An Enthalpy Control Volume Method for Transient Mass and Heat Transport with Solidification

A single domain enthalpy control volume method is developed for solving the coupled fluid flow and heat transfer with solidification problem arising from the continuous casting process. The governing equations consist of the continuity equation, the Navier–Stokes equations and the convection–diffusion equation. The formulation of the method is cast into the framework of the Petrov–Galerkin finite element method with a step test function across the control volume and locally constant approximation to the fluxes of heat and fluid. The use of the step test function and the constant flux approximation leads to the derivation of the exponential interpolating functions for the velocity and temperature fields within each control volume. The exponential fitting makes it possible to capture the sharp boundary layers around the solidification front. The method is then applied to investigate the effect of various casting parameters on the solidification profile and flow pattern of fluids in the casting process.     

Mean Flow Velocities and Mass Transport for Equatorially-Trapped Water Waves with an Underlying Current

In this paper we present an analysis of the mean flow velocities, and related mass transport, which are induced by certain equatorially-trapped water waves. In particular, we examine a recently-derived exact and explicit solution to the geophysical governing equations in the \({\beta}\)-plane approximation at the equator which incorporates a constant underlying current.     

Mass Transport of Adsorbed-Phase in Stochastic Porous Medium with Fluctuating Porosity Field and Nonlinear Gas Adsorption Kinetics

Using an upscaling approach based on small perturbation theory, the authors have previously investigated the influence of local heterogeneities in matrix porosity on Darcy flow and Fickian-type pore diffusion in the presence of linear non-equilibrium gas adsorption Fathi and Akkutlu, J. Transp. Porous Med. 80, 281–3044 (2009). They identified non-trivial macro-transport and -kinetics effects of the heterogeneity which significantly retard gas release from the matrix and influence the ultimate gas recovery adversely. The work was a unique fundamental approach for our understanding of gas production and sequestration in unconventional reservoirs; however, it was simplified and did not consider (i) the presence of nonlinear sorption kinetics and (ii) a transport mechanism for the adsorbed phase. In this article, we incorporate the nonlinearity and surface diffusion effects of the adsorbed-phase into their formulation and apply the same upscaling approach to further study the heterogeneity effects. Gas sorption involves the so-called Langmuir kinetics, which is reduced to the well-known Langmuir isotherm in the equilibrium limit. It is found that the nonlinearity participates into both macro-transport and -kinetics, promoting primarily the surface diffusion effects. Whereas surface diffusion, although commonly ignored during modeling subsurface phenomena, brings an intricate nature to the gas release dynamics. Through macro-transport effect of the heterogeneity, it increases ultimate gas recovery and, through the macro-kinetics effect of the heterogeneity, it significantly decreases the time needed to reach the ultimate recovery. As the consequence of these effects, it is shown that the gas–matrix system practically does not reach the equilibrium adsorption limit during any stage of the matrix gas release.     

Simulation and Analysis of Transport of Gaseous Wastes from Automobile Traffic with Random Characteristics

An approximate model of transport and dispersion of automobile waste gases by a transverse air flow is considered. The motion of cars is assumed to be a random Poisson process. One possible approach to estimating the concentration of the wind–transported waste and determining its statistical characteristics is described. The length of the representative section of a roadway that is sufficient for a correct analysis of the ecological situation is determined. The power of a linear stationary source approximating the distribution of the mathematical expectation of the concentration of wastes exhausted by a random flux of cars is evaluated.     

相变传热问题的灵敏度分析与优化设计方法

研究了相变传热问题的优化设计及其灵敏度分析方法. 在有限元-时间差分和等效热容 法求解相变温度场的基础上,提出了相变温度场对设计变量一阶灵敏度的计算方法,给出直 接法和伴随法两种计算格式并分析了它们的特点,建立了相变温度场优化的模型和算法,在有限元分析与优化设计软件JIFEX中实现了该方法. 数值算例表明了灵敏度计算的精度和优 化方法的有效性.     

