bluuebunny/crossref_metadata_2025 huggingface dataset:
The impact of digital transformation on the quality and safety level of agricultural exports: evidence from Chinese listed companies
Authors: Liu Yuchen , Dong Yinguo , Qian Weiwen
Published: June 2024

Enhancing the quality and safety of exported agricultural products and improving export competitiveness is the key to establishing enhanced competitive advantages in agricultural products, developing a trade powerhouse and realising high-quality development of agriculture. This paper uses the data of Chinese listed companies and Chinese Customs from 2007 to 2016 to discuss the effect and mechanism of digital transformation of enterprises on the quality and safety level of export agricultural products by using the staggered differential method. The study shows that (1) Enterprise digital transformation effectively improves the quality and safety of exported agricultural products, and this result holds after endogeneity, placebo and multiple robustness tests; (2) Heterogeneity analyses reveal that the quality and safety effect of enterprise digital transformation is greater for exporting to developed countries’ markets, non-state-owned enterprises and enterprises in the eastern region, in addition to bulk agricultural products and consumer-oriented agricultural products; (3) Mechanism analyses shows that enterprise digital transformation raises the quality and safety of exported agricultural products through technological innovation, product tracing, information sharing and quality assurance effects.
Morphological characteristics and cleaning effects of collapsing cavitation bubble in fractal cracks
Authors: Shan Minglei , Zha Yuzhu , Yang Yu , Yang Chenghui , Yin Cheng , Han Qingbang
Published: June 2024

When a cavitation bubble collapses in a crack, due to the lack of symmetry, spatial uniformity, and obvious correlations during the collapse process, it is difficult to effectively explore the interaction mechanism between the bubble and crack walls. In this paper, a combination of numerical simulation and experimental approaches are used to explore the collapse process of a cavitation bubble in a fractal crack. The numerical model is based on the pseudopotential multi-relaxation-time lattice Boltzmann method (LBM). The experiment platform including an underwater pulsed discharge device combined with a high-speed camera system. Moreover, the morphological analysis method based on Minkowski functionals is used to quantitatively depict the morphological features in this paper. The validity of the numerical model is qualitatively verified by the experimental platform, whereas the influence of the complexity and geometric features of the crack wall on the cavitation bubble collapse process is quantitatively studied by LBM simulation and Minkowski functionals. The research findings indicate that the complexity and geometric features of the crack wall markedly influence the collapse time and behavior of the cavitation bubble. Specifically, the collapse time of the cavitation bubble increases with the increasing complexity of the crack wall. Moreover, the maximum jet direction of cavitation bubble toward the wall is closest to the cavitation bubble. Furthermore, as the fractal dimension increases, the intensity of the pressure wave and jet acting upon the crack wall increase while the radiation range decreases. Cavitation cleaning can be applied to arbitrary complex solid surfaces in various environments.
A preference-based value framework to assess healthcare provision in an oil and gas industry
Authors: Pak Anton , Pols Thomas , Kondalsamy-Chennakesavan Srinivas , McGrail Matthew , Gurney Tiana , Fox Jordan L. , Tuffaha Haitham
Published: June 2024

Objectives The aim of this study was to develop the Remote Health Value Framework to evaluate the models of healthcare provision for workers in the oil and gas sector, predominantly situated in rural and remote areas. Methods The framework was co-designed with the leadership team in one global oil and gas company using a multi-criteria decision analysis approach with a conjoint analysis component. This was used to elicit and understand preferences and trade-offs among different value domains that were important to the stakeholders with respect to the provision of healthcare for its workers. Preference elicitation and interviews were conducted with a mix of health, safety, and environment (HSE) team and non-HSE managers and leaders. Results Out of five presented value domains, participants considered the attribute ‘Improving health outcomes of employees’ the most important aspect for the model of healthcare which accounted for 37.3% of the total utility score. Alternatively, the ‘Program cost’ attribute was least important to the participants, accounting for only 11.0% of the total utility score. The marginal willingness-to-pay analysis found that participants would be willing to pay A$9090 per utile for an improvement in a particular value attribute. Conclusions This is the first value framework for healthcare delivery in the oil and gas industry, contextualised by its delivery within rural and remote locations. It provides a systematic and transparent method for creating value-based healthcare models. This approach facilitates the evaluation of healthcare investments, ensuring they align with value domains prioritised by the HSE and leadership teams.
The role of topography on the local circulation and formation of fog at Perth Airport
Authors: Roux Belinda , Potts Rodney , Siems Steven , Manton Michael
Published: June 2024

