共查询到19条相似文献,搜索用时 140 毫秒
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用磁荷法计算磁铁产生磁场分布,进而计算圆柱形磁铁在金属管中的下落时间.实验测量圆柱形磁铁在金属管中的下落时间,得到与理论计算相符的结果. 相似文献
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利用落塔的短时微重力条件, 实验研究了与容器连通的毛细管中的流体在微重力条件下的毛细流动过程, 并通过理论分析建立了相应的毛细管中弯月液面高度随时间变化的微分方程. 结果表明, 对于不同的接触角和不同的容器/毛细管参数, 由建立的理论公式得到的数值解结果都与实验结果在定量上较为一致. 此外, 实验中发现, 改变乙醇和去离子水混合液的比例可以明显地改变接触角参数, 但对毛细流动的影响很小, 建立的理论公式也对这一现象给出了合理的解释. 该研究对于预测和分析微流道及空间微重力条件下的毛细流动行为具有明显的应用价值. 相似文献
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柱形容器内部爆炸流场的数值模拟 总被引:5,自引:0,他引:5
采用NND差分格式,同时利用点爆炸解作为计算初值,对圆柱形容器内部的二维轴对称非定常流场进行了数值模拟,清楚地反映了内部流场的变化过程,得到了容器壁面上各点的压力-时间关系。对计算结果进行了讨论,与文献中结果作了比较。 相似文献
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对带孔阵腔体的电磁屏蔽特性进行数值计算时,为减少模型网格数量并降低孔阵建模复杂度,提出一种考虑小孔尺寸效应的孔阵等效建模方法.首先将孔阵等效为面积相同的单孔,然后根据孔数量对单孔尺寸进行缩小.利用孔阵导纳理论和数值仿真拟合方法分别建立缩小比例与小孔数量的关系,对比得出拟合方法得到的缩小比例公式精度较高的结论.通过改变干扰源、监测点位置、孔阵面积、孔阵位置、小孔形状及腔体尺寸等参数,验证了等效方法的适用性.孔阵等效建模方法能在保证仿真精度的前提下显著减少网格数量,可为大型复杂腔体屏蔽特性的数值计算提供一种有效的简化手段. 相似文献
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测定液体表面张力系数的新方法郝兴海(青海民族学院理化系,西宁810007)一、实验现象在一个口径较大的平底容器底部打一小孔,让水流进容器里,我们会发现水没有马上流出,而是在小孔处形成一个半球形液面(图1).当水面上升到一定高度时,水才从小孔中流出.二... 相似文献
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The influence of a posterior gap on the airflow through the human glottis was investigated using a driven synthetic model. Instantaneous orifice discharge coefficient of a glottal shaped orifice was obtained from the time-varying orifice area and the velocity distribution of the pulsated jet measured on the axial plane using a single hot-wire probe. Instantaneous orifice discharge coefficient values were found to undergo a cyclic hysteresis loop when plotted versus Reynolds number and time, indicating a pressure head increase and a net energy transfer from the air flow to the orifice wall. The net energy transferred was estimated to be around 10% of the value presumably required to achieve self-sustained oscillation. The radiated sound pressure was measured to characterize the influence of the minimum flow through the posterior gap on the broadband component of the radiated sound. The presence of a posterior gap was found to significantly increase the broadband sound level produced over the frequency range in which human hearing is most sensitive. 相似文献
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本文发现在测量误差内颗粒物质的下列三个临界角度相等: 1)从直径为D的倾斜孔洞流出的Beverloo颗粒流的流量开始停止的临界倾角θc 向大孔径极限线性外推θc∞≡θc(D→∞) 的补角θs∞= 180°-θc∞;2) 从靠近堆顶的点源向光滑底板缓慢下落颗粒形成的圆锥形堆的休止角θr; 3) 直接剪切矩形颗粒固体测得的库仑内摩擦角φ. 该结果倾向支持倾斜孔洞和颗粒堆自由表面的固-液转变与颗粒固体内部的库仑屈服均来自材料的同一临界性质. 由于三种情况样品的内部应力和变形等都是目前还远不能定量分析的复杂非均匀分布, 我们仅从定性角度对此给出一些讨论. 相似文献
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H. Bailliet R. Boucheron J.-P. Dalmont Ph. Herzog S. Moreau J.-C. Valière 《Applied Acoustics》2012,73(3):191-197
An experiment has been set up to study multimodal acoustic propagation inside a cylindrical duct in presence of a turbulent mean flow. This paper describes the preliminary work which has been found necessary for assembling the experiment together with first measurement results. In order to set up this experimental facility, a high level acoustic source was developed to generate higher propagating modes in the presence of mean flow. A microphonic antenna was designed for detecting the propagating modes. LDV measurements were performed and synchronous detection was used to extract both the mean flow and the acoustic components of the particle velocity. Results of aeraulic measurements are presented. Then, results of acoustic velocity measurements are compared to results obtained from the microphonic antenna. 相似文献
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Empirical model of the acoustic impedance of a circular orifice in grazing mean flow 总被引:1,自引:0,他引:1
Although there are many analytical and empirical models for orifice impedance, the predicted acoustical performance when adopting any one of them sometimes shows a large discrepancy with the measured result in some cases. In order to obtain a new practical and precise empirical impedance model under grazing flow conditions, the acoustic impedance of circular orifices has been measured with a variation of the involved parameters under very carefully tested and controlled measurement conditions. The parameters involved in determining the acoustic impedance of an orifice are comprised of the orifice diameter, orifice thickness, perforation ratio, mean flow velocity, and frequency. The range of involved parameters is chosen to cover the practical data span of perforates in typical exhaust systems of internal combustion engines. The empirical impedance model is obtained by using nonlinear regression analysis of the various results of the parametric tests. The proposed empirical model of orifice impedance, with a very high correlation coefficient, is applied to the prediction of the transmission loss of concentric resonators, which have geometric configurations typical of acoustically short and long through-flow resonators. By comparing the measured and predicted results, in which the predictions are made by employing many previous orifice impedance models as well as the present model, it is confirmed that the proposed orifice impedance model yields the most accurate prediction among all other existing impedance models. 相似文献
