SEARCH · Engineering Papers

Results for “ACOUSTIC VIBRATION”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 901 records · Page 50

All sources NASA NTRS DOE OSTI

NASA NTRS1992

Nonlinear acoustics and the thermal expansivity of glass

The paper shows the intrinsic relationship between acoustical nonlinearity and the thermal expansivity of crystalline solids (a thermal measure of anharmonicity) from consideration of the 'static' radiation field generated by the vibrating lattice (atomic) sources of the crystal. A modification of the theory to account for long-range structural disorder in glass is proposed and applied to an explanation of the zero thermal expansivity at the cross-over temperature in silicate and titanium silicate glasses. Experimental evidence which validates the essential features of the theory is presented. An application of nonlinearity measurement, based on these results, to the processing of ULE glass, where the addition of titanium in various amounts is used to establish the temperature at which the zero thermal expansivity occurs, is suggested.

Cantrell, John H.↗

NASA NTRS2001

Acoustic Issues in Human Spaceflight

NASA is concerned about acute effect of sound on crew performance on International Space Station (ISS), and is developing strategies to assess and reduce acute, chronic, and delayed effects of sound. High noise levels can cause headaches, irritation, fatigue, impaired sleep, headache, and tinnitus and have resulted in an inability to hear alarms. Speech intelligibility may be more impaired for crew understanding non-native language in a noisy environment. No hearing loss occurred, but significant effects on crew performance and communication occurred. Permanent Threshold Shifts (PTS) have not been observed in the US shuttle program. Russian specification for noise in spacecraft is 60 dBA (awake) and 50 dBA (asleep) while the U.S. noise specification on ISS is NC 50 (awake) and NC 40 (asleep) with a 85 dBA hazard limit. Background noise levels of ISS modules have measured 56-69 dBA. Treadmill exercise operations measure 77 dBA. Alarms are required to be 20 dBA above ambient. Hearing protection is recommended when noise exceeds 60 dB 24 hour Leq. Countermeasures include hearing protection and design/ engineering controls. Advanced composite materials with excellent low frequency attenuation properties could be applied as a barrier protection around noisy equipment, or used on personal protective equipment worn by the crew. Hearing protection countermeasures include foam ear inserts, passive muff headsets, and active noise reduction headsets. Oto-acoustic emissions (OAE) could be used to monitor effectiveness of hearing protection countermeasures and tailor hearing protection countermeasures to individual crewmembers. Micro-gravity, vibration, toxic fumes, air quality/composition, stress, temperature, physical exertion or some combination of the above factors may have interacted with moderate long-term noise exposure to cause significant hearing loss. Longitudinal studies will need to address what co-morbidity factors, such as radiation, toxicology, microgravity effects (fluid shift), aging, are involved with hearing loss.

Clark, Jonathan B.↗

NASA NTRS1993

Quality Factor and Microslipping of Fatigue Cracks in Thin Plates at Resonant Vibration

Resonant vibrations have been stimulated in thin metal plates using a non-contacting electromagnetic driver. A sinusoidal force was applied in a swept frequency fashion and the resulting surface displacements were monitored through the use of an acoustic microphone. It has been found that the presence of a fatigue crack in the sample causes a broadening of the second resonance peak. The Q factors of the resonance curves were determined and are directly correlated with the presence of fatigue cracks in the samples. The broadening of the curves is explained in terms of a microslipping at the crack face walls which reduces the amplitude of the resonant vibration by increasing the damping of the system. A comparison is made between the resonance characteristics of fatigue damaged and notched samples, where the stiffness of the two systems is nearly constant while the interaction between crack face walls is eliminated in the latter.

Wincheski, B.↗

DOE OSTI2017

Analysis and Management of Microphonics in Operational SRF Cavities With Bandwidths of approximately 10 Hz

