equilibrium, slows ciliary transport, reduces ciliary length, and attenuates SHH pathway induction. Accordingly, Ep4−/− mice display shortened neuroepithelial PC and altered SHH-dependent neuronal cell fate specification. Thus, SHH initiates coordination between distinct ciliary receptors to maintain PC function and length homeostasis for robust downstream signaling.
Control of intrinsic ferroelectricity and structural phase in pure HfO2 films via crystalline orientation
Authors: Zhang Haiyi , Tu Yuchen , Wang Zijian , Zhou Xiang , Wang Yuchen , Du Xinzhe , Shen Shengchun , Yin Yuewei , Li Xiaoguang
Published: June 2024

The ferroelectricity of hafnia-based thin films has garnered considerable attention in both academic researches and industrial applications. However, the fundamental properties, such as high coercivity, the wake-up effect, and the mechanism of ferroelectricity have not been fully elucidated. Here we report the crystallization orientation control of structural phase and ferroelectricity in pure HfO2 thin films. Both (001)- and (111)-oriented HfO2 thin films exhibit a mixture of ferroelectric orthorhombic and non-ferroelectric monoclinic phases. With decreasing film thickness, the orthorhombic phase ratio increases for both orientations, with a consistently higher proportion for (111)-oriented film. Consequently, the ferroelectricity is significantly enhanced in thinner (111)-oriented film. Remarkably, both (001)- and (111)-oriented pure HfO2 thin films demonstrate an intrinsic ferroelectricity. Moreover, the coercive field of the (001)-oriented film appears to be lower than that of the (111)-oriented film. Additionally, oxygen ions migrate more easily in the (001)-oriented film, which exhibits distinct electronic structure and local atomic ordering compared to the (111)-oriented film. These results provide valuable insights into the ferroelectricity of HfO2 and suggest that crystalline orientation is an effective approach to explore the ferroelectric properties in hafnia-based films.
Plasmonic properties and stability of Au and Cu nanoparticles embedded in cerium oxide
Authors: Spurio Eleonora , Pelatti Samuele , D’Addato Sergio , Luches Paola
Published: June 2024

With the aim of sensitizing cerium oxide—a very important catalytic material—to visible light, its coupling with Au and Cu nanoparticles is investigated. The samples are grown by physical synthesis by embedding a layer of nanoparticles between two cerium oxide films. The films are controlled in composition by in-situ x-ray photoemission spectroscopy and in morphology by ex-situ scanning electron microscopy. The optical properties as a function of the oxide thickness, investigated by spectrophotometry in the UV-Vis range, are interpreted based on the results of the morphological characterization and of simulations based on the Maxwell Garnett model. The stability of chemical and optical properties after air exposure is also investigated. The results, indicating that stable materials with tuneable optical properties can be obtained, are important in view of the potential application of the investigated systems in photocatalysis.
Hyperchaotic color image encryption scheme based on simultaneous color channel confusion-diffusion operations
Authors: Kengnou Telem Adélaïde Nicole , Tchito Tchapga Christian , Nkapkop Jean De Dieu , Nguimfack Ndongmo Jean De Dieu , Tsafack Nestor , Boui A Boya Bertrand Frederick
Published: June 2024

Shortcomings have been identified in current color image encryption methods. Firstly, these methods encrypt each color channel separately, resulting in a time-consuming process and independent encrypted channels, which can make hacking easier. Secondly, the use of XOR operations between image pixel values and code values during encryption can be vulnerable. To address these issues, a novel algorithm is introduced that incorporates a new XOR operation and simultaneous encryption of color channels. This approach creates interdependence between the encrypted channels, reduces encryption time, and enhances security by introducing a more complex XOR operation. The proposed method employs a substitution technique that involves XOR operations between groups of pixels and codes, inspired by the principles of the fast Walsh-Hadamard transform algorithm. The encryption process involves several key phases that enhance the security and efficiency of the system. In the initial phase, line processing involves mixing lines from different channels and application of chaotic substitution permutation operations. Subsequently, a similar operation is applied to columns, and finally, the channels are divided into overlapping squared sub-blocks, with a newly XOR proposed chaos-based confusion operation simultaneously applied to the three-channel sub-blocks. These phases are designed to ensure interdependence between color channels and reduce encryption time, resulting in a more robust encryption method. With this method, the RGB cipher channels become mutually dependent, rendering decryption of one channel impossible without the others. The approach has been evaluated using appropriate metrics and found to be robust, efficient, and resistant to various attacks, outperforming recently published methods. It is suitable for modern image encryption applications, including those related to the Internet of Medical Things (IoMT).
Comprehensive analysis of COVID-19 transmission dynamics: mathematical modeling, stability analysis, and optimal control strategies
Authors: ullah Ibad , Ali Nigar , Ul Haq Ihtisham , Daher Albalwi Mohammed , Muhammad Shah , Shuaib Mohammad
Published: June 2024

