| On the Modeling of Shells in Multibody Dynamics |
NOV 2000 |
24 pages |
| Authors:
Olivier A. Bauchau; Jou-Young Choi; Carlo L. Bottasso; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
 | Energy preserving/decaying schemes are presented for the simulation of the nonlinear multibody systems involving shell components. The proposed schemes are designed to meet four specific requirements: unconditional nonlinear stability of the scheme, a rigorous treatment of both geometric and material nonlinearities, exact satisfaction of the constraints, and the presence of high frequency numerical dissipation. The kinematic nonlinearities associated with arbitrarily large displacements and rotations of ... |
|
| An Energy Decaying Scheme for Nonlinear Dynamics of Shells |
NOV 2000 |
24 pages |
| Authors:
Carlo L. Bottasso; Olivier A. Bauchau; Jou-Young Choi; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| A novel integration scheme for nonlinear dynamics of geometrically exact shells is developed based on the inextensible director assumption. The new algorithm is designed so as to imply the strict decay of the system total mechanical energy at each time step, and consequently unconditional stability is achieved in the nonlinear regime. Furthermore, the scheme features tunable high frequency numerical damping and it is therefore stiffly accurate. The ... |
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| A Gas-Kinetic BGK Scheme for the Compressible Navier-Stokes Equations |
OCT 2000 |
33 pages |
| Authors:
Kun Xu; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| This paper presents an improved gas-kinetic scheme based on the Bhatnagar-Gross-Krook (BGK) model for the compressible Navier-Stokes equations. The current method extends the previous gas-kinetic Navier-Stokes solver developed by Xu and Prendergast by implementing a general nonequilibrium state to represent the gas distribution function at the beginning of each time step. As a result, the requirement in the previous scheme, such as the particle ... |
|
| Arcade: A Web-Java Based Framework for Distributed Computing |
OCT 2000 |
10 pages |
| Authors:
Zhikai Chen; Kurt Maly; Piyush Mehrotra; Mohammad Zubair; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| Distributed heterogeneous environments are being increasingly used to execute a variety of large size simulations and computational problems. We are developing Arcade, a web-based environment to design, execute, monitor, and control distributed applications. These targeted applications consist of independent heterogeneous modules which can be executed on a distributed heterogeneous environment. In this paper we describe the overall design of the system and discuss the prototype ... |
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| On the Local Convergence of Pattern Search |
SEP 2000 |
16 pages |
| Authors:
Elizabeth D. Dolan; Robert M. Lewis; Virginia Torczon; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| We examine the local convergence properties of pattern search methods, complementing the previously established global convergence properties for this class of algorithms. We show that the step-length control parameter which appears in the definition of pattern search algorithms provides a reliable asymptotic measure of first-order stationarity. This gives an analytical justification for a traditional stopping criterion for pattern search methods. Using this measure of first-order ... |
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| Numerical Study of Wave Propagation in a Non-Uniform Flow |
SEP 2000 |
27 pages |
| Authors:
Alex Povitsky; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| The propagation of acoustic waves originating from cylindrical and spherical pulses, in a non-uniform mean flow, and in the presence of a reflecting wall is investigated by Hardin and Pope approach using compact approximation of spatial derivatives. The 2-D and 3-D stagnation flows and a flow around a cylinder are taken as prototypes of real world flows with strong gradients of mean pressure and velocity. ... |
|
| Enhancing Jini for Use Across Non-Multicastable Networks |
SEP 2000 |
9 pages |
| Authors:
Ahmed Al-Theneyan; Piyush Mehrotra; Mohammed Zubair; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| Distributed heterogeneous systems are being increasingly used to execute a variety of large size simulation and computational problems. Resource management is one of the most important issues in building such systems. Recently, Sun introduced the Jini connection technology for building plug-and- play networks of resources. Jini relies on multicasting across the network for its internal protocols. However, in a distributed environment, such as the one ... |
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| An Efficient Parallel Multigrid Solver for 3-D Convection-dominated Problems |
AUG 2000 |
29 pages |
| Authors:
Ignacio M. Llorente; Manuel Prieto-Matias; Boris Diskin; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| Multigrid algorithms are known to be highly efficient in solving systems of elliptic equations. However, standard multi grid algorithms fail to achieve optimal grid-independent convergence rates in solving non-elliptic problems. In many practical cases, the non-elliptic part of a problem is represented by the convection operator. Downstream marching, when it is viable, is the simplest and most efficient way to solve this operator. However, in ... |
