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1.
We obtain an expression for the energy dissipation due to an evolving nonmaterial interface across which the mass density, velocity, stress, energy density, heat flux, entropy density, and temperature may be discontinuous. This expression is a sum of three terms: the product of the interfacial mass flux with the interfacial energy release; the scalar product of the interfacial velocity slip with the interfacial friction; and, the product of the interfacial temperature jump, scaled by the interfacial temperature average, with the interfacial heating. When the surface in question is a phase interface, we propose, on the basis of the interfacial dissipation inequality, supplemental relations that determine the interfacial energy release, the interfacial friction, and the interfacial heating constitutively as functions of the interfacial mass flux, the interfacial velocity slip, and the scaled interfacial temperature jump. As a step toward an understanding of the role that such interfacial relations may serve in theories for phase transitions, we investigate a problem involving the solidification of a pure substance in the absence of flow. Received February 17, 1999  相似文献   

2.
An analysis is performed to present a new self-similar solution of unsteady mixed convection boundary layer flow in the forward stagnation point region of a rotating sphere where the free stream velocity and the angular velocity of the rotating sphere vary continuously with time. It is shown that a self-similar solution is possible when the free stream velocity varies inversely with time. Both constant wall temperature and constant heat flux conditions have been considered in the present study. The system of ordinary differential equations governing the flow have been solved numerically using an implicit finite difference scheme in combination with a quasilinearization technique. It is observed that the surface shear stresses and the surface heat transfer parameters increase with the acceleration and rotation parameters. For a certain value of the acceleration parameter, the surface shear stress in x-direction vanishes and due to further reduction in the value of the acceleration parameter, reverse flow occurs in the x–component of the velocity profiles. The effect of buoyancy parameter is to increase the surface heat transfer rate for buoyancy assisting flow and to decrease it for buoyancy opposing flow. For a fixed buoyancy force, heating by constant heat flux yields a higher value of surface heat transfer rate than heating by constant wall temperature.  相似文献   

3.
This paper describes the results of calculations and experiments on the torsion of plates made of isotropic and transversely isotropic VT-20 and 1163T alloys with low resistance to creep strain in the direction perpendicular to the median surface. The numerical simulation results for plates of different thicknesses related to the class of rigid and flexible plates are compared using the pure bending theory and the finite element method. It is found that the curvature values are smaller in the case of deformation of a plate made of anisotropic material into a sign-variable saddle surface than in the case of a plate of isotropic material. The calculation in the assumption of pure bending provides an upper bound of the curvature difference in the deformation of plates made of transversely isotropic and isotropic materials.  相似文献   

4.
Grain shear flow in a rotating drum   总被引:2,自引:0,他引:2  
 In the present paper we report on the experimental activities carried out on a rotating drum partially filled with grains or glass beads. The experiments give information about rheology through velocity profiles and through the velocity covariance tensor structure. We used a LDV system to measure the velocity of the grains at several points along three vertical sections. The data were also used to obtain the grain volume concentration, with encouraging results. Instantaneous velocity data were elaborated in order to obtain velocity and pseudotemperature profiles for all the experiments; for a subset of the experiments a large set of data were elaborated to obtain the velocity covariance. The velocity covariance is not collinear with the rate of deformation tensor. An attempt to justify the rotation of the tensor axes as a consequence of the kinetically induced anisotropy and of some free surface perturbations slowly moving upstream was partially successful. Received: 23 April 1999 / Accepted: 15 July 2001  相似文献   

5.
When investigating flow structures, and especially flow transitions, research projects often seek to increase insight using complementary numerical and physical experiments. Obtaining exact Reynolds number correspondence can frequently be difficult in experiments, particularly when relatively low values are required. Often, available test facilities were designed and optimised for a specific velocity range, meaning they have restrictions on the minimum flow velocity. This study describes a device to reduce the flow velocity locally in an open surface water channel. The underlying idea is to divert a controlled fraction of the incoming flow from the working section by increasing the pressure there, resulting in reduced velocity. This idea is realised using a ‘sub-channel’ that can be inserted into the main test chamber, with a variable porosity perforated screen at its downstream end. This study assesses and optimises the flow quality inside this structure, such as usable test section length, uniformity of the velocity profiles and turbulence intensity. The results demonstrate that the device creates high quality low Reynolds number flows, which is exemplified with the canonical circular cylinder in cross-flow.  相似文献   

