| Finite Deformations and Internal Forces in Elastic-Plastic Crystals: Interpretations From Nonlinear Elasticity and Anharmonic Lattice Statics |
Sep-2009 |
22 pages |
| Authors:
J D Clayton; D J Bammann; ARMY RESEARCH LAB ABERDEEN PROVING GROUND MD
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 | Large deformation kinematics and internal forces arising from defects in crystalline solids are addressed by a nonlinear kinematic description and multiscale averaging concepts. An element of crystalline material with spatially uniform properties and containing defects such as dislocation lines and loops is considered. The average deformation gradient for this element is decomposed multiplicatively into terms accounting for effects of dislocation flux, recoverable elastic stretch and rotation, and residual elastic deformation ... |
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| Least-Squares Finite Element Formulation for Fluid-Structure Interaction |
Mar-2009 |
276 pages |
| Authors:
Cody C Rasmussen; AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH GRADUATE SCHOOL OF ENGINEERING AND MANAGEMENT
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| Fluid-structure interaction problems prove difficult due to the coupling between fluid and solid behavior. Typically, different theoretical formulations and numerical methods are used to solve fluid and structural problems separately. The least-squares finite element method is capable of accurately solving both fluid and structural problems. This capability allows for a simultaneously coupled fluid structure interaction formulation using a single variational approach to solve complex and nonlinear aeroelasticity problems. The least-squares ... |
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| A Model-Coupling Framework for Nearshore Waves, Currents, Sediment Transport, and Seabed Morphology |
Jan-2009 |
16 pages |
| Authors:
H S Tang; T R Keen; R Khanbilvardi; NAVAL RESEARCH LAB STENNIS SPACE CENTER MS OCEANOGRAPHY DIV
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| This paper presents a framework for synchronously coupling wave, current, sediment transport, and seabed morphology for the accurate simulation of multi-physics coastal ocean processes. The governing equations, which represent models that are commonly adopted in practical simulations, are discretized using finite-difference methods. The resulting system is validated against analytical solutions. In order to test the performance of the proposed framework and the numerical methods, dam-break flow over a mobile-bed and ... |
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| Wave Propagation from Complex 3D Sources Using the Representation Theorem |
30-Sep-2008 |
11 pages |
| Authors:
Heming Xu; Jeffry L Stevens; SCIENCE APPLICATIONS INTERNATIONAL CORP SAN DIEGO CA
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| In spite of extensive prior research on the generation of seismic waves by underground nuclear explosions, it is still not possible to provide a complete explanation for the observed wavefields, particularly at regional distances. Spherically symmetric explosion models embedded in layered elastic media effectively model the P phases generated by explosions and the major characteristics of some reflected and transmitted phases. Nonlinear axisymmetric finite difference calculations of explosions, including gravity ... |
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| Refined Local and Regional Seismic Velocity and Attenuation Models from Finite-Frequency Waveforms |
30-Sep-2008 |
11 pages |
| Authors:
Wei Zhang; Xiaoping Yang; Yang Shen; Li Zhao; SCIENCE APPLICATIONS INTERNATIONAL CORP SAN DIEGO CA
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| In seismic tomography, the reference or starting models are commonly one-dimensional (1D) and the structural sensitivity kernels of seismic data are calculated without considering the finiteness of seismic waves in both time and frequency domains. These simplifications result in a theoretical limit, in addition to that from the data coverage, on the structural resolution in tomography inversions. In small-scale (such as the crustal) structural imaging, however, a higher resolution is ... |
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| Analyses and Simulation of 3D Scattering Due to Heterogeneous Crustal Structure and Surface Topography on Regional Phases, Magnitude Discrimination |
30-Sep-2008 |
13 pages |
| Authors:
Arban Pitarka; Don V Helmberger; Sidao Ni; URS GROUP INC GAITHERSBURG MD
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| The main purpose of this study is the understanding of scattering and its effects through step-by-step numerical experiments and waveform modeling, with the goal of providing useful insights into ongoing research for the development of simple empirical models of scattering that can be used in reducing the scatter in measures of Lg and coda wave magnitude and for discrimination purposes as well. We are performing anelastic 3D finite-difference simulations of ... |