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| General Framework for Achieving Textbook Multigrid Efficiency: One- dimensional Euler Example |
AUG 2000 |
17 pages |
| Authors:
James L. Thomas; Boris Diskin; Achi Brandt; Jerry C. South Jr; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| A general multigrid framework is discussed for obtaining textbook efficiency to solutions of the compressible Euler and Navier-Stokes equations in conservation law form. The general methodology relies on a distributed relaxation procedure to reduce errors in regular (smoothly varying) flow regions; separate and distinct treatments for each of the factors (elliptic and/ or hyperbolic) are used to attain optimal reductions of errors. Near boundaries and discontinuities ... |
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| The Intuitionism Behind Statecharts Steps |
JUL 2000 |
41 pages |
| Authors:
Gerald Luettgen; Michael Mendler; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| The semantics of Statecharts macro steps, as introduced by Pnueli and Shalev, lacks compositionality. This report first analyzes the compositionality problem and traces it back to the invalidity of the Law of the Excluded Middle. It then characterizes the semantics via a particular class of linear, intuitionistic Kripke models, namely stabilization sequences. This yields, for the first time in the literature, a simple fully-abstract semantics ... |
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| Robust Multigrid Algorithms for the Incompressible Navier-Stokes Equations |
MAY 2000 |
17 pages |
| Authors:
Ruben S. Montero; Ignacio M. Llorente; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| Anisotropies occur naturally in CFD where the simulation of small scale physical phenomena, such as boundary layers at high Reynolds numbers, causes the grid to be highly stretched leading to a slow down in convergence of multigrid methods. Several approaches aimed at making multigrid a robust solver have been proposed and analyzed in literature using the scalar diffusion equation. However, they have been rarely applied ... |
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| Direct Search Methods: Then and Now |
MAY 2000 |
17 pages |
| Authors:
Robert M. Lewis; Virginia Torczon; Michael W. Trosset; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| We discuss direct search methods for unconstrained optimization. We give a modern perspective on this classical family of derivative-free algorithms, focusing on the development of direct search methods during their golden age from 1960 to 1971. We discuss how direct search methods are characterized by the absence of the construction of a model of the objective. We then consider a number of the classical direct ... |
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| Trust-Region Proper Orthogonal Decomposition for Flow Control |
MAY 2000 |
19 pages |
| Authors:
E. Arian; M. Fahl; E. W. Sachs; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| The proper orthogonal decomposition (POD) is a model reduction technique for the simulation of physical processes governed by partial differential equations, e.g., fluid flows. It can also be used to develop reduced order control models. Fundamental is the computation of POD basis functions that represent the influence of the control action on the system in order to get a suitable control model. We present an ... |
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| Simultaneous Velocimetry and Thermometry of Air Using Nonresonant Heterodyned Laser-induced Thermal Acoustics |
MAY 2000 |
8 pages |
| Authors:
Roger C. Hart; R. J. Balla; G. C. Herring; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| Non-resonant laser-induced thermal acoustics (LITA) is employed with heterodyne detection to measure temperature (285-295 K) and a single component of velocity (20-150 m/s) in an atmospheric pressure, subsonic, unseeded air jet. Good agreement is found with pitot-tube measurements of velocity (0.2% at 150 m/ s and 2% at 20 m/s) and the isentropic expansion model for temperature (0.3%). |
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| Efficient Parallel Computation of ILU(k) Preconditioners |
MAY 2000 |
17 pages |
| Authors:
David Hysom; Alex Pothen; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| We report the development of a parallel algorithm for computing ILU preconditioners. The algorithm attains a high degree of parallelism through employment of a two-level ordering strategy, coupled with a subdomain graph constraint that regulates the location of nonzeros in the Schur complement. Experimental results include timings on four parallel platforms, for problems with up to 20 million unknowns running on up to 216 processors. ... |
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| Parallel ILU Ordering and Convergence Relationships: Numerical Experiments |
MAY 2000 |
19 pages |
| Authors:
David Hysom; Alex Pothen; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| We recently developed a parallel algorithm for computing ILU preconditioners, which was presented at Super Computing 1999. The algorithm has been shown to be highly scalable, in terms of execution time required for preconditioner factorization and application, for problems with up to 20 million unknowns running on up to 216 processors. However, since the algorithm reorders the matrix, and it is widely known that ordering can ... |
