检索结果-南通市图书馆

Parametric study on supersonic flutter of angle-ply laminated plates using shear deformable finite element method

在线全文

学校读者我要写书评

暂无评论

Acta Mechanica Sinica 2011年第5期27卷 749-756页

作者： wei xia Qiao Ni School of Civil Engineering and Mechanics Huazhong University of Science and Technology430074 Wuhan China MOE Key Laboratory for Strength and VibrationSchool of Aerospace Xi＇an Jiaotong University710049 Xi＇an China

The influence of fiber orientation,flow yaw angle and length-to-thickness ratio on flutter characteristics of angle-ply laminated plates in supersonic flow is studied by finite element *** structural model is established using the Reissner-Mindlin theory in which the transverse shear deformation is *** aerodynamic pressure is evaluated by the quasi-steady first-order piston *** equations of motion are formulated based on the principle of virtual *** the harmonic motion assumption,the flutter boundary is determined by solving a series of complex eigenvalue *** study shows that （1） The flutter dynamic pressure and the coalescence of flutter modes depend on fiber orientation,flow yaw angle and length-to-thickness ratio;（2） The laminated plate with all fibers aligned with the flow direction gives the highest flutter dynamic pressure,but a slight yawing of the flow from the fiber orientation results in a sharp decrease of the flutter dynamic pressure;（3） The angle-ply laminated plate with fiber orientation angle equal to flow yaw angle gives high flutter dynamic pressure,but not the maximum flutter dynamic pressure;（4） With the decrease of length-to-thickness ratio,an adverse effect due to mode transition on the flutter dynamic pressure is found.

关键词： Panel flutter Angle-ply laminates Fiber orientation Flow yaw angle Length-to-thickness ratio

Stability of LCL-filtered grid-connected inverters with capacitor current feedback active damping considering controller time delays

在线全文

学校读者我要写书评

暂无评论

Journal of Modern Power Systems and Clean Energy 2017年第4期5卷 584-598页

作者： wei xia Jinsong KANG School of Electronics and Information Engineering Tongji UniversityShanghai 201804China

This paper investigates the stability of LCL-filtered grid-connected inverters with capacitor current feedback(CCF) active damping. The impact of time delays in the digital controller on active damping and its equivalent virtual impedance is analyzed. The inherent relationship between these time delays and stability is ***, a critical value of the CCF active damping coefficient kdamp_cis proposed to define three distinct regions of stability evaluation. If kdamp_c[ 0, a sufficient but smaller damping coefficient(kdamp\ kdamp_c) is recommended as optimum damping solution;if kdamp_c= 0,system will be unstable irrespective of active damping;and if kdamp_c\ 0, active damping is not necessary to design a stable system. Necessary conditions to ensure stability are identified;guidelines for controller design are then presented to optimize the performance of active damping and dynamic response. Simulation and experimental results confirm the presented analysis.

关键词： LCL filter Grid-connected inverter Controller time delays Stability

Strongly Gauduchon Spaces

在线全文

学校读者我要写书评

暂无评论

Chinese Annals of Mathematics,Series B 2018年第6期39卷 989-1000页

作者： wei xia Lingxu MENG School of Mathematical Sciences Fudan University Department of Mathematics North University of China

The authors define strongly Gauduchon spaces and the class JG, which aregeneralization of strongly Gauduchon manifolds in complex spaces. Comparing with the case of Kohlerian, the strongly Gauduchon space and the class JG are similar to the Kohler space and the Fujiki class L respectively. Some properties about these complex spaces are obtained. Moreover, the relations between the strongly Gauduchon spaces and the class JG are studied.

关键词： Strongly Gauduchon metric Strongly Gauduchon space Class JG Topologically essential map

Remarks on BCOV invariants and degenerations of Calabi-Yau manifolds

在线全文

学校读者我要写书评

暂无评论

Science China Mathematics 2019年第1期62卷 171-184页

作者： Kefeng Liu wei xia Department of Mathematics Capital Normal University Department of Mathematics University of California at Los Angeles Center of Mathematical Sciences Zhejiang University

For a one parameter family of Calabi-Yau threefolds, Green et al.(2009) expressed the total singularities in terms of the degrees of Hodge bundles and Euler number of the general fiber. In this paper,we show that the total singularities can be expressed by the sum of asymptotic values of BCOV(BershadskyCecotti-Ooguri-Vafa) invariants, studied by Fang et al.(2008). On the other hand, by using Yau's Schwarz lemma, we prove Arakelov type inequalities and Euler number bound for Calabi-Yau family over a compact Riemann surface.

