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71.
Faruk Civan 《Transport in Porous Media》2007,67(2):329-334
An Arrhenius-type asymptotic-exponential function is derived to describe the temperature dependence of the power needed for
detachment of fine particles from pore walls in porous media. 相似文献
72.
Experimental investigation on tunnel sonic boom 总被引:1,自引:0,他引:1
Upon the entrance of a high-speed train into a relatively long train tunnel, compression waves are generated in front of the train. These compression waves subsequently coalesce into a weak shock wave so that a unpleasant sonic boom is emitted from the tunnel exit. In order to investigate the generation of the weak shock wave in train tunnels and the emission of the resulting sonic boom from the train tunnel exit and to search for methods for the reduction of these sonic booms, a 1300 scaled train tunnel simulator was constructed and simulation experiments were carried out using this facility.In the train tunnel simulator, an 18 mm dia. and 200 mm long plastic piston moves along a 40 mm dia. and 25 m long test section with speed ranging from 60 to 100 m/s. The tunnel simulator was tilted 8° to the floor so that the attenuation of the piston speed was not more than 10 % of its entrance speed. Pressure measurements along the tunnel simulator and holographic interferometric optical flow visualization of weak shock waves in the tunnel simulator clearly showed that compression waves, with propagation, coalesced into a weak shock wave. Although, for reduction of the sonic boom in prototype train tunnels, the installation of a hood at the entrance of the tunnels was known to be useful for their suppression, this effect was confirmed in the present experiment and found to be effective particularly for low piston speeds. The installation of a partially perforated wall at the exit of the tunnel simulator was found to smear pressure gradients at the shock. This effect is significant for higher piston speeds. Throughout the series of train tunnel simulator experiments, the combination of both the entrance hood and the perforated wall significantly reduces shock overpressures for piston speeds ofu
p
ranging from 60 to 100 m/s. These experimental findings were then applied to a real train tunnel and good agreement was obtained between the tunnel simulator result and the real tunnel measurements. 相似文献
73.
本文将空间轴对称问题的Папковиц-Neuber通解用复变量广义解析函数表示,推导出用复变函数法求解空间轴对称问题的基本公式,并以此为工具求得了含球形空腔或刚性夹杂的中厚圆板在轴对称弯曲变形时的完全解. 相似文献
74.
考虑地基-结构-散粒体相互作用时贮仓结构的静、动力研究[Ⅱ]--有限元分析 总被引:1,自引:0,他引:1
对贮仓结构的静、动力问题进行了系统的分析计算:考虑到地基—结构—散粒体间的相互作用,引入新的计算模式,对不同地基上的贮仓结构模型进行了系统的有限元静、动力分析计算,并与作者所完成的试验结果进行了比较。结果表明,所提出的计算模式及有限元计算模型是正确的。 相似文献
75.
本文通过数值方法求解均匀动脉中的非平稳脉动流,给出了通过测量非平稳脉动血流量确定壁面切应力的方法.作为算例,采用实测的大鼠颈总动脉流量信号,求出了均匀动脉壁面切应力波形.进一步对求得的切应力波形进行经验模态分解(EMD),得到了切应力波形的各内在模态(IMF),以及Hilbert幅值谱.从切应力波形经Hilbert-Huang变换得到的IMF和Hilbert谱图可以明显地看出切应力各频率成分的物理意义.所得结果为进一步深入研究非平稳脉动切应力与血管重建的关系提供了一种方法学基础. 相似文献
76.
不可压缩二维流动Navier—Stokes方程的有限元解 总被引:1,自引:0,他引:1
对不可压缩流体沿二维后台阶流动的N-S方程的流函数-涡量式用有限元方法加以求解,固壁上的涡量用时间迭代法加以确定。分别计算Re=200,400,800和1000时流动区域的流函数和涡量值,并在Re=800时与有关文献的结果相比较,基本吻合。且在此基础上讨论了出口条件对计算结果的影响。本文的方法对分析流经液压阀口等流动问题具有借鉴意义。 相似文献
77.
78.
位错和夹杂的干涉效应对于理解材料的强化和韧化机理具有十分重要的意义。文中研究了晶体材料中刃型位错和多条共圆弧刚性线夹杂的干涉作用。利用Riemann—Schwarz反照原理和复势函数的奇性主部分析技术,得到了问题的一般解答;对于只含一条刚性线夹杂的情况,给出了复势函数的封闭形式解。由Peach-Koehler公式求出了作用在刃型位错上的位错力,并讨论了圆弧形刚性线夹杂对位错力的影响规律,发现弧形刚性线对刃型位错有很强的排斥作用。本文解答不但可作为格林函数获得任意分布位错的相应解答,而且可以用于研究刚性线夹杂和任意形状裂纹的干涉效应问题。 相似文献
79.
Pulsatile flows in a lateral aneurysm anchored on a stented and curved parent vessel 总被引:5,自引:0,他引:5
We present particle tracking velocimetry measurements and flow visualization of pulsatile flow fields in a stented cerebrovascular
lateral aneurysm model with a wide ostium anchored on a curved parent vessel. Among the stent parameters, the blocking ratioC
α ranging from 0% to 75% was selected to study its effect on the changes of intra-aneurysmal hemodynamics for the reference
of minimally invasive endovascular aneurysm treatment. The Womersley number was 3.9 and the mean, peak, and minimal Reynolds
numbers based on the bulk average velocity and diameter of the parent vessel were 600, 850, and 300, respectively. The results
are characterized in terms of velocity vector field, coded streak images, region averaged velocity, vorticity, and wall shear
stress. A critical range ofC
α related to the inflow location as well as the shape and number of intra-aneurysmal vortices is identified. The intra-aneurysmal
flow activity, vortex strength, and wall shear stress are found to decrease with increasingC
α. Among theC
α examined,C
α=75% is the most favorable in attenuating the risk of aneurysmal rupture and promoting intra-aneurysmal thrombus. 相似文献
80.
Near-wall data for the strongly perturbed flow in a neutrally stable boundary layer encountering a steep, smooth, two-dimensional
hill are presented. Observations were made on the centerplane of a water channel at thirteen stations relative to the hill
by laser Doppler anemometry. The large reverse flow region that is formed on the lee of the hill was particularly scrutinized
through seven measuring stations. Results are presented for the mean and turbulent properties of the flow. Wall shear stress
was evaluated through fitting procedures that resorted to the near wall behavior of the velocity profile. Logarithmic fits
as well as predictions through the Reynolds stress profiles are also presented. 相似文献