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  • 1
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    Viscous Effects on Hypervelocity Impact (1971)
    American Institute of Physics
    Details
    Publication Date: 1971-10-01
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics
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    PAPER CURRENT
  • 2
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    Suspension-line wave motion during the lines-first parachute unfurling process (1974)
    In:  Other Sources
    Details
    Publication Date: 2011-08-16
    Description: A new mathematical approach to modeling the lines-first parachute unfurling process is presented. The unfurling process is treated as two distinct phases: a suspension-line unfurling phase, during which a massless-spring model of the suspension-line elasticity may be employed; and a canopy unfurling phase, during which a formulation considering suspension-line wave mechanics is employed. Histories of unfurled length and tension at the vehicle obtained using the model are compared with flight test data, and generally good agreement is observed.
    Keywords: AIRCRAFT
    Type: AIAA Journal; 12; Jan. 197
    Format: text
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  • 3
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    Stability analysis for linear systems with time delays (1977)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: Time delays in the mathematical description of a physical system occur whenever the system is affected not only by conditions at the present time, but also by conditions which have occurred in the past. The tau-decomposition method, as refined by Lee and Hsu, is a method for studying the effects of time delay on the stability of retarded dynamical systems. In this paper, the method is extended to examine the stability and relative stability of: (1) retarded systems with many time delays; and (2) a class of neutral systems with one delay. Applications are included which illustrate the power of the technique.
    Keywords: PHYSICS (GENERAL)
    Type: Journal of Sound and Vibration; 51; Mar. 8
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    Stability of neutral equations with constant time delays (1976)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: A method was developed for determining the stability of a scalar neutral equation with constant coefficients and constant time delays. A neutral equation is basically a differential equation in which the highest derivative appears both with and without a time delay. Time delays may appear also in the lower derivatives or the independent variable itself. The method is easily implemented, and an illustrative example is presented.
    Keywords: NUMERICAL ANALYSIS
    Type: Advan. in Eng. Sci., Vol. 2; p 757-768
    Format: application/pdf
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  • 5
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    Boundary layer effects on the flowfield about flow-through nacelles (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A numerical study has been made of boundary layer effects on the flowfield about flow-through nacelles. A viscous-inviscid interacting computational model for investigating the problem was constructed by coupling a three-dimensional explicit Euler solution procedure with a compressible, 'lag-entrainment' integral boundary layer solution technique. Solutions obtained with the interacting model for long-duct turbofan engine nacelles at a free stream Mach number of 0.8 and an angle of attack of 0 deg are compared with experimental data. The numerical experiments have revealed insight into the boundary layer effects on the interactions between the internal and external flows.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 85-1623
    Format: text
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  • 6
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    Analytical method for determining the stability of linear retarded systems with two delays (1975)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The stability is considered of the solution differential-difference equations of the retarded type with constant coefficients and two constant time delays. A method that makes use of analytical expressions to determine stability boundaries, and the stability of the system, is derived. The method was applied to a system represented by a second-order differential equation with constant coefficients and time delays in the velocity and displacement terms. The results obtained is in agreement with those obtained by other investigators.
    Keywords: MATHEMATICAL AND COMPUTER SCIENCES (GENERAL)
    Type: NASA-TR-R-446 , L-10303
    Format: application/pdf
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  • 7
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    Three-dimensional Euler solutions for long-duct nacelles (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: A three-dimensional Euler-equation computational technique has been developed to solve for the transonic flow past flow-through nacelles. The technique employs an approximately-factored alternating-direction implicit numerical algorithm and a radiation treatment of the outflow boundary. Studies are presented which show that the radiation treatment gives better numerical convergence than the condition of specifying the pressure at the outflow boundary. Calculations made with the technique are presented for a long-duct turbofan engine nacelle at a Mach number of 0.80 and angles of attack of 0 deg and 4 deg. Good agreement is shown between the computational results and wind-tunnel data. Problem areas are identified and recommendations are made for further numerical studies.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 83-0089 , American Institute of Aeronautics and Astronautics, Aerospace Sciences Meeting; Jan 10, 1983 - Jan 13, 1983; Reno, NV
    Format: text
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  • 8
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    A research program in active control/aeroelasticity in the JIAFS at NASA Langley Research Center (1984)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A control law synthesis methodology for multifunctional active control system to satisfy root-mean-square load and response constraints as well as to meet stability robustness requirements at plant input and output was developed. Modern control theory, singular value analysis and optimization techniques were utilized. All stability and response derivative expressions were derived analytically for sensitivity study. The software is incorporated as an update to the AB/LAD general control design software package PADLOCS.
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Type: NASA-CR-174052 , NAS 1.26:174052
    Format: application/pdf
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  • 9
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    Influence of grazing flow on duct wall normal impedances (1975)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: A theory is developed for evaluating the normal impedance of an orifice connecting a cylindrical cavity to a flow duct. The impedance of a piston velocity source at the orifice is calculated in terms of the cavity modes which are modified by the presence of a vortex flow. The strength of the vortex is related to the mean flow in the duct. Results are presented showing the variation of the normal impedance spectrum with the cavity vortex. The trends of these variations are confirmed by comparison with measurements.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 75-494 , American Institute of Aeronautics and Astronautics, Aero-Acoustics Conference; Mar 24, 1975 - Mar 26, 1975; Hampton, VA
    Format: text
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