关键词： BCOV invariants Calabi-Yau manifolds singularities Arakelov inequalities

Low-frequency and broadband vibration energy harvester driven by mechanical impact based on layer-separated piezoelectric beam

在线全文

学校读者我要写书评

暂无评论

Applied Mathematics and Mechanics(English Edition) 2019年第12期40卷 1777-1790页

作者： Dongxing CAO wei xia Wenhua HU College of Mechanical Engineering Beijing University of TechnologyBeijing 100124China Beijing Key Laboratory of Nonlinear Vibrations and Strength of Mechanical Structures Beijing 100124China School of Mechanical Engineering Tianjin University of TechnologyTianjin 300384China

Vibration energy harvesting is to transform the ambient mechanical energy to electricity. How to reduce the resonance frequency and improve the conversion efficiency is very important. In this paper, a layer-separated piezoelectric cantilever beam is proposed for the vibration energy harvester(VEH) for low-frequency and wide-bandwidth operation, which can transform the mechanical impact energy to electric energy. First,the electromechanical coupling equation is obtained by the Euler-Bernoulli beam *** on the average method, the approximate analytical solution is derived and the voltage response is obtained. Furthermore, the physical prototype is fabricated, and the vibration experiment is conducted to validate the theoretical principle. The experimental results show that the maximum power of 0.445 μW of the layer-separated VEH is about3.11 times higher than that of the non-impact harvester when the excitation acceleration is 0.2 g. The operating frequency bandwidth can be widened by increasing the stiffness of the fundamental layer and decreasing the gap distance of the system. But the increasing of operating frequency bandwidth comes at the cost of reducing peak voltage. The theoretical simulation and the experimental results demonstrate good agreement which indicates that the proposed impact-driving VEH device has advantages for low-frequency and wide-bandwidth. The high performance provides great prospect to scavenge the vibration energy in environment.

关键词： vibration energy harvester(VEH) layer-separated piezoelectric b eam low frequency broad-bandwidth

An Adaptive Time Delay Estimator Based on ETDE Algorithm with Noisy Measurements

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Electronics 2017年第4期26卷 760-767页

作者： xia wei JIANG Wenying ZHU Lingfeng School of Electronic Engineering University of Electronic Science and Technology of China

We address the problem of adaptive time delay estimation with noisy measurements. We develop a computationally efficient adaptive time delay estimator based on Explicit time delay estimation(ETDE) algorithm,by applying the unbiased impulse response estimation approach. In this algorithm, a weighted error function is derived, and the time delay is explicitly parameterized in the filter coefficients and iteratively updated directly by utilizing the modified error function. Simulations validate the performance of the proposed algorithm for colored input and low signal-to-noise ratio scenarios.

关键词： Adaptive filter Time delay estimate Noisy measurements Colored input

Nickel nanoparticles supported on nitrogen-doped carbon nanotubes are a highly active,selective and stable CO_(2) methanation catalyst

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Journal of Energy Chemistry 2021年第3期30卷 323-331页

作者： Julian Godde Mariia Merko wei xia Martin Muhler Laboratory of Industrial Chemistry Ruhr University BochumD-44780 BochumGermany

