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991.
以瞬变流模型和随机信号理论为基础,在乌江构皮滩模型的水垫塘边墙上布置了五个测点,运用上举力量测仪量测板块所受的上举力.实验前对仪器进行了动态标定.量测了校核、设计、正常高水位下表孔单泄、表中孔联合泄洪共6种工况下衬砌块上的脉动上举力,得出相应的两个回归经验公式,为边墙衬砌块的设计提供了科学依据.  相似文献   
992.
1 . INTRODUCTIONForthelarge scaleoceanicflow ,peopleusuallyseekthesolutionsfromthequasi geostrophicvortici tyequationderivedfromtheperturbationbyusingRossbynumberεasalittleparameter.Animportantapproximationwhendeductingvorticityequationinthelayeredseawat…  相似文献   
993.
Stress fields on elastic-creep bi-material interfaces with different geometry of the interface edge are analyzed by finite element method. The results reveal that the stress highly concentrates near the interface edge at the loading instant and it gradually decreases as the creep-dominated zone expands from the small-scale creep to the large-scale creep. The stress singularity due to creep which resembles the HRR stress singularity appears near the interface edge in all cases. The stress intensity near the interface edge time-dependently decreases and becomes constant when the transition reaches the steady state. The magnitude is scarcely influenced by the edge shape of elastic material, though it depends on the edge shape of creep material. The stress intensity during the transition can be approximately predicted by the J-integral at the loading instant.  相似文献   
994.
简要介绍胜利三号钻井平台技术改造设计方案;对平台技术改造后的整体性能包括:重量重心、拖航稳性、沉浮稳性、抗滑稳性、抗倾稳性等方面进行了校核计算;并通过建模对平台的总体结构强度进行了校核分析。  相似文献   
995.
A new scheme decreases memory usage and execution time for the evaluation of certain weighted Cauchy type singular integrals. The scheme is incorporated into an algorithm based on an integral equation of Fredholm second kind. The algorithm computes mode I and II stress intensity factors of cracks in infinite elastic domains. Problems with analytical solutions are solved with relative errors less than 10−15. Earlier investigators' results for kinked cracks with one to four corners are improved. Cracks with a large number of corners can also be studied. In an example the stress intensity factors of a crack with 100 corners are calculated with a relative error of less than 10−6.  相似文献   
996.
In the present work a method is proposed to predict stress intensity factors (SIFs) of strongly interacting cracks at spacings that are substantially smaller than crack lengths. The method is intended for applications where cracks are observed in stack-like/staggered arrangements as in damage patterns of some natural materials with dense lamellar microstructures. The new calculation procedure is inspired by the analytical method of Kachanov (1987) that due to its simplicity has shown to be a powerful tool for analysis of crack interactions. Although in 3-D the accuracy of Kachanov’s method remains good at quite close spacings, in 2-D problems it, however, quickly drops as the distance between cracks decreases, underestimating the effect of crack interactions, especially in ordered staggered arrangements. In this work we introduce new modeling assumptions that are suited for problems where stress fields have high gradients – a typical situation in the case of closely spaced parallel cracks. The accuracy of the method is examined on the example of two stacked cracks. The use of SIFs for estimation of material elastic compliance is also discussed.  相似文献   
997.
 推导了变顶高尾水系统小波动过渡过程水流运动的基本方程,对基本方程进行分析与求解,并以某电站为例,探讨了变顶高尾水系统小波动过渡过程的基本规律。通过小波动过程计算分析结果表明:当水流时间惯性常数 T W0 为某一固定值时,改变坡度 i 值, i 到一定值后对小波动过程稳定性影响甚微,这与试验现象一致;若 i 固定,变化 TW0 ,当 T W0 ≥ 4.5 时,小波动过渡过程为等幅振荡至发散,因此,此值宜小于 4.0 ,这与工程规定相符;当其它水力参数变小时, i 应增大,才能使系统达到良好的动态品质。这些说明所建立的方程组及数学模型是合理的。且此变顶高尾水系统的结构方案能节约较大工程投资  相似文献   
998.
激光束空间整形的研究现状   总被引:5,自引:1,他引:4  
阐述了对激光器输出光束进行空间整形的必要性,介绍了目前常用的一些典型的光束整形方法和器件,并分析了各种方法的优点和缺点.  相似文献   
999.
Motivated by the insights it can provide, we revisit the classical problem of liquid fuel-fed idealized steady-flow combustors. New quadrature-based results are presented for the theoretical combustion intensity and corresponding efficiency for well-stirred adiabatic vessels fed with a prescribed polydispersed spray. Each droplet of the spray is assumed to evaporate according to a non-quasi-steady (non-QS) gas-phase energy/mass diffusion-controlled rate for the pseudo-single-component fuel. As a byproduct, we calculate the complete droplet size distribution (DSD) function exiting the chamber, of interest for the design of downstream components. We explicitly assume that the volumetric rate of chemical energy release in such “primary” combustion chambers is controlled by the liquid fuel physical vaporization process (with negligible lags due to propellant droplet heat-up or vapor-phase ignition). In this instructive asymptotic limit, two decisive non-dimensional parameters are shown to be: (1) a vaporization Damköhler number (defined by the ratio of the mean residence time of the chemically reacting vapor mixture in the combustion space, to the reference value of the vaporization lifetime of a droplet with the injector-Sauter-mean diameter, and (2) a single dimensionless non-QS parameter. Illustrative numerical results for a kerosene-like fuel burning in air at pressures up to 24 atm are displayed for the case of a log-normal feedstream DSD with a range of spreads. Our results reveal the existence of an optimum vaporization Damköhler number which maximizes the combustion intensity—with maximum intensities, occurring well before nearly complete fuel evaporation, being quite sensitive to the non-QS parameter at high pressures. These deliberately idealized mathematical model results, spanning more than a 1000 combinations of operational parameters, set instructive bounds to the achievable performance of “real” spray combustors. Even without tractable enhancements (see Section 5.2), this approach can be used to economically map the sensitivity of spray combustor performance to a large number of important design and control parameters.  相似文献   
1000.
Although gas jets injected into fluid beds fluctuate, previous models assumed that they were steady. A new model separates the bed in a zone in which the jet is never present and a zone in which the jet fluctuates (a point in this zone will alternately be in the jet and in the emulsion phase). Its predictions matched the rate of gas entrainment into the jet and the rate of gas recirculation between emulsion and jet which were observed in a large 2 dimensional bed equipped with a “V” grid and a central jet.  相似文献   
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