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  • 1
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    Transient scattering from two-dimensional dielectric cylinders of arbitrary shape (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: In this work, the problem of transient scattering by arbitrary shaped two-dimensional dielectric cylinders is solved using the marching-on-in-time (MOT) technique. The dielectric problem is approached via the surface equivalence principle. A pair of coupled integral equations are derived by enforcing the continuity of the electric and magnetic fields which are solved by using the method of moments. Numerical results are presented for two cross sections, viz. a circle and a square, and compared with inverse discrete Fourier transform (IDFT) techniques. In each case, good agreement is obtained with the IDFT solution.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Antennas and Propagation (ISSN 0018-926X); 40; 9; p. 1054-1060.
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  • 2
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    Transient scattering from dielectric cylinders - E-field, H-field, and combined field solutions (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: In this work, the problem of transient scattering by arbitrarily shaped two-dimensional dielectric cylinders is solved using the marching-on-in-time technique. The dielectric problem is approached via the equivalence principle. Three different formulations, namely, the electric field integral equation formulation, the magnetic field integral equation formulation, and the combined field integral equation formulation are considered. Numerical results are presented for two cross sections, namely, a circle and a square, and compared with inverse discrete Fourier transform (IDFT) techniques. In each case, good agreement is obtained with the IDFT solution.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Radio Science (ISSN 0048-6604); 27; 5; p. 611-622.
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  • 3
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    Electromagnetic scattering from arbitrary shaped conducting bodies coated with lossy materials of arbitrary thickness (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A simple and efficient numerical technique is presented to solve the electromagnetic scattering problem of coated conducting bodies of arbitrary shape. The surface equivalence principle is used to formulate the problem in terms of a set of coupled integral equations involving equivalent electric and magnetic surface currents which represent boundary fields. The conducting structures and the dielectric materials are modeled by planar triangular patches, and the method of moments is used to solve the integral equations. Numerical results for scattering cross sections are given for various structures and compared with other available data. These results are proved accurate by a number of representative examples.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Antennas and Propagation (ISSN 0018-926X); 39; 627-631
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  • 4
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    Analysis of a slot loaded microstrip disk antenna for circular polarisation (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A method is presented to analyze a circular microstrip disk antenna loaded with a narrow, inclined slot at its center and fed by a coaxial probe. Making use of the exact dyadic Green's functions for a grounded dielectric slab due to electric and magnetic currents, Richmond's reaction integral equation in conjunction with the method of moments (Galerkin), a generalized h-parameter equivalent network for the loaded patch is obtained. An expression for the input impedance of a slot loaded microstrip patch is obtained from the equivalent parameters. The theoretical results are compared with the experiment.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Archiv fuer Elektronik und Uebertragungstechnik (ISSN 0001-1096); 45; 386-389
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  • 5
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    Vortex control: Further encounters (1991)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: The progress of continuing investigations on vortex control techniques is updated. The following topics are briefly discussed: (1) vortex flaps adapted for high-alpha control; (2) alleviation of leading edge extension (LEX) vortex induced twin-tail buffet; (3) controlled decoupling of interactive forebody chine and wing vortices; (4) forebody vortex manipulation by mechanical and pneumatic techniques; and (5) stall-departure alleviation of high aspect-ratio wings. Salient results of exploratory low speed wind tunned experiments are presented. The investigations, primarily aimed at concept validation, were performed on generic configurations utilizing flow visualizations and pressure and balance measurements. Selected results illustrate the efficacy and potential for development of specific vortex control concepts for improved high-alpha configuration aerodynamics.
    Keywords: AERODYNAMICS
    Type: AGARD, Vortex Flow Aerodynamics; 12 p
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  • 6
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    Semi-empirical model for prediction of unsteady forces on an airfoil with application to flutter (1992)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A semi-empirical model is described for predicting unsteady aerodynamic forces on arbitrary airfoils under mildly stalled and unstalled conditions. Aerodynamic forces are modeled using second order ordinary differential equations for lift and moment with airfoil motion as the input. This model is simultaneously integrated with structural dynamics equations to determine flutter characteristics for a two degrees-of-freedom system. Results for a number of cases are presented to demonstrate the suitability of this model to predict flutter. Comparison is made to the flutter characteristics determined by a Navier-Stokes solver and also the classical incompressible potential flow theory.
