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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Effect of solar radiation on a swarm of meteoric particles

The theory of the Poynting-Robertson effect is used to study the motion of meteors relative to a parent comet describing an undisturbed elliptical orbit. It is shown that any emitted particle proceeds to move retrogressively away from the comet to a certain maximum angular distance (as seen from the sun) depending on its sigma-s value, and then undergoes relative motion in the opposite forward direction. The time taken to reach this greatest elongation behind the comet is the same for all particles, and after twice this time the particles will have returned to zero angular displacement relative to the comet. For comet Encke the time for the elongation to return to zero is about 6600 y; for Halley it is about 200,000 y; for Temple-Tuttle (1965 IV) it is just over 100,000 y.

Lyttleton, R. A.↗
NASA NTRS1981

The influence of gyroscopic forces on the dynamic behavior of rotating blades

The question of divergent oscillatory stability of an axial turbomachine blade when the bladed rotor system is subjected to a forced precessional motion is studied by using two simplified models of the blade. The simplest (lumped) model is a point mass restrained by three orthogonal linear springs attached to the rotor. An improved distributed parameter model represents the blade by a uniform cantilever beam with bending in one plane. In both instances instability is shown to be strongly dependent upon the ratio of blade root radius to blade length and the magnitude of the rotor spin relative to the nonrotating blade natural frequency for realistic values of precession rate. Results are presented on augmented Campbell diagrams. Implications for design and operation are drawn as are the characteristics of needed future studies.

Sisto, F.↗
NASA NTRS1981

Basic lubrication equations

Lubricants, usually Newtonian fluids, are assumed to experience laminar flow. The basic equations used to describe the flow are the Navier-Stokes equation of motion. The study of hydrodynamic lubrication is, from a mathematical standpoint, the application of a reduced form of these Navier-Stokes equations in association with the continuity equation. The Reynolds equation can also be derived from first principles, provided of course that the same basic assumptions are adopted in each case. Both methods are used in deriving the Reynolds equation, and the assumptions inherent in reducing the Navier-Stokes equations are specified. Because the Reynolds equation contains viscosity and density terms and these properties depend on temperature and pressure, it is often necessary to couple the Reynolds with energy equation. The lubricant properties and the energy equation are presented. Film thickness, a parameter of the Reynolds equation, is a function of the elastic behavior of the bearing surface. The governing elasticity equation is therefore presented.

Hamrock, B. J.↗
NASA NTRS1982

An analytical approach to thermal modeling of Bridgman-type crystal growth. I - One-dimensional analysis

A relatively simple one-dimensional thermal model of the Bridgman growth process has been developed which is applicable to the growth of small diameter samples with conductivities similar to those of metallic alloys. The heat flow in a translating rod is analyzed in a way that is applicable to Biot numbers less than unity. The model accommodates an adiabatic zone, different heat transfer coefficients in the hot and cold zones, and changes in sample material properties associated with phase change. The analysis is applied to several simplified cases. The effect of the rod's motion is studied in a three-zone furnace for a rod sufficiently long that end effects can be neglected; end effects are then investigated for a motionless rod. Finally, the addition of a fourth zone, an independently controlled booster heater between the main heater and the adiabatic zone, is evaluated for its ability to increase the gradient in the sample at the melt interface and to control the position of the interface.

Naumann, R. J.↗
NASA NTRS1982

Morphology and movements of polarization features on Venus

Ground and spacecraft based polarization observations of Venus detected the signature of the so called 1-micron radius cloud particles that constitute the main cloud deck on Venus, as well as that of sub-micron sized particles that form a haze above this main cloud layer. Whether such observations showed any local clustering or organization in the polarimetry data remained uncertain until the relatively high resolution observations from the Pioneer Venus Orbiter Cloud Photopolarimeter (OCPP) became available. The available polarization data from this instrument was studied to see whether local organization was present, to study the morphology of such features or polarization clouds, and finally, to see if they can be followed in a sequence of observations to study their motions.

Limaye, S. S.↗
NASA NTRS1984

Predictability of the Earth's polar motion

A comprehensive, experimental study of the predictability of the polar motion using a homogeneous BIH (Bureau International de l'Heure) data set is presented. Based on knowledge of the physics of the annual and the Chandler wobbles, the numerical model for the polar motion is constructed by allowing the wobble periods to vary. Using an optimum base length of 6 years for prediction, this floating-period model, equipped with a non-linear least-squares estimator, is found to yield polar motion predictions accurate from 0.012 to 0.024 inches depending on the prediction length up to one year, corresponding to a predictability of 91-83%. This represents a considerable improvement over the conventional fixed-period predictor, which does not respond to variations in the apparent wobble periods. The superiority of the floating-period predictor to other predictors based on critically different numerical models is also demonstrated.

