Engineering topics

Tsao, Y. D.

Publications and source records attributed to Tsao, Y. D..

At least 19 records

NASA NTRS1991

Study of Ardmore, Oklahoma storm clouds. I - Convective storm cloud initiation and development based on the remote sensing gravity-wave-induced convection. II - Satellite infrared remote sensing and numerical simulation

The role of gravity waves is discussed with respect to the vertical velocity of convection. Specific attention is given to wave-induced convection which contributes to the fractions of formation and the development of severe convective storms. Large-amplitude gravity waves and convective instability were investigated in storm clouds above Ardmore, Oklahoma. Rapid-scan satellite imagery and radar summaries provide evidence of water-vapor condensation related to convection which is introduced by gravity waves. Gravity wave periods of 35 minutes are found to initiate weak convection, which can be intensified by gravity waves with periods of 20 minutes. The convective motion reaches a maximum about one hour before funnel clouds develop. Other mechanisms which contribute to convective motion are considered, but gravity waves are the major contributor to the initiation, formation, and development of mesoscale storm clouds. Cloud modeling based on satellite imagery and sounding data showed that by overshooting cloud tops that penetrated the tropopause, storm clouds mature; that these clouds collapse about 9 minutes before the touchdown of tornadoes; and that cloud tops collapse at a high rate about 6 minutes before tornadoes lift off.

Hung, R. J.↗

NASA NTRS1990

Observations on thermospheric and mesospheric density disturbances caused by typhoons and convective storms

Atmospheric parameter observations have been conducted during the passage of typhoons and tropical storms, from the troposphere to the middle atmosphere, and thence to the thermosphere, using the VHF radar and HF Doppler sounder at an observation site in Taiwan. The density perturbations caused by the propagation of gravity waves due to the typhoons and tropical storms were calculated on the basis of these observations. The short-term middle atmospheric and thermospheric density changes are significant factors in spacecraft launches. The successful remote measurement of three-dimensional winds, gravity waves, and density perturbations is demonstrated for this subtropical site.

Hung, R. J.↗

NASA NTRS1990

Fluid behavior in microgravity environment

The instability of liquid and gas interface can be induced by the presence of longitudinal and lateral accelerations, vehicle vibration, and rotational fields of spacecraft in a microgravity environment. In a spacecraft design, the requirements of settled propellant are different for tank pressurization, engine restart, venting, or propellent transfer. In this paper, the dynamical behavior of liquid propellant, fluid reorientation, and propellent resettling have been carried out through the execution of a CRAY X-MP super computer to simulate fluid management in a microgravity environment. Characteristics of slosh waves excited by the restoring force field of gravity jitters have also been investigated.

Hung, R. J.↗

NASA NTRS1990

Dynamics of surface tension in microgravity environment

Time-dependent evolutions of the profile of free surface (bubble shapes) for a cylindrical container partially filled with a Newtonian fluid of constant density, rotating about its axis of symmetry, in low and microgravity environments, have been studied. Numerical computations of the dynamics of bubble shapes have been carried out (1) linear time-dependent functions of spin-up and spin-down in low and microgravity environments, (2) linear time-dependent functions of increasing and decreasing gravity environment at high and low rotating cylinder speeds, (3) time-dependent step functions of spin-up and spin-down in a low-gravity environment, and (4) sinusoidal function oscillation of the gravity environment at high and low rotating cylinder speeds.

Hung, R. J.↗

NASA NTRS1989

Atmospheric density remote sensing of mesosphere and thermosphere to be used for spacecraft design by adopting VHF radar and HF Doppler sounder at low latitude west Pacific site during winter time

Simultaneous observations of VHF radar and HF Doppler array systems located at Chung Li (Taiwan) are used to observe three-dimensional wind speeds and gravity waves. The density perturbations are determined at different altitudes of the mesosphere and thermosphere during weak convective motions of the cold front in the winter. The present observations are believed to be valuable for space projects dealing with the low-latitude atmosphere.

