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991.
992.
本文用水下电火花微爆炸产生重复性极佳的球形冲击波,用双曝光全息干涉法测量了液电冲击波的传播,并观察到冲击波与水下电极之间的相互作用.实验结果表明此法适用于液电冲击波的测量,特别适用于由冲击波波前位移来确定其峰值压力分布. 相似文献
993.
40Cr材料动态起裂韧性KId()的实验测试 总被引:4,自引:0,他引:4
描述了利用Hopkinson压杆技术加载三点弯曲试样测试40Cr,材料动态起裂韧性KId()的试验方法。试样上的动态载荷历程由Hopkinson杆直接测得,并分别代入动态有限元程序及近似公式求得动态应力强度因子历史;由贴在试样裂尖附近的应变片确定起裂时间,最终确定起裂时的动态应力强度因子值,即动态起裂韧性KId()。试验结果表明:利用Hopkinson压杆技术加载三点弯曲试样测试材料动态起裂韧性的方法是可行的,起裂时,动态有限元的位移法、应力法及近似公式法求得的动态应力强度因子值比较吻合;在本文的载荷速率下,40Cr材料动态起裂韧性KId()与准静态裂韧性KId()相比,降低了约28%。 相似文献
994.
高速列车穿越有竖井隧道流场的特性研究 总被引:1,自引:0,他引:1
给出了高速列车穿越隧道压力波的三维粘性流场数值模拟过程,控制方程为三维粘性、可压缩、等熵和非定常流的Navier-Stokes方程,空间离散采用了中心有限体积法格式,时间采用预处理二阶精度多步后差分格式进行离散,对隧道壁面采用壁面函数处理。在模拟中考虑了竖井的位置、竖井的断面积、竖井的数目等因素对隧道内压力及压力梯度的影响。计算结果表明,竖井的存在改变了压缩波的波前形状,从而使得隧道内的压力变化的最大值降低,因而能够降低隧道内的压力梯度最大值,但它并不能延长压力上升的时间。 相似文献
995.
Fluid banks sometimes form during gravity-driven counter-current flow in certain natural reservoir processes. Prediction of
flow performance in such systems depends on our understanding of the bank-formation process. Traditional modeling methods
using a single capillary pressure curve based on a final saturation distribution have successfully simulated counter-current
flow without fluid banks. However, it has been difficult to simulate counter-current flow with fluid banks. In this paper,
we describe the successful saturation-history-dependent modeling of counter-current flow experiments that result in fluid
banks. The method used to simulate the experiments takes into account hysteresis in capillary pressure and relative permeabilities.
Each spatial element in the model follows a distinct trajectory on the capillary pressure versus saturation map, which consists
of the capillary hysteresis loop and the associated capillary pressure scanning curves. The new modeling method successfully
captured the formation of the fluid banks observed in the experiments, including their development with time. Results show
that bank formation is favored where the pc-versus-saturation slope is low. Experiments documented in the literature that exhibited formation of fluid banks were also
successfully simulated. 相似文献
996.
Drag Reduction of a Circular Cylinder Using an Upstream Rod 总被引:3,自引:0,他引:3
Experimental studies on the drag reduction of the circular cylinder were conducted by pressure measurement at a Reynolds number
of 82 000 (based on the cylinder diameter). A rod was placed upstream of and parallel to the cylinder to control the flow
around the cylinder. The upstream rod can reduce the resultant force of the cylinder at various spacing between the rod and
the cylinder for α < 5∘(α defined as the staggered angle of the rod and the cylinder). For α > 10∘, the resultant force coefficient has a large value, so the upstream rod cannot reduce the force on the cylinder any more.
For α = 0∘ and d/D = 0.5 (where d and D are the diameter of the rod and the cylinder, respectively), the maximum drag of the cylinder reduces to 2.34% that of the
single cylinder. The mechanism of the drag reduction of the cylinder with an upstream rod in tandem was presented by estimating
the local contributions to the drag reduction of the pressure variation. In the staggered arrangement, the flow structures
have five flow patterns (they are the cavity mode, the wake splitting mode, the wake merge mode, the weak boundary layer interaction
mode and the negligible interaction mode) according to the pressure distribution and the hydrogen bubble flow visualization.
The half plane upwind of the cylinder can be divided to four regions, from which one can easily estimates the force acting
on the circular cylinder with an upstream rod in staggered arrangement. 相似文献
997.
998.
The buckling problem for longitudinally corrugated cylindrical shells under external pressure is solved. The solution makes
practically exact allowance for the geometry and buckling modes of the shell. The inaccuracy of the results is due to the
assumption that the subcritical state is momentless. Shells consisting of cylindrical panels of smaller radius and noncircular
shells with sinusoidal corrugations are analyzed for stability. The practical applicability of such shells is demonstrated
__________
Translated from Prikladnaya Mekhanika, Vol. 43, No. 11, pp. 66–79, October 2007. 相似文献
999.
A. D. Savel’ev 《Fluid Dynamics》2007,42(6):907-913
Supersonic laminar flow past a two-dimensional “flat-plate/wedge“ configuration is numerically investigated. The pressures at the boundary layer separation and reattachment points are calculated over wide Mach and Reynolds number ranges. The minimum angles of the wedge surface inclination at which a return flow occurs are determined. The results are presented in the form of generalized Mach-number-dependences of the theoretical pressure on the wedge surface initiating boundary layer separation and the pressure at the boundary layer reattachment point. 相似文献
1000.
The effect of a non-uniform parallel high magnetic field on flow control characteristics is investigated experimentally for a magnetic fluid single-phase flow and an air—magnetic fluid two-phase flow in a vertical channel. It is found that as the magnetic field strength is increased, the friction factor of the single-phase flow increases significantly. For the two-phase flow, the friction pressure loss and the head pressure loss, which is smaller than the friction loss, are negligibly small compared with the magnetic pressure loss. In the case where air is injected 27.9d upstream from the maximum magnetic field, the air flow is blocked by the magnetic force in the entrance of the magnetic field, which leads to increases in both local void fraction and pressure drop there. In the case where air is injected 1.43d downstream from the maximum magnetic field, the air flow is accelerated, resulting in a decrease in void fraction and an increase in pressure rise. In the latter case and under the present range of experimental conditions, the magnetic pumping head reaches 0.02 MPa at the highest, and the maximum circulation flow rate reaches twice as high as non-magnetically driven flow rate. 相似文献