|
| Semiannual Report October 1, 1999 through March 31, 2000 |
APR 2000 |
47 pages |
| Authors:
INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| This report summarizes research conducted at the Institute for Computer Applications in Science and Engineering in applied mathematics computer science, fluid mechanics and structures and materials during the period October 1, 1999 through March 31, 2000. |
|
| Improving Jet Reactor Configuration for Production of Carbon Nanotubes |
APR 2000 |
21 pages |
| Authors:
Alex Povitsky; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| The jet mixing reactor has been proposed for the industrial production of fullerene carbon nanotubes. Here we study the flow field of this reactor using the SIMPLER algorithm. Hot peripheral jets are used to enhance heating of the central jet by mixing with the ambiance of reactor. Numerous configurations of peripheral jets with various number of jets, distance between nozzles, angles between the central jet ... |
|
| Optical Measurement of the Speed of Sound in Air Over the Temperature Range 300-650 K |
APR 2000 |
5 pages |
| Authors:
Roger C. Hart; R. J. Balla; G. C. Herring; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| Using laser-induced thermal acoustics (LITA), the speed of sound in room air (1 atm) is measured over the temperature range 300-650 K Since the LITA apparatus maintains a fixed sound wavelength as temperature is varied, this temperature range simultaneously corresponds to a sound frequency range 10-15 MHz. The data are compared to a published model and typically agree within 0.1- 0.4% at each of 21 temperatures. ... |
|
| On the Combined Performance of Non-local Artificial Boundary Conditions with the New Generation of Advanced Multigrid Flow Solvers |
APR 2000 |
39 pages |
| Authors:
T. W. Roberts; D. Sidilkover; S. V. Tsynkov; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| We develop theoretically and implement numerically a unified flow solution methodology that combines the advantages relevant to two independent groups of methods in CFD that have recently proven successful: The new factorizable schemes for the equations of hydrodynamics that facilitate the construction of optimally convergent multigrid algorithms, and highly accurate global far-field artificial boundary conditions (ABCs). The primary result that we have obtained is ... |
|
| Aircraft Trajectory Modeling and Alerting Algorithm Verification |
APR 2000 |
21 pages |
| Authors:
Cesar Munoz; Victor Carreno; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| The Airborne Information for Lateral Spacing (AILS) program at NASA Langley Research Center aims at giving pilots the information necessary to make independent approaches to parallel runways with spacing down to 2500 feet in Instrument Meteorological Conditions. The AILS concept consists of accurate traffic information visible at the navigation display and an alerting algorithm which warns the crew when one of the aircraft involved in ... |
|
| Strong Stability Preserving High-order Time Discretization Methods |
APR 2000 |
24 pages |
| Authors:
Sigal Gottlieb; Chi-Wang Shu; Eitan Tadmor; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| In this paper we review and further develop a class of strong- stability preserving (SSP) high-order time discretizations for semi-discrete method-of-lines approximations of partial differential equations. Termed TVD (total variation diminishing) time discretizations before this class of high- order time discretization methods preserves the strong-stability properties of first-order Euler time stepping and has proved very useful especially in solving hyperbolic partial differential equations. The new ... |
|
| Model Checking is Refinement -- Relating Buechi Testing and Linear-Time Temporal Logic |
MAR 2000 |
21 pages |
| Authors:
Rance Cleaveland; Gerald Luettgen; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| This paper develops a semantic foundation for reasoning about reactive systems specifications featuring combinations of labeled transition systems and formulas in linear time temporal logic (LTL). Using Buechi automata as a semantic basis, the paper introduces two refinement preorders based on DeNicola and Hennessy's notion of may- and must-testing. Alternative characterizations for these relations are provided and used to show that the new preorders are ... |
|
| Parallel Performance Investigations of an Unstructured Mesh Navier- Stokes Solver |
MAR 2000 |
19 pages |
| Authors:
Dimitri J. Mavriplis; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| A Reynolds-averaged Navier-Stokes solver based on unstructured mesh techniques for analysis of high-lift configurations is described. The method makes use of an agglomeration multigrid solver for convergence acceleration. Implicit line-smoothing is employed to relieve the stiffness associated with highly stretched meshes. A GMRES technique is also implemented to speed convergence at the expense of additional memory usage. The solver is cache efficient and fully ... |
|
| Compositional Approach to Statecharts Semantics |
MAR 2000 |
16 pages |
| Authors:
