bluuebunny/crossref_metadata_2025 huggingface dataset:
Isochoric thermal conductivity of Kr and Ar crystals. Heat transfer by vacancies
Authors: Bondarenko A. I. , Manzhelii V. G. , Popov V. A. , Strzhemechnyi M. A. , Gavrilko V. G.
Published: December 2024

The isochoric thermal conductivity is measured in Kr crystals with molar volumes from 28.84 to 29.54 cm3/mol and Ar crystals with molar volumes of 24.30 cm3/mol at temperatures of the order of and exceeding the corresponding Debye temperatures. An excess of the thermal conductivity λ above that which would follow from λ∼1/T is found, this excess increasing with temperature. Energy transport by vacancies is proposed as the mechanism responsible for this “excess”thermal conductivity. The temperature dependence of this “excess” thermal conductivity is used to determine the isochoric activation energy for self-diffusion Qv. Recalculated values of the isobaric activation energy Qp are found to be in good agreement with direct diffusion measurements for Ar and Kr.
A challenging future for Carnaby’s Cockatoo (Zanda latirostris) under a changing climate
Authors: Saunders Denis A. , Mawson Peter R. , Dawson Rick , Pickup Geoffrey
Published: December 2024

Context With climate change causing unprecedented and rapid changes, conservation agencies need to establish the impacts on vulnerable and threatened species to prioritise actions to minimise threats associated with those impacts. Aims Carnaby’s Cockatoo (Zanda latirostris) is endemic to south-western Australia and this paper provides data to underpin future conservation management actions. Methods We used data on the commencement of egg laying, breeding success, nestling condition, fledgling survival over their first year, and annual survival from the first year to construct a life table to examine the impacts of decreasing annual rainfall and increasing temperature in south-western Australia on the future viability of Carnaby’s Cockatoos. Key results Long-term survival of Carnaby’s Cockatoos will be impacted by changes in rainfall, projected to be 16% drier in winter and up to 20% drier in spring, and by an increase in the number of days with maxima ≥35°C, conditions when the birds are unable to forage. Conclusions This drying and warming is likely to lead to a further contraction in the range of Carnaby’s Cockatoo. Implications Conservation management needs to address revegetation of foraging and breeding areas, repairs to derelict natural hollows and their maintenance, and provision of artificial hollows. Management should concentrate on areas with the best prospects for species survival and recovery including in the areas identified in this paper based on life table analysis and mapped across regions.
A corollary study to substantiate the therapeutic role of receptor from Shigella flexneri in mitigating the sperm immobilization factor-mediated negative influences on mouse spermatozoa: a molecular mimicry-based approach
Authors: Soni Thomson , Jawanda Ishwerpreet Kaur , Kumari Seema , Prabha Vijay
Published: December 2024

Context Sperm immobilization factor (SIF) isolated from Staphylococcus aureus has been implicated earlier in the laboratory in infertility due to its negative impact on sperm function. Moreover, SIF was found to bind not only to human and mouse spermatozoa but also to several bacteria. Among the array of bacteria, we selected Shigella flexneri to investigate if it shares antigenic determinants with spermatozoa. Aim The study aimed to delineate receptors from S. flexneri that imitate the sperm receptor in binding SIF, to assess its therapeutic role in SIF-mediated sperm impairment. Methods Sperm immobilization binding receptor (SBR) from S. flexneri (SF-SBR) was isolated via ultrasonication and 4 M NaCl treatment, purified via chromatography and its molecular weight was estimated. The ability of SF-SBR to counteract SIF-induced sperm impairment was assessed in vitro. Further analysis included isothermal titration calorimetry and fourier-transform infrared spectroscopy to quantify the interaction of SIF and SF-SBR. Key results SF-SBR ameliorated the sperm parameters adversely affected by SIF. It also interfered with the binding of fluorescein isothiocyanate-labelled SIF to spermatozoa and bacteria. The SIF and SF-SBR interaction showed favourable thermodynamics with an entropy of 28.12 J/mol K and free energy of −18.48 kJ/mol, supporting the concept of mimicry. Conclusions The study confirmed that SF-SBR shares an epitope with the receptor on mouse spermatozoa, affirming the presence of molecular mimicry between spermatozoa and S. flexneri. Implications These findings indicate that SF-SBR can potentially be used to counteract the effects of SIF on spermatozoa, hinting at novel therapeutic approaches for treating infertility caused by microbial sperm immobilization factors.
A tale of two endothelins: the rise and fall of the corpus luteum
Authors: Szymanska Magdalena , Basavaraja Raghavendra , Meidan Rina
Published: December 2024

Endothelins are small 21 amino acid peptides that interact with G-protein-coupled receptors. They are highly conserved across species and play important roles in vascular biology as well as in disease development and progression. Endothelins, mainly endothelin-1 and endothelin-2, are intricately involved in ovarian function and metabolism. These two peptides differ only in two amino acids but are encoded by different genes, which suggests an independent regulation and a cell-specific mode of expression. This review aims to comprehensively discuss the distinct regulation and roles of endothelin-1 and endothelin-2 regarding corpus luteum function throughout its life span.
Mapping wildfires in Canada with Landsat MSS to extend the National Burned Area Composite (NBAC) time series back to 1972
Authors: Skakun Rob , Castilla Guillermo , Jain Piyush
Published: December 2024

