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Numerical Simulation of the Dynamic Behaviors of a Gas Tungsten Welding Arc for Joining Magnesium Alloy AZ61A

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Acta Metallurgica Sinica(English Letters) 2013年第5期26卷 588-596页

作者： Zhenmin WANG Fang YAN Pengcheng ZHAO school of Mechanical & automotive engineering South China University of Technology College of electromechanical engineering Qingdao University of Science and Technology

Based on the Magneto-Hydro-Dynamic（MHD） theory, a united three-dimensional（3D） transient numerical model is developed to investigate the dynamic behaviors of arc plasma for a magnesium alloy AZ61A gas tungsten arc welding（GTAW） arc. The arc, electrode and workpiece are integrated into one calculation domain to avoid both presumed distribution of the current density at the electrode tip and the assumption of constant conditions of interface between welding arc and workpiece. The distributions of electric potential, current density, magnetic flux density, electromagnetic force, velocity, temperature, and pressure of the arc plasma in the 3D space are analyzed by using the numerical model. Results indicate that the maximum gradient of the electric potential in the whole arc space exists around the electrode tip, where the electric current density, electromagnetic force, and temperature are also the maximum. However, maximum pressure is found at the velocity stagnation, which is above the *** between predicted temperature and measured one in arc region shows a good agreement.

关键词： GTAW Arc MHD theory Dynamic behavior Numerical simulation

Vibration analysis and control technologies of hydraulic pipeline system in aircraft:A review

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Chinese Journal of Aeronautics 2021年第4期34卷 83-114页

作者： Peixin GAO Tao YU Yuanlin ZHANG Jiao WANG Jingyu ZHAI school of electromechanical and automotive engineering Yantai UniversityYantai 264005China school of Mechanical engineering Dalian University of TechnologyDalian 116024China

Vibrations in aircraft hydraulic pipeline system,due to multi-source excitation of high fluid pressure fluctuation and serious vibration environment of airframe,can cause the pipeline system vibration failures through overload in engineering *** the vibrations in hydraulic pipeline is a challenging work to ensure the flight safety of *** common vibration control technologies have been demonstrated to be effective in typical structures such as aerospace structures,shipbuilding structures,marine offshore structures,motor structures,***,there are few research literatures on vibration control strategies of aircraft hydraulic *** with the development trend of aircraft hydraulic pipeline system and the requirement of vibration control technologies,this paper provides a detailed review on the current vibration control technologies in hydraulic pipeline system.A review of the general approaches following the passive and active control technologies are presented,which are including optimal layout technique of pipeline and clamps,constrained layer damping technique,vibration absorber technique,hydraulic hose technique,optimal pump structure technique,and active vibration control technique of pipeline ***,some suggestions for the application of vibration control technologies in engineering field are given.

关键词： Aircraft Hydraulic pipeline Vibration analysis Vibration control Vibration failure

Form-fnding methods for deployable mesh reflector antennas

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Chinese Journal of Aeronautics 2013年第5期26卷 1276-1282页

作者： Li Tuanjie Jiang Jie Deng Hanqing Lin Zhanchao Wang Zuowei school of electromechanical engineering Xidian University

Deployable high-frequency mesh reflector antennas for future communications and obser- vations are required to obtain high gain and high directivity. In order to support these new missions, reflectors with high surface accuracy are widely required. The form-finding analysis of deployable mesh reflector antennas becomes more vital which aims to determine the initial surface profile formed by the equilibrium prestress distribution in cables to satisfy the surface accuracy requirement. In this paper, two form-finding methods for mesh reflector antennas, both of which include two steps, are pro- posed. The first step is to investigate the prestress design only for the cable net structure as the circum- ferential nodes connected to the supporting truss are assumed fixed. The second step is to optimize the prestress distribution of the boundary cables connected directly to the supporting truss considering the elastic deformation of the antenna structure. Some numerical examples are carried out and the simulation results demonstrate the proposed form-finding methods can warrant the deformed antenna reflector surface matches the one by design and the cable tension forces fall in a specified range.

关键词： Antenna reflectors Cable net structure Elastic deformation Form-finding analysis Mesh reflector Prestress distribution

Passive inter-modulation scattering analysis of reflector considering contact nonlinearity

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Chinese Journal of Aeronautics 2013年第2期26卷 463-469页

作者： Jiang Jie Li Tuanjie Liu Yicai school of electromechanical engineering Xidian University

Passive inter-modulation （PIM） is a form of nonlinear distortion caused by the inherent nonlinearities of the passive devices and components in RF/microwave system. It will degenerate the performance of communication system with broad-band channel and high-sensitivity receiver. Therefore, it is necessary to construct a model to simulate this process in order to predict the level of PIM. This paper is aimed at constructing some plate models with one-dimensional and two-dimensional contact nonlinearity sections illuminated by two-tone waves, and calculating the scattered field at a fixed-point in space using time-domain physical optics method. By taking fast Fourier transform （FFT）, we get the spectrum of the scattered field and then analyze the generated PIM products. At the end of this paper, some numerical examples are presented to show the influence rules of the relative factors on PIM. The results indicate the variation of the level of PIM with the number of the nonlinear regions, the nonlinear spacing, and the incident power levels.

