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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 631 records · Page 35
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Supersonic flutter of panels loaded with inplane shear

A modal flutter analysis for biaxially loaded, orthotropic panels, using linear piston-theory aerodynamics, was extended in order to include the effects of inplane shear loading. Flutter boundaries for shear loads up to buckling are calculated for simply supported, isotropic panels of various length-width ratios and for a square, isotropic panel with elastic boundary conditions along the leading and trailing edges. These flutter boundaries are used to define conservative design curves. Sample calculations made using these design curves indicate that practical panels, which have otherwise been adequately designed, could become flutter critical if the inplane shear loads approach the buckling value.

Sawyer, J. W.↗
NASA NTRS1979

Effect of time dependent flight loads on JT9D-7 performance deterioration

The results of a modal transient analysis of the engine/aircraft system are presented. The response of the JT9D to analytically simulated vertical gusts and landings was predicted using a NASTRAN finite element mathematical model of the JT9D/747 propulsion system. The NASTRAN finite element model of the propulsion system included engine structural models of the fan, low/high pressure compressors, diffuser/turbine cases, and high/low pressure rotors, as well as nacelle models of the inlet cowl, tailcone, and wing pylon. The analysis conducted predicts that an insignificant level of JT9D-7 performance deterioration would occur due to a typical vertical gust encounter or a typical revenue service landing. Analysis of a high sink rate landing with a heavy fuel load indicates the possibility of local wear, however, the lack of an accurate dynamic rotor/seal interference model precludes an accurate quantitative evaluation of performance change for this once-per-airframe-life event.

Jay, A.↗
NASA NTRS1980

Normal mode analysis of the IUS/TDRS payload in a payload canister/transporter environment

Special modeling techniques were developed to simulate an accurate mathematical model of the transporter/canister/payload system during ground transport of the Inertial Upper Stage/Tracking and Data Relay Satellite (IUS/TDRS) payload. The three finite element models - the transporter, the canister, and the IUS/TDRS payload - were merged into one model and used along with the NASTRAN normal mode analysis. Deficiencies were found in the NASTRAN program that make a total analysis using modal transient response impractical. It was also discovered that inaccuracies may exist for NASTRAN rigid body modes on large models when Given's method for eigenvalue extraction is employed. The deficiencies as well as recommendations for improving the NASTRAN program are discussed.

Meyer, K. A.↗
NASA NTRS1981

Generic model of a large flexible space structure for control concept evaluation

The objective of the paper is to propose a generic model on the shape and attitude control of a representative space structure. Reduction of the finite element model is based on modal identities and modal cost analysis. The model may help to: (a) suggest improved methods for designing reduced order controllers for large elastic spacecraft, (b) enhance coherence between the frequency-response and time-response multivariable applications, (c) examine computational efficiency of the multivariable control algorithms, and (d) suggest other desirable theoretical and numerical research areas.

Hablani, H. B.↗
NASA NTRS1983

A study of the effects of a cubic nonlinearity on a modern modal identification technique

The effect of a geometric nonlinearity on the Ibrahim Time Domain (ITD) modal data analysis technique has been studied using two analytically derived models and one laboratory model. Response data for the three models were analyzed by the ITD method. Indicators of nonlinear response were found which include harmonically related frequencies with repetitive mode shapes, clusters of frequencies in a narrow band around each harmonic, and variations in frequency with amplitude of oscillation. Also,for the cases studied, the presence of a nonlinearity has no detrimental effect on identifying linear responses. A potential for applying the algorithm to the identification of a certain class of nonlinear system was indicated.

Horta, L. G.↗
NASA NTRS1987

Single-mode projection filters for identification and state estimation of flexible structures

Single-mode projection filters are developed for eigensystem parameter identification and state estimation from both analytical results and test data. Explicit formulations of these projection filters are derived using the pseudoinverse matrices of the controllabilty and observability matrices in the general sense. A global minimum optimization algorithm is developed to update the filter parameters by using the interval analysis method. Modal parameters can be identified and updated in the global sense within a specified region of parameters by passing the experimental data through the projection filters. For illustration of this new approach, a numerical example is shown by using a one-dimensional global optimization algorithm to estimate modal frequencies and damping.

Huang, Jen-Kuang↗
NASA NTRS1987

Convergence properties of modal costs for certain distributed parameter systems

A complete modal cost analysis is presented for the vibration of various kinds of simple continua with different boundary conditions. Explicit formulas for the norm of the response (called the 'cost') are derived for these distributed parameter systems. The convergence theorems developed are useful in the model reduction of the equivalent continuum models of large space structures as well as in the selection of finite-element code for control design.

Hu, A.↗
NASA NTRS1990

Technical challenges involved in supporting the Lambda Point Experiment

The Lambda Point Experiment (LPE) is one of the instruments included in the U.S. Microgravity Payload Mission 1 planned for one of the Space Shuttle flights in 1992. The objective of the experiment is to measure the heat capacity of liquid helium within a narrow interval around the transition between superfluid and normal helium (the lambda point) with an unprecedented temperature resolution of about 10 to the -10th. Multiple technical challenges are presented in the areas of structural support, safety analysis, and modal frequency tests. This paper describes the technical challenges of JPL's multidisciplinary involvement in support of these experiments in microgravity.

