Date of Award

2016

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Ocean Engineering

First Advisor

Sau-Lon James Hu

Abstract

The overall objective of this dissertation is to propose a quick and accurate method of updating transducer models. When one makes measurements on a piezoelectric transducer, oftentimes only the impedance function is measured as the experimental data. Thus, to perform model updating for transducers, two major tasks will be covered: (i) developing and verifying an efficient method for estimating the electric impedance function of a transducer, and (ii) developing and testing a FE model updating method for piezoelectric transducers.

The proposed method to estimate the impedance function of a transducer is a Laplace domain method. It expresses both the voltage and current in their partial-fraction forms in the Laplace domain, and obtains the impedance function of the transducer from the ratio of the voltage and current. The Prony-SS method is employed to extract the poles and residues of the voltage and current signals. Compared with traditional methods, the proposed method uses the transient signals, and will not suffer any leakage problems or resolution issues. In addition, this method requires only very short signals to obtain the impedance function, and is excellent for rejecting noise.

This proposed model-updating method is a multi-physics FE model-updating method, including the correction of the elastic material properties based on a short-circuit model, and the correction of dielectric and piezoelectric parameters based on an open-circuit model. The fundamental updating algorithm employed in both steps is the cross-model cross-mode (CMCM) method. In addition to its accuracy and efficiency, this method has the advantages of both the direct matrix methods and indirect physical property-adjustment methods. Implementing the CMCM algorithm requires a knowledge of both the measured modal frequencies and the corresponding mode shapes, but a measured impedance function could provide only modal frequencies for short- and open-circuit transducers. When dealing with the incomplete modal information, an iterative procedure is taken. In each iteration, the “measured” mode shapes are approximated by the mode shapes obtained from the previous iteration’s updated FE model.

In this study, we employed a tube transducer, which is made of piezoceramic material, to develop and test new methods of estimating the impedance function and updating piezoelectric constitutive properties. Both computer simulations and lab experiments have been conducted to verify the accuracy and efficiency of the proposed methods.

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