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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Control and Simulation of Space-Station Vibrations

Adaptive control system reduces effects of model uncertainties. Report outlines method for finite-element dynamic analysis of space station. Purpose is to determine periods and modes of oscillation of structure and to analyze effect of proposed adaptive control system to damp out unwanted vibrations. With simplifications proposed, finite-element simulations performed during dynamic event, like docking of Space Shuttle, and used to control vibration-damping actuators.

Ih, Che-Hang Charles↗
NASA NTRS1988

Adaptive Control For Flexible Structures

Paper discusses ways to cope with measurement noise in adaptive control system for large, flexible structure in outer space. System generates control signals for torque and thrust actuators to turn all or parts of structure to desired orientations while suppressing torsional and other vibrations. Main result of paper is general theory for introduction of filters to suppress measurement noise while preserving stability.

Bayard, David S.↗
NASA NTRS1988

Adaptive Control For Space-Station Joints

Input gain weighting added to existing adaptive-control algorithm. Report discusses concept for adaptive control of rotations of various appended structures about joints on space station, with suppression of vibrations in both station and appendages. Concept relevant to such terrestrial applications as control of aircraft, suppression of vibrations in large buildings, and robotics.

Ih, Che-Hang Charles↗
NASA NTRS1987

Adaptive control for flexible space structures with measurement noise

Simulation results are presented to address the problem of measurement noise in the design of adaptive controllers for large flexible space structures. In order to reduce the unrealistically high overall control demand resulting from the presence of leakage terms, a method has been developed for the introduction of noise filters into the adaptive controller while at the same time ensuring the global stability of the adaptive algorithm. A branch filter allows filtering of the output error without introducing phase lag into the adaptive loop. The technique is demonstrated in the simulation of an adaptive payload articulation control for a Space Station model.

Bayard, David S.↗
NASA NTRS1988

Adaptive control experiment with a large flexible structure

A large space antenna-like ground experiment structure has been developed for conducting research and validation of advanced control technology. A set of proof-of-concept adaptive control experiments for transient and initial deflection regulation with a small set of sensors and actuators were conducted. Very limited knowledge of the plant dynamics and its environment was used in the design of the adaptive controller so that performance could be demonstrated under conditions of gross underlying uncertainties. High performance has been observed under such stringent conditions. These experiments have established a baseline for future studies involving more complex hardware and environmental conditions, and utilizing additional sets of sensors and actuators.

Ih, Che-Hang Charles↗
NASA NTRS1990

Adaptive-Control Experiments On A Large Flexible Structure

Antennalike flexible structure built for research in advanced technology including suppression of vibrations and control of initial deflections. Structure instrumented with sensors and actuators connected to digital electronic control system, programmed with control algorithms to be tested. Particular attention in this research focused on direct model-reference adaptive-control algorithm based on command generator tracker theory. Built to exhibit multiple vibrational modes, low modal frequencies, and low structural damping. Made three-dimensional so complicated interactions among components of structure and control system investigated.

Ih, Che-Hang C.↗
NASA NTRS1989

A finite element approach for large motion dynamic analysis of multibody structures in space

A three-dimensional finite element formulation for modeling the transient dynamics of constrained multibody space sructures with truss-like configurations is presented. Convected coordinate systems are used to define rigid-body motion of individual elements in the system. These systems are located at one end of each element and are oriented such that one axis passes through the other end of the element. Deformation of each element, relative to its convected coordinate system, is defined by cubic flexural shape functions as used in finite element methods of structural analysis. The formulation is oriented toward joint dominated structures and places the generalized coordinates at the joint. A transformation matrix is derived to integrate joint degree-of-freedom into the equations of motion of the element. Based on the derivation, a general-purpose code LATDYN (Large Angle Transient DYNamics) was developed. Two examples are presented to illustrate the application of the code. For the spin-up of a flexible beam, results are compared with existing solutions available in the literature. For the deployment of one bay of a deployable space truss (the Minimast), results are verified by the geometric knowledge of the system and converged solution of a successively refined model.

Chang, Che-Wei↗
NASA NTRS1989

Dynamic analysis of flexible mechanical systems using LATDYN

A 3-D, finite element based simulation tool for flexible multibody systems is presented. Hinge degrees-of-freedom is built into equations of motion to reduce geometric constraints. The approach avoids the difficulty in selecting deformation modes for flexible components by using assumed mode method. The tool is applied to simulate a practical space structure deployment problem. Results of examples demonstrate the capability of the code and approach.

Wu, Shih-Chin↗
NASA NTRS1990

Experimental study of robustness in adaptive control for large flexible structures

An experimental study is performed to investigate the robustness of model reference adaptive control for the large flexible structures control application. The main nonidealities of concern are unmodeled dynamics, input saturation, and time delay effects (here, actuator and sensor dynamics are lumped into the last item for convenience). This study focuses on the robustness with respect to input saturation and time delay effects, since robustness to unmodeled dynamics is inherent to the basic algorithm and has been demonstrated experimentally elsewhere.

