考虑非达西渗流的成层地基一维固结半解析解

在土中渗流遵从Hansbo非达西渗流的前提下,考虑实际工程中的变荷载,利用解析与数值相结合的半解析方法,对成层地基一维固结问题进行数值求解。将基于Hansbo非达西渗流的双层地基一维固结半解析解与相应的差分数值解进行对比,验证了半解析方法计算基于Hansbo非达西渗流下成层地基一维固结问题的可靠性。最后,对某三层地基考虑Hansbo非达西渗流的一维固结实例进行计算分析,结果表明：基于Hansbo非达西渗流下成层地基的沉降发展速率与超孔隙水压力的消散速率是不一致的。     

Propagation of weak discontinuities along the bicharacteristic curves in a vibrationally relaxing gas

The transport equations representing the rate of change of discontinuities in the normal derivatives of flow parameters are obtained along bicharacteristic curves in the characteristic manifold of the differential equations governing the flow of a vibrationally relaxing gas, an explicit criterion for the growth and decay of weak discontinuities along bicharacteristics is given and the specialization is made to the waves of plane, cylindrical and spherical geometry. It is investigated as to how the effects of vibrational relaxation, the magnitude of the initial discontinuity, the initial curvature of the wave front, and the upstream flow Mach number will influence the growth and decay properties of the wave front.     

Characteristics of flow field near sea bottom in a combined wave and current motion

Abstract

A reasonable time‐invariant eddy viscosity model is proposed to describe turbulent flow over a rough sea bottom in a combined wave‐current system. The linearized governing equations are solved for the wave and current kinematics both inside and outside the wave boundary layer. The results of velocity profile, friction factor and apparent roughness in a wave‐current motion are presented. The friction factors are shown to be consistent with previous theoretical results for the limiting cases of pure wave and pure current motions. Present results are compared favorably with the available data.     

Similarity solutions to rotating Couette flow with power law fluids

Summary The nonlinear rheological effects of a power law fluid in rotating Couette flow are addressed. The governing equations are derived and exact similarity solutions to the Cauchy problem for the angular velocity and shear stress distributions are shown and discussed. The case when the flow is generated by a line impulse of angular momentum is considered. The existence of a travelling wave solution for a shear thickening fluid is shown.     

中厚椭球壳自由振动动力刚度法分析

介绍精确动力刚度法分析中厚椭球壳自由振动具体实施方法,据环向波数不同将中厚椭球壳自由振动分解为一系列确定环向波数的一维振动;利用控制方程Hamilton形式建立动力刚度关系,用常微分方程求解器COLSYS求解控制方程获得单元动力刚度,用Wittrick-Williams算法求得该环向波数下椭球壳自振频率。数值算例给出中厚圆球壳及椭球壳不同边界条件的自振频率,验证动力刚度法高效、可靠、精确。     

高超声速稀薄流场AUSM分裂式DSMC-IP方法研究

针对直接模拟蒙特卡洛(DSMC)方法统计耗散较大而传统的信息保存(DSMC-IP)方法难以有效模拟强激波的问题,采用对流迎风分裂(AUSM)通量计算格式对IP方法进行改造.以局部马赫数为标准重构控制方程中的关联项通量,使计算更加准确的符合激波两侧的流动特征,从而形成一种具有较高统计精度和高超声速流动模拟能力的新型DSM...     

Hybrid finite element/volume method for shallow water equations

A hybrid numerical scheme based on finite element and finite volume methods is developed to solve shallow water equations. In the recent past, we introduced a series of hybrid methods to solve incompressible low and high Reynolds number flows for single and two‐fluid flow problems. The present work extends the application of hybrid method to shallow water equations. In our hybrid shallow water flow solver, we write the governing equations in non‐conservation form and solve the non‐linear wave equation using finite element method with linear interpolation functions in space. On the other hand, the momentum equation is solved with highly accurate cell‐center finite volume method. Our hybrid numerical scheme is truly a segregated method with primitive variables stored and solved at both node and element centers. To enhance the stability of the hybrid method around discontinuities, we introduce a new shock capturing which will act only around sharp interfaces without sacrificing the accuracy elsewhere. Matrix‐free GMRES iterative solvers are used to solve both the wave and momentum equations in finite element and finite volume schemes. Several test problems are presented to demonstrate the robustness and applicability of the numerical method. Copyright © 2010 John Wiley & Sons, Ltd.     

