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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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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Pultrusion process development for long space boom models

Long flexible boom models were required to develop ground vibration test methods for very low frequency space structures with applications to the proposed MAST program and Space Station. Pultruded quasi-isotropic composite beams were selected as an option over extruded aluminum alloy structures because of the lower cost potential, higher specific strength, flexural properties, and dynamic similarity considerations. A comparison is made of four different pultrusions having varied matrices and fiber orientations. Test results indicate that the pultrusion process can be used to produce quasi-isotropic composite structures by selective fiber orientation using the knit-lock fabric concept.

Wilson, Maywood L.↗
NASA NTRS1993

Impulse damping control of an experimental structure

The characteristics associated with the fuel optimal control of a harmonic oscillator are extended to develop a near minimum fuel control algorithm for the vibration suppression of spacecraft. The operation of single level thrusters is regulated by recursive calculations of the standard deviations of displacement and velocity resulting in a bang-off-bang controller. A vertically suspended 16 ft cantilevered beam was used in the experiment. Results show that the structure's response was easily manipulated by minor alterations in the control law and the control system performance was not seriously degraded in the presence of multiple actuator failures.

Redmond, J.↗
NASA NTRS1988

Parametric and experimental analysis using a power flow approach

Having defined and developed a structural power flow approach for the analysis of structure-borne transmission of structural vibrations, the technique is used to perform an analysis of the influence of structural parameters on the transmitted energy. As a base for comparison, the parametric analysis is first performed using a Statistical Energy Analysis approach and the results compared with those obtained using the power flow approach. The advantages of using structural power flow are thus demonstrated by comparing the type of results obtained by the two methods. Additionally, to demonstrate the advantages of using the power flow method and to show that the power flow results represent a direct physical parameter that can be measured on a typical structure, an experimental investigation of structural power flow is also presented. Results are presented for an L-shaped beam for which an analytical solution has already been obtained. Furthermore, the various methods available to measure vibrational power flow are compared to investigate the advantages and disadvantages of each method.

Cuschieri, J. M.↗
NASA NTRS1978

Dynamics of a flexible body in orbit

The equations of motion of an arbitrary flexible body in orbit are derived. The model includes the effects of gravity with all its higher harmonics. As a specific example, the motion of a long, slender, uniform beam in circular orbit is modeled. The example considers the inplane motion of the beam in orbit. In the case of planar motion with only flexural vibrations, the pitch motion is not influenced by the elastic motion of the beam. For large values of the square of the ratio of the structural modal frequency to the orbital angular rate the elastic motion is decoupled from the pitch motion. However, for small values of this ratio and small amplitude pitch motion, the elastic motion is governed by a Hill's 3-term equation. Numerical simulation of this equation indicates the possibilities of instability for very low values of the square of the ratio of the modal frequency to the orbit angular rate.

Kumar, V. K.↗
NASA NTRS1957

Differential equations of motion for combined flapwise bending, chordwise bending, and torsion of twisted nonuniform rotor blades

The differential equations of motion for the lateral and torsional deformations of twisted rotating beams are developed for application to helicopter rotor and propeller blades. No assumption is made regarding the coincidence of the neutral, elastic, and mass axes, and the generality is such that previous theories involving various simplifications are contained as subcases to the theory developed and presented in this paper. Special attention is given to coupling terms not found in previous theories, and methods of solution of the equations of motion are indicated by selected examples.

VIBRATION AND FLUTTER - ROTATING-WING AIRCRAFT↗
NASA NTRS1982

Simulation and testing of digital control on a flexible beam

Large space structures are expected to have control problems due to low stiffness and damping, and control laws for these structures must deal with shape and configuration control as well as attitude and orbit maintenance. In general, these control tasks must be accomplished without adversely interacting with the lightly damped and low frequency vibration modes of the structure. Modal control schemes have been proposed to deal with these problems. A discrete time parameter adaptive control scheme which uses modal control has been proposed by Montgomery and Johnson (1978). In the present investigation the method considered by Montgomery and Johnson is applied to a homogeneous free-free beam in both numerical simulation and laboratory experimentation. Mathematical modeling of the beam is treated in a manner expedient for digital simulation and control implementation.

Williams, J. P.↗
NASA NTRS1993

Active Suppression Of Vibrations On Elastic Beams

Pairs of colocated piezoelectric transducers, independently controlled by multichannel adaptive controller, employed as actuators and sensors to achieve simultaneous attenuation of both extensional and flexural motion. Single pair used to provide simultaneous control of flexural and extensional waves, or two pairs used to control torsional motion also. Capability due to nature of piezoelectric transducers, when bonded to surfaces of structures and activated by oscillating voltages, generate corresponding oscillating distributions of stresses in structures. Phases and amplitudes of actuator voltages adjusted by controller to impede flow of vibrational energy simultaneously, in waves of various forms, beyond locations of actuators. Concept applies equally to harmonic or random response of structure and to multiple responses of structure to transverse bending, torsion, and compression within structural element. System has potential for many situations in which predominant vibration transmission path through framelike structure.

Silcox, Richard J.↗
NASA NTRS1980

Vibration modes and frequencies of structures

SUDAN, Substructuring in Direct Analysis, analyzes natural modes and frequencies of vibration of structural systems. Based on direct method of analysis that employs substructures methodology, program is used with structures that may be represented as equivalent system of beam, springs, and rigid bodies.

