检索结果-南通市图书馆

在线全文

学校读者我要写书评

暂无评论

并网逆变器惯性特性与提升策略研究

河南理工大学学报（自然科学版） 2025年第1期44卷 134-144页

作者：李继方韩爱山华北水利水电大学电气工程学院河南郑州450003

目的为解决当前大规模新能源发电并网后电力系统低惯量运行的问题,方法对并网逆变器惯性特性进行分析,并对提升并网逆变器惯性水平的方法进行研究。首先分析电力系统中惯性的本质,推导出并网逆变器惯性水平与自身器件参数的关系,利用... 详细信息

目的为解决当前大规模新能源发电并网后电力系统低惯量运行的问题,方法对并网逆变器惯性特性进行分析,并对提升并网逆变器惯性水平的方法进行研究。首先分析电力系统中惯性的本质,推导出并网逆变器惯性水平与自身器件参数的关系,利用根轨迹法绘出以直流侧电容为变量的直流电压控制环根轨迹,结合根轨迹和不同电网工况场景对逆变器惯性水平的需求优化直流侧电容取值;然后在并网逆变器直流侧电压控制环中引入频率反馈环节,提出一种改进的逆变器直流侧电压控制策略和逆变器调制策略,进而提升并网逆变器的瞬时惯量水平,使直流侧电容根据电网频率波动情况进行充放电,抑制电网频率瞬时变化率;最后,使用MATLAB/Simulink搭建仿真平台对所提惯性提升策略进行验证。结果结果表明,当直流侧电容取0.4 F,虚拟惯性时间常数为5 s时,与未使用本文所提控制策略相比,本文策略的系统频率跌落最大偏移量减小了0.11 Hz,平均跌落速率减小了0.035 Hz/s。结论所提策略能有效提升并网逆变器惯性水平,抑制电网频率瞬时变化。

关键词：电力系统逆变器频率稳定惯性电容电压电压控制

A novel high-order scheme for numerical simulation of wake flow over helicopter rotors in hover

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Aeronautics 2022年第5期35卷 260-274页

作者： Shaoqiang han Wenping SONG Zhonghua han Institute of Aerodynamic and Multidisciplinary Design Optimization National Key Laboratory of Science and Technology on Aerodynamic Design and ResearchSchool of AeronauticsNorthwestern Polytechnical UniversityXi’an 710072China

Accurate prediction of tip vortices is crucial for predicting the hovering performance of a helicopter rotor.A new high-order scheme(we call it WENO-K)proposed by our research group is employed to minimize numerical dissipation and extended to numerical simulation of unsteady compressible viscous flows dominated by tip vortices over hovering ***-K is referred to as an adaptively optimized WENO scheme with Gauss-Kriging reconstruction,and its advantage is to reduce dissipation in smooth regions of flow while preserving high-resolution around *** WENO-K scheme is adopted to reconstruct left and right state values within the Roe Riemann solver updating the inviscid fluxes on a structured dynamic overset *** minimize the accuracy loss for high-order reconstruction on artificial boundaries of overset grid,a method of multilayer fringes is proposed to carry out interpolation between background grid and blade *** parallel computing considering automatic load balance on averagely partitioned overset grid is developed to reduce the wall-clock time of an unsteady *** results for Caradonna-Tung(C-T)rotor in hover at the conditions of subsonic and transonic tip Mach numbers show that the thrust coefficient error for the result of WENO-K scheme is no more than 3%.Compared with WENO-JS scheme,WENO-K scheme achieves about 40%improvement on accuracy of predicting rotor thrust with only 4.1%extra computational *** importantly,WENO-K scheme can capture more sophisticated unsteady flow structures and resolve tip vortices to a larger wake age with an increment of about 270°compared to WENO-JS scheme.

