摘要:

AbstractIn computational mechanics, flow simulation of polymer processing not only must deal with exotic constitutive behaviour and complex geometry, but often faces the presence of moving free boundaries. The cavity‐filling of injection moulding, treated as a Stefan problem, could be better attacked, computationally, by a fixed‐domain approach after a Baiocchi transformation. For thermosetting materials, modelling the rheology and the chemical reaction needs the kinematics in the meniscus region behind the moving front. The fluid mechanics, however, touches on the unresolved question of the moving contact point, fundamental to wetting phenomena. Aspects of particular interest to polymer processing are reviewed. In spite of the imperfections, the simulation of the ASTM standard ‘spiral‐mould test’ for thermosets has recently proved promising as an inverse problem to characterize the rheology of a commercial fast‐reacting thermosetting material. The key was to match the simulation only to portions of the data that were least influenced by the un

ISSN:0029-5981    

DOI:10.1002/nme.1620340302

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractMultiphase solid–liquid pipeline flow with small quantities of free gas is treated in the paper. A 1‐D separated unsteady flow model with liquid and gas virtual mass effect is described. A stable numerical method for the model equations based on the characteristics method is developed. Some accurate iteration procedures at every grid point for the solution of the algebraic equations are shown. The wave speed for flow in a pipeline worked out on the basis of this theoretical model shows a good correspondence with experimental results for two‐ and three‐phase m

ISSN:0029-5981    

DOI:10.1002/nme.1620340303

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractSome recent results are reviewed that indicate the appropriate nature of Taylor–Galerkin based algorithms for solving model convection–diffusion problems accurately in time and for simulating more complex non‐Newtonian flows, such as those arising in the polymer industry. Initially attention is given therefore to linear and non‐linear convection–diffusion model problems in two space dimensions, and then to transient problems involving heating effects. Newtonian and generalized Newtonian models are considered for both power‐law and Carreau models for various parameters. Effects of shear‐rate changes and temperature variations through transient build up periods are discussed in relation to their influence on the viscosity and viscous heating for thermal Péclet number

ISSN:0029-5981    

DOI:10.1002/nme.1620340304

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractFor several years, experimental investigations with magnetoplasmadynamic (MPD) thrusters have been conducted at the Institute for Space Systems (IRS). In order to achieve a better understanding of these thrusters, numerical procedures to calculate these MPD accelerators have been applied. A theoretical model for the calculation of the current, electron temperature and flow distribution in self‐field MPD thrusters has been developed. The extended Ohm's law has been applied to calculate the current contour lines, the electron energy equation is taken to calculate the electron temperature distribution and a two‐dimensional flow code is used to obtain the velocity, pressure and heavy particles temperature distributions. With both temperature distributions, a thermal non‐equilibrium in the plasma flow is obtained. The gas dynamic equations are solved by a finite volume code EUFLEX, which was transformed to cylindrical co‐ordinates and extended for the implementation of j × B and heat source terms. The electromagnetic discharge equation and the electron energy equation are transformed into curvilinear co‐ordinates and solved for the steady phase by a modified Gauss–Seidel algorithm. A comparison of the numerical and experimental results for different currents is presented a

ISSN:0029-5981    

DOI:10.1002/nme.1620340305

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe simulation of flows around single cylinders, tandem cylinders and infinite chains of cylinders with the lattice gas method is presented. The effects of the ratio of the cylinder diameter to channel width and different outflow boundary conditions are discussed. Results obtained applying different lattice gas models are given. Drag coefficient, wake length and Strouhal number are compared with experimental data. The agreement between numerical and experimental results is satisfactory.

ISSN:0029-5981    

DOI:10.1002/nme.1620340306

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractTwo conservative versions of the recently introduced locally exact consistent upwind scheme of second order (LECUSSO‐scheme) are presented which both use four points (two upstream, one downstream) and do not suffer from wiggles. Test calculations using a flow problem with an exact analytical solution show that the two schemes, called LECUSSO‐C and QUICK‐PLUS, are superior to the original LECUSSO‐scheme and to several other standard difference

ISSN:0029-5981    

DOI:10.1002/nme.1620340307

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractWeak form for the solution of the complete second order boundary value problem in one‐dimensional case is derived in a way, which should be easy to comprehend. The starting point is the boundary value problem extended with suitable jump conditions. The aim is a convenient form for numerical calculations and weighting functions giving accurate nodal values. The connections with SUPG‐, GLS‐ and GGLS‐method is discussed with reinvention explaining the selections of ‘free’ parameters related to these methods. Finally some ideas to extend the methods to two‐dimensional cases

ISSN:0029-5981    

DOI:10.1002/nme.1620340308

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractA domain‐adaptive technique and an iterative, block bidiagonal method are used to analyse the unsteady dynamics of annular liquid membranes subject to fluctuations in the mass injected into the volume enclosed by the membranes. The domain‐adaptive technique maps the unknown, time‐dependent, curvilinear geometry of the liquid membrane into a unit interval. The condition that the membrane's radius is zero at the convergence point is used to determine the convergence length, which is governed by an ordinary differential equation. This equation is solved iteratively together with those which govern the fluid dynamics equations. A block bidiagonal technique is used to determine the mass per unit length, radius, and axial and radial velocity components of the membrane. It is shown that the pressure of the gases enclosed by the liquid membrane responds instantaneously to changes in and exhibits the same periodic behaviour as the mass injection rate. The convergence length takes a delay time to respond to the mass injection rate fluctuations. The magnitude of this delay time increases as the Froude and Weber numbers and the nozzle exit angle are increased. The amplitude of the oscillations of both the convergence length and the pressure coefficient increases as the pressure difference across the membrane and the amplitude of the mass injection rate fluctuations are incr

ISSN:0029-5981    

DOI:10.1002/nme.1620340309

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractA generalized hybrid optimal synthesis method is developed for truss structures in which the design variables are the co‐ordinates of the panel points, cross‐sectional areas and discrete material kinds of member elements. The primary design problem is formulated in terms of the shape, material and sizing variables and approximated to a sequence of convex and separable subproblems by using mixed direct/reciprocal design variables. Each subproblem is solved by a dual method in which the continuous shape and sizing variables are optimized by a Newton‐type algorithm and the discrete material and continuous sizing variables are improved by a discrete sensitivity analysis. Using the proposed method, discrete material kinds, shape and sizing variables can be systematically improved to obtain an optimum solution. The rigourness, reliability and efficiency of the method are demonstrated by applying it to the minimum cost design of trusses subjected to stress and displacement constr

ISSN:0029-5981    

DOI:10.1002/nme.1620340310

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe introduction of second order sensitivities to behaviour approximation in structural optimization is applied and investigated. Numerical computation of second derivatives is considered and evaluated. Two approaches in shape optimization are involved, namely shape finding by moving boundaries and shape genesis by distributing mass in a specified design domain. A series of examples is engaged to work out the benefits of second order information in both the above fields.

ISSN:0029-5981    

DOI:10.1002/nme.1620340311

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY