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Design and analysis of bidirectional deployable parabolic cylindrical antenna
Tian Yu, Fu-ling Guan, Lu Dai
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2014, 15(2): 83-96.
https://doi.org/10.1631/jzus.A1300202
A bidirectional deployable parabolic cylindrical reflector for an L-band synthetic aperture radar is presented in this study, in which a self-deployed antenna with low weight was designed. The antenna consists of four curved surfaces formed from thin sheets of composite materials connected by hinges along the edges, and the reflective surface is provided by the front surface. The edge profiles of connecting lines were obtained through geometric analysis. A scaled model, including design and manufacture, was demonstrated to validate the process from the folded state to the fully deployed state. The non-contact synchronous vision measuring method was used to test the basic frequency of the scaled model, and the test results gave the verification of the analyses. Compared with the existing unidirectional deployable antenna, this new type of bidirectional deployable antenna can be applied to larger-size antennas and has better performance because the glass-woven tape connections were substituted with more reliable hinges. Static, modal, harmonic response, and transient response analyses of the full-sized reflector structure were modeled with the commercial finite element (FE) package ABAQUS. The modeling techniques were developed to predict the structural dynamic behavior of the reflector and the results showed that the first natural frequency was 0.865 Hz, and the reflector structure had good stiffness in three directions. This proposed structure has very high stiffness-to-mass ratio because of its hollow solid construction. A preliminary simulation of radiation properties of the parabolic cylindrical antenna, fed by an off-set linear feed horn array, was conducted to obtain the radiation pattern of the feed and the reflector.
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A fast integration method for translating-pulsating source Green’s function in Bessho form
Chao-bang Yao, Wen-cai Dong
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2014, 15(2): 108-119.
https://doi.org/10.1631/jzus.A1300209
The singularities and oscillatory performance of translating-pulsating source Green’s function in Bessho form were analyzed. Relative numerical integration methods such as Gaussian quadrature rule, variable substitution method (VSM), and steepest descent integration method (SDIM) were used to evaluate this type of Green’s function. For SDIM, the complex domain was restricted only on the θ-plane. Meanwhile, the integral along the real axis was computed by use of the VSM to avoid the complication of a numerical search of the steepest descent line. Furthermore, the steepest descent line was represented by the B-spline function. Based on this representation, a new self-compatible integration method corresponding to parametric t was established. The numerical method was validated through comparison with other existing results, and was shown to be efficient and reliable in the calculation of the velocity potentials for the 3D seakeeping and hydrodynamic performance of floating structures moving in waves.
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Target localization based on joint measurement of amplitude and frequency in a LOFAR field
Lin-wei Tao, Ying-min Wang
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2014, 15(2): 130-137.
https://doi.org/10.1631/jzus.A1300263
To estimate the motion parameters of a moving target before its passing by the closest point of approach (CPA) point in a low frequency analyzing and recording (LOFAR) field, an error-free theoretical method based on the joint measurement of target radiated noise’s amplitude and frequency was presented. First, the error-free theoretical equations for target characteristic frequency, absolute velocity, the CPA, and amplitude of the radiation noise were derived by three equal interval measured values of the target amplitude and frequency. Then, the method to improve the calculation accuracy was given. Finally, the simulation and experiments were conducted in the air and showed the correctness of this method. By using one single piece of LOFAR, this method can calculate four target parameters and the relative error of each estimated parameter is less than 10%.
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Microstructure and hardness of Cu-12% Fe composite at different drawing strains
Xiao-pei Lu, Da-wei Yao, Yi Chen, Li-tian Wang, An-ping Dong, Liang Meng, Jia-bin Liu
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2014, 15(2): 149-156.
https://doi.org/10.1631/jzus.A1300164
Cu-12% Fe (in weight) composite was prepared by casting, pretreating, and cold drawing. The microstructure was observed and Vickers hardness was measured for the composite at various drawing strains. Cu and Fe grains could evolve into aligned filaments during the drawing process. X-ray diffraction (XRD) was used to analyze the orientation evolution during the drawing process. The axial direction of the filamentary structure has different preferred orientations from the radial directions. The strain of Fe grains linearly increases with an increase in the drawing strain up to 6.0, and deviates from the linear relation when the drawing strain is higher than 6.0. With an increase in the drawing strain, the microstructure scales of Fe filaments exponentially decrease. The density of the interface between Cu and Fe phases exponentially increases with an increase in the aspect ratio of Fe filaments. There is a similar Hall-Petch relationship between the hardness and Fe filament spacing. The refined microstructure from drawing deformation at drawing strains lower than 3.0 can induce a more significant hardening effect than that at drawing strains higher than 3.0.
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7 articles
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