Background Satellite imaging has improved burned area mapping; however, few studies have taken advantage of the Multi-Spectral Scanner (MSS) in early Landsat satellites, which started acquiring data 10 years earlier than Thematic Mapper (TM). Aims To expand Canada’s National Burned Area Composite (NBAC) annual time series back to 1972 using MSS data and report annual statistics and national trends for 1972–2022. Methods Pre- and post-fire image composites were created using an improved collection of MSS data available from the Google Earth Engine. A Normalized Difference Vegetation Index (NDVI) difference image was adaptively thresholded to extract burned areas, which were then vectorised. To assess accuracy, MSS fire polygons were compared with TM in a year of overlap. Key results Compared with TM, MSS polygons overestimated burned area by 5.6% when the relativised differenced NDVI was used, with significant upward trends for number of fires > 200 ha, fire season length and mean duration of fires. Conclusions MSS is a valuable data source for retrospective mapping of boreal and temperate forest fires where data from finer-resolution sensors are lacking. Implications After the addition of MSS-mapped fires, NBAC is the longest satellite-based time series of annual burned area from individually mapped fires in the world.
The computational learning of construction grammars
Authors: Doumen Jonas , Schmalz Veronica Juliana , Beuls Katrien , Van Eecke Paul
Published: December 2024

This paper documents and reviews the state of the art concerning computational models of construction grammar
learning. It brings together prior work on the computational learning of form-meaning pairings, which has so far been studied in
several distinct areas of research. The goal of this paper is threefold. First of all, it aims to synthesise the variety of
methodologies that have been proposed to date and the results that have been obtained. Second, it aims to identify those parts of
the challenge that have been successfully tackled and reveal those that require further research. Finally, it aims to provide a
roadmap which can help to boost and streamline future research efforts on the computational learning of large-scale, usage-based
construction grammars.
Investigating metaphor comprehension strategies of young Second Language students of Greek
Authors: Christodoulakis Christos , Thomou Paraskevi
Published: December 2024

This study investigates the metaphor comprehension strategies used by elementary school students with Greek as an
L2 when they encounter a Greek metaphorical expression. Using open metaphor comprehension tasks, as well as stimulated recall
interviews, the present study aims to describe students’ cognitive processes in relation to the bodily, conceptual and
sociο-experiential motivation that triggers their emergence (Kimmel, 2006; Zlatev, 2006). The results demonstrate that a variety of strategies are used by the
participants with metaphorical extension of the literal meanings dominating on the others. In the same conditions, mental imagery,
as well as universality of metaphors interact in a variety of respects and define not only the strategy that is used, but also the
extent to which the linguistic metaphors are comprehended in a non-directive context.
Swing limb detection using a convolutional neural network and a sequential hypothesis test based on foot pressure data during gait initialization in individuals with Parkinson’s disease
Authors: Chan Hsiao-Lung , Chang Ya-Ju , Chien Shih-Hsun , Fang Gia-Hao , Kuo Cheng-Chung , Chen Yi-Tao , Chen Rou-Shayn
Published: December 2024

Objective. Start hesitation is a key issue for individuals with Parkinson’s disease (PD) during gait initiation. Visual cues have proven effective in enhancing gait initiation. When applied to laser-light shoes, swing-limb detection efficiently activates the laser on the side of the stance limb, prompting the opposite swing limb to initiate stepping. Approach. This paper presents the development of two models for this purpose: a convolutional neural network that predicts the swing limb’s side using center of pressure data, and a swing onset detection model based on sequential hypothesis test using foot pressure data. Main results. Our findings demonstrate an accuracy rate of 85.4% in predicting the swing limb’s side, with 82.4% of swing onsets correctly detected within 0.05 s. Significance. This study demonstrates the efficiency of swing-limb detection based on foot pressures. Future research aims to comprehensively assess the impact of this method on improving gait initiation in individuals with PD.
Helicon normal modes in radially non-uniform plasma column
Authors: Guittienne Ph , Karimov R , Jacquier R , Furno I
Published: December 2024

