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At least 1,117 records · Page 62
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Internal tibial torsion correction study

A quantitative study of internal torsion in the entire tibial bone was performed by using strain gauges to measure the amount of deformation occuring at different locations. Comparison of strain measurements with physical dimensions of the bone produced the modulus of rigidity and its behavior under increased torque. Computerized analysis of the stress distribution shows that more strain occurs near the torqued ends of the bones where also most of the twisting and fracturing takes place.

Cantu, J. M.↗
NASA NTRS1973

Analytic description of vibrations in a piping system with pulsating flow

Various calculation schemes were proposed for describing vibrations in a piping system with pulsating flow. Methods were selected and applied according to the type of irregularities examined: concentrated ones, extended ones, or complex ones. The selection of a method also depends on comparability of the extent of the irregularities with the pressure wavelength and velocity in the flow. Relations were found which permit a description of the interaction of a pulsating flow with any irregularity in the system. For complex systems with varying temperatures and some irregularities, relations were obtained, which reflect the varying phase displacement of the forces in these irregularities. The effect of the frictional torque on pipeline supports, in the presence of flexural and torsional vibrations was investigated, on the assumption that the frictional torque depends linearly on the angular velocity.

Bosnyatskiy, G. P.↗
NASA NTRS1973

The use of statistical characteristics of reducer vibrations as diagnostic symptoms

The results of a statistical analysis of the vibrations of the experimental RS-1 reducer stand, with a spiral-gear transmission, operating on a closed circuit, are presented. The analysis was carried out on the Minsk-2 and Minsk-32 digital computers, with two-channel analog-digital converter, built in the Institute of the Science of Mechanics. Two-dimensional distribution patterns, conditional dispersions and dispersion ratios were calculated. The octave-band-filtered first harmonics of the tooth frequency f sub z of the vibrations at two different measurement points were considered as the components of the vibration process to be analyzed. The regression lines, corresponding to different values of the loading torque, are presented. Since it was not the gear drive parameters which were determined by diagnostic methods, but the characteristics most sensitive to change in state of the object of the investigation, the loading torque, which is the simplest and most accessible for measurement, was chosen as the condition parameter.

Balitskiy, F. Y.↗
NASA NTRS1974

Comparison of experimental and predicted performance of 150-millimeter-bore solid and drilled ball bearings to 3 million DN

Seven 150-millimeter-bore ball bearings were run under 8900-newton (2000-lbf) thrust load at speeds from 6670 to 20,000 rpm (1 million to 3 million DN). Four of the bearings had conventional solid balls, and three bearings had drilled (cylindrically hollow) balls with 50-percent mass reduction. The bearings were under-race cooled and slot lubricated with a type 2 ester oil at flow rates from 4.35 x 0.001 to 5.94 x 0.001 cubic meter/min (1.15 to 1.57 gal/min). Friction torque and temperature were measured on all bearings. While there was considerable spread in the temperature data, the drilled ball bearings tended to run slightly cooler than the solid ball bearings at higher speeds. No significant difference in torque was noted, however, between the solid and drilled ball bearings. One bearing of each type was rerun at 17,800-newton (4000-lbf) thrust load. The solid ball bearings performed satisfactorily at 3 million DN. However, at about 2 million DN the drilled ball bearing experienced a broken ball, and cracks appeared in other balls as a result of flexure fatigue. Metallurgical examination of the cracked balls indicated a brittle structure in the bore of the drilled balls.

Scibbe, H. W.↗
NASA NTRS1974

Some suggested approaches to solving the Hamilton-Jacobi equation associated with constrained rigid body motion

Some methods of approaching a solution to the Hamilton-Jacobi equation are outlined and examples are given to illustrate particular methods. These methods may be used for cases where the Hamilton-Jacobi equation is not separable and have been particularly useful in solving the rigid body motion of an earth satellite subjected to gravity torques. These general applications may also have usefulness in studying the motion of satellites with aerodynamic torque and in studying space vehicle motion where thrusting is involved.

