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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Robust Assignment Of Eigensystems For Flexible Structures

Improved method for placement of eigenvalues and eigenvectors of closed-loop control system by use of either state or output feedback. Applied to reduced-order finite-element mathematical model of NASA's MAST truss beam structure. Model represents deployer/retractor assembly, inertial properties of Space Shuttle, and rigid platforms for allocation of sensors and actuators. Algorithm formulated in real arithmetic for efficient implementation. Choice of open-loop eigenvector matrix and its closest unitary matrix believed suitable for generating well-conditioned eigensystem with small control gains. Implication of this approach is that element of iterative search for "optimal" unitary matrix appears unnecessary in practice for many test problems.

Juang, Jer-Nan↗
NASA NTRS1991

Integrated adaptive filtering and design for control experiments of flexible structures

A novel method is presented of identifying a state space model and a state estimator for linear stochastic systems from input and output data. The method is primarily based on the relations between the state space model and the finite difference model for linear stochastic systems derived through projection filters. It is proven that least squares identification of a finite difference model converges to the model derived from the projection filters. System pulse response samples are computed from the coefficients of the finite difference model. In estimating the corresponding state estimator gain, a z-domain method is used. First the deterministic component of the output is subtracted out, and then the state estimator gain is obtained by whitening the remaining signal. Experimental example is used to illustrate the feasibility of the method.

Huang, Jen-Kuang↗
NASA NTRS1991

Control of large flexible structures - An experiment on the NASA Mini-Mast facility

The output variance constraint controller design procedure is integrated with model reduction by modal cost analysis. A procedure is given for tuning MIMO controller designs to find the maximal rms performance of the actual system. Controller designs based on a finite-element model of the system are compared with controller designs based on an identified model (obtained using the Q-Markov Cover algorithm). The identified model and the finite-element model led to similar closed-loop performance, when tested in the Mini-Mast facility at NASA Langley.

Hsieh, Chen↗
NASA NTRS1992

Computation of near-minimum-time maneuvers of flexible structures by parameter optimization

Near-minimum-time attitude maneuvers of space structures as well as ground based test articles are considered. Switching nature of the controls for rigid body maneuvers are illustrated using a control-cube and a critical control axis of rotation. The presence of torque smoothing and where appropriate, gravitational effects and connections to other bodies are explicitly included in the mathematical models of the systems to be optimized. A maximum fuel consumption constraint is included besides the required terminal conditions on attitude and angular velocities. The switch times, maximum thrust magnitudes, and smoothing parameters are determined using the Sequential Quadratic Programming method for parameter optimization. Results indicating attitude and angular velocity histories, thruster forces, and structural vibrations are presented for three, four, and five switch maneuvers, as well as maneuvers that involve large coasting arcs.

Vadali, S. R.↗
NASA NTRS1991

An experimental evaluation of uncertainty models for a flexible structure control problem

The authors describe results in applying robust control techniques of an active precision truss structure at the Jet Propulsion Laboratory. The active structure incorporates piezoelectric members which serve as both structural and actuator/sensor elements. Several characterizations of uncertainty are studied and the controllers are compared experimentally.

Smith, Roy S.↗
NASA NTRS1991

Experimental verification of nanometer level optical pathlength control on a flexible structure

This paper describes an experimental facility being developed for demonstration and validation of control concepts arising out of NASA's Control Structure Interaction program. The facility is meant to be a ground testbed with relevance to a broad class of precision optical space systems. The objective of the experimental program is to investigate a multilayer control approach to the maintenance of nanometer-level optical pathlength stability in the presence of external disturbances and multiple structural resonances. The facility is designed to explore the effect of applying, separately and in combinations, structural vibration suppression, vibration isolation, and active optical articulation. This paper describes the testbed facility, the structure, optics, sensors, actuators, and real-time computer and program development environment. Initial optical articulation experimental results are presented.

O'Neal, Michael↗
NASA NTRS1992

Application of adaptive trusses to vibration isolation in flexible structures

It is shown through analysis that force feedback can be used to provide complete vibration isolation in two directions. Simultations were carried out to demonstrate the use of two control methods applied to an adaptive truss as an active mount. The first technique was simple force feedback with a gain. This method has the potential to provide excellent vibration isolation performance. It requires no model of the system and no knowledge of the applied disturbance, and is easily implemented in an adaptive truss. There is some question as to how high the gain can be allowed to go but the experimental results have shown performance advantages over passive techniques even for small gains. The second technique presented is the LQR method, with disturbance modeling. A method is presented for using the LQR method for vibration isolation with the intention of achieving performance with guaranteed stability and relatively lower loop gains. The overhead for those benefits is an accurate system model. It was shown analytically that this method works; however, the performance is not as good as expected. It is believed that the difference in performance is partly due to an increase in active damping which is inadvertently provided by the LQR method.

Clark, William W.↗
NASA NTRS1993

Q-Markov covariance equivalent realization and its application to flexible structure identification

The Q-Markov covariance equivalent realization algorithm is applied to NASA's Minimast structure to identify state-space models for the purpose of designing closed-loop controllers, and laboratory test results are shown for the identification and for the closed-loop performance. The paper also presents for the first time a deterministic formulation of covariance parameters from a pulse response, a stochastic formulation of Markov parameters from a white-noise response, and a simple Q-Markov covariance equivalent realization formulation. This requires only pulse laboratory tests or only white-noise laboratory tests to generate Q-Markov covariance equivalent realizations.

Liu, Ketao↗