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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1996

Modeling of Sound Transmission through Shell Structures with Turbulent Boundary Layer Excitation

The turbulent boundary layer (TBL) pressure field is an important source of cabin noise during cruise of high subsonic and supersonic commercial aircraft. The broadband character of this excitation field results in an interior noise spectrum that dominates the overall sound pressure level (SPL) and speech interference metrics in the forward and midcabins of many aircraft. In the authors' previous study, sound transmission through an aircraft fuselage, modeled by two concentric cylindrical sandwich shells and excited by a TBL statistical model was investigated analytically. An assessment of point and global structural vibration levels and resulting interior noise levels was obtained for different TBL models, flight conditions and fuselage structural designs. However, due to the complication of the shell structure, the important noise transmission mechanisms were difficult to discern. Previous experience has demonstrated that a fundamental understanding of the range of modes (or wavenumbers) generated by the TBL source both in the structure and the acoustic cavity is key to the development of both active and passive control technologies. In an initial effort to provide this insight, the objective of this paper is to develop an analytical model of sound transmission through a simple unstiffened cylindrical aluminum shell excited by a TBL pressure field. The description of the turbulent pressure field is based on the Corcos formulation for the cross-spectral density (CSD) of the pressure fluctuations. The coupled shell and interior and exterior acoustic equations are solved for the structural displacement and the interior acoustic response using a Galerkin approach to obtain analytical solutions. Specifically, this study compares the real part of the normalized CSD of the TBL excitation field, the structural displacement and the interior acoustic field. Further the modal compositions of the structural and cavity response are examined and some inference of the dominant mechanism of noise transmission is made.

Tang, Yvette Y.↗
NASA NTRS1997

Quelling Cabin Noise in Turboprop Aircraft via Active Control

Cabin noise in turboprop aircraft causes passenger discomfort, airframe fatigue, and employee scheduling constraints due to OSHA standards for exposure to high levels of noise. The noise levels in the cabins of turboprop aircraft are typically 10 to 30 decibels louder than commercial jet noise levels. However. unlike jet noise the turboprop noise spectrum is dominated by a few low frequency tones. Active structural acoustic control is a method in which the control inputs (used to reduce interior noise) are applied directly to a vibrating structural acoustic system. The control concept modeled in this work is the application of in-plane force inputs to piezoceramic patches bonded to the wall of a vibrating cylinder. The goal is to determine the force inputs and locations for the piezoceramic actuators so that: (1) the interior noise is effectively damped; (2) the level of vibration of the cylinder shell is not increased; and (3) the power requirements needed to drive the actuators are not excessive. Computational experiments for data taken from a computer generated model and from a laboratory test article at NASA Langley Research Center are provided.

Kincaid, Rex K.↗
NASA NTRS1989

Calculating Buckling And Vibrations Of Lattice Structures

BUNVIS-RG computer program designed to calculate vibration frequencies or buckling loads of prestressed lattice structures used in outer space. For buckling and vibration problems, BUNVIS-RG calculates deadload axial forces caused in members by any combination of externally-applied static point forces and moments at nodes, axial preload or prestrain in members, and such acceleration loads as those due to gravity. BUNVIS-RG is FORTRAN 77 computer program implemented on CDC CYBER and VAX computer.

Anderson, M. S.↗
DOE OSTI2026

New Perspectives on Vibrational Energy Transfer in Energetic Materials: Insights from Pressure-Tuned Ultrafast Spectroscopy

Understanding the manner in which vibrational energy flows between molecular and lattice vibrations is of great interest in physical chemistry due to its central role in reactivity and energy dissipation in molecular materials. Here, in this feature article, we highlight our recent efforts employing ultrafast broadband infrared spectroscopy toward understanding the interplay between molecular and lattice vibrations in energetic materials, motivated by the open questions surrounding the role of vibrational energy transfer (VET) in reaction initiation in these materials. Our work addresses the ongoing debate on the participation of doorway modes in VET. We further present new results from high-pressure ultrafast experiments on RDX, a hydrogen-bonded material, and BNFF, a hydrogen-free material, to explore how intermolecular interaction strength governs VET pathways and time scales. Collectively, our findings reveal that vibrational dynamics in these systems occurs across three distinct time regimes, with VET being incomplete out to hundreds of picoseconds, suggesting the importance of considering nonstatistical reactions in the modeling of these materials. These time scales vary as intermolecular interaction strength is indirectly modified by application of static pressure, indicating dramatic changes to the vibrational structure of these materials under shock-relevant conditions. Our results thus shed light on how intermolecular interactions shape vibrational energy redistribution in molecular materials, and highlight the need for further theoretical and experimental investigation.

