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Lee, Y. C.

Publications and source records attributed to Lee, Y. C..

31 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Electrostatic ion-cyclotron instability caused by a nonuniform electric field perpendicular to the external magnetic field

A new mechanism that can destablize kinetic ion-cyclotron waves in the presence of a nonuniform electric field perpendicular to the uniform ambient magnetic field is given. In the absence of the electric field, the mode energy is positive, while in the presence of a uniform electric field the mode energy could be negative. However, when the electric field is nonuniform, it is possible for a finite region to be of negative wave energy surrounded by regions of positive wave energy. A nonlocal wave packet couples the two regions so that a flow of energy from the region of negative wave energy to the region of positive wave energy will cause the mode to grow. This gives rise to the instability.

Ganguli, G.↗
NASA NTRS1983

Calculation of Shuttle Base Heating Environments and Comparison with Flight Data

The techniques, analytical tools, and experimental programs used initially to generate and later to improve and validate the Shuttle base heating design environments are discussed. In general, the measured base heating environments for STS-1 through STS-5 were in good agreement with the preflight predictions. However, some changes were made in the methodology after reviewing the flight data. The flight data is described, preflight predictions are compared with the flight data, and improvements in the prediction methodology based on the data are discussed.

Greenwood, T. F.↗
NASA NTRS1983

Space Shuttle base heating

First-stage and second-stage heating environments of the base region of the Space Shuttle are characterized in detail in terms of Orbiter-main-engine-plume and booster-plume radiation, freestream-air convective cooling, and reversed-plume-flow convective heating as they affect each base-region design point. Design predictions are compared with selected heating-rate data from flights STS-1 through STS-5; the flight data are found to show excellent interflight repeatability independent of small changes in trajectory, and to verify the validity of the prediction methodology. The impact of individual flight events on base heating is indicated.

Greenwood, T. F.↗
NASA NTRS1980

STS-1 Nominal Cycle 3 March/April Launch, Ascent Base Convective Heating Environments

Ascent base convective heating environments were determined for the nominal ascent trajectory for the STS-1 Cycle 3 March/April launch period. Both first and second stage environments are defined for all base heating DFI locations and design body points of interest. An identical format to the STS-1 dispersed trajectory environment was followed throughout. As expected, STS-1 nominal environments are generally less severe than those determined for the high loft and low loft dispersed trajectory conditions. The reduction in cold wall heating with the nominal trajectory varies for each base location analyzed, but, in general, was approximately twenty percent.

Bender, R. L., Jr.↗
NASA NTRS1979

A computer program for thermal radiation from gaseous rocket exhuast plumes (GASRAD)

A computer code is presented for predicting incident thermal radiation from defined plume gas properties in either axisymmetric or cylindrical coordinate systems. The radiation model is a statistical band model for exponential line strength distribution with Lorentz/Doppler line shapes for 5 gaseous species (H2O, CO2, CO, HCl and HF) and an appoximate (non-scattering) treatment of carbon particles. The Curtis-Godson approximation is used for inhomogeneous gases, but a subroutine is available for using Young's intuitive derivative method for H2O with Lorentz line shape and exponentially-tailed-inverse line strength distribution. The geometry model provides integration over a hemisphere with up to 6 individually oriented identical axisymmetric plumes, a single 3-D plume, Shading surfaces may be used in any of 7 shapes, and a conical limit may be defined for the plume to set individual line-of-signt limits. Intermediate coordinate systems may specified to simplify input of plumes and shading surfaces.

Reardon, J. E.↗
NASA NTRS1979

Choice of method for discretization of continuous systems

The paper discusses and compares several common methods of discretizing the transfer function of a continuous control system so that a digital computer can be used. The discretization effect on the frequency response attenuation of the simple transfer function G(s) = 1/(s + 1) is illustrated for the Tusting, Boxer-Thaler, Madwed, linear segment approximation, and stair-step with half period advanced methods. The input frequency must be significantly lower than one-half the sampling error to have negligible discretization error. Phase differences due to discretization are also plotted, and it is seen that the zero-order hold contributes much more phase shift than that due to discretization. In situations where zero-order hold must follow a computer, the method of discretization of a continuous system is not a major factor if phase shift is important.

Mcvey, E. S.↗
NASA NTRS1978

Space shuttle main engine plume radiation model

The methods are described which are used in predicting the thermal radiation received by space shuttles, from the plumes of the main engines. Radiation to representative surface locations were predicted using the NASA gaseous plume radiation GASRAD program. The plume model is used with the radiative view factor (RAVFAC) program to predict sea level radiation at specified body points. The GASRAD program is described along with the predictions. The RAVFAC model is also discussed.

Reardon, J. E.↗
NASA NTRS1978

SSV Generic OFT first stage ascent base convective heating environments

Space Shuttle Vehicle (SSV) base convective heating environments during the recirculated flow time segment of first stage ascent were determined for the Generic OFT trajectory and performance conditions. These environments are presented in the attachments as cold wall convective heat transfer coefficients for individual or groups of design points for all affected SSV base surfaces. Two gas recovery temperatures applicable to upper and lower base region surfaces are also included. The environments were based upon magnitudes and trends from analysis of data taken during Base Heating Tests IH-39, IH-75, and IH-83. The plume heating trajectory and performance data were supplied by Rockwell International for both the OFT-1 Generic Mission A and Mission C.

Bender, R. L., Jr.↗
NASA NTRS1975

Quiet time inflation of the inner magnetosphere in the afternoon and evening quadrants

The quiet-time depression of the magnetic field magnitude in the equatorial inner magnetosphere was studied for the interval Nov. 1971-June 1972. For periods when Kp was less than 2 and Dst was between +10 and -20 gamma, an inflated field region near the magnetic equator was found between noon and midnight. The inflation was greatest at the lowest altitude studied (L = 3) and appeared to be somewhat greater near midnight (-40 gamma) than near noon (-20 gamma). Protons of energy above 100 keV observed on the same satellite appeared to be sufficient to produce the quiet-time inflation.

Lee, Y. C.↗
NASA NTRS1971

Analysis of cavitation bubble dynamics in a liquid

General differential equations governing the dynamics of the cavitation bubbles in a liquid were derived. With the assumption of spherical symmetry the governing equations were simplified. Closed form solutions were obtained for simple cases, and numerical solutions were calculated for complicated ones. The growth and the collapse of the bubble were analyzed, oscillations of the bubbles were studied, and the stability of the cavitation bubbles were investigated. The results show that the cavitation bubbles are unstable, and the oscillation is not sinusoidal.

Fontenot, L. L.↗
NASA NTRS1971

Forced axisymmetric response of fluid filled spherical shells.

A general solution for the forced, linear axisymmetric response of a fluid filled spherical shell is derived with the effects of shell transverse shear and rotational inertia included. The fluid is assumed to be inviscid and compressible. Expressions for the shell radial displacement are computed for the problem of a uniform radial Heaviside load on a cap of the shell surface. In addition, the time history of the shell inner fiber stresses at the impact pole is obtained. Some comparisons with the in vacuo shell theory are also given.

Lee, Y. C.↗