Perth Airport is located on a coastal plain in the south-west of Australia, with the Indian Ocean to the west and the Darling Scarp running approximately parallel to the coast to the east. On average, there are approximately nine fog events per year at the airport, typically occurring during the cooler months in the early morning hours. Onshore winds bringing moisture from the Indian Ocean can combine with nocturnal cooling in stable atmospheres to encourage fog formation. A previous climatological study of fog at Perth Airport found that the majority of events had north to north-easterly 10-m winds at fog onset time. Two case studies are presented to gain a better understanding of the physical processes associated with the north to north-easterly near-surface flow and their influence on the development of fog. The hypothesis is that the escarpment is blocking the moist environmental flow, resulting in light northerly near-surface winds. This was tested through numerical experiments including altered terrain. The main finding from the case studies was that the northerly winds stem from a blocking of the airmass in the lower level of the atmosphere by the Darling Scarp in moderate wind situations. During calm or very light wind occasions, the winds below the surface inversion level can tend northerly regardless of topography. The trapped airmass and light winds in the near surface layer in combination with nocturnal surface cooling and moisture from the environmental flow, create conditions favourable for the development of fog at Perth Airport.
Sampling with flows, diffusion, and autoregressive neural networks from a spin-glass perspective
Authors: Ghio Davide , Dandi Yatin , Krzakala Florent , Zdeborová Lenka
Published: June 2024

Recent years witnessed the development of powerful generative models based on flows, diffusion, or autoregressive neural networks, achieving remarkable success in generating data from examples with applications in a broad range of areas. A theoretical analysis of the performance and understanding of the limitations of these methods remain, however, challenging. In this paper, we undertake a step in this direction by analyzing the efficiency of sampling by these methods on a class of problems with a known probability distribution and comparing it with the sampling performance of more traditional methods such as the Monte Carlo Markov chain and Langevin dynamics. We focus on a class of probability distribution widely studied in the statistical physics of disordered systems that relate to spin glasses, statistical inference, and constraint satisfaction problems. We leverage the fact that sampling via flow-based, diffusion-based, or autoregressive networks methods can be equivalently mapped to the analysis of a Bayes optimal denoising of a modified probability measure. Our findings demonstrate that these methods encounter difficulties in sampling stemming from the presence of a first-order phase transition along the algorithm’s denoising path. Our conclusions go both ways: We identify regions of parameters where these methods are unable to sample efficiently, while that is possible using standard Monte Carlo or Langevin approaches. We also identify regions where the opposite happens: standard approaches are inefficient while the discussed generative methods work well.
The neuron as a direct data-driven controller
Authors: Moore Jason J. , Genkin Alexander , Tournoy Magnus , Pughe-Sanford Joshua L. , de Ruyter van Steveninck Rob R. , Chklovskii Dmitri B.
Published: June 2024

In the quest to model neuronal function amid gaps in physiological data, a promising strategy is to develop a normative theory that interprets neuronal physiology as optimizing a computational objective. This study extends current normative models, which primarily optimize prediction, by conceptualizing neurons as optimal feedback controllers. We posit that neurons, especially those beyond early sensory areas, steer their environment toward a specific desired state through their output. This environment comprises both synaptically interlinked neurons and external motor sensory feedback loops, enabling neurons to evaluate the effectiveness of their control via synaptic feedback. To model neurons as biologically feasible controllers which implicitly identify loop dynamics, infer latent states, and optimize control we utilize the contemporary direct data-driven control (DD-DC) framework. Our DD-DC neuron model explains various neurophysiological phenomena: the shift from potentiation to depression in spike-timing-dependent plasticity with its asymmetry, the duration and adaptive nature of feedforward and feedback neuronal filters, the imprecision in spike generation under constant stimulation, and the characteristic operational variability and noise in the brain. Our model presents a significant departure from the traditional, feedforward, instant-response McCulloch–Pitts–Rosenblatt neuron, offering a modern, biologically informed fundamental unit for constructing neural networks.
The quick termination of verbal conflicts expressed through disagreement
Authors: Pütz Ole , Hassan Hafsa
Published: June 2024

This paper considers verbal conflicts at the workplace and asks how team members negotiate conflict termination. Our corpus consists of meetings where computer scientists discuss the progress of projects they are working on, a context where conflict resolution is crucial for the continuation of work. Following the literature, we define conflicts as continued disagreement. The analysis focuses on conflict termination formats that show whether a conflict can be resolved as well as episode length and disagreement mitigation that indicate the severity of the conflict. Power relations among participants are also discussed. Our results show that most conflicts end after two or three disagreements. Among the termination formats, submission is the most frequent, followed by stand-off and compromise. We further show that participants minimize conflicts by concluding them as soon as someone indicates their unwillingness to concede, whereas the pattern of conflict minimization varies with the termination format that participants negotiate.
Variational Monte Carlo study of stripes as a function of doping in thet−t′Hubbard model
Authors: Lechiara Antonio , Marino Vito , Tocchio Luca F
Published: June 2024

We perform variational Monte Carlo simulations of the single-band Hubbard model on the square lattice with both nearest (t) and next-nearest (t′) neighbor hoppings. Our work investigates the consequences of increasing hole doping on the instauration of stripes and the behavior of the superconducting order parameter, with a discussion on how the two phenomena affect each other. We consider two different values of the next-nearest neighbor hopping parameter, that are appropriate for describing cuprate superconductors. We observe that stripes are the optimal state in a wide doping range; the stripe wavelength reduces at increasing doping, until stripes melt into a uniform state for large values of doping. Superconducting pair–pair correlations, indicating the presence of superconductivity, are always suppressed in the presence of stripes. Our results suggest that the phase diagram for the single-band Hubbard model is dominated by stripes, with superconductivity being possible only in a narrow doping range between striped states and a nonsuperconducting metal.
Large dynamic scissoring mode displacements coupled to band gap opening in the cubic phase of the methylammonium lead halide perovskites
Authors: A Bird Tobias , Chen Jungshen , Songvilay Manila , Stock Chris , T Wharmby Michael , C Bristowe Nicholas , S Senn Mark
Published: June 2024