Superconducting Radio Frequency Cavity detuning can be due to several effects. These effects include helium pressure variations, vibrations driven by external narrow band sources such as HVAC motors, cooling water systems, tuner motor operation, cryogenic system machinery, and occasionally cryogenic system instabilities such as thermo-acoustic oscillations. They can also be driven by broadband white or pink noise which, in general, will excite the resonant modes of the structure. All of these affect the cavity resonant frequency. Variations that occur at frequencies above a few tenths of a Hertz are considered microphonics. CEBAF 0.7 m C100 cavities operated at 1500 MHz with 20 Hz bandwidths, changes in cavity lengths on the order of 10 nm are sufficient to shift the cavity frequency by more than one bandwidth. Jefferson Lab is the first lab to install and operate a large number of SRF cavities with relatively high loaded-Qs, 88 in CEBAF and 16 in the LERF (previously the FEL). Production was halted for several months after the first 3 production C100 cryomodules were built, and modifications were developed in order to reduce the background microphonics. Additionally, in the spring of 2016 we started a program to harden and damp the cryomodule interface structures in order to reduce the sensitivity to outside perturbations as well as to damp out the natural vibrational modes of the structures. This work will focus on the approaches and measurements that one should consider when designing a system in order to understand the modal nature of the structure, the measurement techniques for determining the extent of the microphonics, and the mitigations that can be implemented in order to reduce the effects of outside perturbances. Examples of results at various other institutions will also be presented.

Powers, Thomas↗

DOE OSTI2021

Phase-weighted slant stacking for surface wave dispersion measurement

SUMMARY Surface wave retrieval from ambient noise records using seismic interferometry techniques has been widely used for multiscale shear wave velocity (Vs) imaging. One key step during Vs imaging is the generation of dispersion spectra and the extraction of a reliable dispersion curve from the retrieved surface waves. However, the sparse array geometry usually affects the ability for high-frequency (>1 Hz) seismic signals’ acquisition. Dispersion measurements are degraded by array response due to sparse sampling and often present smeared dispersion spectra with sidelobe artefacts. Previous studies usually focus on interferograms’ domain (e.g. cross-correlation function) and attempt to enhance coherent signals before dispersion measurement. We propose an alternative technique to explicitly deblur dispersion spectra through use of a phase-weighted slant-stacking algorithm. Numerical examples demonstrate the strength of the proposed technique to attenuate array responses as well as incoherent noise. Three different field examples prove the flexibility and superiority of the proposed technique: the first data set consists of ambient noise records acquired using a nodal seismometer array; the second data set utilizes distributed acoustic sensing (DAS) and a marine fibre-optic cable to acquire a similar ambient noise data set; the last data set is a vibrator-based active-source surface wave data. The enhanced dispersion measurements provide cleaner and higher-resolution spectra without distortions which will assist both human interpreters as well as ML algorithms in efficiently picking curves for subsequent Vs inversion.

58 GEOSCIENCES↗

NASA NTRS1977

Technical highlights in general aviation

Improvements in performance, safety, efficiency, and emissions control in general aviation craft are reviewed. While change is slow, the U.S. industries still account for the bulk (90%) of the world's general aviation fleet. Advances in general aviation aerodynamics, structures and materials, acoustics, avionics, and propulsion are described. Supercritical airfoils, drag reduction design, stall/spin studies, crashworthiness and passenger safety, fiberglass materials, flight noise abatement, interior noise and vibration reduction, navigation systems, quieter and cleaner (reciprocating, turboprop, turbofan) engines, and possible benefits of the Global Position Satellite System to general aviation navigation are covered in the discussion. Some of the developments are illustrated.

Stickle, J. W.↗

NASA NTRS1983

A finite element model for sound transmission through panels

A finite element method (FEM) is applied to predicting coupled frequencies and pressures within an acoustic cavity in order to characterize sound transmission through a panel. Structural equations of motion are defined and the FEM model is configured with four-noded plate elements, the lateral displacement and two slopes being the unknowns at every node. Each element then has 12 degrees of freedom (DOF) and the displacement variation is expressed by a 12-term nonconforming polynomial. A consistent mass matrix is used to represent the panel mass matrix and a wave equation governs the acoustic volume. Analysis of pressure and displacement over the panel yields a square coupling matrix, and an eigenanalysis leads to a solution of the forced vibration problem.

Ramakrishnan, J. V.↗

NASA NTRS1991

New Sensors For Flow Velocity And Acoustics

Paper describes two sensor-development programs at Fluid Mechanics Laboratory at NASA Ames Research Center. One program for digital image velocimetry (DIV) sensors, and other program, for advanced acoustic sensors for wind tunnels. DIV measures, in real time, instantaneous velocity fields of time-varying flow or of collection of objects moving with varying velocities. Advanced acoustic sensors for wind tunnels being developed to reduce effects of interference from wind noise, noise from interactions between flows and sensors, flow-induced vibrations of sensors, deflections of accoustic waves by boundary layers induced by sensors, and reflections from walls and sensor supports.

