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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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NASA NTRS1986

Implementation of the Lanczos method for structural vibration analysis on a parallel computer

The use of the Lanczos method in a parallel environment is investigated by implementing the algorithm for structural vibration problems on a parallel computer. It is shown that introducing shifts, assigning each processor a different region in the eigenvalue spectrum, and implementing the Lanczos method in parallel is an effective strategy for speeding up calculations. Test problem results include examples of the 'Lanczos phenomenon' where roundoff error in the vector orthogonalization can result in spurious eigenvalues which must be identified and discarded. The calculation strategy described here permits straightforward determination of these spurious eigenvalues. It is demonstrated that significant speedups in calculation time can be realized over traditional sequential methods.

Bostic, S. W.↗

NASA NTRS2004

Pressure Oscillations and Structural Vibrations in Space Shuttle RSRM and ETM-3 Motors

The complex interactions between internal motor pressure oscillations resulting from vortex shedding, the motor's internal acoustic modes, and the motor's structural vibration modes were assessed for the Space Shuttle four-segment booster Reusable Solid Rocket Motor and for the five-segment engineering test motor ETM-3. Two approaches were applied 1) a predictive procedure based on numerically solving modal representations of a solid rocket motor s acoustic equations of motion and 2) a computational fluid dynamics two-dimensional axi-symmetric large eddy simulation at discrete motor burn times.

Mason, D. R.↗

NASA NTRS1993

Noncolocated Structural Vibration Suppression Using Zero Annihilation Periodic Control

The Zero Annihilation Periodic (ZAP) controller is applied to the problem of vibration control of a noncolocated flexible structure. It is shown that even though the transfer function is nonminimum-phase, a plant inverse controller can be designed which elicits a deadbeat closed-loop response.

periodic control noncolocated systems non-minimum ↗

NASA NTRS1964

Viscous-pendulum damper suppresses structural vibrations

The viscous pendulum damper consists of a cylinder containing round trays on which round lead slugs rest. When assembled, the container is filled with a viscous liquid and attached, with axis vertical, to the structure. The device permits varying the damping of structural vibrations.

Reed, W. H., III↗

NASA NTRS1971

Aerospace vehicle noise-induced structural vibrations.

The nature of aerospace noise-induced vibration problems is summarized, with emphasis placed on reviewing and categorizing types and sources of noise which are significant in such problems. Physical characteristics of representative noise loads associated with propellers, turbojet engine exhausts, and sonic boom waves are presented. Examples of noise-induced structural vibrations are discussed.

Hubbard, H. H.↗

NASA NTRS1974

Current structural vibration problems associated with noise

As the performance of aerospace vehicles has increased, the noise generated by the propulsion system and by the passage of the vehicle through the air has also increased. Further increases in performance are now underway for space vehicles such as the space shuttle vehicle and for short distance takeoff and landing (STOL) aircraft, and are being planned for supersonic aircraft. The flight profiles and design features of these high-performance vehicles are reviewed and an estimate made of selected noise-induced structural vibration problems. Considerations for the prevention of acoustic fatigue, noise transmission, and electronic instrument malfunction are discussed.

Mixson, J. S.↗

NASA NTRS1995

A Coupled-Cluster Study of the Molecular Structure, Vibrational Spectrum, and Heats of Formation of XONO2 (X=H, F, Cl)

The equilibrium structures, harmonic vibrational frequencies, dipole moments, and IR intensities of nitric acid, fluorine nitrate, and chlorine nitrate have been investigated by using the singles and doubles coupled cluster method that also includes a perturbational estimate of the effects of connected triple excitations, CCSD(T). A standard triple-zeta double-polarized basis set was utilized. The equilibrium geometries and vibrational spectra of HONO2 and ClONO2 are shown to be in excellent agreement with the available experimental data. The ab initio vibrational spectrum of FONO2 is also shown to be in excellent agreement with experiment. Unlike the FOOF and FON molecules, but similar to the cis- and trans-FONO molecules, FONO2 is shown to possess normal bond distances. The bonding in FONO2 is shown to be more similar to that in ClONO2 than that in HONO2, although there are still significant differences, especially in the partial atomic charges as deduced from Mulliken populations. This causes FONO2 to possess almost no dipole moment, which is very different to both HONO2 and ClONO2. By using large atomic natural orbital basis sets, CCSD(T) energies are computed for four isodesmic reactions in order to determine an accurate heat of formation for FONO2. Our best estimate for DELTA H(raised circle) (sub f,298) is 3.1 plus or minus 2.0 kcal/mol, indicating that the F-ONO2 bond energy is 31.3 kcal/mol.