Hybrid perovskites are a rapidly growing research area, having reached photovoltaic power conversion efficiencies of over 25%. There is a increasing consensus that the structures of these materials, and hence their electronic structures, cannot be understood purely from the time and space averaged crystal structures observable by conventional methods. We apply a symmetry-motivated analysis method to analyse x-ray pair distribution function data of the cubic phases of the hybrid perovskites MAPbX
3 (X = I, Br, Cl). We demonstrate that, even in the cubic phase, the local structure of the inorganic components of MAPbX
3 (X = I, Br, Cl), are dominated by scissoring type deformations of the PbX
6 octahedra. We find these modes to have a larger amplitude than equivalent distortions in the A-site deficient perovskite ScF3 and demonstrate that they show a significant departure from the harmonic approximation. Calculations performed on an inorganic perovskite analogue, FrPbBr3, show that the large amplitudes of the scissoring modes are coupled to a dynamic opening of the electronic band gap. Finally, we use density functional theory calculations to show that the organic MA cations reorientate to accommodate the large amplitude scissoring modes.
SFD-SLAM: a novel dynamic RGB-D SLAM based on saliency region detection
Authors: Gong Can , Sun Ying , Zou Chunlong , Jiang Du , Huang Li , Tao Bo
Published: June 2024

In dynamic environments, several simultaneous localization and mapping (SLAM) systems effectively utilize optical flow fields to distinguish dynamic from static feature points. Commonly, these systems leverage the amplitude information within the optical flow field to develop adaptive thresholding segmentation models for identifying dynamic scene regions. Nevertheless, designing adaptive thresholding models typically necessitates meticulous planning and extensive experimentation. This study introduces a dynamic RGBD SLAM system, SFD-SLAM, which innovates by employing a saliency detection network for the direct extraction of dynamic regions via scene flow. This approach notably streamlines the design process associated with conventional adaptive thresholding models. Furthermore, SFD-SLAM incorporates a geometric module that merges depth residuals with hyperpixel segmentation to enhance the refinement of the dynamic mask. This is followed by integration with FCM clustering for the precise identification of moving objects. The efficacy of SFD-SLAM is assessed using the widely recognized TUM dynamic dataset. Experimental results demonstrate that the proposed system surpasses DGFlow-SLAM, which relies on an adaptive thresholding model for dynamic object segmentation, in terms of trajectory accuracy. It also achieves comparable localization accuracy to DynaSLAM. Moreover, SFD-SLAM maintains robust tracking capabilities, even in scenarios where DynaSLAM experiences tracking loss, thereby augmenting the robustness of RGBD-SLAM in dynamic settings.
Promoting abstract thinking and scientific argumentation in the teaching of physics
Authors: Sabín Juan
Published: June 2024

Abstract thinking and scientific argumentation are two of the more important high-order cognitive skills that students at secondary level need to develop in the learning of physics. In this paper a new methodology based on constructivism’s view of education is presented by using counterintuitive experiments under a POE strategy (Predict, Explain, Observe). The experiments consist in a race of two soda can, one of them previously shaken, over an inclined plane; and the movement of a double cone object, built by two joined funnels, over two convergent inclined rails. The unexpected outcome of both experiments challenges the prior ideas of the students and provokes a higher engagement in their learning process. The results of a pilot experience applying this methodology suggest that using counterintuitive experiments under PEO strategy is an effective methodology to introduce the teaching of abstract concepts as moment of inertia and centre of mass. It also helps identifying students’ prior knowledge, promoting the use of scientific reasoning, and training students in the activation of their abstraction skills.
Size effect on the response of superconductivity in NbN nanowires to external magnetic field
Authors: Xu Zulei , Wang Xiaoni , Liu Xiaoyu , Yang Ming , Liu Yixin , Peng Wei , Mu Gang , Lin Zhi-Rong
Published: June 2024

Reducing the negative impact of magnetic vortex motion is a long-term challenge for superconducting applications. Here, we conduct an in-depth investigation on the response of NbN nanowires on applied magnetic fields with the transverse size down to 10 nm. It is found that the vortex-free state can sustain under field up to 9 T in the sample of this dimension, demonstrating a unique approach to reduce the negative effects of flux motion in applications. Such a conclusion is further confirmed by the vanished flux-low instability velocity. Moreover, the upper critical field of the NbN nanowires reveals clear anisotropic features, which can be interpreted based on the framework of the Ginzburg–Landau model. Our results provide important information for understanding the behavior of nanoscale superconducting materials under magnetic fields, which is significant for the application of superconducting micro/nano devices.
Fabrication of microstrips of iron-based superconductor NdFeAs(O,H)
Authors: Yoshikawa Atsuro , Hatano Takafumi , Hibino Hiroto , Imanaka Hiroya , Ikuta Hiroshi
Published: June 2024