Cho, Y. C.↗

DOE OSTI2022

Noninvasive acoustical property measurement of fluids

Methods for noninvasive determination of acoustical properties of flowing in pipes having a large ratio (>10) of pipe diameter to wall thickness, and in highly attenuating fluids are described. When vibrations are excited on the outer surface of the wall of a pipe, the resulting vibrations propagate directly through the wall in a normal direction and through the pipe wall as guided waves, appearing on the opposite side of the pipe. This dual path propagation through pipes, where guided waves take the circumferential path in the wall of the pipe and may interfere with the time of-flight measurement obtained from the direct path through the fluid, is at least in part resolved by subtracting the signal from the guided wave from the combined signal, thereby permitting improved observation of the direct path propagation through the fluid.

Sinha, Dipen N.↗

DOE OSTI2016

Annular spherically focused ring transducers for improved single-beam acoustical tweezers

The use of ultrasonic transducers with a central hollow is suggested for improved single-beam acoustical tweezers applications. Within the framework of the Fresnel-Kirchhoff parabolic approximation, a closed-form partial-wave series expansion (PWSE) for the incident velocity potential (or pressure) field is derived for an annular spherically focused ring (asfr) with uniform vibration across its surface in spherical coordinates. The Rayleigh-Sommerfeld diffraction integral and the addition theorems for the Legendre and spherical wave functions are used to obtain the PWSE assuming a weakly focused beam (with a focusing angle α ≤ 20°). The PWSE allows evaluating the incident field from the finite asfr in 3D. Moreover, the obtained solution allows computing efficiently the acoustic scattering and radiation force on a sphere centered on the beam's axis of wave propagation. The analytical solution is valid for wavelengths largely exceeding the radius of the asfr and when the viscosity of the surrounding fluid can be neglected. Numerical predictions for the beam-forming, scattering, and axial time-averaged radiation force are performed with particular emphasis on the asfr thickness, the axial distance separating the sphere from the center of the transducer, the (non-dimensional) size of the transducer, as well as the sphere's elastic properties without restriction to the long- (i.e., Rayleigh) or the short-wavelength (i.e., ray acoustics) regimes. Potential applications of the present solution are in beam-forming design, particle tweezing, and manipulation due to negative forces using ultrasonic asfr transducers.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

NASA NTRS1983

Acoustic measurements of a full-scale coaxial hingeless rotor helicopter

Acoustic data were obtained during a full-scale test of the XH-59A Advancing Blade Concept Technology Demonstrator in the 40- by 80-Foot Wind Tunnel. The XH-59A is a research helicopter with two coaxial rotors and hingeless blades. Performance, vibration, and noise at various forward speeds, rotor lift coefficients and rotor shaft angles of attack were investigated. The noise data were acquired over an isolated rotor lift coefficient range of 0.024 to 0.162, an advance ratio range of 0.23 to 0.45 corresponding to tunnel wind speeds of 89 to 160 knots, and angles of attack from 0 deg to 10 deg. Acoustic data are presented for seven microphone locations for all run conditions where the model noise is above the background noise. Model test configuration and performance information are also listed. Acoustic waveforms, dBA, and 1/3-octave spectra as functions of operating condition for selected data points and microphones are presented. In general, the noise level is shown to increase with rotor lift coefficient except under certain operating conditions where significant impulsive blade/vortex interactions increase noise levels.

Peterson, R. L.↗

NASA NTRS1979

SEP solar array development testing

This paper describes the test program of a lightweight 25 kW solar array for solar electric propulsion. A full-scale development wing was made of aluminum with the containment box cover of graphite-epoxy, while the flight design array wing uses a graphite-epoxy structure. The full-scale continuous longeron array extension mast was tested for performance on a water table, and the full scale wing was functionally tested to demonstrate automatic containment box unlocking, wing extension, and retraction, blanket tensioning, and automatic application of blanket preload. The wing was then tested to the Shuttle acoustic environment, followed by a thermal/vacuum test in which the wing was extended and retracted at high and low temperature. Finally, the wing was tested in vibration with sine and random vibration environments.

