1,025 Matching Results

Search Results

Advanced search parameters have been applied.

Multidimensional first and second order symmetric strang splitting for hyperbolic systems

Description: We propose an algebraic basis for symmetric Strang splitting for first and second order accurate schemes for hyperbolic systems in N dimensions. Examples are given for two and three dimensions. Optimal stability is shown for symmetric systems. Lack of strong stability is shown for a non-symmetric example. Some numerical examples are presented for some Euler-like constant coefficient problems.
Date: January 1, 2008
Creator: Kucharik, Milan & Wendroff, Burton
Partner: UNT Libraries Government Documents Department

A 3-axis force balanced accelerometer using a single proof-mass

Description: This paper presents a new method for wideband force balancing a proof-mass in multiple axes simultaneously. Capacitive position sense and force feedback are accomplished using the same air-gap capacitors through time multiplexing. Proof of concept is experimentally demonstrated with a single-mass monolithic surface micromachined 3-axis accelerometer.
Date: April 1997
Creator: Lemkin, M.A.; Boser, B.E.; Auslander, D. & Smith, J.
Partner: UNT Libraries Government Documents Department

Application of Integrated Reservoir Management and Reservoir Characterization to Optimize Infill Drilling

Description: Infill drilling if wells on a uniform spacing without regard to reservoir performance and characterization foes not optimize reservoir development because it fails to account for the complex nature of reservoir heterogeneities present in many low permeability reservoirs, and carbonate reservoirs in particular. New and emerging technologies, such as geostatistical modeling, rigorous decline curve analysis, reservoir rock typing, and special core analysis can be used to develop a 3-D simulation model for prediction of infill locations.
Date: January 1, 1998
Partner: UNT Libraries Government Documents Department

The interaction of laser driven shock waves with a spherical density perturbation

Description: Strong shock waves produced by illumination of a CH target by laser produced x-rays were driven through a copper sphere. The motion and deformation of the sphere were measured using radiographs generated by backlighting the sphere with a large area backlighter. The sphere became non-spherical after the passage of the shock, having a complicated down-stream structure. This was an instability-induced structure that was predicted by calculations. The experiment is a convenient laboratory model of the complicated interactions occurring in much larger systems such as in astrophysics in the interaction of shocks formed in the interstellar medium with various types of clouds. In particular, the experiment is a useful tool for checking the computational ability of the new generation ASCI computers, as it requires three-dimensional modeling. This experiment has shown that three dimensional calculations seem to be necessary to describe major features observed in the experiment. Any attempt to explain hydrodynamic behavior with similar instabilities must take into account these three dimensional effects.
Date: January 8, 1999
Creator: Perry, T S; Klein, R I; Budil, K S & Bach, D R
Partner: UNT Libraries Government Documents Department

Exact de Rham Sequences of Spaces Defined on Macro-elements in Two and Three Spatial Dimensions

Description: This paper proposes new finite element spaces that can be constructed for agglomerates of standard elements that have certain regular structure. The main requirement is that the agglomerates share faces that have closed boundaries composed of 1-d edges. The spaces resulting from the agglomerated elements are subspaces of the original de Rham sequence of H{sup 1}-conforming, H(curl) conforming, H(div) conforming and piecewise constant spaces associated with an unstructured 'fine' mesh. The procedure can be recursively applied so that a sequence of nested de Rham complexes can be constructed. As an illustration we generate coarser spaces from the sequence corresponding to the lowest order Nedelec spaces, lowest order Raviart-Thomas spaces, and for piecewise linear H{sup 1}-conforming spaces, all in three-dimensions. The resulting V-cycle multigrid methods used in preconditioned conjugate gradient iterations appear to perform similar to those of the geometrically refined case.
Date: July 23, 2007
Creator: Pasciak, J. & Vassilevski, P.
Partner: UNT Libraries Government Documents Department

A new paradigm for 3D collisionless magnetic reconnection.

Description: A new paradigm is emerging for 3D magnetic reconnection where the interaction of reconnection processes with current aligned instabilities plays an important role. According to the new paradigm, the initial equilibrium is rendered unstable by current aligned instabilities (lower-hybrid drift instability first, drift-kink instability later) and the non-uniform development of kinking modes leads to a compression of magnetic field lines in certain locations and a rarefaction in others. The areas where the flow is compressional are subjected to a driven reconnection process on the time scale of the driving mechanism (the kink mode). In the present paper we illustrate this series of event with a selection of simulation results.
Date: January 1, 2002
Creator: Lapenta, G. M. (Giovanni M.)
Partner: UNT Libraries Government Documents Department

Topological excitations and second order transitions in 3D O(N) models

Description: I discuss several examples of critical phenomena in O(N) models where topological excitations play an important role at criticality. I focus particular attention on the O(2) model in 3D, where recent measurements of the vortex string length distribution in equilibrium suggest the existence of a quantitative picture of the critical behavior in terms of defects. The compatibility of this perspective with renormalization group predictions is examined.
Date: January 1, 2001
Creator: Bettencourt, L. (Luis M. A.)
Partner: UNT Libraries Government Documents Department

A fully implicit method for 3D quasi-steady state magnetic advection-diffusion.