CO_(2) methanation using nickel-based catalysts has attracted large interest as a promising power-to-gas *** nanoparticles supported on nitrogen-doped CNTs with Ni loadings in the range from 10 wt% to 50 wt% were synthesized by impregnation,calcination and reduction and characterized by elemental analysis,X-ray powder diffraction,H_(2) temperature-programmed reduction,CO pulse chemisorption and transmission electron *** Ni/NCNT catalysts were highly active in CO_(2) methanation at atmospheric pressure,reaching over 50% CO_(2) conversion and over 95% CH_(4) selectivity at 340℃ and a GHSV of50,000 mL g^(-1) h^(-1) under kinetically controlled *** small Ni particle sizes below 10 nm despite the high Ni loading is ascribed to the efficient anchoring on the N-doped *** optimum loading of 30 wt%-40 wt% Ni was found to result in the highest Ni surface area,the highest degree of conversion and the highest selectivity to methane.A constant TOF of 0.3 s^(-1) was obtained indicating similar catalytic properties of the Ni nanoparticles in the range from 10 wt%to 50 wt% Ni ***-term experiments showed that the Ni/NCNT catalyst with 30 wt% Ni was highly stable for 100 h time on stream.

关键词： CO_(2)methanation Nickel nanoparticles Carbon nanotubes Nitrogen doping

Agile Earth Observation Satellite Scheduling Algorithm for Emergency Tasks Based on Multiple Strategies

在线全文

学校读者我要写书评

暂无评论

Journal of Systems Science and Systems Engineering 2021年第5期30卷 626-646页

作者： Haiquan Sun wei xia Zhilong Wang xiaoxuan Hu aSchool of Management Hefei University of TechnologyHefeiChina Key Laboratory of Process Optimization and Intelligent Decision-making Ministry of EducationHefeiChina

During the execution of imaging tasks,satellites are often required to observe natural disasters,local wars,and other emergencies,which regularly interferes with the execution of existing ***,rapid satellite scheduling is urgently *** a new generation of three degree-of-freedom(roll,pitch,and yaw)satellites,agile earth observation satellites(AEOSs)have longer variable-pitch visible time windows for ground targets and are capable of observing at any time within the time ***,they are very suitable for emergency ***,current task scheduling models and algorithms ignore the time,storage and energy consumed by ***,these cannot make full use of the AEOS capabilities to optimize the scheduling for emergency *** this study,we present a fine scheduling model and algorithm to realize the AEOS scheduling for emergency ***,a novel time window division method is proposed to convert a variable-pitch visible time window to multiple fixed-pitch visible time ***,a model that considers flexible pitch and roll capabilities is ***,a scheduling algorithm based on merging insertion,direct insertion,shifting insertion,deleting insertion,and reinsertion strategies is proposed to solve conflicting problems *** verify the effectiveness of the algorithm,48 groups of comparative experiments are carried *** experimental results show that the model and algorithm can improve the emergency task completion efficiency of AEOSs and reduce the disturbance measure of the ***,the proposed method can support hybrid satellite resource scheduling for emergency tasks.

关键词： Agile earth observation satellites emergency tasks merging insertion shifting insertion

Boosting electrocatalytic hydrazine oxidation at single-crystalline Ni nanosheets with embedded NiZn

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Progress in Natural Science:Materials International 2023年第5期33卷 710-717页

作者： xia wei Hongbin Dai Chuangwei Liu Song Li School of Material Science and Engineering Northeastern University

Hydrazine oxidation reaction(Hz OR) plays a crucial role in direct hydrazine fuel cells and holds promise for replacing the kinetics-sluggish oxygen evolution reaction in splitting water. While Ni–Zn alloys exhibit exceptional activity for Hz OR, their synthesis under mild conditions remains a challenge. Herein, a Ni–Zn nanosheet catalyst with Ni Zn inclusion was prepared on Ni foam by controllable chemical etching together with ethylene glycol reduction. X-ray diffraction and transmission electron microscopy confirmed the single-crystalline nature and the presence of intermetallic Ni Zn. The strong interaction between Ni and Zn O, along with defects, facilitated the formation of this intermetallic compound. The Ni–Zn/Ni foam exhibits remarkable catalytic activity(214.3m A cm-2at 0.1 V) and durability(87.8 % retention after 24 h) towards hydrazine electrooxidation, thanks to the combined benefits of intermetallic Ni Zn, mesoporous nanosheets, microscopic defects, single-crystalline characteristics, and a coherent Ni–Ni Zn interface. This study provides a new method for designing highly active Ni–Zn electrocatalysts for Hz OR.

关键词： Hydrazine electrooxidation Intermetallic NiZn Single-crystalline Coherent interface Microscopic defects