Acoustic properties of additive manufactured narrow tube periodic structures

Double cylinder structures (Yamamoto, et al., 2014), (Tamura, et al., 1999) are frequently used as machine elements and tube elements of equipments such as reactors (Fujiwara, et al., 2000), catalysts, heat exchangers (Alkan and Al-Nimr, 1999), and thermal insulators. A clearance exists between double cylinders of annular cross-section. This has engineering benefits if we can predict the acoustic properties such as the sound absorption coefficient of a sound incident on the clearance of such an annular cross-section based on the geometric dimensions of the tubes and the physical properties of the gas. With respect to the propagation of a sound wave in a narrow tubule structures, several studies have been performed on the propagation constant and particle velocity distribution (Tijdeman, 1975), complex density and complex compressibility (Stinson, 1991), complex density and complex bulk modulus (Allard and Atalla, 2009) in a circular hole, in an equilateral-triangular tube, or in between two planes (Stinson and Champou, 1992). Further, analysis using the finite element method of the vibration of the air in a rectangular tube (Beltman, et al., 1998), and on the propagation of a sound wave in the clearance created by the close packing of cylinders has also been conducted (Matsuzawa, 1963). With respect to naturally derived narrow tubes, studies have been performed on the acoustic absorption properties of straw (McGinnes, et al., 2005) and rice straw (Sakamoto, et al., 2011). The authors experimentally clarified that acoustic absorption effect in the clearance of an annular cross-section of a rice straw was useful (Sakamoto, et al., 2-8050 Ikarashi, Nishi-ku, Niigata, 950-2181, Japan

Estimation and experiment for sound absorption coefficient of cross-sectional shape of clearance by concentric cylinder

/pdf/study-for-sound-absorbing-materials-of-biomass-tubule-4wws5ble65.pdf

Study for sound-absorbing materials of biomass tubule (Oblique incident sound-absorption coefficient of oblique arrangement of rice straws)

In this study, we theoretically and experimentally explore the acoustic leak of an entire acoustic system as well as the various gap occurring between a gasket and flange. We conducted the first-ever fundamental research related to sound transmission loss through a narrow gap between a gasket and flange. In the experiments, we constructed pipeline elements, including the gap and the leakage path, in the impedance measurement tube. In the theoretical analysis, we replaced the fluid path, including the gap, with acoustic elements that comprise an electrical equivalent circuit. We then conducted the analysis using the transfer matrix method. To calculate the attenuation of sound waves propagating through the gap, we considered friction in association with viscosity, primarily in the boundary layers of the inner wall, to derive the characteristic impedance and propagation constant. The trends between the calculated and the actual experimental values for transmission loss in the entire acoustic system coincided enough with regard to a large gap size range between 0.01 and 0.2 mm. Furthermore, the transmission loss linearly increased with the decreasing logarithm of gap for the calculated regions. Furthermore, the theoretical analysis and experimental results show agreement for incline gap conditions between the gasket and flange. The maximum gap also greatly affects the acoustic transmission loss for the inclined gaps. This was confirmed both by the experimental and the calculated values. We consider that these results provide fundamental acoustic knowledge specific to the narrow gap between the gasket and flange in an acoustic system.

Fundamental study of acoustic leakage through a gap between gasket and flange surface

The interactions of guided acoustic waves with pipelines and associated components has become a topic of interest due to their application in water pipeline condition assessment. In this paper, guided acoustic wave interactions with flanged junctions in a water-filled pipeline are investigated by an analytical model and experimental measurements. In the model, axial wavenumbers, displacement, and stress profiles of the main pipeline and flange junction components are calculated by an existing cylindrical waveguide analytical model. These components are then concatenated together using mode matching to determine the overall theoretical characteristics. Experiments with a flanged water-filled steel pipeline are carried out to verify model predictions. Transmitted signals are acquired using acoustic transducers uniformly spaced along the pipeline axis to separate individual modes and extract mode amplitudes. Transmission losses are estimated by comparing the extracted amplitudes in a pipeline with and without the flanged junction. Both theoretical predictions and experimental results indicate that the flanged junction interacts with pipeline wall dominant modes by transforming them into waterborne modes and as a result guides acoustic power into the water medium. The flange is shown to cause a small transmission loss in waterborne modes as compared to the pipeline without flanges.

Guided acoustic wave interaction with flanged junctions in water-filled steel pipelines.

/pdf/theoretical-analysis-of-the-sound-absorption-coefficient-and-39drh8tchg.pdf

Theoretical analysis of the sound-absorption coefficient and transmission loss for longitudinal clearances among the close-packed cylinders (Three kinds of estimation and experiment)

We performed a theoretical analysis on collection of equilateral triangular holes with consideration for sound wave attenuation within the tube and then calculated the sound-absorption coefficient and transmission loss. We then compared these results with experimental values. In the
 experiment, we measured the sound-absorption coefficient and transmission loss of a test sample using impedance measurement tubes with two and four microphones. We estimated the sound-absorption coefficient and transmission loss because of the dimensions of a collection of equilateral triangular
 holes through theoretical analysis and then compared these results with experimental values. In the present analysis, the propagation constant and characteristic impedance were introduced into a one-dimensional transfer matrix. Considering the effects of sound wave attenuation in the tubule
 from three-dimensional analysis, we derived the propagation constant and characteristic impedance. Values for the sound-absorption coefficient and transmission loss obtained through the analysis of holes as triangles rather than as circles gave calculation results closer to the experimental
 values. This is because this method more suitably simulates the effects of the boundary layer that occupies the space within the hole. The results show that the sound absorption coefficient and transmission loss of triangular honeycombs can be estimated with sufficient accuracy using only
 geometric dimensions and physical properties.

Comparison of estimated and measured sound-absorption coefficient and transmission loss by geometric dimensions of a collection of equilateral triangular holes of equilateral triangular holes

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Theoretical analysis of the sound-absorption coefficient and transmission loss for longitudinal clearances among the close-packed cylinders (Three kinds of estimation and experiment)

Fundamental study of acoustic leakage through a gap between gasket and flange surface

Comparison of estimated and measured sound-absorption coefficient and transmission loss by geometric dimensions of a collection of equilateral triangular holes of equilateral triangular holes