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91.
92.
An accurate and practical modeling technique is proposed to analyze cracked metal plates with patch repair. In the single-model approach, a p-convergent high-precision element is developed with three-dimensional elasticity theory. Whereas, in the mixed-model approach, a p-convergent transition element is developed to connect the p-convergent high-precision elements for threedimensional response and p-convergent ESL (equivalent single layer) elements for two-dimensional response. For the developed elements, two- and three-dimensional virtual crack closure techniques based on linear elastic fracture mechanics are modified to estimate the stress intensity factor. Modeling simplicity and calculation efficiency of the mixed-model approach using the p-convergent transition elements is shown for the analysis of patch repaired plates. Some results of present analysis are verified by comparison with published results. Also, performance of analysis using the proposed technique with simplicity and efficacy of modeling is investigated for patch repaired plates with respect to a number of parameters such as thicknesses of patch and adhesive, patch size, single-sided patch vs. double-sided patch. 相似文献
93.
The present study examines the tensile behaviour of composite structures repaired by bonding external patches. Various patches of different stacking sequences placed on both sides of the parent plate were considered. Damage development and the failure process of the repaired plates were analyzed and a parent plate fracture model has been proposed. Optimised patch repairs were calculated by finite element modelling. It was found that high stress concentration along the longitudinal edges of circular patches and/or at the transverse edges of the hole leads to early damage initiation in the parent plate. However, the position of damage initiation and the process of damage progression depend particularly on the properties of repair patches. In order to optimise patch repairs, finite element modelling was used and it was founded possible to attain over 90% of the strength of an unnotched specimen. The optimised patch design can be characterised by an optimal strength ratio R*, which should be minimized when selecting repair parameters. 相似文献
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96.
准八木天线是由巴伦、辐射单元和引向器构成的一种微带天线,文中提出了一种具有宽带、宽角特性的改进型准八木天线。通过CST仿真分析软件,对振子双臂后折和利用矩形微带贴片对辐射单元进行改进的微带贴片式准八木天线进行仿真分析,仿真和实测结果显示,微带贴片式准八木天线在带宽达到40%频带内(8 GHz~12 GHz),驻波比(VSWR)≤2,3 dB的波束宽度均能达到120°以上。 相似文献
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论述了微带天线的基本理论、经典分析方法、天线单元的馈电方法以及微带阵列天线的形式、特性及馈电网络,从毫米波天线单元入手,研究了16元矩形微带贴片天线阵的设计方法,并给出了仿真结果,与理论计算值相符。 相似文献
99.
C. R. Dohrmann M. M. Rashid 《International journal for numerical methods in engineering》2002,53(4):945-958
A method is presented for the polynomial approximation of shape function gradients based solely on the geometry of finite element boundaries. The method is founded on a least squares approach which leads to an integration scheme satisfying a necessary condition for convergence. In its simplest form the method reduces to the well‐known uniform strain approach for finite elements. The method is applicable to a broad class of problems such as connecting dissimilar meshes, mesh adaptivity and transitioning, and the construction of finite elements with variable topologies. Finite elements based on the polynomial approximations are shown to pass patch tests of various orders. In contrast to standard elements, higher‐order patch tests are passed without the need for nodes internal to element boundaries. Less sensitivity to volumetric locking under plane strain conditions is demonstrated through comparisons with a standard element formulation. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
100.
Let S be an arbitrarily given bicubic Bézier patch and P an arbitrarily given plane. In this paper, a necessary and sufficient condition for S ∩ P to be non-empty is given, and some properties of S ∩ P, if non-empty, are included. Furthermore an efficient and robust algorithm for finding S ∩ P is described, and many interesting examples are shown. 相似文献