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Results for “vibrational analysis”

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 523 records · Page 29

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NASA NTRS1984

Analysis of lateral and torsional vibration characteristics of beams and shafts with end located rotational masses

Partial differential equations are derived for free lateral and torsional vibration of a uniform free-free beam with a rotational mass attached to each extremity. For appropriate boundary conditions, nonlinear algebraic equations are obtained using a symbolic manipulation computer program, the solutions of which enable the computation of the neutral frequencies and mode-shapes. The mode-shapes are linear combinations of trigonometric and hyperbolic sine and cosine functions. A computer program is written for the numerical solution of the algebraic equations mentioned above, which can compute the natural frequencies, mode-shapes, and node points for any given set of parameters, for any given number of modes.

Robertson, D. K.↗

NASA NTRS1984

An Analysis of the High Frequency Vibrations in Early Thematic Mapper Scenes

The potential effects of high frequency vibrations on the final Thematic Mapper (TM) image are evaluated for 26 scenes. The angular displacements of the TM detectors from their nominal pointing directions as measured by the TM Angular Displacement Sensor (ADS) and the spacecraft Dry Rotor Inertial Reference Unit (DRIRU) give data on the along scan and cross scan high frequency vibrations present in each scan of a scene. These measurements are to find the maximum overlap and underlap between successive scans, and to analyze the spectrum of the high frequency vibrations acting on the detectors. The Fourier spectrum of the along scan and cross scan vibrations for each scene also evaluated. The spectra of the scenes examined indicate that the high frequency vibrations arise primarily from the motion of the TM and MSS mirrors, and that their amplitudes are well within expected ranges.

Kogut, J.↗

NASA NTRS1983

Investigation of the external flow analysis for density measurements at high altitude

A Monte Carlo program was developed for modeling the flow field around the space shuttle in the vicinity of the shuttle upper atmosphere mass spectrometer experiment. The operation of the EXTERNAL code is summarized. Issues associated with geometric modeling of the shuttle nose region and the modeling of intermolecular collisions including rotational energy exchange are discussed as well as a preliminary analysis of vibrational excitation and dissociation effects. The selection of trial runs is described and the parameters used for them is justified. The original version and the modified INTERNAL code for the entrance problem are reviewed. The code listing is included.

Bienkowski, G. K.↗

NASA NTRS1984

Investigation of the external flow analysis for density measurements at high altitude

The results of analysis performed on the external flow around the shuttle orbiter nose regions at the Shuttle Upper Atmosphere Mass Spectrometer (SUMS) inlet orifice are presented. The purpose of the analysis is to quantitatively characterize the flow conditions to facilitate SUMS flight data reduction and subsequent determination of orbiter aerodynamic force coefficients in the hypersonic rarefied flow regime. Experimental determination of aerodynamic force coefficients requires accurate simultaneous measurement of forces (or acceleration) and dynamic pressure along with independent knowledge of density and velocity. The SUMS provides independent measurement of dynamic pressure; however, it does so indirectly and requires knowledge of the relationship between measured orifice conditions and the dynamic pressure which can only be determined on the basis of molecule or theory for a winged configuration. Monte Carlo direct simulation computer codes were developed for both the flow field solution at the orifice and for the internal orifice flow. These codes were used to study issues associated with geometric modeling of the orbiter nose geometry and the modeling of intermolecular collisions including rotational energy exchange and a preliminary analysis of vibrational excitation and dissociation effects. Data obtained from preliminary simulation runs are presented.

Bienkowski, G. K.↗

NASA NTRS1987

Recent advances in structural dynamics of large space structures

Recent progress in the area of structural dynamics of large space structures is reviewed. Topics include system identification, large angle slewing of flexible structures, definition of scaling limitations in structural models, and recent results on a tension-stabilized antenna concept known as the hoop-column. Increasingly complex laboratory experiments guide most of the activities leading to realistic technological developments. Theoretical progress in system identification based on system realization theory resulting in unification of several methods is reviewed. Experimental results from implementation of a theoretical large-angle slewing control approach are shown. Status and results of the development of a research computer program for analysis of the transient dynamics of large angle motion of flexible structures are presented. Correlation of results from analysis and vibration tests of the hoop-column antenna concepts are summarized.

