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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Flutter clearance of the F-14 variable-sweep transition flight experiment airplane, phase 1

An F-14 airplane was modified to become the test bed aircraft for the variable sweep transition flight experiment (VSTFE) program. The latter is a laminar flow program designed to measure the effects of wing sweep on boundary layer transition from laminar to turbulent flow. The airplane was modified by adding an upper surface foam-fiberglass glove over a portion of the left wing. Ground vibration and flight flutter testing were accomplished to clear a sufficient flight envelope to conduct the laminar flow experiments. Flight test data indicated satisfactory damping levels and damping trends for the elastic structural modes of the airplane. The data presented include frequency and damping as functions of Mach number.

Kehoe, Michael W.↗
NASA NTRS1988

Asymptotic modal analysis and statistical energy analysis

Statistical Energy Analysis (SEA) is defined by considering the asymptotic limit of Classical Modal Analysis, an approach called Asymptotic Modal Analysis (AMA). The general approach is described for both structural and acoustical systems. The theoretical foundation is presented for structural systems, and experimental verification is presented for a structural plate responding to a random force. Work accomplished subsequent to the grant initiation focusses on the acoustic response of an interior cavity (i.e., an aircraft or spacecraft fuselage) with a portion of the wall vibrating in a large number of structural modes. First results were presented at the ASME Winter Annual Meeting in December, 1987, and accepted for publication in the Journal of Vibration, Acoustics, Stress and Reliability in Design. It is shown that asymptotically as the number of acoustic modes excited becomes large, the pressure level in the cavity becomes uniform except at the cavity boundaries. However, the mean square pressure at the cavity corner, edge and wall is, respectively, 8, 4, and 2 times the value in the cavity interior. Also it is shown that when the portion of the wall which is vibrating is near a cavity corner or edge, the response is significantly higher.

Dowell, Earl H.↗
NASA NTRS1988

Real-time flight test analysis and display techniques for the X-29A aircraft

The X-29A advanced technology demonstrator flight envelope expansion program and the subsequent flight research phase gave impetus to the development of several innovative real-time analysis and display techniques. These new techniques produced significant improvements in flight test productivity, flight research capabilities, and flight safety. These techniques include real-time measurement and display of in-flight structural loads, dynamic structural mode frequency and damping, flight control system dynamic stability and control response, aeroperformance drag polars, and aircraft specific excess power. Several of these analysis techniques also provided for direct comparisons of flight-measured results with analytical predictions. The aeroperformance technique was made possible by the concurrent development of a new simplified in-flight net thrust computation method. To achieve these levels of on-line flight test analysis, integration of ground and airborne systems was required. The capability of NASA Ames Research Center, Dryden Flight Research Facility's Western Aeronautical Test Range was a key factor in enabling implementation of these methods.

Hicks, John W.↗
NASA NTRS1989

Pulse modulated control synthesis for a flexible spacecraft

The describing function method is employed for the nonlinear control analysis and design of a flexible spacecraft equipped with pulse modulated reaction jets. The method provides a means of characterizing the pulse modulator in terms of its gain and phase for structural mode limit cycle analysis. Although the describing function method is inherently inexact and is not widely used in practice, a new way of utilizing it for practical control design problems is presented. It is shown that the approximations inherent in the method can be accounted as a modeling uncertainty for the nonlinear control robustness analysis. The pulse modulated control system of the Intelsat 5 spacecraft is used as an example to illustrate the concept and methodology developed in the paper. The nonlinear stability margins predicted by the describing function analysis are verified from nonlinear simulations.

Anthony, Tobin C.↗
NASA NTRS1989

Flexible missile autopilot design studies with PC-MATLAB/386

Development of a responsive, high-bandwidth missile autopilot for airframes which have structural modes of unusually low frequency presents a challenging design task. Such systems are viable candidates for modern, state-space control design methods. The PC-MATLAB interactive software package provides an environment well-suited to the development of candidate linear control laws for flexible missile autopilots. The strengths of MATLAB include: (1) exceptionally high speed (MATLAB's version for 80386-based PC's offers benchmarks approaching minicomputer and mainframe performance); (2) ability to handle large design models of several hundred degrees of freedom, if necessary; and (3) broad extensibility through user-defined functions. To characterize MATLAB capabilities, a simplified design example is presented. This involves interactive definition of an observer-based state-space compensator for a flexible missile autopilot design task. MATLAB capabilities and limitations, in the context of this design task, are then summarized.

