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A FINITE-DIFFERENCE SCHEME FOR A CLASS OF 1ST-ORDER ELLIPTIC PARTIAL-DIFFERENTIAL EQUATIONS

computerS & MATHEMATICS WITH applications 1985年第4期11卷 411-417页

作者： PHILLIPS, TN ROSE, ME Institute for Computer Applications in Science and Engineering NASA Langley Research Center Hampton VA 23665 USA U.S.A.

We describe a compact finite difference scheme to solve div v − q 2 u = 0, v = ϱ grad u , which does not depend upon first eliminating v , so as to obtain a single, higher-order equation. The finite difference equations can be efficiently solved by standard iterative methods, however, by first algebraically eliminating the flux components from the compact form. Energy estimates show that u is approximated to second-order accuracy.

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A compact finite element method for elastic bodies

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Numerical Methods for Partial Differential Equations 1985年第3期1卷 209-228页

作者： Rose, Milton E. Institute for Computer Applications in Science and Engineering

A nonconforming finite element method is described for treating linear equilibrium problems, and a convergence proof showing second order accuracy is given. The close relationship to a related compact finite difference scheme due to Phillips and Rose [1] is examined. A Condensation technique is shown to preserve the compactness property and suggests an approach to a certain type of homogenization. Copyright © 1985 Wiley Periodicals, Inc.

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Spectral methods for modeling supersonic chemically reacting flow fields

Spectral methods for modeling supersonic chemically reacting...

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AlAA 23rd Aerospace sciences Meeting, 1985

作者： Drummond, J. Philip Hussaini, M. Yousuff Zang, Thomas A. Computational Methods Branch High-speed Aerodynamics Division NASA Langley Research Center HamptonVA United States Institute for Computer Applications in Science and Engineering NASA Langley Research Center HamptonVA United States

A partial implicit numerical algorithm has been developed for solving the equations describing chemically reacting supersonic flows. The algorithm employs a two-stage Runge-Kutta method for integrating the equations in time and a Chebyshev spectral method for integrating the equations in space. The accuracy and efficiency of the new technique have been assessed by comparison with an existing implicit finite-difference procedure for modeling chemically reacting flows. The comparison showed that the new procedure yielded equivalent accuracy on much coarser grids as compared to the finite-difference procedure with resultant significant gains in computational efficiency. © 1985, American institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.

关键词： Runge Kutta methods

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Numerical experiments on subcritical transition mechanisms

Numerical experiments on subcritical transition mechanisms

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AlAA 23rd Aerospace sciences Meeting, 1985

作者： Zang, Thomas A. Hussaini, M. Yousuff Computational Methods Branch High-speed Aerodynamics Division NASA Langley Research Center HamptonVA United States Institute for Computer Applications in Science and Engineering NASA Langley Research Center HamptonVA United States

A spectral algorithm for simulating three-dimensional, incompressible, parallel shear flows is described. It applies to the channel, to the parallel boundary layer, and to other shear flows with one wall-bounded and two periodic directions. Simulations performed for the channel identify the one nonlinear interaction which is crucial to the secondary instability. Moreover, it is shown that subharmonic instability ensues for Reynolds numbers as low as 1500. Simulations performed for the heated water boundary layer reveal the operation of the secondary instability in this controlled flow. © 1985, American institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.

关键词： Boundary layers

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Forced magnetohydrodynamic turbulence in a uniform external magnetic field

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The Physics of Fluids 1985年第10期28卷 3074-3081页

作者： Murshed Hossain George Vahala David Montgomery Institute for Computer Applications in Science and Engineering NASA Langley Research Center Hampton Virginia 23665 Physics Department College of William and Mary Williamsburg Virginia 23185 and Institute for Computer Applications in Science and Engineering NASA Langley Research Center Hampton Virginia 23665 Physics and Astronomy Department Dartmouth College Hanover New Hampshire 03755

Two‐dimensional dissipative magnetohydrodynamic turbulence is randomly driven at small spatial scales and is studied by numerical simulation in the presence of a strong uniform external magnetic field. A novel behavior is observed which is apparently distinct from the inverse cascade that prevails in the absence of an external magnetic field. The magnetic spectrum becomes dominated by the three longest‐wavelength Alfvén waves in the system allowed by the boundary conditions: those which, in a box size of edge 2π, have wavenumbers (kx,ky) =(1,0),(1,1), and (1,−1), where the external magnetic field is in the x direction. At any given instant, one of these three modes dominates the vector potential spectrum, but they do not constitute a resonantly coupled triad. Rather, they are apparently coupled by the smaller‐scale turbulence.

