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Results for “Vibration Attenuation”

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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All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Pointing and tracking control for freedom's Solar Dynamic modules and vibration control of freedom

A control strategy is presented for pointing particular modules of flexible multibody space structures while simultaneously attenuating structural vibrations. The application that is addressed is the planned Space Station Freedom in a growth configuration with Solar Dynamic (SD) module. A NASTRAN model of Freedom is used to demonstrate the control strategy. Two cases of SD concentrator fine-pointing controller bandwidths are studied with examples. The effect of limiting the controller motor torques to realistic baseline values is examined. SD pointing and station vibration control is accomplished during realistic disturbances due to aerodynamic drag, Shuttle docking, and Shuttle reaction control system plume impingement on SD. Gravity gradient induced torques on SD are relatively small and pseudo-steady.

Quinn, Roger D.↗
NASA NTRS1992

Method and apparatus for minimizing multiple degree of freedom vibration transmission between two regions of a structure

Arrays of actuators are affixed to structural elements to impede the transmission of vibrational energy. A single pair is used to provide control of bending and extensional waves and two pairs are used to control torsional motion. The arrays are applied to a wide variety of structural elements such as a beam structure that is part of a larger framework that may or may not support a rigid or non-rigid skin. Electrical excitation is applied to the actuators that generate forces on the structure. These electrical inputs may be adjusted in their amplitude and phase by a controller in communication with appropriate vibrational wave sensors to impede the flow of vibrational power in all of the above mentioned wave forms beyond the actuator location. Additional sensor elements can be used to monitor the performance and adjust the electrical inputs to maximize the attenuation of vibrational energy.

Silcox, Richard J.↗
NASA NTRS1992

Control-structures Interaction Test of the LACE Satellite

It is clear that additional experience and validation of Control Structures Interaction (CSI) techniques are needed in controlling the structural dynamics of flexible spacecraft. It is also clear that the effects of the space environment such as weightlessness dictate that this be done in space. Unfortunately, orbital tests are difficult to achieve because of the high cost of the test article, the launch into orbit, the instrumentation, and communication systems. The Low-power Atmospheric Compensation Experiment (LACE) Satellite has provided an opportunity to achieve a CSI test in space for very little cost. First, the CSI test rode piggy-back and did not interfere with the primary objective of LACE. Second, the novel technique of using ground based measurements of vibration of the orbiting satellite was employed. The LACE has a heavy central body to which is attached booms with lengths as long as 150 feet. The ground measurements were obtained using laser Doppler radar at the MIT Lincoln Laboratory Firepond Facility. The initial tests demonstrated the accuracy of the vibration measurements and obtained structural responses for enhancing the accuracy of the mathematical model of the structural dynamics. Germanium corner-cube retroreflectors attached to the central body and a boom deployed to 18 feet ensured a high strength return signal. Subsequent tests demonstrated the ability of an open-loop damper to attenuate the vibrations of the orbiting satellite. The LACE test results are important in contributing to the validation of a CSI technique, and demonstrating a novel ground measurement technique for orbital tests that is accurate but which has very low cost.

Taylor, Lawrence W., Jr.↗
NASA NTRS1976

Translatory shock absorber for attitude sensors

A translatory shock absorber is provided for mounting an attitude sensor thereon for isolating a sensor from translatory vibrations. The translatory shock absorber includes a hollow block structure formed as one piece to form a parallelogram. The absorber block structure includes a movable top plate for supporting the attitude sensor and a fixed base plate with opposed side plates interposed between. At the junctions of the side plates, and the base and top plates, there are provided grooves which act as flexible hinges for attenuating translatory vibrations. A damping material is supported on a pedestal which is carried on the base plate between the side plates thereof. The top of the damping material rests against the bottom surface of the top plate for eliminating the resonant peaks of vibration.

Vonpragenau, G. L.↗
NASA NTRS1983

A 10 deg K triple-expansion Stirling-cycle cryocooler

The design of a triple expansion closed cycle Stirling cryocooler optimized for a cooling load of 50 mW at 10 K is described. The cooler was designed with the objectives of low power, low weight, compactness, low mechanical motion, low electromagnetic noise, and low output temperature fluctuations. The design employs a direct drive linear motion piston motor and a triple expansion free displacer. Piston motion is controlled by feedback from an optical position transducer. Mechanical vibrations are attenuated with a passive resonant counterbalance. Electromagnetic noise is attenuated with layered high permeability magnetic shielding. The regenerators move with the displacer within a thin titanium cold finger. The piston and displacer oscillate at 8.33 Hz on bearings and seals of reinforced Teflon. The cooler is designed to provide the desired 50 mW of cooling at 10 K with a power input of less than 100 W. The piston can be driven at a greater stroke to produce up to 200 mW of cooling with an input power of 250 W. A lead and copper cold tip heat exchanger will limit temperature fluctuations to within 0.01 K.