This paper presents a mathematical model for comprehensively analyzing the transmission dynamics of COVID-19. We investigate the model’s various properties, such as positivity, boundedness, and the existence and uniqueness of solutions. Additionally, we calculate the basic reproductive number, denoted as R
0, to gauge the epidemic’s potential spread. Furthermore, we conduct a stability analysis to understand the long-term behavior of the model. Furthermore, we devised an optimal control strategy to effectively curb disease transmission. Using graphical analysis, we assess the impact of secondary infection rates and quarantine rates across different population groups. Finally, we compare our proposed numerical scheme with the well-known RK-4 scheme, emphasizing the NSFD scheme’s ability to maintain positivity, unlike the RK-4 scheme. Our numerical simulations offer strong evidence supporting the theoretical findings, demonstrating the effectiveness of our results.
Three-dimensional transient multilayer heat conduction sphere comprising metallic particles
Authors: Riasat Saima , Ramzan Muhammad , Alshahrani Saad , Kumar R S Varun , K Chandan
Published: June 2024

A numerical approach employing finite element methodology is utilized to analyze the thermal behavior of a three-dimensional multilayer sphere composed of copper, single-wall, and multi-wall carbon nanotubes. The study investigates the external heat flux, temperatures within the three spherical layers, and their associated contours. Notably, this research diverges from prior studies by opting for copper, single-wall, and multiwall carbon nanotubes instead of generic metallic layers. Graphs are generated to illustrate the relationships between various effects and profiles. Analysis of temperature contours and distributions under non-uniform heat flux reveals that temperatures are more concentrated towards the center when the initial temperature is non-zero compared to scenarios where the inner surface starts at zero temperature. Temperature contours at t = 2, 5, 7, 9, 11, 13, 15, 27, 35, and 45 s with non-zero initial temperature are calculated. For non-zero initial temperature contours are drawn for t = 2, 45 s temperature contours are drawn. Temperature in radial azimuthal and tangential directions for t = 1, 1.5, 2, 2.5, 3 s and steady state are drawn. The initial temperature of the ith surface is kept at

f

i

(
r
,
θ
,
ϕ
)

,

where

r

o

≤
r
≤

r

3

,
0
≤
θ
≤
π
,
0
≤
ϕ
≤
2
π
.

It has been concluded that for zero initial temperatures after 45 s, the temperature is at

0.005

K

and Temperature contours for non-zero inner layer temperature t = 5 s shows

10.7

K
.
Enhanced floating debris detection algorithm based on CDW-YOLOv8
Authors: Shi Chenan , Lei Meizhen , You Weiqi , Ye Haitao , Sun Haozhe
Published: June 2024

The issue of floating debris on water surfaces is becoming increasingly prominent, posing significant threats to aquatic ecosystems and human habitats. The detection of floating debris is impeded by complex backgrounds and water currents, resulting in suboptimal detection accuracy. To enhance detection effectiveness, this study presents a floating debris detection algorithm rooted in CDW-YOLOv8. Firstly, the study augments the original C2f module by incorporating the Coordinate Attention (CA) mechanism, resulting in the C2f-CA module, to boost the model’s sensitivity to target locations. Secondly, the study substitutes the standard Upsample module with the DySample module to diminish model parameters and increase flexibility. Furthermore, the study incorporates a small object detection layer to enhance the detection performance of small floating debris. Lastly, the Complete-IOU (CIOU) loss function is substituted by the Focaler-Wise-IOU v3 (Focaler-WIoUv3) loss function, which aims to minimize the impact of low-quality anchor boxes and improve regression accuracy. Experimental results demonstrate that the improved CDW-YOLOv8 algorithm has realized a comprehensive performance improvement in accuracy, recall rate, mAP@0.5, and mAP@0.5:0.95, noting increases of 2.9%, 0.6%, 2.5%, and 1.5%, respectively, relative to the original YOLOv8 algorithm. This offers a robust reference for the intelligent detection and identification of floating debris on water surfaces.
Delay segmented tristable stochastic resonance system driven by non-gaussian colored noise and its application in bearing fault detection
Authors: He Lifang , Cao Longmei , Zhang Junsheng
Published: June 2024