Gerald Luettgen; Michael von der Beeck; Rance Cleaveland; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| Statecharts is a visual language for specifying reactive system behavior. The formalism extends traditional finite-state machines with notions of hierarchy and concurrency, and it is used in many popular software design notations. A large part of the appeal of Statecharts derives from its basis in state machines, with their intuitive operational interpretation. The traditional semantics of Statecharts however, suffers from a serious defect: it is not ... |
|
| Automated Parallelization of Discrete State-space Generation |
MAR 2000 |
20 pages |
| Authors:
David M. Nicol; Gianfranco Ciardo; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| We consider the problem of generating a large state-space in a distributed fashion. Unlike previously proposed solutions that partition the set of reachable states according to a hashing function provided by the user, we explore heuristic methods that completely automate the process. The first step is an initial random walk through the state space to initialize a search tree, duplicated in each processor. Then, the reachability ... |
|
| Nondestructive Evaluation Using a Reduced Order Computational Methodology |
MAR 2000 |
18 pages |
| Authors:
Michele L. Joyner; H. T. Banks; Buzz Wincheski; William P. Winfree; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| This paper uses eddy current based techniques and reduced order modeling to explore the feasibility of detecting a subsurface damage in structures such as air foils and pipelines. To identify the geometry of a damage, an optimization algorithm is employed which requires solving the forward problem numerous times. To implement these methods in a practical setting, the forward algorithm must be solved with extremely fast and ... |
|
| Active Shielding and Control of Environmental Noise |
FEB 2000 |
31 pages |
| Authors:
J. Loncaric; V. S. Ryabenkii; S. V. Tsynkov; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| We present a mathematical framework for the active control of time- harmonic acoustic disturbances. Unlike many existing methodologies, our approach provides for the exact volumetric cancellation of unwanted noise in a given predetermined region of space while leaving unaltered those components of the total acoustic field that are deemed as friendly. Our key finding is that for eliminating the unwanted component of the acoustic field in ... |
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| Some Recent Results on Discrete Velocity Model and Ramifications for Lattice Boltzmann Equation |
FEB 2000 |
14 pages |
| Authors:
Li-Shi Luo; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| Some rigorous results on discrete velocity models are briefly reviewed and their ramifications for the lattice Boltzmann equation (LBE) are discussed. In particular, issues related to thermodynamics and H-theorem of the lattice Boltzmann equation are addressed. It is argued that for the lattice Boltzmann equation satisfying the correct hydrodynamic equations, there cannot exist an H-theorem. Nevertheless, the equilibrium distribution function of the lattice Boltzmann ... |
|
| Electrical Properties and Power Considerations of a Piezoelectric Actuator |
FEB 2000 |
9 pages |
| Authors:
T. Jordan; Z. Ounaies; J. Tripp; P. Tcheng; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| This paper assesses the electrical characteristics of piezoelectric wafers for use in aeronautical applications such as active noise control in aircraft. Determination of capacitive behavior and power consumption is necessary to optimize the system configuration and to design efficient driving electronics. Empirical relations are developed from experimental data to predict the capacitance and loss tangent of a PZT5A ceramic as nonlinear functions of both applied ... |
|
| An Accurate Curved Boundary Treatment in the Lattice Boltzmann Method |
FEB 2000 |
21 pages |
| Authors:
Renwei Mei; Li-Shi Luo; Wei Shyy; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| The lattice Boltzmann equation (LBE) is an alternative kinetic method capable of solving hydrodynamics for various systems. Major advantages of the method are owing to the fact that the solution for the particle distribution functions is explicit, easy to implement, and natural to parallelize. Because the method often uses uniform regular Cartesian lattices in space, curved boundaries are often approximated by a series of stairs that ... |
|
| Formulation of a Two-scale Model of Turbulence |
FEB 2000 |
14 pages |
| Authors:
Robert Rubinstein; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| A two-scale turbulence model is derived by averaging the two-point spectral evolution equation. In this model, the inertial range energy transfer and the dissipation rate can be unequal. The model is shown to reduce to a standard two-equation model in decaying turbulence. |
|
| Towards a Customizable PVS |
JAN 2000 |
15 pages |
| Authors:
Gerald Luttgen; Cesar Munoz; Ricky Butler; Ben DiVito; Paul Miner; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| PVS is a state-of-the-art theorem-proving tool developed by SRI international. It is used in a variety of academic and real-world applications by NASA and ICASE researchers, for whom tool customization and extensibility are becoming increasingly important issues. This paper shows by referring to past experiences with several projects and case studies, that the customization features currently offered by PVS are often insufficient. It also suggests ... |