NdFeAs(O,H) microstrips with line widths of about 1–5 µm were fabricated by photolithography and Ar-ion dry etching. The microstrips were fabricated under two different etching conditions: 25 min etching at a power of 20 W (long duration, low power) and 3 min etching at 100 W (short duration, high power). For both conditions, the narrowest microstrips, which were 0.9 µm in width, retained high critical temperatures of about 85% of those before microfabrication. Further, the 0.9 µm microstrip fabricated under the high-power, short-duration condition exhibited a high critical current density (J
c) of more than 4 MA cm−2 at 4 K. However, J
c of the microstrip fabricated under the low-power, long-duration condition was somewhat lower. Our analysis suggests that the edges of the microstrips were damaged more than twice as wide as those of the microstrips fabricated under the high-power, short-duration condition. This indicates that a short duration is more effective to reduce the damage than using a lower etching power.
Preparation of β-cyclodextrin/PVDF composite films for efficient adsorption of Cu2+
Authors: He Fengli , Qian Yuebao , He Guanglei , Wang Xi , Yu Fangli
Published: June 2024

Water pollution issues are becoming more and more serious, particularly those caused by heavy metal ions. In this paper, β-cyclodextrin (β-CD) and polyvinylidene fluoride (PVDF) were chosen to prepare composite films by electrospinning technology. The microstructure, crystalline phases, mechanical properties, porosity, and adsorption performance of β-CD/PVDF composite films were analyzed. The results show that the β-CD/PVDF composite fibers were smooth and randomly deposited to form an interconnected three-dimensional network structure. The diameter of the β-CD/PVDF composite fibers ranged from 0.22 to 0.33 μm, and the fiber diameter distribution was uniform. The maximum porosity was 79.56% when the content of β-CD was 2%. After adding the β-CD, the tensile strength increased to 13.33 MPa and the elongation at break increased to 14.20% as well. With the β-CD content increasing, the adsorption capacity of the β-CD/PVDF composite films for Cu2+ increased to 182.65 mg g−1. In addition, the second-order kinetic model was suitable to describe the adsorption process, and the chemical adsorption was the predominant mechanism of the adsorption process due to the presence of β-CD. The results suggest that the β-CD/PVDF composite films may be a potential adsorbent for Cu2+ adsorption.
Optical properties of meso-tetra(sulphonatophenyl) porphyrins (TPPS
4) and their Fe
3+, Mn
3+, Zn
2+ complexes with different pH values studied using by picosecond pulse trains
Authors: Miao Quan , Song Rengang , Liang Min , Sun Erping , Xu Yan
Published: June 2024

Applying picosecond pulse trains propagating in meso-tetra(sulphonatophenyl) porphyrins and their Fe
3+, Mn
3+, Zn
2+ complexes, we studied the nonlinear dynamics at different pH values. The pulse train at wavelength 532nm is comprised of 20 subpulses with 70ps width and 13ns spacing. We simplified the energy structures of porphyrins and metalloporphyrins to five-level models. In solving coupled rate equations and two-dimensional paraxial field, we used Crank-Nicholson numerical method to do the calculations. The results revealed that in irregular metalloporphyrins with central paramagnetic ion Mn
3+ or Fe
3+, the central ion would act as electron acceptor, which leads to charge transfer of unpaired metal electron to the porphyrin ring π conjugated system, and strengthen the spin–orbit coupling of electronic systems and weaken the transition prohibition between electronic states in porphyrins. However regular metalloporphyrins with central diamagnetic ion Zn
2+ has similar optical properties to free base porphyrins, and Zn
2+
TPPS
4 has much longer excited state lifetimes and slower intersystem crossing. In solutions, hydrogen bond would be formed to porphyrin, which can change the transitions of π electrons and thus the charge transfer can be strengthened in the porphyrin ring. In weak intensity region with linear absorption, nonprotonated porphyrins with high pH value show better optical limiting (OL) effect. Conversely in high intensity region, protonated porphyrins with low pH value show better OL effect. Besides, increasing interaction distances of porphyrins and metalloporphyrins with laser pulses is another important factor to raise the OL effects.
Large-scale particle trapping by acoustic vortices with a continuously variable topological charge
Authors: Zhuang 庄 Haofei 昊霏 , Zhang 张 Qingyuan 清源 , Hu 胡 Gehao 格昊 , Wang 王 Qingdong 青东 , Du 杜 Libin 立彬
Published: June 2024

