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The Viscosity of Solids

Description: Preface: This bulletin is a second contribution to the general investigation of the physical contents of rocks, the experiments concerning which follow a general plan devised by Mr. Clarence King.
Date: 1891
Creator: Barus, Carl
Partner: UNT Libraries Government Documents Department

Hypersonic Viscous Flow Over Slender Cones

Description: Note presenting viscous self-induced pressures on 3 degree semivertex angle cones measured over a free-stream Mach number range and viscous-interaction parameter range. Results regarding the experiment, comparison between theory and experiment, and hole-size effect are provided.
Date: September 1958
Creator: Talbot, Lawrence; Koga, Toyoki & Sherman, Pauline M.
Partner: UNT Libraries Government Documents Department

Frequency-dependent viscous flow in channels with fractal rough surfaces

Description: The viscous dynamic permeability of some fractal-like channels is studied. For our particular class of geometries, the ratio of the pore surface area-to-volume tends to {infinity} (but has a finite cutoff), and the universal scaling of the dynamic permeability, k({omega}), needs modification. We performed accurate numerical computations of k({omega}) for channels characterized by deterministic fractal wall surfaces, for a broad range of fractal dimensions. The pertinent scaling model for k({omega}) introduces explicitly the fractal dimension of the wall surface for a range of frequencies across the transition between viscous and inertia dominated regimes. The new model provides excellent agreement with our numerical simulations.
Date: May 1, 2010
Creator: Cortis, A. & Berryman, J.G.
Partner: UNT Libraries Government Documents Department

Deformation mechanisms in crystalline solids and Newtonian viscous behavior

Description: The three principal mechanisms of plastic flow in crystalline solids at elevated temperature are crystal slip, grain boundary sliding, and diffusional flow. All three mechanisms involve the diffusion of atoms as the rate-controlling process, either in the lattice or in the grain boundary. Under the correct conditions of microstructure, temperature, and stress, each mechanism can lead to Newtonian-viscous behavior. That is, the strain rate increases linearly with the applied stress. In the case of crystal slip, Newtonian-viscous behavior is observed at very � low stresses and, in pure metals, is known as Harper-Dom (H-D) creep. This Newtonian behavior can also be observed in anisotropic crystalline solids that are deformed under thermal cycling conditions. The dislocation density and the stacking fault energy are important structural factors that contribute to crystal slip-controlled Newtonian flow. In the case of grain boundary sliding, Newtonian-viscous behavior is observed in fine-grained, solid solution alloys under conditions where grain-boundary sliding is accommodated by dislocation glide controlled by the diffusion of solute atoms. In the case of diffusional creep, which is rigorously described by the Nabarro-Herring (N-H) theory, the creep rate is controlled by grain size and by the rate of atom diffusion in the lattice and in the grain boundary. Deformation mechanism maps describe the conditions of dislocation density, grain size, stress, and temperature under which each deformation process can be expected to be rate-controlling.
Date: November 4, 1999
Creator: Ruano, O A; Sherby, O D & Wadsworth, J
Partner: UNT Libraries Government Documents Department

Variable High Order Multiblock Overlapping Grid Methods for Mixed Steady and Unsteady Multiscale Viscous Flows

Description: Flows containing steady or nearly steady strong shocks in parts of the flow field, and unsteady turbulence with shocklets on other parts of the flow field are difficult to capture accurately and efficiently employing the same numerical scheme even under the multiblock grid or adaptive grid refinement framework. On one hand, sixth-order or higher shock-capturing methods are appropriate for unsteady turbulence with shocklets. On the other hand, lower order shock-capturing methods are more effective for strong steady shocks in terms of convergence. In order to minimize the shortcomings of low order and high order shock-capturing schemes for the subject flows, a multi-block overlapping grid with different orders of accuracy on different blocks is proposed. Test cases to illustrate the performance of the new solver are included.
Date: December 12, 2007
Creator: Sjogreen, B & Yee, H C
Partner: UNT Libraries Government Documents Department

