A Numerical Study on the Excitation of Guided Waves in Rectangular Plates Using Multiple Point Sources

Abstract

Ultrasonic guided waves are widely used to inspect and monitor the structural integrity of plates and plate-like structures, such as ship hulls and large storage-tank floors. Recently, ultrasonic guided waves have also been used to remove ice and fouling from ship hulls, wind-turbine blades and aeroplane wings. In these applications, the strength of the sound source must be high for scanning a large area, or to break the bond between ice, fouling and plate substrate. More than one transducer may be used to achieve maximum sound power output. However, multiple sources can interact with each other, and form a sound field in the structure with local constructive and destructive regions. Destructive regions are weak regions and shall be avoided. When multiple transducers are used it is important that they are arranged in a particular way so that the desired wave modes can be excited to cover the whole structure. The objective of this paper is to provide a theoretical basis for generating particular wave mode patterns in finite-width rectangular plates whose length is assumed to be infinitely long with respect to its width and thickness. The wave modes have displacements in both width and thickness directions, and are thus different from the classical Lamb-type wave modes. A two-dimensional semi-analytical finite element (SAFE) method was used to study dispersion characteristics and mode shapes in the plate up to ultrasonic frequencies. The modal analysis provided information on the generation of modes suitable for a particular application. The number of point sources and direction of loading for the excitation of a few representative modes was investigated. Based on the SAFE analysis, a standard finite element modelling package, Abaqus, was used to excite the designed modes in a three-dimensional plate. The generated wave patterns in Abaqus were then compared with mode shapes predicted in the SAFE model. Good agreement was observed between the intended modes calculated in SAFE and the actual, excited modes in Abaqus.

Selective Generation of Lamb Wave Modes in a Finite-Width Plate by Angle-Beam Excitation Method

“…A few studies have been conducted to selectively generate the Lamb wave mode in a finite-width plate. In one study, a selective excitation method using multiple point sources was numerically studied, and it was found that the performance of the proposed method varied with the number of point sources [ 13 ]. In another study, a mode selection method using phased array was investigated [ 14 ].…”

Improved Defect Detection Using Adaptive Leaky NLMS Filter in Guided-Wave Testing of Pipelines

“…The schematic of this setup is illustrated in Figure 6. This type of FEM synthesis of guided wave signals in pipes was developed in previous studies [37,[46][47][48][49][50]. The generated models have also been validated by confirming the accuracy of the received signals from both the device [50], and 3D laser vibrometer [46,47].…”

Mechanical and Microstructural Properties of A36 Marine Steel Subjected to Underwater Wet Welding

“…Recent work by Surojo et al [29] discussed the influence of the water flow and depth/location on welding performance using mechanical testing. Another possibility for extension of this work could involve marine vessels, e.g., the hull structure of a ship [30][31][32][33][34][35][36]. The subject is no longer on the material specimen scale, but the use of a down-scaled hull prototype or weld could be used to represent parts of the ship structure, such as the frame and side hull.…”