Carlson, Daniel Ryan [Sandia National Laboratories↗
NASA NTRS1997

Electronics for Piezoelectric Smart Structures

This paper briefly presents work addressing some of the basic considerations for the electronic components used in smart structures incorporating piezoelectric elements. After general remarks on the application of piezoelectric elements to the problem of structural vibration control, three main topics are described. Work to date on the development of techniques for embedding electronic components within structural parts is presented, followed by a description of the power flow and dissipation requirements of those components. Finally current work on the development of electronic circuits for use in an 'active wall' for acoustic noise is introduced.

Warkentin, D. J.↗
NASA NTRS1985

Evaluation of a pulse control law for flexible spacecraft

The following analytical and experimental studies were conducted: (1) A simple algorithm was developed to suppress the structural vibrations of 3-dimensional distributed parameter systems, subjected to interface motion and/or directly applied forces. The algorithm is designed to cope with structural oscillations superposed on top of rigid-body motion: a situation identical to that encountered by the SCOLE components. A significant feature of the method is that only local measurements of the structural displacements and velocities relative to the moving frame of reference are needed. (2) A numerical simulation study was conducted on a simple linear finite element model of a cantilevered plate which was subjected to test excitations consisting of impulsive base motion and of nonstationary wide-band random excitation applied at its root. In each situation, the aim was to suppress the vibrations of the plate relative to the moving base. (3) A small mechanical model resembling an aircraft wing was designed and fabricated to investigate the control algorithm under realistic laboratory conditions.

Source record↗
DOE OSTI2025

Discrepancies between Theory and Experiment in Determining the Ionization Energy of NF 3

High-accuracy ab initio thermochemical predictions for the ionization energy of NF 3 , the barrier height (to inversion) of NF 3 + , and the dissociative ionization threshold of NF 3 to NF 2 + + F are presented and incorporated into Active Thermochemical Tables. The adiabatic ionization energy of the first ionization band of NF 3 , calculated at 12.647 ± 0.010 eV, is at odds with previous experimental interpretations by nearly 0.36 eV due to unfavorable Franck-Condon factors associated with this transition. The barrier (to inversion) height is calculated to be about 0.6 eV lower in energy than the prior interpretation, which instigates a discussion of the supposed vibrational structure of the first ionization band of NF 3 . Updated assignments of the photoelectron spectrum are proposed, and the loss in vibrational spacing on the high-energy side of the experimental ionization band is discussed. Rudimentary anharmonic Franck-Condon simulations qualitatively reproduce the broad spectral features observed in experiment.

Active Thermochemical Tables↗
NASA NTRS1976

Vibrational spectra and structure of dimethyl oxalate and dimethyl oxalate-d6

The vibrational spectra of dimethyl oxalate-d6 have been examined in connection with a re-examination of the spectra and structure of dimethyl oxalate. The vibrational spectra of the compound had previously been interpreted as being consistent with a trans C2h structure in the solid phase and a non-planar C2 form in the liquid and gas phases. This behavior is not consistent with that observed in similar compounds and a re-evaluation of the facts suggests that the major spectral changes which are observed may be caused by destroying an intermolecular association in going from the solid to the liquid phase, which allows the methyl groups to assume positions out of the plane. Some modifications and additions have been made in the vibrational assignment and assignments are presented for the deuterated compound.

Durig, J. R.↗
NASA NTRS1992

A six degree-of-freedom Lorentz vibration isolator with nonlinear controller

The results of a phase 2 Small Business Innovation Research Program sponsored by MSFC are presented. Technology is developed for isolating acceleration sensitive microgravity experiments from structural vibration of a spacecraft, such as a space station. Two hardware articles are constructed: a six degree of freedom Lorentz force isolation and a one degree of freedom low acceleration testbed capable of tests at typical experiment accelerations.

Fenn, Ralph C.↗
NASA NTRS1992

Coupled multi-disciplinary simulation of composite engine structures in propulsion environment

A computational simulation procedure is described for the coupled response of multi-layered multi-material composite engine structural components which are subjected to simultaneous multi-disciplinary thermal, structural, vibration, and acoustic loadings including the effect of hostile environments. The simulation is based on a three dimensional finite element analysis technique in conjunction with structural mechanics codes and with acoustic analysis methods. The composite material behavior is assessed at the various composite scales, i.e., the laminate/ply/constituents (fiber/matrix), via nonlinear material characterization model. Sample cases exhibiting nonlinear geometrical, material, loading, and environmental behavior of aircraft engine fan blades, are presented. Results for deformed shape, vibration frequency mode shapes, and acoustic noise emitted from the fan blade, are discussed for their coupled effect in hot and humid environments. Results such as acoustic noise for coupled composite-mechanics/heat transfer/structural/vibration/acoustic analyses demonstrate the effectiveness of coupled multi-disciplinary computational simulation the various advantages of composite materials compared to metals.