Nanoscale manipulation of Ge nanowires by ion hammering

Description: Nanowires generated considerable interest as nanoscale interconnects and as active components of both electronic and electromechanical devices. However, in many cases, manipulation and modification of nanowires are required to realize their full potential. It is essential, for instance, to control the orientation and positioning of nanowires in some specific applications. This work demonstrates a simple method to reversibly control the shape and the orientation of Ge nanowires by using ion beams. Initially, crystalline nanowires were partially amorphized by 30 keY Ga+-implantation. After amorphization, viscous flow and plastic deformation occurred due to the ion hammering effect, causing the nanowires to bend toward the beam direction. The bending was reversed multiple times by ion-implanting the opposite side of the nanowires, resulting in straightening of the nanowires and subsequent bending in the opposite direction. This ion hammering effect demonstrates the detailed manipulation of nanoscale structures is possible through the use of ion irradiation.
Date: January 1, 2009
Creator: Picraux, Samuel T; Romano, Lucia; Rudawski, Nicholas G; Holzworth, Monta R; Jones, Kevin S & Choi, S G
Partner: UNT Libraries Government Documents Department

A 2-D Pore-Network Model of the Drying of Single-Component Liquids in Porous Media

Description: The drying of liquid-saturated porous media is typically approaching using macroscopic continuum models involving phenomenological coefficients. Insight on these coefficients can be obtained by a more fundamental study at the pore- and pore-network levels. In this report, a model based on pore-network representation of porous media that accounts for various process at the pore-scale is presented. These include mass transfer by advection and diffusion in the gas phase, viscous flow in liquid and gas phases and capillary effects at the gas-liquid menisci in the pore throats.
Date: January 20, 2000
Creator: Yortsos, Yanic C.; Yiotis, A. G.; Stubos, A. K. & Boundovis, A. G.
Partner: UNT Libraries Government Documents Department

Simulations of hydrodynamic interactions among immersed particles in stokes flow using a massively parallel computer

Description: In this paper, a massively parallel implementation of the boundary element method to study particle transport in Stokes flow is discussed. The numerical algorithm couples the quasistatic Stokes equations for the fluid with kinematic and equilibrium equations for the particles. The formation and assembly of the discretized boundary element equations is based on the torus-wrap mapping as opposed to the more traditional row- or column-wrap mappings. The equation set is solved using a block Jacobi iteration method. Results are shown for an example application problem, which requires solving a dense system of 6240 equations more than 1200 times.
Date: May 1, 1995
Creator: Ingber, M.S.; Womble, D.E. & Mondy, L.A.
Partner: UNT Libraries Government Documents Department

Retained gas sampler visualization guide

Description: In a series of experiments performed in Phase II of the retained gas sampler visualization task, the effect of sampler tip geometry on waste sampling process has been investigated. From flow visualizations, which were captured on video, it is clear that disturbances on the surrounding fluid and the fluid entering the sampler were reduced as the tip changed from a flat to a sharper truncated cone shape. It has been shown, throughout this report, that deformation and disturbance of the waste is dominated by shape of the sampler tip, which moves the stagnation point, and not by viscosity of the fluid or sampling rate.
Date: September 1, 1994
Creator: Shekarriz, A.
Partner: UNT Libraries Government Documents Department

Modeling Complex Biological Flows in Multi-Scale Systems using the APDEC Framework

Description: We have developed advanced numerical algorithms to model biological fluids in multiscale flow environments using the software framework developed under the SciDAC APDEC ISIC. The foundation of our computational effort is an approach for modeling DNA-laden fluids as ''bead-rod'' polymers whose dynamics are fully coupled to an incompressible viscous solvent. The method is capable of modeling short range forces and interactions between particles using soft potentials and rigid constraints. Our methods are based on higher-order finite difference methods in complex geometry with adaptivity, leveraging algorithms and solvers in the APDEC Framework. Our Cartesian grid embedded boundary approach to incompressible viscous flow in irregular geometries has also been interfaced to a fast and accurate level-sets method within the APDEC Framework for extracting surfaces from volume renderings of medical image data and used to simulate cardio-vascular and pulmonary flows in critical anatomies.
Date: June 24, 2006
Creator: Trebotich, D
Partner: UNT Libraries Government Documents Department