Description: We describe the implementation of a prototype fully implicit method for solving three-dimensional quasi-steady state magnetic advection-diffusion problems. This method allows us to solve the magnetic advection diffusion equations in an Eulerian frame with a fixed, user-prescribed velocity field. We have verified the correctness of method and implementation on two standard verification problems, the Solberg-White magnetic shear problem and the Perry-Jones-White rotating cylinder problem.
Date: September 1, 2009
Creator: Siefert, Christopher & Robinson, Allen Conrad
Partner: UNT Libraries Government Documents Department

Dislocation emission from a three-dimensional crack -- A large-scale molecular dynamics study

Description: A series of massively parallel molecular dynamics simulations with up to 35 million atoms is performed to investigate dislocation emission from a three-dimensional crack. The authors observe dislocation loops emitted from the crack front--the first time this has been seen in computer simulations. The sequence of dislocation emission in the process of crack blunting process strongly depends on the crystallographic orientation of the crack front and differs strikingly from anything previously conjectured. This finding is essential to establish a precise dislocation emission criterion (i.e., intrinsic ductility criterion). They also find that boundary conditions and interatomic force laws have a significant effect on jogging or blunting dislocation emission modes.
Date: December 31, 1996
Creator: Zhou, S.J.; Beazley, D.M.; Lomdahl, P.S.; Voter, A.F. & Holian, B.L.
Partner: UNT Libraries Government Documents Department

Automatic differentiation as a tool for sensitivity analysis of a convective storm in a 3-D cloud model

Description: The ADIFOR automatic differentiation tool is applied to a 3-D storm-scale meteorological model to generate a sensitivity-enhanced code capable of providing derivatives of all model output variables and related diagnostic (derived) parameters as a function of specified control parameters. The tangent linear approximation, applied to a deep convective storm by the first of its kind using a full-physics compressible model, is valid up to 50 min for a 1% water vapor perturbations. The result is very encouraging considering the highly nonlinear and discontinuous properties of solutions. The ADIFOR-generated code has provided valuable sensitivity information on storm dynamics. Especially, it is very efficient and useful for investigating how a perturbation inserted at earlier time propagates through the model variables at later times. However, it is computationally very expensive to be applied to the variational data assimilation, especially for 3-D meteorological models, which potentially have a large number of input variables.
Date: October 1996
Creator: Park, S. K.; Droegemeier, K. K. & Bischof, C. H.
Partner: UNT Libraries Government Documents Department

Climate signal and weather noise

Description: A signal of small climate change in either the real atmosphere or numerical simulation of it tends to be obscured by chaotic weather fluctuations. Time-lagged covariances of such weather processes are used to estimate the sampling errors of time average estimates of climate parameters. Climate sensitivity to changing external influences may also be estimated using the fluctuation dissipation relation of statistical mechanics. Answers to many climate questions could be provided by a realistic stochastic model of weather and climate.
Date: April 1, 1995
Creator: Leith, C.E.
Partner: UNT Libraries Government Documents Department

A Method for Connecting Dissimilar Finite Element Meshes in Three Dimensions

Description: A method is presented for connecting dissimilar finite element meshes in three dimensions. The method combines the concept of master and slave surfaces with the uniform strain approach for surface, corrections finite elements- By modifyhg the are made to element formulations boundaries of elements on the slave such that first-order patch tests are passed. The method can be used to connect meshes which use different element types. In addition, master and slave surfaces can be designated independently of relative mesh resolutions. Example problems in three-dimensional linear elasticity are presented.
Date: November 12, 1998
Creator: Dohrmann, C.R.; Heinstein, M.W. & Key, S.W.
Partner: UNT Libraries Government Documents Department

Acoustic 3D imaging of dental structures

Description: Our goals for the first year of this three dimensional electodynamic imaging project was to determine how to combine flexible, individual addressable; preprocessing of array source signals; spectral extrapolation or received signals; acoustic tomography codes; and acoustic propagation modeling code. We investigated flexible, individually addressable acoustic array material to find the best match in power, sensitivity and cost and settled on PVDF sheet arrays and 3-1 composite material.
Date: February 1, 1997
Creator: Lewis, D.K.; Hume, W.R. & Douglass, G.D.
Partner: UNT Libraries Government Documents Department

Behavior of the finite-sized, three-dimensional, Ising model near the critical point