关键词： Dynamic overset grid Helicopter rotors High-order scheme Unsteady flow Vortex flow WENO scheme

Differences in clinical and genetic characteristics between early-and late-onset narcolepsy in a han Chinese cohort

在线全文

学校读者我要写书评

暂无评论

Neural Regeneration Research 2020年第10期15卷 1887-1893页

作者： Hui Ouyang Fang han Ze-Chen Zhou Jun Zhang Department of Clinical Neurology Peking University People’s HospitalBeijingChina Department of Clinical Pulmonology Peking University People’s HospitalBeijingChina Department of Epidemiology and Biostatistics School of Public HealthPeking University Health Science CenterBeijingChina

Early-and late-onset narcolepsy constitutes two distinct diagnostic ***,it is not clear whether symptomology and genetic risk factors differ between early-and late-onset *** study compared clinical data and single-nucleotide polymorphisms(SNPs)between early-and late-onset patients in a large cohort of 899 han Chinese narcolepsy ***,cerebrospinal fluid,and clinical data were prospectively collected from patients,and patients were genotyped for 40 previously reported narcolepsy risk-conferring *** risk scores(GRSs),associations of five different sets of SNPs(GRS1–GRS5)with early-and late-onset narcolepsy,were evaluated using logistic regression and receiver operating characteristic *** sleep latency was significantly shorter in early-onset cases than in late-onset *** severity was greater among late-onset patients,with higher rates of sleep paralysis,hypnagogic hallucinations,health-related quality of life impairment,and concurrent presentation with four or more *** levels did not differ significantly between early-and late-onset *** rs3181077(CCR1/CCR3)and rs9274477(HLA-DQB1)were more prevalent among early-onset *** GRS1(26 SNPs;OR=1.513,95%CI:0.893–2.585;P<0.05)and GRS5(6 SNPs;OR=1.893,95%CI:1.204–2.993;P<0.05)were associated with early-onset narcolepsy,with areas under the receiver operating characteristic curves of 0.731 and 0.732,*** GRS1 nor GRS5 included SNPs in HLA *** results indicate that symptomology and genetic risk factors differ between early-and late-onset *** protocol was approved by the Institutional Review Board(IRB)Panels on Medical Human Subjects at Peking University People’s Hospital,China(approval *** 86)in October 2011.

关键词： case-control studies clinical features genetic association studies genetic load genetic loci genetic phenomena hypothalamic diseases precision medicine risk assessment single nucleotide polymorphism

Data-Driven Based Fault Prognosis for Industrial Systems:A Concise Overview

在线全文

学校读者我要写书评

暂无评论

IEEE/CAA Journal of Automatica Sinica 2020年第2期7卷 330-345页

作者： Kai Zhong Min han Bing han Faculty of Electronic Information and Electrical Engineering Dalian University of TechnologyDalian 116024China Key Laboratory of Intelligent Control and Optimization for Industrial Equipment of Ministry of Education Dalian University of TechnologyDalian 116024China State Key Laboratory of Navigation and Safety Technology Shanghai Ship and Shipping Research InstituteShanghai 200135China

Fault prognosis is mainly referred to the estimation of the operating time before a failure occurs,which is vital for ensuring the stability,safety and long lifetime of degrading industrial *** to the results of fault prognosis,the maintenance strategy for underlying industrial systems can realize the conversion from passive maintenance to active *** the increased complexity and the improved automation level of industrial systems,fault prognosis techniques have become more and more ***,the datadriven based prognosis approaches,which tend to find the hidden fault factors and determine the specific fault occurrence time of the system by analysing historical or real-time measurement data,gain great attention from different industrial *** this context,the major task of this paper is to present a systematic overview of data-driven fault prognosis for industrial ***,the characteristics of different prognosis methods are revealed with the data-based ones being ***,based on the different data characteristics that exist in industrial systems,the corresponding fault prognosis methodologies are illustrated,with emphasis on analyses and comparisons of different prognosis ***,we reveal the current research trends and look forward to the future challenges in this *** review is expected to serve as a tutorial and source of references for fault prognosis researchers.

