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At least 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Performance of a superconducting large-angle magnetic suspension

SatCon Technology Corporation is working toward the development of an advanced-concept Control Moment Gyro (CMG). The advanced-concept CMG is sized for use as a slewing actuator for large space-based payloads. The design features a magnetically suspended composite rotor which contains a persistent-mode superconducting solenoid magnet. The rotor is suspended and gimballed by the interaction of the fields produced by the superconductor and an array of cryoresistive coils. The rotor spins in a liquid helium environment, while the control coils are liquid-hydrogen cooled. This design is capable of meeting the requirements of many high-performance slewing applications (27,000 Nm). The use of the magnetic suspension as rotor bearings, gimbal bearings, and gimbal torquers also substantially reduces the mass of the CMG system.

Downer, James R.↗
NASA NTRS1992

Dynamics and control of a five degree-of-freedom magnetic suspension system

A large-gap magnetic suspension system with five degrees-of-freedom is presented. The system is multi-input/multi-output with coupling between degrees-of-freedom. Simulation was performed on this multi degree-of-freedom system in order to control each degree-of-freedom separately. Two types of controllers are considered by adding white noise to a single degree-of-freedom system in order to test their behavior and determine which is the best choice for the system. The responses of the system are produced in continuous and discrete time where a sample interval and delay time was introduced. Using these responses, a comparison between each degree-of-freedom was made and the maximum value of the delay time was determined.

Haj, Anwar Mohammed↗
NASA NTRS1991

A fiber-optic probe for particle sizing in concentrated suspensions

A fiber-optic probe employing two monomode optical fibers, one for transmitting a Gaussian laser beam to the scattering volume and the second, positioned at some backscatter angle, for receiving the scattered light is described. Performance and suitability of the system for a process control environment is assessed by studying a suspension of polystyrene latex particles over a wide range of sizes and concentrations. The results show that the probe is ideal for a process control environment in industrial and laboratory applications. Particle size is recovered, without any additional corrections for multiple light scattering, in concentrations containing up to 10 percent solids of 39-nm polystyrene latex spheres.

Dhadwal, Harbans S.↗
NASA NTRS1992

Influences of chemical sympathectomy, demedullation, and hindlimb suspension on the V(O2)max of rats

The contributions of catecholamines from the adrenal medulla to the reduction in maximal oxygen consumption is investigated in chemically sympathectomized rats. The rats are injected with saline and chemically sympathectomized, and approximately half of the rats are surgically demedullated. The subjects undergo head-down suspension for two weeks and are examined in terms of submaximal mechanical efficiency, treadmill run time, and maximal oxygen consumption. Rats with adrenal medullas and injected with saline demonstrate reduced levels of maximal O consumption, whereas chemically sympathectomized rats with adrenal medullas showed no significant reduction. Reduced levels of maximal O consumption is also noted in the sympathectomized demedullated rats. The paper concludes that circulating epinephrine enhances the attenuation of the decrease in the maximal O consumption caused by chemical sympathectomy.

Woodman, Christopher R.↗
NASA NTRS1992

Skeletal muscle responses to lower limb suspension in humans

The morphological responses of human skeletal muscle to unweighting were assessed by analyzing multiple transaxial magnetic resonance (MR) images of both lower limbs and skeletal muscle biopsies of the unweighted lower limb before and after six weeks of unilaterial (left) lower limb suspension (ULLS). Results indicated that, as a results of 6 weeks of unweighting (by the subjects walking on crutches using only one limb), the cross sectional area (CSA) of the thigh muscle of the unweighted left limb decreased 12 percent, while the CSA of the right thigh muscle did not change. The decrease was due to a twofold greater response of the knee extensors than the knee flexors. The pre- and post-ULLS biopsies of the left vastus lateralis showed a 14 percent decrease in average fiber CSA due to unweighting. The number of capillaries surrounding the different fiber types was unchanged after ULLS. Results showed that the adaptive responses of human skeletal muscle to unweighting are qualitatively, but not quantitatively, similar to those of lower mammals and not necessarily dependent on the fiber-type composition.

Hather, Bruce M.↗
NASA NTRS1991

Muscle strength and endurance following lowerlimb suspension in man

The effect of lower-limb suspension on the muscle strength and muscle endurance was investigated in six men subjected to four weeks of unilateral unloading of a lower limb (using of a harness attached to a modified shoe), followed by seven weeks of weight-bearing recovery. Results showed a decrease in the cross-sectional area (CSA) of the thigh muscle and in the average peak torque (APT) during three bouts of 30 concentric knee extensions. While the the thigh muscle CSA returned to normal after seven weeks of recovery, the APT recovery was still reduced by 11 percent, suggesting that muscle metabolic function was severely affected by unloading and was not restored by ambulation.