This study investigates the Delayed Segmented Tristable Stochastic Resonance (DSTSR) system under the influence of additive non-Gaussian colored noise. The research employs an improved segmented tristable potential function, wherein the equilibrium points and barrier heights can be independently controlled by parameters. Simultaneously, the segmented function on both sides reduces the restrictions of higher-order terms on the walls of the potential wells. The equivalent Langevin equation for the DSTSR system is obtained using the path integral method, the unified colored noise approximation method, and the small-delay approximation. Subsequently, the theoretical expressions for the steady-state probability density, mean first passage time (MFPT), and Signal-to-Noise Ratio (SNR) are derived from the resulting equations, and the impact of variations in system parameters on these performance metrics is discussed. Additionally, Monte Carlo simulations for MFPT are conducted to verify the accuracy of the theoretical derivations. Combining the results from the theoretical section and the impact of parameters on system performance, the article employs an adaptive genetic algorithm to optimize system parameters. This algorithm is then applied to simulation experiments and bearing fault detection. In the simulation experiments, the DSTSR system is compared with other systems. The results indicate that the DSTSR system exhibits the highest SNR improvement. Furthermore, in bearing fault detection under non-Gaussian colored noise, the DSTSR system shows higher spectral amplitude and SNR at the fault frequency compared to the tristable stochastic resonance system and the segmented tristable stochastic resonance system without time delay feedback. This suggests that stochastic resonance can effectively detect weak signals in non-Gaussian non-white noise scenarios, and the introduction of time delay contributes to the occurrence of stochastic resonance to a certain extent.
Design and analysis of the C6H6-filled circular photonic crystal fiber with ultra-flat dispersion for broadband supercontinuum generation with peak power of 130 W and 250 W
Authors: Trong Duc Hoang , Van Lanh Chu , Thi Thuy Nguyen
Published: June 2024

This article introduces a new model of a circular silica-based photonic crystal fiber with a hollow core filled with C6H6. The difference in the air hole size and the distance between them in the first ring around the core has a profound effect on the dispersion, leading to ultra-flat dispersion with values as low as ±0.996 ps nm−1· km in wavelength range 0.74 µm. The high nonlinear coefficient of several 1000 W−1 · km−1 and the low confinement loss of a few tens of dB m−1 suggest proposing three fibers with dispersion and nonlinear properties suitable for broadband supercontinuum generation at low peak power. The influence of peak power on the broadening of the supercontinuum spectrum is also investigated. Fibers with a flat all-normal dispersion profile provide a smooth spectrum with bandwidths of 1.215 and 1.626 µm at 30 dB with a peak power of 250 W. A fiber with an anomalous dispersion regime generates a supercontinuous spectrum, broadening to 3.868 µm in the mid-infrared region (2.467 µm bandwidth at 30 dB) under laser pulse excitation with 130 W peak power. Our results provide further insights into the generation of broadband mid-infrared supercontinuum using liquid-core silica-fibers, which have great potential for applications in the fields of optical communications and optical sensing.
Connection strength analysis for composite fuselage gate structures of civil aircraft
Authors: Wu Yang , Qiu Xudong , Bai Chunyu , Liu Hu
Published: June 2024

Civil aircraft boarding gate is an important channel for passengers to enter and exit the aircraft, and is also an important part of the aircraft structure, with the function of maintaining cockpit pressure. Traditional boarding doors are made of metal, and with the large number of composite materials used in the bearing structure of civil aircraft, composite boarding doors are also used in new civil aircraft. The strength of the connection inside the new composite boarding gate is related to the safety of passengers and crew. This paper focuses on the connection problem of the internal structure of composite boarding gate, aiming to analyze its connection strength under working conditions. This paper establishes a real finite element model of the boarding gate according to the loading condition and force transmission characteristics of the civil aircraft door and analyzes the connection strength of the structure such as the skin and the transverse and longitudinal beams, the skin and the side frame, the transverse and longitudinal beams connection, and the stop block in turn. The study shows that the strength of the connecting structures of the boarding gate designed by using composite materials is reasonable and can meet the service requirements of the boarding gate, thus demonstrating the rationality of the boarding gate structure designed with composite materials.
On modelling strain gradient viscoelasticity of polymer nanocomposites
Authors: Jiang Yiyuan , Li Li , Hu Yujin
Published: June 2024