Strengthened directivity with higher-order side lobes can be generated by the transducer with a larger radius at a higher frequency. The multi-annular pressure distributions are displayed in the cross-section of the acoustic vortices (AVs) which are formed by side lobes. In the near field, particles can be trapped in the valley region between the two annuli of the pressure peak, and cannot be moved to the vortex center. In this paper, a trapping method based on a sector transducer array is proposed, which is characterized by the continuously variable topological charge (CVTC). This acoustic field can not only enlarge the range of particle trapping but also improve the aggregation degree of the trapped particles. In the experiments, polyethylene particles with a diameter of 0.2 mm are trapped into the multi-annular valleys by the AV with a fixed topological charge. Nevertheless, by applying the CVTC, particles outside the radius of the AV can cross the pressure peak successfully and move to the vortex center. Theoretical studies are also verified by the experimental particles trapping using the AV with the continuous variation of three topological charges, and suggest the potential application of large-scale particle trapping in biomedical engineering.
Collective flow and fluid behavior in p/d/3He+Au collisions at
GeV*
Authors: Wu 吴 Zeming 泽明 , Fu 付 Baochi 宝迟 , Zhao 赵 Shujun 沭钧 , Liu 刘 Runsheng 润生 , Song 宋 Huichao 慧超
Published: June 2024

By varying the intrinsic initial geometry, p/d/3He+Au collisions at the Relativistic Heavy Ion Collider (RHIC) provide a unique opportunity to understand the collective behavior and probe possible sub-nucleon fluctuations in small systems. In this study, we employed the hybrid model

under TRENTo initial conditions to study the collective flow and fluid behavior in p/d/3He+Au collisions. With fine-tuned parameters,

can describe the

and

data from the PHENIX and STAR collaborations. However, for certain parameter sets with initial sub-nucleon fluctuations, the hydrodynamic simulations already go beyond their limits with an average Knudsen number

clearly larger than unity. Our calculations demonstrate that, for a meaningful evaluation of the fluid behavior in small systems, model simulations must also pay attention to the validity range of hydrodynamics.
A Comprehensive Classification and Analysis of Geomagnetic Storms Over Solar Cycle 24
Authors: Raja Halim Shah Raja Adibah , Abdul Hamid Nurul Shazana , Abdullah Mardina , Annuar Adlyka , Sarudin Idahwati , Mohd Radzi Zahira , Yoshikawa Akimasa
Published: June 2024

A geomagnetic storm is a global disturbance of Earth's magnetosphere, occurring as a result of the interaction with magnetic plasma ejected from the Sun. Despite considerable research, a comprehensive classification of storms for a complete solar cycle has not yet been fully developed, as most previous studies have been limited to specific storm types. This study, therefore, attempted to present complete statistics for solar cycle 24, detailing the occurrence of geomagnetic storm events and classifying them by type of intensity (moderate, intense, and severe), type of complete interval (normal or complex), duration of the recovery phase (rapid or long), and the number of steps in the storm's development. The analysis was applied to data from ground-based magnetometers, which measured the Dst index as provided by the World Data Center for Geomagnetism, Kyoto, Japan. This study identified 211 storm events, comprising moderate (177 events), intense (33 events), and severe (1 event) types. About 36% of ICMEs and 23% of CIRs are found to be geoeffective, which caused geomagnetic storms. Up to four-step development of geomagnetic storms was exhibited during the main phase for this solar cycle. Analysis showed the geomagnetic storms developed one or more steps in the main phase, which were probably related to the driver that triggered the geomagnetic storms. A case study was additionally conducted to observe the variations of the ionospheric disturbance dynamo (Ddyn) phenomenon that resulted from the geomagnetic storm event of 2015 July 13. The attenuation of the Ddyn in the equatorial region was analyzed using the H component of geomagnetic field data from stations in the Asian sector (Malaysia and India). The variations in the Ddyn signatures were observed at both stations, with the TIR station (India) showing higher intensity than the LKW station (Malaysia).
Numerical simulation of fish damage in a bulb tubular turbine with different guide vane openings
Authors: Qian Li , Yang Yu , Chunxia Yang , Qianxu Zhang , Yuan Zheng
Published: June 2024

Tubular turbines have advantages in developing low-head hydropower, however, the development of hydropower shouldn’t forget to maintain a balance with ecology. In this paper, a three-dimensional model of the flow channel of a low-head power plant bulb tubular turbine unit is established using Unigraphics NX, and the hydraulic characteristics and fish damage mechanisms of the turbine under different guide vane openings of 45∼85 mm in rated operating conditions are simulated and analyzed using STAR-CCM+, and it is found that the fish mainly suffers from impact damage and pressure damage in the downstream process with the highest probabilities of 15.73% and 15.72%, respectively. Furthermore, with the increase of the opening of the guide vane, the probability of shear damage to the fish first decreases and then increases, while the probability of pressure, pressure gradient, and impact damage all gradually increase, and the probability of all four types of damage reaches the highest when the opening of the guide vane is 85 mm. Although the unit will have a large output at large opening operating conditions, from the point of view of fish protection, it is better for such turbines not to be operated with large opening of the guide vane for a long time.
Investigation of hydraulic characteristics of Pelton turbine with casing structure using a moving particle simulation method
Authors: Gong Sheng , Zhou Hengte , Wang Zhaoning , Liang Quanwei
Published: June 2024

