There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Power ultrasound and its applications: A state-of-the-art review.

Ultrasonic guided wave (UGW) is one of the most commonly used technologies for non-destructive evaluation (NDE) and structural health monitoring (SHM) of structural components. Because of its excellent long-range diagnostic capability, this method is effective in detecting cracks, material loss, and fatigue-based defects in isotropic and anisotropic structures. The shape and orientation of structural defects are critical parameters during the investigation of crack propagation, assessment of damage severity, and prediction of remaining useful life (RUL) of structures. These parameters become even more important in cases where the crack intensity is associated with the safety of men, environment, and material, such as ship’s hull, aero-structures, rail tracks and subsea pipelines. This paper reviews the research literature on UGWs and their application in defect diagnosis and health monitoring of metallic structures. It has been observed that no significant research work has been convened to identify the shape and orientation of defects in plate-like structures. We also propose an experimental research work assisted by numerical simulations to investigate the response of UGWs upon interaction with cracks in different shapes and orientations. A framework for an empirical model may be considered to determine these structural flaws.

Structural Health Monitoring (SHM) and Determination of Surface Defects in Large Metallic Structures using Ultrasonic Guided Waves.

8. Review the internal auditors’ audit needs assessment, strategy and programme; consider major findings of internal audit investigations and management's response, and any other matters the external auditors may wish to discuss (in the absence of management where necessary); and promote coordination between the internal and external auditors. The Committee will ensure that the resources made available for internal audit are sufficient to meet the College’s needs.

留学体験記 (Imperial College London)

Bubble interactions and bursting behaviors near a free surface

https://bura.brunel.ac.uk/bitstream/2438/15975/4/Fulltext.pdf

Numerical modelling of acoustic pressure fields to optimize the ultrasonic cleaning technique for cylinders.

Less attention has been given to the inspection using the first longitudinal guided wave mode due to its attenuative and dispersive properties at commonly used ultrasonic guided waves (UGWs) operating frequency region (20–100 kHz). However, the first longitudinal guided wave mode has higher flaw sensitivity due to having a shorter wave length and having higher number of non-axisymmetric wave modes at a given frequency. This enhances the capabilities of advanced UGW techniques which require higher number of non-axisymmetric modes. This study has been performed to investigate the potential of mode purity and flaw sensitivity of the first longitudinal guided wave mode compared with other axisymmetric modes in the UGW operating frequency region. Numerical and experimental investigation have been conducted to investigate pure excitation and flaw sensitivity of the first longitudinal guided wave mode. It has been validated that the first longitudinal guided wave mode can be used in the UGW inspection effectively in isolation by adopting transducers with out-of-plane vibration. This reduces the cost and the weight of the UGW inspection tooling. The flaw sensitivity of the first longitudinal guided wave mode has been investigated by aid of an empirically validated UGW focusing technique. Under the studied conditions in this paper, the first longitudinal guided wave mode has $\sim5$ times higher flaw sensitivity compared with the second longitudinal guided wave mode and $\sim 2.5$ times higher than the first torsional guided wave mode. This enhances the capability of UGW flaw detection and sizing.

/pdf/inspection-of-cylindrical-structures-using-the-first-3a7t8yt7b2.pdf

Inspection of Cylindrical Structures Using the First Longitudinal Guided Wave Mode in Isolation for Higher Flaw Sensitivity

Ultrasonic guided waves (UGW) can be used to inspect and monitor a structure from a single test location. Piezoelectric transducers are commonly dry-coupled with force to the surface of the waveguide in order to excite UGWs. These UGWs propagating within the waveguide will interact and reflect from known features, thus possible damage could be detected. In this paper, the interaction of UGWs with piezoelectric transducers is reported and investigated. A Finite Element Analysis (FEA) approach has been used to conduct a parametric study in order to quantify the effect of the waveguide diameter on the guided wave response. Laboratory experiments are carried out to measure the effect of the force on the dry-coupled piezoelectric transducers and the corresponding guided wave response, including reflections and mode conversions. A test rig is used to apply and measure the force on the piezoelectric transducers. For verification, a 3D Laser Doppler Vibrometry (3D-LDV) scan is performed on the waveguide in order to quantitatively identify the modes of interest. The conclusions reached this paper, particularly with respect to the quantification of the wave mode properties, lead to useful recommendations which may contribute to field inspection scenarios.

/pdf/investigation-of-ultrasonic-guided-waves-interacting-with-586sycs7cs.pdf

Investigation of Ultrasonic Guided Waves Interacting With Piezoelectric Transducers

Inspection of Pipelines Using the First Longitudinal Guided Wave Mode

The application of the fundamental shear-horizontal wave mode for guided wave structural health monitoring is undoubtedly beneficial due to its nondispersive characteristics. Existing guided wave shear mode transducers are rigid and brittle, because of these characteristics, bonding them to irregular surfaces (i.e., curved surfaces) is challenging. There is a huge market interest in the development of a flexible shear mode transducer, which eases the transducer bonding process onto irregular surfaces and improves the surface contact between the transducer and the structure. This study presents a flexible shear mode transducer for structural health monitoring using low-frequency guided waves (20–120 kHz). The proposed transducer is manufactured using piezoceramic, and based on the results of this study, it exhibits the directional excitation of fundamental shear-horizontal mode at 20–120 kHz. Finite element analysis and laboratory experiments were conducted to study the behavior of the proposed transducer. Field trials were conducted on a liquid storage tank with an undulated surface (due to corrosion). The performance of the proposed transducer is also compared to the commercially available macro fiber composite transducers. The proposed transducer was driven by the industrialized ultrasonic guided wave inspection system; Teletest Focus+ in line with the application of tank floor inspection using ultrasonic guided waves.

/pdf/flexible-shear-mode-transducer-for-structural-health-4uqris4lxm.pdf

Premesh Shehan Lowe

Papers

Numerical modelling of acoustic pressure fields to optimize the ultrasonic cleaning technique for cylinders.

Inspection of Cylindrical Structures Using the First Longitudinal Guided Wave Mode in Isolation for Higher Flaw Sensitivity

Investigation of Ultrasonic Guided Waves Interacting With Piezoelectric Transducers

Inspection of Pipelines Using the First Longitudinal Guided Wave Mode

Flexible Shear Mode Transducer for Structural Health Monitoring Using Ultrasonic Guided Waves