Theories of generalized continuum mechanics have found great success in the analysis of nanostructures. However, there exists no work on analysing composites whose constituents are generalized continua. The present work fills this gap and studies the strain gradient viscoelasticity of polymeric nanocomposites. The key problem is to assign the nonclassical boundary condition of the representative volume element (RVE). To resolve it, a perturbation field is superposed on the homogeneous displacement boundary condition. The wavelength of perturbation is comparable to the strain gradient characteristic length. Simulations to obtain the macroscopic effective mechanical properties are performed, which agree well with the experimental data. The frequency dependence of the perturbation field is revealed, and it has a clear physical interpretation in terms of the segmental motions of polymer chains.
Study on the corrosion fatigue properties of ultrasonic surface strengthened axle steel
Authors: Liu Yu , Zhao Xiaocan
Published: June 2024

Owing to fatigue damage and environmental erosion, locomotive axles are prone to premature failure during service. It is therefore very important to improve the corrosion fatigue properties of axles. In this paper, the fatigue behavior of ultrasonic surface strengthened axle steel under corrosive environment was studied. The surface integrity of ultrasonic strengthened axle steel was characterized by microscopic analysis and hardness test. The fatigue data and fatigue fracture of axle steel under corrosion environment were compared. Also, the mechanism of the corrosion environment on fatigue crack initiation and propagation was analyzed. Results show that serious plastic deformation is generated in the surface of axle steel after ultrasonic strengthening. The grains in surface layer are obviously refined and get coarse gradually as deep into the matrix. The hardness of surface layer is greatly improved as well. The maximum value is located on the outermost surface, about 2 times of the matrix. Under the same fatigue load, the fatigue cycle number for ultrasonic strengthened axle steel is more than that of original sample. This is due to grain refinement, work hardening, and residual compressive stress induced by ultrasonic strengthening, which inhibits fatigue crack initiation in corrosion environment.
Analysis of crack propagation of annular butt weld and distribution of weld-induced residual stress
Authors: Zhu Jin , Xia Jie , Jin Hui
Published: June 2024

The circumferential surface crack propagation and the effect of weld-induced residual stress were analyzed to comprehensively understand the mechanical behavior and fracture resistance of dissimilar girth welded joints of steel castings. The evaluation of stress intensity factors is conducted for circumferential cracks on internal surfaces, aiming to predict the fracture toughness of dissimilar welded joints. The distribution of weld-induced residual stress is obtained by thermal elastic-plastic finite element methods. The impact of residual stress on the propagation of cracks is investigated through the application of extended finite element theory. The high-stress intensity factors were found in such dissimilar welded joints due to the local bending and distortion caused by the asymmetrical weld geometry. The tensile residual stress and distortion were applied to the weld root area and its vicinity. Both the asymmetrical weld geometry and tensile residual stress contribute to the tensile distortion of the inner surface around the weld root, and enable the growth of internal surface cracks in the circumferential direction and radially from inside out of the welded joint. The fracture resistance decreases with the simultaneous influence of residual stress and welds’ asymmetry.
Highly elastic polymer substrates with local strain management for stretchable electronic applications
Authors: Chen Sujie , Li Ming , Han Lei
Published: June 2024

Stretchable electronic devices have been extensively investigated in healthcare and wearable electronics. The stretchable substrate with strain control is paramount to integrating rigid devices into stretchable electronic systems for high mechanical strain. The common approach utilizes rigid strain control islands integrated on the surface of the soft stretchable matrix, but strain concentration effect and poor adhesion at the interface between the rigid islands and the elastic substrate are challenges. In this work, a stretchable substrate is developed by embedding the bottom strain control islands into the interior of an elastic substrate and the top strain control islands on the substrate surface to minimize strain concentration and improve the adhesion of the interface. The simulation results show that the strain concentration at the interface of the top island is suppressed and the maximum strain on the substrate surface is reduced by more than 30%. The interface between strain control islands of PI film and elastic substrate of Ecoflex can maintain more than 3000 stretch cycles under repeated strain of 100%. A stretchable inverter is fabricated based on this stretchable substrate with stretchable conductive wire. It is shown that the voltage transfer characteristics of the stretchable inverter have no significant change under strain of 100% for more than 3000 stretch cycles, demonstrating the capability of this stretchable substrate to integrate rigid devices for reliable stretchable electronic systems.
Effects of T6 treatment on the microstructure and mechanical properties of az80 magnesium alloy
Authors: Jiang Rui , Wang Ruolan , Ding Boyuan , Zhang Zhenwei
Published: June 2024

