Subtle Differences in Jet Noise Scaling with Narrow Band Spectra Compared to 1/3-Octave Band

Abstract A finite-element based engine system model is developed for predicting the structural vibration of the engine. The engine system model combines modal models of the major bolted-together sub-structures of the engine, with non-structural mass models of the remaining engine components added to bring the inertial properties to those of the running engine. The model is developed and experimentally evaluated with impact and shaker excitation tests. Comparisons are made of the predicted and measured vibration response for various partially assembled engine configurations, as well as for the fully assembled engine. The comparisons illustrate the accuracy of the model in predicting the narrow-band and one-third octave-band vibration response for excitation frequencies up to 2 kHz.

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Initial- versus final-state effects in the narrow-band spectra of heavy-fermion systems

Physical Review B ◽

10.1103/physrevb.42.6446 ◽

1990 ◽

Vol 42 (10) ◽

pp. 6446-6457 ◽

Cited By ~ 12

Author(s):

B. Gumhalter ◽

V. Zlatić

Keyword(s):

Heavy Fermion ◽

Narrow Band ◽

Final State ◽

Fermion Systems ◽

Heavy Fermion Systems ◽

Band Spectra

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On Sequence of High Waves in Nonlinear Groups

Volume 2: Structures, Safety and Reliability ◽

10.1115/omae2008-57889 ◽

2008 ◽

Author(s):

Felice Arena ◽

C. Guedes Soares

Keyword(s):

Time Domain ◽

Wind Wave ◽

Narrow Band ◽

Second Order ◽

Wave Groups ◽

Before And After ◽

The Difference ◽

Band Spectra ◽

Two Peaks ◽

The Waves

The structure of wave groups in time domain depends upon the spectrum. For narrow-band spectra, if a wave with a very large height H occurs, the waves that precede and follow the highest one have height (H′ and H″ respectively) very close to H. For real spectra, the difference between H and either H′ or H″ depends on the bandwidth of the spectrum: it increases as larger is the spectrum. For bimodal spectra, the authors have shown [1] that the wave groups are strongly modified and they are function of the energy associated to the swell and to the wind wave components, as well as of the distance between the two peaks. This paper analyzes the structure of the succession of three waves, given by the high waves and the two that come before and after the highest one, in time domain. The results are analyzed, up to the second-order, for wind wave unimodal and for bimodal spectra, by comparing the height H with H′ and H″.

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