Anisotropy effects on non–Darcy natural convection from concentrated heat sources in porous media

Summary In this investigation, closed-form exact similarity solutions are obtained for non-Darcian natural convection arising above a line heat source or a point source embedded in an unbounded porous medium saturated by an incompressible fluid. The porous medium is assumed to be hydrodynamically anisotropic with its principal axes oriented in a direction that is oblique to the gravity vector. In the formulation of the problem, use is made of the Forchheimer model to take into account the inertia effects which are expected to be significant for high permeabilities and Rayleigh numbers. Scale analysis is applied to predict the orders of magnitudes involved in the boundary-layer regime for which the conditions of validity are presented. Effects of both anisotropy parameters (K* and θ) and Forchheimer number Fs are observed to be strongly significant. It is demonstrated that a minimum (maximum) intensity of the thermal convective plume above concentrated heat sources can be obtained if the porous matrix is oriented with its principal axis with higher permeability parallel (perpendicular) to the vertical direction. Moreover, it is shown that for a fixed Rayleigh number an increase of the inertia effects tends to reduce the convective flow induced upward.     

The stability of the narrow-gap Taylor-Couette system with an axial flow

Summary The stability of viscous flow between concentric rotating cylinders with an axial flow due to an axial pressure gradient is considered. The governing equations with respect to three-dimensional disturbances are derived and solved by a direct numerical procedure. Results are given for the case of small-gap approximation. Three typical cases =–1,0 and 0.5 are studied, where represents the ratio of angular velocity of the outer cylinder to that of the inner cylinder. The value of the axial Reynolds numberR is up to 100. It is found that the critical disturbance is a non-axisymmetric mode when the value ofR is sufficiently large, and the transition of the onset mode withR is demonstrated in detail. Results for the critical Taylor number, wave number, vortex incline angle, and relative wave velocity are also determined. The present stability analysis is found to be in agreement with previous experimental studies and particularly reveals the stability characteristics with the variation of .     

Robust topology optimization of optical cloaks under uncertainties in wave number and angle of incident wave

This article presents a robust topology optimization method for optical cloaks under uncertainties in the wave number and angle in the incident wave. We first discuss the governing equation derived from Maxwell's equation, and extend it to the entire domain including the dielectric material and air, based on the level set-based topology optimization method. Next, a robust optimization problem is formulated as a minimization problem of the weighted sum of the scattered wave norm and its standard deviation with respect to the wave number and angle of the incident wave. The standard deviation is mathematically expressed by the Taylor series approximation and the use of the adjoint variable method. The design sensitivity of the objective functional is also derived by the adjoint variable method. An optimization algorithm is then constructed, based on the proposed formulation for robust designs of optical cloaks. Several numerical examples are finally provided to demonstrate the validity and utility of the proposed method.     

Entropy generation of micropolar fluid flow in an inclined porous pipe with convective boundary conditions

The objective of this paper is to examine the nature of irreversibilities in the form of entropy generation for a micropolar fluid flow through an inclined porous pipe with convective boundary conditions. The governing equations are non-dimensionlized and then linearized using a quasilinearization method. The resulting linearized equations are solved by Chebyshev spectral collocation method. The velocity, microrotation and temperature profiles are presented graphically for various values of governing parameters. Further, these profiles are used to evaluate the entropy generation and Bejan number.     

NSM analysis of time-dependent nonlinear buoyancy-driven double-diffusive radiative convection flow in non-Darcy geological porous media

A network numerical simulator is developed and described to simulate the transient, nonlinear buoyancy-driven double diffusive heat and mass transfer of a viscous, incompressible, gray, absorbing–emitting fluid flowing past an impulsively started moving vertical plate adjacent to a non-Darcian geological porous regime. The governing boundary-layer equations are formulated in an (X ^*, Y ^*, t ^*) coordinate system with appropriate boundary conditions. An algebraic diffusion approximation is used to simplify the radiation heat transfer contribution. The non-dimensionalized transport equations are solved in an (X, Y, t) coordinate system using the network simulation model (NSM) and the computer code, Pspice. A detailed discussion of the network design is provided. The effects of Prandtl number, radiation–conduction parameter (Stark number), thermal Grashof number, species Grashof number, Schmidt number, Darcy number and Forchheimer number on the transient dimensionless velocities (U, V), non-dimensional temperature (T) and dimensionless concentration function (C) are illustrated graphically. Additionally, we have computed plots of U, V, T, C versus time and average Nusselt number and Sherwood number versus X, Y coordinate, for various thermophysical parameters. The model finds applications in geological contamination, geothermal energy systems and radioactive waste-repository near-field thermo-geofluid mechanics.     

