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Erosion Characteristics of Oil-immersed On-load Tap Changer Contacts Under Varying Contact Speeds and Pressures

Chinese Journal of Electrical Engineering 2024年第1期10卷 21-34页

作者： Zongying li Shuaibing li Yongqiang Kang Zheng li Hongwei Li School of New Energy and Power Engineering Lanzhou Jiaotong UniversityLanzhou 730070China School of Electrical Engineering Southwest Jiaotong UniversityChengdu 611756China School of Automation and Electrical Engineering Lanzhou Jiaotong UniversityLanzhou 730070China

With the growing demand for precise voltage adjustment and reactive regulation,the frequent operation of on-load tap changers(OLTCs)in oil-immersed systems has led to increased erosion of switch contacts by arcs during the switching process.This erosion causes significant wear on the contacts,thereby reducing their lifespan.Therefore,the present study aims to investigate the behavior and mechanism of arc erosion on contact surfaces in oil-immersed OLTCs.To achieve this,a self-designed friction and wear test device for OLTC contacts was utilized to conduct experiments at various sliding speeds and contact pressures.Additionally,finite element analysis was employed to validate the experimental results regarding the influence of sliding speed on arc energy.The surface morphology of the contacts was observed using an optical microscope.The findings revealed that as the sliding speed increased,the arc energy,arc initiation rate,and contact resistance initially exhibited an upward trend,then decreased,and eventually increased again.The minimum values were observed at a sliding speed of 90 mm/s.Moreover,the arc energy,arc initiation rate,and contact resistance decreased gradually as the contact pressure increased.After reaching a contact pressure of 1.5 N,the variation in the arc energy stabilized.At lower contact pressures,arc erosion dominated the wear on the contact surface.However,at higher contact pressures,the wear transitioned from predominantly arc erosion to a combination of mechanical wear and arc erosion.In summary,experimental and analytical investigations provided insights into the effects of sliding speed and contact pressure on the behavior of arc erosion,contact resistance,and surface damage of OLTC contacts in oil-immersed systems.

关键词： Oil-immersed on-load tap changer arc energy contact resistance friction and wear arc erosion

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CFD-DEM investigation into flow characteristics in mixed pulsed fluidized bed under electrostatic effects

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Particuology 2022年第7期20卷 100-112页

作者： Hongwei Li Lei Wang Changhe Du Wenpeng Hong School of Energy and Power Engineering Northeast Electric Power UniversityJilin 132012China

Static electricity has an important effect on gas–solid fluidized bed reactor fluidization performance.In the process of fluidization,electrostatic interaction between particles will obviously accelerate particle agglomerate formation,which consequently reduces the fluidization performance.Pulsed gas flow injection is an efficient method to enhance particle mixing,thereby weakening the occurrence of particle agglomerate.In this study,the two-dimensional hybrid pulsed fluidized bed is established.The flow characteristics are studied by using the coupled CFD-DEM numerical simulation model considering electrostatic effects.Influences of different pulsed frequencies and gas flow ratios on fluidized bed fluidization performance are investigated to obtain the optimal pulsed gas flow condition.Results show that in the presence of static electricity,the bubble generation position is lower,which is conducive to the particle flow.Pulsed gas flow can increase the particle velocity and improve the diffusion ability.The bubble generation time is different at different frequencies,and the frequency of 2.5 Hz has the most obvious effect on the flow characteristics.Different gas flow ratios have significant impacts on the particle movement amplitude.When the pulse gas flow accounts for a large ratio,the particle agglomerate tends to be larger.Therefore,in order to improve the fluidization effect,the ratio of pulsed gas flow to stable gas flow should be appropriately reduced to 0.5 or less.

