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All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Excitation and relaxation of the wobble, precession, and libration of the moon

The rate of meteorite-impact excitation of the free wobble, free precession, and free libration of the moon above a given amplitude is estimated for two crater-size scaling laws and is compared with the rate of damping by tidal and rotational distortion as well as by a possible core-mantle interaction. Criteria for the probable existence and the probable nonexistence of observable amplitudes of the free motions are developed in terms of upper bounds on the damping factor for the various motions and in terms of ranges for the kinematic viscosity of a possible core. It is shown that although observable amplitudes are compatible with reasonable values of the damping factor and kinematic viscosity, other reasonable values could keep the amplitudes below the observable level most of the time. It is found that the free libration is the least likely motion to be observed and that a lunar core with earthlike properties might keep some of the free motions damped, but not all of them. Uncertainties in some of the assumptions used in the analysis are discussed.

Peale, S. J.↗
NASA NTRS1979

Io's wobbling flux tube and nonuniform surface conductivity - Longitude control of decametric emission and other magnetospheric interactions

Study of systematic relations between Io's flux tube orientation, decametric emission control, and areal surface properties suggest a model that can account for longitude control of principal Io-associated decametric emissions and other observed Io/magnetosphere interactions. The model is based on the fact that Jupiter's magnetic field structure is dominated by a tilted dipole rotating at a different angular velocity than Io's orbital motion. This caused Io's flux tube near Io to wobble (precess) with respect to Io's rotational axis. Discrete contact junctions are invoked between the active current-sheet regions in the flux tube and Io's surface.

Nash, D. B.↗
NASA NTRS1979

Observation of self-excited wobble in face seals

A face seal model consisting of a rigidly mounted rotor and a flexibly mounted stator was tested under conditions of eccentric loading. Self-excited oscillations in the form of combined precession and nutation of the stator were observed. The nature of the motion and its frequency are dependent on rotational speed, seal clearance, and external tilting moment. It is possible that some unexplained seal failures and waviness of seal faces are the result of such self excited wobble.

Etsion, I.↗
NASA NTRS1981

The period and Q of the Chandler wobble

The calculation of the theoretical period of the Chandler wobble is extended to account for the non-hydrostatic portion of the earth's equatorial bulge and the effect of the fluid core upon the lengthening of the period due to the pole tide. The theoretical period of a realistic perfectly elastic earth with an equilibrium pole tide is found to be 426.7 sidereal days, which is 8.5 days shorter than the observed period of 435.2 days. Using Rayleigh's principle for a rotating earth, this discrepancy is exploited together with the observed Chandler Q to place constraints on the frequency dependence of mantle anelasticity. In all cases these limits arise from exceeding the 68 percent confidence limits of + or - 2.6 days in the observed period. Since slight departures from an equilibrium pole tide affect the Q much more strongly than the period, these limits are believed to be robust.

Smith, M. L.↗
NASA NTRS1996

Measuring Motor-Shaft Clearance And Wobble During Operation

Noncontact proximity sensor, preferably eddy-current liftoff probe, provides realtime measurement of distance and small variations of distance between two mechanical components designed to be maintained at precise, fixed distance. In particular, system intended for use in measuring lateral clearance and variations in lateral clearance (wobble) of motor shaft relative to motor housing while shaft turning. Provides early indication of wear in motor bearings. Rate of rotation also measured.

Chern, Engmin James↗
NASA NTRS2002

G-induced vestibular dysfunction ('the wobblies') among aerobatic pilots: a case report and review

G-induced vestibular dysfunction (GIVD) is a condition well known to aircraft pilots who experience high positive and negative G loads during unlimited-aerobatic competitions and air-show demonstrations. After landing and walking from their aircraft, pilots with GIVD manifest an extremely unstable gait, which they call the wobblies. This article includes a report of one such case of GIVD, which to the author's knowledge is the first published case report of this condition in the medical literature. The author also discusses what is known and theorized about the pathogenesis of GIVD, and he reviews its diagnosis, treatment, and prevention.

Case Reports↗
NASA NTRS2001

Chandler wobble

Explore the source record for details and available documents.

Earth rotation polar motion Chandler wobble↗
NASA NTRS1983

On excitation of Earth's free wobble and reference frames

The excitation of the Earth's polar motion in connection with problems that are associated with the diversity of reference frames involved in observations and theoretical computations is studied. Following the dynamics of the Earth's polar motion, the kinematics that relates observations from different reference frames is developed. The conventional procedures of studying the seismic excitation of polar motion are re-examined, subject to the question: relative to what reference frame? It is concluded that an inconsistency in reference frames has prevailed in the literature. While this inconsistency is indeed far from trivial, the resultant discrepancy, however, is small for all practical purposes.

Chao, B. F.↗
NASA NTRS1984

On the excitation of the earth's free wobble and reference frames

The excitation of the earth's polar motion in connection with problems that are associated with the diversity of reference frames involved in observations and theoretical computations is studied. Following the dynamics of the earth's polar motion, the kinematics that relates observations from different reference frames is developed. The conventional procedures of studying the seismic excitation of polar motion are re-examined, subject to the question: relative to what reference frame? It is concluded that an inconsistency in reference frames has prevailed in the literature. While this inconsistency is indeed far from trivial, the resultant discrepancy, however, is small for all practical purposes.

Chao, B. F.↗