Newman, W.↗
NASA NTRS1991

Robust decentralized control laws for the ACES structure

Control system design for the Active Control Technique Evaluation for Spacecraft (ACES) structure at NASA Marshall Space Flight Center is discussed. The primary objective of this experiment is to design controllers that provide substantial reduction of the line-of-sight pointing errors. Satisfaction of this objective requires the controllers to attenuate beam vibration significantly. The primary method chosen for control design is the optimal projection approach for uncertain systems (OPUS). The OPUS design process allows the simultaneous tradeoff of five fundamental issues in control design: actuator sizing, sensor accuracy, controller order, robustness, and system performance. A brief description of the basic ACES configuration is given. The development of the models used for control design and control design for eight system loops that were selected by analysis of test data collected from the structure are discussed. Experimental results showing that very significant performance improvement is achieved when all eight feedback loops are closed are presented.

Collins, Emmanuel G., Jr.↗
NASA NTRS2010

Mars Science Laboratory Sample Acquisition, Sample Processing and Handling: Subsystem Design and Test Challenges

The Sample Acquisition/Sample Processing and Handling subsystem for the Mars Science Laboratory is a highly-mechanized, Rover-based sampling system that acquires powdered rock and regolith samples from the Martian surface, sorts the samples into fine particles through sieving, and delivers small portions of the powder into two science instruments inside the Rover. SA/SPaH utilizes 17 actuated degrees-of-freedom to perform the functions needed to produce 5 sample pathways in support of the scientific investigation on Mars. Both hardware redundancy and functional redundancy are employed in configuring this sampling system so some functionality is retained even with the loss of a degree-of-freedom. Intentional dynamic environments are created to move sample while vibration isolators attenuate this environment at the sensitive instruments located near the dynamic sources. In addition to the typical flight hardware qualification test program, two additional types of testing are essential for this kind of sampling system: characterization of the intentionally-created dynamic environment and testing of the sample acquisition and processing hardware functions using Mars analog materials in a low pressure environment. The overall subsystem design and configuration are discussed along with some of the challenges, tradeoffs, and lessons learned in the areas of fault tolerance, intentional dynamic environments, and special testing

Jandura, Louise↗
NASA NTRS2004

Relative-Motion Sensors and Actuators for Two Optical Tables

Optoelectronic sensors and magnetic actuators have been developed as parts of a system for controlling the relative position and attitude of two massive optical tables that float on separate standard air suspensions that attenuate ground vibrations. In the specific application for which these sensors and actuators were developed, one of the optical tables holds an optical system that mimics distant stars, while the other optical table holds a test article that simulates a spaceborne stellar interferometer that would be used to observe the stars. The control system is designed to suppress relative motion of the tables or, on demand, to impose controlled relative motion between the tables. The control system includes a sensor system that detects relative motion of the tables in six independent degrees of freedom and a drive system that can apply force to the star-simulator table in the six degrees of freedom. The sensor system includes (1) a set of laser heterodyne gauges and (2) a set of four diode lasers on the star-simulator table, each aimed at one of four quadrant photodiodes at nominal corresponding positions on the test-article table. The heterodyne gauges are used to measure relative displacements along the x axis.

Gursel, Yekta↗
NASA NTRS1983

Vibration isolation and pressure compensation apparatus for sensitive instrumentation

A system for attenuating the inherent vibration associated with a mechanical refrigeration unit employed to cryogenically cool sensitive instruments used in measuring chemical constituents of the atmosphere is described. A modular system including an instrument housing and a reaction bracket with a refrigerator unit floated there between comprise the instrumentation system. A pair of evacuated bellows that "float' refrigerator unit and provide pressure compensation at all levels of pressure from seal level to the vacuum of space. Vibration isolators and when needed provide additional vibration damping for the refrigerator unit. A flexible thermal strap (20 K) serves to provide essentially vibration free thermal contact between cold tip of the refrigerator unit and the instrument component mounted on the IDL mount. Another flexible strap (77 K) serves to provide vibration free thermal contact between the TDL mount thermal shroud and a thermal shroud disposed about the thermal shaft.