Ruth, Michael J.↗
NASA NTRS1989

Real-time flight test analysis and display techniques for the X-29A aircraft

The X-29A advanced technology demonstrator flight envelope expansion program and the subsequent flight research phase gave impetus to the development of several innovative real-time analysis and display techniques. These new techniques produced significant improvements in flight test productivity, flight research capabilities, and flight safety. These techniques include real-time measurement and display of in-flight structural loads, dynamic structural mode frequency and damping, flight control system dynamic stability and control response, aeroperformance drag polars, and aircraft specific excess power. Several of these analysis techniques also provided for direct comparisons of flight-measured results with analytical predictions. The aeroperformance technique was made possible by the concurrent development of a new simplified in-flight net thrust computation method. To achieve these levels of on-line flight test analysis, integration of ground and airborne systems was required. The capability of NASA Ames Research Center, Dryden Flight Research Facility's Western Aeronautical Test Range was a key factor to enable implementation of these methods.

Hicks, John W.↗
NASA NTRS1988

Pointing control for LDR

One important aspect of the LDR control problem is the possible excitations of structural modes due to random disturbances, mirror chopping, and slewing maneuvers. An analysis was performed to yield a first order estimate of the effects of such dynamic excitations. The analysis involved a study of slewing jitters, chopping jitters, disturbance responses, and pointing errors, making use of a simplified planar LDR model which describes the LDR dynamics on a plane perpendicular to the primary reflector. Briefly, the results indicate that the command slewing profile plays an important role in minimizing the resultant jitter, even to a level acceptable without any control action. An optimal profile should therefore be studied.

Yam, Y.↗
NASA NTRS1988

Space telescope pointing control

The Space Telescope pointing control system is designed to meet the fine pointing performance of 0.007 arc-sec stability, maneuver the telescope 90 deg in 18 min, or less, and provide the capability for deployment from, and retrieval by, the space shuttle. The pointing control system objectives are met using fine guidance sensors for attitude information, reaction wheel assemblies sized to provide both the torque required for pointing, and magnetometers and magnetic torquers for momentum management. A digital computer is used to calculate the control law, attitude reference, momentum management law, and command generator. The command generator shapes the acceleration and incremental angle commands to the control system to limit structural mode excitation. The control techniques are briefly discussed.

Dougherty, Hugh↗
NASA NTRS1989

A new second-order integration algorithm for simulating mechanical dynamic systems

A new integration algorithm which has the simplicity of Euler integration but exhibits second-order accuracy is described. In fixed-step numerical integration of differential equations for mechanical dynamic systems the method represents displacement and acceleration variables at integer step times and velocity variables at half-integer step times. Asymptotic accuracy of the algorithm is twice that of trapezoidal integration and ten times that of second-order Adams-Bashforth integration. The algorithm is also compatible with real-time inputs when used for a real-time simulation. It can be used to produce simulation outputs at double the integration frame rate, i.e., at both half-integer and integer frame times, even though it requires only one evaluation of state-variable derivatives per integration step. The new algorithm is shown to be especially effective in the simulation of lightly-damped structural modes. Both time-domain and frequency-domain accuracy comparisons with traditional integration methods are presented. Stability of the new algorithm is also examined.

Howe, R. M.↗
NASA NTRS1990

Flutter Clearance of the F-14A Variable-Sweep Transition Flight Experiment Airplane, Phase 2

An F-14A aircraft was modified for use as the test-bed aircraft for the variable-sweep transition flight experiment (VSTFE) program. The VSTFE program was a laminar flow research program designed to measure the effects of wing sweep on laminar flow. The airplane was modified by adding an upper surface foam and fiberglass glove to the right wing. An existing left wing glove had been added for the previous phase of the program. Ground vibration and flight flutter testing were accomplished to verify the absence of aeroelastic instabilities within a flight envelope of Mach 0.9 or 450 knots, calibrated airspeed, whichever was less. Flight test data indicated satisfactory damping levels and trends for the elastic structural modes of the airplane. Ground vibration test data are presented along with in-flight frequency and damping estimates, time histories and power spectral densities of in-flight sensors, and pressure distribution data.

Freudinger, Lawrence C.↗
NASA NTRS1990

Active control of structurally-coupled sound fields in elastic cylinders by vibrational force inputs

Active control of structurally-coupled sound fields in elastic cylinders is analytically and experimentally studied. The primary (noise) field in the cylinder model is generated by the coupled dynamic response of the shell under loading by a single exterior acoustic source. Control of the interior sound field is achieved by applying vibrational force inputs directly to the shell wall. Action of the point controllers serve to increase the input impedance of select structural modes of the shell which are well-coupled to the interior acoustic cavity, thus substantially reducing sound transmission into the cavity. Spatially-averaged noise reductions in excess of 30 dB are demonstrated for acoustic resonant conditions within the cavity. Twin controller configurations are presented which demonstrate the ability to independently control orthogonal modes of the interior acoustic space. Benefits and drawbacks of this new methodology for noise control are discussed and clearly demonstrated.