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| Nonlinear Dynamic Response Optimization Using the Equivalent Static Loads for a Joined-Wing |
01-Sep-2008 |
49 pages |
| Authors:
Gyung-Jin Park; HANYANG UNIV GYEONGGI-DO (SOUTH KOREA) DEPT OF MECHANICAL ENGINEERING
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| The joined-wing airplane proposed by Wolkovich in 1986 is defined as an airplane that incorporates tandem wings arranged to form diamond shapes in both top and front views. The joined-wing can lead to increased aerodynamic performances as well as reduction of the structural weight. However, the joined-wing has high geometric nonlinearity under the gust load. The gust load acts as a dynamic load. In previous researches, linear dynamic response optimization ... |
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| Holographically Fabricated Photonic Crystals with Large Reflectance |
16-Jul-2008 |
5 pages |
| Authors:
Y C Chen; Geddes; J B III; J T Lee; P V Braun; P Wiltzius; ILLINOIS UNIV AT URBANA-CHAMAPIGN
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| We report reflection and transmission spectra from three-dimensional polymer photonic crystals fabricated by holographic lithography. The measured peak reflectance matches that predicted by both a finite-difference time-domain method a simple transfer matrix theory and is 70%, significantly higher than previous reports of 30% reflectance. |
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| High Order Accuracy Methods for Supersonic Reactive Flows |
25-Jun-2008 |
|
| Authors:
David Gottlieb; Wai-Sun Don; BROWN UNIV PROVIDENCE RI DIV OF APPLIED MATHEMATICS
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 | A multi-domain spectral method with stable and conservative penalty interface conditions for the numerical simulation of supersonic reactive recessed cavity flows with inhomogeneous grid is developed. The high order hybrid Spectral-WENO finite difference method under multi-domain framework is also introduced for the numerical solution of two dimensional nonlinear hyperbolic conservation laws in a Cartesian physical domain. A different approach in attempting to get more meaningful resultss is to model statistically ... |
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| Development of Surface Wave Dispersion and Attenuation Maps and Improved Methods for Measuring Surface Waves |
30-May-2008 |
65 pages |
| Authors:
Heming Xu; Jeffry L Stevens; G E Baker; Jeffrey W Given; SCIENCE APPLICATIONS INTERNATIONAL CORP SAN DIEGO CA
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| The objective of this project is to optimize surface wave measurements, particularly at regional and local distances, and over the high frequency period band of 8-15 seconds. There are three main parts to this study: 1) We collect and then invert Eurasian surface wave amplitude data for attenuation and Q structure; 2) we develop amplitude corrections using the Born approximation and then compare them with observations and with the results ... |
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| Modeling of Flow about Pitching and Plunging Airfoil Using High-Order Schemes |
13 MAR 2008 |
39 pages |
| Authors:
A. Povitsky; H. Gopalan; AKRON UNIV OH
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| A high-order non-uniform compact finite-difference algorithm with numerical filtering and low storage Runga-Kutta scheme is developed to perform numerical simulations on orthogonal grids generated about plunging and pitching airfoils. The grids, which move with the pitching and plunging airfoil, are generated using "Streamfunction as a coordinate approach" (SFC). SFC is widely used in combination with lower-order schemes in Computational Fluid Dynamics. The straightforward implementation of SFC create rather coarse grid ... |
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| Numerical Study of Active Flow Control for a Transitional Highly-Loaded Low-Pressure Turbine |
FEB 2008 |
45 pages |
| Authors:
Donald P. Rizzetta; Miguel R. Visbal; AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH AERONAUTICAL SCIENCES DIVISION
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| Active control was simulated numerically for subsonic flow through a highly-loaded low-pressure turbine. At a nominal Reynolds number of 25,000 based upon axial chord and inlet conditions, massive separation occurred on the suction surface of each blade. Vortex generating jets were then used to help mitigate separation, thereby reducing wake losses. Computations were performed using both steady blowing and pulsed mass injections. The numerical method utilized a centered compact finite-difference ... |
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| Transformed Flux-Form Semi-Lagrangian Scheme |
01-Jan-2008 |
26 pages |
| Authors:
Chenwu Fan; Peter C Chu; NAVAL POSTGRADUATE SCHOOL MONTEREY CA NAVAL OCEAN ANALYSIS AND PREDICTION LAB