Lee, Timothy J.↗

NASA NTRS1985

On the Computation of Structural Vibrations Induced by a Low-speed Turbulent Flow

A method for numerical evaluation of the vibrations of a cylindrical shell structure induced by a low speed external turbulent flow is discussed. The direction of flow is along the axis of revolution of the shell, and the source of excitation is the pressure fluctuations in the turbulent boundary layer. For the investigation of vibration and noise problems it is usually more desirable to utilize the modal expansion approach. The axisymmetric shell structure can be modeled by the assemblage of conical-shell finite-elements. This modeling allows the eigenfunction psi sub mn (x,theta) to be represented in a rectangular product of a longitudinal modal function f sub mn (x) and a circular harmonic function cos m theta (or sin m theta).

Hwang, Y. F.↗

NASA NTRS1983

Partitioning of large space structures vibration control computations

The vibration control of large space structures is studied. It is found to be computationally demanding. Distribution of the vibration control computations among central and local processors can significantly reduce the throughput required from the central processor and may also result in improved performance due to reduced transport lag.

Kernan, J.↗

NASA NTRS1973

The use of a digital computer for calculation of acoustic fields of complex vibrating structures by the reciprocity principle

A program was compiled for calculating acoustical pressure levels, which might be created by vibrations of complex structures (an assembly of shells and rods), under the influence of a given force, for cases when these fields cannot be measured directly. The acoustical field is determined according to transition frequency and pulse characteristics of the structure in the projection mode. Projection characteristics are equal to the reception characteristics, for vibrating systems in which the reciprocity principle holds true. Characteristics in the receiving mode are calculated on the basis of experimental data on a point pulse space velocity source (input signal) and vibration response of the structure (output signal). The space velocity of a pulse source, set at a point in space r, where it is necessary to calculate the sound field of the structure p(r,t), is determined by measurements of acoustic pressure, created by a point source at a distance R. The vibration response is measured at the point where the forces F and f exciting the system should act.

Rimskiy-Korsakov, A. V.↗

DOE OSTI2024

Validation of a Tapered Impact Damper for Traffic Signal Structure Vibrations Using the Method of Harmonic Balance

Significant vibration amplitudes and cycles can be produced when traffic signal structures with low inherent damping are excited near one of their natural frequencies. For the mitigation of wind-induced vibrations, dynamic vibration absorbers coupled to the structure are often used. Here, this research investigates the performance of a tapered impact damper, consisting of a hanging spring-mass oscillator inside a housing capable of reducing vibration amplitude over a broader frequency range than the conventional tuned mass damper. A nonlinear, two degree-of-freedom model is developed with coordinates representing the traffic structure and the tapered impact damper. This research focuses on the application of the harmonic balance method to approximate the periodic solutions of the nonlinear equations to compute the nonlinear dynamics of the damped traffic signal structure. After designing and manufacturing a tapered impact damper, the traffic signal structure is tested with and without the damper using free vibration snapback tests. The experimental frequency and damping backbone curves are used to validate the analytical model, and the effectiveness of the damper is discussed.

42 ENGINEERING↗

NASA NTRS1984

Space structure vibration modes: How many exist? Which ones are important?

This report attempts to shed some light on the two issues raised in the title, namely, how many vibration modes does a real structure have, and which of these modes are important? The surprise-free answers to these two questions are, respectively, an infinite number and the first several modes. The author argues that the absurd subspace (all but the first billion modes) is not a strength of continuum modeling, but, in fact, a weakness. Partial differential equations are not real structures, only mathematical models. This note also explains (1) that the PDE model and the finite element model are, in fact, the same model, the latter being a numerical method for dealing with the former, (2) that modes may be selected on dynamical grounds other than frequency alone, and (3) that long slender rods are useful as primitive cases but dangerous to extrapolate from.

