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Showing papers by "Prabhu Rajagopal published in 2021"


Journal ArticleDOI
TL;DR: The feasibility of detection of delamination is experimentally demonstrated, whose size is comparable to the ultrasonic wavelength with probability of detection better than 90% using <1% of the total number of samples required for conventional imaging, even under conditions wherein the SNR is as low as 5 dB.

75 citations


Journal ArticleDOI
TL;DR: In this paper, the authors developed a technique for estimating an aluminium/epoxy/aluminium lap shear joint stiffness using periodic permanent magnet electromagnetic acoustic transducers (PPM EMATs).

16 citations


Journal ArticleDOI
TL;DR: In this article, a method to quantify the interface shear stiffness, adhesive shear modulus and adhesive thickness in an aluminium-epoxy-aluminium joint is presented, where the dispersion analysis reveals that higher-order anti-symmetric modes are sensitive to all three parameters.

14 citations


Journal ArticleDOI
TL;DR: In this paper, a waveguide metamaterial rod is used as a mechanical acoustic filter for suppression of higher harmonic components in the measured signal, which is used for early stage material diagnosis in engineering, biomedicine, and health monitoring of critical engineering assets.
Abstract: Nonlinear ultrasonic guided waves are among the most promising new tools for early stage damage detection owing to their high sensitivity and long-range propagation features. However, signatures from instrumentation, transducers, and couplant effects create false positives mixing with the material- or defect-induced nonlinearities, leading to inaccurate measurements. Here, we propose a novel technique using a waveguide metamaterial rod, which acts as a mechanical acoustic filter for suppression of higher harmonic components in the measured signal. The proposed waveguide metamaterial consists of an array of flat axisymmetric ridges arranged periodically on the surface of the rod. It is experimentally demonstrated that the higher harmonic components are filtered when the proposed metamaterial rod is placed at the transmission side, thus removing unwanted nonlinearities from the received signal in a pitch-catch configuration. Furthermore, the application of this method is demonstrated by detecting a discontinuity in the workpiece through its nonlinear response enhanced using the metamaterial. This technique is attractive for early stage material diagnosis in engineering, biomedicine, and health monitoring of critical engineering assets.

13 citations


Journal ArticleDOI
TL;DR: In this paper, the influence of the absorptivity of the material surface during defect detection using LT and its influence in detecting surface-breaking cracks was investigated and the term Crack Thermal Contrast (CTC) was introduced to indicate the detectability of the surface crack.
Abstract: Laser thermography (LT) is one of the novel NDT methods for detecting surface-breaking cracks in metals. LT technique is well known for its non-contact nature and relatively fast-detection of surface defects for objects that are at room temperature. In LT, a continuous-wave (CW) laser is used to make a laser spot/line/area, which excites the sample under inspection to create local heating. Using optical mirrors, the spot is then rapidly made to move over the surface of the test sample. The temperature distribution over the sample due to the laser excitation is then monitored using an infrared (IR) thermal camera. This paper investigates the influence of the absorptivity of the material surface during defect detection using LT and its influence in detecting surface-breaking cracks. Six different materials were used under this study, i.e., Aluminum, Brass, Copper, mild Steel, Stainless Steel, and Titanium and with two surface conditions i.e., with and without black paint. 3D FEM numerical models were developed and validated with experiments for the different case studies for surface crack detection. The term Crack Thermal Contrast (CTC) is introduced to indicate the detectability of the surface crack and found to increase linearly with absorptivity of the material.

10 citations


Journal ArticleDOI
TL;DR: M-Hull is developed, a subsurface mapping AUV with a modular-split hull design that provides better manoeuvrability than a conventional torpedo-shaped vehicle and has more agility than an unconventional bio-inspired snake-like vehicle though their designs look similar.
Abstract: There is much need for autonomous underwater vehicles (AUVs) for inspection and mapping purposes. Most conventional AUVs use torpedo-shaped single-rigid hull, because of which their manoeuvrability is limited. Moreover, any increase in payload results in a larger hull size and the turning diameter, limiting its operation in constrained areas. As a solution to this problem, we develop M-Hull, a subsurface mapping AUV with a modular-split hull design that provides better manoeuvrability than a conventional torpedo-shaped vehicle. At the same time, it has more agility than an unconventional bio-inspired snake-like vehicle though their designs look similar. This approach makes it a hybrid solution between conventional torpedo-shaped AUVs and unconventional bio-inspired vehicles. We focus on improving the turning diameter during the mapping operation, and hence this paper concentrates on the dynamic aspects of the 2D turning motion of the vehicle. It will provide the relationship between turning speed, thrust, and joint torque requirements for the multi-hull underwater vehicle. Different turning modes are compared to choose an optimum turning configuration, and the critical speed is calculated for the vehicle’s safe operation. In the end, the modelling is verified using the experimental data. One can follow the method followed here for the 2D motion analysis of similar underwater vehicles.