Chao, B. F.↗
NASA NTRS1984

Lateral fluid forces acting on a whirling centrifugal impeller in vaneless and vaned diffuser

Fluid forces on a rotating centrifugal impeller in whirling motion were studied. A two dimensional impeller installed in a parallel-walled vaneless and vaned diffuser whirled on a circular orbit with various positive and negative angular velocities. It is shown that the fluid forces exert a damping effect on the rotor in most operating conditions, but become excitatory when the impeller operates at very low partial discharge while rotating far faster than the whirl speed. The fluid forces were expressed in terms of mass, damping and stiffness matrices. Impellers with the same geometry and whirl condition are calculated. Quantitative agreement is obtained especially in positive whirl.

Ohashi, H.↗
NASA NTRS1985

ISEE particle observations of surface waves at the magnetopause boundary layer

The dual-spacecraft ISEE mission provides a unique opportunity to study the motions of the magnetopause and adjacent boundary layer. By comparing high-time-resolution energetic particle data from ISEE 1 to those of ISEE 2, the velocity and orientation of the inner boundary of the boundary layer can be determined. Two cases are presented. In one, tailward propagating sinusoidally shaped surface waves with a wavelength in excess of 42,000 km and an amplitude of approximately 5000 km are found. In the other, surface waves are indicated with a wavelength of approximately 40,000 km and an amplitude of approximately 11,000 km having steepened nonsinusoidal shapes. The existence of such large-amplitude waves suggests that the particle dynamics near the magnetopause support nonlinear processes.

Couzens, D.↗
NASA NTRS1985

Parametric testing of a linearly driven Stirling cryogenic refrigerator

The parametric testing of a novel Stirling cycle cryogenic refrigerator which incorporates electromagnetic bearings, clearance seals and electronically controlled linear motion was studied. The last feature, which involves the use of two linear motors, position transducers and a highly accurate electronic feedback network, produces the system capability which forms the basis for the tests. The test results provide designers with an understanding of the basic operation of the Stirling cycle and give potential users some indication of the capabilities of this refrigerator under off design conditions.

Stolfi, F. R.↗
NASA NTRS1986

Observations of mesoscale vertical velocities around frontal zones

Vertical velocity and reflectivity data obtained with a VHF Doppler radar over a 15-day period in October and November of 1981 are analyzed. Standard radiosonde data and surface observations were used to locate two occluded fronts, two warm fronts, and a cold front that passed the radar site. These fronts are also evident in the radar reflectivity data. Most studies of the vertical circulation patterns associated with mososcale systems have used precipitation and cloud formations as tracers. Unlike other observational techniques, the VHF radar permits the continuous measurement of the three-dimensional air velocity vector in time and height from a fixed location. With the beam in a vertically pointing position, signals are scattered from turbulent variations in the refractive index with half the scale of the radar wavelength and by regions with sudden changes in the refractive index associated with horizontally stratified layers. Generally, the strongest echoes occur at the maximum in the vertical gradient of refractivity, usually at the base of a temperature inversion, such as the tropopause. VHF radars can also be used to locate atmospheric fronts, which are characterized by static stability, large horizontal temperature gradients, large vorticities, and vertical wind shears. These radars can provide the velocity field data needed to study wave motions associated with fronts and compare the actual vertical circulation to theoretical predictions.

Dennis, T. S.↗
NASA NTRS1987

A versatile and low order hybrid stress element for general shell geometry

A hybrid stress general shell element is developed based on the Hellinger-Reissner principle modified for relaxed element compatibility conditions. The element is based on a consistent first order thin shell theory with Love Kirchhoff hypotheses. It is of quadrilateral shape with only four corner nodes and five degrees of freedom per node. The geometry of the element is approximated through a bi-cubic polynomial surface patch. Numerical examples consist of torsion-loaded slit cylinder and pinched cylinder with open ends and rigid diaphragmed ends. Also, the representation of the rigid body motion is studied by series of parametric eigenvalue analysis of the stiffness matrix.

Kang, David S.↗
NASA NTRS1988

Eye and head motion during head turns in spaceflight

Eye-head motion was studied pre-, in- and postflight during single voluntary head turns. A transient increase in vestibulo-ocular reflex (VOR) gain occurred early in the flight, but later trended toward normal. This increased gain was produced by a relative increase in eye counterrotation velocity. Asymmetries in gain with right and left turns also occurred, caused by asymmetries in eye counterrotation velocities. These findings were remarkably similar to those from Soviet primate studies using gaze fixation targets, except the human study trended more rapidly toward normal. These findings differ substantially from those measuring VOR gain by head oscillation, in which no significant changes were found inflight. No visual disturbances were noted in either test condition or in normal activities. These head turn studies are the only ones to date documenting any functional change in VOR in weightlessness.

Thornton, William E.↗
NASA NTRS1989

Orbit design and perturbation analysis for Mars rover and sample return mission concepts

Mission options using out-of-orbit entry and Mars orbit rendezvous before earth return are discussed. The following major flight elements are required to conduct a Mars rover and sample return mission: the rover, the sample return orbiter, and the Mars ascent vehicle. The effects of perturbations on orbital motion are studied using Cowell's method and an averaging technique.