Elms, R. V., Jr.↗

NASA NTRS1981

Propagation of sound through the Earth's atmosphere. 1: Measurement of sound absorption in the air: 2: Measurement of ground impedance

Parts were fabricated for the acoustic ground impedance meter and the instrument was tested. A rubber hose was used to connect the resonator neck to the chamber in order to suppress vibration from the volume velocity source which caused chatter. An analog to digital converter was successfully hardwired to the computer detection system. The cooling system for the resonant tube was modified to use liquid nitrogen cooling. This produced the required temperature for the tube, but the temperature gradients within each of the four tube sections reached unacceptable levels. Final measurements of the deexcitation of nitrogen by water vapor indicate that the responsible physical process is not the direct vibration-translation energy transfer, but is a vibration-vibration energy transfer.

Meredith, R. W.↗

NASA NTRS1989

Digital Controller For Acoustic Levitation

Acoustic driver digitally controls sound fields along three axes. Allows computerized acoustic levitation and manipulation of small objects for such purposes as containerless processing and nuclear-fusion power experiments. Also used for controlling motion of vibration-testing tables in three dimensions.

Tarver, D. Kent↗

NASA NTRS1995

Estimating Vibrational Powers Of Parts In Fluid Machinery

In new method of estimating vibrational power associated with component of fluid-machinery system, physics of flow through (or in vicinity of) component regarded as governing vibrations. Devised to generate scaling estimates for design of new parts of rocket engines (e.g., pumps, combustors, nozzles) but applicable to terrestrial pumps, turbines, and other machinery in which turbulent flows and vibrations caused by such flows are significant. Validity of method depends on assumption that fluid flows quasi-steadily and that flow gives rise to uncorrelated acoustic powers in different parts of pump.

Harvey, S. A.↗

DOE OSTI2014

Anomalous phonon characteristics of unconventional novel III-N superlattices

Comprehensive results of atomic vibrations are reported in the unconventional short-period zb BN/GaN superlatices (SLs) by exploiting a rigid-ion-model and taking into account both the short- and long-range Coulomb interactions. Besides anisotropic mode behavior of optical phonons, our study provided evidence of acoustic-mode anti-crossing, mini-gap formation, confinement as well as BN-like modes falling within the gap that separates optical phonon bands of the two materials. A bond-polarizability scheme is employed within the second-nearest-neighbor linear-chain model to simulate the Raman intensity profiles of BN/GaN SLs revealing major expected trends of the vibrational characteristics observed experimentally in many conventional superlattice systems while eliciting some interesting contrasts.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

NASA NTRS1976

Development of modified vibration test criteria for qualifying space vehicle components

The results of the evaluation of two response prediction methods relating to the prediction of structural responses of stiffened shell structures with or without attached components, and subjected to broadband acoustic excitations are presented. The methods under evaluation were the constant mass attenuation method and the impedance ratio method. Example problems were used to illustrate the application procedures of these two methods and to compare their predicted results with the experimentally measured data. It is found that more realistic estimates of the structural response can be obtained by the impedance ratio method.

Chang, K. Y.↗

DOE OSTI2011

Magnetic properties of magnetite nanoparticles coated with mesoporous silica by sonochemical method

Highlights: Black-Right-Pointing-Pointer MCM-41-coating of magnetite nanoparticles performed under ultrasonic irradiation. Black-Right-Pointing-Pointer Ultrasonic irradiation accelerates the formation of the MCM-41 framework. Black-Right-Pointing-Pointer The hysteretic response to an applied field was investigated applying FORC diagram. Black-Right-Pointing-Pointer The average coercive field of the Fe{sub 3}O{sub 4} nanoparticles increased after coating. -- Abstract: In this paper we present the magnetic properties of mesoporous silica-coated Fe{sub 3}O{sub 4} nanoparticles. The coating of magnetite nanoparticles with mesoporous silica shell was performed under ultrasonic irradiation. The obtained mesoporous silica-coated magnetite nanoparticles were characterized by powder X-ray diffraction, focused ion beam-scanning electron microscopy, nitrogen adsorption-desorption isotherms and vibrating sample magnetometer. The hysteretic behavior was studied using first-order reversal curves diagrams. The X-ray diffraction result indicates that the extreme chemical and physical conditions created by acoustic cavitations have an insignificant effect on crystallographic structural characteristic of magnetite nanoparticles. Changes in the coercivity distributions of the magnetite nanoparticles were observed on the first-order reversal curves diagrams for the samples with coated particles compared with the samples containing uncoated particles of magnetite. The coated particles show an increased most probable coercivity of about 20% compared with the uncoated particles which can be associated with an increased anisotropy due to coating even if the interaction field distribution measured on the diagrams are virtually identical for coated/uncoated samples.

36 MATERIALS SCIENCE↗