Hung, R. J.↗

NASA NTRS1989

Effect of G-jitters on the stability of rotating bubble under microgravity environment

The instability of liquid and gas interface can be induced by the pressure of longitudinal and lateral accelerations, vehicle vibration, and rotational fields of spacecraft in a microgravity environment. Characteristics of slosh waves excited by the restoring force field of gravity jitters have been investigated. Results show that lower frequency gravity jitters excite slosh waves with higher ratio of maximum amplitude to wave length than that of the slosh waves generated by the higher frequency gravity jitters.

Hung, R. J.↗

NASA NTRS1989

Response of gravity level fluctuations on the Gravity Probe-B spacecraft propellant system

Time-dependent computations have been performed to investigate the dynamical behaviors of fluid under a microgravity environment. A computer algorithm is introduced which can be used to simulate the fluid behavior in that environment, in particular the excitation of sloshing waves due to different gravity environments and rotation speeds. A suggestion on the proper handling and managing of cryogenic fluid propellant to be used in the Gravity Probe-B spacecraft propulsion is made.

Hung, R. J.↗

NASA NTRS1989

Bubble behaviors in a slowly rotating helium dewar in a Gravity Probe-B spacecraft experiment

Potential problems for the Gravity Probe-B (GP-B) spacecraft design requirements and the operational considerations could arise because of the free surface configurations between liquid helium and helium vapor in the rotating dewar. This free surface is present in the partially filled liquid helium dewar. The liquid helium in the dewar is depleted as it is consumed as propellant for the spacecraft. In this study, the doughnut-shaped helium bubble equilibrium profiles in the rotating dewar have been numerically calculated. These calculations were performed under the conditions imposed during the period of the GP-B experiment instrument calibration (gyro spinup period) and also during the normal operational stages of the GP-B spacecraft.

Hung, R. J.↗

NASA NTRS1989

Dynamical behavior of surface tension on rotating fluids in low and microgravity environments

Consideration is given to the time-dependent evolutions of the free surface profile (bubble shapes) of a cylindrical container, partially filled with a Newtonian fluid of constant density, rotating about its axis of symmetry in low and microgravity environments. The dynamics of the bubble shapes are calculated for four cases: linear time-dependent functions of spin-up and spin-down in low and microgravity, linear time-dependent functions of increasing and decreasing gravity at high and low rotating cylinder speeds, time-dependent step functions of spin-up and spin-down in low gravity, and sinusoidal function oscillation of the gravity environment in high and low rotating cylinder speeds. It is shown that the computer algorithms developed by Hung et al. (1988) may be used to simulate the profile of time-dependent bubble shapes under variations of centrifugal, capillary, and gravity forces.

Hung, R. J.↗

NASA NTRS1989

Axisymmetric bubble profiles in a slowly rotating helium dewar under low and microgravity environments

The Gravity Probe-B (GP-B) Spacecraft is designed to test the General Theory of Relativity through long-term monitoring the precession of a set of gyros in free-fall around the earth. The potential problems for GP-B Spacecraft design requirements could be due to asymmetry in the static liquid helium distribution, or to perturbations in free surface which is present in the partially-filled liquid helium dewar. In this study, doughnut-shaped helium bubble equilibrium profiles in rotating dewar, under the conditions during the period of GP-B experiment instrument calibration and also during the period of normal operation stages of GP-B Spacecraft, have been numerically calculated. For academic interest, the range of coverage has been extended beyond the conditions assigned by the GP-B Spacecraft experiment.

Hung, R. J.↗

NASA NTRS1989

Spectroscopic study of combustion diagnostics on hydroxyl radicals

Experimental observations of propane/air flames have been carried out. Measurements of hydroxyl (OH) radical concentration have been made using resonance line absorption techniques. A microwave-pumped low pressure discharge in argon and water vapor is employed to produce strong OH radical band radiation in the 308 nm region. This radiation is transmitted through the plume and absorption data is taken at various radial positions using an optical multichannel analyzer. This absorption data is used to compute OH number density using a model for the absorption band characteristics as a function of temperature based on an atlas of line strengths. A numerical computation of flow fields, temperature profile, OH number density and water vapor mass fraction profiles was carried out by using a technique of computational fluid dynamics (CFD). The results of CFD computation are compared with experimental observation with a good agreement.