关键词： Mixed pulsed fluidized bed CFD-DEM Electrostatic effects Flow characteristics

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Kinematic modeling and control of a novel pneumatic soft robotic arm

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Chinese Journal of Aeronautics 2022年第7期35卷 310-319页

作者： Hongwei Li Yan XU Chao ZHANG Huxiao YANG School of Aeronautics and Astronautics Zhejiang UniversityHangzhouZhejiangChina

A novel soft robotic arm(SRA)composed of two soft extensible arms(SEAs)and a soft bendable joint(SBJ)for space capture systems is presented in this paper.A diamond origami pattern was applied in the design of the SEAs,and large deformations of the SEAs in positive pressure were simulated using the nonlinear finite element method.A kinematic model of the SRA using the Denavit–Hartenberg method based on the assumption of constant curvatures was proposed.A closed-loop model-free control system based on a PID controller was developed using real-time data from a vision sensor system.The kinematic model and closed-loop model-free control system are experimentally evaluated on an SRA prototype by four experiments.The experimental results demonstrate that the derived kinematic model can finely describe the movement of the SRA and that the closed-loop control system can control the SRA to reach the desired destination or trajectory within an acceptable error and performs well in long-term repeated operations.

关键词： Arm control Kinematics Repeated precision Soft robotic arm Trajectory tracking

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Runoff-and erosion-reducing effects of vegetation on the loess hillslopes of China under concentrated flow

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International Soil and Water Conservation Research 2022年第4期10卷 662-676页

作者： Wenzhao Guo li Luo Hongwei Li Wenlong Wang Yun Bai State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau Institute of Water and Soil ConservationNorthwest A&F UniversityYangling712100ShaanxiChina School of Water Conservancy and Architectural Engineering Northwest A&F UniversityYangling712100ShaanxiChina Hanjiang-to-Weihe River Valley Water Diversion Project Construction Co.Ltd. Xian710000ShaanxiChina Yulin University Yulin719000ShaanxiChina

Evaluating the effects of revegetation on runoff and erosion reduction is essential for studying soil and water conservation on the Loess Plateau after implementation of China's Grain for Green Project.However,quantifying the influence of revegetation on the erosion caused by concentrated runoff in extreme rainstorms is still challenging.To evaluate this influence,scouring-erosion experiments were implemented in situ on the vegetated hillslope plots(GR)and bare hillslope plots(CK).The runoffreducing effects of grass(GRR)averaged 31%,20%and 8%,and the erosion-reducing effects of grass(GER)averaged 93%,95%and 93%on the 5-plots,10-plots and 18-plots,respectively.The ratios of GRR to GER were 0.09e0.33,implying that the ability of vegetation to reduce erosion was greater than its ability to reduce runoff.The GRR and GER obviously decreased as the inflow rate increased,and the GRR decreased as the hillslope gradient increased,but there were no obvious differences in the GER between hillslope gradients.Vegetation could decrease the ability of the concentrated flow to carry and transport sediment and increase the energy consumption of the concentrated flow in response to hydraulic resistance.Vegetation also significantly reduced the degree of rill development.The degree of rill dissection on the GR(0.054e0.087 m^(2)m^(2))was lower than that on the CK(0.061e0.184 m^(2)m^(2)).Our findings provide an essential reference for ecological environment and vegetation restoration on loess hillslopes.

关键词： Soil erosion Concentrated runoff China's grain for green project Vegetation Hydraulic parameters Chinese loess plateau

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A Review on Ultrasonic-Assisted Forming:Mechanism,Model,and Process

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Chinese Journal of Mechanical Engineering 2021年第5期34卷 147-170页

作者： Guangda Shao Hongwei Li Mei Zhan Shaanxi Key Laboratory of Precision Forming Technology and Equipment School of Materials Science and Engineering Northwestern Polytechnical University Xi’an China

Compared with conventional forming processes,ultrasonic-assisted forming technology with a high frequency and small amplitude can significantly improve the forming quality of materials.Owing to the advantages of reduced forming force,improved surface quality,avoidance of forming defects,and strengthened surface structure,ultrasonic-assisted forming technology has been applied to increasingly advanced forming processes,such as incremental forming,spinning,and micro-forming.However,in the ultrasonic-assisted forming process,there are multiple ultrasonic mechanisms,such as the volume effect and surface effect.The explanation of the effect of ultrasonic vibration(UV)on plastic deformation remains controversial,hindering the development of related technologies.Recently,many researchers have proposed many new theories and technologies for ultrasonic-assisted forming.To summarize these developments,systematic discussions on mechanisms,theoretical models,and forming performances are provided in this review.On this basis,the limitations of the current study are discussed.In addition,an outlook for ultrasonic-assisted forming is proposed:efficient and stable UV systems,difficulty forming components with complex geometry,explanation of the in-depth mechanism,a systematic theoretical prediction model,and multi-field-coupling energy-assisted forming are considered to be hot spots in future studies.The present review enhances existing knowledge of ultrasonic-assisted forming,and facilitates a fast reference for related researchers.

