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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Charging and discharging characteristics of a rigid solar array

Two rigid solar array panels were subjected to a simulated geosynchronous orbit substorm environment. During the charging sequence, distributions of accumulated surface charge were measured under eclipse and sunlight conditions. Discharge events were characterized with respect to voltage pulse signatures and amplitudes on the solar array bus leads. Post-exposure analysis of the solar array panels indicated that the electrical characteristics were not degraded in spite of the substantial discharge actvity. However, significant cratering and discoloration of the Tedlar dielectric were observed.

Brady, G. F., Jr.↗
NASA NTRS1982

The motion of a drop in a rigid surface

The assumptions of a region of slip near a moving contact line (to remove the force singularity) and a constant contact angle are used to obtain the equation for the shape of a thin drop of liquid resting on a rigid plane. Three asymptotic expansions are matched together to obtain an expression for the rate at which the drop spreads. Some cases of sliding motion are also examined. Although the technique is presented here for thin drops only, it can also be applied to drops of arbitrary size.

Hocking, L. M.↗
NASA NTRS1982

Lubrication of rigid ellipsida solids

The influence of geometry on the isothermal hydrodynamic film separating two rigid solids was investigated. The minimum film thickness is derived for fully flooded conjunctions by using the Reynolds boundary conditions. It was found that the minimum film thickness had the same speed, viscosity, and load dependence as Kapitza' classical solution. However, the incorporation of Reynolds boundary conditions resulted in an additional geometry effect. Solutions using the parabolic film approximation are compared by using the exact expression for the film in the analysis. Contour plots are known that indicate in detail the pressure developed between the solids.

Hamrock, B. J.↗
NASA NTRS1981

Acoustic radiation force on a rigid sphere in a resonance chamber

The acoustic radiation force on a rigid sphere has been measured in a resonance chamber for a range of pressures, positions, sizes, and for various gases. In the low to medium intensity region of less than 150 dB, the measured force is consistent with King's theory (1934) when analyzed in terms of the fundamental pressure. However, in the high intensity region of greater than 150 dB, the measured force starts to deviate systematically from King's calculations.

Leung, E.↗
NASA NTRS1982

Torques on a nearly rigid body in a relativistic gravitational field

The effect of post-Newtonian potentials on the rotation of a perfect fluid, nearly rigid body is shown to consist of a precession and a torque. The frequency of the precession can be exactly represented by means of suitable differential operators. The relativistic torques, in the quadrupole approximation, depend on the instantaneous orientation of the principal axes of one body with respect to the position - like the classical torque - and velocity of the other. For a relatively low-mass body, such as a gyroscope, these velocity-dependent torques have no observable consequences.

Caporali, A.↗
NASA NTRS1982

On the dynamic collapse of a column impacting a rigid surface

Results are presented of an analytical investigation on the dynamic collapse of an elastic periodically supported column. The column has an attached mass at one end and impacts a rigid surface with prescribed velocity and angle of incidence at the other end. A first-order approximate nonlinear analysis is developed in which it is assumed that only first-order nonlinear terms need be retained. Differential equations are derived and solved numerically by explicit time integration in order to determine specific ranges of the basic nondimensional parameters for which the response characteristics are markedly different. To assess modeling sophistication relative to prediction accuracy, a comparison is made of the results from this approximate analysis with those of a finite element computer code based on a convected coordinate formulation.

Housner, J. M.↗
NASA NTRS1982

Acoustic propagation in a rigid torus

The acoustic propagation in a rigid torus is analyzed using a Green's function method. Three types of surface elements are developed; a flat quadrilateral element used in modeling polygonal cavities, a curved conical element appropriate for surfaces with one curvature, and a toroidal element developed for such doubly curved surfaces as the torus. Curved elements are necessary since the acoustic pressure is sensitive to slope discontinuities between consecutive surface elements especially near cavity resonances. The acoustic characteristics of the torus are compared to those of a bend of square cross section for a frequency range that includes the transverse acoustic resonance. Two equivalences between the different sections are tested; the first conserves curvature and cross-sectional dimension while the second matches transverse resonance and duct volume. The second equivalence accurately matches the acoustic characteristics of the torus up to the cutoff frequency corresponding to a mode with two circumferential waves.

