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At least 127 records · Page 7

[Actuator placement for active sound and vibration control]

Two refereed journal publications and ten talks given at conferences, seminars, and colloquia resulted from research supported by NASA. They are itemized in this report. The two publications were entitled "Reactive Tabu and Search Sensor Selection in Active Structural Acoustic Control Problems" and "Quelling Cabin Noise in Turboprop Aircraft via Active Control." The conference presentations covered various aspects of actuator placement, including location problems, for active sound and vibration control of cylinders, of commuter jets, of propeller driven or turboprop aircraft, and for quelling aircraft cabin or interior noise.

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Optimizing Sensor and Actuator Arrays for ASAC Noise Control

This paper summarizes the development of an approach to optimizing the locations for arrays of sensors and actuators in active noise control systems. A type of directed combinatorial search, called Tabu Search, is used to select an optimal configuration from a much larger set of candidate locations. The benefit of using an optimized set is demonstrated. The importance of limiting actuator forces to realistic levels when evaluating the cost function is discussed. Results of flight testing an optimized system are presented. Although the technique has been applied primarily to Active Structural Acoustic Control systems, it can be adapted for use in other active noise control implementations.

Palumbo, Dan↗

Active member control of a precision structure with an H(infinity) performance objective

This paper addresses the noncollocated control of active structures using active structural elements. A top level architecture for active structures is presented, and issues pertaining to robust control of structures are discussed. Controllers optimized for an H sub inf performance specification are implemented on a test structure and the results are compared with analytical predictions. Directions for further research are identified.

Fanson, J. L.↗

Orbital operations study. Volume 2: Interfacing activities analysis. Part 2: Structural and mechanical group

The activities of the structural and mechanical activity group of the orbital operations study project are discussed. Element interfaces, alternate approaches, design concepts, operational procedures, functional requirements, design influences, and approach selection are presented. The following areas are considered: (1) mating, (2) orbital assembly, (3) separation, EOS payload deployment, and EOS payload retraction.

Mattson, H. L.↗

U.S.-Japan Workshop on Smart/Intelligent Materials and Systems, Honolulu, HI, Mar. 19-23, 1990, Proceedings

Topics presented include the concept of intelligent materials, the molecular engineering of channel proteins, the prospects, limitations, and requirements of intelligent micro motion systems, the modeling of a shape memory integrated actuator for vibration control of large space structures, and intelligent materials for future electronics. Also presented are the slewing of an active structure, the health monitoring of control system components, the numerical modeling of the microstructure of crystals with symmetry-related variants, and the intelligent material system concept.

Ahmad, Iqbal↗

Control/structure interaction design methodology

The Control Structure Interaction Program is a technology development program for spacecraft that exhibit interactions between the control system and structural dynamics. The program objectives include development and verification of new design concepts (such as active structure) and new tools (such as a combined structure and control optimization algorithm) and their verification in ground and possibly flight test. The new CSI design methodology is centered around interdisciplinary engineers using new tools that closely integrate structures and controls. Verification is an important CSI theme and analysts will be closely integrated to the CSI Test Bed laboratory. Components, concepts, tools and algorithms will be developed and tested in the lab and in future Shuttle-based flight experiments. The design methodology is summarized in block diagrams depicting the evolution of a spacecraft design and descriptions of analytical capabilities used in the process. The multiyear JPL CSI implementation plan is described along with the essentials of several new tools. A distributed network of computation servers and workstations was designed that will provide a state-of-the-art development base for the CSI technologies.

Briggs, Hugh C.↗

Structural defect characterization of silicon dendritic web ribbons

An EBIC study of the cross section of silicon dendritic web ribbon has revealed that recombination-active structural defects are mainly concentrated in the inner part of the ribbon, particularly at and near the twin plane, whereas the material near the surface has significantly fewer defects. An analysis of the distribution of etch pits due to slip dislocations created by shear stress indicates that a minimum in the dislocation density is frequently observed in the ribbon adjacent to the dendrite.