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| Transformed flux-form semi-Lagrangian (TFSL) scheme provides stable and accurate algorithm to solve the advection-diffusion equation. Different from the existing flux-form semi- Lagrangian schemes, the flux at boundary of grid cell is treated as the temporal mean between present and next time steps. After the temporal-spatial transformation using the characteristic-line concept, the temporal integration of the flux from present to next time step becomes the spatial integration of the flux at ... |
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| Advances in High-Fidelity Multi-Physics Simulation Techniques |
JAN 2008 |
56 pages |
| Authors:
Datta Gaitonde; Eswar Josyula; Miguel Visbal; AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH AIR VEHICLES DIRECTORATE
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| Efforts performed under this task to evolve a high-fidelity methodology for multi-physics applications in all speed regimes are summarized. Among the disciplines considered are fluid dynamics (turbulence, acoustics), electromagnetics, magnetogasdynamics, aero-structural interactions and thermo-chemical nonequilibrium. For high-order accuracy, a compact-difference based method is developed, supplemented by a filtering procedure to guarantee numerical stability in the presence of boundary truncation, stretching and non-linearity. The filter is also shown to be suitable ... |
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| A High-Order Compact Finite-Difference Scheme for Large-Eddy Simulation of Active Flow Control |
JAN 2008 |
105 pages |
| Authors:
Donald P. Rizzetta; Miguel R. Visbal; Philip E. Morgan; AIR FORCE RESEARCH LAB WRIGHT-PATTERSON AFB OH AIR VEHICLES DIRECTORATE
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| A computational approach for performing large-eddy simulation (LES) of flows with active control is summarized. Simulation of these problems typically characterized by small-scale fluid structures cannot be carried out accurately by methods less sophisticated than LES. The numerical scheme is predicated upon an implicit time-marching algorithm, and utilizes a high order compact finite-difference approximation to represent spatial derivatives. Robustness of the scheme is maintained by employing a low-pass Pade-type non-dispersive ... |
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| Algorithm Development and Application of High Order Numerical Methods for Shocked and Rapid Changing Solutions |
06 DEC 2007 |
18 pages |
| Authors:
Chi-Wang Shu; BROWN UNIV PROVIDENCE RI DIV OF APPLIED MATHEMATICS
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| We have investigated high order finite difference weighted essentially non-oscillatory (WENO) schemes, finite volume WENO schemes and discontinuous Galerkin finite element methods, for solving partial differential equations with discontinuous or rapidly changing solutions. Algorithm development, analysis, implementation and applications have been carried out. Research has been performed in all areas listed in the original proposal, and progress and results consistent with the original objectives have been obtained. There are 53 ... |
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| Math-Based Simulation Tools and Methods |
10 OCT 2007 |
17 pages |
| Authors:
Sudhakar Arepally; ARMY RESEARCH DEVELOPMENT AND ENGINEERING COMMAND WARREN MI
|
| These briefing charts review numerous mathematical methods for simulating crashworthiness and occupant protection in motor vehicles. The following methods are reviewed: matrix operations, ordinary and partial differential system of equations, Lagrangian operations, Fourier transforms, Taylor Series, Finite Difference Methods, implicit and explicit finite element methods, and statistical methods (probabilistic and regression analysis). The slides are labeled as follows: HMMWV 30-mph Rollover Test, Soldier Gear Effects, Occupant Performance in Blast Effects, ... |
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| BTEC Thermal Model |
OCT 2007 |
99 pages |
| Authors:
Lance J. Irvin; P. D. Maseberg; Gavin D. Buffington; III. Clark Clifton D.; Robert J. Thomas; Michael L. Edwards; Jacob Stolarski; FORT HAYS STATE UNIV HAYS KS
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| AFRL/RHDO has developed a configurable, laser-tissue interaction model that includes components from various areas of Biophysics. The model predicts heat transfer in biological tissue, in either one-dimension or two-dimensional cylindrical coordinates, and is coupled to an Arrhenius damage model. A simulation can be configured as a single run, or a damage-threshold search. Multiple models for describing the laser-tissue interaction are available, including linear absorption (1D, 2D), Monte Carlo scattering (2D) ... |
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| The Physical Basis of the Explosion Source and Generation of Regional Seismic Phases |
