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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Robustified time-optimal control of uncertain structural dynamic systems

A new approach for computing open-loop time-optimal control inputs for uncertain linear dynamical systems is developed. In particular, the single-axis, rest-to-rest maneuvering problem of flexible spacecraft in the presence of uncertainty in model parameters is considered. Robustified time-optimal control inputs are obtained by solving a parameter optimization problem subject to robustness constraints. A simple dynamical system with a rigid-body mode and one flexible mode is used to illustrate the concept.

Liu, Qiang↗
NASA NTRS1984

Dynamics and control simulation of large space structures

Attention is given to the dynamics and control simulation techniques applicable to large space structures, encompassing the model of the large structure as well as models of its dynamics, its onboard controller, its sensor/actuator systems, and various disturbances to which it may be subjected. Control performance parameters must be computed as functions of time, or of such other design parameters as control gain. A large space antenna is used as an example of the structures in question, illustrating the way in which an efficient dynamics and control simulation structure program can be developed, and how antenna parameters such as reflector surface distortions can be computed, without having to solve a large number of equations for each computation time interval.

Lin, Y. H.↗
NASA NTRS1987

Actuators for actively controlled space structures

A free-flying platform of about 4 x 17 m overall dimensions, carrying a variety of imaging and sounding payloads, calls for an intelligent structure with active dynamic control of structural resonances. The actuators for such a structure must be lightweight, require low power, and allow integration into the structure without degradation of its integrity; the dc-to-100 Hz dynamic range required may entail several types of actuators, as is presently emphasized. Broadband damping of higher-order modes requires modeling of the structure with a distributed array of sensors and actuators.

Studer, P.↗
NASA NTRS1981

The dynamics and control of large flexible space structures

The dynamics and attitude and shape control of very large, inherently flexible spacecraft systems were investigated. Increasingly more complex examples were examined, beginning with a uniform free-free beam, next a free-free uniform plate/platform and finally by considering a thin shallow spherical shell structure in orbit. The effects devices were modeled. For given sets of assumed actuator locations, the controllability of these systems was first established. Control laws for each of the actuators were developed based on decoupling techniques (including distributed modal control) pole placement algorithms and a application of the linear regulator problem for optical control theory.

Bainum, P. M.↗
NASA NTRS1997

Direct Adaptive Aircraft Control Using Dynamic Cell Structure Neural Networks

A Dynamic Cell Structure (DCS) Neural Network was developed which learns topology representing networks (TRNS) of F-15 aircraft aerodynamic stability and control derivatives. The network is integrated into a direct adaptive tracking controller. The combination produces a robust adaptive architecture capable of handling multiple accident and off- nominal flight scenarios. This paper describes the DCS network and modifications to the parameter estimation procedure. The work represents one step towards an integrated real-time reconfiguration control architecture for rapid prototyping of new aircraft designs. Performance was evaluated using three off-line benchmarks and on-line nonlinear Virtual Reality simulation. Flight control was evaluated under scenarios including differential stabilator lock, soft sensor failure, control and stability derivative variations, and air turbulence.

Jorgensen, Charles C.↗
NASA NTRS1998

Feedback Linearized Aircraft Control Using Dynamic Cell Structure

A Dynamic Cell Structure (DCS ) Neural Network was developed which learns a topology representing network (TRN) of F-15 aircraft aerodynamic stability and control derivatives. The network is combined with a feedback linearized tracking controller to produce a robust control architecture capable of handling multiple accident and off-nominal flight scenarios. This paper describes network and its performance for accident scenarios including differential stabilator lock, soft sensor failure, control, stability derivative variation, and turbulence.

Jorgensen, C. C.↗
NASA NTRS1987

Structural dynamics and attitude control study of early manned capability space station configurations

A study was performed to determine the vibration and attitude control characteristics of critical space station configurations featuring early manned capability during buildup from initial user support through the operations capability reference station. Five configurations were selected and were examined thus determining the changes that are likely to occur in the characteristics of the system as the station progresses from a single boom structure to a mature, dual keel, operations capability reference station. Both 9 foot and 5 meter truss bay sizes were investigated. All configurations analyzed were stable; however, the 5 meter truss bay size structure exhibited superior stability characteristics.

Ayers, J. Kirk↗
DOE OSTI2023

Optical control of ultrafast structural dynamics in a fluorescent protein

The photoisomerization reaction of a fluorescent protein chromophore occurs on the ultrafast timescale. The structural dynamics that result from femtosecond optical excitation have contributions from vibrational and electronic processes and from reaction dynamics that involve the crossing through a conical intersection. The creation and progression of the ultrafast structural dynamics strongly depends on optical and molecular parameters. When using X-ray crystallography as a probe of ultrafast dynamics, the origin of the observed nuclear motions is not known. Now, high-resolution pump–probe X-ray crystallography reveals complex sub-ångström, ultrafast motions and hydrogen-bonding rearrangements in the active site of a fluorescent protein. However, we demonstrate that the measured motions are not part of the photoisomerization reaction but instead arise from impulsively driven coherent vibrational processes in the electronic ground state. A coherent-control experiment using a two-colour and two-pulse optical excitation strongly amplifies the X-ray crystallographic difference density, while it fully depletes the photoisomerization process. A coherent control mechanism was tested and confirmed the wave packets assignment.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1976

Structural dynamics, stability, and control of helicopters

The dynamic synthesis of a helicopter is reported. The method of approach is a variation of the component mode synthesis in the sense that it regards the aircraft as an assemblage of interconnected substructures. The equations of motion are derived in general form by means of the Lagrangian formulation in conjunction with an orderly kinematical procedure that takes into account the superposition of motion of various substructures, thus circumventing constraint problems.

