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排序方式: 共有199条查询结果,搜索用时 15 毫秒
1.
Short duration stress pulses are of particular interest in determining the interfacial crack tip instability criteria for
the dynamic fracture behavior of laminated carbon-fiber/epoxy composites. However, the heterogeneous architectures of laminated
composites can alter the characteristics of a stress pulse as it propagates toward a crack tip. This makes it difficult to
use standard dynamic testing techniques for characterizing these materials, since these techniques assume the characteristics
of the stress pulse do not change as a result of propagation and can therefore be unambiguously determined from impact conditions.
This paper presents a novel experimental technique that has been developed for characterizing short duration stress pulse
propagation in laminated composite materials. In this technique, a dynamic moiré interferometer is used to capture fringe
patterns corresponding to displacement fields associated with short duration stress pulses that were generated by impacting
0° and 90°/0°/90° carbon-fiber/epoxy composites with a magnetic flyer plate. Appropriate dynamic testing conditions for capturing
high fidelity fringe patterns were determined using the recently developed dynamic moiré fringe contrast factor. The effects
of the composite architecture on the propagation of short duration stress pulses observed with the dynamic moiré interferometer
were confirmed by transient dynamic finite element analysis. From comparisons of experimental and numerical data, it was determined
that the impact conditions for the magnetic flyer plate and laminated composite will not necessarily be planar, which has
a significant effect on the intensity and duration of the propagating stress pulse. 相似文献
2.
We develop a methodology for the estimation of extreme loss event probability and the value at risk, which takes into account both the magnitudes and the intensity of the extreme losses. Specifically, the extreme loss magnitudes are modeled with a generalized Pareto distribution, whereas their intensity is captured by an autoregressive conditional duration model, a type of self‐exciting point process. This allows for an explicit interaction between the magnitude of the past losses and the intensity of future extreme losses. The intensity is further used in the estimation of extreme loss event probability. The method is illustrated and backtested on 10 assets and compared with the established and baseline methods. The results show that our method outperforms the baseline methods, competes with an established method, and provides additional insight and interpretation into the prediction of extreme loss event probability. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
3.
Based on the Timoshenko beam model the equations of motion are obtained for large deflection of off-center impact of a column by a rigid mass via Hamilton's principle. These are a set of coupled nonlinear partial differential equations. The Newmark time integration scheme and differential quadrature method are employed to convert the equations into a set of nonlinear algebraic equations for displacement components. The equations are solved numerically and the effects of weight and velocity of the rigid mass and also off-center distance on deformation of the column are studied. 相似文献
4.
LOSEV V F PANCHENKO Yu N DUDAREV V V IVANOV N G KONOVALOV I N PAVLINSKY A V PUCHIKIN A V 《中国光学与应用光学文摘》2011,(1)
研究了脉冲宽度为25~40 ns的放电脉冲XeCl准分子激光器的工作参数。结果显示,激光器产生的脉冲能量为0.2~0.7 J,重复频率为100 Hz,表明在泵浦功率为2.8~3.3 MW/cm3时,激光器实现了2.6%的激光效率和3.8%的本征效率。 相似文献
5.
LOSEV V F PANCHENKO Yu N DUDAREV V V IVANOV N G KONOVALOV I N PAVLINSKY A V PUCHIKIN A V 《中国光学》2011,4(1):1-8
研究了脉冲宽度为25~40ns的放电脉冲XeCl准分子激光器的工作参数。结果显示,激光器产生的脉冲能量为0.2~0.7J,重复频率为100Hz,表明在泵浦功率为2.8~3.3MW/cm。时,激光器实现了2.6%的激光效率和3.8%的本征效率。 相似文献
6.
7.
从高频和超高频金融数据的基本统计特征出发,回顾了(超)高频金融时间序列模型化研究的发展历程及相关特征,并详细介绍了高频数据模型研究中针对久期序列建立ACD模型族的研究与进展.对ACD模型族,介绍了两种主要类型:强ACD模型和弱ACD模型.最后展望了高频金融时间序列中ACD模型的研究. 相似文献
8.
Xia Liu Hang Song Guoqing MiaoHong Jiang Lianzhen Cao Dabing LiXiaojuan Sun Yiren Chen 《Applied Surface Science》2011,257(6):1996-1999
In0.82Ga0.18As epilayers were grown on InP substrates using a two-step growth technique by LP-MOCVD. A homogeneous low-temperature (450 °C) In0.82Ga0.18As buffer layer was introduced to improve the crystalline quality of epilayers. The influence of low-temperature buffer layer deposition condition, such as thermal annealing duration, on the crystalline quality of the In0.82Ga0.18As epilayer was investigated. Double-crystal X-ray diffraction measurement, Hall measurement, and Raman scattering spectrum were used to evaluate the In0.82Ga0.18As epilayers. Atomic force microscope was used to study the surface morphology. It is found that the In0.82Ga0.18As epilayer, with buffer layer thermal annealing for 5 min, exhibits the best crystalline quality. The change of the surface morphology of the buffer layer after thermal annealing treatment was suggested to explain the phenomenon. 相似文献
9.
承包商在项目执行过程中的现金流均衡是保证项目成功的关键因素。本文研究基于随机活动工期的多模式现金流均衡项目调度问题,旨是在项目工期及鲁棒性阈值约束下合理安排活动执行模式与开始时间,实现承包商现金流均衡。本文通过构建整数规划优化模型对研究问题进行刻画,随后设计模拟退火算法进行求解,最后进行案例分析。结果表明:鲁棒性阈值虽然可以保证基准进度的稳定性,但是提高鲁棒性阈值水平反而不利于承包商的现金流均衡,该值过高时甚至得不到可行解。本文研究可为随机活动工期背景下承包商的现金流控制提供定量化决策支持。 相似文献
10.
We consider trapezoidal load-time pulses with linearly increasing and affinely decreasing durations equal to integer multiples of the time period of the first bending mode of vibration of a linearly elastic structure. For arbitrary spatial distributions of loads applied to monolithic and laminated orthotropic plates, it is shown through numerical solutions that plates’ vibrations become miniscule after the load is removed. This phenomenon is independent of the dwell time (i.e., the time duration between the rising and the falling portions) during which the load is kept constant. The primary reason for this response is that for such time-dependent loads, nearly all of plate’s strain energy is concentrated in deformations corresponding to the fundamental bending mode of vibration. Thus plate’s deformations can be studied by taking the mode shape of the 1st bending mode as the basis function and reducing the problem to that of solving a single second-order ordinary differential equation. We have verified this postulate by comparing strain energies computed from the 3-dimensional deformations of different plate geometries and boundary conditions with those determined by using the single degree of freedom (DoF) model. Thus for trapezoidal time-dependent loads applied on plates, the 1 DoF model provides reasonably accurate results and saves considerable computational effort. 相似文献