5 citations


Journal ArticleDOI
TL;DR: The concentric-shell GRIN lens proposed in this paper has a simple design, and has a potential to be used in dynamic focusing without advanced lenses or electronic steering, but it is not suitable for the use in medical applications.

5 citations


Book ChapterDOI
01 Jan 2021
TL;DR: In this article, the authors present a methodology of rapidly estimating thickness of the steel members in the splash zone and deeper underwater zones using pulsed eddy current (PEC) without removing marine growth or insulation on a remotely operated robotic vehicle (ROV).
Abstract: Jacket-type steel members are widely used in near and offshore structures wherein tubular members are welded together to either form or protect the load-carrying member. Tubular joints are subject to damage as a result of fatigue, marine growth and corrosion from the environment. These structures are conventionally inspected for loss of wall thickness and pitting to prevent catastrophic damage and improve failure prediction systems using the conventional ultrasonic testing (UT). However, especially in the case of marine structures, direct access to the structure is hindered by marine growth, insulation or coating. Surface preparation is an essential step before conventional nondestructive testing modalities can be used. Marine growth is removed using powered brushes, high-pressure water jets or in some cases, manually using chisels causing the procedure to be time consuming and expensive. An alternative technology which can be used for wall thickness estimation without removing marine growth (that is thicker than 10 mm) is pulsed eddy current (PEC) which uses a stepped input signal to detect wall-thinning areas. In this paper, the authors present a methodology of rapidly estimating thickness of the steel members in the splash-zone and deeper underwater zones using PEC without removing marine growth or insulation on a remotely operated robotic vehicle (ROV). The results are compared to the conventional ultrasonic testing methodology performed both by professional divers and an ROV using a commercially available 2.25 MHz ultrasonic transducer. Key advantages and limitations of the ROV-based PEC system are discussed in detail.

3 citations


Journal ArticleDOI
TL;DR: In this article, a feasibility study aimed to detect subsurface white etching area (WEA) formation using ultrasonic surface (Rayleigh) waves, using impact loading experiments at 2'GPa contact pressure with loading frequency 4.5'Hz on AISI 52100 bearing steel balls by varying test durations.

3 citations


Journal ArticleDOI
TL;DR: In this paper, the potential of higher frequency ultrasonic guided wave mode cluster (HOMC) waves to be used for remote inspection of notch defects in plate-like structures is investigated, at room and elevated temperatures.
Abstract: The potential of higher frequency ultrasonic guided wave mode cluster (HOMC) waves to be used for remote inspection of notch defects in plate-like structures is investigated, at room and elevated temperatures. Quantitative studies of HOMC interaction with notch defects ranging from 5% to 50% of plate thickness are performed using 2D finite element simulations, and are validated by controlled experiments performed, firstly at room temperature. Analysis using reciprocity-based relations is used to uncover for the first time, how the constituent modes of HOMC play a vital role in their scattering processes. Further experiments are used to show that the results are stable up to 300 C, thereby demonstrating the feasibility of short range higher-resolution remote inspection of notch defects using non-dispersive higher frequency mode clusters in industrial conditions.

3 citations


Journal ArticleDOI
TL;DR: In this paper, the authors proposed a hermetically sealable device, consisting of charged linear and nonlinear membranes driven in the gigahertz range in vacuum setting, as a source of antibunched single phonons.
Abstract: This paper proposes a novel design for a hermetically sealable device, consisting of charged linear and nonlinear membranes driven in the gigahertz range in vacuum setting, as a source of antibunched single phonons. Constraints for effecting phonon antibunching are found using the stationary Liouville–von Neumann master equation. Using analytical calculations and material and geometry optimization, we show that sizes of the proposed system can be upscaled to the near-micrometer range in a trade-off with the system operating temperature. The results are significant to realize quantum phononics, which has much promise as a modality for sensing and computing applications.