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A. N. Pavlenko E. A. Tairov V. E. Zhukov A. A. Levin M. I. Moiseev 《Journal of Engineering Thermophysics》2014,23(3):173-193
Results on experimental investigation of the dynamics of boiling-up at stepwise heat release on a horizontally oriented cylindrical surface in a large volume of freon-21 are presented. Experimental data on the propagation velocity, structure, and other local characteristics of development of self-sustained evaporation fronts at different temperature differences of boiling-up in saturated liquid were obtained. New experimental results on the dynamics of vapor phase incipience and evolution on the surface of a vertical heat releasing tube and on the dynamics of changing the heater temperature and pressure in a flow of liquid (water, ethanol) subcooled to saturation temperature in the channel under nonstationary heat release conditions are represented. It was revealed that the dependence of the expectation time of intense bubble growth on the water motion velocity is nonmonotonic. 相似文献
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A. A. Pikulev 《Technical Physics》2003,48(6):693-696
Heat exchange between a linear heat source and a gas flow is studied theoretically. The coefficient of source-to-gas heat
transfer is found as a function of the gas velocity in the limit of zero temperature drop. It is shown that the heat-transfer
coefficient depends linearly on the gas flow velocity for Peclet numbers 0.1–1.0. 相似文献
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Molecular (or granular) dynamics methods are used to study the gravity-driven flow of granular material through a horizontal
aperture in three dimensions. The grains are spherical and modeled using a short-range repulsive interaction, together with
normal and tangential frictional damping forces. The material is contained in a rough-walled cylindrical container with a
circular hole in its base, and to permit flow measurements under steady-state conditions a continuous feed approach is employed
in which exiting grains are replaced at the upper surface of the material. The dependence of flow velocity and discharge rate
on aperture diameter is found to agree with experiment; other quantities such as the kinetic energy and pressure distributions
are also examined.
Received 5 June 2000 and Received in final form 21 September 2000 相似文献
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Physicochemical approach to the theory of foam drainage 总被引:1,自引:0,他引:1
We have investigated theoretically the effect of surface viscoelasticity on the drainage of an aqueous foam. Former theories
consider that the flow in Plateau borders is either Poiseuille flow or plug-flow. In the last case, the dissipation is attributed
to flow in the nodes connecting Plateau borders. Although we do not include this dissipation in our model, we obtain a drainage
equation that includes terms equivalent to those of the earlier models. We show that when the water solubility of the surfactant
stabilizing the foam is low, the control parameter M for the transition between the two regimes is the ratio , where μ is the bulk viscosity, D
s the surface diffusion coefficient, R the radius of curvature of the Plateau border and ɛ the surface elasticity. When the surfactant is more soluble M is rather related to the bulk diffusion coefficient. Within the frame of this approach and in view of the estimated M values, we show that the flow in Plateau borders is Poiseuille-like.
Received 26 June 2001 相似文献
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An experimental study of the flow inside a saxophone mouthpiece in playing conditions is carried out by means of particle image velocimetry at high acquisition rate. Planar velocity measurements on the midsection of a Plexiglas tenor saxophone mouthpiece are performed, respectively, in the mouthpiece baffle and in the reed channel. Sequences of velocity fields inside the mouthpiece baffle and around the reed tip are shown for one reed duty cycle. Maxima of the velocity fluctuations are observed at the upper surface of the mouthpiece at a distance between five and ten reed apertures from the tip. The proper orthogonal decomposition analysis reveals that almost 50% of the kinetic energy in the baffle is distributed in the first two modes displaying a periodic behavior at the fundamental frequency, the rest being turbulent flow behavior. The measured dynamical vena contracta coefficient at the inlet is reasonably constant around the value of 0.6 for reed positions far from closure. This is in agreement with existing steady flow analytical models and previous experimental results. 相似文献