Helicon discharges are often considered somewhat mysterious, exhibiting experimental behaviors that are challenging to explain, such as abrupt plasma density jumps, hysteresis, and ‘blue core’ formation, among others. A significant part of the difficulty in modeling helicon plasmas stems from the limitations of simple analytical approaches that rely on approximations, such as constant plasma density or collisionless plasma, which fail to accurately describe helicon wave physics. We developed a semi-analytical approach to determine helicon normal modes in a collisional plasma column with an arbitrary radial plasma density profile. The influence of radial density profiles on modes propagation, and particularly on their energy deposition patterns, is then investigated. Notably, the study shows that sharp density drops at the plasma column edge lead to edge-localized power deposition, whereas gently varying radial plasma profiles (bell shapes) result in axially peaked power deposition. In the former case, the rapid damping of the Trivelpiece-Gould (TG) component of the wave at the plasma edge is clearly responsible for the observed energy deposition profile. As the profile sharpness decreases, as in bell-shaped plasmas, the TG component of the modes becomes less dominant, and the radial power deposition profile is mainly determined by the Helicon (H) component. Overall, this study of normal modes also demonstrates that dominant H modes are expected to experience much less axial damping than predicted when considering constant densities. Finally, it is also shown that smooth radial density profiles allow a new family of modes to propagate, characterized by long axial wavelengths and slightly off-axis energy deposition patterns.
Resonant-cavity-enhanced Ge/Ge1−
xSnx metal-semiconductor-metal photodetector for 2 μm-band applications
Authors: Kumar Harshvardhan , Sharma Apoorv , Chen Shean-Jen
Published: December 2024

In this work, we propose high-speed and efficient resonant-cavity-enhanced (RCE) Ge/Ge1−x
Sn
x
metal-semiconductor-metal (MSM) photodetectors (PDs) integrated with p-Si interlayer that operate in the 2 um band. Additionally, the p-Si interlayer is employed in the proposed device structure to increase the Schottky barrier height and hence decrease the dark current. With the introduction of a bottom mirror, the Si/SiO2 Distributed-Bragg reflector (DBR) significantly improves the poor absorption of the conventional GeSn MSM PD. Furthermore, in the optical cavity formed by the bottom mirror and SiO2 top mirror, we incorporate an ultrathin i- Ge1−x
Sn
x
active layer. As a result, the proposed RCE PD exhibits exceptionally strong optical fields within the optical cavity as a result of the light resonance. Moreover, this work presents techniques to balance the trade-off between responsivity and the 3 dB bandwidth. Hence, the proposed RCE MSM PD with Ge1−x
Sn
x
(x = 9%) thickness of 25 nm demonstrates outstanding performance at λ = 2 μm, attaining a responsivity of 0.76 A W−1 and a 3 dB bandwidth of 58.1 GHz, all achieved with only two pairs of DBR. These values are significantly higher than the majority of the theoretical values that are currently available. This efficient and fast PD opens up new possibilities for silicon-integrated photonic circuits and their potential applications at 2 um bands.
Deep neural network-based method for designing tunable band gaps metamaterials based on shape memory alloy embedded perforated elastic metamaterials
Authors: Mao Zhuxin , Liu Shutian
Published: December 2024

This paper proposes deep neural networks (DNNs)-based optimization strategy for elastic metamaterials. It aims to attain excellent tunable elastic wave attenuation performance of shape memory alloy (SMA) embedded perforated plates by optimizing the shapes of the SMA inclusions. Firstly, the design of the SMA-embedded perforated plate is presented. By utilizing the property of SMA to phase change between martensite and austenite, a new design for achieving tunable bandgaps is introduced. The finite element method based on the Bloch–Floquet theorem is used to solve the tunable energy band structure, and the effects of geometrical variations of the SMA on the width and position of the tunable bandgap are explored. Next, DNNs is employed to establish the relationship between the geometrical parameters of the SMA and the tunable bandgap. The accuracy of the agent model is verified by performance evaluation. Finally, a strategy combining genetic algorithms and DNNs is proposed for inverse design optimization to obtain metamaterials with superior tunable bandgap performance. The results of five optimization cases demonstrate that the proposed strategy performs well in terms of computational efficiency and real-time design of multiple sets of targets. This study provides an important reference for the development and application of advanced elastic metamaterials with tunable functions.
Origin of the strong anharmonic-induced abnormal thermal conductivity in semiconductors
Authors: Yang Kaike , Liao Fang-Xiu , Zhou Xiao , Zhou Benliang , Zhai Yaxin , He Meng-Dong , Zhou Guanghui , D’Agosta Roberto
Published: December 2024

Semiconducting materials are the foundations of electronics and optoelectronics, and their heat management guides the design of highly efficient devices. For most semiconductors, the thermal conductivity of materials composed of light chemical species is higher than that of the iso-structured materials with heavy elements. For example, bulk Si shows a thermal conductivity higher than Ge. However, for many copper-based compounds, e.g. Cu halides, the thermal conductivity increases monotonously as the atomic number of halogens increases. On the other hand, for lead chalcogenides, the thermal conductivity of PbSe is lower than PbS and PbTe. In this work, we reveal that the combined effect of electronic states coupling and phonon collisions, giving rise to strong anharmonicity, is responsible for the abnormal trend of thermal conductivity of Cu halides and Pb chalcogenides. From CuCl to CuBr and CuI, the increasing thermal conductivity is due to the decreasing electronic coupling strength between Cu-occupied 3d and unoccupied 4s states when crystal symmetry is reduced, which leads to the increase of atomic vibrational potential energy and reduction of lattice anharmonicity. In Pb chalcogenides, the unusually lower thermal conductivity of PbSe than PbTe and PbS is mainly due to the intensive scattering between phonons caused by the localized transverse acoustic modes and soft optical modes, which outweigh the contribution of the crystal anharmonicity due to the anharmonic potential energy surface.
Spin-orbit coupling mediated photon-like resonance for a single atom trapped in a symmetric double well
Authors: Fan Changwei , Hu Xiaoxiao , Yan Xin , Wu Hongzheng , Li Zhiqiang , Xiao Jinpeng , Chen Yajiang , Luo Xiaobing
Published: December 2024

