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1.
This paper develops a mathematical model of the ring-spinning process that takes into account its non-stationary nature. A complex system of differential equations is obtained, which from a mathematical point of view constitutes a ‘free-boundary’ problem. Its solution involves definition of suitable boundary conditions related to the mechanical characteristics of the process and of the spinning machine itself. The boundary conditions which determine the solution are pointed out. A numerical solution of the system of differential equations can be obtained by the Finite-Segments method, as shown in an example.  相似文献   

2.
A coupled thermomechanical model to simulate light alloy solidification problems in permanent composite moulds is presented. This model is based on a general isotropic thermoelasto-plasticity theory and considers the different thermomechanical behaviours of each component of the mould as well as those of the solidifying material during its evolution from liquid to solid. To this end, plastic evolution equations, a phase-change variable and a specific free energy function are proposed in order to derive temperature-dependent material constitutive laws.The corresponding finite element formulation and the staggered scheme used to solve the coupled non-linear system of equations are also presented. Finally, the temperature and displacement predictions of the model are validated with laboratory measurements obtained during an experimental trial.  相似文献   

3.
This paper deals with the experimental and theoretical investigation of the influence of an electric field on the heat transfer rate during stable film boiling of the electrically insulating fluid FC-72. In particular the case of stable saturated film boiling from a horizontal plate is studied. The experiments show that the heat transfer rate increases ±50 when an electric field of 27.3 kV/cm is applied. A new correlation for the heat transfer rate in the presence of an electric field based on the heat transfer model of Klimenko is derived in this paper. Therefore the behavior of the liquid-vapor interface is studied in more detail. This study shows that the electric field has a two fold effect on the interface. On the one hand the distance between adjacent bubbles decreases and on the other hand the bubbles elongate in the presence of the electric field. The new correlation is in good agreement with the experiments. Received on 20 October 1998  相似文献   

4.
Attempts have been made to alter the solidification microstructures of fiber reinforced aluminum composites by cooling the ends of the fibers extending out of the mold. Experimental observations indicate that cooling the extended ends of the reinforcement results in finer microstructures in the matrix and changes the nature of the interface. In this paper, numerical simulation is performed on a two-dimensional axi-symmetric model to investigate the solidification process of metal matrix composite (MMC) with the extended ends of the fibers cooled by a heat sink. The numerical simulation is based on the source-based enthalpy method with finite volume discretization. The temperature profiles obtained by simulation are compared to the cooling curves measured experimentally in order to validate the current mathematical model. It is found that the simulation result matches the experimental data with reasonable agreement.  相似文献   

5.
A Petrov-Galerkin finite element method is presented for calculation of the steady, axisymmetric thermosolutal convection and interface morphology in a model for vertical Bridgman crystal growth of nondilute binary alloys. The Petrov-Galerkin method is based on the formulation for biquadratic elements developed by Heinrich and Zienkiewicz and is introduced into the calculation of the velocity, temperature and concentration fields. The algebraic system is solved simultaneously for the field variables and interface shape by Newton's method. The results of the Petrov-Galerkin method are compared critically with those of Galerkin's method using the same finite element grids. Significant improvements in accuracy are found with the Petrov-Galerkin method only when the mesh is refined and when the formulation of the residual equations is modified to account for the mixed boundary conditions that arise at the solidification interface. Calculations for alloys with stable and unstable solute gradients show the occurrence of classical flow transitions and morphological instabilities in the solidification system.  相似文献   

6.
A technique to determine the thermal boundary conditions existing during the solidification of metallic alloys in the investment casting process is presented. Quantitative information about these conditions is needed so that numerical models of heat transfer in this process produce accurate results. In particular, the variation of the boundary conditions both spatially and temporally must be known. The method used involves the application of a new inverse heat conduction method to thermal data recorded during laboratory experiments of aluminium alloy solidification in investment casting shell moulds. The resultant heat transfer coefficient for the alloy/mould interface is calculated. An experimental programme to determine requisite mould thermal properties was also undertaken. It was observed that there is significant variation of the alloy/mould heat transfer coefficient during solidification. It is found to be highly dependent on the alloy type and on the vertical position below the initial free surface of the liquid metal. The aluminium casting alloys used in this study were 413, A356, 319 (Aluminum Association designations), and commercially pure aluminium. These alloys have significantly different freezing ranges. In particular, it was found that alloys with a high freezing range solidify with rates of heat transfer to the mould which are very sensitive to metallostatic head.  相似文献   

7.
8.
Non-linear Oberbeck-electroconvection (OBEC) in a poorly electrically conducting fluid through a vertical channel, when the walls are held at different temperatures with temperature difference perpendicular to gravity, is studied using the modified Navier stokes equation in the presence of both induced and an applied electric field. Both analytical and numerical solutions for the non-linear coupled equations governing the motion are obtained and found that analytical solutions agree well with numerical solutions for values of the buoyancy parameter N<1. It is shown that OBEC can be controlled by maintaining the temperature difference either in the same direction or opposing the potential difference with a suitable value of electric number W. The effect of W on velocity, temperature, rate of heat transfer, skin friction and mass flow rate are computed and the results are depicted graphically. We found that analytical results agree well with numerical results for small values of N. We also found that an increase in W accelerates the flow and hence increases linearly the skin friction and mass flow rate.  相似文献   

