Modeling, numerical methods, and simulation for particle-fluid two-phase flow problems

In this paper, we study the issues of modeling, numerical methods, and simulation with comparison to experimental data for the particle-fluid two-phase flow problem involving a solid-liquid mixed medium. The physical situation being considered is a pulsed liquid fluidized bed. The mathematical model is based on the assumption of one-dimensional flows, incompressible in both particle and fluid phases, equal particle diameters, and the wall friction force on both phases being ignored. The model consists of a set of coupled differential equations describing the conservation of mass and momentum in both phases with coupling and interaction between the two phases. We demonstrate conditions under which the system is either mathematically well posed or ill posed. We consider the general model with additional physical viscosities and/or additional virtual mass forces, both of which stabilize the system. Two numerical methods, one of them is first-order accurate and the other fifth-order accurate, are used to solve the models. A change of variable technique effectively handles the changing domain and boundary conditions. The numerical methods are demonstrated to be stable and convergent through careful numerical experiments. Simulation results for realistic pulsed liquid fluidized bed are provided and compared with experimental data. (C) 2004 Elsevier Ltd. All rights reserved.

Centrifuge modeling of suction bucket foundations for platforms under ice-sheet-induced cyclic lateral loadings

This paper presents the results of a series of centrifuge model tests performed to study the behavior of suction bucket foundations for a tension leg platform in the Bohai Bay, China. The target lateral loadings were from ice-sheet-induced structural vibrations at a frequency of 0.8-1.0 Hz. The results indicate that excess pore water pressures reach the highest values within a depth of 1.0-1.5 in below the mud line. The pore pressures and the induced settlement and lateral displacement increase with the amplitude of the cyclic loading. Two failure modes were observed: liquefaction in early excitations and settlement-induced problems after long-term excitations. (c) 2006 Elsevier Ltd. All rights reserved.

Numerical modeling of 3-D turbulent two-phase flow and coal combustion in a pulverized-coal combustor

In the present paper, a multifluid model of two-phase flows with pulverized-coal combustion, based on a continuum-trajectory model with reacting particle phase, is developed and employed to simulate the 3-D turbulent two-phase hows and combustion in a new type of pulverized-coal combustor with one primary-air jet placed along the wall of the combustor. The results show that: (1) this continuum-trajectory model with reacting particle phase can be used in practical engineering to qualitatively predict the flame stability, concentrations of gas species, possibilities of slag formation and soot deposition, etc.; (2) large recirculation zones can be created in the combustor, which is favorable to the ignition and flame stabilization.

Self-consistent kinetic modeling of electron distribution function in a low-pressure inductively coupled plasma

Based upon the spatially inhomogeneous Boltzmann equation in two-term approximation coupled with electromagnetic and fluid model analysis for the recently developed inductively coupled plasma sources, a self-consistent electron kinetic model is developed. The electron distribution function, spatial distributions of the electron density and ionization rate are calculated and discussed.

Two-dimensional simulation of inductive plasma sources with self-consistent power deposition

A time averaged two-dimensional fluid model including an electromagnetic module with self-consistent power deposition was developed to simulate the transport of a low pressure radio frequency inductively coupled plasma source. Comparsions with experiment and previous simulation results show, that the fluid model is feasible in a certain range of gas pressure. In addition, the effects of gas pressure and power input have been discussed.

Mechanical modeling of grain boundary sliding of polycrystals

Using a variational method, a general three-dimensional solution to the problem of a sliding spherical inclusion embedded in an infinite anisotropic medium is presented in this paper. The inclusion itself is also a general anisotropic elastic medium. The interface is treated as a thin interface layer with interphase anisotropic properties. The displacements in the matrix and the inclusion are expressed as polynomial series of the cartesian coordinate components. Using the virtual work principle, a set of linear algebraic equations about unknown coefficients are obtained. Then the general sliding spherical inclusion problem is accurately solved. Based on this solution, a self-consistent method for sliding polycrystals is proposed. Combining this with a two-dimensional model of an aggregate polycrystal, a systematic analysis of the mechanical behaviour of sliding polycrystals is given in detail. Numerical results are given to show the significant effect of grain boundary sliding on the overall mechanical properties of aggregate polycrystals.

Statistical modeling of damage evolution in spallation

In order to understand the mechanism of the incipient spallation in rolled metals, a one dimensional statistical mode1 on evolution of microcracks in spallation was proposed. The crack length appears to be the fundamental variable in the statistical description. Two dynamic processes, crack nucleation and growth, were involved in the model of damage evolution. A simplified case was examined and preliminary correlation to experimental observations of spallation was made.