We employ a method involving coherent periodic modulation of Raman laser intensity to induce resonance transitions between energy levels of a spin-orbit coupled atom in a symmetric double-well trap. By integrating photon-assisted tunneling technique with spin–orbit coupling (SOC), we achieve resonance transitions between the predefined energy levels of the atom, thereby enabling further precise control of the atom’s dynamics. We observe that such photon-like resonance can induce a transition from a localized state to atomic Rabi oscillation between two wells, or effectively reduce tunneling as manifested by a quantum beating phenomenon. Moreover, such resonance transitions have the potential to induce spin flipping in a spin-orbit coupled atom. Additionally, the SOC-mediated transition from multiphoton resonance to fundamental resonance and the SOC-induced resonance suppression are also discovered. In these cases, the analytical results of the effective coupling coefficients of the resonance transition derived from a four-level model can account for the entire dynamics, demonstrating surprisingly good agreement with the numerically exact results based on the realistic continuous model.
Reconstruction of electron velocity distribution function and Gibbs entropy from electron cyclotron emission in magnetized plasmas
Authors: Eiichirou Kawamori
Published: December 2024

We propose a method for reconstructing the fluctuation components of the electron velocity distribution function (EVDF), and the electron entropy, which is a functional of the fluctuation components of the EVDF, using the harmonic spectrum from pure X-mode electron cyclotron emission (ECE) in optically thin plasmas. This formulation employs the maximum entropy method in velocity space using the Hankel transform, which converts from v
⊥ space to p space (where, v
⊥ and p are the electron velocity perpendicular to the background magnetic field and the index of the wavenumber in velocity space). Numerical tests validated the effectiveness of the proposed method, which is applicable across a wide range of magnetized plasma conditions, including conditions with both non-relativistic and relativistic electrons, except in cases of harmonic overlap or under optically thick conditions. Notably, this method does not require radiometer calibration for ECE measurements. This method facilitates the experimental evaluation of electron entropy transport in fusion plasma experiments. Moreover, when combined with measurements in k-space (spatial distribution), this approach enables entropy distribution acquisition in phase space (k-p space).
Positive and negative sequence impedance measurement method based on inductance switching for converters
Authors: Wang Jiajia
Published: December 2024

Nowadays, the impedance-based method is a common method to study the small-signal stability of converters. Impedance measurement is the key to using this method. Common impedance measurement methods usually inject disturbances on the primary side and calculate the converter’s impedance by measuring the response excited by the disturbance. The high price and troublesome operation are the drawbacks of this method. In this paper, an impedance measurement method of the grid-tied converters by switching the grid-side inductance is proposed. By changing the grid-side inductance and injecting the same disturbance into the control system before and after the alteration, the positive and negative sequence impedance of the converters can be measured. This paper explains the measurement principle and elaborates the measurement steps. In the end, the effectiveness of the method is verified by simulations.
Neutral-point voltage balancing method for three-phase four-leg three-level ANPC inverter based on modulation waveform splitting
Authors: Zhang Hengkang , Wang Fusheng , Liu Guorui , Wu Wei , Zuo Qingfeng
Published: December 2024

A neutral-point (NP) voltage balancing method based on modulation wave splitting is proposed for a three-phase four-leg (3P4L) three-level (3L) active NP clamped (ANPC) inverter. According to the principle of changing the NP current by adjusting the o-state duty cycle, the NP current injected by each carrier period is made zero by splitting the modulation waveforms of the mid-phase and N-phase. This approach eliminates low-frequency fluctuation in NP voltage under various load conditions. On this basis, according to the inverter operating state and limiting conditions, the output o-state duty cycle of the modulation wave for the intermediate phase and N-phase is adjusted to suppress the NP voltage deviation caused by various non-ideal factors. Finally, the effectiveness of the method is verified through simulation.
Corrosion analysis of switchgear moving contacts in a 66 kV substation of shenyang
Authors: Wang Tianpeng , Xia Yongfeng , Wang Zhongyu , Xiao Shaoyang
Published: December 2024

