Modal power flow analysis of a damaged plate

Pao Yue-kong Library Electronic Theses Database

Modal power flow analysis of a damaged plate

 

Author: Liu, Xiao
Title: Modal power flow analysis of a damaged plate
Degree: M.Sc.
Year: 2010
Subject: Hong Kong Polytechnic University -- Dissertations
Modal analysis
Plates (Engineering) -- Vibration.
Department: Dept. of Mechanical Engineering
Pages: xii, 130 leaves : ill. ; 30 cm.
InnoPac Record: http://library.polyu.edu.hk/record=b2353058
URI: http://theses.lib.polyu.edu.hk/handle/200/5669
Abstract: Variation of the modal reactive power distribution of a damaged plate is analyzed theoretically and experimentally. Large variation of local reactive power flow in or around the damage region of a plate under resonant vibration is related to the change of strain and kinetic energies in the damage region. Feasibility of damage identification based on the detection of this local variation of modal reactive power flow in a plate is validated. Compared with the damage identification techniques based on the determination of the active power flow in a damaged plate, the proposed method only requires data of a vibration mode shape of the structure and it is easier to apply in practice. A scanning Laser Doppler Vibrometer is implemented to measure vibration mode shapes of a damaged plate. According to the theory of the power flow and energy distribution of a vibration mode of a damaged plate, the measurement data of vibration mode shapes require higher order derivatives and therefore noise reduction in deriving the reactive power flow and energy is crucial to the success of the detection method. A wavelet based denoising method is presented and applied during the differentiation of the measured mode shape data to suppress the amplification of noise signal. Three common types of damage have been tested for identification, the first and the second with a region of reduced stiffness and a small hole in the plate respectively, while the third with a region of loosed boundary condition. Numerical tests show that the proposed method is effective for all types of damage. Experiments illustrate that two types of damage with a region of reduced stiffness and loosed boundary condition are validated and consistent with the prediction as depicted.

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