Nonstandard Analysis and Shock Wave Jump Conditions in a One-Dimensional Compressible Gas

Description: Nonstandard analysis is a relatively new area of mathematics in which infinitesimal numbers can be defined and manipulated rigorously like real numbers. This report presents a fairly comprehensive tutorial on nonstandard analysis for physicists and engineers with many examples applicable to generalized functions. To demonstrate the power of the subject, the problem of shock wave jump conditions is studied for a one-dimensional compressible gas. It is assumed that the shock thickness occurs on an infinitesimal interval and the jump functions in the thermodynamic and fluid dynamic parameters occur smoothly across this interval. To use conservations laws, smooth pre-distributions of the Dirac delta measure are applied whose supports are contained within the shock thickness. Furthermore, smooth pre-distributions of the Heaviside function are applied which vary from zero to one across the shock wave. It is shown that if the equations of motion are expressed in nonconservative form then the relationships between the jump functions for the flow parameters may be found unambiguously. The analysis yields the classical Rankine-Hugoniot jump conditions for an inviscid shock wave. Moreover, non-monotonic entropy jump conditions are obtained for both inviscid and viscous flows. The report shows that products of generalized functions may be defined consistently using nonstandard analysis; however, physically meaningful products of generalized functions must be determined from the physics of the problem and not the mathematical form of the governing equations.
Date: May 25, 2007
Creator: Roy S. Baty, F. Farassat, John A. Hargreaves
Partner: UNT Libraries Government Documents Department

Simulations of non-uniform embossing:the effect of asymmetric neighbor cavities on polymer flow during nanoimprint lithography.

Description: This paper presents continuum simulations of viscous polymer flow during nanoimprint lithography (NIL) for embossing tools having irregular spacings and sizes. Simulations varied non-uniform embossing tool geometry to distinguish geometric quantities governing cavity filling order, polymer peak deformation, and global mold filling times. A characteristic NIL velocity predicts cavity filling order. In general, small cavities fill more quickly than large cavities, while cavity spacing modulates polymer deformation mode. Individual cavity size, not total filling volume, dominates replication time, with large differences in individual cavity size resulting in non-uniform, squeeze flow filling. High density features can be modeled as a solid indenter in squeeze flow to accurately predict polymer flow and allow for optimization of wafer-scale replication. The present simulations make it possible to design imprint templates capable of distributing pressure evenly across the mold surface and facilitating symmetric polymer flow over large areas to prevent mold deformation and non-uniform residual layer thickness.
Date: August 1, 2007
Creator: Schunk, Peter Randall; King, William P. (Georgia Institute of Technology, Atlanta, GA); Sun, Amy Cha-Tien & Rowland, Harry D. (Georgia Institute of Technology, Atlanta, GA)
Partner: UNT Libraries Government Documents Department

A Cell-Centered Adaptive Projection Method for the IncompressibleNavier-Stokes Equations in Three Dimensions

Description: We present a method for computing incompressible viscousflows in three dimensions using block-structured local refinement in bothspace and time. This method uses a projection formulation based on acell-centered approximate projection, combined with the systematic use ofmultilevel elliptic solvers to compute increments in the solutiongenerated at boundaries between refinement levels due to refinement intime. We use an L_0-stable second-order semi-implicit scheme to evaluatethe viscous terms. Results are presentedto demonstrate the accuracy andeffectiveness of this approach.
Date: September 25, 2007
Creator: Martin, D.F.; Colella, P. & Graves, D.T.
Partner: UNT Libraries Government Documents Department

Interfacial Dynamics of Abelian Domains: Differential Geometric Methods

Description: The equation: ReF`(T,Z)ZF`(T,Z) = 1 for conformal maps f(t,z) is important in interfacial dynamics. We extend the results by Gustafsson on existence and uniqueness of solutions of this equation from the case when f(t,z) is a rational function of z to the case when the spatial derivative f`(t,z) is rational.
Date: December 1997
Creator: Owczarek, Robert M. & Makaruk, Hanna E.
Partner: UNT Libraries Government Documents Department