A serious burn accident occurred in the 10 kV secondary switchgear of a 66 kV substation in Shenyang. The moving contacts of other switchgear that were replaced at the same time showed corrosion and blackening. In order to analyze the causes of the corrosion of the switchgear moving contacts, macroscopic morphology observation, chemical composition analysis, metallographic structure observation, and scanning electron microscopy were utilized. The results indicated that the thickness of the silver plating layer on the contact parts of the switchgear met the standard requirements, and the chemical composition of the spring used for fixing the contacts met the requirements of non-magnetic stainless steel chemical composition. A uniform and continuous corrosion product layer was observed on the outer side, with the presence of sulfur elements detected. The main reason for corrosion was attributed to the presence of a large number of microorganisms and sulfides in the sewage entering the cable tunnel. These elements generated hydrogen sulfide gas under the influence of alienation, which entered the substation along the cable tunnel and reacted with the silver plating layer on the switchgear contacts, resulting in the production of corrosion products such as silver sulfide. This process led to an increase in contact resistance and overheating of the contacts, ultimately causing the burnout of the switchgear.
Research and design of high gain DC-DC converter based on coupled inductor
Authors: Du Fengchen , Xu Song
Published: December 2024

A high-gain DC-DC converter with soft-switching characteristics is proposed to meet the application requirements of new energy transportation and power systems. By using a coupled inductor boost structure and adding a voltage doubling unit, the boost capability of the converter is further enhanced. By constructing a resonant cavity, the switching transistor can operate in ZVS (Zero Voltage Switching), and all diodes can operate in ZCS (Zero Current Switching), significantly reducing device losses. The coupled inductor boost structure can achieve a higher voltage output at a lower switching transistor voltage stress and only requires control by a single switching transistor. The article analyzes a 300W experimental prototype of the converter, which can achieve an efficiency of 90% at a 10-fold voltage gain, verifying the feasibility and superiority of the converter.
32nd IAHR Symposium on Hydraulic Machinery and Systems
Authors: Kumar Arun , Gandhi Bhupendra K
Published: December 2024

Hydropower is a reliable, versatile, and low-cost source of clean electricity generation and responsible for water management. Hydraulic machinery is an essential component of a hydropower plant to generate electricity. It is always vital to share current knowledge on research and development, including numerical analysis, design, operation, and monitoring of hydraulic machinery and systems. Research and development from academia and industry have constantly been improving the hydraulic turbine and its components design. The IAHR symposium on hydraulic machinery and systems provides unique opportunity to the academic and industrial research teams to exchange the state-of-the-art knowledge and ideas on the development of the next generation of hydropower technology. The 32nd Symposium on Hydraulic Machinery and Systems was jointly organized by the Department of Hydro and Renewable Energy and the Department of Mechanical and Industrial Engineering, Indian Institute of Technology Roorkee, India, during September 11 – 14, 2024. This preface describes the overall summary of the symposium, including the plenary & technical sessions, cultural events, and technical tour. The scientific papers reviewed by the expert reviewers, accepted and presented during the symposium are published in a proceeding at IOP Science EES conference series.

List of Introduction, Themes of the symposium, Highlights of the symposium, Keynote Speech, Organizing Committee, Executive Committee, Scientific Committee and Acknowledgement are available in this Pdf.
Chain-reaction collapse of cavitation clouds in Francis turbine runner during start-up
Authors: Mukai T , Nakazono M , Hashidate T , Uchida T , Tezuka K , Matsui J
Published: December 2024

This paper elucidates the hydrodynamic generation mechanism of the extraordinary stress in Francis turbine runner that occurs during start-up, which is called “Hydro Drum”, by unsteady CFD analysis with a cavitation model and model test. The analysis results revealed the pressure wave generated by the collapse of one cavitation cloud caused the collapse of other cavitation clouds. In addition, the magnitude of the pressure wave generated by collapse of the cavitation cloud resulting from the chain-reaction was much larger than that of the cavitation cloud that triggered the chain-reaction, resulting in an impulsive pressure rise. Model tests were conducted to measure the relationship between the extraordinary stress and the pressure on blades, and the mechanism was verified. In conclusion, it is elucidated that the extraordinary stress on runner blades during start-up of a Francis turbines is caused by impulsive pressure rises accompanied by the chain-reaction of collapse of cavitation clouds.
Mitigation of vibrations caused by inter-blade vortices using pumping cap for natural aeration
Authors: Afara S , Nennemann B , Disciullo J
Published: December 2024

In 2014, Andritz received a contract to refurbish six Francis turbines with a total capacity of 840 MW. During the commissioning of the first unit, unexpected vibrations occurred within a power range of 25 to 65 MW, and Andritz was requested to find a solution. Unsteady computational fluid dynamics CFD simulations, revealed that the vibrations originated from intermittently cavitating inter-blade vortices. Conventional solutions involving compressed air injection were rejected, leaving natural aeration as the only viable option. Andritz explored various options for natural aeration by CFD and later, by means of homologous model tests. The solution was able to accommodate suction heads of approximately 10 meters and consisted of a specialized runner cap, referred to as pumping cap, which allowed for natural aeration through the hollow turbine shaft. The cap was optimized using two-phase CFD, and once installed on the prototype, it demonstrated a reduction of aproximately 50% in the peak level of vibration and noise. This achievement fully satisfied the customer, leading to the acceptance of the machine.
Investigation On Various Hard Coating Technologies
Authors: Mack Reiner , Kratzsch Axel
Published: December 2024

For high head hydropower applications, the predominant coating material is 86% tungsten carbide embedded in a cobalt chromium matrix. This material is applied using a high velocity spraying application, which can be powered by either gas or liquid fuels.