31 AUG 2007 |
156 pages |
| Authors:
Jeffrey L. Stevens; G. E. Baker; Heming Xu; SCIENCE APPLICATIONS INTERNATIONAL CORP SAN DIEGO CA
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| The goal of this project is to understand explosion generation of shear waves. We quantify contribution of surface reflected pS, S*, scattered Rg, and S directly generated by non-spherical source elements to local and regional S-wave phases in high and low velocity source media through simulations and data analysis. Data include a large set of historical local records of Semipalatinsk nuclear explosions digitized for this project by Institute for the ... |
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| High-Order Higdon Non-Reflecting Boundary Conditions for the Linearized Euler Equations |
APR 2007 |
17 pages |
| Authors:
John R. Dea; Francis X. Giraldo; Beny Neta; NAVAL POSTGRADUATE SCHOOL MONTEREY CA DEPT OF MATHEMATICS
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| In this report we document the implementation of high-order Higdon nonreflecting boundary conditions. We suggest a way to choose the parameters and demonstrate numerically the efficiency of our choice. The model we used is the linearized 2-D Euler equations with zero advection. These equations are solved by the finite difference method. We close with a list of topics for research. |
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| Optical Add-Drop Filters Based on Photonic Crystal Ring Resonators |
19-Feb-2007 |
10 pages |
| Authors:
Zexuan Qiang; Weidong Zhou; Richard A Soref; TEXAS UNIV AT ARLINGTON DEPT OF ELECTRICAL ENGINEERING
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| We present here an optical add-drop filter (ADF) design based on ultra-compact photonic crystal ring resonators (PCRRs). The normalized transmission spectra for single-ring and dual-ring configurations have been investigated by using the two-dimensional finite-difference time-domain (FDTD) technique in a square lattice dielectric-rod photonic-crystal structure. With the introduction of four scatterers at the corners of quasisquare-ring PCRR, high wavelength selectivity and close to 100% drop efficiency can be obtained. Both backward- ... |
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| A High Order WENO Scheme for a Hierarchical Size-Structured Model |
2007 |
18 pages |
| Authors:
Jun Shen; Chi-Wang Shu; Mengping Zhang; BROWN UNIV PROVIDENCE RI DIV OF APPLIED MATHEMATICS
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| In this paper we develop a high order explicit finite difference weighted essentially non-oscillatory (WENO) scheme for solving a hierarchical size-structured population model with nonlinear growth, mortality and reproduction rates. The main technical complication is the existence of global terms in the coefficient and boundary condition for this model. We carefully design approximations to these global terms and boundary conditions to ensure high order accuracy. Comparing with the first order ... |
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| Numerical Methods for Analysis of Charged Vacancy Diffusion in Dielectric Solids |
DEC 2006 |
40 pages |
| Authors:
John D. Clayton; Peter W. Chung; Michael A. Greenfield; WIlliam D. Nothwang; ARMY RESEARCH LAB ABERDEEN PROVING GROUND MD
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| A theory for charged vacancy diffusion in elastic dielectric materials is formulated and implemented numerically in a finite difference code. The governing equations consist of Maxwell's equations of electrostatics coupled with kinetic equations for vacancy diffusion, with the chemical potential accounting for both mixing energy of vacancies and electrostatically-driven charge migration. A second-order accurate implicit scheme is used to solve Maxwell's parabolic equations, while an explicit method is used to ... |
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| Seismic Propagation From Activity in Tunnels and Underground Facilities |
01 NOV 2006 |
9 pages |
| Authors:
STEPHEN A. KETCHAM; Jason R. McKenna; Roy J. Greenfield; Thomas S. Anderson; ENGINEER RESEARCH AND DEVELOPMENT CENTER HANOVER NH COLD REGIONS RESEARCH AND ENGINEERING LAB
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| Dynamic mechanical activity in a tunnel can be measured as ground vibrations at offset distances. These signals can be processed in sensing algorithms for detection, location, and discrimination of the activity. The objective of this work is to demonstrate that seismic simulations can reveal the effect of the environment on seismic energy as it propagates from tunnels. Using massively parallel high-performance computers, the work applies a finite-difference solution to the ... |
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| Computing the Observed Information Matrix for Dynamic Mixture Models |
25 SEP 2006 |
87 pages |
| Authors:
Michael J. Walsh; NAVAL UNDERSEA WARFARE CENTER DIV NEWPORT RI