Fitzpatrick, P. M.↗
NASA NTRS1973

Continuous and discrete describing function analysis of the LST system

A describing function of the control moment gyros (CMG) frictional nonlinearity is derived using the analytic torque equation. Computer simulation of the simplified Large Space Telescope (LST) system with the analytic torque expression is discussed along with the transfer functions of the sampled-data LST system, and the discrete describing function of the GMC frictionality.

Kuo, B. C.↗
NASA NTRS1974

Rigid body mode pointing accuracy and stability criteria for an orbiting spacecraft

The effect of gravity gradient torque disturbances (which is an order of magnitude greater than the other torque disturbances and is sinusoidal with a frequency of two cycles per orbit) on pointing accuracy can be predicted very precisely. However, since the sensor noise such as star tracker and gyro inherent noise, is random, their effect can only be predicted statistically. The most common method used is computer simulation with appropriate sensor model and adjusting spacecraft control laws for minimum pointing error, as presented by Harris (1972). The general investigation outlined theoretically relates spacecraft controls to pointing accuracy in terms of the sensor noise power spectrum. The results are presented in graphical form.

Sandhu, G. S.↗
NASA NTRS1974

Transient and steady-state velocity of domain walls for a complete range of drive fields

Approximate analytic solutions for transient and steady-state 180 deg domain wall motion in bulk magnetic material are obtained from the dynamic torque equations with a Gilbert damping term. The results for the Walker region in which the transient solution approaches the familiar Walker steady-state solution are presented in a slightly new form for completeness. An analytic solution corresponding to larger drive fields predicts an oscillatory motion with an average value which decreases with drive field for reasonable values of the damping parameter. These results agree with those obtained by a computer solution of the torque equation and those obtained with the assumption of a very large anisotropy field.

Bourne, H. C., Jr.↗
NASA NTRS1974

Phase-locked servo system

A phase lock servo system is described for synchronizing the rotation of a slip ring assembly with the rotation of an air bearing table so that a minimum of torque will be imparted through cables extending from the slip ring assembly to the air bearing table as such is rotated. The system includes two servo loops. The first servo loop includes a rate gyroscope carried on the air bearing table which generates a signal through a summing junction to be compared with a signal coming from a tachometer coupled to the slip ring assembly. The corrective signal is applied to a torque motor for rotating the slip ring assembly. The second servo loop includes a pair of photo detector cells which generate pulses responsive to the rotation of the air bearing table and slip ring assembly which are fed through a phase detector, and a variable gain amplifier to the summing junction circuit to provide a fine adjustment for rotating the slip ring assembly.

Burdin, C.↗
NASA NTRS1975

Meteorological Measurements from Satellite Platforms

The stability of stochastic satellites and the stability and control of flexible satellites were investigated. The effects of random environmental torques and noises in the moments of inertia of spinning and three-axes stabilized satellites were first compared analytically by four methods and by analog simulations. Among the analytical methods, it was shown that the Fokker-Planck formulation yields predictions which most coincide with the simulation results. It was then shown that the required stability criterion of a satellite is quite different from that obtained by a deterministic approach, under the assumption that the environmental and control torques experienced by the satellite are random. Finally, it was demonstrated that, by monitoring the deformations of the flexible elements of a satellite, the effectiveness of the satellite control system can be increased considerably.

Suomi, V. E.↗
NASA NTRS1975

Dynamic testing of the Kearfott 2401 accelerometer

A Kearfott pendulous accelerometer was integrated with a United Aircraft pulse torque servo assembly (PTSA) forced binary loop. The test objective was to measure dynamic errors due to anisoinertia and OA coupling effects. The instrument and its torque loop are described, and the technique for isolating the anisoinertia error from centripetal acceleration effects is discussed in detail. The measured anisoinertia error coefficient was 3.0 cm, and the testing confirmed that no rectified OA coupling error was present.

