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901.
Lower bounds on the scalar dissipation rate in rectilinear flows are found for three sets of constraints. The bounding dissipation rates provide upper bound estimates of the scalar concentration variance. One of the lower bounds on the dissipation rate is close to the dissipation rate assessed from detailed numerical simulation. This proximity enables a simplified model of concentration variance. For a pulse input of solute, the predictions of concentration variance by the simplified model are in agreement with the results of detailed simulation. The large-time bimodality of the concentration variance and its rate of decay observed in the detailed numerical simulations is predicted by the simplified model. 相似文献
902.
动脉狭窄内低密度脂蛋白传输的数值研究:LDL的浓度极化现象 总被引:6,自引:0,他引:6
用计算机数值模拟的方法 ,对低密度脂蛋白 ( LDL)在动脉狭窄血管段内的质量传输进行了研究。计算结果表明 ,由于血管壁渗流的存在 ,LDL这样的脂质大分子会聚积在血管的内壁表面 ,发生一种工程上称为浓度极化的现象。LDL浓度在动脉狭窄口后的流动分离点出现峰值。该浓度峰值随雷诺数和动脉狭窄度的增加而呈逐渐下降的趋势。作者认为 ,该区域 LDL浓度的局部升高是引发动脉粥样硬化局部性和动脉狭窄产生的一个非常重要的原因。 相似文献
903.
Stress concentrations at the periphery of elliptic and circular openings are determined experimentally by the photoelastic method for three compressed cylindrical shells of medium thickness made of epoxy resin. The experimental values are compared with numerical values obtained by the theory of thin shells 相似文献
904.
研究具有界面相电磁弹性纤维增强复合材料的反平面剪切问题,利用复变函数方法,获得了无穷域中带界面相纤维问题在远场力、电、磁多场作用下的闭合解,得到了复合材料内部各区域电磁弹性物理量的精确表达式.利用所得结果,考虑纤维和基体间的界面相效应,研究了界面相厚度及弹性模量对复合材料内部应力场、电场强度和磁场强度的影响,数值结果给出了复合材料电磁弹性物理量随界面相参数变化的规律,为该类复合材料的设计与计算提供了有价值的参考. 相似文献
905.
I. S. Chernyshenko E. A. Storozhuk S. B. Kharenko 《International Applied Mechanics》2007,43(4):418-424
The elastoplastic state of thin conical shells with a curvilinear (circular) hole is analyzed assuming finite deflections.
The distribution of stresses, strains, and displacements along the hole boundary and in the zone of their concentration are
studied. The stress-strain state around a circular hole in shells subject to internal pressure of prescribed intensity is
analyzed taking into account two nonlinear factors
__________
Translated from Prikladnaya Mekhanika, Vol. 43, No. 4, pp. 73–79, April 2007. 相似文献
906.
Explosion characteristics of coal gas under various initial temperatures and pressures 总被引:2,自引:0,他引:2
Explosion limits data are essential for a quantitative risk assessment of explosion hazard associated with the use of coal gas. The present work is to investigate the influence of various initial temperatures and pressures on explosion characteristics of coal gas/air mixture. The explosion limits and the minimum ignition energy of coal gas/air mixture are obtained experimentally at various temperatures ranging from 20 to 80°C and pressures ranging from 0.1 to 0.2 MPa. An empirical equation is established from the experimental results for the effects of initial temperatures and pressures on explosion limits. By adding diluent (nitrogen) into coal gas/air mixtures, the dilution effects on the explosion limits have been explored as well, and a critical flammable concentration of coal gas is determined to be at 7.4–9.0% by volume. By means of a high-speed digital video camera, the flame front development is recorded and analyzed. The tests are carried out with lean, stoichiometric and rich mixtures of coal gas in air under the conditions of initial pressure and nitrogen addition. Furthermore, the influence of the initial pressure and the concentration on the explosion pressure is measured and compared against theoretical results, where a good agreement is observed. 相似文献
907.
An experimental strain analysis of the losipescu shear test specimen was performed, utilizing a 20-ply AS4/3501-6 carbon/epoxy
unidirectional composite. Using three-element strain-gage rosettes, it was shown that the presence of loading-point-induced
transverse normal strains in the gage section do not affect the measured shear strain. Thus, the shear modulus determined
using the standard notch specimen is not affected. Likewise, modulus determination is not influenced by cracking at the notch
tips, since this occurs at strains beyond the range over which modulus is determined. To further evaluate the effect of notch-tip
cracking, material was removed adjacent to the standard V-notches where these cracks initiate. The measured shear strength
was unaffected by removing this material, although the shear modulus was reduced slightly (by as much as eight percent for
the more grossly exaggerated geometries).
E.Q. Lewis, former graduate student, is now Engineer, Lockheed Corporation. 相似文献
908.
909.
The general solution of the electroelastic problem for a transversely isotropic hyperboloid of revolution is used to find the stress concentration near a hyperboloidal neck in a piezoceramic body subjected to bending. The solution is a sum of four partial solutions for the case where the forces and the normal component of the induction vector on the neck surface are equal to zero. Numerical examples are given for specific external loads and properties of the body. The stress components and normal component of the induction vector near the neck vertex are plotted as a function of the external load and neck curvature 相似文献
910.
针对采用整模结构的冷镦模具疲劳寿命极低的现状,提出以三层圆筒组合模具结构
替代整体模具, 改变模具受力方式, 使冷镦件模具达到较高寿命的设计方法. 以螺栓
圆头的冷镦试验结果为依据,以力学的应力分析方法为基础,应用力学理论,导出了生产实
践中实用的组合模具设计原理与经验公式,并举例说明了该方法的应用. 相似文献