Melt fracture revisited

Description: In a previous paper the author and Demay advanced a model to explain the melt fracture instability observed when molten linear polymer melts are extruded in a capillary rheometer operating under the controlled condition that the inlet flow rate was held constant. The model postulated that the melts were a slightly compressible viscous fluid and allowed for slipping of the melt at the wall. The novel feature of that model was the use of an empirical switch law which governed the amount of wall slip. The model successfully accounted for the oscillatory behavior of the exit flow rate, typically referred to as the melt fracture instability, but did not simultaneously yield the fine scale spatial oscillations in the melt typically referred to as shark skin. In this note a new model is advanced which simultaneously explains the melt fracture instability and shark skin phenomena. The model postulates that the polymer is a slightly compressible linearly viscous fluid but assumes no slip boundary conditions at the capillary wall. In simple shear the shear stress {tau}and strain rate d are assumed to be related by d = F{tau} where F ranges between F{sub 2} and F{sub 1} > F{sub 2}. A strain rate dependent yield function is introduced and this function governs whether F evolves towards F{sub 2} or F{sub 1}. This model accounts for the empirical observation that at high shears polymers align and slide more easily than at low shears and explains both the melt fracture and shark skin phenomena.
Date: July 16, 2003
Creator: Greenberg, J. M.
Partner: UNT Libraries Government Documents Department

Parallel Simulation of Three-Dimensional Free Surface Fluid Flow Problems

Description: Simulation of viscous three-dimensional fluid flow typically involves a large number of unknowns. When free surfaces are included, the number of unknowns increases dramatically. Consequently, this class of problem is an obvious application of parallel high performance computing. We describe parallel computation of viscous, incompressible, free surface, Newtonian fluid flow problems that include dynamic contact fines. The Galerkin finite element method was used to discretize the fully-coupled governing conservation equations and a ''pseudo-solid'' mesh mapping approach was used to determine the shape of the free surface. In this approach, the finite element mesh is allowed to deform to satisfy quasi-static solid mechanics equations subject to geometric or kinematic constraints on the boundaries. As a result, nodal displacements must be included in the set of unknowns. Other issues discussed are the proper constraints appearing along the dynamic contact line in three dimensions. Issues affecting efficient parallel simulations include problem decomposition to equally distribute computational work among a SPMD computer and determination of robust, scalable preconditioners for the distributed matrix systems that must be solved. Solution continuation strategies important for serial simulations have an enhanced relevance in a parallel coquting environment due to the difficulty of solving large scale systems. Parallel computations will be demonstrated on an example taken from the coating flow industry: flow in the vicinity of a slot coater edge. This is a three dimensional free surface problem possessing a contact line that advances at the web speed in one region but transitions to static behavior in another region. As such, a significant fraction of the computational time is devoted to processing boundary data. Discussion focuses on parallel speed ups for fixed problem size, a class of problems of immediate practical importance.
Date: October 14, 1999
Partner: UNT Libraries Government Documents Department

Mathematical Modeling of Charged Liquid Droplets: Numerical Simulation and Stability Analysis

Description: The goal of this thesis is to study of the evolution of 3D electrically charged liquid droplets of fluid evolving under the influence of surface tension and electrostatic forces. In the first part of the thesis, an appropriate mathematical model of the problem is introduced and the linear stability analysis is developed by perturbing a sphere with spherical harmonics. In the second part, the numerical solution of the problem is described with the use of the boundary elements method (BEM) on an adaptive mesh of triangular elements. The numerical method is validated by comparison with exact solutions. Finally, various numerical results are presented. These include neck formation in droplets, the evolution of surfaces with holes, singularity formation on droplets with various symmetries and numerical evidence that oblate spheroids are unstable.
Date: May 2006
Creator: Vantzos, Orestis
Partner: UNT Libraries