This paper outlines the application and wear characteristics for three different scenarios: HVOF (high velocity oxygen fuel) with gas or liquid fuel, and HVAF (high velocity air fuel) with propane as the fuel source. After providing an overview of the distinct technologies and their corresponding application equipment, the discussion delves into the observed coating efficiency during standardized applications with varying coating angles.

To assess the wear resistance of the coatings applied by the different systems, a water jet test rig was developed, that allows the variation of the impingement angle and velocity of the sediment. In the test rig laboratory samples were analyzed against standard sediment with different grain size impacting at predefined angles on the probe. The results clearly demonstrate the superiority of HVAF technology over both HVOF systems. Even at lower coating angles, enhanced wear resistance is evident when utilizing HVAF. Further laboratory investigations on porosity and hardness in the coating support the analysis and the test rig findings.

However, it is worth noting that the deposition rate of HVAF with coating angles smaller than 90° is significant lower compared to the HVOF systems as confirmed by measurements during the application. Consequently, the economic feasibility of the HVAF system is limited to geometries where the coating alignment can be maintained close to perpendicular. Given that the coating system necessitates robotic manipulation, only hydraulic components with sufficient space for the access are suitable for HVAF, while others are more suited to HVOF systems.
Numerical study of flow phenomena and erosion in three guide vane cascade rig
Authors: Shrestha Kushal , Lal Bijukchhe Pawan , Thapa Bhola , Chitrakar Sailesh , Guo Zhiwei , Qian Zhongdong
Published: December 2024

The rivers in certain geological regions like South Asia have sediment particles in them. These particles cause erosion in turbine components which is a major cause of deterioration of turbine and hampers efficient energy production. Out of different modes of erosion in Francis turbines, past studies have shown that erosion is prominent in its guide vanes. Its criticality stems from the ability of eroded guide vane can disturb the flow that reaches the runner and cause erosion in the runner inlet. Numerical study is widely used to study erosion. However, their inability to evolve the geometry with the advent of erosion limits their use. The study uses a three-guide vane cascade geometry, modeled after Jhimruk HPP, to conduct the flow analysis and erosion study. In this study, a RANS-based SST turbulence model has been applied for the flow along with sediments modelled as particles carried by the fluid. The erosion study used the Finnie erosion model to visualize how the erosion occurs in the guide vane. A new framework has been developed that interprets the mathematical values of erosion into the corresponding geometrical changes. Additionally, the study has observed the flow-patterns disruption due to the erosion of the guide vane. This offers a comprehensive overview of the flow in guide vanes cascade and erosion in the guide vanes.
Numerical investigation for intake and discharge conditions of horizontal multi-jet Pelton turbines
Authors: Mössinger Peter , Mack Reiner , Jörg Necker J
Published: December 2024

Modernization of existing Pelton turbines comes with a required increase in power and efficiency. At the same time, maintainability and accessibility should be improved. Here a replacement of the existing units with horizontal multi-jet turbines can achieve these requirements. Concurrently, the hydraulic inlet and outlet conditions are challenging as the penstock and tailwater are often reused. At two examples, one in operation, one in construction, the possibilities to design and improve the inflow and discharge situation with the aid of numerical methods is shown. Efficiency and flow conditions can be significantly improved when the turbine in- and outlet is designed for the specific on-site situation.
Multidisciplinary optimization of an axial turbine
Authors: Fraas S , Tismer A , Riedelbauch S
Published: December 2024

The results of three different optimization setups for an axial propeller turbine consisting of a guide vane, a runner and a draft tube are presented. The first setup only contains the efficiency as objective and the design head as a constraint. In the second setup, the minimization of the cavitation volume is added as a further objective while in the third, the compliance with a permissible stress is included as an additional constraint. Three operating points are simulated during the optimization. Comparing the results of the first two setups, the minimization of the cavitation volume leads to a lower plant efficiency at all operating points. Including structural mechanical aspects results in a further decrease of the plant efficiency at all operating points. Nevertheless, none of the best individuals from the setups have a maximum von Mises stress below the permissible stress without taking the structural stress limits into account. This points out the importance of considering both, structural as well as fluid mechanical aspects in the optimization process of hydraulic machines.
Comparison of discharge characteristics of Pelton injector estimated by empirical relation, numerical simulation and experiment
Authors: Shrestha Sajan , Pandey Arun , Satyal Sajan , Abregu Jim , Prasad Neopane Hari , Gunnar Dahlhaug Ole
Published: December 2024