The mechanical and microstructure properties of the AZ80 magnesium alloy in deformed and T6 states were evaluated and analyzed by tensile testing and metallographic analysis. The results showed that the grain size of the magnesium alloy increased after T6 treatment, whereas the number of deformed grains decreased considerably. These changes were accompanied by a transformation of the β-Mg17Al12 phase from a discontinuous point-like morphology to a continuous lath-like morphology. After T6 treatment, the tensile strength and yield strength of the material were significantly improved. These findings indicated that the microstructure of the AZ80 magnesium alloy was altered through T6 treatment, and its mechanical properties were markedly enhanced.
Experimental study of scaled-down model ejection water ballistics and two-phase flow of gas and water
Authors: Diao Zhenting , Fang Dengjian , Zhou Yuan
Published: June 2024

There are many factors affecting the hydrodynamic and water ballistic trajectory of vehicles launched underwater, among which the ejection gas pressure, initial motion parameters of the submarine launch platform and the launching water depth have a particularly significant influence. Since it is costly and too long time to carry out a real-size study on the influence of underwater launching parameters, this paper adopts a scaled-down model ejection test to study the evolution characteristics of the flow field of vehicle launched underwater with different ejection pressures and initial ejection angles to reveal the influence of the above parameters on the characteristics of the water ballistics.
Study on the influence of vibration characteristics of ship’s stern structure
Authors: Zhou Quan , Gu Ruizhao , Liao Shuting , Wang Hongfu , Lv Yang , Chen Lin
Published: June 2024

The stern structure of the ship, as the primary source of vibration and noise, has always been widely studied. Conducting an analysis of the vibration characteristics of the stern and determining the impact of local structures on the complex coupled vibration in the stern section are particularly important aspects of research. This paper employs the structural-acoustic coupling methodology to investigate the vibration features of the stern of a ship. The study explores the influence of variations in parameters such as the rudder, stern frame, and shaft system on the vibration response of the stern. The results provide valuable insights into controlling vibration and noise in the stern section of ships, as well as informing the design of related structures.
Three-point support analysis and optimization design under the change of gravity center of diamond lathe
Authors: Hu Jiongfeng , Xia Huiheng , Zhang De , Li Jingtong
Published: June 2024

The position of three-point support has an important impact on the stiffness and accuracy of the diamond lathe. To determine the position of the support, this paper commences by conducting static and dynamic analysis on the large-size platform machine tool whose base is 2340×1540 mm under the two support schemes. It determines the basic layout scheme of the support points of the machine tool under the change of gravity center. Subsequently, by combining the least squares fitting and particle swarm optimization algorithm with the optimization goal of minimum deformation of the machine tool base working surface, the position of the support points is optimized under the influence of the Change of Gravity center. The results indicate that the optimal solution of the design variable within the design interval can be obtained through limited sampling points and optimization iterations. The average and maximum deformation of the base working surface are 0.867 μm and 1.45 μm. They decreased by 11.17% and 26.02% compared with before optimization.
Numerical investigation of the vortical structures in the near wake of a model wind turbine
Authors: Weislein Tobias , Seel Ferdinand , Lutz Thorsten , Krämer Ewald
Published: June 2024