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| The observed information matrix for an important class of finite mixture models, called dynamic mixture models, is derived in this report. Dynamic mixture models are useful probability models for random data originating from a number of distinct moving sources. The multiple-target tracking problem is one application of these models. For these models, the inverse of the observed information matrix is a consistent estimate of the error-covariance matrix for the mixture ... |
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| Seismic Calibration of Group 1 IMS Stations in Eastern Asia for Improved IDC Event Location |
APR 2006 |
144 pages |
| Authors:
J. R. Murphy; W. L. Rodi; M. Johnson; J. D. Sultanov; T. J. Bennett; M. N. Toksoz; V. Ovtchinnikov; B. W. Barker; A. M. Rosca; Y. Shchukin; SCIENCE APPLICATIONS INTERNATIONAL CORP SAN DIEGO CA
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| The determination of accurate seismic locations for detected events is one of the most important functions of nuclear test monitoring because location plays such a key role in nuclear test monitoring. In order to establish a robust nuclear test monitoring capability, it is necessary to calibrate the IMS seismic stations used in monitoring, to account for systematic deviations from the nominal travel time curves. This report presents a summary of ... |
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| 1-D Thermal Modeling of Layered Materials in Outdoor Environments. Countermine Phenomenology Program |
FEB 2006 |
84 pages |
| Authors:
John O. Curtis; ENGINEER RESEARCH AND DEVELOPMENT CENTER VICKSBURG MS ENVIRONMENTAL LAB
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| This report describes a physics-based, but relatively simple, thermal infrared computational tool that can be used in a personal computer (PC) environment to predict temperature profiles of layered media. The tool is a one-dimensional finite difference simulation code (written in FORTRAN) that is executed through a graphical user interface. Its current utility is in helping to design field tests of airborne mine detection sensor systems and to analyze the results ... |
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| A Distributed Lagrange Multiplier Based Fictitious Domain Method for Maxwell's Equations |
19 JAN 2006 |
35 pages |
| Authors:
V. A. Bokil; R. Glowinski; NORTH CAROLINA STATE UNIV AT RALEIGH CENTER FOR RESEARCH IN SCIENTIFIC COMPUTATION
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| We consider a time-dependent problem of scattering by an obstacle involving the solution of the two dimensional Maxwell's equations in the exterior of a domain with a perfectly conducting condition on the boundary of this domain. We propose a novel fictitious domain method based on a distributed Lagrange multiplier technique for the solution of this problem. Perfectly matched layers are constructed to model the unbounded problem. Comparisons are performed with ... |
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| Microphysical Influences on Electro-Optic Signal Propagation in Complex Areas |
DEC 2005 |
22 pages |
| Authors:
Arnold Tunick; Gary Carhart; ARMY RESEARCH LAB ADELPHI MD
|
| This paper presents a finite-difference computer model to predict the microphysical influences on electro-optic signal propagation in complex areas. e.g.. around single and mutltiple building arrays and forests. The model incorporates physics-based algorithms to account for advection. the pressure gradient. eddy diffusion. and drag forces due to vegetation (e.g.. open fields or forests). Note that mechanisms to account for heating, cooling, and moisture flux are not included at this time. ... |
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| Intersubband Photoconduction in CdTe/DcS and CdTe/CdSe Nanowires |
31 OCT 2005 |
10 pages |
| Authors:
David Crouse; CITY COLL NEW YORK
|
| The aim of the project is the theoretical analysis of intersubband IR detection in semiconductor nanowires and the nonlithographic fabrication and the structural, optical and electrical characterization of II-VI semiconductor nanowires and II-VI/II-VI semiconductor nanowire heterostructures. Significant progress has been made on the theoretical analysis and fabrication portions of the project. The theory has used both analytical and finite difference algorithms and has shown that the method of fabricating the ... |
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| An Experimental, Numerical, and CFD Investigation into the Heat Transfer and Flow Characteristics in Porous Media Using a Thermal Non-Equilibrium Model |
01 OCT 2005 |
16 pages |
| Authors:
Andrew M. Hayes; Aly H. Shaaban; Jamil A. Khan; Ian G. Spearing; Reza Salavani; APPLIED RESEARCH ASSOCIATES INC TYNDALL AFB FL