Kwok, Johnny H.↗
NASA NTRS1990

The peculiar velocity field in the Perseus-Pisces supercluster

Results are reported from a program to study peculiar motions of galaxies in the Per-Psc supercluster. The data set consists of newly obtained CCD photometry and published 21-cm line widths for 320 spiral galaxies. The peculiar velocities of these objects are estimated using the Tully-Fisher relation, calibrated with respect to an independent sample of cluster galaxies. Analysis shows that the principal feature of the velocity field in the Per-Psc region is a coherent streaming toward the Local Group. Nearly all the galaxies well in the foreground (cz less than about 2000 km/sec) have negtive peculiar velocities of amplitude about 1000 km/sec. A great majority of objects in the background of the supercluster, out to redshifts of about 7000 km/sec, also have very large negative peculiar velocities. The supercluster ridge itself, at a redshift or about 5000 km/sec, appears to consist of positive and negative peculiar-velocity groups of galaxies, but with negative peculiar velocities predominating both in amplitude and in number of objects involved.

Willick, Jeffrey A.↗
NASA NTRS1990

Heart rate and pulmonary function while wearing the launch-entry crew escape suit (LES) during + Gx acceleration and simulated Shuttle launch

Space shuttle crewmembers have been equipped with a launch-entry crew escape system (LES) since the Challenger accident in 1986. Some crewmembers, wearing the new pressure suit, have reported breathing difficulties and increased effort to achieve the desired range of motion. This study was conducted to quantify the reported increased physical workloads and breathing difficulty associated with wearing the LES. Both veteran astronauts and centrifuge panel members were exposed to various + Gx profiles (including simulated shuttle launch) + Gx on the USAF School of Aerospace Medicine (USAFSAM) human-use centrifuge. Maximum heart rate data showed no increased workload associated with arm and head movement in the LES when compared to the flight suit/helmet ensemble (LEH). However, the LES did impose a significant increase in breathing difficulty beginning at +2.5 Gx which was demonstrated by a decrease in forced vital capacity and subjected questionnaries.

Krutz, Robert W., Jr.↗
NASA NTRS1989

Creation of fully vectorized FORTRAN code for integrating the movement of dust grains in interplanetary environments

The main objective is to improve the performance of a specific FORTRAN computer code from the Planetary Sciences Division of NASA/Johnson Space Center when used on a modern vectorizing supercomputer. The code is used to calculate orbits of dust grains that separate from comets and asteroids. This code accounts for influences of the sun and 8 planets (neglecting Pluto), solar wind, and solar light pressure including Poynting-Robertson drag. Calculations allow one to study the motion of these particles as they are influenced by the Earth or one of the other planets. Some of these particles become trapped just beyond the Earth for long periods of time. These integer period resonances vary from 3 orbits of the Earth and 2 orbits of the particles to as high as 14 to 13.

Colquitt, Walter↗
NASA NTRS1990

A parametric shell analysis of the shuttle 51-L SRB AFT field joint

Following the Shuttle 51-L accident, an investigation was conducted to determine the cause of the failure. Investigators at the Langley Research Center focused attention on the structural behavior of the field joints with O-ring seals in the steel solid rocket booster (SRB) cases. The shell-of-revolution computer program BOSOR4 was used to model the aft field joint of the solid rocket booster case. The shell model consisted of the SRB wall and joint geometry present during the Shuttle 51-L flight. A parametric study of the joint was performed on the geometry, including joint clearances, contact between the joint components, and on the loads, induced and applied. In addition combinations of geometry and loads were evaluated. The analytical results from the parametric study showed that contact between the joint components was a primary contributor to allowing hot gases to blow by the O-rings. Based upon understanding the original joint behavior, various proposed joint modifications are shown and analyzed in order to provide additional insight and information. Finally, experimental results from a hydro-static pressurization of a test rocket booster case to study joint motion are presented and verified analytically.

Davis, Randall C.↗
NASA NTRS1991

Development of advanced control schemes for telerobot manipulators

To study space applications of telerobotics, Goddard Space Flight Center (NASA) has recently built a testbed composed mainly of a pair of redundant slave arms having seven degrees of freedom and a master hand controller system. The mathematical developments required for the computerized simulation study and motion control of the slave arms are presented. The slave arm forward kinematic transformation is presented which is derived using the D-H notation and is then reduced to its most simplified form suitable for real-time control applications. The vector cross product method is then applied to obtain the slave arm Jacobian matrix. Using the developed forward kinematic transformation and quaternions representation of the slave arm end-effector orientation, computer simulation is conducted to evaluate the efficiency of the Jacobian in converting joint velocities into Cartesian velocities and to investigate the accuracy of the Jacobian pseudo-inverse for various sampling times. In addition, the equivalence between Cartesian velocities and quaternion is also verified using computer simulation. The motion control of the slave arm is examined. Three control schemes, the joint-space adaptive control scheme, the Cartesian adaptive control scheme, and the hybrid position/force control scheme are proposed for controlling the motion of the slave arm end-effector. Development of the Cartesian adaptive control scheme is presented and some preliminary results of the remaining control schemes are presented and discussed.

Nguyen, Charles C.↗