Tesch, Per A.↗
NASA NTRS1991

Variations in recovery and readaptation to load bearing conditions after space flight and whole body suspension in the rat

Result are presented on studies of the effects of space flight and simulated microgravity on the cardiovascular and electrolyte characteristics, the adrenal gland weight, and hormonal responses of rats flown aboard Cosmos-605 and -782 or exposed to whole-body tail suspension. Results indicate an age-independent decrease in circulating antinatriuretic factor (ANF) in suspended rats, indicating that ANF may not significantly contribute to the sustained elevated bariuresis and diuresis observed in chronic head-down-suspended rats.

Musacchia, X. J.↗
NASA NTRS1992

Adaptations to unilateral lower limb suspension in humans

The effect of unilateral lower limb suspension (ULLS) on neuromuscular function in humans is analyzed. All ambulatory activity on crutches was performed by eight subjects for 6 weeks who wear a shoe with a 10 cm sole on the right foot to unweight the left lower limb. Results show that average muscle cross sectional area (CSA) of the left knee extensor (KE) decreased 16 percent whereas the KE of the nonsuspended right limb showed no changes. Maximal integrated electromyography of vastus lateralis and overall mean power frequency of gastrocnemius medialis and soleus for submaximal isometric actions were both decreased post-ULLS. It is concluded that six weeks of ULLS induces adaptations in the neuromuscular system of humans which are comparable to those induced by bed rest and spaceflight.

Dudley, Gary A.↗
NASA NTRS1992

Effects of microgravity and tail suspension on enzymes of individual soleus and tibialis anterior fibers

Selected enzymes of energy metabolism were measured in random individual fibers of soleus and tibialis anterior (TA) muscles from rats exposed for 2 wk to spaceflight (F) aboard Cosmos 2044 or tail suspension (T) and from synchronous controls. Average size of soleus fibers (dry weight per unit length) was reduced 37 percent in F and T fibers; there was little change in Ta fibers. Enzyme changes were more pronounced in soleus than in TA fibers. Three enzymes characteristic of fast-twitch muscles, pyruvate kinase, glycerol-3-phosphate dehydrogenase, and 1-phosphofructokinase, were elevated in F and T soleus fibers, but changes in phosphofructokinase were not statistically significant. In TA fibers analyzed for hexokinase, malate dehydrogenase, phosphohexoisomerase, and pyruvate kinase, only hexokinase and malate dehydrogenase showed significant changes. Hexokinase incresed 83 percent in one of two T muscles. Enzyme data for TA fibers typed by myosin adenosinetriphosphatase were more informative: phosphofructokinase, phosphorylase, and glycerol-3-phosphate dehydrogenase were increased in type IIn fibers of either F or T muscles or both. Malate dehydrogenase was not changed in fibers of any type in either F or T muscle.

Chi, Maggie M.-Y.↗
NASA NTRS1992

Fatigability and blood flow in the rat gastrocnemius-plantaris-soleus after hindlimb suspension

The hypothesis that hindlimb suspension (HS) increases the fatigability of the soleus during intense contractile activity and that the increased fatigue is associated with a reduced muscle blood flow was tested using caged control rats and rats subjected to HS for 15 days. After 15 days, either the soleus or the gastrocnemius-plantaris-soleus (G-P-S) muscle group was stimulated in situ (10 min at 100 Hz, 100 ms trains at 120/min), and in the G-P-S preparation, blood flow was measured with radiolabeled microspheres before and at 2 min and 10 min after the start of contractile activity. The results indicate that 15 days of HS resulted in increased fatigability of the soleus, but the effect was not caused by a reduced muscle blood flow.

Mcdonald, K. S.↗
NASA NTRS1992

Open-loop characteristics of magnetic suspension systems using electromagnets mounted in a planar array

The open-loop characteristics of a Large-Gap Magnetic Suspension System (LGMSS) were studied and numerical results are presented. The LGMSS considered provides five-degree-of-freedom control. The suspended element is a cylinder that contains a core composed of permanent magnet material. The magnetic actuators are air core electromagnets mounted in a planar array. Configurations utilizing five, six, seven, and eight electromagnets were investigated and all configurations were found to be controllable from coil currents and observable from suspended element positions. Results indicate that increasing the number of coils has an insignificant effect on mode shapes and frequencies.