Jones, J. D.↗
NASA NTRS1990

A method for optimal actuator and sensor placement for large flexible structures

A method of finding the optimal sensor and actuator locations for the control of flexible structures has been developed. The method is based on the orthogonal projection of structural modes into the intersection subspace of the controllable and observable subspaces. The controllability and observability grammians are then used to weight the projections to reflect the degrees of controllability and observability. This method produces a three-dimensional design space wherein sets of optimal actuator and sensors may be selected.

Lim, K. B.↗
NASA NTRS1991

Active vibration absorber for CSI evolutionary model: Design and experimental results

The development of control of large flexible structures technology must include practical demonstration to aid in the understanding and characterization of controlled structures in space. To support this effort, a testbed facility was developed to study practical implementation of new control technologies under realistic conditions. The design is discussed of a second order, acceleration feedback controller which acts as an active vibration absorber. This controller provides guaranteed stability margins for collocated sensor/actuator pairs in the absence of sensor/actuator dynamics and computational time delay. The primary performance objective considered is damping augmentation of the first nine structural modes. Comparison of experimental and predicted closed loop damping is presented, including test and simulation time histories for open and closed loop cases. Although the simulation and test results are not in full agreement, robustness of this design under model uncertainty is demonstrated. The basic advantage of this second order controller design is that the stability of the controller is model independent.

Bruner, Anne M.↗
NASA NTRS1991

An overview of the essential differences and similarities of system identification techniques

Information is given in the form of outlines, graphs, tables and charts. Topics include system identification, Bayesian statistical decision theory, Maximum Likelihood Estimation, identification methods, structural mode identification using a stochastic realization algorithm, and identification results regarding membrane simulations and X-29 flutter flight test data.

Mehra, Raman K.↗
NASA NTRS1991

Advanced launch system

The Advanced Launch System (ALS) is presented. The costs, reliability, capabilities, infrastructure are briefly described. Quality approach, failure modes, structural design, technology benefits, and key facilities are outlined. This presentation is represented by viewgraphs.

Monk, Jan C.↗
NASA NTRS1991

ASTROP2 users manual: A program for aeroelastic stability analysis of propfans

A user's manual is presented for the aeroelastic stability and response of propulsion systems computer program called ASTROP2. The ASTROP2 code preforms aeroelastic stability analysis of rotating propfan blades. This analysis uses a two-dimensional, unsteady cascade aerodynamics model and a three-dimensional, normal-mode structural model. Analytical stability results from this code are compared with published experimental results of a rotating composite advanced turboprop model and of nonrotating metallic wing model.

Narayanan, G. V.↗
NASA NTRS1991

Modal identification experiment design for large space structures

This paper describes an on-orbit modal identification experiment design for large space structures. Space Station Freedom (SSF) systems design definition and structural dynamic models were used as representative large space structures for optimizing experiment design. Important structural modes of study models were selected to provide a guide for experiment design and used to assess the design performance. A pulsed random excitation technique using propulsion jets was developed to identify closely-spaced modes. A measuremenat location selection approach was developed to estimate accurate mode shapes as well as frequencies and damping factors. The data acquisition system and operational scenarios were designed to have minimal impacts on the SSF. A comprehensive simulation was conducted to assess the overall performance of the experiment design.

Kim, Hyoung M.↗
NASA NTRS1992

Robust control of flexible space vehicles with minimum structural excitation: On-off pulse control of flexible space vehicles

Both feedback and feedforward control approaches for uncertain dynamical systems (in particular, with uncertainty in structural mode frequency) are investigated. The control objective is to achieve a fast settling time (high performance) and robustness (insensitivity) to plant uncertainty. Preshaping of an ideal, time optimal control input using a tapped-delay filter is shown to provide a fast settling time with robust performance. A robust, non-minimum-phase feedback controller is synthesized with particular emphasis on its proper implementation for a non-zero set-point control problem. It is shown that a properly designed, feedback controller performs well, as compared with a time optimal open loop controller with special preshaping for performance robustness. Also included are two separate papers by the same authors on this subject.

Wie, Bong↗