Reduction Principle and Asymptotic Phase for Center Manifolds of Parabolic Systems with Nonlinear Boundary Conditions

We prove the reduction principle and study other attractivity properties of the center and center-unstable manifolds in the vicinity of a steady-state solution for quasilinear systems of parabolic partial differential equations with fully nonlinear boundary conditions on bounded or exterior domains.     

Radiative and Thermal Dispersion Effects on Non-Darcy Natural Convection with Lateral Mass Flux for Non-Newtonian Fluid from a Vertical Flat Plate in a Saturated Porous Medium

The problem of natural convective heat transfer for a non-Newtonian fluid from an impermeable vertical plate embedded in a fluid-saturated porous medium has been analyzed. Non-Darcian, radiative and thermal dispersion effects have been considered in the present analysis. The governing boundary layer equations and boundary conditions are cast into a dimensionless form and simplified by using a similarity transformation. The resulting system of equations is solved by using a double shooting Runge–Kutta method. The effect of viscosity index n, the conduction–radiation parameter R, the non-Darcy parameter Gr*, the thermal dispersion parameter Ds and the suction/injection parameter f_w on the fluid velocities, temperatures and the local Nusselt number are discussed.     

Interfaces of Phase Transition and Disappearance and Method of Negative Saturation for Compositional Flow with Diffusion and Capillarity in Porous Media

The specific case of interfaces separating a single-phase fluid and a two-phase continuum appears in the theory of compositional flow through porous media. They are usually called the interfaces of phase transition (PT-interfaces) or the interfaces of phase disappearing (PD-interfaces). The principle of equivalence is proved which shows that a single-phase multi-component fluid may be replaced by an equivalent fictitious two-phase fluid having specific properties. The equivalent properties are such that the extended saturation of a fictitious phase is negative. This principle enables us to develop the uniform system of two-phase equations in the overall domain in terms of the extended saturation (the NegSat model), and to apply the direct numerical simulation. In the case with diffusion, the uniform NegSat model contains a new term proportional to the gradient of saturation in the relation for flow velocity. The canonical NegSat model represents a transport equation with discontinuous nonlinearities. The qualitative analysis of this model shows that the PT-interfaces represent the shocks of the extended saturation, or, in some cases, can transform into weak shocks. The diffusion and capillarity do not destroy necessarily the shocks, but change their velocity. The analytical technique is developed which allows capturing PT-shocks. The method is illustrated by several examples of miscible gas injection in oil reservoir. In two-dimensional case, the effects of multiple shock collisions in heterogeneous media are automatically modeled. In the case of immiscible fluids and a classic interface, the suggested method converges to the VOF-method.     

The Multi-point Optimization of Shock Control Bump with Constant-Lift Constraint Enhanced with Suction and Blowing for a Supercritical Airfoil

Both shock control bump (SCB) and suction and blowing are flow control methods used to control the shock wave/boundary layer interaction (SWBLI) in order to reduce the resulting wave drag in transonic flows. A SCB uses a small local surface deformation to reduce the shock-wave strength, while suction decreases the boundary-layer thickness and blowing delays the flow separation. Here a multi-point optimization method under a constant-lift-coefficient constraint is used to find the optimum design of SCB and suction and blowing. These flow control methods are used separately or together on a RAE-2822 supercritical airfoil for a wide range of off-design transonic Mach numbers. The RANS flow equations are solved using Roe’s averages scheme and a gradient-based adjoint algorithm is used to find the optimum location and shape of all devices. It is shown that the simultaneous application of blowing and SCB (hybrid blowing/SCB) improves the average aerodynamic efficiency at off-design conditions by 18.2 % in comparison with the clean airfoil, while this increase is only 16.9 % for the hybrid suction/SCB. We have also studied the SWBLI and how the optimization algorithm makes the flow wave structure and interactions of the shock wave with the boundary layer favorable.     

