摘要:

AbstractThe paper proposes a generalized least‐squares time finite element procedure for analysis of transient field problems. It leads to a very general four parameter and two time level family of schemes. The free parameters are optimized in terms of accuracy, stability and oscillatory behaviour of the computational algorithm. In the case of linear problems an unconditionally stable scheme of fourth‐order accuracy is obtained. Special choices of the free parameters also give a number of well‐known time‐integration schemes, such as the Zienkiewicz–Lewis third‐order algorithm, the Goodrich scheme and standard schemes such as the Crank–Nicolson and backward fully implicit schemes. The main disadvantage of the higher order algorithm is a large bandwidth of the system matrix owing to the matrix terms of the formKTK. This drawback is reduced for special choices of the parameters by forming a product formula. Somewhat more computation is required than for popular schemes such as the generalized midpoint rule, depending on the prescribed variables. Numerical comparisons are made between the proposed higher order schemes and sta

ISSN:0029-5981    

DOI:10.1002/nme.1620240112

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractThis article describes numerical modelling of heat transfer and thermoelasticity effects that are significant in thermo‐optical designs of solid state slab lasers capable of high average output power. The heat equation and equations of thermoelasticity are solved simultaneously to evaluate thermal stresses and microscopic deformations in isotropic and anisotropic laser host media. An efficient dynamic alternating‐direction implicit method has been developed and applied in this work to solve the steady state heat transfer and stress potential equations in two dimensions. Numerical results are presented for some problems that arise in baseline designs of experimental slab laser syst

ISSN:0029-5981    

DOI:10.1002/nme.1620240113

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractThe behaviour of coal particles undergoing pyrolysis in a downflow reactor is modelled in two dimensions using integral approximation. The governing equations are solved numerically by marching procedures using Adams–Moulton and Romberg integration methods. The conversion of coal particles is studied in terms of chemical kinetics, hydrodynamic flow of volatiles and the heat transfer mechanism at the interface. The conversion increases with decreasing velocity, solid loading, particle diameter and total pressure. Owing to large amounts of gas production, the influence of pyrolysis on the gas‐particle heat transfer and drag coefficients becomes important at large particle diameters. For particle diameters less than 100 μm, such influence is min

ISSN:0029-5981    

DOI:10.1002/nme.1620240114

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractMicroporosities often appear during the solidification of foundry pieces. They result from the volume contraction of the alloy during its solidification. Thermal transfers between alloy and mould check the solidification. They are estimated by a finite volume method, including specific calculation of the mould filling‐up, the alloy solidification and the resulting feeding of the mould.The calculation uses a geometrical enmeshment of the whole mould, generating numerous elements of different sizes. From the experimental fluid flow measurement, the mould filling‐up may be described step by step by the computer, as can the initial thermal transfer. Thermal transfers are related to the solidification enthalpic release obtained from quantitative differential thermal analysis. They are also related to the fluid flow induced by solidification shrinkage.Such a calculation leads to the location of the microporosities, from which pressure drops can be estimated during solidificat

ISSN:0029-5981    

DOI:10.1002/nme.1620240115

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractA mathematical model has been developed to quantify the effects of process conditions during turbulent solidification and mixing of a liquid metal jet in a confined co‐flowing molten metal stream.The modelling has been split into three parts. First, a single phase model with no latent heat effects to consider the solidification potential. Secondly, a two phase model where the second phase is comprised of solid particles which solidify during mixing of the two streams. Thirdly, a two phase model where the second phase consists of the inner jet, which is assumed to break up into droplets of given size, and solid particles are allowed to form by solidification within the droplets.The results show that the thermal history (solidification path) of the solid phase formed is affected by latent heat and particle size, which implies that solidification, nucleation and jet fragmentation events should be included dynamically to ensure realistic prediction

ISSN:0029-5981    

DOI:10.1002/nme.1620240116

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractAn analysis technique that uses the Lanczos vectors to construct a Reyleigh–Ritz solution for the transient heat conduction problem is presented. The Lanczos vectors are derived from the heat supply vector and incorporate all the information peculiar to a given problem. They are orthonormal with respect to the heat capacitance matrix and are generated with a minimum of computational effort. Furthermore, an error bound is derived that can be used to terminate the Lanczos algorithm as soon as the number of vectors required to obtain a desired degree of accuracy has been generated. A summary of the algorithm is presented and the accuracy and efficiency of the method is illustrated using a numerical exampl

ISSN:0029-5981    

DOI:10.1002/nme.1620240117

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractThe die‐swell occurring during the extrusion of a visco‐elastic fluid has been extensively examined in recent years, both experimentally and numerically. These investigations have been mainly confined to isothermal flows. If the material is initially relatively cool, however, viscous heating may lead to proportionally large changes in temperature and material properties, with significant effects on die‐swell. An iterative computational model is presented which describes the flow of Maxwell and Oldroyed fluids subject to the effect of temperature gradients induced by viscous heating and thermal boundary conditions. Predictions are presented for extrusion from both slit and axisymmetric

ISSN:0029-5981    

DOI:10.1002/nme.1620240118

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

摘要:

AbstractAn enthalpy formulation for convection/diffusion phase change is developed. The essential feature of this formulation is that latent heat effects are isolated in a source term. This formulation is applicable to a general convection/diffusion phase change, i.e. it is valid in the cases of evolution of latent heat either at an isothermal temperature or over a temperature range. Before implementation of the enthalpy formulation, a technique is required to ensure that velocities predicted to be in a solid region actually take the value zero. Three alternative schemes for achieving this are presented.The enthalpy formulation and velocity correction schemes are independent of the numerical technique. As an example of how the method can be implemented a control volume numerical discretization is chosen. This implementation is applied to two test problems: a solidification phase change in a cavity under conduction and the same phase change under conduction and natural convection. The natural convection problem is used to compare the performances of the various velocity correction schemes. The results of the problems are in good agreement with available analytical solutions and previous numerical solutions.

ISSN:0029-5981    

DOI:10.1002/nme.1620240119

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

ISSN:0029-5981    

DOI:10.1002/nme.1620240120

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY

ISSN:0029-5981    

DOI:10.1002/nme.1620240101

出版商:John Wiley&Sons, Ltd    

年代:1987

数据来源: WILEY