9.
The time-dependent process of charge accumulation on an electrically insulated sphere located in a turbulent stream with the ion component in the presence of an electric field is considered. The process is simulated numerically on the basis of the time-dependent electrodynamic equations and averaged Navier-Stokes equations (RANS approximation) using the Sekundov single-parameter turbulent viscosity model. The distributions of the ion number density, electric current, and potential are determined. Features of the obtained time dependence of the sphere potential are analyzed.  相似文献   

10.
The problem of the ejection of a flat piston from a half-space occupied by a uniform magnetic field parallel to the piston and a gas with an electrical conductivity of σ dependent on the temperature T, in which σ=0 when T*, is considered.  相似文献   

11.
Steady flow of a completely ionized plasma between parallel plates moving in their own plane in the presence of an electric field is examined. The distribution functions of the ions and electrons are derived from the kinetic Boltzmann equations supplemented by equations for the electric field. The solution is constructed by means of a variation of the method of moments; at the same time, it is assumed that momentum is transferred only by ions and heat is transferred by electrons. The analysis takes into account near collisions between particles for an arbitrary degree of rarefaction of the plasma. An example of calculation of the principal characteristics of the flow is given.The boundary problems connected with the presence of solid surfaces in the flow are of far less practical importance in plasma dynamics than in gasdynamics. This is because a plasma can exist only at very high temperatures which destroy the majority of materials to a greater or lesser extent. As a rule, in order to contain a plasma within definite bounds, strong magnetic fields are utilized, not solid walls. Nevertheless, consideration of problems with bounding surfaces is still of definite interest in the case of plasma. An approximate solution of one of the simplest problems of this kind is given below.  相似文献   

12.
The nonlinear electrohydrodynamic stability of an irrotational jet in the presence of capillary force and weak viscous stress on the surface has been studied. Two nonlinear modified Schrödinger equations are obtained. Neglecting the viscous stress, the classic Schrödinger equations are obtained. The stability conditions of steady state solutions are investigated, using the modulation concept. It is found that the viscous stress produces a resonance (say a viscous resonance) away from the critical point. For the progressive waves, we obtained modified transition curves inserting the viscous stress. The classic nonlinear cutoff wave number is obtained and this means that the viscous stress has a fluctuating effect on the perturbed jet, away from the critical points.  相似文献   

13.
14.
The linear stability, both stationary and oscillatory, of a horizontal layer of a dielectric Oldroyd fluid under the simultaneous action of a vertical a.c. field and a vertical temperature gradient is analysed. The stability regions in the space of the characteristic parameters are determined by means of a finite difference method. The physical mechanisms relevant to the problem are expounded using a heuristic argument.  相似文献   

15.
In this paper we study electrohydrodynamic instability (EHDI) in a poorly conducting parallel inviscid fluid in the presence of an electric field and space variation of electrical conductivity. It is shown that EHDI causes inhomogeniety in the material science processing. This inhomogeniety can be controlled by understanding the nature of EHDI in the presence of an electric field and a shear due to horizontal basic velocity. The condition for EHDI is determined in terms of the electric number rather than the point of inflexion of the basic velocity profile using both moment and energy methods combined with Galerkin expansion technique. From this analysis, it is shown that a proper choice of electric number controls inhomogeniety by controlling instability of a parallel poorly conducting inviscid fluid. For unstable motion it is shown that the growth rate, Ci, is confined in a semi circle region
  相似文献   

16.
Summary A solution is outlined for the problem of an electric dipole which is located outside and parallel to the axis of a circular cylinder fo infinite length. The corrugated surface of the cylinder is assumed to be described by an anisotropic boundary impedance which specifies the ratios of the tangential electric and magnetic fields. It is shown that, in general, the radiated field is elliptically polarized.  相似文献   

17.
We investigate the nonlinear current distribution in an electrode of finite dimensions with a pre-electrode layer in which the potential locally depends on the current density. The electrode is in contact with a medium of anisotropic conductivity caused by the Hall effect. The problem is reduced to the solution of a nonlinear integrodifferential equation. It is shown that the structure of the field is determined by the Hall parameter and the form of the volt-ampere characteristic in the pre-electrode layer.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 1, pp. 19–23, January–February, 1971.  相似文献   

18.
This paper presents a large strain thermoviscoplastic formulation for the analysis of the solidification process of spheroidal graphite (S.G.) cast iron in a green sand mould. This formulation includes two different non-associate constitutive models in order to describe the thermomechanical behaviour of each of such materials during the whole process. The performance of these models is evaluated in the analysis of a solidification test.  相似文献   

19.
We examine the problem of water injection into a limited reservoir, initially completely filled with oil, consisting of two permeable strata separated by an impermeable layer.  相似文献   

20.
Oscillatory MHD Couette flow of electrically conducting fluid between two parallel plates in a rotating system in the presence of an inclined magnetic field is considered when the upper plate is held at rest and the lower plate oscillates non-torsionally . An exact solution of the governing equations has been obtained by using Laplace transform technique. Asymptotic behavior of the solution is analyzed for M 2 1, K 2 1 and ω 1 and for large M 2, K 2 and ω. Numerical results of velocities are depicted graphically and the frictional shearing stresses are presented in tables. It is found that a thin boundary layer is formed near the lower plate, for large values of rotation parameter K 2, Hartman number M 2 and frequency parameter ω. The thickness of this boundary layer increases with increase in inclination of the magnetic field with the axis of rotation.  相似文献   

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