It is well known that the vortex system in a horizontal axis wind turbine wake is highly relevant in terms of fatigue loads and performance of wind turbines located in the wake of other wind turbines. The breakdown process of tip vortices particularly influences the mixing process of the low-speed wake region with the undisturbed flow outside the wake. As a collaboration with the Technische Universität Berlin (TUB), a major goal in a joint research is to study the effects involved in tip vortex breakdown. TUB designed a model turbine that will be towed through a large water tank to analyse and to control the tip vortex decay. To accommodate the measurement equipment, the ratio of blade length to nacelle length is unconventionally small, leading to uncertainty regarding the effect on the breakdown of the tip vortex. Due to the dimensions of the model wind turbine the root vortex system and the nacelle wake are not comparable to former studies and should therefore be investigated in detail. To do so computational fluid dynamics, in particular delayed detached eddy simulations, are conducted for the model turbine with the compressible flow solver FLOWer and the two-equation Menter-SST turbulence model. Two simulations are conducted with and without the nacelle. The results indicate that the root vortices propagate downstream and interact with each other. Additionally, these vortical structures are also influenced by the geometry of the turbine nacelle which causes faster decay of the root vortices compared to a configuration without the nacelle. However, the root vortex breakdown does not influence the tip vortices as the turbulent intensity matches for the area where tip vortices are present. In short, this investigation shows that the influence of the nacelle geometry and root vortex system on the tip vortices is negligible. Thus, the model wind turbine designed by TUB is suitable for the investigation of tip vortices.
Numerical prediction of aerodynamic loads acting on a blade section-model oscillating in stall
Authors: Cortes N , Amandolese X , Pfister JL , Blondel F , Boisard R , Schotté JS , Mauffrey Y
Published: June 2024

For blades operating close to stall angle of attack, one of the potential instabilities is known as stall flutter. It is a dynamic instability in torsion for which the mechanism of energy transfer relies on a dynamic stall process where the flow separates partially or completely during each cycle of oscillation. It leads to dynamic loops in lift, drag and moment that affect the aerodynamic performance of the blade, create unsteady stresses in the blades and can lead to fatigue damage. In the present study, dynamic loops of a NACA 634421 airfoil in forced pitch oscillations have been simulated with the FastS CFD solver based on a URANS modelling approach and compared to benchmark experiments as well as results obtained with the ONERA semi-empirical dynamic stall model using a unique set of dynamic parameters that best fit the experimental dynamic loops. The dynamic tests have been conducted for a mean angle of attack of 13.5°, an amplitude of oscillation of 8° and three reduced frequencies k
1 = 0.0183, k
2 = 0.0785 and k
3 = 0.183. This study has shown that the CFD FastS solver can satisfactorily reproduce the unsteady lift and moment coefficients experienced by a section model oscillating in stall.
Performance improvement of a Vestas V52 850kW wind turbine by retrofitting passive flow control devices
Authors: Manolesos M , Celik Y , Ramsay H , Karande R , Wood B , Dinwoodie I , Masters I , Harrold M , Papadakis G
Published: June 2024

This study presents the results of a collaborative effort between academia and industry aimed at further enhancing the benefits provided by Vortex Generators and Gurney Flaps. To achieve this objective, an integrated approach was employed, involving wind tunnel experiments, on-site measurements, and computational simulations to design devices tailored for an onshore (Vestas V52, 850 kW) turbine and assess their influence on turbine performance. Device selection was based on wind tunnel measurements, while their positioning on the blade was based on infrared thermography images from the field. A Reynolds Averaged Navier Stokes solver was used to predict the performance of the devices on both airfoil and blade level. The final assessment of the upgrade pack was based on SCADA data and Lidar measurements. The results show that an Annual Energy Production uplift of 5.77% is measured for this turbine.
Validation of a BEM correction model for swept blades using experimental data
Authors: Fritz Erik , Boorsma Koen , Ferreira Carlos
Published: June 2024

This study validates a correction model, which extends standard blade element momentum theory to swept blades and, by doing so, enhances wind turbine simulation predictability for these advanced geometries. This correction model addresses limitations in BEM algorithms, accommodating the complexities of swept blades by considering the sweep-induced tip vortex displacement and curved bound vortex self-induction. The validation is based on previously published results from wind tunnel experiments on a horizontal axis wind turbine with straight and swept blades, providing blade-level aerodynamic data for comprehensive numerical comparisons. In both blade configurations (straight and swept), good agreement is found between experimental and numerical results, validating the numerical approach. For the swept blade case, an additional comparison to a BEM algorithm assuming a straight blade and to one accounting for crossflow is drawn, underscoring the former’s inadequacy for swept blades. Comparably minor differences between the fully-corrected and only crossflow-corrected algorithms render the assessment of the proposed BEM correction model’s added benefit uncertain. Using the validated BEM algorithm, the experimental results are corrected for twist deformations of individual blades, enabling a direct comparison of the campaigns with straight and swept blades. Results align with expectations, indicating sweep-induced reductions in axial induction and blade loads in the swept blade section.
Validating low- and high-fidelity simulations of a yawed 8 MW wind turbine against measurements
Authors: Höning L , Meyer P J , Huhn M L , Theron J N , Thomas P , Wegner A , Mechler S , Gottschall J , Stoevesandt B
Published: June 2024

This paper presents a comparison study of the aerodynamic behavior of an 8 MW wind turbine operating under yawed conditions using field measurements, Blade Element Momentum (BEM) theory and Computational Fluid Dynamics (CFD). Turbulent inflow wind field measurements are used to generate an IEC-compliant turbulence box upstream of the wind turbine that is used within the BEM tool MoWiT and the CFD tool chain by IWES in OpenFOAM. Both simulation approaches take into account blade flexibility using modal reduced, anisotropic beam elements in BEM and Geometrically Exact Beam Therory (GEBT) in CFD. While the focus is being set towards the CFD approach, turbine power output, blade root bending moments and blade tip deflections are analyzed. It is shown that both modeling approaches react differently towards the generated wind field.
Design of an efficient experiment for identification-based stability analysis of operating wind turbines
Authors: Hermes Armin , Riva Riccardo , Zahle Frederik , Madsen Jesper , Bergami Leonardo , Skovby Casper
Published: June 2024

This paper proposes a new approach to calculate aeroelastic stability of operating wind turbines using system identification, and explores how an efficient numerical experiment can be designed. The data-driven method is based on time series including induced motion of the blades, which can stem from any fidelity simulation. While this study utilises HAWC2, the findings enable the usage of e.g. computational fluid dynamics in a fluid-structure-interaction simulation. Different forcing sequences are suitable to excite the blade, but especially the doublet and chirp show favourable characteristics and results for an application of no more than five seconds. System identification, the Multivariable Output-Error State sPace (MOESP) algorithm in particular, is used to find an algebraic equivalent of the simulated turbine. Using the output-only version, about 20 seconds of simulated time are sufficient to identify the system such that the predicted response matches the input with an R
2-score of > 99.8 %. A comparison with HAWCStab2 shows frequency differences of < 0.5% across the wind speed range, matching mode shapes but some bigger deviations in aeroelastic damping.
High-fidelity simulations of airfoil vortex-induced vibrations: from 2D to blade-like aspect ratios
Authors: Fernandez-Aldama Ricardo , Papadakis George , Lopez-Garcia Oscar , Avila-Sanchez Sergio , Riziotis Vasilis A
Published: June 2024

Large edgewise vibrations due to vortex shedding can be suffered by a wind turbine blade when the rotor is stopped or idling and there is massively separated flow. High-fidelity simulations of these vortex-induced vibrations (VIV) with a full-blade model are very computationally expensive, and so currently reported results of this type are limited to short time series or reduced parameter spaces, far from being sufficient to predict the lock-in range and other characteristics of a full-scale blade response to VIV under real conditions. This computational cost has led researchers to, alternatively, study VIV using simplified approaches, like simulations of 2D and short-span airfoil sections. To help bridge the gap between expensive full-blade and short-span airfoil section simulations, in this work the VIV response of an airfoil section is obtained for three different aspect ratios —from 2D to a blade-like aspect ratio—, using CFD simulations coupled with a one-degree-of-freedom structural oscillator model. The results obtained show that inside the lock-in range the airfoil’s initial VIV response is very similar for all aspect ratios studied, despite notable differences in the Strouhal number obtained. In contrast, outside lock-in the aerodynamic forces vary substantially from one case to another.
On the role of induced power in turbine wake scaling: bridging 100-m to 0.1-m rotors
Authors: Major Desirae , Schmitz Sven
Published: June 2024

A wake scaling methodology is proposed in which turbine power is separated into its induced and profile power components. It is shown that preserving induced power as a function of thrust coefficient in conjunction with the radial circulation distribution are sufficient conditions for wake scaling. This work demonstrates the primary role of induced power in scaling turbine wakes over three orders of magnitude from full-scale down to model-scale rotors. The extended theory is verified using blade-element momentum theory (BEMT) and large-eddy simulation (LES), and an example set of model-scale turbine wake experiments is proposed for known wind tunnel facilities around the world.
Efficient Prediction of Turbulent Inflow and Leading-Edge Interaction Noise Using a Vortex Particle Method with Look-up Table Approach
Authors: Sharma Sparsh , Herr Michaela
Published: June 2024