Cheng, L. J.↗

Quasi-perpendicular/quasi-parallel divisions of earth's bow shock

Computer-drawn diagrams of the boundaries between quasi-perpendicular and quasi-parallel areas of earth's bow shock are displayed for a few selected cone angles of static interplanetary magnetic field (IMF). The effect on the boundary of variable IMF in the foreshock is also discussed and shown for one nominal case. The boundaries demand caution in applying them to the realistic, dynamic conditions of the solar wind and in interpreting the effects of small cone angles on the distributions of structures at the shock. However, the calculated, first-order boundaries are helpful in defining areas of the shock where contributions from active structures inherent in quasi-parallel geometry may be distinguishable from those derived secondarily from upstream reflected ion dynamics. The boundaries are also compatible with known behavior of daytime ULF geomagnetic waves and pulsations according to models postulating that cone angle-controlled, time-dependent ULF activity around the subsolar point of the bow shock provides the source of geomagnetic excitation.

Greenstadt, E. W.↗

Integrated design of structures, controls, and materials

In this talk we shall discuss algorithms and CAD tools for the design and analysis of structures for high performance applications using advanced composite materials. An extensive mathematical theory for optimal structural (e.g., shape) design was developed over the past thirty years. Aspects of this theory have been used in the design of components for hypersonic vehicles and thermal diffusion systems based on homogeneous materials. Enhancement of the design methods to include optimization of the microstructure of the component is a significant innovation which can lead to major enhancements in component performance. Our work is focused on the adaptation of existing theories of optimal structural design (e.g., optimal shape design) to treat the design of structures using advanced composite materials (e.g., fiber reinforced, resin matrix materials). In this talk we shall discuss models and algorithms for the design of simple structures from composite materials, focussing on a problem in thermal management. We shall also discuss methods for the integration of active structural controls into the design process.

Blankenship, G. L.↗

Support trusses for large precision segmented reflectors: Preliminary design and analysis

Precision Segmented Reflector (PSR) technology is currently being developed for a range of future applications such as the Large Deployable Reflector. The structures activities at NASA-Langley are outlined in support of the PSR program. Design concepts are explored for erectable and deployable support structures which are envisioned to be the backbone of these precision reflectors. Important functional requirements for the support trusses related to stiffness, mass, and surface accuracy are reviewed. Proposed geometries for these structures and factors motivating the erectable and deployable designs are discussed. Analytical results related to stiffness, dynamic behavior, and surface accuracy are presented and considered in light of the functional requirements. Results are included for both a 4-meter-diameter prototype support truss which is currently being designed as the Test Bed for the PSR technology development program, and for two 20-meter support structures.

Collins, Timothy J.↗

A New Approach to Identify Optimal Properties of Shunting Elements for Maximum Damping of Structural Vibration Using Piezoelectric Patches

The use of shunted piezoelectric patches in reducing vibration and sound radiation of structures has several advantages over passive viscoelastic elements, e.g., lower weight with increased controllability. The performance of the piezoelectric patches depends on the shunting electronics that are designed to dissipate vibration energy through a resistive element. In past efforts most of the proposed tuning methods were based on modal properties of the structure. In these cases, the tuning applies only to one mode of interest and maximum tuning is limited to invariant points when based on den Hartog's invariant points concept. In this study, a design method based on the wave propagation approach is proposed. Optimal tuning is investigated depending on the dynamic and geometric properties that include effects from boundary conditions and position of the shunted piezoelectric patch relative to the structure. Active filters are proposed as shunting electronics to implement the tuning criteria. The developed tuning methods resulted in superior capabilities in minimizing structural vibration and noise radiation compared to other tuning methods. The tuned circuits are relatively insensitive to changes in modal properties and boundary conditions, and can applied to frequency ranges in which multiple modes have effects.

Park, Junhong↗

Active damping of modal vibrations by force apportioning

Force apportioning, a method of active structural damping based on that used in modal vibration testing of isolating modes by multiple shaker excitation, was analyzed and numerically simulated. A distribution of as few forces as possible on the structure is chosen so as to maximally affect selected vibration modes while minimally exciting all other modes. The accuracy of numerical simulations of active damping, active damping of higher-frequency modes, and studies of imperfection sensitivity are discussed. The computer programs developed are described and possible refinements of the research are examined.