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| Heat transfer and fluid flow through porous media was investigated using numerical simulations and experiment. For the numerical simulations, two models were created. The first consisted of a two-dimensional numerical model created in MathCAD and was solved using the finite difference approach. The MathCAD model's flow in the porous media was described by the Brinkman-Forchheimer-extended Darcy equation. The second model consisted of a computational fluid dynamics (CFD) porous media model ... |
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| Quantum Lattice Representations for Vector Solitons in External Potentials |
29 SEP 2005 |
8 pages |
| Authors:
George Vahala; Linda Vahala; Jeffrey Yepez; COLLEGE OF WILLIAM AND MARY WILLIAMSBURG VA DEPT OF PHYSICS
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| A quantum lattice algorithm is developed to examine the effect of an external potential well on exactly integrable Vector Manakov solitons. It is found that the exact solutions to the coupled nonlinear Schrodinger equations act like quasi-solitons in weak potentials, leading to mode-locking, trapping and untrapping. Stronger potential wells will lead to the emission of radiation modes from the quasi-soliton initial conditions. If the external potential is applied to that ... |
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| Analytical Simulation and Verification of Air Gun Impact Testing |
28 SEP 2005 |
54 pages |
| Authors:
Adam Bouland; Mostafiz R. Chowdhury; ARMY RESEARCH LAB ADELPHI MD
|
| This report presents an analytical method to simulate the acceleration pulses and forces experienced by test objects during air gun impact testing. The purpose of an air gun impact test is to determine the survivability of sensitive artillery components during launch. It does so by simulating the acceleration pulse and shock waves experienced by such objects during firing. In an air gun impact test, these forces are generated by the ... |
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| Modeling Ion Beam Neutralization and Near-Thruster Plume Interactions (POSTPRINT) |
31 AUG 2005 |
13 pages |
| Authors:
Lubos Brieda; Douglas VanGilder; Joseph Wang; ENGINEERING RESEARCH AND CONSULTING INC (ERC INC) EDWARDS AFB CA
|
| Ion thruster plume interaction has been studied extensively in recent years. While most existing plume models have focused on charge-exchange ion interactions with the spacecraft and/or plume-induced contamination, few studies have examined the detailed physics near the thruster exit. In particular, the ion beam neutralization process and the characteristics of the neutralizing electrons are not well understood. This paper presents a full-PIC model for the near-thruster plume of a single ... |
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| Sensitivity of Neurotransmitter Release to Radiofrequency Fields |
10 AUG 2005 |
31 pages |
| Authors:
Gale L. Craviso; Indira Chatterjee; NEVADA UNIV RENO
|
| Exploring the interactions between radiofrequency (RF) radiation and biological systems is essential for developing RF-based non-lethal stunning/immobilizing weaponry. To this end a research effort was initiated to identify RF parameters potentially capable of selectively altering exocytosis, the process underlying neurotransmitter release and hence nervous system functioning. Major accomplishments included designing, setting up, testing, characterizing and optimizing a waveguide-based RF exposure system for assessing effects on exocytosis, using neurosecretory adrenal chromaffin ... |
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| Simulations of Chemotaxis and Random Motility in Finite Domains |
13 JUL 2005 |
12 pages |
| Authors:
Ehsan Jabbarzadeh; Cameron F. Abrams; DREXEL UNIV PHILADELPHIA PA
|
| Rational design and selection of candidate porous biomaterials to serve as tissue engineering constructs rests on our ability to understand the influence of the porous microarchitecture on the transport of chemical species (e.g., nutrients and signaling compounds), fluid flow, and cellular locomotion and growth. We have begun to study the behavior of chemotactically mobile cells in response to unsteady signaling molecule concentration fields using a computational simulation-based model. The model ... |
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| Diffusiophoresis of a Spherical Volatile Particle |
13 JUL 2005 |
7 pages |
| Authors:
Kazuo Aoki; Masatake Hatano; Shingo Kosuge; Shigeru Takata; KYOTO UNIV (JAPAN) DEPT OF AERONAUTICS AND ASTRONAUTICS
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| A spherical condensed phase (volatile particle) is placed in an infinite expanse of a binary mixture consisting of the vapor of the condensed phase and another noncondensable gas. The mixture is assumed to be at rest with uniform pressure and temperature at infinity. However, the vapor and the noncondensable gas have small uniform density (or concentration) gradients of the same magnitude but in the opposite direction. The flows of both ... |
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| Direct Numerical Solution Of The Boltzmann Equation |