It is difficult to define a general relationship for discharge characteristics of a Pelton injector due to high degree of variability in geometry of injector amongst different Pelton turbine designs. This study has been aimed to determine discharge characteristics of injector of Pelton rig at Waterpower Laboratory, NTNU. Three different approaches have been undertaken, viz. calculation based on empirical relations, numerical simulations, and experimental validation. For empirical calculation, the injector has been simplified into series of flow geometries with equivalent cross-sectional area and axial length for multiple stroke to constant aperture diameter ratio (s/D
0). Discharge coefficient has been calculated for a constant pressure difference between inlet and atmospheric outlet for each case of s/D
0, based on head loss estimated using empirical resistance coefficient (ζ - values) available in engineering handbooks. Discharge has been determined through numerical simulations for same s/D
0 values. Results from numerical and empirical calculations are compared and correction factor (CF) has been determined. It is found that the CF is almost constant, at value of 0.85, for all values of s/D
0. The discharge coefficient calculated by numerical simulation is around 0.02 lower than the values obtained by experimental observation.
Diagnosis of the unstable behaviour of a Kaplan turbine before synchronizing to the grid
Authors: Moraga G , Mut V , Hijón C , Girardelo J , Valentín D , Egusquiza M , Egusquiza E , Presas A
Published: December 2024

This work reports on a new Kaplan turbine that experienced an unstable behaviour during its start up. The unit experienced strong sound and vibration in that phase. To identify the origin of this unstable behaviour, a set of sensors were installed within the turbine. Subsequently, tests were performed to determine the response of the different sensors during the acceleration of the machine to the speed no load stage. Following a thorough analysis of the results, the problem was identified as the air admission openings of the head cover and their distribution. To address this issue, a reconfiguration of these openings was implemented and their performance was evaluated. Following this rearrangement, the vibrations in the head cover were significantly reduced and the unit was successfully commissioned.
Analysis of the flow interference on a Pelton turbine at different operating heads
Authors: Xiao Y , Min H , Liang Q , Liu Z , Wang X , Zhou H , Tang D
Published: December 2024

Flow interference is a phenomenon harmful for the Pelton turbines stable and high efficiency operation. In this paper, numerical simulation of unsteady multiphase flow on a Pelton turbine runner buckets and entire flow passage was carried out at three operating heads. Different types of flow interference were occurred for the turbine with larger nozzle opening: the water sheet interference on the same bucket surface from the adjacent jets, the bucket cutout-flow and jet flow interference, as well as the interference between bucket brim outflow and the following bucket rear surface. The highest turbine efficiency is about 88.0% appears at 1.00H
0, and efficiency decreases when deviating from the design head, especially at the low head decrease dramatically. The predicted unsteady flow patterns with bucket torque curves show that the self-designed Pelton turbine model with six nozzles opened at larger needle stroke is remains to be optimized. The relationship between the predicted flow interference and the decrease of runner torque and hydraulic performance is summarized.
Pump start instability on a low head pump turbine and testing with partial deaeration
Authors: Nennemann B , Bergweiler M , Herrero Prada C
Published: December 2024

Since 2019 Iberdrola has had an interest in enabling pump operation of the Valparaiso hydropower plant. Iberdrola contacted Andritz, the original manufacturer of the machines, and a collaboration for that purpose was started. This powerplant was equipped with two pump turbine units in the 1980ies but pump operation has not been possible since strong vibrations occurred during pump commissioning in 1995. Therefore, the units had only been operated in turbine mode since then. In 2020 Iberdrola and Andritz performed a renewed pump start test with a fully rewatered machine. This again led to high vibrations during the initial phase of guide vane opening. Subsequently, guide vane flutter (self-excitation) was investigated as a potential cause of the vibrations but could not be established as the cause. Instead, it was found, that due to a transient effect, the machine entered the unstable part of the pump characteristic. Partial deaeration before guide vane opening during pump start was then considered as a solution and successfully tested in 2021.
Numerical study of pressure fluctuation in vaneless space of variable speed reversible pump-turbine in turbine mode at maximum head
Authors: Rode Bhushan R , Kumar Arun , Segoufin Claire , Laurant Yann
Published: December 2024

Efficiency and grid stability of pumped storage plants with significant head variations can be enhanced by the implementation of variable speed operation. The reversible pump-turbine (RPT) operating in turbine mode is particularly prone to fatigue and vibrations when operating at maximum head conditions, primarily due to hydraulic instabilities caused by pressure fluctuations in vaneless space and thus, the performance of the RPT becomes increasingly critical under such operating conditions. It is, therefore, important to examine the pressure fluctuations in vaneless space of RPTs operating at higher heads. The findings indicate that the main source of pressure fluctuations across all operating conditions is rotor-stator interaction (RSI), where the dominant frequency is blade passing frequency (9fn
) and its harmonics.
Effect of wrap angle on performance of Pump As Turbine (PAT) in both pump and turbine modes
Authors: Bhukya N K , Rai A K
Published: December 2024