Durling, R. J.↗
NASA NTRS1990

The dynamics and control of large flexible space structures - 13

The optimal control of three-dimensional large angle maneuvers and vibrations of a Shuttle-mast-reflector system is considered. The nonlinear equations of motion are formulated by using Lagrange's formula, with the mast modeled as a continuous beam subject to three-dimensional deformations. Pontryagin's Maximum Principle is applied to the slewing problem, to derive the necessary conditions for the optimal controls, which are bounded by given saturation levels. The resulting two point boundary value problem is then solved by using the quasilinearization algorithm and the method of particular solutions. The study of the large angle maneuvering of the Shuttle-beam-reflector spacecraft in the plane of a circular earth orbit is extended to consider the effects of the structural offset connection, the axial shortening, and the gravitational torque on the slewing motion. Finally the effect of additional design parameters (such as related to additional payload requirement) on the linear quadratic regulator based design of an orbiting control/structural system is examined.

Bainum, Peter M.↗
NASA NTRS1991

Damping of structural vibrations with piezoelectric materials and passive electrical networks

The possibility of dissipating mechanical energy with piezoelectric material shunted with passive electrical circuits is investigated. The effective mechanical impedance for the piezoelectric element shunted by an arbitrary circuit is derived. The shunted piezoelectric is shown to possess frequency dependent stiffness and loss factor which are also dependent on the shunting circuit. The generally shunted model is specialized for two shunting circuits: the case of a resistor alone and that of a resistor and inductor. For resistive shunting, the material properties exhibit frequency dependence similar to viscoelastic materials, but are much stiffer and more independent of temperature. Shunting with a resistor and inductor introduces an electrical resonance, which can be optimally tuned to structural resonances in a manner analogous to a mechanical vibration arsorber. Techniques for analyzing systems which incorporate these shunting cases are presented and applied to a cantilevered beam experiment. The experimental results for both the resistive and resonant shunting circuits validate the shunted piezoelectric damping models.

Hagood, N. 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 NTRS1996

Structural dynamic model obtained from flight use with piloted simulation and handling qualities analysis

The ability to use flight data to determine an aircraft model with structural dynamic effects suitable for piloted simulation. and handling qualities analysis has been developed. This technique was demonstrated using SR-71 flight test data. For the SR-71 aircraft, the most significant structural response is the longitudinal first-bending mode. This mode was modeled as a second-order system, and the other higher order modes were modeled as a time delay. The distribution of the modal response at various fuselage locations was developed using a uniform beam solution, which can be calibrated using flight data. This approach was compared to the mode shape obtained from the ground vibration test, and the general form of the uniform beam solution was found to be a good representation of the mode shape in the areas of interest. To calibrate the solution, pitch-rate and normal-acceleration instrumentation is required for at least two locations. With the resulting structural model incorporated into the simulation, a good representation of the flight characteristics was provided for handling qualities analysis and piloted simulation.

Powers, Bruce G.↗
NASA NTRS1971

Vibration analysis of a 1/15 scale dynamic model of a space shuttle configuration

The natural frequencies and mode shapes of a 1/15 scale space shuttle dynamics model are analytically determined. The model, a parallel beam type structure with delta wings, is dynamically representative of the stiffness and mass properties of an early space shuttle design. Important characteristics of the model are elastic interfaces with adjustable spring rates. Normal mode computations are made using the finite element modeling technique as implemented in the NASTRAN (NASA Structural Analysis) computer program. The feasibility of neglecting elastic deformations in the lower modes was investigated using a rigid body model. Using NASTRAN, natural frequencies and mode shapes were first calculated for the booster fuselage, orbiter fuselage, and both delta wings in a free-free condition. Next, the fuselages were connected for various spring rates. Then the wings were attached to each fuselage, and the booster and orbiter were analyzed as separate airplanes. Finally, the two airplanes were elastically joined, and the complete model was analyzed.

Thornton, E. A.↗
NASA NTRS1984

Dynamic characterization and microprocessor control of the NASA/UVA proof mass actuator

The self-contained electromagnetic-reaction-type force-actuator system developed by NASA/UVA for the verification of spacecraft-structure vibration-control laws is characterized and demonstrated. The device is controlled by a dedicated microprocessor and has dynamic characteristics determined by Fourier analysis. Test data on a cantilevered beam are shown.

Zimmerman, D. C.↗
NASA NTRS1972

Infrared spectra of group III A metal oxides

The measurement of infrared frequencies of metal-oxygen species which could be formed in the matrix and to investigate with an oxygen-18 enrichment study the controversy on the vibrational assignments for the suboxide. Several new molecules, Al3O2, Ga3O, In3O, In4O2, IntaO, IntaO2, and In2WO4, were found by mass spectrometric sampling to exist in extremely minor concentrations in the vapor phase. The latter three species were formed by reaction with the crucible materials and were unimportant for an infrared analysis. The infrared spectroscopic measurements were obtained by the matrix isolation technique of molecular beam sampling. The MO2 species were formed by direct reaction between metal and O2 in the matrix. A C2v structure and an O-M-O bond angle near 40 deg was favored for these molecules by analogy with a similar investigation of the alkali metals. The vibrational frequencies which were determined are given.

Lynch, D. A., Jr.↗