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Motion induced errors in a tuned, flexure-mounted strapdown gyro are investigated. Analytic expressions are developed for errors induced by linear vibrations, angular motion, and detuning. Sensor-level errors (gyro drift rate) and system-level errors (navigation errors) that are stimulated by an actual dynamic motion environment are computed.
It is hypothesized that exposure to prolonged free fall is a form of sensory/motor rearrangement rather than a direct change in otolith sensitivity or sensory compensation for a reduced otolith input. The rearrangement of stimuli will force a new interpretation by the CNS of otolith input. This reinterpretation is necessary for a structured and meaningful interaction with the new environment. Data from two flight experiments are presented which support an otolith reinterpretation hypothesis. The first experiment measured vestibulo-spinal reflex changes as a function of sustained free fall. Findings indicate that when a monosynaptic reflex (H-reflex), measured from the major postural muscles (soleus), is used adaptation to space flight includes a change in how the CNS interprets a fall. In a normal gravity environment a sudden unexpected fall will produce a potentiated H reflex. After seven days in flight an equivalent fall does not potentiate the reflex. During postflight a greatly increased reflex is observed in those crewmen most susceptible to space motion sickness. In the second experiment self motion perception and torsional eyemovements were modified as a function of exposure to sustained free fall. Preflight roll motion (about the X axis) was perceived as pure roll, and the eye movements recorded were countertorsional. Postflight, roll stimulation was perceived as linear translation (side to side movement) with a small angular motion component. Eye movement measurements confirmed significantly more horizontal motion.
The effect of motion on the ability of men to perform a variety of control actions was investigated. Special attention was given to experimental and analytical studies of the dynamic characteristics of the otoliths and semicircular canals using a two axis angular motion simulator and a one axis linear motion simulator.
Simulation of structural response of multi-flexible-body systems by linearized flexible motion combined with nonlinear rigid motion is discussed. Advantages and applicability of such an approach for accurate simulation with greatly reduced computational costs and turnaround times are described, restricting attention to the control design environment. Requirements for updating the linearized flexibility model to track large angular motions are discussed. Validation of such an approach by comparison with other existing codes is included. Application to a flexible robot manipulator system is described.
An approximate six-parameter analytic model for Earth-based differential range measurements is presented and is used to derive a representative analytic approximation for differenced Doppler measurements. The analytical models are tasked to investigate the ability of these data types to estimate spacecraft geocentric angular motion, Deep Space Network station oscillator (clock/frequency) offsets, and signal-path calibration errors over a period of a few days, in the presence of systematic station location and transmission media calibration errors. Quantitative results indicate that a few differenced Doppler plus ranging passes yield angular position estimates with a precision on the order of 0.1 to 0.4 micro-rad, and angular rate precision on the order of 10 to 25 x 10(exp -12) rad/sec, assuming no a priori information on the coordinate parameters. Sensitivity analyses suggest that troposphere zenith delay calibration error is the dominant systematic error source in most of the tracking scenarios investigated; as expected, the differenced Doppler data were found to be much more sensitive to troposphere calibration errors than differenced range. By comparison, results computed using wideband and narrowband (delta) VLBI under similar circumstances yielded angular precisions of 0.07 to 0.4 micro-rad, and angular rate precisions of 0.5 to 1.0 x 10(exp -12) rad/sec.
The purpose of this study was to investigate the coordination of the head relative to the trunk within a gait cycle during gaze fixation. Nine normal subjects walked on a motorized treadmill driven at 1.79 m/s (20 s trials) while fixing their gaze on a centrally located earth-fixed target positioned at a distance of 2 m from their eyes. The net and relative angular motions of the head about the three axes of rotations, as well as the corresponding values for the moments acting on it relative to the trunk during the gait cycle were quantified and used as measures of coordination. The average net moment, as well as the average moments about the different axes were significantly different (P<0.01) between the high impact and low/no impact phases of the gait cycle. However, the average net angular displacement as well as the average angular displacement about the axial rotation axis of the head relative to the trunk was maintained uniform (P>0.01) throughout the gait cycle. The average angular displacement about the lateral bending axis was significantly increased (P<0.01) during the high impact phase while that about the flexion-extension axis was significantly decreased (P<0.01) throughout the gait cycle. Thus, the coordination of the motion of the head relative to the trunk during walking is dynamically modulated depending on the behavioral events occurring in the gait cycle. This modulation may serve to aid stabilization of the head by counteracting the force variations acting on the upper body that may aid in the visual fixation of targets during walking.
The Spin-Down and Active Nutation Controller stabilizes the Galileo spacecraft during spin-down from approximately 70 to 1 rpm. Angular motion of the spacecraft is sensed through a pair of accelerometers and a sun sensor which is needed only at low spin rates. Spin and nutation information is derived by a set of 'loosely coupled' spin and transverse rate estimators. Spin rate is reduced by two spin-down thrusters. The transverse angular rate is compared with a variable threshold; exceeding the threshold activates axial thrusters which impart appropriate transverse torque to reduce the nutation. The scheme was verified by extensive computer simulations and has been demonstrated over a wide range of initial conditions.
