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GOMA - A full-Newton finite element program for free and moving boundary problems with coupled fluid/solid momentum, energy, mass, and chemical species transport: User`s guide

Description: GOMA is a two- and three-dimensional finite element program which excels in analyses of manufacturing processes, particularly those involving free or moving interfaces. Specifically, the full-Newton-coupled heat, mass, momentum, and pseudo-solid mesh motion algorithm makes GOMA ideally suited for simulating processes in which the bulk fluid transport is closely coupled to the interfacial physics. Examples include, but are not limited to, coating and polymer processing flows, soldering, crystal growth, and solid-network or solution film drying. The code is based on the premise that any boundary can be (1) moving or free, with an apriori unknown position dictated by the distinguishing physics, (2) fixed, according to a global analytical representation, or (3) moving in time and space under user-prescribed kinematics. The goal is to enable the user to predict boundary position or motion simultaneously with the physics of the problem being analyzed and to pursue geometrical design studies and fluid-structure interaction problems. The moving mesh algorithm treats the entire domain as a computational Lagrangian solid that deforms subject to the physical principles which dictate boundary position. As an added benefit, the same Lagrangian solid mechanics can be exploited to solve multi-field problems for which the solid motion and stresses interact with other transport phenomena, either within the same material phase (e.g. shrinking coating) or in neighboring material phases (e.g. flexible blade coating). Thus, analyses of many fluid-structure interaction problems and deformable porous media problems are accessible. This document serves as a user`s guide and reference for GOMA and provides a brief overview of GOMA`s capabilities, theoretical background, and classes of problems for which it is targeted.
Date: January 1, 1996
Creator: Schunk, P.R.; Sackinger, P.A. & Rao, R.R.
Partner: UNT Libraries Government Documents Department

Finite element modeling of evaporation and condensation during sol-gel film and fiber formation

Description: Free surfaces, multicomponent phase change, volume expansion and compression, and surface tension gradients make for challenging application of the finite element method to sol-gel (ceramic) film and fiber formation. The microstructure of the final product is largely controlled by the competition between the drying, curing, and underlying fluid mechanics of formation. Sol-gel materials are peculiar because they often contain more than one solvent, each solvent differing in volatility and surface tension. Hence, nonuniform evaporation can produce surface tension gradients that dramatically change the meniscus shape. These processes are complicated further by a volume change that accompanies evaporation and condensation, making for shock-like discontinuities in concentration and velocity at the free surface. Computer-aided predictions of film formation by dip coating and of fiber spinning (see Figure 1) are made for alcohol-water mixtures with one non-volatile species. The Navier-Stokes system is augmented with two convective-diffusion equations to track the concentration of alcohol and water, and an energy equation to monitor temperature changes. The equations are solved in both phases by discretizing them first with the Galerkin/finite element method. The resulting non-linear algebraic equation set is solved with Newton`s method. The subdomaining technique is based on elliptic grid generation and is designed to parameterize the moving meniscus. Special treatment of the functional representations of velocity and concentration within the elements lining the free surface are made to accommodate the volume change that accompanies mass exchange between phases.
Date: July 1, 1993
Creator: Schunk, P. R.; Hurd, A. J.; Brinker, C. J. & Rao, R. R.
Partner: UNT Libraries Government Documents Department

A Finite Element Method for Free-Surface Flows of Incompressible Fluids in Three Dimensions, Part II: Dynamic Wetting Lines

Description: To date, few researchers have solved three-dimensional free-surface problems with dynamic wetting lines. This paper extends the free-surface finite element method described in a companion paper [Cairncross, R.A., P.R. Schunk, T.A. Baer, P.A. Sackinger, R.R. Rao, "A finite element method for free surface flows of incompressible fluid in three dimensions, Part I: Boundary-Fitted mesh motion.", to be published (1998)] to handle dynamic wetting. A generalization of the technique used in two dimensional modeling to circumvent double-valued velocities at the wetting line, the so-called kinematic paradox, is presented for a wetting line in three dimensions. This approach requires the fluid velocity normal to the contact line to be zero, the fluid velocity tangent to the contact line to be equal to the tangential component of web velocity, and the fluid velocity into the web to be zero. In addition, slip is allowed in a narrow strip along the substrate surface near the dynamic contact line. For realistic wetting-line motion, a contact angle which varies with wetting speed is required because contact lines in three dimensions typically advance or recede a different rates depending upon location and/or have both advancing and receding portions. The theory is applied to capillary rise of static fluid in a corner, the initial motion of a Newtonian droplet down an inclined plane, and extrusion of a Newtonian fluid from a nozzle onto a moving substrate. The extrusion results are compared to experimental visualization. Subject Categories
Date: January 29, 1999
Creator: Baer, T.A.; Cairncross, R.A.; Rao, R.R.; Sackinger, P.A. & Schunk, P.R.
Partner: UNT Libraries Government Documents Department

Treatment of uncertainty in low-level waste performance assessment

Description: Uncertainties arise from a number of different sources in low-level waste performance assessment. In this paper the types of uncertainty are reviewed, and existing methods for quantifying and reducing each type of uncertainty are discussed. These approaches are examined in the context of the current low-level radioactive waste regulatory performance objectives, which are deterministic. The types of uncertainty discussed in this paper are model uncertainty, uncertainty about future conditions, and parameter uncertainty. The advantages and disadvantages of available methods for addressing uncertainty in low-level waste performance assessment are presented. 25 refs.
Date: January 1, 1991
Creator: Kozak, M.W.; Olague, N.E.; Gallegos, D.P. & Rao, R.R.
Partner: UNT Libraries Government Documents Department