破裂岩石非达西渗流的试验研究

为研究破裂岩石非线性渗透规律,研制了一种与MTS815.02岩石力学试验系统配套的附加装置。本文介绍了试验原理与方案、试验系统、数据处理方法及一些试验现象,并给出了破裂岩石渗透率、非达西流β因子与轴向应变的回归关系。研究表明破裂岩石渗透特性的统计指标与轴向应变关系可以用二次多项式拟合,渗透特性的变异系数随轴向应变增大而减小。     

Heat and mass transfer in MHD flow by natural convection from a permeable, inclined surface with variable wall temperature and concentration

Summary. An analysis is performed to study the momentum, heat and mass transfer characteristics of MHD natural convection flow over a permeable, inclined surface with variable wall temperature and concentration, taking into consideration the effects of ohmic heating and viscous dissipation. Power-law temperature and concentration variations are assumed at the inclined surface. The resulting governing equations are transformed using suitable transformations and then solved numerically by an implicit finite-difference method. The solution is found to be dependent on several governing parameters, including the magnetic field strength parameter, Eckert number, the buoyancy ratio between species and thermal diffusion, Prandtl number, Schmidt number, wall temperature and concentration exponent, the inclination angle from the vertical direction, and the injection parameter. A parametric study of all the governing parameters is carried out and representative results are illustrated to reveal a typical tendency of the solutions. Representative results are presented for the velocity, temperature, and concentration distributions as well as the local friction coefficient, local Nusselt number, and the local Sherwood number.     

Analysis of wave in a functionally graded magneto-electro-elastic nano-rod using nonlocal elasticity model subjected to electric and magnetic potentials

The purpose of this research is to present the wave propagation analysis of a functionally graded nano-rod made ofmagneto-electro-elastic material subjected to an electric and magnetic potential. The unified nonlocal elasticity theory andLove's rod model are used in this study. All mechanical, electrical and magnetic properties are assumed to be variable along thethickness direction based on a power law distribution. Two-dimensional electric and magnetic potential distributions due toan applied potential and a magnet at the top of the rod are considered. The governing equations of motion are obtained using equilibrium and nonlocal theory of elasticity in conjunction with the Hamilton principle. The effect of important parameters of the functionally graded magneto-electro-elastic nano-rod such as nonlocal parameters, power index, wave number, applied magnetic and electric potentials on the wave propagation characteristics is studied.     

Radiation and thermal diffusion effects on an unsteady MHD free convection mass-transfer flow past an infinite vertical porous plate with the hall current and a heat source

An analysis is performed to study the effects of radiation and thermal diffusion on an unsteady MHD free convection heat- and mass-transfer flow of an incompressible, electrically conducting, viscous fluid past an infinite vertical porous plate with the Hall current and a heat source. The flow is considered under the influence of a constant suction velocity and a uniform magnetic field applied normally to the flow. The dimensionless governing equations are solved numerically by the Galerkin finite element method. The effects of the flow parameters on the primary and secondary velocities, temperature, species concentration, shearing stresses, Nusselt number, and Sherwood number are calculated and presented in figures and tables. The results obtained show that a decrease in the temperature boundary layer thickness occurs when the Prandtl number and radiation parameter are increased and an increase in the Schmidt number leads to a decrease in the concentration boundary layer thickness.     

The influence of gas-liquid properties on gas driven waves in a film

The paper deals with a two-layer flow in microgravity, when the upper light fluid (gas) drives the lower layer and forces the wave motion at the interface. The flow is simulated numerically by solving the coupled 2D problem for the Navier-Stokes equations. Gas phases with different viscosities and densities are considered and the influence of these properties on wave characteristics is investigated. It has been shown that film Reynolds number depends on density ratio when the viscosity ratio is fixed. Another result is that the wave amplitude and phase speed at a given film Reynolds number depend on gas viscosity and density. The flow with heavy gas can result in waves with equal amplitudes but different phase speed.     

Exact flow/heat solutions for the non-axisymmetric flow over a rotating disk

The present note is concerned with the exact non-axisymmetric solutions for the flow over a rotating disk. The governing non-axisymmetric flow equations of motion generate exact flow solutions from which analytic expressions for the vorticity, shear stresses, flow/thermal layer thicknesses and rate of heat transfer are obtained. The effects of Brinkman number, heat generation/absorption as well as thermal radiation on the temperature field can be better pursued from the extracted formulae.     

物理靶上自由飞流场全息干涉诊断

在马赫数为15的条件下,采用激光全息干涉技术在物理靶上拍摄到直径12mm的球标模自 由飞流场全息干涉图和阴影照片。通过干涉照片获得了流场中六个截面的密度分布曲线,同时从阴影照片上测量出弓形激波的归一化脱体距离为0.046。将实验照片与计算流场干涉图进行比较,二者的激波位置、条纹变化量及条纹连接基本一致。     

Flow Expansion behind a Shock Wave Discharged from a Channel

The results are given of experimental and numerical investigations of the structure of flow behind a shock wave discharged from open ends of round and square channels. It is demonstrated that the expansion regions arising in a flow behind a diffracted wave are characterized by a larger volume and a higher expansion ratio than those arising in a stationary underexpanded jet with the same value of the Mach number of flow at the channel exit section.