Sivaramanivas Ramaswamy

Finite Element Modeling of Guided Wave Propagation in Plates

This paper aims at developing a numerical model for guided wave propagation in plates and the interaction of modes with defects using Finite Element Modeling (FEM). Guided waves propagate as extensional, flexural and torsional waves. Theoretically, these modes are infinite in number, but only some of these propagate and the others are attenuated. The dispersion curves for a structure reveal the plausibility of these modes. In this paper, FEM is used to examine interaction of first few symmetric and anti‐symmetric modes independently with the cracks of various sizes in a plate. A time‐frequency representation of the acquired guided wave mode signals will be discussed to show the mode sensitivity with crack size.

Sensitivity of Time‐Frequency Representations in the Presence of Noise in Guided Waves NDE

Time frequency representation (TFR) of ultrasonic signals plays an important role in describing the propagation and dispersive effects in thin walled structures. In this paper, Generalized time‐frequency representations viz. the Wigner‐Ville distribution, Choi‐William distribution and Short‐Time Fourier Transform are discussed in the context of mode analysis. A comparison on the estimation of various modes and the obscuring interference terms, due to bilinear structure of TFRs, is presented for lamb waves in aluminum plates. Studies on the performance of TFRs in the presence of strong colored noise are presented.

Finite Element Analysis of Capacitive Micromachined Ultrasonic Transducer (CMUT) for NDE Applications

This paper presents a comparison of three Finite Element approaches for modeling the behavior of a Capacitive Micromachined Ultrasonic Transducer (CMUT). CMUTs have become very popular over the last decade because of the comparable bandwidth, sensitivity and dynamic range with its piezoelectric counterparts. The ease of fabrication is an added advantage. Modeling of CMUTs is a coupled physics problem, which involves solving Electrostatics and Structural interactions simultaneous. Finite Element models of the CMUT are constructed using the commercial code ANSYS (9.0). Three different approaches of solving the coupled field problem are discussed and the results are compared for resonance frequency, collapse voltage, capacitance and electromechanical coupling coefficient. The approaches discussed involve sequentially coupled‐field analysis, direct coupled‐field analysis and reduced order modeling. Detailed results have been presented for the effect of variation in geometrical factors as predicted by the thre...