Averill, R. D.↗
NASA NTRS1985

Vibration control of flexible beams using an active hinge

The use of an active hinge to attenuate the transverse vibrations of a flexible beam is examined. A slender aluminum beam is suspended vertically, cantilevered at the top. An active hinge is placed at the node of the second vibration mode. The active hinge consists of a torque motor, strain gauge, and tachometer. A control law is implemented using both beam-bending strain and the relative angular velocity measured at this hinge, thereby configuring the hinge to act as an active damper. Results from implementing this control law show little improvement in the first mode damping ratio, 130 percent increase in the second mode damping ratio, and 180 percent increase in the third mode damping ratio. The merits of using a motor with a gearbox are discussed.

Cudney, H. H., Jr.↗
NASA NTRS1999

A TREETOPS Simulation of the STABLE Microgravity Vibration Isolation System

As a research facility for microgravity science, the International Space Station (ISS) will be used for numerous experiments which require a quiescent acceleration environment across a broad spectrum of frequencies. For many micro-gravity science experiments, the ambient acceleration environment on ISS will significantly exceed desirable levels. The ubiquity of acceleration disturbance sources and the difficulty in characterization of these sources precludes source isolation, requiring, vibration isolation to attenuate the disturbances to an acceptable level at the experiment. To provide a more quiescent acceleration environment, a vibration isolation system named STABLE (Suppression of Transient Accelerations By LEvitation) was developed. STABLE was the first successful flight test of an active isolation device for micro-gravity science payloads and was flown on STS-73/USML-2 in October 1995. This report documents the development of the high fidelity, nonlinear, multibody simulation developed using TREETOPS which was used to design the control laws and define the expected performance of the STABLE isolation system.

Nurre, G. S.↗
NASA NTRS1998

Damping Mechanisms for Microgravity Vibration Isolation (MSFC Center Director's Discretionary Fund Final Report, Project No. 94-07)

As a research facility for microgravity science, the International Space Station (ISS) will be used for numerous investigations such as protein crystal growth, combustion, and fluid mechanics experiments which require a quiescent acceleration environment across a broad spectrum of frequencies. These experiments are most sensitive to low-frequency accelerations and can tolerate much higher accelerations at higher frequency. However, the anticipated acceleration environment on ISS significantly exceeds the required acceleration level. The ubiquity and difficulty in characterization of the disturbance sources precludes source isolation, requiring vibration isolation to attenuate the anticipated disturbances to an acceptable level. This memorandum reports the results of research in active control methods for microgravity vibration isolation.

Whorton, M. S.↗
NASA NTRS1988

Active control and system identification of rotordynamic structure

Four current research projects are summarized: (1) active control of rotor system dynamics; (2) attenuation of rotor vibration using controlled pressure hydrostatic bearings; (3) a new seal test facility for measuring isotropic and anisotropic linear rotordynamic characteristics; and (4) the use of rotordynamic instability thresholds to accurately measure bearing rotordynamic characteristics.

Adams, M. L.↗
NASA NTRS1988

Active control of transient rotordynamic vibration by optimal control methods

Although considerable effort has been put into the study of steady state vibration control, there are few methods applicable to transient vibration control of rotorbearing systems. In this paper optimal control theory has been adopted to minimize rotor vibration due to sudden imbalance, e.g., blade loss. The system gain matrix is obtained by choosing the weighting matrices and solving the Riccati equation. Control forces are applied to the system via a feedback loop. A seven mass rotor system is simulated for illustration. A relationship between the number of sensors and the number of modes used in the optimal control model is investigated. Comparisons of responses are made for various configurations of modes, sensors, and actuators. Furthermore, spillover effect is examined by comparing results from collocated and noncollocated sensor configurations. Results show that shaft vibration is significantly attenuated in the closed loop system.

Palazzolo, A. B.↗
NASA NTRS1990

Design and implementation of robust decentralized control laws for the ACES structure at Marshall Space Flight Center

An experiment was conducted to design controllers that would provide substantial reduction of line-of-sight control errors. The satisfaction of this objective required the controllers to attenuate the beam vibration significantly. Particular emphasis was placed on controller simplicity (i.e., reduced-order and decentralized controller architectures). Complexity reduction in control law implementation is of paramount interest due to stringent limitations on throughput of even state-of-the-art space qualified processors. The results of this experiment successfully demonstrate active vibrator control for a flexible structure. The testbed is the ACES structure at the NASA Marshall Space Flight Center. The ACES structure is dynamically traceable to future space systems and especially allows the study of line-of-sight control issues.

Collins, Emmanuel G., Jr.↗