This paper reports the initial results of three dimensional simulation of the jet/bucket interactions in the vertical Pelton turbine with different casing structures. The casing is an important part of the Pelton turbine, and a reasonable casing structure can reduce the interaction between the jet and bucket, so as to improve the hydraulic efficiency of the turbine. Previous research has little numerical simulation analysis on the casing. In this paper, a Moving Particle Simulation(MPS) method without grid generation is adopted to compare and analyze the hydraulic characteristics of the runner under the regular hexagonal and circular casing structures. The simulation results show that the hydraulic efficiency of the runner under the hexagonal casing structure is better, and the runner time average torque is improved by 3.09%, which compared with the circular casing. The distribution of free surface flows in the hexagonal casing is analysis, and the obvious interference phenomenon between jets can be observed, which has an important guiding role in the design of the casing structure of Pelton turbine in the future.
Investigation into the Vortex Evolution characteristics of the Francis Turbine During the Runaway Process
Authors: Li Yanyan , Guo Pengcheng , Sun Longgang , Zheng Xiaobo
Published: June 2024

The runaway process is a dynamic transition process that gradually deviates from the optimal operating condition. The flow passage components dissipate all of the energy corresponding to the hydraulic turbine’s head, causing the internal flow of the hydraulic turbine to gradually deteriorate and produce a large-scale vortex structure during the runaway process. A model Francis turbine is used as the research object in this paper to understand the evolution characteristics of an unsteady vortex during a runaway. The runaway process is investigated using high-precision simulation technology of gas-liquid two-phase flow, and the runaway speed is obtained, consistent with the experimental results. The results show that the cavitation volume increases as the rotating speed increases. The large incidence angle between the inlet flow and the blade causes large-scale flow separation in the runner, which leads to forming of a sheet vortex band near the hub of the runner hub and a columnar vortex in the blade passage of the runner blade suction surface. As the runaway process continues, the flow separation in the runner intensifies and the induced vortex size increases, obstructing the runner’s passage. In addition, pressure signal analysis reveals that the pressure fluctuation caused by the sheet vortex band is low-frequency. On the other hand, the pressure fluctuation caused by the columnar vortex is frequent. These two types of vortex structures with high-energy pressure fields degrade the flow in the runner and reduce the hydraulic performance of the turbine.
Study on partial load vortex and pressure pulsation characteristics of Francis turbine
Authors: Zheng XB , Sun SH , Wang ZR , Ren P , Qin ZL , Yu Y , Zhou H
Published: June 2024

Under partial load condition of the Francis turbine, problems such as hydraulic vibration, noise, and high amplitude pressure pulsation that endanger the safe and efficient operation of the unit are inevitable during the transient process. Based on dynamic grid technology and CFD technology, unsteady numerical simulation was conducted for the closing process of the active guide vane from 54% opening to 38% opening, and the evolution characteristics of internal vortex and pressure pulsation were analyzed. The results show that there is always a vortex structure at the crown of the runner during the transition process of variable load. Because of the vortex structure, a “banded” low-pressure zone appears on the suction surface of the blade, which gradually approaches the lower ring of the runner as the vortex structure develops. The analysis of the pressure signal in the runner region shows that the pressure coefficient on the suction surface fluctuates greatly due to the influence of the distribution position of the vortex structure, and the evolution of the vortex structure from continuous to local fracture will lead to a sudden increase of the pressure coefficient. In addition, the frequency components within the runner domain include the frequency of the movable guide vanes passing through the blade and the low-frequency components caused by the evolution of eddy currents within the runner.
Study on the design of short blade offset for the long and short blade runner of 1000 MW hydraulic turbine units
Authors: Lu Yonggang , Zhang Zequan , Chen Hao , Liu Kui , Huang Xingxing , Li Honghui , Wang Zhengwei , Presas Alexandre
Published: June 2024

For such complex rotating machinery as hydraulic turbine, the hydraulic operation characteristics of the hydraulic turbine unit are significantly impacted by the short blade of the runner used as the splitter blade. To find the optimum position of the short blade, the study object is the 1000 MW hydraulic turbine, selects three circumferential offset positions of the short blade for numerical simulation calculation, obtains the runner flow pattern at different offsets, and explores the impact on the short blade offset on the vortex and pressure pulsation in the runner. The results show that the counterclockwise offset of the short blade will improve the flow pattern of the runner, reduce the scale of vortex in the runner and enhance the efficiency of the hydraulic turbine. The counterclockwise offset will increase the interference while decreasing the pressure pulsation in the vaneless region, at the runner’s inlet, and downstream of the short blade. When the offset δ=0.6, the peak-valley difference of pressure fluctuation in the vaneless zone is the smallest, accounting for only 1.38 % of the rated head. The main frequency of the vaneless zone gradually changes from 15fn
to 30fn
, and the main frequency of the runner inlet and the short blade downstream is 24fn
. Due to the different weakening effects of short blades on the interference, low-frequency pulsation components of 4fn
and 8fn
appear.
Study of hydraulic turbine flow-induced noise distribution law based on defective runner blade
Authors: Pan Hongjiang , Yu Fengrong , Zeng Yun , Liu Yuchen , Guo Jianping
Published: June 2024