关键词： Data-driven fault prognosis feature extraction industrial systems

Elastic, Piezoelectric and Acoustic Properties of Wurtzite MnO from Density Functional Calculation

在线全文

学校读者我要写书评

暂无评论

Communications in Theoretical Physics 2013年第6期59卷 751-755页

作者： han han Surface Physics Laboratory (National Key Laboratory) Key Laboratory of Computational Physical Sciencesand Department of Physics ~dan University Shanghai 200433 China

The wurtzite MnO has been obtained lately and is expected to have large potentiai in varies applications. Since elastic properties are the bases of various applications, we calculate these properties of wurtzite MnO based on the density-functionai theory and compare it with other two phases of MnO （rocksalt and zinc-blende MnO）. The Young＇s modulus of wurtzite and zinc-blende MnO are 65.6 GPa and 73.4 GPa, respectively, which are much lower than those of rocksaJt MnO （177.6 GPa）. More importantly, both the Poisson ratio and the bulk modulus to shear modulus ratio indicate that wurtzite MnO should have much better ductile properties than rocksalt MnO. The calculated piezoelectric constants of wurtzite MnO are comparable to those of ZnO, This suggests wurtzite MnO is a good piezoelectric material. Furthermore, the slowness surfaces of acoustic waves of them are given from Christoffel equation.

关键词： wurtzite MnO density functional calculation elastic properties piezoelectric properties acousticproperties

Cell-protecting regeneration from anode carbon deposition using in situ produced oxygen and steam:A combined experimental and theoretical study

在线全文

学校读者我要写书评

暂无评论

Journal of Materials Science & Technology 2018年第12期34卷 2375-2383页

作者： Zongying han Zhibin Yang Minfang han Union Research Center of Fuel Cell School of Chemical and Environmental EngineeringChina University of Mining and Technology Department of Energy and Power Engineering Tsinghua University College of Chemical and Environmental Engineering Shandong University of Science and Technology

Carbon deposition is a primary concern during the operation of solid oxide fuel cells（SOFCs） fueled with hydrocarbon fuels, leading to cell degradation and even cell damage. Carbon elimination is expected to be a promising approach to prolong cell life. This work reports on a combined experimental and theoretical investigation of cell regeneration from anode carbon deposition of tubular SOFCs fabricated by phase-inversion and co-sintering techniques. The as-prepared cell exhibits a maximum power density of 0.20 W cm;at 800 ℃ fueling with wet CH;, but fails to stable operation due to severe carbon *** on thermodynamic predictions, a successive cell-protecting regeneration process is proposed to eliminate deposited carbon without oxidizing Ni catalysts, during which CH;and H;fuels are provided in circulation. Through a total of 35 cycling tests, cell performance can always successfully restore to the initial *** possible carbon elimination mechanism is investigated in detail based on thermodynamic and first-principle calculations. The feasibility of carbon elimination using in situ produced oxygen or steam through electrochemical reaction has been revealed, providing a novel continuous operation mode for hydrocarbon-based SOFCs.

关键词： Solid oxide fuel cells Carbon deposition Cell regeneration Carbon elimination First-principle

在线全文

学校读者我要写书评

暂无评论

食物饱腹感研究及其测试技术进展

食品科学 2025年第2期46卷 299-307页

作者：姚孟丽韩晓峰王若永韩小伟韩忠曾新安黄京美刘义凤苑鹏柳嘉段盛林中国食品发酵工业研究院北京100020 空军特色医学中心北京100142 中国人民解放军总医院第五医学中心北京100139 华南理工大学食品科学与工程学院广东广州510640

饱腹感,即为进食后满足感和不再渴望进食的状态,在维护正常食欲、控制体质量、预防肥胖及改善代谢性疾病方面具有重要意义。文章系统分析影响饱腹感的多种因素,包括食物成分、感官特征、能量密度、心理因素及饮食行为等,并阐述这些因素... 详细信息