Meirovitch, L.↗
NASA NTRS1985

Space Technology Experiments Platform (STEP) Status: an In-space Test Facility

Designed for utilization of the space transportation system for technology experiments in space, the space technology experiment platform (STEP) is a shuttle-borne experiment support facility for use primarily for structures, structural dynamics, and control flexible structures technology flight experiments. The STEP concept is discussed as well as shows its relationship to broad NASA goals and objectives. The development chronology is presented and the current system capability in block diagram format is described. The STEP development schedule is included.

Harris, J. E.↗
NASA NTRS1988

Emulating a flexible space structure: Modeling

Control Dynamics, in conjunction with Marshall Space Flight Center, has participated in the modeling and testing of Flexible Space Structures. Through the series of configurations tested and the many techniques used for collecting, analyzing, and modeling the data, many valuable insights have been gained and important lessons learned. This paper discusses the background of the Large Space Structure program, Control Dynamics' involvement in testing and modeling of the configurations (especially the Active Control Technique Evaluation for Spacecraft (ACES) configuration), the results from these two processes, and insights gained from this work.

Waites, H. B.↗
NASA NTRS1985

Identification and control of structures in space

Work during the period July 1 - December 31, 1985, has concentrated on the application of the equations derived in the preceding period to the maneuvering and vibration suppression of the Spacecraft Control Laboratory Experiment (SCOLE) model. Two different situations have been considered: (1) a space environment and (2) a laboratory environment. This report covers the first case and consists of a paper entitled Maneuvering and Vibration Control of Flexible Spacecraft, presented at the Workshop on Structural Dynamics and Control Interaction of Flexible Structures, Marshall Space flight Center, Huntsville, AL, April 22 to 24, 1986. The second case will be covered in the report for the next period.

Meirovitch, L.↗
NASA NTRS1991

PDEMOD: Software for control/structures optimization

Because of the possibility of adverse interaction between the control system and the structural dynamics of large, flexible spacecraft, great care must be taken to ensure stability and system performance. Because of the high cost of insertion of mass into low earth orbit, it is prudent to optimize the roles of structure and control systems simultaneously. Because of the difficulty and the computational burden in modeling and analyzing the control structure system dynamics, the total problem is often split and treated iteratively. It would aid design if the control structure system dynamics could be represented in a single system of equations. With the use of the software PDEMOD (Partial Differential Equation Model), it is now possible to optimize structure and control systems simultaneously. The distributed parameter modeling approach enables embedding the control system dynamics into the same equations for the structural dynamics model. By doing this, the current difficulties involved in model order reduction are avoided. The NASA Mini-MAST truss is used an an example for studying integrated control structure design.

Taylor, Lawrence W., Jr.↗
NASA NTRS1992

Dynamics and control of coherent structure in turbulent jets

Current understanding of coherent structure dynamics in incompressible turbulent jets as explained by the nonlinear stability theory is reviewed, focusing on nonswirling turbulent jets. Topics addressed include hydrodynamic stability theory and coherent structures; dynamics of energy transfers among different scales of motion; nonlinear development of amplitude; development of single-frequency coherent mode; fundamental-subharmonic interaction and vortex pairing; and reversal of Reynolds stresses. Attention is also given to the effect of initial phase-difference angle between fundamental and subharmonic, conditions for resonance interaction, modulation of spreading rate by controlling coherent structure, turbulence enhancement or suppression due to excitation, 3D effects, jet noise, and swirling jets.

Mankbadi, Reda R.↗
NASA NTRS1990

Computational methods and software systems for dynamics and control of large space structures

This final report on computational methods and software systems for dynamics and control of large space structures covers progress to date, projected developments in the final months of the grant, and conclusions. Pertinent reports and papers that have not appeared in scientific journals (or have not yet appeared in final form) are enclosed. The grant has supported research in two key areas of crucial importance to the computer-based simulation of large space structure. The first area involves multibody dynamics (MBD) of flexible space structures, with applications directed to deployment, construction, and maneuvering. The second area deals with advanced software systems, with emphasis on parallel processing. The latest research thrust in the second area, as reported here, involves massively parallel computers.

Park, K. C.↗
NASA NTRS1985

AFWAL space control technology program

An overview of space oriented control technology programs which are applicable to flexible large space structures is presented. The spacecraft control activity is interdisciplinary with activities in structures, structural dynamics and control brought together. The large flexible structures to be controlled have many physical factors that influence the final controllability of the vehicle. Factors are studied such as rigidity of both structural elements and joints, damping inherent in both material as well as discrete dampers located throughout the structure, and the bandwidth of both sensors and actuators used to sense motion and control it. Descriptions of programs both in-house and contracted are given.

Hoehne, V. O.↗