The data acquisition conducted at IAD is the very beginning of the LFN study. The recordings made insure that there are an adequate variety of aircraft type and number of events to provide a thorough analysis. Prelimi...
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ISBN:
(纸本)9781622762712
The data acquisition conducted at IAD is the very beginning of the LFN study. The recordings made insure that there are an adequate variety of aircraft type and number of events to provide a thorough analysis. Preliminary findings show the difference between the house responses. These differences will be investigated further to better understand the impact upon humans and the effects of house construction on attenuating the impact of the noise events. Though the original rattle design did not produce rattle in either location, the loose window in the stone house, as well as the modified rattle design, provided the opportunity to capture rattle signatures on both the indoor microphone and the HEAD system for a wide selection of events. Further work is planned for a subjective study of annoyance for the rattle signatures that were captured at the stone house. These recordings, as well as signatures without rattle, will be presented to subjects for evaluation. Objective metrics will be calculated for signatures used in the jury evaluation, and these metrics will be correlated with subjective ratings to assess the metric's ability to predict rattle impact. The findings will assist in identifying metrics that best correlate with the human perception of rattle.
The standard metric currently in use by the U.S. government for community noise from aircraft is the Day-Night Level (DNL), which is based on the A-weighting network. However, residents of communities near airports ha...
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ISBN:
(纸本)9781622762712
The standard metric currently in use by the U.S. government for community noise from aircraft is the Day-Night Level (DNL), which is based on the A-weighting network. However, residents of communities near airports have reported annoyance due to aircraft noise in greater proportion than what the DNL contour associated with their address predicts1. Complaints of "distant rumbling" appear to be related to the low-frequency noise that aircraft produce for which the DNL metric does not fully account 2. This presentation discusses measurements made in October 2004 at two residences near runways at Washington-Dulles International Airport. Noise data are recorded on indoor and outdoor microphones, allowing for a measure of the events' impact both inside and outside the structure, as well as the filtering effect of the structure on the signal. Experimental design for a laboratory subjective study of the recorded aircraft signatures is discussed. Objective metrics, those that are designed for low-frequency noise and those that are not, are to be calculated and correlated with subjective rankings of the signatures. These correlations will gauge the metrics' effectiveness in predicting subjective perception of aircraft noise signatures.
The noise radiated by a subsonic, axial‐flow fan at its rotational frequency and harmonics is related to the nonsteady force field created at the rotor blade/fluid interface. This force field is highly dependent on t...
The noise radiated by a subsonic, axial‐flow fan at its rotational frequency and harmonics is related to the nonsteady force field created at the rotor blade/fluid interface. This force field is highly dependent on the time‐invariant flow distortions that enter the fan. In this basic study, a typical cooling fan used in the electronic and computer industry was instrumented with an unsteady axial force sensor. Its output is proportional to the total unsteady axial force created by the rotor. The inflow field of the fan was systematically distorted by placing a small cylinder at various positions in the inlet plane. The nonuniform, three‐dimensional flow field entering the rotor was measured by traversing a miniature five‐hole pressure probe. The total pressure outputs from this probe can be related to the axial, tangential, and radial velocity vectors. Fourier decomposition of the inflow velocity data is coupled with analysis to give information on the unsteady rotor force harmonic content. The on‐axis sound pressure levels were measured and compared to coherent output power spectra involving the unsteady force sensor and the microphone. Very good coherence at the discrete tones is observed. [Work supported by IBM Corp.]
A lumped‐parameter equivalent circuit of a tonpilz transducer is used to predict element amplitude and phase tolerance for different radiation loadings, based on in‐air measurements of the transducers. Relationships...
A lumped‐parameter equivalent circuit of a tonpilz transducer is used to predict element amplitude and phase tolerance for different radiation loadings, based on in‐air measurements of the transducers. Relationships among the measurable parameters of a transducer and its performance characteristics have been explored. Preliminary estimates of acceptable tolerances for each circuit parameter have been established. A two‐part technique to determine the placement of transducer elements in an array which minimizes the impact of element tolerances on the directional beam pattern has been developed. This technique has been used to place, in an array, elements with tolerances of ± 9% in amplitude and ± 11° in phase. The resulting theoretical array response achieved sidelobe levels that were within 1 dB of the −40‐dB design. The first half of the technique selects four elements at a time from a larger selection pool, and places them in a manner that partially cancels their respective amplitude and phase variations. The second half of the technique uses a permutation search algorithm which rearranges the initial placement of elements in and out of the array looking for improvements in the array response.
