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991.
The structural,elastic,and electronic properties of Zr_x Nb_(1-x)C alloys from first principle calculations
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The structural,elastic,electronic,and thermodynamic properties of Zr x Nb1-x C alloys are investigated using the first principles method based on the density functional theory.The results show that the structural properties of Zr x Nb1-x C alloys vary continuously with the increase of Zr composition.The alloy possesses both the highest shear modulus(215 GPa)and a higher bulk modulus(294 GPa),with a Zr composition of 0.21.Meanwhile,the Zr0.21Nb0.79C alloy shows metallic conductivity based on the analysis of the density of states.In addition,the thermodynamic stability of the designed alloys is estimated using the calculated enthalpy of mixing. 相似文献
992.
Niloufar Mahmoudnejad Klaus A. Hoffmann 《International Journal of Computational Fluid Dynamics》2013,27(9):469-486
To address accuracy issues for direct numerical simulation, a hybrid scheme based on the weighted compact scheme (WCS) and weighted essentially non-oscillatory (WENO) scheme is developed. The new hybrid method incorporates the advantages of both schemes. Time integration is performed using the fourth-order total variation diminishing Runge–Kutta method with a characteristic filter. The accuracy of the scheme is assessed using several benchmark problems. Results show that the proposed scheme produces a more accurate solution for problems involving shocks and discontinuities in comparison with the traditional shock-capturing methods. 相似文献
993.
This letter mainly aims to investigate the mechanical behavior within shear bands in regolith both under the Earth and the Moon conditions via the distinct element method, in which a novel contact model considering interparticle van der Waals forces and rolling resistance is employed. The results show that for regolith under both conditions the stress paths are almost identical inside and outside the shear bands but void ratio, average pure rotation rate, and strain paths are rather distinct with dilation, particle rotation and the second invariant of strain tensor mainly occurring within the bands. However, the regolith under the Moon condition has higher peak strength and more significant strain localization than those under the Earth condition. 相似文献
994.
Alvaro Valencia 《International Journal of Computational Fluid Dynamics》2013,27(4):337-345
Blood flow dynamics play an important role in the pathogenesis and treatment of intracranial aneurysms. The evaluation of the velocity field in the aneurysm dome and neck is important for the correct placement of endovascular coils, in addition the temporal and spatial variations of wall shear stress in the aneurysm are correlated with its growth and rupture. The present numerical investigation describes the hemodynamics in two models of terminal aneurysm of the basilar artery. Aneurysm models with an aspect ratio of 1.0 and 1.67 were studied. Each model was subject to a steady, sinusoidal and physiologically representative waveform of inflow for a mean Reynolds number of 560. Symmetric and asymmetric outflow conditions in the branches were also studied. The three-dimensional continuity and the Navier-Stokes equations for incompressible, unsteady laminar flow with Newtonian properties were solved with a commercial software using non structured grids with 61334 and 65961 cells for models 1 and 2, respectively. The grids were primarily composed of tetrahedral elements. The intra-aneurysmal flow was unsteady for all input conditions and in both models, the flow always showed a complex vortex structure. The inflow and outflow zones in the aneurysm neck were determined. The wall shear stress on the aneurysm showed large temporal and spatial variations. The asymmetric outflow increased the wall shear stress in both models. 相似文献
995.
Inchul Kim 《International Journal of Computational Fluid Dynamics》2013,27(2):137-141
When particles are submerged in a shear flow, there are lateral (lift) forces on the particles, and these lateral forces affect the dispersion of the particles very much. Recent literature survey indicates that there are large discrepancies among the results from the previous numerical investigations on this subject. A small computational domain ranging between 20–30 sphere radii was used in all the previous numerical investigations. However, the result from the present study reveals that the value of lift coefficient strongly depends on the size of computational domain. To provide correct numerical data and physical interpretation for the forces on a spherical particle in linear shear flow, accurate numerical computations were performed for 5≤Re≤200 using a computational domain of 101 sphere radii. 相似文献
996.
997.
Asymptotic and transient stability analyses of unbounded uniform shear flows of dense, slightly inelastic, spherical particles were carried out using a frictional-kinetic theory. This model proposed for describing dense flows is based on a critical state plasticity theory and a simplified kinetic theory. In this model, the bulk and shear viscosities, the “thermal” conductivity, and the energy dissipation rate are proportional to a “mean pressure” which is composed of a quasistatic-frictional-contribution pressure considered for slow, plasticity deformations and a granular-kinetic-theorycollisional-contribution pressure. We studied two-dimensional stability analyses of layering disturbances (i.e., the perturbations whose wave number vectors are aligned only in the gradient) as well as nonlayering disturbances (the wave number vectors have nonzero streamwise components). Although this model has a simpler framework, it predicted similar results to those obtained using a more elaborate frictional-kinetic model. For instance, nonlayering disturbances are asymptotically stable at large time; the maximum transient growth of disturbances increases as the solids fraction or the friction coefficient is increased; and transient growths of disturbances can be significant due to the non-normality of the system. However, the prediction of the asymptotic stability of layering disturbances may be questionable because the collisional-contribution terms of the present model were over-simplified. 相似文献
998.
This paper analyses the downstream developments of the mean and the turbulent velocity fields of a plane jet. Based on the conservation of mass and the conservation of momentum, the mean-velocity half width (reflecting the jet spread rate) and the relative mass flow rate (jet entrainment) are related to the decay rate of the centreline mean velocity. These relations are not subject to self-preservation. Both analytical and experimental results suggest that the jet spread rate (K1) and the entrainment rate (K3) (and thus the decay rate K2) can be well estimated from the centreline velocity, i.e., K1 ≈ 0.6K2 and K3 ∝ K_2. The effect of initial mean velocity and RMS velocity profiles on the downstream mean velocity field appears to be embodied in the constants K1 K2 and K3. The analytical relationship for the self-preserving Reynolds shear stress, obtained for the first time, works well. 相似文献
999.
1000.
采用VOF模型对倾角为45°、80°、85°三种情况下倾斜上升管内弹状流的壁面传质特性进行了研究.传质特性通过其与壁面切应力的类比关系来体现.数值模拟结果表明,低混合物流速时,上管壁面切应力在液膜区有明显波动,而下管壁面切应力分布则比较光滑.随着混合流速的增大,液膜区上下壁面切应力分布趋于一致.管子下壁面切应力平均值大于管子上壁面,在Taylor气泡运动速度较低时较为突出.随着Taylor气泡速度的增大,管子上下壁面的切应力平均值趋于相同.相同的混合流速下倾斜角度越大,上下管壁的切应力分布越趋于近似.下降液膜区的壁面切应力平均值大于Taylor气泡尾迹区域.根据Chilton-Colburn的类比关系,壁面切应力的规律完全适用于壁面传质系数. 相似文献