In order to analyse flow-induced noise distribution law under the defective runner blade, this paper performs defective treatment on the runner blade according to the HLA855a-LJ-250 hydraulic turbine model. Two kinds of blade models, intact blade and outlet side abrasive blade, are established respectively, and the Realizable k-ε turbulence model and broadband noise source model are used to simulate the hydraulic turbine under rated operating conditions. The simulation results show: 1)Double-row leaf grilles and runner blade are the main dipole flow-induced noise sources; 2)Significant differences in the distribution of the acoustic power levels of the double-row leaf grilles’ characteristic blades and the runners’ characteristic blades under different Schemes; 3)Runner defective blades have less effect on the acoustic power level of spiral case, the rest of the overflow components acoustic power level has a tendency to increase, especially the runner has the greatest impact. The maximum increase in acoustic power level of the runner is almost 17 dB, followed by double-row leaf grilles with an increase of around 8 dB. Therefore, critical attention needs to be paid to the abnormal noise signals of runner and double-row leaf grilles.
Study on the relationship between draft tube pressure pulsation and unit vibration based on mutual information method
Authors: Xu Yiting , Zeng Yun , Pan Liping , Zhang Huan , Sun Yanfei , Qian Jing
Published: June 2024

Draft tube pressure pulsation, as a long-term phenomenon, affects the key to stable unit operation. Based on data from actual power plants, this study qualitatively analyses the relationship between unit vibration parameters and draft tube pressure pulsation under variable load. Then the nonlinear correlation coefficient of mutual information (MI) between draft tube pressure pulsation and external vibration factors is obtained by quantitative calculation from data analysis and probability statistics. The feasibility of this method is demonstrated, and it provides a basis for the subsequent prediction of draft tube pressure pulsation based on the external vibration factors screened by mutual information.
Hydraulic analysis of jet deflection on Pelton turbine deflector based on CFD simulation
Authors: Simin Yuan , Hengte Zhou , Zhaoning Wang , Qiyuan He , Quanwei Liang
Published: June 2024

The deflector of the external regulating mechanism of the Pelton turbine can reduce the pressure of the nozzle structure during the emergency load rejection of the unit, and solve the problem that the pressure in the pressure pipe increases too much and the rotate speed of the unit gets too fast. This paper mainly introduces the flow pattern analysis of jet deflection when the Pelton turbine deflector is in working state. The results of calculation and analysis in this paper are based on the Navier-Stokes equations and k-ω SST turbulent model of CFD simulation.
Calculation method for natural frequency and damping ratio of hydropower units based on motion model separation
Authors: Yu Shige , Zeng Yun , Dao Fang , Li Xiang , Xu Yiting , Qian Jing
Published: June 2024

In recent years, the research on characteristic extraction methods for non-stationary and non-linear vibration signals of hydroelectric units has been a hot topic in the fault diagnosis of hydroelectric units. The effectiveness of feature extraction directly affects the accuracy of fault diagnosis. This article proposes a vibration signal feature extraction method for hydroelectric units based on motion model separation and logarithmic attenuation rate method. The under-damped decay oscillation motion trajectory is obtained from the signal after motion model separation. And then, the logarithmic attenuation rate method in the time domain analysis is used to calculate the system damping ratio and natural frequency. In this process, the principle of selecting the envelope interpolation function is proposed, and the effectiveness of the cubic Hermite interpolation function is determined. Based on the calculation effectiveness and accuracy requirements, the effective step length of the vibration signal is determined to be Δt = 0.001, and the effective calculation interval for extracting the decay oscillation characteristics is [ts
, tend
]. The results show that the proposed method is more straightforward, efficient, has higher computational accuracy and better signal-to-noise ratio adaptability, and can provide a theoretical basis for practical engineering applications.
Numerical Study on Valve Closing Criteria during Pump-turbine Start-up on Pump Mode
Authors: Shu Lingfeng , Zheng Yinxia , He Zhongwei , Fang Jie , Li Chengjun
Published: June 2024

Vibrations of exhaust pipes have been observed in some hydropower stations during the exhaust process of pump-turbine start-up on pump mode due to water ingress into the pipes. It may have a safety risk for the pump-turbine start-up process when exhaust pipes are operating under the compressed air-water two phase flow. Since the numerical simulation researches about pump start-up process have been rarely reported and the development of flow field in exhaust pipe is lack of quantitative cognition, it calls for an urgent need to supplement related works. In this paper, the transient full-channel two-phase numerical simulation research on the pump mode return water exhaust process of a pumped power station is carried out by Reynolds-Averaged Navier-Stokes approach. This work put emphasis on the characteristics of cone water level, runner torque and air speed in exhaust pipes after the compressed air released from the runner chamber. Then development laws and relationship with the exhaust valve closing timing are analysed and concluded. Results show that the cone water level, runner torque and air speed pulsation signal of exhaust pipes can be used as exhaust valve closing criteria, and the third criterion has the largest time margin.
Research and application of Qingyuan pumped-storage power station multi units control strategy during simultaneous load rejection
Authors: Zhao Bushi , Peng Yumin , Luo Yixi , Zhang Hao , Huang Fanqi
Published: June 2024