饱腹感,即为进食后满足感和不再渴望进食的状态,在维护正常食欲、控制体质量、预防肥胖及改善代谢性疾病方面具有重要意义。文章系统分析影响饱腹感的多种因素,包括食物成分、感官特征、能量密度、心理因素及饮食行为等,并阐述这些因素对饱腹感的作用机制。同时,重点介绍模拟视觉量表、胃肠道激素检测及闪烁扫描等新兴技术在饱腹感测试中的应用,展示这些技术在评估饱腹感方面的科学性和有效性。此外,文章还讨论饱腹感及其测试技术的研究意义与未来展望,旨在为饱腹感相关机制的深入研究、饱腹感测试技术的创新以及高饱腹感食品的开发提供理论支持和实践参考。

关键词：饱腹感食物成分感官特征能量密度心理因素饮食行为模拟视觉量表生化指标

Diffusion-reaction compromise the polymorphs of precipitated calcium carbonate

在线全文

学校读者我要写书评

暂无评论

Particuology 2013年第3期11卷 301-308页

作者： han Wang Wenlai Huang Yongsheng han EMMS Group State Key Laboratory of Multiphase Complex SystemsInstitute of Process EngineeringChinese Academy of Sciences Graduate School of Chinese Academy of Sciences

Diffusion is seldom considered by chemists and materialists in the preparation of materials while it plays an important role in the field of chemical engineering. If we look at crystallization at the atomic level, crystal growth in a solution starts from the diffusion of ions to the growing surface followed by the incorporation of ions into its lattice. Diffusion can be a rate determining step for the growth of crystals. In this paper, we take the crystallization of calcium carbonate as an example to illustrate the microscopic processes of diffusion and reaction and their compromising influence on the morphology of the crystals produced. The diffusion effect is studied in a specially designed three-cell reactor. Experiments show that a decrease of diffusion leads to retardation of supersaturation and the formation of a continuous concen- tration gradient in the reaction cell, thus promoting the formation of cubic calcite particles. The reaction rate is regulated by temperature. Increase of reaction rate favors the formation of needle-like aragonite particles. When diffusion and reaction play joint roles in the reaction system, their compromise dominates the formation of products, leading to a mixture of cubic and needle-like particles with a controllable ratio. Since diffusion and reaction are universal factors in the preparation of materials, the finding of this paper could be helpful in the controlled synthesis of other materials.

关键词： Calcium carbonate Shape control Crystallization Diffusion Compromise

Pitch link loads reduction of variable speed rotors by variable tuning frequency fluidlastic isolators

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Aeronautics 2015年第5期28卷 1408-1415页

作者： han Dong National Key Laboratory of Science and Technology on Rotorcraft Aeronautics College of Aerospace EngineeringNanjing University of Aeronautics and Astronautics

To reduce the pitch link loads of variable speed rotors, variable tuning frequency fluid- lastic isolators are proposed. This isolator utilizes the variation of centrifugal force due to the change of rotor speed to change the tuning port area ratio, which can change the tuning frequency of the isolator. A rotor model including the model of fluidlastic isolator is coupled with a fuselage model to predict the steady responses of the rotor system in forward flight. The aeroelastic analyses indicate that distinct performance improvement in pitch link load control can be achieved by the utilization of variable frequency isolators compared with the constant tuning frequency isolators. The 4/rev （per revolution） pitch link load is observed to be reduced by 87.6% compared with the increase of 56.3% by the constant frequency isolator, when the rotor speed is reduced by 16.7%. The isolation ability at different rotor speeds in different flight states is investigated. To achieve overall load reduction within the whole range of rotor speed, the strategy of the variation of tuning frequency is adjusted. The results indicate that the 4/rev pitch link load within the whole rotor speed range is decreased.

关键词： Fluidlastic isolator Loads Pitch link Reduction Rotor Variable frequency Variable speed