Pinson, Larry D.↗

NASA NTRS1987

Recent advances in structural dynamics of large space structures

Pinson, Larry D.↗

NASA NTRS1988

Multiple input/output random vibration control system

A multi-input/output random vibration control algorithm was developed based on system identification concepts derived from random vibration spectral analysis theory. The unique features of the algorithm are: (1) the number of input excitors and the number of output control responses need not be identical; (2) the system inverse response matrix is obtained directly from the input/output spectral matrix; and (3) the system inverse response matrix is updated every control loop cycle to accommodate system amplitude nonlinearities. A laboratory demonstration case of two imputs with three outputs is presented to demonstrate the system capabilities.

Unruh, James F.↗

NASA NTRS1988

Variable gravity research facility

Spin and despin requirements; sequence of activities required to assemble the Variable Gravity Research Facility (VGRF); power systems technology; life support; thermal control systems; emergencies; communication systems; space station applications; experimental activities; computer modeling and simulation of tether vibration; cost analysis; configuration of the crew compartments; and tether lengths and rotation speeds are discussed.

Allan, Sean↗

NASA NTRS1988

Experimental study of thin-walled composite beams

Thin-walled rectangular section composite beams are built out of graphite-epoxy prepreg tape using an autoclave molding technique. Cantilevered beams are tested under static loads using a specially-built apparatus and bending slope and elastic twist at a station are measured using a laser system. Measured bending slope and bending-induced twist distributions are correlated with predicted results obtained using a simple beam analysis as well as a refined finite element analysis. Natural vibration characteristics at different rotational speeds are determined experimentally by testing beams in a specially built 10 ft diameter vacuum chamber. The rotor is excited by piezo-electric crystals and response is determined from strain gages mounted on the surface. For composite beams with bending-twisting couplings (symmetric layup), effects of section warping and transverse shear on structural response are found to be substantial. These results were substantiated by the analyses.

Chandra, Ramesh↗

NASA NTRS1989

Evaluation of a procedure for the analysis of nonstationary vibroacoustic data

Numerical techniques for the spectral analysis of vibration data from space-vehicle launches are described and demonstrated. A nonstationary product model described by Bendat and Piersol (1986) and its locally stationary version (Silverman, 1957) are applied to Space Shuttle flight data, and the results are presented in extensive graphs. It is shown that the nonstationary model can analyze data from longer sampling periods and thus significantly reduce random error; this in turn leads to vibration spectra lower than those obtained with short-duration models.

Himelblau, Harry↗

NASA NTRS1990

Rubbing Between Rotors And Stators

Report describes experimental and numerical-simulation studies of dynamical effects of rubbing between rotors and stators in turbomachinery. Purpose of study to gain improved understanding of such rubbing phenomena, with view toward: contributing to techniques for diagnosis of rubbing (e.g., via analysis of vibrations); predicting more accurately limiting operating conditions; and improving design criteria to prevent rubbing damage in high-performance rotating machinery.

Muszynska, Agnes↗

NASA NTRS1991

Algorithm Reveals Sinusoidal Component Of Noisy Signal

Algorithm performs simple statistical analysis of noisy signal to yield preliminary indication of whether or not signal contains sinusoidal component. Suitable for preprocessing or preliminary analysis of vibrations, fluctuations in pressure, and other signals that include large random components. Implemented on personal computer by easy-to-use program.

Kwok, Lloyd C.↗

NASA NTRS1991

Time domain convergence properties of Lyapunov stable penalty methods

Linear hyperbolic partial differential equations are analyzed using standard techniques to show that a sequence of solutions generated by the Liapunov stable penalty equations approaches the solution of the differential-algebraic equations governing the dynamics of multibody problems arising in linear vibrations. The analysis does not require that the system be conservative and does not impose any specific integration scheme. Variational statements are derived which bound the error in approximation by the norm of the constraint violation obtained in the approximate solutions.