Hallauer, W. L., Jr.↗

Sound transmission reduction with intelligent panel systems

Experimental and theoretical investigations are performed of the use of intelligent panel systems to control the sound transmission and radiation. An intelligent structure is defined as a structural system with integrated actuators and sensors under the guidance of an adaptive, learning type controller. The system configuration is based on the Active Structural Acoustic Control (ASAC) concept where control inputs are applied directly to the structure to minimize an error quantity related to the radiated sound field. In this case multiple piezoelectric elements are employed as sensors. The importance of optimal shape and location is demonstrated to be of the same order of influence as increasing the number of channels of control.

Fuller, Chris R.↗

A Cognitive System Model for Human/Automation Dynamics in Airspace Management

NASA has initiated a significant thrust of research and development focused on providing the flight crew and air traffic managers automation aids to increase capacity in en route and terminal area operations through the use of flexible, more fuel-efficient routing, while improving the level of safety in commercial carrier operations. In that system development, definition of cognitive requirements for integrated multi-operator dynamic aiding systems is fundamental. In order to support that cognitive function definition, we have extended the Man Machine Integrated Design and Analysis System (MIDAS) to include representation of multiple cognitive agents (both human operators and intelligent aiding systems) operating aircraft, airline operations centers and air traffic control centers in the evolving airspace. The demands of this application require representation of many intelligent agents sharing world-models, and coordinating action/intention with cooperative scheduling of goals and actions in a potentially unpredictable world of operations. The MIDAS operator models have undergone significant development in order to understand the requirements for operator aiding and the impact of that aiding in the complex nondeterminate system of national airspace operations. The operator model's structure has been modified to include attention functions, action priority, and situation assessment. The cognitive function model has been expanded to include working memory operations including retrieval from long-term store, interference, visual-motor and verbal articulatory loop functions, and time-based losses. The operator's activity structures have been developed to include prioritization and interruption of multiple parallel activities among multiple operators, to provide for anticipation (knowledge of the intention and action of remote operators), and to respond to failures of the system and other operators in the system in situation-specific paradigms. The model's internal representation has been be modified so that multiple, autonomous sets of equipment will function in a scenario as the single equipment sets do now. In order to support the analysis requirements with multiple items of equipment, it is necessary for equipment to access the state of other equipment objects at initialization time (a radar object may need to access the position and speed of aircraft in its area, for example), and as a function of perception and sensor system interaction. The model has been improved to include multiple world-states as a function of equipment am operator interaction. The model has been used -1o predict the impact of warning and alert zones in aircraft operation, and, more critic-ally, the interaction of flight-deck based warning mechanisms and air traffic controller action in response to ground-based conflict prediction and alerting systems. In this operation, two operating systems provide alerting to two autonomous, but linked sets of operators, whose view of the system and whose dynamics in response are radically different. System stability and operator action was predicted using the MIDAS model.

Corker, Kevin M.↗

Large space structures - Fantasies and facts

A review of large space structures activities from 1973 to 1979 is presented. Long-range studies of space colonies, gigantic solar power stations and projected earth applications revived interest in space activities. Studies suggest opportunities for advanced antenna and platform applications. Matching low-thrust propulsion to large flexible vehicles will be a key technology. Current structures technology investigations include deployable and erectable structures and assembly techniques. Based on orbited structures experience, deployment reliability is a critical issue for deployable structures. For erectable structures, concepts for earth-fabricated and space-fabricated memb

Card, M. F.↗

Lightweight Material Patches Allow for Quick Repairs

Cornerstone Research Group Inc., of Dayton, Ohio, has been the recipient of 16 Small Business Innovation Research (SBIR) contracts with NASA with a variety of different focuses, including projects like creating inflatable structures for radio frequency antennas and, most recently, healable polymer matrix composites for future space vehicles. One of its earlier SBIR contracts, with Kennedy Space Center, led to the development of a new type of structural patch for a variety of consumer uses: Rubbn Repair, for automotive uses; and Rec Repair for the outdoors and adventure market. Both are flexible, heat-activated structural patches.

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