13 JUL 2005 |
10 pages |
| Authors:
Felix Tcheremissine; RUSSIAN ACADEMY OF SCIENCES MOSCOW COMPUTING CENTER
|
| Progress in computer hardware and improvement of numerical methods made solution of the Boltzmann equation for rather complex gas dynamic problems real. The method developed by the author is based on a projection technique for evaluation of the collision operator. The computed collision integral is conservative by density, impulse, and energy, and became equal to zero when the solution has a form of the Maxwellian distribution. The later feature sharply ... |
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| Three-Dimensional Rayleigh-Benard Convection of a Rarefied Gas: DSMC and Navier-Stokes Calculations |
13 JUL 2005 |
7 pages |
| Authors:
S. K. Stefanov; V. M. Roussinov; C. Cercignani; BULGARIAN ACADEMY OF SCIENCES SOFIA INST OF MECHANICS
|
| The three-dimensional Rayleigh-Benard convection of a rarefied gas is studied numerically by using DSMC and Navier-Stokes finite difference methods. We present the results obtained in a three-dimensional box with an aspect ratio A=Lx:Ly:Lz at a fixed wall temperature ratio r=Tc/Th=0.1. In general, the three-dimensional results confirm the validity of the zone of convection obtained in the previous author's two-dimensional considerations. A detailed analysis has been performed for Knudsen number Kn=0.02 ... |
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| Seismic Imaging of UXO-Contaminated Underwater Sites |
JUL 2005 |
74 pages |
| Authors:
Roland Gritto; Valeri Korneev; Kurt Nihei; Lane Johnson; CALIFORNIA UNIV BERKELEY LAWRENCE BERKELEY LAB
|
| Two- and three-dimensional numerical modeling was conducted to evaluate the performance of source-receiver arrays to "detect" and "locate" UXO in littoral environments. While the 2-D investigations were based on finite difference (FD) modeling, the 3-D study used an analytical solution for the scattering of elastic waves by spherical objects to model the interaction of waves with UXO. The forward modeling or "detection" phase generated seismic data that reveal the presence ... |
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| Quality Factors in Single-Defect Photonic-Crystal Lasers with Asymmetric Cladding Layers |
01 JUN 2005 |
6 pages |
| Authors:
Cheolwoo Kim; Woo J. Kim; Andrew Stapleton; Jiang-Rong Cao; John D. O'Brien; P. D. Dapkus; UNIVERSITY OF SOUTHERN CALIFORNIA LOS ANGELES DEPT OF ELECTRICAL ENGINEERING AND ELECTROPHYSICS
|
| We present quality factors of single-defect photonic-crystal resonant cavities with asymmetric cladding layers. The resonators studied here are dielectric slabs patterned with two-dimensional photonic crystals on a sapphire substrate. Three-dimensional finite-element and finite-difference time-domain routines were used to analyze the electromagnetic properties of these cavities. We observe that high quality factors (~800) can be obtained in these cavities for reasonable structures with thick enough dielectric slabs. This work was motivated ... |
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| CTH Analyses of Fragment Penetration Through Heat Sink Fins |
JUN 2005 |
29 pages |
| Authors:
Anand Prakash; ARMY RESEARCH LAB ABERDEEN PROVING GROUND MD
|
| Vulnerability/lethality analysis codes (e.g., MUVES-S2) generally use the FATEPEN (fast air target encounter penetration) and THOR penetration models to determine damage produced by impacts of fragments. For simple impact scenarios, e.g., normal fragment impact on monolithic plates, these two models give reasonable predictions for penetration, perforation, and residual velocity. It is, however, not clear how realistic the predictions of these models are for more complicated scenarios. This report presents more ... |
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| Higher Order Wall Boundary Conditions for Incompressible Flow Simulations |
14 APR 2005 |
9 pages |
| Authors:
Hidetoshi Nishida; KYOTO INST OF TECH (JAPAN) DEPT OF MECHANICAL AND SYSTEM ENGINEERING
|
| In this paper, the new higher order wall boundary conditions are proposed for solving the incompressible flows. The square driven cavity flows are simulated by using the variable order method of lines with the present wall boundary conditions. The variable order method of lines is constructed by the spatial discretization, i.e., the variable order proper convective scheme for convective terms and the modified differential quadrature method for diffusive terms, and ... |
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| Numerical Analysis of Flow Around Rectangular Cylinders with Various Side Ratios |
14 APR 2005 |
9 pages |
| Authors:
Akira Rokugou; Atsushi Okajima; Kohji Kamiyama; YKK CORP TOYAMA (JAPAN)
|
