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Research Papers: Fluid-Structure Interaction

Experimental Validation of Inverse Techniques for the Remote Identification of Impact Forces in Gap-Supported Systems Subjected to Local and Flow Turbulence Excitations

[+] Author and Article Information
Xavier Delaune

 Laboratoire d’Etudes de Dynamique, Commissariat à l’Energie Atomique et aux Energies Alternatives, CEA, DEN, DM2S, SEMT, F-91191 Gif-sur-Yvette, Francexavier.delaune@cea.fr

Philippe Piteau

 Laboratoire d’Etudes de Dynamique, Commissariat à l’Energie Atomique et aux Energies Alternatives, CEA, DEN, DM2S, SEMT, F-91191 Gif-sur-Yvette, France

Vincent Debut, Jose Antunes

Applied Dynamics Laboratory, Instituto Tecnologico e Nuclear, ITN/ADL, 2686 Sacavem, Portugal

J. Pressure Vessel Technol 133(5), 051301 (Jul 11, 2011) (9 pages) doi:10.1115/1.4002926 History: Received April 16, 2010; Revised August 31, 2010; Published July 11, 2011; Online July 11, 2011

Predictive computations of the nonlinear dynamical responses of gap-supported tubes subjected to flow excitation have been the subject of active research. Nevertheless, experimental results are still necessary for validation of the theoretical predictions as well as for asserting the integrity of field components. Because carefully instrumented test tubes and tube-supports are seldom possible, due to space limitations and to the severe environment conditions, there is a need for robust techniques capable of extracting relevant information from the actual vibratory response data. Although at the present time such analysis is overambitious, as far as the multisupported tube bundles of real-life components are concerned, the same instrumentation difficulties frequently apply in the case of laboratory test rigs. Therefore, the subject of this paper is of practical significance even in the more modest realm of laboratory experiments. The knowledge of the dynamical contact/impact (vibro-impact) forces is of paramount significance, and also the tube/support gaps. Following our previous studies in this area using wave-propagation techniques (De Araújo et al., 1998; Antunes et al., 1998; Paulino et al., 1999), we recently applied modal methods for extracting such information. Based on numerically simulated time-domain vibro-impact responses, the dynamical support forces, as well as the vibratory responses at the support locations, were identified from one or several vibratory responses at remote locations, from which the support gaps could also be inferred (Delaune et al., 2010). Also recently, for the related problem of friction force identification on bowed strings, preliminary experiments have shown the feasibility of these identification techniques (Debut et al., 2010). In the present paper, the modal identification techniques developed by Delaune et al. (2010) and Debut et al. (2010) are tested using an experimental rig built at Commissariat à l’Energie Atomique et aux Energies Alternatives (CEA/Saclay), consisting of a randomly excited clamped-free beam which impacts on an intermediate gap-support. Identification of the impact force, as well as of the beam motion at the gap-support, is achieved based on remote measurements of the beam response provided by two accelerometers. A significant feature of the experimental identifications presented in this paper is that, beyond the results obtained under a point-force shaker excitation, we test here an original technique to identify the gap-supported reactions in flow-excited systems, which was recently introduced by Delaune et al. (2010). As for most inverse problems, the identification results may prove sensitive to both noise and modeling errors. Therefore, regularization techniques discussed by Delaune et al. (2010) are used to mitigate the effects of unmeasured noise perturbations. Overall, the experimentally identified results compare reasonably well with the measured contact forces and motions at the gap-supports. Actually, even if our identifications are not immaculate at the present time, they remain nevertheless quite usable.

Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Procedure for sources identification

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Figure 2

Experimental vibro-impact system. (a) Point-excitation by a shaker and (b) distributed flow turbulence excitation.

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Figure 3

Experimental rig. (a) General view and (b) detail of the instrumented gap-support.

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Figure 4

Transfer functions H(xc,x1,ω) and H(xc,x2,ω) built from the experimentally identified modal parameters

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Figure 5

Acceleration measurements under shaker excitation with a gap-support (time domain and spectra)

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Figure 6

Shaker excitation with a gap-support. Measured and identified impact force and shaker excitation force.

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Figure 7

Shaker excitation with a gap-support. Measured and identified displacement at the gap-support.

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Figure 8

Condition number of transformation matrix [M(a)(ω)], SVD decomposition and filtering

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Figure 9

Acceleration measurements under shaker excitation with a no-gap-support (time domain and spectra)

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Figure 10

Shaker excitation with a no-gap-support. Measured and identified impact force and shaker excitation force.

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Figure 11

Acceleration measurements under turbulence excitation with a gap-support (time domain and spectra)

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Figure 12

Turbulence excitation with a gap-support. Measured and identified impact force and equivalent generalized excitation force.

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Figure 13

Turbulence excitation with a gap-support. Measured and identified displacement at the gap-support.

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Figure 14

Condition number of transformation matrix [M(b)(ω)], SVD decomposition and filtering as a function of frequency

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Figure 15

Acceleration measurements under turbulence excitation with a no-gap-support (time domain and spectra)

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Figure 16

Turbulence excitation with a no-gap-support. Measured and identified impact force and equivalent generalized excitation force

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