El-Raheb, M.↗
NASA NTRS1982

Resonance frequency shift of an acoustic chamber containing a rigid sphere

The resonance frequency shift of an acoustic rectangular chamber due to the presence of a rigid sphere has been measured for l = 1,2 modes as a function of sphere size and position. The frequency shift is the results of volume exclusion and wave scattering. An analytical Green's function calculation was used to explain the data, providing excellent agreement between the measured and the calculated values. Also reported are similar measurements for a thin disk and the ratio of second harmonic to fundamental pressure as a function of sphere position. The measurement shows that the sphere reduces the first harmonic content, with sharply peaked suppression minima at specific sphere positions.

Leung, E.↗
NASA NTRS1982

Verification and transfer of thermal pollution model. Volume 3: Verification of 3-dimensional rigid-lid model

The six-volume report: describes the theory of a three dimensional (3-D) mathematical thermal discharge model and a related one dimensional (1-D) model, includes model verification at two sites, and provides a separate user's manual for each model. The 3-D model has two forms: free surface and rigid lid. The former, verified at Anclote Anchorage (FL), allows a free air/water interface and is suited for significant surface wave heights compared to mean water depth; e.g., estuaries and coastal regions. The latter, verified at Lake Keowee (SC), is suited for small surface wave heights compared to depth (e.g., natural or man-made inland lakes) because surface elevation has been removed as a parameter. These models allow computation of time-dependent velocity and temperature fields for given initial conditions and time-varying boundary conditions. The free-surface model also provides surface height variations with time.

Lee, S. S.↗
NASA NTRS1982

Verification and transfer of thermal pollution model. Volume 4: User's manual for three-dimensional rigid-lid model

The theory of a three dimensional (3-D) mathematical thermal discharge model and a related one dimensional (1-D) model are described. Model verification at two sites, a separate user's manual for each model are included. The 3-D model has two forms: free surface and rigid lid. The former allows a free air/water interface and is suited for significant surface wave heights compared to mean water depth, estuaries and coastal regions. The latter is suited for small surface wave heights compared to depth because surface elevation was removed as a parameter. These models allow computation of time dependent velocity and temperature fields for given initial conditions and time-varying boundary conditions. The free surface model also provides surface height variations with time.

Lee, S. S.↗
NASA NTRS1983

A high strength, torsionally rigid, deployable and retractable mast for space applications

A structural mast was developed which during and after full deployment produces a supporting structure with the characteristics of a high bending moment capability, high stiffness and, particularly important for instrument deployment, a high degree of position repeatability and torsional rigidity. These features were accomplished while providing and easily retractable mast with a high life cycle capability. Since these properties are consistent throughout the full range of deployed lengths, partial deployments or retractions can be utilized for checkout, balance, fine tuning or whatever other reason may be deemed necessary for operation modes or spacecraft stability.

Dibiasi, L.↗
NASA NTRS1983

SYMBOD - A computer program for the automatic generation of symbolic equations of motion for systems of hinge-connected rigid bodies

A computer program is described that can automatically generate symbolic equations of motion for systems of hinge-connected rigid bodies with tree topologies. The dynamical formulation underlying the program is outlined, and examples are given to show how a symbolic language is used to code the formulation. The program is applied to generate the equations of motion for a four-body model of the Galileo spacecraft. The resulting equations are shown to be a factor of three faster in execution time than conventional numerical subroutines.

Macala, G. A.↗
NASA NTRS1983

Turbulent drag characteristic of small amplitude rigid surface waves

The paper discusses an experimental and theoretical investigation of low speed turbulent flow over transverse rigid wavy surfaces having a wavelength on the order of the boundary layer thickness. In addition the results of theoretical investigations of laminar flow over short wavelength waves and turbulent flow over long wavelength (wavelength much greater than the boundary layer thickness) wavy walls are presented. Surface pressure and net drag measurements obtained for the short wavelength symmetric and asymmetric waves in a turbulent flow agreed with the results obtained with a Navier-Stokes spectral code and indicated no significant drag reduction. Several asymmetric wave configurations did significantly reduce the pressure drag compared to sine wave geometries, but these waves still did not produce a net drag reduction. The Navier-Stokes calculations for laminar flow indicated a drag reduction of up to 17 percent for certain short wavelength waves. Boundary layer calculations for turbulent flow over long wavelength surface waves indicated that net drag reductions on the order of 10 percent may be possible for large-radius waisted bodies.