Groom, Nelson J.↗
NASA NTRS1993

Six degrees of freedom vibration isolation using electromagnetic suspension

Experimental data are presented for modeling an electromagnet. Control laws are considered with and without flux feedback and with position and orientation information of the suspended body. Base motion and sensor noise are the principal disturbances. Proper selection of the geometrical operating point minimizes the passive coupling above the bandwidth of the control and filtering can attenuate the high frequency content of sensor noise. Six electromagnets are arranged in a configuration which optimizes the load support and provides control over all six degrees of freedom of the suspended body. The design is based on experimental data generated with a specially designed test facility. Application for suspension of a gravity wave antenna is discussed.

Lee, Sang-Il↗
NASA NTRS1993

Magnetic suspension characteristics of electromagnetic actuators

Electromagnetic actuators that use a current-carrying coil (which is placed in a magnetic field) to generate mechanical force are conceptually attractive components for active control of rotating shafts. In one concept that is being tested in the laboratory, the control forces from such actuators are applied on the flexibly supported bearing housings of the rotor. Development of this concept into a practical reality requires a clear and thorough understanding of the role of electromechanical parameters of these actuators in delivering the right amount of control force at the right phase into the rotor. The electromechanical parameters of the actuators investigated are the mass of the armature, stiffness of its suspension, electrical resistance, and inductance of the coils. Improper selection of these parameters can result in degradation in their performance, leading to mistuning between the actuator and the rotor. Through a simple analysis, it is shown that use of such mistuned actuators could result in sharp fluctuations in the phase of the control force delivered into the rotor around the critical speeds. These sharp fluctuations in phase, called 'Phase Glitches', are undesirable. Hence, future designs of controllers should take into account the undesirable mistuning effects between the actuator and the rotor caused by the phase glitches.

Rao, Dantam K.↗
NASA NTRS1992

Analysis, modelling and simulation of the large-angle magnetic suspension test fixture

The large-angle magnetic suspension test fixture (LAMSTF) research project is described which is based on a sophisticated finite element computer program, VF/GFUN, for calculating magnetic fields. The LAMSTF design includes eddy current paths the effect of which on system dynamics is being studied to modify the system dynamic model and the digital controller. Linearized equations of motions have been developed for system modelling and analysis of controllers.

Britcher, Colin P.↗
NASA NTRS1993

Gravity and suspension effects on the dynamics of controlled structures

The effects of gravity on the actuators, sensors and structural plant of a controlled flexible structure are investigated. These influences include gravity stiffening, gravity induced deformations, gravity influence on inertial sensors and actuators, and the interaction with the suspension system. For each of the four influences, a simplified model is derived, from which the appropriate non-dimensional parameter can be identified, and the magnitude of the influence estimated. The construction of a detailed numerical model, which includes the four gravity influences, is outlined. This modeling procedure is then applied to a simplified model of the Middeck Active Control Eperiment (MACE). The influence on the poles and input-output transfer function is examined for several variations in the plant. The modeling procedure is also applied to the MACE experimental hardware. Experimental and model-based transfer functions are compared to demonstrate the significant improvement by incorporating gravity effects.

Rey, Daniel A.↗
NASA NTRS1951

Flight Camera for Photographing Cloud Droplets in Natural Suspension in the Atmosphere

A camera designed for use in flight has been developed by the NACA Lewis laboratory t o photograph cloud droplets in their natural suspension in the atmosphere. A magnification of 32 times is employed to distinguish for measurement purposes all sizes of droplets greater than 5 microns in diameter. Photographs can be taken at flight speeds up to 150 miles per hour at 5-second intervals, A field area of 0.025 square inch is photographed on 7-inch-width roll film accommodating 40 exposures on an 18-foot length. Flight tests conducted in cumulus clouds have shown that approximate droplet-size distribution studies can be obtained and that a studies of the microstructure and physics of clouds can be made with the camera.

Mccullough, Stuart↗
NASA NTRS1924

Calculation of the hull and of the car-suspension systems of airships

Differential and integral curves are presented and well as numerous calculations relating to hulls. Some of the calculations include those relating to hulls, those relating to the invariability of the shape of the hulls, and those relating to the suspension of the hull.

AIRSHIP CARS↗
NASA NTRS1994

Preliminary eddy current modelling for the large angle magnetic suspension test fixture

This report presents some recent developments in the mathematical modeling of the Large Angle Magnetic Suspension Test Fixture (LAMSTF) at NASA Langley Research Center. It is shown that these effects are significant, but may be amenable to analysis, modeling and measurement. A theoretical framework is presented, together with a comparison of computed and experimental data.

Britcher, Colin↗