6.
对梯度飞片撞击复杂路径加载实验中,具有冲击加载-斜波加载-斜波卸载的金属铝材料的波剖面信息进行了数据分析和处理,不同加载路径用不同力学响应关系式进行描述,以铝材料\氟化锂窗口界面处的速度剖面作为初始条件,用反积分方法向铝材料内部直至加载面进行了反向计算,所得计算结果与正向计算结果比较吻合较好。计算得到了材料内能、温度、声速及应变率在复杂路径加载中变化规律,并给出了材料的P-V参考线,所得结果可与正向积分计算结果相互校核。  相似文献   

7.
 The steady mixed convection flow over a vertical wedge with a magnetic field embedded in a porous medium has been investigated. The effects of the permeability of the medium, surface mass transfer and viscous dissipation on the flow and temperature fields have been included in the analysis. The coupled nonlinear partial differential equations governing the flow field have been solved numerically using the Keller box method. The skin friction and heat transfer are found to increase with the parameters characterizing the permeability of the medium, buoyancy force, magnetic field and pressure gradient. However the effect of the permeability and magnetic field on the heat transfer is very small. The heat transfer increases with the Prandtl number, but the skin friction decreases. The buoyancy force which assists the forced convection flow causes an overshoot in the velocity profiles. Both the skin friction and heat transfer increase with suction and the effect of injection is just the reverse. Received on 21 May 1999  相似文献   

8.
The dependence of the propagation velocity of ultrasonic waves on the acting stress in plastically deformable polycrystalline metals and alloys is examined. The relationship between the acting stress and the velocity of ultrasound is found to be linear; this dependence is typical of all materials studied. A method is proposed for determining the time resistance to breakdown of materials (ultimate strength) for the case of deformation in the region of small plastic strains without failure of the specimens.  相似文献   

9.
金属材料层裂破坏的内聚力模型   总被引:1,自引:0,他引:1  
本文把内聚力单元嵌入到连续介质有限元单元之间,构建了一个层裂破坏的内聚力模型,以计及层裂破坏过程中能量耗散行为。采用该模型对平板撞击条件下的20号钢层裂实验进行了数值模拟研究,重点讨论了内聚力模型特征参数对计算结果的影响规律。研究结果表明采用指数型损伤演化行为的内聚力模型可以较好地描述弹塑性材料层裂破坏过程中的非线性能量耗散行为。利用一发实测自由面速度波剖面对计算结果进行对比校准,可确定内聚力模型特征参数。该特征参数可同样成功地预示不同撞击速度下的层裂实验,获得的模拟曲线与实验曲线之间符合程度很好,特别是自由面速度“回跳”后波形振荡周期和幅值与实验结果非常接近。这表明了内聚力模型在描述层裂过程中能量耗散行为方面具有较好适用性,并且不难由简单实验标定相关的特征参数。  相似文献   

10.
 The flow of isotropic and liquid crystalline (LC) hydroxypropylcellulose (HPC) aqueous solutions into an abrupt axisymmetric contraction has been quantitatively measured by pulsed-field-gradient NMR techniques. Steady-state axial velocity profiles, acquired upstream of the contraction, reveal a large contraction entry length for the LC solution. This entry flow field exists over an order of magnitude change in flow rate and is attributed to elasticity that is associated with polydomain liquid crystallinity. Pronounced, off-centerline velocity maxima (in an axisymmetric flow field) were present upstream of the contraction, in the entry flow region. Apparently, a more viscous and elastic core of fluid was present along the centerline; this fluid resisted elongational strain more than the fluid closer to the walls. Quantitative velocity profiles were extracted from displacement distributions and corrected for elongational dispersion. The isotropic solution velocity profiles matched those obtained from viscoelastic simulations using an approximate Doi-Edwards model, parameterized with independent rheological data. Received: 29 April 1999/Accepted: 30 August 1999  相似文献   

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