粗纤维压电复合材料(MFC)对旋翼桨叶模型扭转控制的实验及数值研究

对直升机旋翼桨叶进行主动扭转控制是直升机减振主动控制技术中的有效方法之一.本文采用粗纤维压电复合材料(MFC)对旋翼模型进行了扭转控制的实验研究,并建立该结构的有限元模型,将数值结果与实验结果进行了对比分析.实验中,我们采用预扭的悬臂梁模拟旋翼桨叶,在其上表面贴有MFC压电片进行作动.测量得到了不同作动电压下结构的扭转变形,与数值结果进行对比,两者具有很好的一致性.实验及数值结果表明,随着作动电压的增大,结构的扭转角呈线性增加;MFC材料各向异性系数增大,梁的扭转角亦相应增加,采用MFC材料对旋翼进行扭转控制是行之有效的.     

Scaling Transformation for the Effect of Temperature-Dependent Fluid Viscosity with Thermophoresis Particle Deposition on MHD-Free Convective Heat and Mass Transfer Over a Porous Stretching Surface

This article concerns with a steady two-dimensional flow of an electrically conducting incompressible fluid over a vertical stretching sheet. The flow is permeated by a uniform transverse magnetic field. The fluid viscosity is assumed to vary as a linear function of temperature. A scaling group of transformations is applied to the governing equations. The system remains invariant due to some relations among the parameters of the transformations. After finding three absolute invariants, a third-order ordinary differential equation corresponding to the momentum equation, and two second-order ordinary differential equations corresponding to energy and diffusion equations are derived. The equations along with the boundary conditions are solved numerically. It is found that the decrease in the temperature-dependent fluid viscosity makes the velocity to decrease with the increasing distance of the stretching sheet. At a particular point of the sheet, the fluid velocity decreases with the decreasing viscosity but the temperature increases in this case. Impact of thermophoresis particle deposition in the presence of temperature-dependent fluid viscosity plays an important role on the concentration boundary layer. The results, thus, obtained are presented graphically and discussed.     

Comments on Comparison of Observations from a Laboratory Model with Stochastic Theory: Initial Analysis of Hydraulic and Tracer Experiments,Transport in Porous Media 42, 85–107, 2001

Transport in Porous Media -     

Reply to Comments on Comparison of Observations from a Laboratory Model with Stochastic Theory: Initial Analysis of Hydraulic and Tracer Experiments,Transport in Porous Media 52, 111–115, 2003

Transport in Porous Media -     

Constitutive equation for friction with transition from static to kinetic friction and recovery of static friction

A high friction coefficient is first observed as a sliding between bodies commences, which is called the static friction. Then, the friction coefficient decreases approaching the lowest stationary value, which is called the kinetic friction. Thereafter, if the sliding stops for a while and then it starts again, the friction coefficient recovers and a similar behavior as that in the first sliding is reproduced. In this article the subloading-friction model with a smooth elastic–plastic sliding transition [Hashiguchi, K., Ozaki, S., Okayasu, T., 2005. Unconventional friction theory based on the subloading surface concept. Int. J. Solids Struct. 42, 1705–1727] is extended so as to describe the reduction from the static to kinetic friction and the recovery of the static friction. The reduction is formulated as the plastic softening due to the separations of the adhesions of surface asperities induced by the sliding and the recovery is formulated as the viscoplastic (creep) hardening due to the reconstructions of the adhesions of surface asperities during the elapse of time under a quite high actual contact pressure between edges of asperities.     

Method for reprocessing and recycling of aqueous rinsing liquids from car painting with water-based paints in automobile industry

In the paint processes of modern car plants the paint to be applied on the car bodies change after every few numbers. In order to avoid intermixtures of different lacquers the application systems has to be cleaned before every change by means of a rinsing liquid. Water based lacquers require water based cleaning agents. For these rinsing waters a new recycling process based on an evaporation process, a fractionated condensation and an after treatment of the condensates is described. The compatibility of the recycled system for lacquers is investigated. After a test with ten recycling loops no accumulation of harmful substances occurs. In comparison to original agents the recycled rinsing liquids show comparable or better cleaning abilities. The comparison of the energy consumption and the disposal of CO₂ and of volatile organic compounds between the application of fresh rinsing liquid with disposal after usage and recycled rinsing liquid show major advantages of the recycling process.