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41.
Strain invariant failure theory (SIFT) is a micro-mechanics-based failure theory for multi-scale failure analysis of composite materials originally proposed by Gosse and Christensen. In this paper, the approach for obtaining strain amplification matrix which is a key step for the execution of SIFT is improved by adopting representative volume element (RVE) finite element models considering periodical boundary condition, based on which more actual deformation mode is reflected. The deformation modes and strain data at the characteristic points of the centroid cell of multi-cell RVE model are analyzed and taken as a reference. It can be concluded that more reasonable deformation mode and relationship between the micro-mechanical and macro-mechanical strain states are obtained by employing the new model. Finally, numerical examples are provided to illustrate the determination of strain amplification factors within the RVEs considering periodical boundary condition at the characteristic points. 相似文献
42.
The rate equations and the power evolution equations based on excited state absorption (ESA) and cooperative upconversion (CUC) of high concentration erbium-doped yttrium aluminum garnet (YAG) transparent ceramic waveguide amplifier are set up to analyze the effects of the pump power, active ion concentration and waveguide length on the amplifier gain and noise figure (NF). The numerical analysis predicts that with a pump power of 100mW, an active ion concentration of 1.0×1026 ion/m3 and a waveguide length of 3 cm, a small-signal gain of 30 dB and an NF of 5 dB can be achieved in the micro-chip amplifier. 相似文献
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介绍了粘贴应变片和激光焊接应变片两种销轴式测力传感器,以及它们各自的优缺点。指出起重机销轴式测力传感器选用激光焊接薄膜应变片,能够收到高精度、高稳定性、好重复性的良好效果。 相似文献
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交通网络是灾害发生后实施及时救援和应急疏散的重要物质基础之一.为提高交通网络在灾害中的抗毁能力,保证交通网络的可靠性,针对不确定环境下的交通网络应急预防护问题,以灾前养护加固成本和灾后修复费用最小化为目标,同时考虑资金预算、灾后网络连通性、旅行时间可靠性和灾后路段通行能力等约束,构建了双层规划模型进行问题描述,并利用基... 相似文献
49.
Two degree of freedom flow-induced vibration of cylindrical structures in marine environments: frequency ratio effects 总被引:1,自引:0,他引:1
Xiangxi Han Wei Lin Xiaojun Zhang Youhong Tang Chengbi Zhao 《Journal of Marine Science and Technology》2016,21(3):479-492
The flow-induced vibration of a cylindrical structure is a very common problem in marine environments such as undersea pipelines, offshore risers, and cables. In this study, the vortex-induced vibration (VIV) of an elastically mounted cylinder at a low Reynolds number is simulated by a transient coupled fluid–structure interaction numerical model. Considering VIV with low damping ratio, the response, hydrodynamic forces, and vortex shedding modes of the cylinder is systematically analyzed and summed up the universal rule under different frequency ratios. On the basis of the analysis, we find that the frequency ratio α is a very important parameter. It decides the locked-in, beat, and phase-switch phenomena of the cylinder, meanwhile, it also influence the vortex mode of the cylinder. The trajectory of the two degrees of freedom (2 DOF) case at different natural frequency ratios is discussed, with most trajectories having a “figure of 8” shape and a few having a “crescent” shape. A fast Fourier transformation technique is used to obtain the frequency characteristics of the vibration of the cylindrical structure. Using the 2 DOF cylinder model in place of the 1 DOF model presents several advantages in simulating the nonlinear characteristics of cylindrical structures, including the capacity to model the crosswise vibration generated by in-line vibration. 相似文献
50.
Naoji Toki 《Journal of Marine Science and Technology》2016,21(1):1-22
Almost all the existing analysis methods of speed trial results were proposed before 1970s, and the actual analysis procedures are very old-fashioned with instructions like “plot the results on a chart and draw a smooth mean line”, “read a value from the mean line” and so on. Such instructions not only show up the analysis procedures old-fashioned, but also make them very ambiguous and unclear. They should be up-dated to a method which is clear not only in logic but also in calculation procedure, and also fits the present computing technology. At first, the author reviewed the major analysis methods and concluded that the logic of the up-dated analysis procedure can be composed of the logics of the existing ones. Then, the analysis procedure is composed of three stages; namely (1) correction of power and propeller revolution to the ones corresponding to no air condition, (2) correction of tidal current effect, and (3) correction of power and propeller revolution to the ones corresponding to no wind condition. For the stages (1) and (3), there seems to be no big issue except the estimation of the amount of environmentally added resistance in the stage (1). Then, the author focused on the correction of tidal current effect in this paper. For the correction of tidal current effect, the author considers the essential points for the up-date are in the direction of finding out appropriate functions for the variation of tidal current velocity and the ship speed through the water. Then, he investigated to find out such functions and made his proposal. Finally, the applicability of the new procedure is assessed by the analysis of simulated speed trial results of a VLCC. 相似文献