Kurdila, A. J.↗

NASA NTRS1993

Analysis of hypersonic nozzles including vibrational nonequilibrium and intermolecular force effects

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Canupp, P. W.↗

NASA NTRS1993

Applications of computer algebra to distributed parameter systems

In the analysis of vibrations of continuous elastic systems, one often encounters complicated transcendental equations with roots directly related to the system's natural frequencies. Typically, these equations contain system parameters whose values must be specified before a numerical solution can be obtained. The present paper presents a method whereby the fundamental frequency can be obtained in analytical form to any desired degree of accuracy. The method is based upon truncation of rapidly converging series involving inverse powers of the system natural frequencies. A straightforward method to developing these series and summing them in closed form is presented. It is demonstrated how Computer Algebra can be exploited to perform the intricate analytical procedures which otherwise would render the technique difficult to apply in practice. We illustrate the method by developing two analytical approximations to the fundamental frequency of a vibrating cantilever carrying a rigid tip body. The results are compared to the numerical solution of the exact (transcendental) frequency equation over a range of system parameters.

Storch, Joel A.↗

NASA NTRS1967

Matrix Analysis of Longitudinal and Torsional Vibrations in Nonuniform Multibranch Beams

Since longitudinal modes and frequencies provide basic data for dynamic analyses of arbitrary beam-like structures and since closed-form solutions for the modes are generally not feasible to obtain, an approximate method is developed for computing the natural frequencies and the corresponding mode shapes for a variable-section, unconstrained multibranch beam. A lumped mass analogy employing influence coefficients is used to represent the beam. The simultaneous equations of motion for the lumped mass system are derived in matrix form and algebraically manipulated to yield a classical eigenvalue equation solvable by standard procedures. The orthogonality relationship of the natural modes is derived and used to form the basis of an orthogonal sweeping process for determination of modes above the fundamental. Numerical examples including an application to a solid-fuel launch system are presented. Also, a detailed discussion is devoted to the theoretical verifications of the approximate modes and frequencies.

Wingate, Robert T.↗

NASA NTRS2002

Spiral Bevel Gear Damage Detection Using Decision Fusion Analysis

A diagnostic tool for detecting damage to spiral bevel gears was developed. Two different monitoring technologies, oil debris analysis and vibration, were integrated using data fusion into a health monitoring system for detecting surface fatigue pitting damage on gears. This integrated system showed improved detection and decision-making capabilities as compared to using individual monitoring technologies. This diagnostic tool was evaluated by collecting vibration and oil debris data from fatigue tests performed in the NASA Glenn Spiral Bevel Gear Fatigue Rigs. Data was collected during experiments performed in this test rig when pitting damage occurred. Results show that combining the vibration and oil debris measurement technologies improves the detection of pitting damage on spiral bevel gears.

Dempsey, Paula J.↗

NASA NTRS2003

Umbilical Stiffness Matrix Characterization and Testing for Microgravity Science Payloads

This paper describes efforts of testing and analysis of various candidate cables and umbilicals for International Space Station microgravity science payloads. The effects of looping, large vs. small displacements, and umbilical mounting configurations were assessed. A 3-DOF stepper motor driven fixture was used to excite the umbilicals. Forces and moments were directly measured in all three axes with a 6-DOF load cell in order to derive suitable stiffness matrices for design and analysis of vibration isolation controllers. Data obtained from these tests were used to help determine the optimum type and configuration of umbilical cables for the International Space Station microgravity science glovebox (MSG) vibration isolation platform. The data and procedures can also be implemented into control algorithm simulations to assist in validation of actively controlled vibration isolation systems. The experimental results of this work are specific in support of the Glovebox Integrated Microgravity Isolation Technology (g-LIMIT) isolation platform, to be located in the microgravity science glovebox aboard the U.S. Destiny Laboratory Module.

Engberg, Robert C.↗