Control of Large-size SiC Growth Process Using Modeling tool

Large size bulk silicon carbide (SiC) crystals are commonly grown by the physical vapor transport (PVT) method. The PVT growth of SiC crystals involves sublimation and condensation, chemical reactions, stoichiometry, mass transport, induced thermal stress, as well as defect and micropipes generation and propagation. The quality and polytype of as-grown SiC crystals are related to the temperature distribution inside the growth chamber during the growth process, it is critical to predict the temperature distribution from the measured temperatures outside the crucible by pyrometers. A radio-frequency induction-heating furnace was used for the growth of large-size SiC crystals by the PVT method in the present study. Modeling and simulation have been used to develop the SiC growth process and to improve the SiC crystal quality. Parameters such as the temperature measured at the top of crucible, temperature measured at the bottom of the crucible, and inert gas pressure are used to control the SiC growth process. By measuring the temperatures at the top and bottom of the crucible, the temperatures inside the crucible were predicted with the help of modeling tool. SiC crystals of 6H polytype were obtained and characterized by the Raman scattering spectroscopy and SEM, and crystals of few millimeter size grown inside the crucible were found without micropipes. Expansion of the crystals were also performed with the help of modeling and simulation.

Modeling of a Laminar DC Arc Plasma Torch

In recent years, stable and long laminarplasma jets have been successfully generated, and thus it is possible to achieve low-noise working surroundings, better process repeatability and controllability, and reduced metal-oxidation degree in plasma materials processing. With such a recent development in thermal plasma science and technology as the main research background, modeling studies are performed concerning the DCarcplasmatorch for generating the long laminar argon plasma jet. Two different two-dimensional modeling approaches are employed to deal with the arc-root attachment at the anode surface. The first approach is based on circumferentially uniform arc-root attachment, while the second uses the so-called fictitious anode method. Modeling results show that the highest temperature and maximum axial-velocity at the plasmatorch exit are ～15000 K and ～1100 m/s, respectively, for the case with arc current of 160 A and argon flow rate of 1.95×10{sup}(-4)kg/s.

Physical Modeling of Current-Induced Seabed Scour around a Vibrating Submarine Pipeline

Most of the existing researches either focus on vortex-induced-vibrations (VIV) of a pipeline near a rigid boundary, or on seabed scour around a fixed pipeline. In the fields, pipeline vibration and seabed scour are actually always coupled. Based on the similarity analysis, a series of tests were conducted with a hydro-elastic facility to investigate the influence of pipe vibration on the local scour and the effects of scour process on the pipeline dynamic responses. Experimental results indicate that, there exist two phases in the process of sand scouring around the pipeline with small embedment, i.e. Phase I: scour beneath pipe without VIV, and Phase II: scour with VIV of pipe. It is also found that the gap-to-diameter ratio (e/D) has much effect upon the scour depth for the fixed pipes. For a given value of e/D, the vibrating pipes with close proximity to seabed may induce a deeper scour hole than the fixed ones. Within the examined gap-to-diameter ratio range (425 < e/D < 0.75), the influences of gap-to-diameter ratio on the maximum values of scour-depth for the case of vibrating pipes are not as much as those for the case of fixed pipes.

Modeling Study of Shrouding Gas Effects on a Laminar Argon Plasma Jet Impinging Upon a Flat Substrate in Air Surroundings

With the laminar plasma materials processing as the research background, modeling study is conducted concerning the effects of argon shroud on the characteristics of the laminar argon plasma jet impinging normally upon a flat substrate located in air surroundings. It is shown that adding shrouding gas is an effective method to reduce and control the entrainment of ambient air into the laminar plasma jet. The shrouding gas flow rate or velocity, the injection slot width and the stand-off distance of the substrate appreciably affect the air contents in the plasma near the substrate surface.

Modeling of Ammonothermal Growth of Gallium Nitride Single Crystals

Ammonothermal growth of GaN crystals with a retrograde solubility has been modeled and simulated here using fluid dynamics, thermodynamics and heat transfer models. The nutrient is considered as a porous media bed and the flow in the porous charge is simulated using the Darcy-Brinkman-Forchheimer model. The resulting governing equations are solved using the finite volume method. For the case of retrograde solubility, the charge is put above the baffle. The temperature difference between the dissolving zone and growth zone is found smaller than that applied on the sidewall of autoclave. The baffle opening has a strong effect on the nutrient transport and supersaturation of GaN species in the growth zone.