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181.
对斜拉立体桁架常用的一塔柱两跨结构体系,基于UL列式,采用混合有限元,分别按空间(面外自由)和平面(面外自由度约束)两种模型,进行了线性、几何非线性、材料非线性以及同时考虑两种非线性屈曲分析,得出结构的极限承载力。研究表明,空间模型比平面模型的安全因子低。线性屈曲和只考虑几何非线性屈曲两种模型的安全因子差别较大,而考虑材料非线性和双重非线性两种模型的安全因子比较接近。几何非线性对斜拉立体桁架的极限承载力影响较小,其结构极限承载力主要由材料非线性控制。立体桁架的塑性部位出现在距塔柱(5/8~3/4)主跨附近的弦杆、塔柱附近弦杆以及靠近塔柱拉索附近的弦杆。此外,探讨了塔高、桁架高度、索距以及拉索刚度对结构极限承载力的影响,其中索距对结构的极限承载力影响最大。 相似文献
182.
183.
索道桥是以拉索作为主要受力构件,钢横梁及木板等作为局部受力构件的一种悬索体系桥梁,其作为非永久使用桥梁,目前我国还没有关于其设计施工的标准。本文以某工程大跨度索道桥为例,运用有限元软件MIDAS/civil对索力及横向稳定性进行了计算分析,并对拉索、钢横梁、锚杆的设计进行了验算,所得结果及计算过程可为类似索道桥提供参考。 相似文献
184.
This paper introduces a modified structure for parallel-plate-based MEMS tunable capacitors. The capacitor has triangular electrodes with geometric and structural asymmetry, which enhances its performance. The device structure is also equipped with a set of cantilever beams between capacitor’s electrodes, called middle beams. These beams provide extra stiffness as tuning voltage increases and delay the pull-in which results in a higher tunability. They also reduce the high sensitivity of the capacitance to the voltage change and linearize the C-V response. An analytical model is developed to optimize the capacitor’s dimensions for maximum linearity of the response. Numerical simulations demonstrate tunabilities over 150% where more than 2/3 of which is highly linear. Capacitors fabricated with PolyMUMPs verify that the design technique proposed in this paper can improve the linearity of the device and increase the maximum tunability. The proposed design has a simple geometry and is fabricated using three structural layers, and therefore, it can be easily integrated in tunable filters or other RF circuits. 相似文献
185.
186.
WU ZhongRu PENG Yan LI ZhanChao LI Bo YU Hong & ZHENG ShouRen State Key Laboratory of Hydrology-Water Resources Hydraulic Engineering Hohai University Nanjing China College of Water Conservancy Hydropower Engineering National Engineering Research Center of Water Resources Efficient Utilization Engineering Safety Changjiang Water Resource Commission Wuhan 《中国科学:信息科学(英文版)》2011,(4)
In order to utilize water and hydropower resources in China,multitudes of water projects are established or to be constructed as an integral part of the national economy's infrastructure.Under these circumstances,there are two outstanding problems:1) a mass of existing dams are in danger and 2) in the southwest water-conservancy construction plan,dozens of existing or planned dams are high dams or even super high dams with heights between 200 and 300 m.In accordance with demands of the National Program for ... 相似文献
187.
马汝建 《中国海上油气(工程)》1997,(2)
本文应用理论推导及数值计算方法,对浅海非线性随机波浪的荷载谱进行了研究;将波面方程、海水质点的水平速度及加速度分解成一阶和二阶分量,通过引入Hermite多项式,得到了波面方程与其一阶分量的自相关函数之间的关系,从而确定了一阶波面分量的谱密度,进而得到了单位桩柱长度上的波浪力及总波浪力的谱密度。 相似文献
188.
We propose an efficient optical packet addressing technique for optical packet-switched networks, where the pre-assigned RF frequency carriers are used to represent the packet addresses. It can simplify the control process of optical packet switching so that it results in reduced address processing time and smaller complexity of the packet address processor due to simple extraction of address information. We also analyze the performance of the proposed packet addressing scheme in the transmission aspect taking into account packet address wavelength beating and laser nonlinearity. 相似文献
189.
光纤线路性能制约着高速率、大容量,远距离光传输系统的发展与应用,文章简要分析了光纤线路技术的最新发展,展望了主要技术的应用前景。 相似文献
190.
Dhananjay Joshi Pradeep Mahadevan Amol Marathe Anindya Chatterjee 《International Journal of Pressure Vessels and Piping》2007
Gasketless flanged joints with metal to metal contact offer some advantages over gasketed joints such as lower weight and better fatigue life. Design of such joints is often based on finite element analyses, and complicated by the fact that the area of contact between the flanges changes upon application of loads. Such analyses can be done using commercial software, which can incorporate geometrical nonlinearities as well as contact nonlinearities. Engineering intuition suggests that the role of geometrical nonlinearities might be small for such problems. However, many engineers continue to use the fully nonlinear analyses. Our aim in this paper is simply to put on record that significant savings in time can be obtained by “turning off” geometric nonlinearities in such analyses, with negligible loss of accuracy. To this end, a nonautomated implementation of the basic ideas is first demonstrated for a simple geometry; more automated analyses for a more general geometry follow. 相似文献