Prabhu Rajagopal

Bio: Prabhu Rajagopal is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Ultrasonic sensor & Guided wave testing. The author has an hindex of 18, co-authored 129 publications receiving 1035 citations. Previous affiliations of Prabhu Rajagopal include Imperial College London & Indian Institutes of Technology.

Comparison of bio-inspired flapping foil propulsion systems with rotary propulsion

Abstract: Conventional rotary thrusters used in underwater Remotely Operated Vehicles (ROV) suffer from disadvantages such as high noise, entangling with floating objects and limited efficiency. Our group has studied bio-inspired propulsion with a single caudal fin which overcomes some of these disadvantages. However, it still faces some problems such as low thrust density (thrust generated per unit volume of the thruster), pitch/yaw and centre of mass (COM) oscillations in the body increasing the energy cost of transport. The solution being proposed is a novel dual flapping foil arrangement actuated using a single motor which tackles the limitations of single flapping foil. Comparison of efficiency, maximum thrust and thrust density has been performed between single and dual flapping foil propulsion. Also, this solution is benchmarked against commercially available rotary thrusters. The results showed that thrust density of bioinspired propulsion was not at par with rotary thrusters. However, the efficiency obtained was comparable.

Thickness Estimation of Marine Structures Using an ROV-Based Pulsed Eddy Current Technique

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.

Numerical Study on Swimming Performance Based on Flapping Orientations of Caudal Fins for Bio-robotic Systems

Abstract: Set in the context of the development of bioinspired robotics systems, this paper seeks to understand the influence of the choice of the flapping orientation of fins on the propulsive performance of small underwater vehicles. In particular, the thunniform mode of Body and/or Caudal Fin (BCF) propelled systems is studied. This research is motivated by the fact that not much literature is available on the influence of flapping orientation of marine organisms and a number of mechanisms are found in nature. Dorso-ventral flapping with a positive metacentric height is shown to yield better self-stabilizing effects and lesser energy consumption compared to sideways flapping. Moreover, with dorso-ventral flapping, the choice of metacentric height could lead to the possibility of adjusting the body's rotational oscillation amplitudes to positively affect the downstream fluid interactions for the caudal fin. This is not possible with sideways flapping where the designer would be forced to change the flapping kinematics or the body shape in the sagittal plane, to adjust the body oscillation amplitudes. While the main body of results are obtained using simulations for underwater vehicle dynamics with coefficients of the REMUS underwater vehicle, stability analysis for a generalised case is also presented.

Probability and Statistical Inference

Abstract: The Foundations of Statistics By Prof. Leonard J. Savage. (Wiley Publications in Statistics.) Pp. xv + 294. (New York; John Wiley and Sons, Inc.; London: Chapman and Hall, Ltd., 1954.) 48s. net.

X-ray computed tomography for additive manufacturing: a review

Abstract: In this review, the use of x-ray computed tomography (XCT) is examined, identifying the requirement for volumetric dimensional measurements in industrial verification of additively manufactured (AM) parts. The XCT technology and AM processes are summarised, and their historical use is documented. The use of XCT and AM as tools for medical reverse engineering is discussed, and the transition of XCT from a tool used solely for imaging to a vital metrological instrument is documented. The current states of the combined technologies are then examined in detail, separated into porosity measurements and general dimensional measurements. In the conclusions of this review, the limitation of resolution on improvement of porosity measurements and the lack of research regarding the measurement of surface texture are identified as the primary barriers to ongoing adoption of XCT in AM. The limitations of both AM and XCT regarding slow speeds and high costs, when compared to other manufacturing and measurement techniques, are also noted as general barriers to continued adoption of XCT and AM.