Description: Recent work showing the validity of hyperscaling involved results for finite size systems very near the critical point. The authors study this problem in more detail, and give estimators related to the Binder cumulant ratio which seem to approach the critical temperature from above and below. Based on these results, they estimate that the renormalized coupling constant, computed for the temperature fixed at the critical temperature and then taking the large system-size limit, is about 4.9 {+-} 0.1, and give a likely lower bound for it of 4.5. These estimates are argued to suffice to show the validity of hyperscaling.
Date: May 1, 1996
Creator: Baker, G.A. Jr. & Gupta, R.
Partner: UNT Libraries Government Documents Department

Three-dimensional high-resolution simulations of compressible rayleigh-taylor instability and turbuelnt mixing

Description: Preliminary results of three-dimensional simulations of compressible Rayleigh-Taylor instabilities and turbulent mixing in an ideal gas using the piecewise-parabolic method (PPM) with and without molecular dissipation terms are presented. Simulations with spatial resolutions up to 512 were performed. Two types of convergence studies are presented. The first investigates the Reynolds numbers for which the simulations with molecular dissipation are converged with respect to spatial resolution, and the second investigates whether PPM simulations at different spatial resolutions reproduce fully-resolved PPM simulations with molecular dissipation. Finally, statistical analyses of the data are discussed, including spectra and horizontally-averaged terms in the kinetic energy and enstrophy density evolution equations. The application of this statistical data to the development and testing of subgrid-scale models appropriate for compressible Rayleigh-Taylor instability-induced turbulent mixing is discussed.
Date: June 12, 1997
Creator: Schilling, O.; Cohen, R.H.; Dannevik, W.P.; Dimits, A.M.; Eliason, D.E.; Mirin, A.A. et al.
Partner: UNT Libraries Government Documents Department

On Boundary Misorientation Distribution Functions and How to Incorporate them into 3D Models of Microstructural Evolution

Description: The fundamental difficulties incorporating experimentally obtained-boundary disorientation distributions (BMD) into 3D microstructural models are discussed. An algorithm is described which overcomes these difficulties. The boundary misorientations are treated as a statistical ensemble which is evolved toward the desired BMD using a Monte Carlo method. The application of this algorithm to a number complex arbitrary BMDs shows that the approach is effective for both conserved and non-conserved textures. The algorithm is successfully used to create the BMDs observed in deformation microstructure containing both incidental dislocation boundaries (IDBs) and geometrically necessary boundaries (GNBs).
Date: December 23, 1998
Creator: Godfrey, A.W.; Holm, E.A.; Hughes, D.A. & Miodownik, M.
Partner: UNT Libraries Government Documents Department

Models of the solvent-accessible surface of biopolymers

Description: Many biopolymers such as proteins, DNA, and RNA have been studied because they have important biomedical roles and may be good targets for therapeutic action in treating diseases. This report describes how plastic models of the solvent-accessible surface of biopolymers were made. Computer files containing sets of triangles were calculated, then used on a stereolithography machine to make the models. Small (2 in.) models were made to test whether the computer calculations were done correctly. Also, files of the type (.stl) required by any ISO 9001 rapid prototyping machine were written onto a CD-ROM for distribution to American companies.
Date: September 1, 1996
Creator: Smith, R.E.
Partner: UNT Libraries Government Documents Department

Three-dimensional elastic lidar winds

Description: Maximum cross-correlation techniques have been used with satellite data to estimate winds and sea surface velocities for several years. Los Alamos National Laboratory (LANL) is currently using a variation of the basic maximum cross-correlation technique, coupled with a deterministic application of a vector median filter, to measure transverse winds as a function of range and altitude from incoherent elastic backscatter lidar data taken throughout large volumes within the atmospheric boundary layer. Hourly representations of three- dimensional wind fields, derived from elastic lidar data taken during an air-quality study performed in a region of complex terrain near Sunland Park, New Mexico, are presented and compared with results from an Environmental Protection Agency (EPA) approved laser doppler velocimeter. The wind fields showed persistent large scale eddies as well as general terrain following winds in the Rio Grande valley.
Date: July 1, 1996
Creator: Buttler, W.T.
Partner: UNT Libraries Government Documents Department

Extension to 3-D of the low-frequency electromagnetic plasma simulation models, LDRD Final Report 95-ERD-036

Description: Low-frequency electromagnetic simulation models have a wide range of industrial applications. We have built several models, differentiated by slightly different physics approximations or computational solution methods, that have proven quite useful in a variety of applications. Our models been used to investigate beam plasma interactions in ICF targets, antenna plasma coupling in plasma processing, and magnetic implosion drive in Z-pinch pulsed power generators. The common feature of these models is that they retain inductive effects but implicitly ignore computationally intensive, fully electromagnetic effects. However, the preponderance of our work has been limited to only two dimensions. We have made significant progress modeling low-frequency electromagnetic physics with a new model in 2-D that is now capable of modeling antenna structures in 3-D. Although LLNL`s interest in plasma processing has diminished, we have certainly added to LLNL`s capabilities. Interestingly, we have already found another application, the magnetic behavior of read/write heads in the magnetic storage industry, that can make use of many of the computational methods described here, rewarding us again for maintaining a strong core competency in low-frequency EM plasmas.
Date: February 3, 1997
Creator: Hewett, D.W.; DiPeso, G.; Gibbons, M; Lambert, M. & Tung, L.S.
Partner: UNT Libraries Government Documents Department