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Chandrasekhar equations for infinite dimensional systems

Chandrasekhar equations for infinite dimensional systems

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IEEE Conference on Decision and Control

作者： Kazufumi Ito Robert Powers Division of Applied Mathematics Brown University Providence RI USA Institute of Computer Applications in Science and Engineering NASA-Langley Research Center Hampton VA USA

In this paper we state results on the existence of Chandrasekhar equations for linear time invariant systems defined on Hilbert spaces. An important consequence of this is that the solution to the evolutional Riccati equation is strongly differentiable in time and one can define a 'strong' solution of the Riccati differential equation. A discussion of the linear quadratic optimal control problem for hereditary differential systems is also included.

关键词： Equations Control systems Postal services NASA Tellurium

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AUTOMATION OF PROPELLER INSPECTION AND FINISHING

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NAVAL ENGINEERS JOURNAL 1985年第4期97卷 124-131页

作者： STERN, H METZGER, R Howard K. Stern:is presently vice president of Robotic Vision Systems Inc. He received a bachelor of electrical engineering degree from College of the City of New York in 1960. Mr. Stern joined Dynell Electronics Corporation in 1971 and became part of the Robotic Vision Systems Inc. staff at the time of its spin-off from Dynell. He was program manager of the various three-dimensional sensing and replication systems constructed by Dynell and Robotic Vision Systems. As program manager his responsibilities encompassed technical administrative and operational areas. The first two portrait sculpture studio systems and the first three replication systems built by Robotic Vision Systems Inc. were designed manufactured and operated under his direction. Before joining Dynell Mr. Stern was a senior engineer at Instrument Systems Corporation and chief engineer of the Special Products Division of General Instrument Corporation. Prior to these positions Mr. Stern was chief engineer of Edo Commercial Corporation. At General Instrument and Edo Commercial he was responsible for the design and manufacture of military and commercial avionics equipment. Mr. Stern is presently responsible for directing the systems design and development for all of the company's programs. Robert J. Metzger:is currently engineering group leader at Robotic Vision Systems Inc. He graduated summa cum laude from the Cooper Union in 1972 with a bachelor of electrical engineering degree. Under sponsorship of a National Science Foundation graduate fellowship he graduated from the Massachusetts Institute of Technology in 1974 with the degrees of electrical engineer and master of science (electrical engineering). In 1979 Mr. Metzger graduated from Polytechnic Institute of New York with the degree of master of science (computer science). Since 1974 Mr. Metzger has been actively engaged in the design of systems and software for noncontact threedimensional optical measurement for both military and commercial applications. Of particular note are his c

Ship's propellers are currently measured by manual procedures using pitchometers, templates and gauges. This measurement process is extremely tedious, labor intensive and time consuming. In an effort to provide increased accuracy, repeatability and cost effectiveness in propeller manufacture, an automated propeller optical measurement system (APOMS) has been built which rapidly and automatically scans an entire ship's propeller using a 3-D vision sensor. This equipment is integrated with a propeller robotic automated templating system (PRATS) and the propeller optical finishing system (PROFS) which robotically template and grind the propeller to its final shape, using the APOMS-derived data for control feedback. The optical scanning and the final shape are both controlled by CAD/CAM data files describing the desired propeller shape. An automated propeller balancing system is incorporated into the PROFS equipment. The APOMS/PRATS/PROFS equipment is expected to provide lower propeller manufacturing costs.

关键词： PROPELLERS

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A ROTATIONALLY BIASED UPWIND DIFFERENCE SCHEME FOR THE EULER EQUATIONS

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JOURNAL OF COMPUTATIONAL PHYSICS 1984年第1期56卷 65-92页

作者： DAVIS, SF Institute for Computer Applications in Science and Engineering NASA Langley Research Center Hampton Virginia 23665 USA

The upwind difference schemes of Godunov, Osher, Roe and van Leer are able to resolve one-dimensional steady shocks for the Euler equations within one or two mesh intervals. Unfortunately, this resolution is lost in two dimensions when the shock crosses the computing grid at an oblique angle. To correct this problem, a numerical scheme is developed which automatically locates the angle at which a shock might be expected to cross the computing grid then constructs separate finite difference formulas for the flux components normal and tangential to this direction. Numerical results are presented which illustrate the ability of this new method to resolve steady oblique shocks.