关键词： Contact nonlinearity Nonlinear distortion Passive inter-modulation Reflector antennas Scattered field Time-domain physical optics

A Computational Study on Lateral Flight Stability of the Cranefly in Hover

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Computer Modeling in engineering & Sciences 2021年第8期128卷 669-685页

作者： Na Xu Shuaizhi Zhou Chunchen Zhang Xiaolei Mou school of electromechanical and automotive engineering Yantai UniversityYantai264005China school of Civil engineering Yantai UniversityYantai264005China

The dynamic flight stability of hovering insects includes the longitudinal and lateral *** results have shown that for the majority of hovering insects the same longitudinal natural modes are identified and the hovering flight in longitudinal is ***,in lateral,the modal structure for hovering insects could be different and the stability property of lateral disturbance motion is not as robust as that of longitudinal *** cranefly possesses larger aspect ratio and lower Reynolds number,and such differences in morphology and kinematics may make the lateral dynamic stability *** this paper,the lateral flight stability of the cranefly in hover is investigated by numerical ***,the stability derivatives are acquired by solving the incompressible Navier–Stokes ***,the dynamic stability characteristics are checked by analyzing the eigenvalues and eigenvectors of the linearized *** results indicate that the lateral dynamic modal structure of cranefly is different from most other insects,consisting of three natural modes,and the weakly oscillatory mode illustrates the hovering lateral flight is nearly *** neutral stability is mainly caused by the negative derivative of roll-moment ***-velocity,which can be attributed to the weaker‘changingLEV-axial-velocity’*** results suggest that insects in nature may exhibit different dynamic stabilities with different morphological and kinematic parameters,which should be considered in the designs of flapping wing air vehicles.

关键词： Flapping flight cranefly lateral flight stability natural modes of motion computational fluid dynamics

Large-signal modeling method for power FETs and diodes

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Journal of Semiconductors 2009年第6期30卷 57-60页

作者：孙璐王家礼王珊李雪铮石慧王娜郭生平 school of electromechanical engineering Xidian University

Under a large signal drive level,a frequency domain black box model of the nonlinear scattering function is introduced into power FETs and diodes.A time domain measurement system and a calibration method based on a digital oscilloscope are designed to extract the nonlinear scattering function of semiconductor *** extracted models can reflect the real electrical performance of semiconductor devices and propose a new large-signal model to the design of microwave semiconductor circuits.

关键词： large signal model extraction method nonlinear scattering function semiconductor devices

Measurement of micro weld joint position based on magneto-optical imaging

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Chinese Physics B 2015年第1期24卷 517-523页

作者：高向东陈子琴 school of electromechanical engineering Guangdong University of Technology

In a laser butt joint welding process, it is required that the laser beam focus should be controlled to follow the weld joint path accurately. Small focus wandering off the weld joint may result in insufficient penetration or unacceptable *** of joint position offset, which describes the deviation between the laser beam focus and the weld joint, is important for adjusting the laser beam focus and obtaining high quality welds. A new method based on the magneto-optical（MO） imaging is applied to measure the micro weld joint whose gap is less than 0.2 mm. The weldments are excited by an external magnetic field, and an MO sensor based on principle of Faraday magneto effect is used to capture the weld joint images. A sequence of MO images which are tested under different magnetic field intensities and different weld joint widths are acquired. By analyzing the MO image characteristics and extracting the weld joint features, the influence of magnetic field intensity and weld joint width on the MO images and detection of weld joint position is observed and summarized.

关键词： micro weld joint magneto-optical imaging laser welding

Prediction of heat transfer of nanofluid on critical heat flux based on fractal geometry

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Chinese Physics B 2013年第1期22卷 344-349页

作者：肖波齐 school of Physics and electromechanical engineering Sanming University

Analytical expressions for nucleate pool boiling heat transfer of nanofluid in the critical heat flux （CHF） region are derived taking into account the effect of nanoparticles moving in liquid based on the fractal geometry theory. The proposed fractal model for the CHF of nanofluid is explicitly related to the average diameter of the nanoparticles, the volumetric nanoparticle concentration, the thermal conductivity of nanoparticles, the fractal dimension of nanoparticles, the fractal dimension of active cavities on the heated surfaces, the temperature, and the properties of the fluid. It is found that the CHF of nanofluid decreases with the increase of the average diameter of nanoparticles. Each parameter of the proposed formulas on CHF has a clear physical meaning. The model predictions are compared with the existing experimental data, and a good agreement between the model predictions and experimental data is found. The validity of the present model is thus verified. The proposed fractal model can reveal the mechanism of heat transfer in nanofluid.

关键词： nanofluid fractal geometry heat transfer

Containment consensus with measurement noises and time-varying communication delays

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Chinese Physics B 2015年第2期24卷 23-29页

作者：周峰王正杰范宁军 school of electromechanical engineering Beijing Institute of Technology

In this paper,we consider the containment consensus control problem for multi-agent systems with measurement noises and time-varying communication delays under directed *** using stochastic analysis tools and algebraic graph theory,we prove that the followers can converge to the convex hull spanned by the leaders in the sense of mean square if the allowed upper bound of the time-varying delays satisfies a certain sufficient ***,the time-varying delays are asymmetric for each follower agent,and the time-delay-dependent consensus condition is ***,numerical simulations are provided to illustrate the effectiveness of the obtained theoretical results.

关键词： multi-agent systems containment consensus noise communication delays