Other affiliations: Indian Institutes of Technology
Bio: Santhosh Ravichandran is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topic(s): Screw conveyor & Flapping. The author has an hindex of 2, co-authored 7 publication(s) receiving 29 citation(s). Previous affiliations of Santhosh Ravichandran include Indian Institutes of Technology.
01 Apr 2018-Ocean Engineering
TL;DR: Numerical simulations are performed assuming laminar flow and the underlying mechanisms and the cause for high thrust and power consumption are discussed in detail, with more focus on relating such parameters directly with the geometrical features such as the amount of forking and fin leading edge angle.
Abstract: Biomimetic caudal fin propulsion systems are a topic of growing interest recently. However, the choice of a particular caudal fin shape for a given robotized underwater vehicle is not straightforward. In order to address this problem, numerical simulations are performed assuming laminar flow, considering the operational regimes of small underwater vehicles. The numerical models are validated against results from literature and then used to compare the propulsive performance of caudal fin shapes ranging from a rectangular fin to a highly forked tail with various combinations of geometric parameters. The optimal shape of the tail based on propulsive efficiency is shown to exist between these two extremes. The presence of leading edge vortices in caudal fins is also shown to have an important role in achieving propulsive performance. The underlying mechanisms and the cause for high thrust and power consumption are discussed in detail with more focus on relating such parameters directly with the geometrical features such as the amount of forking and fin leading edge angle. Researchers can use these insights to arrive at optimal designs for small robotic vehicles with flapping fin-like propulsion, as the relations between geometric features and swimming performance are clearly brought out.
02 Jul 2019
TL;DR: Dorso-ventral flapping with a positive metacentric height is shown to yield better self-stabilizing effects and lesser energy consumption compared to sideways flapping, and stability analysis for a generalised case is presented.
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.
TL;DR: A key feature of this design is that the reconfigurability is achieved without additional actuators - helpful in the development of autonomous swarm robots with good maneuverability and efficiency.
Abstract: Maneuverability and propulsive efficiency are of much interest in autonomous underwater robots. In this paper, we present a novel underwater robot design with two reconfigurable and detachable swimming modules that would be capable of offering both maneuverability and propulsive efficiency. They are also capable of reconfiguring automatically to take two different orientations favoring reduced drag in the swimming direction. A key feature of this design is that the reconfigurability is achieved without additional actuators - helpful in the development of autonomous swarm robots with good maneuverability and efficiency.
02 Jul 2019
TL;DR: In this article, a screw conveyor based sludge cleaning mechanism is proposed to clean the sticky sludge from the floor of aboveground oil storage tanks and interface effectively with tank inspection robots to perform cleaning and inspection synchronously.
Abstract: Oily sludge on the floor of the tank is a significant problem for petrochemical industries and floor inspection robots. Oily sludge is a hazardous material containing a complex mixture of hydrocarbon, water, sand, and minerals deposited on the floor of the oil storage tanks. Sludge accelerates corrosion, reduces storage capacity, sticks to floor inspection robots and disrupts further tank operations Industries have started deploying robots in a tank to automate and replace the hazardous manual tank tasks. This paper presents the design of a screw conveyor based sludge cleaning mechanism to clean the sticky sludge from the floor of aboveground oil storage tanks and interface effectively with tank inspection robots to perform cleaning and inspection synchronously. The cleaning mechanism consists of a screw conveyor mounted on a 'C' shaped case with a bearing on both sides, a waterproof motor connected to the screw conveyor with a worm-wheel gear. A Rheometer is used for measuring sludge properties to understand its flow behavior. Computational fluid dynamics (CFD) based numerical simulation is performed to visualize the flow of oily sludge through the proposed cleaning mechanism.
••01 Jun 2020
TL;DR: It is found that dorso-ventral flapping could lead to better self-stabilizing effects and lesser energy consumption compared to sideways flapping, and is an appealing advantage for underwater surveying robots carrying cameras and sensors as controlled body oscillations could yield better results from its payloads.