Hughes, P. C.↗

NASA NTRS1995

Stabilizing Optical Path Length On A Vibrating Structure

Prototype apparatus constructed to test feasibility of feedback control concept for stabilization of length of optical path between two points on vibrating flexible structure. In original intended application, structure is truss having dimensions of order of meters and supports optical components of stellar interferometer. Interferometry and feedback control reduce path-length disturbances. Some aspects of present feedback control concept and prototype apparatus described in "Controllable Optical Delay Line for Stellar Interferometry" (NPO-18686), and "Test Bed for Control of Optical-Path Lengths" (NPO-18487).

Spanos, John T.↗

NASA NTRS1985

A concurrent processing implementation for structural vibration analysis

A concurrent processing algorithm for analysis of large aerospace structures is presented. A general description of the implementation criteria for the algorithm is given, and the results from applications to two vibration test problems are discussed. The test problems included a flexural vibration analysis of a long beam with 16 uniformly spaced supports, and a torsional vibration analysis. The computer system used to implement the algorithm was an experimental MIND system. The concurrent processing speedups for the test problems are given in a table.

Bostic, S. W.↗

NASA NTRS1983

Estimating Design Loads in Coupled Vibrating Structures

Approximate spectral analysis faster and less expensive than transient analysis. Method of vibration analysis combines separate modes of spacecraft and launcher to determine approximate conditions for resonance. Useful for analysis of any complex structure made up of substructures not coupled too closely; however important to note, method includes effect of dynamic impedance between launcher and payload.

Trubert, M. R.↗

NASA NTRS1992

Evaluation of human response to structural vibration induced by sonic boom

This paper addresses the topic of building vibration response to sonic boom and the evaluation of the associated human response to this vibration. The paper reexamines some of the issues addressed in the previous extensive coverage of the topic, primarily by NASA, and attempts to offer a fresh viewpoint for some of the problems that may assist in reassessing the potential impact of sonic boom over populated areas. The topics addressed are: (1) human response to vibration; (2) criteria for, and acoustic signature of rattle; (3) structural response to shaped booms, including definition of two new descriptors for assessing the structural response to sonic boom; and (4) a detailed review of the previous NASA/FAA Sonic Boom Test Program involving structural response measurements at Edwards AFB and an initial estimate of structural response to sonic booms from possible high speed civil transport configurations. Finally, these estimated vibration responses are shown to be substantially greater than the human response and rattle criteria developed earlier.

Sutherland, L. C.↗

NASA NTRS2012

Applications of Fault Detection in Vibrating Structures

Structural fault detection and identification remains an area of active research. Solutions to fault detection and identification may be based on subtle changes in the time series history of vibration signals originating from various sensor locations throughout the structure. The purpose of this paper is to document the application of vibration based fault detection methods applied to several structures. Overall, this paper demonstrates the utility of vibration based methods for fault detection in a controlled laboratory setting and limitations of applying the same methods to a similar structure during flight on an experimental subscale aircraft.

Eure, Kenneth W.↗

NASA NTRSDate not supplied

The Impact of Structural Vibration on Flying Qualities of a Supersonic Transport

A piloted simulation experiment has been conducted in the NASA Langley Visual/Motion Simulator facility to address the impact of dynamic aeroelastic effects on flying qualities of a supersonic transport. The intent of this experiment was to determine the effectiveness of several measures that may be taken to reduce the impact of aircraft flexibility on piloting tasks. Potential solutions that were examined included structural stiffening, active vibration suppression, and elimination of visual cues associated with the elastic modes. A series of parametric configurations was evaluated by six test pilots for several types of maneuver tasks. During the investigation, several incidents were encountered in which cockpit vibrations due to elastic modes fed back into the control stick through involuntary motions of the pilot's upper body and arm. The phenomenon, referred to as biodynamic coupling, is evidenced by a resonant peak in the power spectrum of the pilot's stick inputs at a structural mode frequency. The results of the investigation indicate that structural stiffening and compensation of the visual display were of little benefit in alleviating the impact of elastic dynamics on the piloting tasks, while increased damping and elimination of control-effector excitation of the lowest frequency modes offered great improvements when applied in sufficient degree.

David L Raney↗