关键词： Ultrasonic vibration Forming Mechanism Model Processing performance

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Mean Curvature Flow of Arbitrary Codimension in Complex Projective Spaces

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Chinese Annals of Mathematics,Series B 2023年第6期44卷 857-892页

作者： li LEI hongwei XU School of Mathematical Sciences Chongqing Normal UniversityChongqing 401331China. Center of Mathematical Sciences Zhejiang UniversityHangzhou 310027China

Recently,Pipoli and Sinestrari[Pipoli,G.and Sinestrari,C.,Mean curvature flow of pinched submanifolds of CPn,Comm.Anal.Geom.,25,2017,799-846]initiated the study of convergence problem for the mean curvature flow of small codimension in the complex projective space CPm.The purpose of this paper is to develop the work due to Pipoli and Sinestrari,and verify a new convergence theorem for the mean curvature flow of arbitrary codimension in the complex projective space.Namely,the authors prove that if the initial submanifold in CPm satisfies a suitable pinching condition,then the mean curvature flow converges to a round point in finite time,or converges to a totally geodesic submanifold as t→∞.Consequently,they obtain a differentiable sphere theorem for submanifolds in the complex projective space.

关键词： Mean curvature flow Submanifolds of arbitrary codimension Complex projective space Convergence theorem Differentiable sphere theorem

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Abnormal State Detection of OLTC Based on Improved Fuzzy C-means Clustering

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Chinese Journal of Electrical Engineering 2023年第1期9卷 129-141页

作者： Hongwei Li lilong Dou Shuaibing li Yongqiang Kang Xingzu Yang Haiying Dong School of Automation and Electrical Engineering Lanzhou Jiaotong UniversityLanzhou 730070China School of New Energy and Power Engineering Lanzhou Jiaotong UniversityLanzhou 730070China

An accurate extraction of vibration signal characteristics of an on-load tap changer(OLTC)during contact switching can effectively help detect its abnormal state.Therefore,an improved fuzzy C-means clustering method for abnormal state detection of the OLTC contact is proposed.First,the wavelet packet and singular spectrum analysis are used to denoise the vibration signal generated by the moving and static contacts of the OLTC.Then,the Hilbert-Huang transform that is optimized by the ensemble empirical mode decomposition(EEMD)is used to decompose the vibration signal and extract the boundary spectrum features.Finally,the gray wolf algorithm-based fuzzy C-means clustering is used to denoise the signal and determine the abnormal states of the OLTC contact.An analysis of the experimental data shows that the proposed secondary denoising method has a better denoising effect compared to the single denoising method.The EEMD can improve the modal aliasing effect,and the improved fuzzy C-means clustering can effectively identify the abnormal state of the OLTC contacts.The analysis results of field measured data further verify the effectiveness of the proposed method and provide a reference for the abnormal state detection of the OLTC.

关键词： On-load tap changer singular spectrum analysis Hilbert-Huang transform gray wolf optimization algorithm fuzzy C-means clustering

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Black phosphorus-based heterostructures for photocatalysis and photoelectrochemical water splitting

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Journal of Energy Chemistry 2022年第4期31卷 745-779页

作者： Shutao li Yihe Zhang hongwei Huang Beijing Key Laboratory of Materials Utilization of Nonmetallic Minerals and Solid Wastes and School of Materials Science and Technology China University of GeosciencesBeijing 100083China