This paper presents a new, efficient approach for predicting turbulent inflow, also known as leading-edge interaction noise. The method combines a low-fidelity Vortex Particle Method (VPM) with a look-up table approach. Its goal is to reconstruct realistic inflow turbulence and airfoil contours using stochastic control variables within a limited vortex window. To model far-field sound emission, Curle’s equation and a vortex sound database are employed. To increase confidence in the methodology, an analysis of inflow turbulence parameters and source characteristics was performed using systematic Large Eddy Simulations (LES). A generic NACA 0012 airfoil test case with different inflow turbulence grids was used for direct comparisons with semi-theoretical and semi-empirical predictions from the literature. The comparison is restricted to Amiet/Gershfeld predictions as the current model is only capable of dealing with homogeneous and isotropic turbulence. However, their usefulness is limited to narrower parameter ranges when compared to the more generally applicable new method. A satisfactory agreement of the results demonstrates the versatility of the proposed method.
The Influence of Floating Turbine Dynamics on the Helix Wake Mixing Method
Authors: Van Den Berg Daniel , De Tavernier Delphine , Gutknecht Jonas , Viré Axelle , Van Wingerden Jan-Willem
Published: June 2024

Wake mixing techniques like the Helix have shown to be effective at reducing the wake interaction between turbines, which improves wind farm power production. When these techniques are applied to a floating turbine it will excite movement. The type and magnitude of movement are dependent on floater dynamics. This work investigates four different floating turbines. Of these four turbines, two are optimised variants of the TripleSpar and Softwind platforms with enhanced yaw motion. The other two are the unaltered versions of these platforms. When the Helix is applied to all four floating turbines, the increased yaw motion of the optimised TripleSpar results in a reduction in windspeed whereas the optimised Softwind sees an increase in windspeed with increased yaw motion. From simulations using prescribed yaw motion at different phase offsets between blade pitch and yaw motion, we can conclude that this is the driving factor for this difference.
Assessing risks for the use of drones for wind turbine inspections
Authors: Kolios Athanasios
Published: June 2024

This paper presents a comprehensive risk assessment framework for integrating drones into wind turbine inspections, addressing technical, operational, human factors, environmental, and regulatory risks. Utilizing a multidimensional approach based on Failure Modes Effects and Criticality Analysis (FMECA), the study evaluates potential risks in drone-assisted wind turbine inspections, considering various factors like communication reliability, sensor functionality, battery performance, and environmental impacts. The research emphasizes the importance of systematic risk identification, evaluation, and prioritization in enhancing the safety and reliability of drone operations in the renewable energy sector. The framework’s practical application is demonstrated through a case study involving real-world offshore wind farms, engaging industry experts and employing structured data collection methods. The study identifies, assesses, and offers mitigation strategies for critical risks, underlining the significant potential of drones in optimizing maintenance processes and advancing sustainable energy production. Future research directions include refining risk assessment methodologies, advancing drone technology, and fostering international collaboration for broader adoption of drone-based inspections in renewable energy.
About control of bi-wind turbine single-point-moored floating offshore wind turbines
Authors: Sandua-Fernández I , Martín-San-Román R , Eguinoa I , Cascales-Gómez A , Iribas-Latour M
Published: June 2024

In the last years, several novel floating offshore wind energy concepts have appeared in the market, whose goal is the reduction of floating offshore wind energy costs. Among them, bi-wind turbine floating offshore wind turbines, which use a single floating platform to place two wind turbines, are one of the most promising ones. However, they face some challenges in their full deployment. For example, depending on the wind direction, one of the rotors could be found downstream of the other one and hence be affected by its wake. To avoid this, the turbines of this type of systems do not use a conventional active yaw mechanism, but a single-point-mooring configuration, to allow the platform rotation around the vertical axis. This way, the alignment of the rotors with the wind can be achieved, avoiding wake issues. However, as stated in the literature, at least for single-rotor wind turbines, this alignment is not straightforward and some yaw drift could appear in the platform. Therefore, the main goal of this paper is to confirm that this platform yaw drift could also arise in bi-wind turbine single-point-moored floating wind energy systems, and analyse its impact in terms of performance, while shedding some light on the performance improvements when applying new advanced control strategies.