    Keywords: AERODYNAMICS
    Type: NASA-TM-105414 , E-6820 , NAS 1.15:105414
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  • 7
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    Subsonic investigations of vortex interaction control for enhanced high-alpha aerodynamics of a chine forebody/Delta wing configuration (1992)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A proposed concept to alleviate high alpha asymmetry and lateral/directional instability by decoupling of forebody and wing vortices was studied on a generic chine forebody/ 60 deg. delta configuration in the NASA Langley 7 by 10 foot High Speed Tunnel. The decoupling technique involved inboard leading edge flaps of varying span and deflection angle. Six component force/moment characteristics, surface pressure distributions and vapor-screen flow visualizations were acquired, on the basic wing-body configuration and with both single and twin vertical tails at M sub infinity = 0.1 and 0.4, and in the range alpha = 0 to 50 deg and beta = -10 to +10 degs. Results are presented which highlight the potential of vortex decoupling via leading edge flaps for enhanced high alpha lateral/directional characteristics.
    Keywords: AERODYNAMICS
    Type: NASA-CR-189641 , NAS 1.26:189641
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  • 8
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    High-alpha vortex decoupling investigations on a chine forebody/Delta wing configuration at transonic Mach numbers (1992)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A test program conducted in the LaRC 8-foot Transonic Pressure Tunnel on a blended chine/delta wing model to verify the concept of controlled vortex decoupling via inboard leading-edge flaps for improved high-alpha lateral/directional characteristics is discussed. This test extended the Mach number range of a data base previously generated in a LaRC 7 ft. by 10 ft High Speed Tunnel investigation. Six-component force/moment, forebody surface pressures, and central and twin tall static and dynamic loads were measured at Mach numbers of 0.4 to 1.2; laser light-sheet visualizations were also performed. Selected data are analyzed and discussed, emphasizing lateral/directional improvements and tail environment enhanced attainable by leading-edge flaps in the maximum lift region.
    Keywords: AERODYNAMICS
    Type: NASA-CR-189642 , NAS 1.26:189642
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  • 9
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    Simulation and analysis of a delta planform with multiple jets in ground effect (1990)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The three-dimensional, thin-layer Navier-Stokes equations on a body-conforming, overset, multiple-grid topology are solved in the present numerical simulations of the flow around a 60-deg delta-planform wing equipped with two thrust-reverser jets in ground-effect conditions. Such experimentally flow-visualized features as jet-deformation and ground vertex-formation are captured by these simulations; the loss of wing-borne lift due to the 'suck-down' phenomenon, which arises as the delta planform flies at low speeds in close proximity to the ground, is also well simulated.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 90-0299
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  • 10
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    A low-speed wind tunnel study of vortex interaction control techniques on a chine-forebody/delta-wing configuration (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A low speed wind tunnel evaluation was conducted of passive and active techniques proposed as a means to impede the interaction of forebody chine and delta wing vortices, when such interaction leads to undesirable aerodynamic characteristics particularly in the post stall regime. The passive method was based on physically disconnecting the chine/wing junction; the active technique employed deflection of inboard leading edge flaps. In either case, the intent was to forcibly shed the chine vortices before they encountered the downwash of wing vortices. Flow visualizations, wing pressures, and six component force/moment measurements confirmed the benefits of forced vortex de-coupling at post stall angles of attack and in sideslip, viz., alleviation of post stall zero beta asymmetry, lateral instability and twin tail buffet, with insignificant loss of maximum lift.
    Keywords: AERODYNAMICS
    Type: In: ICAS, Congress, 18th, Beijing, China, Sept. 20-25, 1992, Proceedings. Vol. 2 (A93-14151 03-01); p. 2092-2103.
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