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ARCTIC TRAFFICABILITY PROGRAM - A REVIEW

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NAVAL ENGINEERS JOURNAL 1984年第3期96卷 169-175页

作者： VOELKER, R GLEN, IF SEIBOLD, F BAYLY, I Richard Voelker:is Vice President of ARCTEC Incorporated a firm specializing in cold regions technology. He has been responsible for the management of thePolarClass Traffic-ability Program since its inception and annually participates in the field data collection in the Arctic. His prior experience includes positions with the U.S. Coast Guard in the icebreaker design project the Military Sealift Command and at Newport News Shipbuilding. He is a graduate of N. Y.S. Maritime College and has a MS degree from the University of Michigan. I.F. Glen:received his professional degrees in naval architecture from the Royal Naval Engineering College Manadon Plymouth and RN College Greenwich London entering the Royal Corps of Naval Constructors in 1967. After serving as a Constructor Lieutenant in the Royal Navy's Far East Fleet for a short period he joined the Polaris submarine project team in Bath England in 1968. In 1971 he was seconded to the Canadian Department of National Defense in Ottawa as a Constructor Lieutenant Commander under NATO exchange arrangements where he had responsibilities initially for conventional submarines and latterly for computer aided conceptual design. He ventured to Bath England in 1974 and joined Forward Design Group. In 1975 he took a position as a civilian engineer in the Canadian Defense Department and was Head of Hull Systems Engineering from 1977 to 1979. He joined ARCTEC CANADA LIMITED in 1980 and in addition to managing ice model testing projects and full scale trials has specialized in structural response of ships to ice impact. He headed ARCTEC's Kanata Laboratory from 1981 to 1983 when he was promoted to president. Frederick Seibold:is a research program manager with the Maritime Administration's Office of Advanced Ship Development and Technology. He is responsible for the marine science program which includes research in the areas of ship powering structures and propeller performance and Arctic technology. Mr. Seibold has been employed by Mar Ad since 1961 having hel

This paper describes a multiyear program to make an operational assessment on the feasibility of a year-round Arctic marine transportation system to serve Alaska. Specifically, the three objectives were to: collect meteorological and ice data along potential marine routes; instrument the hull and propulsion machinery to improve design critera for ice-worthy ships; and demonstrate that ships can operate in midwinter Alaskan Arctic ice conditions. The U.S. Coast Guard's Polar class icebreakers were used to make the operational assessment by annually extending the route northward and by operating throughout the winter season. This paper reviews some of the operational and technical achievements to date, as well as plans for future Arctic deployments.

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AN ADVANCED METHODOLOGY FOR PRELIMINARY HULL FORM DEVELOPMENT

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NAVAL ENGINEERS JOURNAL 1984年第4期96卷 147-161页

作者： LIN, WC DAY, WG HOUGH, JJ KEANE, RG WALDEN, DA KOH, IY Wen-Chin Lin:heads the Ship Powering Division at the David Taylor Naval Ship R&D Center (DTNSRDC). Dr. Lin received his B.S. degree in mechanical engineering from the National Taiwan University in 1957. He was awarded his M.S. degree in naval architecture and Ph.D. in engineering science from the University of California at Berkeley in 1963 and 1966 respectively. From 1966 to 1969 he was employed by ESSO Research and Engineering Company to conduct marine hydrodynamic research for oil tankers and offshore structures. Since joining DTNSRDC in 1969 he has actively conducted and directed hydrodynamic research to advance naval ship design technology and improve ship performance. Active in national and international symposia on ship hydrodynamic research he is recognized for contributions to the ship research community. For the past six years he has been a member of the Performance Committee of the ITTC and currently serves as secretary of the committee. He is a member of SNAME and the Society of Naval Architects of Japan. William G. Day Jr:. has been employed as a naval architect at the David Taylor Naval Ship R&D Center since receiving a B.E.S. degree from the Johns Hopkins University in 1966. He obtained an M.S. E. degree from George Washington University in 1971. As Head Design Evaluation Branch of the Ship Performance Department he is responsible for model experiments to evaluate the hydrodynamic performance of ships and propulsors. He is a member of ASNE and SNAME. In-Young Koh:received his B.S. and M.S. degrees in electrical engineering from Lowell University in 1969 and 1971 respectively and his Ph.D. in applied mechanics from Rensselaer Polytechnic Institute in 1976. Dr. Koh joined DTNSRDC as an electronic engineer specializing in the application of advanced instrumentation and computer techniques to ship research and design. He is currently engaged in research and development of active control systems for naval ship applications. Dr. Koh is a member of ASNE SNAME and IEEE. David Andrew Walden:is

A ship design methodology is presented for developing hull forms that attain improved performance in both seakeeping and resistance. Contrary to traditional practice, the methodology starts with developing a seakeeping-optimized hull form without making concessions to other performance considerations, such as resistance. The seakeeping-optimized hull is then modified to improve other performance characteristics without degrading the seakeeping. Presented is a point-design example produced by this methodology. Merits of the methodology and the point design are assessed on the basis of theoretical calculations and model experiments. This methodology is an integral part of the Hull Form Design System (HFDS) being developed for computer-supported naval ship design. The modularized character of HFDS and its application to hull form development are discussed.

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