The effect of dispersion on parametric array formation is investigated via solutions of the second‐order paraxial wave equation for Gaussian source excitations. Only when |δ| > αT/k− does dispersion noticeably i...
The effect of dispersion on parametric array formation is investigated via solutions of the second‐order paraxial wave equation for Gaussian source excitations. Only when |δ| > αT/k− does dispersion noticeably influence the nonlinear interaction, where δ = 1 − (k1 − k2)/k− is the dispersion parameter, kj (j = 1,2) and k− are primary‐beam and difference‐frequency wavenumbers (f1 − f2 = f−) , respectively, and αT = α1 + α2 − α− is the combined attenuation coefficient. In contrast with one‐dimensional dispersive wave interactions, the entire difference‐frequency pressure field depends significantly on the sign of δ (δ > 0 if the sound speed increases with frequency). Axial pressure field curves [F. H. Fenlon and M. F. Hamilton, J. Acoust. Soc. Am. Suppl. 1 69, S81 (1981)], farfield directivity patterns, and three‐dimensional field plots will be presented. For an absorption‐limited array the directivity function reduces to [1 + i(2k−/αT)(sin2 θ/2 − δ/2)]−1 . The maximum radiation is therefore shifted off axis to a direction determined by k1 − k2 = k− cos θ , which is the resonance condition for collimated plane‐wave interactions. [Work supported by ONR.]
In a previous paper at the 99th meeting of the Acoustical Society of America in Atlanta in 1980 a new viscoelastometer was described. This instrument enables the Young's modulus and loss factor to be easily obtain...
In a previous paper at the 99th meeting of the Acoustical Society of America in Atlanta in 1980 a new viscoelastometer was described. This instrument enables the Young's modulus and loss factor to be easily obtained over a wide range of frequencies and temperatures. The prototype of this instrument is being used in a continuing project for the systematic evaluation of the properties of a wide variety of commercially available materials. The method will be. described and some examples given.
Refined models for plate deformation allow for new types of thickness and extensional displacements not currently feasible in the classical or Timoshenko‐Mindlin plate theories. An infinite bilaminar composite plate ...
Refined models for plate deformation allow for new types of thickness and extensional displacements not currently feasible in the classical or Timoshenko‐Mindlin plate theories. An infinite bilaminar composite plate is fabricated in such a way that the two plates, made of different isotropic, homogeneous materials, are perfectly bonded. A new mathematical model of the vibration of an infinite bilaminar composite plate has been obtained by using energy methods. The displacement field is based on symmetric and antisymmetric displacement functions in both the thickness stretch and the thickness shear of each layer. From this model, the Timoshenko‐Mindlin thick plate theory and the Bernoulli‐Euler classic plate theory for a single plate can be recovered as special limiting cases. For this model, a six‐branched frequency‐wavenumber spectrum of the composite layer is computed. This allows the introduction of suitable correction coefficients to correct the resulting frequency spectra so that they correspond to those of the exact elasticity theory.
This paper theoretically and experimentally examines the effect of a downstream ventilated gas cavity on the spectrum of turbulent boundary layer wall pressure fluctuations. The theoretical model predicts that the rat...
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The relationship between the signal bandwidth and the correlation of a single surface reflected arrival with the transmitted signal has been investigated experimentally and compared with two theories. The dependence o...
The relationship between the signal bandwidth and the correlation of a single surface reflected arrival with the transmitted signal has been investigated experimentally and compared with two theories. The dependence of correlation on signal bandwidth is termed frequency correlation. Decorrelation of surface scattered signals is a direct consequence of time spread. Thus the acoustic measurement utilized two pure tone signals, from which time spread has been estimated, and four broadband signals with different bandwidths, from which correlation with the transmitted signal has been calculated. A model developed by Dahl for the ocean surface bistatic scattering cross section was used to predict time spread, which agreed very well with the measured time spread. Next, scattering cross section prediction was employed in two theories that predict frequency correlation. The first, published by Reeves in 1974, compared well with the measurements for bandwidths up to 2 kHz, but under predicted correlation for signal bandwidth between 7 and 22 kHz. In the second, linear systems theory was used to develop a mathematical relationship between time spread and frequency correlation. Predictions made using the linear systems theory agree well with the measured values for signal bandwidths up to 22kHz. Further work is required to evaluate the linear systems theory under higher sea state conditions.
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