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Research Papers

Experimental Study of a Vibrating Disk Submerged in a Fluid-Filled Tank and Confined With a Nonrigid Cover

[+] Author and Article Information
David Valentín

Centre for Industrial Diagnostics and
Fluid Dynamics (CDIF),
Polytechnic University of Catalonia (UPC),
Avinguda Diagonal, 647 ETSEIB,
Barcelona 08028, Spain
e-mail: david.valentin@mf.upc.edu

Alexandre Presas

Centre for Industrial Diagnostics and
Fluid Dynamics (CDIF),
Polytechnic University of Catalonia (UPC),
Avinguda Diagonal, 647 ETSEIB,
Barcelona 08028, Spain
e-mail: alex.presas@mf.upc.edu

Eduard Egusquiza

Centre for Industrial Diagnostics and
Fluid Dynamics (CDIF),
Polytechnic University of Catalonia (UPC),
Avinguda Diagonal, 647 ETSEIB,
Barcelona 08028, Spain
e-mail: egusquiza@mf.upc.edu

Carme Valero

Centre for Industrial Diagnostics and
Fluid Dynamics (CDIF),
Polytechnic University of Catalonia (UPC),
Avinguda Diagonal, 647 ETSEIB,
Barcelona 08028, Spain
e-mail: valero@mf.upc.edu

Mònica Egusquiza

Centre for Industrial Diagnostics and
Fluid Dynamics (CDIF),
Polytechnic University of Catalonia (UPC),
Avinguda Diagonal, 647 ETSEIB,
Barcelona 08028, Spain
e-mail: monica.egusquiza@upc.edu

1Corresponding author.

Contributed by the Technical Committee on Vibration and Sound of ASME for publication in the JOURNAL OF VIBRATION AND ACOUSTICS. Manuscript received July 25, 2016; final manuscript received September 27, 2016; published online February 3, 2017. Assoc. Editor: Marco Amabili.

J. Vib. Acoust 139(2), 021005 (Feb 03, 2017) (11 pages) Paper No: VIB-16-1370; doi: 10.1115/1.4035105 History: Received July 25, 2016; Revised September 27, 2016

Determining the dynamic response of submerged and confined disklike structures is of interest in engineering applications, such as in hydraulic turbine runners. This dynamic response is heavily affected by the added mass and damping as well as the proximity of solid boundaries. These solid boundaries are normally considered as completely rigid in theoretical or numerical calculations, however, this assumption is not always valid. Some hydraulic turbines have noncompletely stiff casings, which can modify the dynamic response of the runner itself, affecting specially its natural frequencies and damping behavior. To determine the influence of noncompletely rigid nearby surfaces in the dynamic behavior of a submerged structure, an experimental test rig has been constructed. This test rig is based on a disk attached to a shaft and confined in a tank covered with two different casings with different mass and stiffness. For both covers and different disk to cover distances, natural frequencies and damping ratios of the disk have been obtained experimentally. Accelerometers installed on the disk and covers as well as pressure sensors are used for this purpose. Results obtained for all the cases are discussed in detail and compared with a simplified theoretical model.

FIGURES IN THIS ARTICLE
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Copyright © 2017 by ASME
Topics: Fluids , Disks , Vibration
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References

Figures

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Fig. 1

Example of a hydraulic turbine and detail of the runner

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Fig. 2

Disk submerged in a completely rigid container filled with fluid

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Fig. 3

Disk submerged in a tank with a nonrigid cover

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Fig. 4

(a) Natural frequency of the disk in the nonrigid case (fn,nonrigid) over the natural frequency in the rigid case (fn,rigid) against the normalized distances (H1/hD) and (H2/hD) for different values of α. (b) AVMI factor in the nonrigid case (βn,nonrigid) over the AVMI factor in the rigid case (βn,rigid) against the normalized distances (H1/hD) and (H2/hD) for different values of α (n = 2).

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Fig. 5

Test rig description: sensors disposition over both thin and thick covers

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Fig. 6

Experimental mode-shapes of the disk in air and submerged in water with the two different covers tested. FRF of AD0 against the force applied by the hammer: H1 = 47 mm and H2 = 60 mm.

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Fig. 7

Experimental mode-shapes of both covers in air and with water. FRF of AC0 against the force applied by the hammer: H1 = 47 mm and H2 = 60 mm.

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Fig. 8

Amplitude ratio (α) between the vibration of the cover and the vibration of the disk for each natural frequency of the disk

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Fig. 9

Natural frequency in water (fw) over the natural frequency in the air (fa) for different distances to the rigid bottom surface (H2/hD) and the cover (H1/hD) for the thick cover (a) and the thin cover (b), as well as AVMI factors for the thick cover (c) and the thin cover (d)

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Fig. 10

FRFs of AD0 against the hammer for different distances of the disk to the thick cover (n = 2, 3, and 6)

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Fig. 11

FRFs of AD0 against the hammer for different distances of the disk to the thin cover (n = 2, 3, and 4)

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Fig. 12

Damping ratio in water (ξw) over the damping ratio in air (ξa) for different distances to the rigid bottom surface (H2/hD) and the cover (H1/hD) (a) thick cover and (b) thin cover

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Fig. 13

FRFs of P0 and P90 using the hammer signal as a reference H1 = 10 mm (a) thick cover and (b) thin cover

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Fig. 14

Normalized pressure amplitude for different distances to the rigid bottom surface (H2/hD) and the cover (H1/hD) n = 2 (a) thick cover and (b) thin cover

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