Residual stresses in Mo/Si and Mo2C/Si multilayers

Description: The authors report a study of the residual stresses and residual stress relaxation in Mo/Si and Mo{sub 2}C/Si EUV multilayers. The multilayers were fabricated by magnetron sputter deposition, and stress measured using the substrate curvature laser scanning technique. It was found that Mo{sub 2}C/Si multilayers exhibit higher compressive stress than Mo/Si of comparable period and layer thickness ratio. the multilayers sputtered at 0.5 mT Ar pressure have higher compressive stress than those sputtered at 2 mT Ar pressure. The data indicate that the residual stresses in the multilayers are primarily determined by the Si layers. Annealing of the multilayers at a heating rate of 5 C/minute as well as at a fixed temperature (isothermal) results in a reduction of the compressive stresses. Near zero stress is achieved after annealing at 300 C. The time dependence of the residual stress decrease during isothermal annealing was found to fit best to a bimolecular viscous flow model of defect annihilation in the amorphous Si layers. The relationships between the effects of annealing on the multilayer microstructure and the observed stress reduction are discussed.
Date: April 1, 1999
Creator: Barbee, T W & Nguyen, T D
Partner: UNT Libraries Government Documents Department

GILA User's Manual

Description: GILA is a finite element code that has been developed specifically to attack the class of transient, incompressible, viscous, fluid dynamics problems that are predominant in the world that surrounds us. The purpose for this document is to provide sufficient information for an experienced analyst to use GILA in an effective way. The GILA User's Manual presents a technical outline of the governing equations for time-dependent incompressible flow, and the explicit and semi-implicit projection methods used in GILA to solve the equations. This manual also presents a brief overview of some of GILA's capabilities along with the keyword input syntax and sample problems.
Date: June 1, 2003
Partner: UNT Libraries Government Documents Department

Newtonian Flow in Bulk Amorphous Alloys

Description: Bulk amorphous alloys have many unique properties, e.g., superior strength and hardness, excellent corrosion resistance, reduced sliding friction and improved wear resistance, and easy formability in a viscous state. These properties, and particularly easy formability, are expected to lead to applications in the fields of near-net-shape fabrication of structural components. Whereas large tensile ductility has generally been observed in the supercooled liquid region in metallic glasses, the exact deformation mechanism, and in particular whether such alloys deform by Newtonian viscous flow, remains a controversial issue. In this paper, existing data are analyzed and an interpretation for the apparent controversy is offered. In addition, new results obtained from an amorphous alloy (composition: Zr-10Al-5TI-17.9Cu-14.6Ni, in at. %) are presented. Structural evolution during plastic deformation is particularly characterized. It is suggested that the appearance of non-Newtonian behavior is a result of the concurrent crystallization of the amorphous structure during deformation.
Date: September 27, 2000
Creator: Wadsworth, J. & Nieh, T. G.
Partner: UNT Libraries Government Documents Department

Acoustic Wave Equations for a Linear Viscous Fluid and An Ideal Fluid

Description: The mathematical description of acoustic wave propagation within a time- and space-varying, and moving, linear viscous fluid is formulated as a system of coupled linear equations. This system is rigorously developed from fundamental principles of continuum mechanics (conservation of mass, balance of linear and angular momentum, balance of entropy) and various constitutive relations (for stress, entropy production, and entropy conduction) by linearizing all expressions with respect to the small-amplitude acoustic wavefield variables. A significant simplification arises if the fluid medium is neither viscous nor heat conducting (i.e., an ideal fluid). In this case the mathematical system can be reduced to a set of five, coupled, first-order partial differential equations. Coefficients in the systems depend on various mechanical and thermodynamic properties of the ambient medium that supports acoustic wave propagation. These material properties cannot all be arbitrarily specified, but must satisfy another system of nonlinear expressions characterizing the dynamic behavior of the background medium. Dramatic simplifications in both systems occur if the ambient medium is simultaneously adiabatic and stationary.
Date: July 1, 2002
Partner: UNT Libraries Government Documents Department

An analysis of lift forces on aerosols in a wall bounded turbulent shear flow

Description: This paper describes work that will lead to a better understanding of the role of lift forces in the deposition of aerosols on the walls bounding a turbulent shear flow. After providing some background information about aerosol trajectories that has been obtained from computer simulations, new results for the lift force in the relevant parameter ranges are presented.
Date: December 31, 1992
Creator: Cherukat, P. & McLaughlin, J. B.
Partner: UNT Libraries Government Documents Department