We compute the polar-motion excitation function due to the atmospheric angular momentum (AAM) for both IB (inverted-barometer) and non-IB cases, as well as the excitation function from geodetically observed Earth orientation data for the period 1980-1990. The two are then compared in studying the AAM contribution to the polar motion excitation. The polar drifts with periods longer than about two years have similar characteristics, but the comparison is inconclusive because of data uncertainties. For the seasonal wobble excitation, the agreement is poor except for the prograde annual wobble, indicating the influence of other geophysical excitations than AAM. For the Chandler wobble excitation, a correlation coefficient of 0.53 for non-IB and 0.58 for IB are found for 1986-1990. Together with a coherence spectral analysis, they clearly demonstrate a strong contribution of AAM to the Chandler wobble excitation.
Flight records are presented from an early flight test of a wing-tip mounted tilting-ducted-fan, vertical-take-off and landing (VTOL) aircraft configuration. Time histories of the aircraft motions, control positions, and duct pitching-moment variation are presented to illustrate the characteristics of the aircraft in hovering, in conversion from hovering to forward flight, and in conversion from forward flight to hovering. The results indicate that during essentially continuous slow level- flight conversions, this aircraft experiences excessive longitudinal trim changes. Studies have shown that the large trim changes are caused primarily by the variation of aerodynamic moments acting on the duct units. Action of the duct-induced downwash on the horizontal stabilizer during the conversion also contributes to the longitudinal trim variations. Time histories of hovering and slow vertical descent in the final stages of landing in calm air show angular motions of the aircraft as great as +/- 10 deg. about all axes. Stick and pedal displacements required to control the aircraft during the landing maneuver were on the order of 50 to 60 percent of the total travel available.
Except for the lowest harmonics, small-amplitude stellar pulsation modes possess many simple properties whose evaluation does not require numerical integration of the fourth-order equations of motion. All antinodes tend to have the same total kinetic energy except for those lying near physical or geometric boundaries. However, when kinetic energy per unit volume is considered, order-of-magnitude enhancements are seen in antinodes lying near the center of the star, and factor-of-2 enhancements occur near the polar axis. The nodes are distributed very regularly along the radius. They follow an exponential law in g-regions, and their separation is proportional to the sound travel time in p-regions. A simple graphical procedure is described for surveying the oscillation frequencies of a new stellar model. A precise condition is derived giving the division of energy between radial and angular motion. Another condition gives the fractional contribution to the velocity field of its two sources, the divergence and the curl. Certain simplifying results of weak coupling among the linear modes are briefly described.
Present experiments were designed to quantify the alternating current (AC) component of the semicircular canal microphonic for angular motion stimulation as a function of stimulus frequency and amplitude. The oyster toadfish, Opsanus tau, was used as the experimental model. Calibrated mechanical indentation of the horizontal canal duct was used as a stimulus to generate hair-cell and afferent responses reproducing those present during head rotation. Sensitivity to polarization of the endolymph DC voltage re: perilymph was also investigated. Modulation of endolymph voltage was recorded using conventional glass electrodes and lock-in amplification over the frequency range 0.2-80 Hz. Access to the endolymph for inserting voltage recording and current passing electrodes was obtained by sectioning the anterior canal at its apex and isolating the cut ends in air. For sinusoidal stimulation below approx.10 Hz, the horizontal semicircular canal AC microphonic was nearly independent of stimulus frequency and equal to approximately 4 microV per micron indent (equivalent to approx. 1 microV per deg/s). A saturating nonlinearity decreasing the microphonic gain was present for stimuli exceeding approx.3 micron indent (approx. 12 deg/s angular velocity). The phase was not sensitive to the saturating nonlinearity. The microphonic exhibited a resonance near 30Hz consistent with basolateral current hair cell resonance observed previously in voltage-clamp records from semicircular canal hair cells. The magnitude and phase of the microphonic exhibited sensitivity to endolymphatic polarization consistent with electro-chemical reversal of hair cell transduction currents.
Elliptic restricted problem of periodic Trojan orbit and nonperiodic librational frequency and angular motion of Jupiter
Solution for angular motion analysis on spinning atmospheric entry vehicle
Mathematical input-output model for vestibular system, relating linear and angular motions to nonvisual perception of orientation, motion and nystagmus for physiological characteristics
Electromagnetic wave enters reflector array consisting of grid work of metallic reflectors with each reflector obscuring a portion of its neighbors to prevent direct passage of wave through grid. Antenna movement involves reduced amplitude of angular motion and internal concellations of translational and rotational inertias.
A new model for the response of the semicircular canals to angular motion is postulated. This model is based on evidence that the bony canal is not compartmentalized and assumes that the ampulla wall is highly flexible. It is shown that the perilymph induces a cupula displacement far greater than that produced by the endolymph alone. The predicted dynamic behavior of the canals on the basis of this model is found to be consistent with experimental observations.
A new model for the response of the semicircular canals to angular motion is postulated. This model is based on evidence that the bony canal is not compartmentalized and assumes that the ampulla wall is highly flexible. It is shown that the perilymph induces a cupula displacement far greater than that produced by the endolymph alone. The predicted dynamic behavior of the canals on the basis of this model is found to be consistent with experimental observations.
The solution to the steady state magnetohydrodynamic equations governing the supersonic expansion of the solar corona into interplanetary space is obtained for various assumptions regarding the form in which proton thermal energy is carried away from the sun. The one-fluid, inviscid, formulation of the MHD equations is considered assuming that thermal energy is carried away by conduction from a heat source located at the base of the corona. Angular motion of the solar wind led to the existence of three critical points through which the numerical solutions must pass to extend from the sun's surface to large heliocentric distances. The results show that the amount of magnetic field energy converted into kinetic energy in the solar wind is only a small fraction of the total expansion energy flux and has little effect upon the final radial expansion velocity.