bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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.