This paper studies the qingyuan pumped-storage power station multi units safety control strategy during load rejection at the same time, through the comparative analysis of several schemes, design the transmission line trip trigger generator tripping logic, optimize the existing protection system control strategy, the formation of the single line power station a few units safety control strategy during load rejection at the same time, the realization of multiple units in the case of lines correctly load rejection, Ensure the safety of unit operation.
Cause Analysis and Mitigation Measures of Vertical Vibration of Head-Cover of a Pump-Turbine
Authors: Hongyu Chen , Yunfa Lin , Kaiming Li , Chao Zhang , Zan Zhou , Yongguang Cheng
Published: June 2024

The abnormal vertical vibration of the head cover of a 306 MW pump-turbine was found in the 150 to 240 MW part load region of generating condition. To reveal the causes and find mitigation measures, field tests on vibration and pressure pulsations, and the ODS (Operational Deflection Shape) analysis of the head cover were conducted. It was found that the vibration of the head-cover is transferred by means of the clearance water body from the runner vibration, which in induced by pressure pulsations. Several vibration reduction measures were analysed and injecting compressed-air into the clearance between the head-cover and the runner-crown was proposed. The field test showed that the abnormal vibration was effectively eliminated because the fluid characteristics between the head-cover and the runner can be changed by just adding a small amount of compressed-air, which destroys the critical conditions of inducing vibration. This first attempt is of reference values, because it is a simple, effective, and economical.
Variations of flow patterns and pressure pulsations in variable speed pump-turbine during start-up process
Authors: Zhang Pengcheng , Cheng Yongguang , Liu Demin , Zheng Jinsheng , Li Guofeng
Published: June 2024

In recent years, variable speed pumped-storage (VSPS) technology has become a hotspot of research and application due to its excellent power grid regulation capabilities. Since the speed of a VSPS unit is changeable, when switching operating conditions, more stable operating trajectories can be chosen to reduce vibration and damage. The simulations of transient processes of VSPS units normally use 1D method, which cannot judge the quality of operating conditions because of no flow pattern and pressure pulsation information. Using 3D CFD simulation based on OpenFOAM, we analyse the flow patterns and pressure pulsations when a VSPS unit with a full size frequency converter (FSFC) is in the turbine start-up process. The typical operating points in the variable speed transient trajectories obtained from 1D simulation are studied. It is found that in the initial stage of start-up, high-speed circulation flow arises in the vaneless space, leading to flow separation and large pressure pulsation. The results can provide a reference for the operation of VSPS power stations, so as to avoid operating conditions with adverse flow patterns and pressure pulsations.
Study on load rejection test of pumped storage units
Authors: Luo Guohu , Wang Xi , Zhao Wenjun , Huang Shaozheng , Li Jinwei
Published: June 2024

The rise rate of rotating speed, the maximum inlet pressure of the spiral casing and the minimum inlet pressure of the draft tube cone of unit 2 in Jinzhai pumped storage power station were analyzed when 50% and 100% of the rated load were rejected in this paper. The low pass filtering method (cut off frequency is 0.2 times of the frequency) was used to process the pressure data at the inlet of the spiral casing and the draft tube cone to retain the trend term. The peak to peak values (97% confidence) of the pressure pulsation term under different data durations were studied, which provided technical support for rational and accurate calculation of the maximum inlet pressure of the spiral casing and the minimum inlet pressure of the draft tube cone, and provided an example reference for the load rejection test analysis of pumped storage units.
Redesign of Adjustable Guide Vane Cascades of Pump Turbine and Its Effect on Self-Excited Vibrations at Slight Opening During Pump Mode’s Starting Up Process
Authors: Hao Z J , Wang M K , He Q Y , Shi Q H , Chen H , Ding X L
Published: June 2024

Abnormal sounds and vibrations have occurred at several pumped storage power stations, when the guide vanes are at a slight opening during the pump mode’s starting up process. This paper proposes a modification method for active guide vanes to reduce the probability of abnormal vibration caused by self-excited vibration. A set of real machine guide vanes was selected to investigate the influence of different geometric parameters on self-excited vibration. Comprehensive analyses were conducted on the modified blades by the unsteady Reynolds-averaged Navier-Stokes solver and the 1DOF oscillator model (URANS-1DOF) coupling simulations. The results indicate that the probability of self-excited vibration divergence of the guide vanes is closely related to the degree of contraction and diffusion of the narrow gap flow channel. The self-excited vibration of the guide vane can be effectively suppressed by selecting appropriate overlapping length, contraction coefficient and diffusion coefficient. In addition, model tests have verified that the modification method has a slight impact on hydraulic performance.
Study on vibration characteristics of pump-turbines with different runner characteristics
Authors: Li Hailing , Ren Shaocheng , Liu Yang
Published: June 2024

In terms of the problems of large vibration pendulum in some working conditions and obvious vibration sensation in local plant and water delivery system of Heimifeng pumped storage power station, test and analysis were carried out on two different runner units before and after transformation in the same flow channel, revealing the difference of pressure pulsation transmission characteristics and vibration response of different runner hydrostatic interference. The test results show that the modified runner with long and short blades is feasible and effective for reducing the pressure pulsation caused by dynamic and static interference and controlling the vibration of the plant, which can provide a reference for the vibration of the unit and the plant in the same type of pumped storage power station.