Ih, Che-Hang Charles↗
NASA NTRS1991

Experiments In Multivariable Adaptive Control Of A Flexible Structure

Report describes experiments in use of six-input/six-output multivariable adaptive control system to suppress vibrations in complicated flexible structure. Represents significant upgrade relative to two-input/two-output system, yielding significant improvement in spatial controllability and effective damping of largest set of modes. Structure exhibits low modal frequencies and complicated dynamics like those of large structures in outer space. Conclusions drawn from research relevant to such applications as active suppression of wind and earthquake vibrations in tall buildings and other large terrestrial structures.

Ih, Che-Hang C.↗
NASA NTRS1991

Damping Of Vibrations In Graphite/Epoxy Structures

Report describes study of vibration-damping properties, in air and vacuum, of graphite/epoxy composite structural members joined by adhesives. Determines vibration-damping effects of specimens representative of members and joints of truss, particularly after gases and moisture trapped during manufacture released in vacuum. Damping ratios measured under free and forced vibrations and before and after outgassing in vacuum. Effects of end-support conditions and high and low temperatures on damping also measured.

Crocker, Malcolm J.↗
NASA NTRS1991

Large Angle Transient Dynamics (LATDYN) user's manual

A computer code for modeling the large angle transient dynamics (LATDYN) of structures was developed to investigate techniques for analyzing flexible deformation and control/structure interaction problems associated with large angular motions of spacecraft. This type of analysis is beyond the routine capability of conventional analytical tools without simplifying assumptions. In some instances, the motion may be sufficiently slow and the spacecraft (or component) sufficiently rigid to simplify analyses of dynamics and controls by making pseudo-static and/or rigid body assumptions. The LATDYN introduces a new approach to the problem by combining finite element structural analysis, multi-body dynamics, and control system analysis in a single tool. It includes a type of finite element that can deform and rotate through large angles at the same time, and which can be connected to other finite elements either rigidly or through mechanical joints. The LATDYN also provides symbolic capabilities for modeling control systems which are interfaced directly with the finite element structural model. Thus, the nonlinear equations representing the structural model are integrated along with the equations representing sensors, processing, and controls as a coupled system.

Abrahamson, A. Louis↗
NASA NTRS1991

A finite element approach for the dynamic analysis of joint-dominated structures

A finite element method to model dynamic structural systems undergoing large rotations is presented. The dynamic systems are composed of rigid joint bodies and flexible beam elements. The configurations of these systems are subject to change due to the relative motion in the joints among interconnected elastic beams. A body fixed reference is defined for each joint body to describe the joint body's displacements. Using the finite element method and the kinematic relations between each flexible element and its corotational reference, the total displacement field of an element, which contains gross rigid as well as elastic effects, can be derived in terms of the translational and rotational displacements of the two end nodes. If one end of an element is hinged to a joint body, the joint body's displacements and the hinge degree of freedom at the end are used to represent the nodal displacements. This results in a highly coupled system of differential equations written in terms of hinge degrees of freedom as well as the rotational and translational displacements of joint bodies and element nodes.

Chang, Che-Wei↗
NASA NTRS1990

Modeling and stability of segmented reflector telescopes - A decentralized approach

The decentralization of a segmented reflector telescope based on a finite-element model of its structure is considered. The decentralization of the system at the panel level is considered. Each panel is originally treated as an isolated subsystem so that the controller design is performed independently at the local level, and then applied to the composite system for stability analysis. The panel-level control laws were designed by means of pole placement using local output feedback. Simulation results show a better 1000:1 vibration attenuation in panel position when compared to the open-loop system. It is shown that the overall closed-loop system is exponentially stable provided that certain conditions are met. The advantage to the decentralized approach is that the design is performed in terms of the low-dimensionality subsystems, thus drastically reducing the design computational complexities.

Ryaciotaki-Boussalis, Helen A.↗
NASA NTRS1992

Computing Large-Angle Transients In Structures

LATDYN is computer code for calculating large-angle transient dynamics of flexible articulating structures and mechanisms including joints about which members rotate through large angles. Extends and brings together some of aspects of finite-element analysis of structures, dynamics of multiple bodies, and analysis of control systems. Combines significant portions of their distinct capabilities into one analysis software tool. Software consists of three FORTRAN computer programs: LATDYN program, Preprocessor, and Postprocessor. Written in FORTRAN 77.

Housner, Jerrold M.↗
NASA NTRS1992

Modeling For Stabilization Of Segmented Telescope Reflector

Report discusses mathematical modeling of vibrations and active control to suppress vibrations of large, segmented telescope reflector. Vibrating structure treated as collection of substructures, each initially treated separately. Vibrations suppressed considerably, in comparison with open-loop vibration-attenuation mechanism.

Ih, Che-Hang C.↗
NASA NTRS1992

Dynamics And Control Of Flexible Manipulator

Nonlinear equations solved with linear approximations applicable during small increments of time. Report presents theoretical study of selected aspects of dynamics and control of robotic manipulator that includes multiple flexible links. Addresses problem of control primarily from perspective of inverse-dynamics problem.

Gawronski, Wodek K.↗
NASA NTRS1991

Dynamic performance modeling and stability analysis of a segmented reflector telescope

The problem of vibration suppression in segmented reflector telescopes is considered. The decomposition of the structure into smaller components is discussed, and control laws for vibration suppression and conditions for stability at the local and global levels are presented. The states of the reflector segments are mapped into ray displacements on the detector plane.

Ryaciotaki-Boussalis, Helen A.↗