摘要:

AbstractIt is argued that ‘sifting’ phenomena, in which fragments of fluid subjected to larger body forces move through those subjected to smaller body forces, are prevalent in turbulent flows, and that they can be simulated by means of mathematical methods which have been developed for two‐phase flows.A connection with Prandtl's mixing‐length theory is established; and it is deduced from the success of that theory for shear flows that there must exist a source term in the normal‐to‐wall‐velocity equations which is proportional to the gradient of along‐the‐wall velocity. This term is then included in the two‐fluid‐model equations.Solutions of the equations are presented for a turbulent Couette flow in which the heating of one of the walls and the presence of a gravitational field can cause ‘sifting’ phenomena to become dominant. The friction and heat‐transfer coefficients, and the profiles of velocity and temperature, are computed and discussed, for flows both with and

ISSN:0029-5981    

DOI:10.1002/nme.1620240102

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractThe proposed method is the direct boundary integral equation (BIE) method applied to three‐dimensional transient heat transfer analyses and to corresponding elastostatic analyses under thermal loading. The mechanical and thermal problems are decoupled. For those not familiar with the BIE method, a short survey of the basic principles is given to help them understand the mathematical treatment, which is performed in the frame of distribution theory. The tempered elementary solution of the transient heat transfer problem contains time and space variables. The numerical treatment of the thermal equation is performed analytically with respect to time and numerically with respect to space in the same way as for steady state equations. Great care is paid to space integration in order to compute the values of the kernels precisely enough on the surface and inside the volume. The computational treatments of both problems are realized in such a way as to minimize computing time. Differences between transient and steady state analyses, on the one hand, and between elastostatic analyses with and without thermal loading, on the other, are emphasized. Finally, an analytical example shows the good behaviour of the proposed method to solve singular thermal problems and an industrial example shows the accuracy of the results obtained by using the BIE method to solve three‐dimensional thermo‐elastic pro

ISSN:0029-5981    

DOI:10.1002/nme.1620240103

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractA moving finite element method that calculates the transient temperature distribution, the density distribution and the stress distribution during the sintering cycle has been developed. Coupled two‐dimensional axisymmetric energy, continuity and stress equilibrium equations along with a constraint, specifying the direction of the initial material velocity, are solved in a Lagrangian co‐ordinate system. The nodes move at the same speed as the material and therefore the convective terms in the differential equations drop out. At every time step, the energy equation is solved, and the computed temperatures are then used to find the densification rate. In two‐dimensional problems, the continuity equation is not sufficient to calculate the two components of material velocity. Here, it is assumed that the diffusion caused by the density gradient is the driving force. This implies that the velocity vector of the material is perpendicular to the lines of constant density. Therefore, the combination of the diffusion and continuity equations will generate the initial sintering strains. The elastic stress equilibrium equations are then solved using the thermal and initial sintering strains as the driving forces. As a result, the final shape of the material and the stresses are deter

ISSN:0029-5981    

DOI:10.1002/nme.1620240104

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractThis paper describes practical experiences in dealing with non‐linearities in temperature field calculations. First the use of the load vector for representing the heat radiation on the outer surfaces is reported. However, if there are also additional non‐linearities in the conductance matrix, then it may happen that because of possible counteractions of the non‐linearities no convergence is achieved, at least with the direct iteration. Therefore it is more appropriate to put the radiation terms into the conductance matrix where the other non‐linearities, such as temperature dependent thermal conductivity and natural convection also appear. It is shown how the Newton–Raphson iteration can be applied in an easy way. In the case of temperature dependent heat sources the load vector also needs to be considered. The appropriate special measures are

ISSN:0029-5981    

DOI:10.1002/nme.1620240105

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractDuring the propagation of a hydraulically induced fracture in a porous material, fluid leak‐off occurs from the fracture to the formation. Conduction and convection of heat also take place, owing to the large difference between the fluid injection temperature and that of the reservoir. The paper describes a quasi‐two‐dimensional heat transfer model coupled with a filtration model. It is then coupled into different coupled fracture propagation models (two‐dimensional and quasi‐three‐dimensional).The rheological characteristics of the fracturing fluid are temperature‐dependent with a sharp breakdown. The fluid diffusion model combines cake growth at the fracture face with two‐fluid flow in the formation. Temperature profiles along the fracture and the formation are computed during fract

ISSN:0029-5981    

DOI:10.1002/nme.1620240106

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractIn this paper some numerical predictions are presented for the buoyancy‐driven turbulent flow and heat transfer in a large cavity using both a prescribed eddy viscosity model and ak–ϵ model. The results from these models are in good agreement, although the calculations with the prescribed eddy viscosity model are considerably cheaper. The results also show the correct qualitative behaviour, but there are some differences between the predictions and the available experimental data. Possible reasons for these are discu

ISSN:0029-5981    

DOI:10.1002/nme.1620240107

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractA multigrid algorithm for implementation on unstructured meshes is proposed. The algorithm uses a sequence of unnested grids and requires the development of efficient inter‐grid interpolation procedures. It is demonstrated how elliptic problems can be solved in this fashion by using Jacobi smoother

ISSN:0029-5981    

DOI:10.1002/nme.1620240108

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractA new finite element method is presented. This new method contains several novel features including a streamline upwind formulation for the advection terms and equal order interpolations for all variables: velocities, pressure, temperature and other fluid properties. This new formulation uses an iterative solution method greatly reducing the computer storage requirements. The validity of the new finite element method was tested on both a natural convection problem, a thermally driven cavity, and a forced convection problem, a heated cylinder in cross‐flow. The predicted results compared favourably with a benchmark solution for the cavity and an empirical correlation for the cylinder in cross‐f

ISSN:0029-5981    

DOI:10.1002/nme.1620240109

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractThe two‐dimensional Navier–Stokes equations, suitably amplified to include the effects of chemical reactions and turbulence, are discretized by employing a finite‐volume technique. A weighted upwind/central differencing scheme, the weight depending on the grid Peclet number, is used for the convection terms. Velocities are calculated on staggered grids. The source terms are treated in a quasi‐implicit manner by combining linearization of these terms with an ICE procedure providing a time‐advanced pressure. The effect of turbulence is included through the eddy‐viscosity concept by solving equations for turbulent kinetic energy and its rate of decay. Combustion is modelled by an equation for mass fraction of fuel containing a fuel consumption term based on mixing‐limited combustion.The resulting code, called FLACS‐ICE, is employed in simulating the influence of confinement on flame acceleration in premixed, stoichiometric propane‐air mixtures. Calculations are performed for large (425m3), medium (35m3) and small scale (0·0036m3) vessels. Satisfactory agreement with experimental data, published by Solberg1is obtained. Some limitations of the code ar

ISSN:0029-5981    

DOI:10.1002/nme.1620240110

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractWe have developed a versatile finite element approach to analyse stresses and displacements induced in thermally thinned and thickened geological structures. Material and geometric non‐linearities form an important aspect of the finite element simulation. The changes in geometry are incorporated by a multipoint constraint procedure. The method takes into account temperature‐dependent variations in rheological properties of the medium, including the presence of a brittle–ductile transition. We illustrate the application of the method for specific geophysical problems associated with the temperature history of the earth's crust at continental margins of the Atlantic

ISSN:0029-5981    

DOI:10.1002/nme.1620240111

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY