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Results for “frictional force”

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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Friction and wear of metals with a single-crystal abrasive grit of silicon carbide: Effect of shear strength of metal

Sliding friction experiments were conducted with spherical, single-crystal silicon carbide riders in contact with various metals and with metal riders in contact with silicon carbide flats. Results indicate that: (1) the friction force in the plowing of metal and (2) the groove height (corresponding to the volume of the groove) are related to the shear strength of the metal. That is, they decrease linearly as the shear strength of the bulk metal increases. Grooves are formed in metals primarily from plastic deformation, with occasional metal removal. The relation between the groove width D and the load W can be expressed by W = kD, superscript n which satisfies Meyer's law.

Miyoshi, K.↗
NASA NTRS1978

Induced velocities of grains embedded in a turbulent gas

A theory is presented for the dynamics of dust particles in an incompressible turbulent fluid. Grain-gas coupling occurs through friction forces that are proportional to the mean grain velocity relative to the gas. This test particle theory is applied to the case of Kolmogoroff spectrum in a protostellar cloud. The mean turbulence induced grain velocity and the mean turbulent relative velocity of two grains are calculated. Whereas the former should determine the dust scale height, grain-grain collisions are influenced by the latter. For a reasonable strength of turbulence, the mean induced relative velocity of two particles turns out to be at least as large as the corresponding terminal velocity difference during gravitational settling.

Voelk, H. J.↗
NASA NTRS1980

Collisions between grains in a turbulent gas

Turbulent gas motions will induce random velocities of small dust grains that are imbedded in the gas. Within large eddies the friction forces from the gas lead to strongly correlated velocities for neighboring grains, whereas small eddies cause uncorrelated grain motions. The nonlinear response of a grain to eddy motion is calculated. This leads to a turbulent pressure within the dust component as well as to collisions between pairs of grains. The results are evaluated numerically for a Kolmogoroff spectrum and turbulent collision rates are calculated for molecular clouds and protostellar environments. Whereas grain-grain collisions should not modify the initial size distribution in molecular clouds to a significant extent, they will lead to an entirely different grain population in protostars.

Voelk, H. J.↗
NASA NTRS1981

Behavior of aircraft antiskid braking systems on dry and wet runway surfaces: Hydromechanically controlled system

The investigation utilized one main gear wheel, brake, and tire assembly of a McDonnell Douglas DC-9 series 10 airplane. The landing-gear strut was replaced by a dynamometer. During maximum braking, average braking behavior indexes based upon brake pressure, brake torque, and drag-force friction coefficient developed by the antiskid system were generally higher on dry surfaces than on wet surfaces. The three braking behavior indexes gave similar results but should not be used interchangeably as a measure of the braking of this antiskid sytem. During the transition from a dry to a flooded surface under heavy braking, the wheel entered into a deep skid but the antiskid system reacted quickly by reducing brake pressure and performed normally during the remainder of the run on the flooded surface. The brake-pressure recovery following transition from a flooded to a dry surface was shown to be a function of the antiskid modulating orifice.

Tanner, J. A.↗
NASA NTRS1983

Padded Allen Wrench Grips Fastener

Addition of PTFE pressure pad increases utility of hexagonal socket wrench. Pad presses against opposing inside socket walls, causing frictional force that retains socket-head screw against gravitational and handling forces. Developed for spacecraft repairs, tool is useful wherever tight clearance prevents insertion or removal of screw by hand.

Salisbury, M. K.↗
NASA NTRS1980

Spherical roller bearing analysis. SKF computer program SPHERBEAN. Volume 1: Analysis

The models and associated mathematics used within the SPHERBEAN computer program for prediction of the thermomechanical performance characteristics of high speed lubricated double row spherical roller bearings are presented. The analysis allows six degrees of freedom for each roller and three for each half of an optionally split cage. Roller skew, free lubricant, inertial loads, appropriate elastic and friction forces, and flexible outer ring are considered. Roller quasidynamic equilibrium is calculated for a bearing with up to 30 rollers per row, and distinct roller and flange geometries are specifiable. The user is referred to the material contained here for formulation assumptions and algorithm detail.

Kleckner, R. J.↗
NASA NTRS1983

Tribological measurements on a Charnley-type artificial hip joint

A total hip simulator was used to determine the friction and wear properties of Charnley-type (316L stainless steel balls and sterile ultrahigh molecular weight polyethylene cups) hip prostheses. Three different sets of specimens were tested to 395,000, 101,500 and 233,000 walking cycles, respectively. All tests were run unlubricated, at ambient conditions (22 to 26 C, 30 to 50 percent relative humidity), at 30 walking cycles per minute, under a dynamic load simulating walking. Polyethylene cup wear rates ranged from 1.4 to 39 ten billions cu m which corresponds to dimensional losses of 4.0 to 11 microns per year. Although these wear rates are lower than those obtained from other hip simulators and from in vivo X-ray measurements, they are comparable when taking run-in and plastic deformation into account. Maximum tangential friction forces ranged from 93 to 129 N under variable load (267 to 3090 N range) and from 93 to 143 N under a static load of 3090 N. A portion of one test 250,000 walking cycles) run under dry air ( 1 percent relative humidity) yielded a wear rate almost 6 times greater than that obtained under wet air ( 70 percent relative humidity) conditions.

Jones, W. R., Jr.↗
NASA NTRS1983

Friction damping studies in multiple turbine blade systems by lumped mass method

Analytical studies were conducted on multiple turbine blade systems using the lumped mass method. Each blade was idealized by a two mass-two spring model whose modal values were determined from the known frequencies corresponding to the first two bending modes and the frequency corresponding to the platform lockup condition. Two friction damping models were considered namely, the blade-to-blade and the blade-damper-blade. The equations of motion derived on the basis of these models were solved by a method of harmonic balance, assuming, in effect, that under cyclic excitation the blades will exhibit cyclic response at the same frequency. The solutions for 8 blade, 16 blade, and 4 blade systems were obtained using the computer program BLADE. The levels of damping produced by the two friction damping models were compared and evaluated. The optimal values of the friction force, for which the tip amplitude of the blades had a minimum value, were determined.

Raju, B. B.↗
NASA NTRS1985

Improved Coulomb-Friction Damper

Equal damping provided on forward and reverse strokes. Improved damper has springs and wedge rings symmetrically placed on both ends of piston wedge, so friction force same in both directions of travel. Unlike conventional automotive shock absorbers, they resemble on outside, both versions require no viscous liquid and operate over wide temperature range.

Campbell, G. E.↗
NASA NTRS1983

An experimental investigation of a free-tip rotor configuration in a forward flight wind-tunnel test

Results from an experimental evaluation of a free-tip rotor are presented. The evaluation included whirl tests and wind tunnel tests up to advance ratios of 0.4. The free tip extended over the outer 5% of the rotor blade and included a passive mechanical controller whose output characteristics were varied. The controller configuration combined with the free tip aerodynamics resulted in higher power requirements, because the tip's pitch angle was 5 to 10 degrees greater than that of the inboard portion of the blade, and its pitching motion capability was considered to be inhibited by frictional forces. Recommendations are included for design features for a follow-on test.

Stroub, R. H.↗
NASA NTRS1984

Validation of an Active Gear, Flexible Aircraft Take-off and Landing analysis (AGFATL)

The results of an analytical investigation using a computer program for active gear, flexible aircraft take off and landing analysis (AGFATL) are compared with experimental data from shaker tests, drop tests, and simulated landing tests to validate the AGFATL computer program. Comparison of experimental and analytical responses for both passive and active gears indicates good agreement for shaker tests and drop tests. For the simulated landing tests, the passive and active gears were influenced by large strut binding friction forces. The inclusion of these undefined forces in the analytical simulations was difficult, and consequently only fair to good agreement was obtained. An assessment of the results from the investigation indicates that the AGFATL computer program is a valid tool for the study and initial design of series hydraulic active control landing gear systems.

Mcgehee, J. R.↗
NASA NTRS1983

Surface roughness effects with solid lubricants dispersed in mineral oils

The lubricating effectiveness of solid-lubricant dispersions are investigated in both point and line contacts using surfaces with both random and directional roughness characteristics. Friction and wear data obtained at relatively low speeds and at room temperature, indicate that the existence of solid lubricants such as graphite, MoS2, and PTFE in a plain mineral oil generally will not improve the effectiveness of the oil as a lubricant for such surfaces. Under boundary lubrication conditions, the friction force, as a function of time, initially depends upon the directional roughness properties of the contacting surfaces irrespective of whether the base oil or dispersions are used as lubricants.

Cusano, C.↗
NASA NTRS1987

Initial investigations into the damping characteristics of wire rope vibration isolators

Passive dampers composed of coils of multi-strand wire rope are investigated. Analytical results range from those produced by complex NASTRAN models to those of a Coulomb damping model with variable friction force. The latter agrees well with experiment. The Coulomb model is also utilized to generate hysteresis loops. Various other models related to early experimental investigations are described. Significant closed-form static solutions for physical properties of single-and multi-strand wire ropes are developed for certain specific geometries and loading conditions. NASTRAN models concentrate on model generation and mode shapes of 2-strand and 7-strand straight wire ropes with interfacial forces.

Cutchins, M. A.↗
NASA NTRS1987

Comparative plasma tails of Venus and comets

A review of current models of solar wind flow in the plasma tails of weakly magnetized bodies is presented. Measurements conducted by the Mariner 5 spacecraft, the Veneras 9 and 10, and the PVO orbiters, in the Venus tail, and with the ICE spacecraft in the tail of Comet Giacobini-Zinner, reveal common plasma properties which suggest that similar physical processes are operative. Most notable is the observation of decreased flow velocities and enhanced plasma temperatures in the vicinity of their plasma tails. In Venus, the measured velocity and temperature fields are consistent with the effects of frictional forces between the mass-loaded ionosheath flow and the ionosphere along the (magnetic) polar regions of the ionopause. It is argued that similar conditions exist at a cometary ionopause and that the distribution of magnetic fluxes in a cometary tail is controlled by the entry of plasma fluxes from the (magnetic) polar regions of the comet's ionospheric obstacle. This question is further addressed in connection with the two-step shape of the magnetic profile measured across the tail of the comet. It is suggested that the low intensity outer increases of the magnetic lobes are associated with the draping of the interplanetary magnetic field lines around the comet's ionospheric obstacle, and that the higher intensity increases seen in the inner regions of the magnetic lobes are due to an additional compression of magnetic fluxes produced by the entry of plasma particles into the tail.

Perezdetejada, H.↗
NASA NTRS1988

Advances in contact algorithms and their application to tires

Currently used techniques for tire contact analysis are reviewed. Discussion focuses on the different techniques used in modeling frictional forces and the treatment of contact conditions. A status report is presented on a new computational strategy for the modeling and analysis of tires, including the solution of the contact problem. The key elements of the proposed strategy are: (1) use of semianalytic mixed finite elements in which the shell variables are represented by Fourier series in the circumferential direction and piecewise polynomials in the meridional direction; (2) use of perturbed Lagrangian formulation for the determination of the contact area and pressure; and (3) application of multilevel iterative procedures and reduction techniques to generate the response of the tire. Numerical results are presented to demonstrate the effectiveness of a proposed procedure for generating the tire response associated with different Fourier harmonics.

Noor, Ahmed K.↗
NASA NTRS1987

An investigation of the damping phenomena in wire rope isolators

Early investigations into analytically modeling the dynamics of wire rope vibration isolators are described. Results from both very simple and very complex models are shown. The dynamic model which has the best agreement to date with simple one-dimensional experiments is one which includes a Coulomb friction force which varies with frequency. There are many yet unexplained phenomena, however. The fundamentals which underly multistrand NASTRAN models are given, and some early results are shown. An application simulation is briefly described, as is ongoing research.

Cutchins, M. A.↗
NASA NTRS1989

Damper Of Small Vibrations

Vibration damper has no rubbing parts. Thus eliminates even very small static frictional forces and therefore responds to and damps extremely low levels of vibration. Damper dissipates vibration by motion of piston in volume of silicone oil. Coaxial rigid shaft holds upper and lower bellows at constant length while piston vibrates up and down. Although volumes of upper and lower bellows change continually, total volume of bellows assembly stays same.

Davis, L. P.↗
NASA NTRS1988

Automated seed manipulation and planting

Activities for the Fall Semester, 1987 focused on investigating the mechanical/electrical properties of wheat seeds and forming various Seed Planting System (SPS) concepts based on those properties. The Electrical Division of the design group was formed to devise an SPS using electrostatic charge fields for seeding operations. Experiments concerning seed separation using electrical induction (rearranging of the charges within the seed) were conducted with promising results. The seeds, when exposed to the high voltage and low current field produced by a Van de Graff generator, were observed to move back and forth between two electrodes. An SPS concept has been developed based on this phenomena, and will be developed throughout the Spring Semester, 1988. The Mechanical Division centered on SPS concepts involving valves, pumps, and fluids to separate and deliver seeds. An SPS idea utilizing the pressure difference caused by air as it rushes out of holes drilled in the wall of a closed container has been formulated and will be considered for future development. Also, a system of seed separation and delivery employing a combination of centrifugal force, friction, and air flow was considered.

Garcia, Ray↗