Pump as turbine (PAT) is used in small hydropower plants to generate electricity for remote hill regions and the integration of other renewable resources. Generally, the efficiency of centrifugal pumps operating in turbine mode is low. To improve efficiency, variables such as wrap angle, blade thickness, and blade count can be optimized for turbine mode; however, such changes may lead to a decrease in PAT performance in pump mode. To explore the effect of wrap angle on PAT performance in pump mode, flow simulations were carried out at conditions with wrap angle and discharge variations between 85°-120° and 8-16 kg/s, respectively. With a decrease in wrap angle in pump mode compared to the rated design condition, both efficiency and head rise were improved at the partial load condition. A design with a 120° wrap angle provided a 5.15 % improvement of efficiency in turbine mode compared with the available empirical relation; however, a minor decrease of 0.5% in pump mode was observed. Such zones with high efficiency in turbine mode with less compromise in pump mode should be identified for PAT.
Experimental investigation of a FSFC variable speed pump-turbine prototype – Part2: runner fatigue reduction
Authors: Biner D , Hasmatuchi V , Lecointre C L , Quarroz A , Nicolet C , Alligné S , Dreyer M , Hugo N , Dujic D , Münch-Alligné C
Published: December 2024

The demonstration of flexibility technologies to enhance ancillary services of Hydropower Plants (HPPs) is showcased by the XFLEX HYDRO H2020 European Project. The potential of Full Size Frequency Converters (FSFC) is numerically and experimentally assessed by a case study on the Z’Mutt HPP. The investigated unit is a 5 MW variable speed reversible Francis pump-turbine fed by a FSFC that provides full speed control from −100% to +100%, allowing for fast start-up and mitigation of damage caused to different components. In this context, several turbine start-up sequences with controlled guide vane opening and rotational speed are developed, implemented, and tested on prototype scale. The definition of the different sequences, their impact on penstock fatigue and further FSFC capabilities like fast active power control in pump mode and fast power reversion are presented in part 1 of this contribution. Part 2 deals with fatigue damage investigations of the runner with respect to variable speed operation in generating mode using coupled numerical and experimental techniques. Strain signals from the runner blades are extrapolated to the critical areas to assess the relative fatigue damage induced by each turbine start-up. The scaled normal stress approach is applied, which is a critical plane method, adapted for multiaxial stress states. The results reveal that runner damage is mitigated by more than two orders performing a variable speed start-up compared to a classical one with fixed speed technology. Simultaneously, the delay for active power provision is significantly shortened. Thus, the study approves that fast and frequent turbine start-ups are realizable without affecting the runner’s service life thanks to the FSFC.
Evaluation of the fatigue-related influence of start-ups on Pelton turbines based on reduced scale model stress measurements
Authors: Leonardo Alerci Aldo , Vagnoni Elena , Paolone Mario
Published: December 2024

In recent decades, the electricity industry has undergone a significant transformation from a vertically integrated supply system to a market-regulated structure. This shift, along with the intermittent nature of increasingly prevalent non-dispatchable renewable energy sources, induces system operators to redistribute portions of the power generation included in the market schedule to preserve the energy balance within the power system. For hydropower plants, this translates in increasingly frequent operations in transient condition, with significant fatigue-related consequences on the lifetime of hydraulic machines. The understanding of fatigue phenomena during transient operations requires therefore experimental investigations, modeling and optimization of such operations, representing today a relevant research subject. This paper proposes the comparison between two methodologies which aim to estimate and optimize the operational cost, with respect to the lifetime of a Pelton turbine, of the specific case of the back-to-back start-up of a multistage pump performed with the Pelton runner of the same ternary group. These methodologies are developed on data collected during an experimental campaign performed with the reduced scale model of the investigated turbine, homologous to the real test case pumped-storage power plant. Despite the substantial distinction in the adopted approaches, the two methodologies show common features in terms of the fatigue damage trend as a function of the turbine operating conditions, and of the optimal strategy minimizing the structural impact of start-up sequences.
On the modelling of the fatigue-induced damage in Francis turbines start-up sequences
Authors: Vagnoni E , Muser T , Seydoux M , Morabito A , Krymova E
Published: December 2024

The European Green Deal is prescribing a very ambitious rise in the annual production of renewable energy sources, and grid regulation services are increasingly important in the course of a massive integration of intermittent renewable energy sources. Although hydropower effectively regulates power, the growing demand for flexibility in the coming decades means that hydroelectric technologies must be adaptable, often operating in conditions for which they were not originally designed to ensure availability and system reliability. This also includes a significant increase of the number of start-ups per year. To address these challenges, this paper suggests a two-fold forecasting method to predict damage due to fatigue in the runner blades of Francis turbines. Firstly, stresses during transient operations are predicted using a quasi-steady approach that concatenates measurements from steady-state operations through Voronoi tessellation. Following that, a neural network is trained on an existing dataset of recorded blade stresses during transient operations. The effectiveness of both approaches is validated against measurements in a reduced scale model of a Francis turbine. The comparative analysis highlights the strengths and weaknesses of each method, offering a detailed understanding of dynamic damage accumulation during start-up sequences compared to steady-state operations.