Self-consistent 3D simulations of longitudinal halo in rf -linacs

Description: In order to prevent activation of the beam pipe walls and components of a high power ion accelera- tor: beam loss must be minimized. Here we present self-consistent, 3D particle-in-cell simulations of longi- tudinally mismatched beams including the effects of rf non-linearities using parameters based on the Acceler- ator Production of Tritium linac design. In particular, we explore the evolution of the longitudinal halo distri- bution, i.e., the distribution of particles in longitudinal phase space with oscillation amplitudes significantly larger than amplitudes of particles in the main body or ''core'' of the beam. When a particle reaches a suf- ficiently large amplitude longitudinally it can he lost from the rf bucket and consequently loses synchro- nism with thr rf wave. Such particles will lose energy and so be poorly matched to the transverse focusing field and consequently can be lost transversely. We compare the present simulations in which all particles contribute self-consistently to the self-field to predic- tions of a core/test particle model in which the core distribution has uniformly distributed charge and does not evolve self-consistently. Effects of self-consistent, non-linear space-charge forces, non-linear rf focusing on envelope mismatch induced beam halo are explored through comparisons of both models.
Date: August 19, 1998
Creator: Barnard, J J; Lund, S M & Ryne, R D
Partner: UNT Libraries Government Documents Department

Three-dimensional high-resolution simulations of Rayleigh-Taylor instability and turbulent mixing

Description: Preliminary results of three-dimensional simulations of compressible Rayleigh-Taylor instability and turbulent mixing in an ideal gas using the piecewise-parabolic method (PPM) (with and without molecular dissipation terms) are presented. Simulations with spatial resolutions up to 512{sup 3} were performed. Two types of convergence studies are presented. Statistical analyses of the data are discussed, include: 1: spectra, and; 2) horizontally-averaged terms in the kinetic energy and onstrophy density evolution equations. The application of this statistical data to the development and testing of subgrid-scale models appropriate for compressible Rayleigh-Taylor instability-induced turbulent mixing is discussed.
Date: June 1, 1997
Creator: Schilling, O.; Cohen, R.H.; Dannevik, W.P.; Dimits, A.M.; Eliason, D.E.; Mirin, D.H. et al.
Partner: UNT Libraries Government Documents Department

The impact of recent model improvements on GISS GCM predictions of climate change. Final technical report, September 15, 1992--September 14, 1994

Description: The response of the 8 x 10{degree} horizontal resolution version of Model 2 to the forcing of globally observed SST (1980--1986) was evaluated. The simulations showed a realistic interannual variability of interhemispheric gradients of layer mean temperatures in response to observed SST gradients, but modeled near-surface winds over the Atlantic Ocean were much weaker than observed, a symptom of the Model 2 planetary boundary layer (PBL). In addition, the interannual variability of peak-season rainfall rates over Northeast Brazil (Nordeste) from the experiment was considerably smaller than the observed, although the observed negative association between seasonal Nordeste rainfall and interhemispheric Atlantic SST differences was weakly present. Preliminary experiments at 4 x 5{degree} resolution incorporating two of the new model parameterizations show more variability of the simulated Nordeste rainfall in response to the SST forcing, but only slight improvement in the correlation with observations.
Date: December 31, 1994
Creator: Druyan, L.M.
Partner: UNT Libraries Government Documents Department

Spiraling Edge: Fast Surface Reconstruction from Partially Organized Sample Points

Description: Many applications produce three-dimensional points that must be further processed to generate a surface. Surface reconstruction algorithms that start with a set of unorganized points are extremely time-consuming. Often, however, points are generated such that there is additional information available to the reconstruction algorithm. We present a specialized algorithm for surface reconstruction that is three orders of magnitude faster than algorithms for the general case. In addition to sample point locations, our algorithm starts with normal information and knowledge of each point's neighbors. Our algorithm produces a localized approximation to the surface by creating a star-shaped triangulation between a point and a subset of its nearest neighbors. This surface patch is extended by locally triangulating each of the points along the edge of the patch. As each edge point is triangulated, it is removed from the edge and new edge points along the patch's edge are inserted in its place. The updated edge spirals out over the surface until the edge encounters a surface boundary and stops growing in that direction, or until the edge reduces to a small hole that fills itself in.
Date: January 6, 1999
Creator: Angel, E. & Crossno, P.
Partner: UNT Libraries Government Documents Department