Chamis, Christos C.↗
NASA NTRS1992

Coupled multi-disciplinary simulation of composite engine structures in propulsion environment

A computational simulation procedure is described for the coupled response of multi-layered multi-material composite engine structural components which are subjected to simultaneous multi-disciplinary thermal, structural, vibration, and acoustic loadings including the effect of hostile environments. The simulation is based on a three dimensional finite element analysis technique in conjunction with structural mechanics codes and with acoustic analysis methods. The composite material behavior is assessed at the various composite scales, i.e., the laminate/ply/constituents (fiber/matrix), via a nonlinear material characterization model. Sample cases exhibiting nonlinear geometrical, material, loading, and environmental behavior of aircraft engine fan blades, are presented. Results for deformed shape, vibration frequency, mode shapes, and acoustic noise emitted from the fan blade, are discussed for their coupled effect in hot and humid environments. Results such as acoustic noise for coupled composite-mechanics/heat transfer/structural/vibration/acoustic analyses demonstrate the effectiveness of coupled multi-disciplinary computational simulation and the various advantages of composite materials compared to metals.

Chamis, Christos C.↗
NASA NTRS1991

Structural design considerations for the Space Infrared Telescope Facility

To assess the design feasibility of the Space Infrared Telescope Facility (SIRTF) and to identify parameters that might impose constraints on performance such as frequencies of vibration, structural concepts for both the telescope and spacecraft are developed and evaluated. Trade studies of key design features are carried out using FEM and analysis. In most cases, the margin of safety was greater than 0.50. An example of stress in the octagonal equipment bus panels is shown. The strap-supported mass is predicted to deflect 6 mm relative to the outer shell when subjected to 8.0 G in the X direction, and to deflect about 5 mm in the Y and Z directions when subjected to 10.0 G. Deflections for the top of the solar panel are predicted to be about 35 mm when subjected to the 10.0 G quasi-static load in the Z direction. The liquid helium tank, thermal isolation, and primary mirror and mount are discussed.

Macneal, Paul D.↗
NASA NTRS1984

Component mode synthesis and large deflection vibrations of complex structures

The accuracy of the NASTRAN modal synthesis analysis was assessed by comparing it with full structure NASTRAN and nine other modal synthesis results using a nine-bay truss. A NASTRAN component mode transient response analysis was also performed on the free-free truss structure. A finite element method was developed for nonlinear vibration of beam structures subjected to harmonic excitation. Longitudinal deformation and inertia are both included in the formula. Tables show the finite element free vibration results with and without considering the effects of longitudinal deformation and inertia as well as the frequency ratios for a simply supported and a clamped beam subjected to a uniform harmonic force.

Mei, C.↗
NASA NTRS1994

Test Bed For Control Of Optical-Path Lengths

Truss structure and ancillary equipment constitute test bed for experiments in methods of controlling lengths of optical paths under conditions of structural vibration and deformation. Accommodates both passive and active methods of control. Experimental control system reduces millimeter-level disturbances in optical path length to nanometers. Developed for control, alignment, and aiming of distributed optical systems on large flexible structures. Test bed includes tower 2.5 meters high with two horizontal arms extending at right angles from its top. Rigidly mounted on massive steel block providing measure of isolation from ground vibrations. Optical motion-compensation system similar to one described previously in NASA Tech Briefs enclosed in flexure-mounted frame, called "trolley," at end of longer horizontal arm.

O'Neal, Michael C.↗
NASA NTRS1997

STS-74/Mir Photogrammetric Appendage Structural Dynamics Experiment Preliminary Data Analysis

The Photogrammetric Appendage Structural Dynamics Experiment was designed, developed, and flown to demonstrate and prove measurement of the structural vibration response of a Russian Space Station Mir solar array using photogrammetric methods. The experiment flew on the STS-74 Space Shuttle mission to Mir in November 1995 and obtained video imagery of solar array structural response to various excitation events. The video imagery has been digitized and triangulated to obtain response time history data at discrete points on the solar array. This data has been further processed using the Eigensystem Realization Algorithm modal identification technique to determine the natural vibration frequencies, damping, and mode shapes of the solar array. The results demonstrate that photogrammetric measurement of articulating, non-optically targeted, flexible solar arrays and appendages is a viable, low-cost measurement option for the International Space Station.

Gilbert, Michael G.↗
NASA NTRS1997

STS-74/MIR Photogrammetric Appendage Structural Dynamics Experiment Preliminary Data Analysis

The Photogrammetric Appendage Structural Dynamics Experiment was designed, developed, and flown to demonstrate and prove measurement of the structural vibration response of a Russian Space Station Mir solar array using photogrammetric methods. The experiment flew on the STS-74 Space Shuttle mission to Mir in November 1995 and obtained video imagery of solar array structural response to various excitation events. The video imagery has been digitized and triangulated to obtain response time history data at discrete points on the solar array. This data has been further processed using the Eigensystem Realization Algorithm modal identification technique to determine the natural vibration frequencies, damping, and mode shapes of the solar array. The results demonstrate that photogrammetric measurement of articulating, nonoptically targeted, flexible solar arrays and appendages is a viable, low-cost measurement option for the International Space Station.

Gilbert, Michael G.↗