Semiconductor-based photocatalytic and photoelectrochemical(PEC) processes can convert solar energy into high-density chemical energy or for the treatment of environmental pollutants, which are ideal ways to deal with environmental and energy crises. The development of high-efficiency photocatalysts and photoelectrodes is the key to the in-depth development and practical application of the two technologies.Black phosphorus(BP) has excellent physicalcochemical properties such as adjustable band gap, high carrier mobility, large specific surface area and anisotropy, making it one of the most promising catalysts.BP-based heterostructure can not only realize the effective separation of photogenerated carriers but also improve the stability of BP, and is widely used in photocatalytic and PEC reactions. In this review, we first introduce the crystal structure, band structure, anisotropy, and preparation of BP with different dimensions(bulk, zero-dimension and two-dimension). Then, according to the transfer path of the photogenerated carriers and the components, the BP-based heterostructures are divided into type I heterojunction, type II heterojunction, Z-scheme heterojunction, S-scheme heterojunction, BP/carbonbased material heterostructure, BP/metal heterostructure and multi-component heterostructure.Highlighted are the diverse photocatalytic applications of BP-based heterostructure, such as water splitting and CO_(2)reduction, N_(2)fixation, pollutant degradation, photothermal and photodynamic therapy.Finally, some concluding views and opinions are stated on the challenges and opportunities faced by the further development of BP-based heterostructures in photocatalysis and PEC water splitting.

关键词： Black phosphorus Heterostructure Photocatalysis Photoelectrochemical water splitting

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Synergistic effect of diethylene triamine penta(methylene phosphonic acid) and graphene oxide barrier on anti-scaling and anti-corrosion performance of superhydrophobic coatings

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Frontiers of Materials Science 2023年第3期17卷 131-144页

作者： Mingliang Zhu Hongwei Li Ruixia Yuan Huijuan Qian Huaiyuan Wang College of Chemistry and Chemical Engineering Northeast Petroleum UniversityDaqing 163318China College of Chemical Engineering Daqing Normal UniversityDaqing 163712China

In this study,a novel diethylene triamine penta(methylene phosphonic acid)(DTPMPA)-and graphene oxide(GO)-modified superhydrophobic anodized aluminum(DGSAA)coating was fabricated.The obtained coatings were characterized by scan electron microscopy,X-ray diffraction,Fourier transform infrared spectroscopy,and Raman analysis.After immersion in the supersaturated CaCO_(3) solution for 240 h,the scaling mass of the DGSAA coating is only 50%of that of the SAA coating.The excellent anti-scaling performance of the DGSAA coating comes from three barriers of the air layer,the DTPMPA:Ca^(2+)chelate,and the lamellar GO,as well as the further active anti-scaling of DTPMPA:Ca^(2+)at the coating–solution interface.DTPMPA and GO at the surface of the DGSAA coating exhibit an insertion structure.In the electrochemical impedance spectroscopy measurement,the impedance modulus of the DGSAA coating is three orders-of-magnitude higher than that of the anodized aluminum.The synergistic effect of DTPMPA stored in the porous structure of anodized aluminum and the barrier protection of superhydrophobicity and GO contributes to the excellent comprehensive performance of the DGSAA coating.This research provides a new perspective for designing anti-scaling and anti-corrosion superhydrophobic bi-functional coatings.

关键词： anti-scaling anti-corrosion DTPMPA graphene oxide synergistic effect barrier

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Convex optimization of asteroid landing trajectories driven by solar radiation pressure

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Chinese Journal of Aeronautics 2022年第12期35卷 200-211页

作者： Chuanjun DONG hongwei YANG Shuang li Bo li College of Astronautics Nanjing University of Aeronautics and AstronauticsNanjing 211106China Tianjin Key Laboratory of Microgravity and Hypogravity Environment Simulation Technology Tianjin 300458China Tianjin Institute of Aerospace Mechanical and Electrical Equipment Tianjin 300458China

High-area/mass ratio landers driven by Solar Radiation Pressure(SRP)have potential applications for future asteroid landing missions.This paper develops a new convex optimization-based method for planning trajectories driven by SRP.A Minimum Landing Error(MLE)control problem is formulated to enable planning SRP-controlled trajectories with different flight times.It is transformed into Second Order Cone Programming(SOCP)successfully by a series of different convexification technologies.A trust region constraint and a modified MLE objective function are used to guarantee the convergence performance of the optimization algorithm.Thereafter,the SRP-driven trajectory optimal control problem is converted equivalently into a sequence of convex optimal control problems that can be solved effectively.A set of numerical simulation results has verified the effectiveness and feasibility of the proposed optimization method.

关键词： Asteroids Convex optimization Optimal control Soft landing Solar radiation pressure Trajectory optimization

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