VIBRATION ANALYSIS OF FLEXIBLE NARROW TUBES USING ACOUSTIC EXCITATION

Hase, Aniket A and Akiwate, Deepak C and B, Venkatesham and et al, . (2018) VIBRATION ANALYSIS OF FLEXIBLE NARROW TUBES USING ACOUSTIC EXCITATION. In: Western Pacific Commission for Acoustics (WESPAC), 11-15 November 2018, New Delhi, India.

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Abstract

Thin flexible narrow tube structures are used widely in various applications and industries such as, medical devices, mechanical structures, wire protections, marine applications, food processing and superconducting transmission lines. Vibration analysis of thin narrow flexible structures is necessary to understand the dynamic behaviour under specified boundary conditions and external load. Primarily, dynamic characteristics of a structure are expressed in terms of modal parameters such as natural frequencies, mode shapes and damping. The flexible narrow tube structures have very thin walls making measuring modal parameters a quite challenging task using contact type excitation methods such as shaker or impact hammer. Similar challenges exist for measuring vibration response on thin walls using contact type sensor such as accelerometer. So, the present study discusses considering acoustic source as vibration excitation and laser vibrometer as a vibration response measurement device. An experimental test setup is developed to measure modal parameters using an impedance tube. The impedance tube has speaker at one end while another end is exposed to thin narrow tubes. Acoustic excitation is generated using a speaker in the interested frequency range. Laser vibrometer is used to pick up response of tube wall at the same instance. The experiments are carried out under free-free boundary conditions and quiet surrounding environment was maintained to minimize effect of background noise. Modal parameters are extracted from the measured Frequency Response Function (FRF). Natural frequency obtained from experimental method for thin flexible narrow tubes are validated with Finite Element Method (FEM) results. In FEM environment, classical eigen value problem is solved using Block-Lanczos modal extraction method where sparse matrix solver is used. In order to examine the effect of geometrical properties, samples with varying diameter and length are considered for study. The results shown in this paper help in characterizing vibration response of thin structures like mechanical filters and thin acoustic metamaterials, where usage of traditional contact-type excitation, as well as contact-type sensors is not feasible to use

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