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| Achieving High Sustained Performance in an Unstructured Mesh CFD application |
JAN 2000 |
17 pages |
| Authors:
W. K. Anderson; W. D. Gropp; D. K. Kaushik; D. E. Keyes; B. F. Smith; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| This paper highlights a three-year project by an interdisciplinary team on a legacy F77 computational fluid dynamics code, with the aim of demonstrating that implicit unstructured grid simulations can execute at rates not far from those of explicit structured grid codes, provided attention is paid to data motion complexity and the reuse of data positioned at the levels of the memory hierarchy closest to the processor, ... |
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| A Model for Asymmetric Hysteresis in Piezoceramic Materials |
JAN 2000 |
7 pages |
| Authors:
Ralph C. Smith; Zoubeida Ounaies; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| This paper focuses on the characterization of hysteresis exhibited by piezoelectric materials at moderate to high field levels. For soft materials in which dipoles are easily reconfigured, the hysteresis loop is observed to be rotationally symmetric about the zero field, zero polarization point and symmetric models can be employed. In harder materials, however, the loops are no longer rotationally symmetric which necessitates the development of commensurate characterization ... |
|
| Non-Ideal Gas Effects on Shock Waves in Weakly Ionized Gases |
JAN 2000 |
9 pages |
| Authors:
Robert Rubinstein; Aaron H. Auslender; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| A shock wave in a weakly ionized gas can be preceeded by a charge separation region if the Debye length is larger than the shock width. It has been proposed that electrostatic contributions to pressure in the charge separation region can increase the sound speed ahead of the shock well above the sound speed in a neutral gas at the same temperature and therefore increase the ... |
|
| High Order Finite Difference Methods, Multidimensional Linear Problems and Curvilinear Coordinates |
DEC 1999 |
32 pages |
| Authors:
Jan Nordstroem; Mark H. Carpenter; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| Boundary and interface conditions are derived for high order finite difference methods applied to multidimensional linear problems in curvilinear coordinates. The boundary and interface conditions lead to conservative schemes and strict and strong stability provided that certain metric conditions are met. |
|
| Polarization Stability of Amorphous Piezoelectric Polyimides |
DEC 1999 |
7 pages |
| Authors:
C. Park; Z. Ounaies; J. Su; J. G. Smith Jr.; J. S. Harrison; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| Amorphous polyimides containing polar functional groups have been synthesized and investigated for potential use as high temperature piezoelectric sensors. The thermal stability of the piezoelectric effect of one polyimide was evaluated as a function of various curing and poling conditions under dynamic and static thermal stimuli. First, the polymer samples were thermally cycled under strain by systematically increasing the maximum temperature from 50 deg C ... |
|
| A Domain Wall Model for Hysteresis in Piezoelectric Materials |
DEC 1999 |
27 pages |
| Authors:
Ralph C. Smith; Zoubeida Ounaies; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| This paper addresses the modeling of hysteresis and nonlinear constitutive relations in piezoelectric materials at moderate to high drive levels. Hysteresis and nonlinearities are due to the domain structure inherent to the materials and both aspects must be addressed to attain the full potential of the materials as sensors and actuators in high performance applications. The model employed here is based on previously developed theory for ... |
|
| Textbook Multigrid Efficiency for the Incompressible Navier-Stokes Equations: High Reynolds Number Wakes and Boundary Layers |
DEC 1999 |
23 pages |
| Authors:
James L. Thomas; Boris Diskin; Achi Brandt; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| Textbook multigrid efficiencies for high Reynolds number simulations based on the incompressible Navier Stokes equations are attained for a model problem of flow past a finite flat plate. Elements of the Full Approximation Scheme multigrid algorithm, including distributed relaxation, defect correction, and boundary treatment, are presented for the three main physical aspects encountered: entering flow, wake flow, and boundary layer flow. Textbook efficiencies, i.e., reduction ... |
|
| Efficient Symbolic State-Space Construction for Asynchronous Systems |
DEC 1999 |
39 pages |
| Authors:
Gianfranco Ciardo; Gerald Luttgen; Radu Siminiceanu; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| Many state of the art techniques for the verification of today's complex embedded systems rely on the analysis of their reachable state spaces. In this paper, we develop a new algorithm for the symbolic generation of the state space of asynchronous system models, such as Petri nets. The algorithm is based on previous work that employs Multi-valued Decision Diagrams (MDDs) for efficiently storing sets of ... |
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| Optimization With Variable-Fidelity Models Applied to Wing Design |