Proceedings ArticleDOI
16 Jul 2021
TL;DR: In this paper, a nonlinear dynamic model of the underwater vehicle is discussed and a sliding mode control for the heading and diving plane manoeuvres of AUV is proposed, which is validated through simulation using a dynamic and kinematic model developed.
Abstract: This paper presents the dynamic modelling and control design of an underactuated, Autonomous Underwater Vehicle (AUV). The motion dynamics of an AUV are coupled and nonlinear, which makes the design of a control law a challenging task. In this work, a nonlinear dynamic model of the underwater vehicle is discussed. The paper further proposes the design of a sliding mode control for the heading and diving plane manoeuvres of AUV. The stability of the designed controller is validated through simulation using a dynamic and kinematic model developed. The dynamic model and control policy proposed in this work is generic and thus not restricted to any particular underwater vehicle.

Book ChapterDOI
01 Jan 2021
TL;DR: A review of the recent developments in acoustic and elastic wave (ultrasonic) metamaterials and the exciting opportunities they offer for the NDE community can be found in this paper.
Abstract: This paper reviews the recent developments in acoustic and elastic wave (ultrasonic) metamaterials and the exciting opportunities they offer for the NDE community. An overview of the physics and fabrication of phononic crystals and acoustic and elastodynamic metamaterials is presented. Results on manipulation for bulk and guided ultrasound using various metamaterial concepts studied or developed at the authors’ laboratory are highlighted. The paper concludes with an outline for the exciting prospects ahead for NDE and SHM using such metamaterials.

Proceedings ArticleDOI
01 Jan 2021
TL;DR: In this paper, the authors demonstrate the visualization of ultrasonic wave propagation in a metallic plate using a surface-bonded fiber Bragg grating sensor and non-contact excitation of the desired guided mode.
Abstract: We experimentally demonstrate the visualization of ultrasonic wave propagation in a metallic plate using a surface-bonded fiber Bragg grating sensor and non-contact excitation of the desired guided mode.

Posted Content
TL;DR: In this article, a novel T-BERT framework is proposed to show the enhanced performance obtainable by combining latent topics with contextual BERT embeddings, achieving an accuracy of 90.81% on sentiment classification using BERT with the proposed approach.
Abstract: Sentiment analysis (SA) has become an extensive research area in recent years impacting diverse fields including ecommerce, consumer business, and politics, driven by increasing adoption and usage of social media platforms. It is challenging to extract topics and sentiments from unsupervised short texts emerging in such contexts, as they may contain figurative words, strident data, and co-existence of many possible meanings for a single word or phrase, all contributing to obtaining incorrect topics. Most prior research is based on a specific theme/rhetoric/focused-content on a clean dataset. In the work reported here, the effectiveness of BERT(Bidirectional Encoder Representations from Transformers) in sentiment classification tasks from a raw live dataset taken from a popular microblogging platform is demonstrated. A novel T-BERT framework is proposed to show the enhanced performance obtainable by combining latent topics with contextual BERT embeddings. Numerical experiments were conducted on an ensemble with about 42000 datasets using this http URL platform with a hardware configuration consisting of Nvidia Tesla K80(CUDA), 4 core CPU, 15GB RAM running on an isolated Google Cloud Platform instance. The empirical results show that the model improves in performance while adding topics to BERT and an accuracy rate of 90.81% on sentiment classification using BERT with the proposed approach.

Journal ArticleDOI
01 Feb 2021
TL;DR: In this paper, a screw-convex screw conveyor based system was proposed to scoop crude oil sludge from the floor of oil storage tanks using a worm drive and a bearing on both sides driven by a waterproof motor.
Abstract: This paper presents the design optimization and testing of a novel screw conveyor based system to scoop crude oil sludge from the floor of oil storage tanks This proposed new system consists of a screw conveyor mounted on a ‘C’ shaped casing with a bearing on both sides driven by a waterproof motor through a worm drive A novel mathematical model is developed to help the design of a screw conveyor for a maximum amount of sludge scooping per turn, and numerical simulations are performed using computational fluid dynamics to visualize the flow of material particles in various possible designs of the system The proposed mechanism was 3D printed, and laboratory tests were conducted to quantify the amount of sludge removal by the different designs of the screw Optimized design of a mechanism screw with a radius ratio of 040 and a pitch ratio of 015 scoops up to a maximum of 588 kg hr of material at 110 rev min