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791.
基于平均建模法并考虑到正极性输出罗(positive output super-lift Luo, POSL Luo)变换器中能量传输电容电压存在突变的事实, 建立了POSL Luo变换器的改进平均模型, 推导并分析了POSL Luo变换器输出电压对占空比的传递函数. 建立了电压控制POSL Luo变换器的输出电压对基准电压的传递函数, 分析了系统的稳定性. 采用PSIM软件进行电路仿真以及设计硬件电路进行电路实验, 以PSIM仿真结果和电路实验结果验证了模型的有效性和理论分析的正确性. 研究结果表明: 相比于POSL Luo变换器已有的平均模型, 采用本文的改进平均模型可有效的分析POSL Luo变换器的特性及电压控制POSL Luo变换器的稳定性. 相似文献
792.
In this paper an on-going research effort aimed at detecting and localizing damage in plate-like structures by using mode shape curvature based damage detection algorithm is described. The proposed damage index uses exclusively mode shape curvature data from the damaged structure. This method was originally developed for beam-like structures. In this paper, the method is generalized to plate-like structures which are characterized by two-dimensional mode shape curvature. To calculate mode shape curvatures from the measured mode shapes, three approaches are proposed: the first one is the well-known central difference approximation, the other two are classical approaches based on Tikhonov's regularization technique with smoothing functional. The applicability and effectiveness of the proposed damage detection algorithms are demonstrated experimentally on an aluminium plate containing mill-cut damage. The validity of the method is assessed by comparing the identification results of the experimental test case to the results obtained from the simulated test case. The modal frequencies and the corresponding mode shapes of the aluminium plate are obtained via finite element models for numerical simulations and by using a scanning laser vibrometer (SLV) for the experimental study. 相似文献
793.
C.V. Pao Yu‐Hsien Chang Guo‐Chin Jau 《Numerical Methods for Partial Differential Equations》2013,29(1):251-279
This article is concerned with monotone iterative methods for numerical solutions of a coupled system of a first‐order partial differential equation and an ordinary differential equation which arises from fast‐igniting catalytic converters in automobile engineering. The monotone iterative scheme yields a straightforward marching process for the corresponding discrete system by the finite‐difference method, and it gives not only a computational algorithm for numerical solutions of the problem but also the existence and uniqueness of a finite‐difference solution. Particular attention is given to the “finite‐time” blow‐up property of the solution. In terms of minimal sequence of the monotone iterations, some necessary and sufficient conditions for the blow‐up solution are obtained. Also given is the convergence of the finite‐difference solution to the continuous solution as the mesh size tends to zero. Numerical results of the problem, including a case where the continuous solution is explicitly known, are presented and are compared with the known solution. Special attention is devoted to the computation of the blow‐up time and the critical value of a physical parameter which determines the global existence and the blow‐up property of the solution. © 2012 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 2013 相似文献
794.
In high head Francis turbines and pump-turbines in particular, Rotor Stator Interaction (RSI) is an unavoidable source of excitation that needs to be predicted accurately. Precise knowledge of turbine dynamic characteristics, notably the variation of the rotor natural frequencies with rotation speed and added mass of the surrounding water, is essential to assess potential resonance and resulting amplification of vibrations. In these machines, the disk-like structures of the runner crown and band as well as the head cover and bottom ring give rise to the emergence of diametrical modes and a mode split phenomenon for which no efficient prediction method exists to date. Fully coupled Fluid–Structure Interaction (FSI) methods are too computationally expensive; hence, we seek a simplified modeling tool for the design and the expected-life prediction of these turbines.We present the development of both an analytical modal analysis based on the assumed mode approach and potential flow theory, and a modal force Computational Fluid Dynamics (CFD) approach for rotating disks in dense fluid. Both methods accurately predict the natural frequency split as well as the natural frequency drift within 7.9% of the values measured experimentally. The analytical model explains how mode split and drift are respectively caused by linear and quadratic dependence of the added mass with relative circumferential velocity between flexural waves and fluid rotation. 相似文献
795.
A stereo vision is applied to evaluate crack-tip parameters for fracture specimens subjected to a mixed-mode loading (tension and shear). By using a special loading device, the applied remote loading is oriented at an angle with respect to the axis of the crack. At each loading angle, the calibrated vision system was rotated so that the axis of the crack is parallel to the horizontal or vertical axis of the image frame. At a load close to the crack initiation, the displacement field around the crack-tip region of the fracture specimen was measured relative to a specimen coordinate system located at the crack tip of the fracture specimen. During the experiment, the fracture specimen was subjected to rigid body translation and rotation. Hence, the displacement fields are affected by the rigid body translation and rotation. Using the experimentally determined displacements and the analytically determined displacements with several higher order terms being included, the stress intensity factors and the amount of rigid body translation and rotation were calculated through a least-squares fit. The effect of the rigid body motion on the measured displacements was then eliminated using the computed rigid body translation and rotation. Experimental results indicate that a KI and KII dominant region is observed in the corrected displacement fields. 相似文献
796.
The 60 Hz AC discharges generated by a leakage transformer instead of an isolation one, which is usually used in the power supply of DC CO2 laser, are employed as a pumping source in this experiment. The laser performance characteristics as functions of pressure and discharge current have been investigated. The maximum laser power is about 40 W at conditions of 18 Torr and 35 mA. The output power is not less than that of DC discharge at the same condition. In addition, the laser outputs of 60 Hz AC discharges obtained by different transformers such as a leakage type and an isolation one have been measured. It was found that the laser power obtained by the leakage transformer is saturated at the higher current compared with the isolation transformer. 相似文献
797.
798.
Y. Hirata K. Hayashi Y. Mitsunaka Y. Itoh T. Sugawara 《International Journal of Infrared and Millimeter Waves》1995,16(4):713-733
The design of a 170 GHz, 1 MW-CW gyrotron for electron cyclotron heating of nuclear fusion plasmas is presented. The designed gyrotron incorporates a coaxial cavity to reduce mode competition, and a coaxial electron gun to support the cavity inner conductor. A new mode converter splits the generated wave into two beams and radiates them in different directions. The radiated beams are transmitted to two output windows through two mirror systems, being transformed into Gaussian-like beams. A single-stage depressed collector improves the overall efficiency of the gyrotron and reduces the heat flux to the collector surface. 相似文献
799.
Mingxin Huang 《Journal of the mechanics and physics of solids》2004,52(9):1991-2003
Simple closed-form solutions for critical stress intensity factors were developed for edge dislocation emission from a blunt crack under mode I and mode II loading conditions. The solutions are applicable both for a slender elliptical hole and a long slit with blunted head. When the blunt crack considered degenerates to a sharp crack, the present solutions reduce to those previously reported in literature. 相似文献
800.
P. Glas M. Naumann I. Reng A. Schirrmacher L. Dong J. Caplen 《Fiber and Integrated Optics》1998,17(3):207-212
An experimental investigation is presented for obtaining picosecond (ps) pulses at a repetition rate of 11 GHz using a fiber laser coupled to an external cavity. Without applying active mode locking and without a nonlinear element in the coupled cavity, pulses of about 15 ps with an average power of 20 mW have been generated using a (cw) diode pump laser. The pulse duration decreases with increasing repetition rate. 相似文献