Petrac, D.↗
NASA NTRS1990

Closed loop lab tests of NASA's Mini-Mast

A design strategy which integrates model reduction by modal cost analysis and a multiobjective controller synthesis algorithm is used to design controllers for NASA's Mini-Mast system. The necessary modeling and control algorithms are easily programmed in Matlab standard software. Hence, this method is very practical for controller design for large space structures. The design algorithm also presents a solution for the important problem of tuning multiple-loop controllers.

Hsieh, C.↗
NASA NTRS1990

An iterative algorithm combining model reduction and control design

A design strategy which integrates model reduction by modal cost analysis and a multiobjective controller design is proposed. The necessary modeling and control algorithms are easily programmed in Matlab standard software. Hence, this method is very practical for controller design for large space structures. The design algorithm also solves the very important problem of tuning multiple loop controllers (multi-input, multi-output, or MIMO). Instead of the single gain change that is used in standard root locus and gain and phase margin theories, this method tunes multiple loop controllers from low to high gain in a systematic way in the design procedure. This design strategy is applied to NASA's Mini-Mast system.

Hsieh, C.↗
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

Getting up to speed in hypersonic structures

An overview is presented of some of the hypersonic technology that will become the baseline for more advanced commercial aerospace systems and new military transportation systems for carrying astronauts and equipment into space. Attention is given to the X-15 aeronautical research program, the X-20 DYNA-SOAR, and the current X-30 National Aerospace Plane. Consideration is given to FEM analysis methods, modal testing conducted to measure the structure's resonant frequencies, dampings, and mode shapes, and high-temperature, high-speed wind tunnel testing and in-flight measurement of steady and unsteady pressures at Mach 3 and above.

Kehoe, Michael W.↗
NASA NTRS1993

Model reduction of mechanical systems

A reduced model of a stable mechanical system with proportional damping represented in modal coordinates is developed, based on a procedure reported by Commault and Guerin (1978). In this model, model error is calculated a priori and is used to determine the dominant modes. Two examples are presented showing that reduced models generated as described will be better or at least as good as those produced by the popular modal cost analysis scheme of Skelton and Hughes (1980).

Yousuff, Ajmal↗
NASA NTRS1993

An application of the IMC software to controller design for the JPL LSCL Experiment Facility

A software package which Integrates Model reduction and Controller design (The IMC software) is applied to design controllers for the JPL Large Spacecraft Control Laboratory Experiment Facility. Modal Cost Analysis is used for the model reduction, and various Output Covariance Constraints are guaranteed by the controller design. The main motivation is to find the controller with the 'best' performance with respect to output variances. Indeed it is shown that by iterating on the reduced order design model, the controller designed does have better performance than that obtained with the first model reduction.

Zhu, Guoming↗
NASA NTRS1999

OVERAERO-MPI: Parallel Overset Aeroelasticity Code

An overset modal structures analysis code was integrated with a parallel overset Navier-Stokes flow solver to obtain a code capable of static aeroelastic computations. The new code was used to compute the static aeroelastic deformation of an arrow-wing-body geometry and a complex, full aircraft configuration. For the simple geometry, the results were similar to the results obtained with the ENSAERO code and the PVM version of OVERAERO. The full potential of this code suite was illustrated in the complex, full aircraft computations.

Gee, Ken↗
NASA NTRS1997

Rotary Piezoelectric Motors Actuated by Traveling Waves (abstract)

Piezoelectric rotary motors are being developed as a drive mechanism for miniature spacecraft instruments and subsystems. The technology that has recently emerged in commercial products requires more rigorous analytical tools for effective design. The theoretical predictions and the experimental corraboration showed a remarkable agreement and they will be presented and discussed in this paper.

Actuators piezoelectric motors active materials ul↗
NASA NTRS1994

Active Members to Establish On-Orbit Modal Data for Modal Correlation

The paper presents an approach to experimentally determine the modal sensitivity derivitives with respect to physical parameters of a structure in space or on the ground. The information experimentally validates the Jacobian used to update the analytical model to correlate with the experimental modal data. The approach is applicable to Adaptive Structures and utilizes active members. For verification of the approach, numerical simulations of a 4.5 meter diameter truss structure and experimental verification plan and progress are presented.

space structures modal analysis dynamic models ada↗
NASA NTRS2009

NASA Tech Briefs, April 2009

Topics covered include: Direct-Solve Image-Based Wavefront Sensing; Use of UV Sources for Detection and Identification of Explosives; Using Fluorescent Viruses for Detecting Bacteria in Water; Gradiometer Using Middle Loops as Sensing Elements in a Low-Field SQUID MRI System; Volcano Monitor: Autonomous Triggering of In-Situ Sensors; Wireless Fluid-Level Sensors for Harsh Environments; Interference-Detection Module in a Digital Radar Receiver; Modal Vibration Analysis of Large Castings; Structural/Radiation-Shielding Epoxies; Integrated Multilayer Insulation; Apparatus for Screening Multiple Oxygen-Reduction Catalysts; Determining Aliasing in Isolated Signal Conditioning Modules; Composite Bipolar Plate for Unitized Fuel Cell/Electrolyzer Systems; Spectrum Analyzers Incorporating Tunable WGM Resonators; Quantum-Well Thermophotovoltaic Cells; Bounded-Angle Iterative Decoding of LDPC Codes; Conversion from Tree to Graph Representation of Requirements; Parallel Hybrid Vehicle Optimal Storage System; and Anaerobic Digestion in a Flooded Densified Leachbed.

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