DEC 1999 |
19 pages |
| Authors:
Natalia M. Alexandrov; Robert Michael Lewis; Clyde R. Gumbert; Larry L. Green; Perry A. Newman; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| This work discusses an approach, the Approximation Management Framework (AMF), for solving optimization problems that involve computationally expensive simulations. AMF aims to maximize the use of lower fidelity, cheaper models in iterative procedures with occasional, but systematic, recourse to higher fidelity, more expensive models for monitoring the progress of the algorithm. The method is globally convergent to a solution of the original, high fidelity problem. ... |
|
| On Aeroacoustics of a Stagnation Flow Near a Rigid Wall |
DEC 1999 |
20 pages |
| Authors:
Alex Povitsky; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| We consider propagation of disturbances in a non-uniform mean flow by high order numerical simulation. Monopole and dipole acoustic, vortical and entropy pulses are embedded in an incompressible stagnation flow, which is taken as a prototype of a non-uniform low Mach number mean flow near a rigid wall at high angle of attack. Numerical results are discussed in terms of baroclinic generation of disturbance vorticity that appear ... |
|
| Semiannual Report, April 1 1999 through September 30, 1999 |
NOV 1999 |
71 pages |
| Authors:
INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| This report summarizes research conducted at the Institute for Computer Applications in Science and Engineering in applied mathematics, fluid mechanics, and computer science during the period April 1, 1999 through September 30, 1999. |
|
| Proof-Term Synthesis on Dependent-Type Systems via Explicit Substitutions |
NOV 1999 |
33 pages |
| Authors:
Cesar Munoz; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| Typed lambda-terms are used as a compact and linear representation of proofs in intuitionistic logic. This is possible since the Curry-Howard isomorphism relates proof trees with typed lambda-terms. The proofs-as-terms principle can be used to check a proof by type checking the lambda-term extracted from the complete proof tree. However, proof trees and typed lambda- terms are built differently. Usually, an auxiliary representation of unfinished ... |
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| Large-Scale Parallel Viscous Flow Computations Using an Unstructured Multigrid Algorithm |
NOV 1999 |
16 pages |
| Authors:
Dimitri J. Mavriplis; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| The development and testing of a parallel unstructured agglomeration multigrid algorithm for steady-state aerodynamic flows is discussed. The agglomeration multigrid strategy uses a graph algorithm to construct the coarse multigrid levels from the given fine grid, similar to an algebraic multigrid approach, but operates directly on the non-linear system using the FAS approach. The scalability and convergence rate of the multigrid algorithm are examined on ... |
|
| Minimization of the Truncation Error by Grid Adaptation |
NOV 1999 |
36 pages |
| Authors:
Nail K. Yamaleev; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| A new grid adaptation strategy, which minimizes the truncation error of a pth order finite difference approximation, is proposed. The main idea of the method is based on the observation that the global truncation error associated with discretization on nonuniform meshes can be minimized if the interior grid points are redistributed in an optimal sequence. The method does not explicitly require the truncation error estimate ... |
|
| Dependent Types and Explicit Substitutions |
NOV 1999 |
31 pages |
| Authors:
Cesar Munoz; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| We present a dependent-type system for a lambda-calculus with explicit substitutions. In this system, meta-variables, as well as substitutions, are first-class objects. We show that the system enjoys properties like type uniqueness, subject reduction, soundness, confluence and weak normalization. |
|
| Statecharts via Process Algebra |
OCT 1999 |
12 pages |
| Authors:
Gerald Luettgen; Michael von der Beeck; Rance Cleaveland; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| State charts is a visual language for specifying the behavior of reactive system. The language extends finite-state machines with concepts of hierarchy, concurrency, and priority. Despite its popularity as a design notation for embedded systems, precisely defining its semantics has proved extremely challenging. In this paper, a simple process algebra, called State charts Process Language (SPL), is presented, which is expressive enough for encoding ... |
|
| Wavefront Cache-friendly Algorithm for Compact Numerical Schemes |
OCT 1999 |
13 pages |
| Authors:
Alex Povitsky; INSTITUTE FOR COMPUTER APPLICATIONS IN SCIENCE AND ENGINEERING HAMPTON VA
|
| This paper reports the performance of a parallel volume rendering algorithm for visualizing a large-scale unstructured-grid dataset produced by a three-dimensional aerodynamics simulation. This dataset, containing over 18 million tetrahedra, allows us to extend our performance results to a problem which is more than 30 times larger than the one we examined previously. This high resolution dataset also allows us to see fine, three-dimensional features ... |
|
Reports by Corporate Author
