A probabilistic averaging technique

A new technique is presented for decomposing unsteady turbulent flow variables into their organized unsteady and turbulent components, which appears to offer some significant advantages over existing ones. The technique uses power-spectral estimates of data to deduce the optimal frequency-domain filter for determining the organized and turbulent components of a time series of data. When contrasted with the phase-averaging technique, this method can be thought of as replacing the assumption that the organized motion is identically reproduced in successive cycles of known periodicity by a more general condition: the cross-correlation of the organized and turbulent components is minimized for a time series of measurement data, given the expected shape of the turbulence power spectrum. The method is significantly more general than the phase average in its applicability and makes more efficient use of available data. Performance evaluations for time series of unsteady turbulent velocity measurements attest to the accuracy of the technique and illustrate the improved performance of this method over the phase-averaging technique when cycle-to-cycle variations in organized motion are present.

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Trial applications at gymnasiums of in-situ sound absorption measurement method by ensemble averaging technique

INTER-NOISE and NOISE-CON Congress and Conference Proceedings ◽

10.3397/in-2021-2729 ◽

2021 ◽

Vol 263 (2) ◽

pp. 4532-4537

Author(s):

Toru Otsuru ◽

Reiji Tomiku ◽

Noriko Okamoto ◽

Siwat Lawanwadeekul

Keyword(s):

Measurement Method ◽

Sound Absorption ◽

Glass Wool ◽

Absorption Measurement ◽

Ensemble Averaging ◽

Averaging Technique ◽

In Situ Conditions ◽

Measurement Consistency ◽

Absorption Characteristics

The authors have been published a series of papers on a measurement method for sound absorption characteristics of materials using ensemble averaging technique, i.e., EA method. The papers' results included measurement mechanisms, measurement uncertainty, and so on. Herein, to examine adaptability, especially in in-situ conditions, the EA method is applied to measure absorption characteristics of materials installed in two gymnasiums. A glass-wool panel with the dimension of 0.5 m by 0.5 m by 0.05 m and with the density of 32 kg m^-3 was brought around and measured to check the measurement consistency. Several measurements were conducted during badminton plays were undergoing. Measured sound absorption coefficients revealed that most results agree well with those measured in reverberation rooms. Certain improvement is necessary for the specimen brought to the in-situ measurement to keep the consistency. The inconsistency is considered to originate from unstable conditions between the specimen and floor.

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