Eskridge, Richard↗

NASA NTRS1989

Vibration of microgravity environment for rotating fluids in high and low rotating speeds

Time dependent evolutions of the profile of free surface (bubble shapes) for a cylindrical container partially filled with a Newtonian fluid of constant density, rotating about its axis of symmetry, have been studied. Numerical computations of the dynamics of bubble shapes have been carried out with the sinusoidal function vibration of gravity environment in high and low rotating cylinder speeds. The initial condition of bubble profiles was adopted from the steady-state formulations in which the computer algorithms have been developed by Hung and Leslie (1988), and Hung et al. (1988).

Hung, R. J.↗

NASA NTRS1989

VHF radar observations of mesospheric density distrubance caused by Typhoon Susan and tropical storms in the western Pacific area

The atmospheric parameters from the toposphere to the middle atmosphere during Typhoon Susan and tropical storms in May and June 1988 were observed by VHF radar in Taiwan. Time-dependent wind velocities with three-dimensional profiles are plotted by processing the backscattered echo power data and the Doppler spectral width of the signal returns from the VHF radar. The propagation characteristics of the gravity waves excited by the enhanced convection motions of the storms and the density perturbations caused by this gravity wave progagation are determined.

Hung, R. J.↗

NASA NTRS1989

Lower thermospheric density fluctuations during the time period of Typhoon Dinah

High frequency Doppler sounder arrays were used to study the thermospheric density fluctuations caused by Typhoon Dinah in August, 1987. The results show that the maximum density fluctuations caused by the typhoon at altitudes of 150 to 350 km were close to + or - 30 percent deviation from the quiet background. The time-dependent density fluctuations were in phase with the horizontal phase velocity of major gravity waves excited by the storm. It is suggested that the study demonstrates the use of HF Doppler sounder measurement of gravity waves, horizontal wind velocity in the direction of gravity wave propagation, and density perturbations at thermospheric heights.

Hung, R. J.↗

NASA NTRS1989

Satellite observation and mesoscale cloud modeling of St. Anthony, Minnesota storm clouds

Both rawinsonde data and geosynchronous satellite imagery were used to study the life cycles of St. Anthony, Minnesota's severe convective storms. Cloud modeling, with input sounding data from Saint Cloud, Minnesota, and rapid-scan imagery from GOES were used to investigate storm cloud formation, development and dissipation. Comparisons were made among the seven groups of severe storms which produced an outbreak of 30 tornadoes across the United States.

Hung, R. J.↗

NASA NTRS1989

Effect of gravity level fluctuations for rotating fluids in high and low rotating speeds

Hung, R. J.↗

NASA NTRS1989

Computer modeling of the dynamics of surface tension on rotating fluids in low and microgravity environments

Time-dependent evolutions of the profile of the free surface (bubble shapes) for a cylindrical container partially filled with a Newtonian fluid of constant density, rotating about its axis of symmetry, have been studied. Numerical computations have been carried out with the following situations: (1) linear functions of spin-up and spin-down in low- and microgravity environments, (2) linear functions of increasing and decreasing gravity environments at high- and low-rotating cylinder speeds, and (3) step functions of spin-up and spin-down in a low-gravity environment.

Hung, R. J.↗

NASA NTRS1988

Satellite remote sensing and cloud modeling of St. Anthony, Minnesota storm clouds and dew point depression

Rawinsonde data and geosynchronous satellite imagery were used to investigate the life cycles of St. Anthony, Minnesota's severe convective storms. It is found that the fully developed storm clouds, with overshooting cloud tops penetrating above the tropopause, collapsed about three minutes before the touchdown of the tornadoes. Results indicate that the probability of producing an outbreak of tornadoes causing greater damage increases when there are higher values of potential energy storage per unit area for overshooting cloud tops penetrating the tropopause. It is also found that there is less chance for clouds with a lower moisture content to be outgrown as a storm cloud than clouds with a higher moisture content.

Hung, R. J.↗