| Three-dimensional numerical analysis of the flow around rectangular cylinders with various side ratios, D/H, from 0.2 to 2.0, was carried out for Reynolds number of 1000 by using a multi directional finite difference method on a regular-arranged multi grid. The predicted results are in good agreement with the experimental data. It is found that fluid dynamic characteristics of rectangular cylinders alternate between the high-pressure mode and the low-pressure mode of ... |
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| Numerical Analysis of Laminar Natural Convection Heat Transfer Around Two Vertical Fins by a Spectral Finite Difference Method |
14 APR 2005 |
9 pages |
| Authors:
HaeHwan Song; Yoshihiro Mochimaru; TOKYO INST OF TECHNOLOGY (JAPAN)
|
| A numerical solution is presented for the natural convection heat transfer from two vertical fins using a spectral finite difference method. Virtual distant boundary conditions for two bodies that are compatible with plume behavior and with an overall continuity condition are introduced. A boundary-fitted coordinate system is formed. Streamlines, isotherms, mean Nusselt numbers and drag and lift coefficients are presented for a variety of dimensionless parameters such as a Grashof ... |
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| Convergence of Laplacian Diffusion Versus Resolution of an Ocean Model |
APR 2005 |
5 pages |
| Authors:
Alan J. Wallcraft; A. B. Kara; Harley E. Hurlburt; NAVAL RESEARCH LAB STENNIS SPACE CENTER MS OCEANOGRAPHY DIV
|
| This paper presents a convergence study for second order finite difference Laplacian diffusion used in ocean models. For demonstration, ocean model simulations are performed over a rectangular domain, based on the North Pacific subtropical gyre region with grid resolution between 1/2 deg. and 1/32 deg. and with horizontal eddy viscosity coefficient (A(sub H)) ranging from 8000 to 30 m2s-1. A range of A(sub H) which is appropriate for useful model ... |
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| Finite Difference Time Domain (FDTD) Analysis of a Leaky Traveling Wave Microstrip Antenna |
21 MAR 2005 |
158 pages |
| Authors:
Gregory M. Zelinski; AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH DEPT OF ELECTRICAL AND COMPUTER ENGINEERING
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| This thesis provides the groundwork that will enable the development of a lightweight, inexpensive, aerodynamic, and broadband antenna. Whether for radar or communication, an antenna with these properties would be a force multiplier for the smaller, limited payload air vehicles the United States Air Force will pursue in the coming years. Several microstrip antennas using the first higher order mode were simulated with the Finite-Difference Time-Domain (FDTD) method. The propagation ... |
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| Pulse Detonation Engine Thrust Tube Heat Exchanger for Flash Vaporization and Supercritical Heating of JP-8 |
MAR 2005 |
202 pages |
| Authors:
Christen L. Miser; AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH SCHOOL OF ENGINEERING AND MANAGEMENT
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| Research has shown that performance of liquid hydrocarbon fueled pulse detonation engines is limited by the time required to evaporate liquid fuel droplets within the mixture. Vaporization of liquid fuels prior to injection has been shown to decrease ignition times and also increases fuel efficiency; however, the size and efficiency of the vaporization system used are not feasible for use in future pulse detonation aircraft concepts. The purpose of this ... |
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| Lattice Spacing Effect on Scan Loss for Bat-Wing Phased Array Antennas |
01 JAN 2005 |
5 pages |
| Authors:
Thinh Q. Ho; Charles A. Hewett; Lilton N. Hunt; Thomas G. Ready; Raj Mittra; SPACE AND NAVAL WARFARE SYSTEMS CENTER SAN DIEGO CA
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| Phased array antennas are becoming increasingly more important in communications and radar applications. In general, these arrays are designed to produce narrow directional beams with hemispherical coverage. From the system design perspective, a phased array antenna must be implemented using multiple co-located antenna panels to meet the gain requirement over the entire scan volume. In order to accomplish this technical objective, and yet at the same time minimize the total ... |
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| Improvement of Frequency Response of Waveguide-Diaphragm-Type Resistive Sensors for High Power Microwave Pulse Measurement |
2005 |
28 pages |
| Authors:
Zilvinas Kancleris; EUROPEAN OFFICE OF AEROSPACE RESEARCH AND DEVELOPMENT FPO NEW YORK 09510
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| This report results from a contract tasking Semiconductor Physics Institute as follows: The contractor will investigate resistive sensors for measuring high power microwave pulses. At the end of this investigation, the contractor will design, fabricate and test a waveguide-type resistive sensors. |
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Reports by Keyword(s)
FINITE DIFFERENCE THEORY