Lin, J. C.↗
NASA NTRS1982

Contact between a rigid cylinder and an orthotropic beam under initial stress

The contact behavior between a smooth rigid cylinder and a simply-supported orthotropic beam under uniaxial initial stresses is studied. The displacements are computed by superposing Mindlin plate solution with the solution obtained from Biot's theory of incremental deformation. Finite Fourier transforms are used in solving the equations. The effects of orthotropy and initial stresses on the contact stress distribution are investigated. An indentation law is established from the numerical results.

Sun, C. T.↗
NASA NTRS1983

Observed departure of the Io plasma torus from rigid corotation with Jupiter

A study of forbidden S II red doublet spectra indicates that the Io plasma torus at 5.9 Jupiter radii does not corotate rigidly with Jupiter. The lag is found to be 6 percent + or 4 percent, where the variability range, not the uncertainty, is indicated. Comparison with existing models indicates the lag may be due primarily to ion creation in the Io torus.

Brown, R. A.↗
NASA NTRS1984

Hydrodynamic lubrication of rigid nonconformal contacts in combined rolling and normal motion

A numerical solution to the problem of hydrodynamic lubrication of rigid point contacts with an isoviscous, incompressible lubricant was obtained. The hydrodynamic load-carrying capacity under unsteady (or dynamic) conditions arising from the combined effects of squeeze motion superposed upon the entraining motion was determined for both normal approach and separation. Superposed normal motion considerably increases net load-carrying capacity during normal approach and substantially reduces net load-carrying capacity during separation. Geometry was also found to have a significant influence on the dynamic load-carrying capacity. The ratio of dynamic to steady state load-carrying capacity increases with increasing geometry parameter for normal approach and decreases during separation. The cavitation (film rupture) boundary is also influenced significantly by the normal motion, moving downstream during approach and upstream during separation. For sufficiently high normal separation velocity the rupture boundary may even move upstream of the minimum-film-thickness position. Sixty-three cases were used to derive a functional relationship for the ratio of the dynamic to steady state load-carrying capacity in terms of the dimensionless normal velocity parameter (incorporating normal velocity, entraining velocity, and film thickness) and the geometry parameter.

Ghosh, M. K.↗
NASA NTRS1983

Normal mode study of the earth's rigid body motions

In this paper it is shown that the earth's rigid body (rb) motions can be represented by an analytical set of eigensolutions to the equation of motion for elastic-gravitational free oscillations. Thus each degree of freedom in the rb motion is associated with a rb normal mode. Cases of both nonrotating and rotating earth models are studied, and it is shown that the rb modes do incorporate neatly into the earth's system of normal modes of free oscillation. The excitation formula for the rb modes are also obtained, based on normal mode theory. Physical implications of the results are summarized and the fundamental differences between rb modes and seismic modes are emphasized. In particular, it is ascertained that the Chandler wobble, being one of the rb modes belonging to the rotating earth, can be studied using the established theory of normal modes.

Chao, B. F.↗
NASA NTRS1984

Annihilation of angular momentum drift during spinning-up and thrusting maneuvers of rigid bodies

A very simple, yet accurate, heuristic solution for the spiral path of the angular momentum vector during spin-up and spin-down maneuvers of rigid body spacecraft is presented. A two-burn scheme is proposed consisting of a burn, a coast, and a second burn of the spin thruster. The appropriate burn times are found by a transcendental equation similar to Kepler's equation. Numerical results verify the accuracy of the burn, coast, and burn times given by closed form expressions. The scheme can also be applied to the problem of axial thrusting during constant spin.

Longuski, J. M.↗