Katz, B.↗
NASA NTRS1975

Effects of low frequency vibration of a limb

Low frequency oscillations were applied on the ankle joint in plantarflexion/dorsiflexion rotation using a torque motor. The torque, the angular rotation and the evoked electromyogram from the gastronemius soleus and the anterior tibial muscles were recorded. Significant nonlinearities were observed in the angular rotation from 8 to 12 Hz. The following methods are used for data analysis: (1) Two cycle averaged response; (2) Fourier transform; and (3) Fourier analysis at the driving frequency. Important observations are: (1) resonance near 6 to 8 Hz; (2) slowly increasing amplitudes of oscillation near resonance; (3) self sustaining oscillations after the motor is turned off, particularly in the fatigued limb; and (4) distortion of angular rotation during which there are spontaneous recurrences of oscillation at the driving frequency.

Agarwal, G. C.↗
NASA NTRS1974

An optimal control of a rigid spinning satellite

An analytical solution is provided of a simple control problem. A rigid symmetric spinning satellite is considered and the optimal control torque vector is obtained. It is pointed out that optimal control can be obtained even with unequal torque magnitudes.

Das, A.↗
NASA NTRS1974

Transient and steady-state velocity of domain walls for a complete range of drive fields

Approximate analytic solutions for transient and steady-state 180 deg domain-wall motion in bulk magnetic material are obtained from the dynamic torque equations with a Gilbert damping term. The results for the Walker region in which the transient solution approaches the familiar Walker steady-state solution are presented in a slightly new form for completeness. An analytic solution corresponding to larger drive fields predicts an oscillatory motion with an average value of the velocity which decreases with drive field for reasonable values of the damping parameter. These results agree with those obtained by others from a computer solution of the torque equation and those obtained by others with the assumption of a very large anisotropy field.

Bourne, H. C., Jr.↗
NASA NTRS1975

Large Space Telescope oscillations induced by CMG friction

Conditions are predicted under which limit cycles may be caused by the friction torque of the control moment gyroscope (CMG) output gimbal used in the Large Space Telescope (LST). The parameter plane analysis technique is described, and three separate models of the CMG output friction nonlinearity are used in three separate analyses. The results suggest that the Dahl model (included in model 3) is the best available friction model for use in dynamic analysis. The analysis and analog simulation indicate the absence of limit cycle behavior due to the CMG output gimbal friction nonlinearity for presently estimated LST numerical parameters and the occurrence of one stable and one unstable limit cycle if substantially larger numerical values are allowed for the CMG gimbal pivot friction parameter and/or the running friction torque.

Seltzer, S. M.↗
NASA NTRS1975

An optimal control of a flexible spinning satellite

A modification of optimal spinning satellite control theory is proposed, based on introducing an additional vector into the equation for control torque components. This modification essentially means that the amplitudes of the time-dependent satellite perturbation functions can be made small when the amplitudes of the control torque components are allowed to be different. An algorithm for computer simulation of the satellite control theory is provided. A singular perturbation scheme is used which greatly reduces the number of degrees of freedom in the flexible satellite motion equations.

Das, A.↗
NASA NTRS1975

Analytical stability and simulation response study for a coupled two-body system

An analytical stability study and a digital simulation response study of two connected rigid bodies are documented. Relative rotation of the bodies at the connection is allowed, thereby providing a model suitable for studying system stability and response during a soft-dock regime. Provisions are made of a docking port axes alignment torque and a despin torque capability for encountering spinning payloads. Although the stability analysis is based on linearized equations, the digital simulation is based on nonlinear models.

Tao, K. M.↗
NASA NTRS1975

Development of a digital electronic rebalance loop for a dry tuned-rotor two degree-of-freedom gyroscope

Digital electronic rebalance loops were designed and implemented in brassboard form to capture both X and Y axes of the Kearfott Gyroflex. The loops were width-modulated binary types using a 614.4 kHz keying signal and a 2.4 kHz sample frequency. The loops were designed for a torquing rate of 2 deg/sec (70.6 mA torquing current) and a data resolution of 23.4 milli-arc-sec per data pulse. Design considerations, implementation details, and preliminary experimental results are presented.

Blalock, T. V.↗