Abstract: Aquatic animals and mammals in nature, in particular, the Body and/or Caudal Fin (BCF) swimmers swim either by flapping their fins in the sideways direction or the dorso-ventral direction. Not much literature is available on the effects of the performance of these robots based on the choice of its flapping orientation. In this research, it is found that dorso-ventral flapping could lead to better self-stabilizing effects and lesser energy consumption compared to sideways flapping. It is also found that the choice of dorso-ventral flapping offers the possibility of controlling the body’s oscillation amplitude while flapping. This is an appealing advantage for underwater surveying robots carrying cameras and sensors as controlled body oscillations could yield better results from its payloads. The main body of results is obtained with simulations for underwater vehicle dynamics with the coefficients of the REMUS underwater vehicle, while stability analysis for a generalised case is also presented.
01 Nov 2002
TL;DR: In this article, the authors developed and verified a non-linear simulation model for the REMUS AUV, the first such model for this platform, where the external forces and moments resulting from hydrostatics, hydrodynamic lift and drag, added mass, and the control inputs of the vehicle propeller and fins are all defined in terms of vehicle coefficients.
Abstract: Describes the development and verification of a six degree of freedom, non-linear simulation model for the REMUS AUV, the first such model for this platform. In this model, the external forces and moments resulting from hydrostatics, hydrodynamic lift and drag, added mass, and the control inputs of the vehicle propeller and fins are all defined in terms of vehicle coefficients. The paper briefly describes the derivation of these coefficients. The equations determining the coefficients, as well as those describing the vehicle rigid-body dynamics, are left in non-linear form to better simulate the inherently non-linear behavior of the vehicle. Simulation of the vehicle motion is achieved through numeric integration of the equations of motion. The simulator output is then verified against vehicle dynamics data collected in experiments performed at sea. The simulator is shown to accurately model the motion of the vehicle. The paper concludes with recommendations for future model validation experiments.
01 Jun 2014
TL;DR: IMU can be helpful to diagnose of musculoskeletal disorders by range of motion and develop of customized rehabilitation program and help to diagnose early therapy for a musculo-knee disorders.
Abstract: This research aims to measure and analyze of range of motion in real time with inertial measurement unit(IMU). It can provided help to diagnose early therapy for a musculoskeletal disorders. Also, IMU can be evaluated state of joint motion in each direction, transverse, sagittal and coronal, respectively. As a result, it can be helpful to diagnose of musculoskeletal disorders by range of motion and develop of customized rehabilitation program.
TL;DR: A novel type of folding pectoral fins for the fish robot is proposed, which provides a simple approach in generating effective thrust only through one degree of freedom of fin actuator.
Abstract: Biological fish can create high forward swimming speed due to change of thrust/drag area of pectoral fins between power stroke and recovery stroke in rowing mode. In this paper, we proposed a novel type of folding pectoral fins for the fish robot, which provides a simple approach in generating effective thrust only through one degree of freedom of fin actuator. Its structure consists of two elemental fin panels for each pectoral fin that connects to a hinge base through the flexible joints. The Morison force model is adopted to discover the relationship of the dynamic interaction between fin panels and surrounding fluid. An experimental platform for the robot motion using the pectoral fin with different flexible joints was built to validate the proposed design. The results express that the performance of swimming velocity and turning radius of the robot are enhanced effectively. The forward swimming velocity can reach 0.231 m/s (0.58 BL/s) at the frequency near 0.75 Hz. By comparison, we found an accord between the proposed dynamic model and the experimental behavior of the robot. The attained results can be used to design controllers and optimize performances of the robot propelled by the folding pectoral fins.
07 Nov 2020-Bioinspiration & Biomimetics
TL;DR: The results show that it is feasible to replicate the similar kinematics and propulsive capability to that of the real fish via purely passive structural deformations through purely passive fluid-structure interaction solver.
Abstract: The work in this paper focuses on the examination of the effect of variable stiffness distributions on the kinematics and propulsion performance of a tuna-like swimmer. This is performed with the use of a recently developed fully coupled fluid-structure interaction solver. The two different scenarios considered in the present study are the stiffness varied along the fish body and the caudal fin, respectively. Our results show that it is feasible to replicate the similar kinematics and propulsive capability to that of the real fish via purely passive structural deformations. In addition, propulsion performance improvement is mainly dependent on the better orientation of the force near the posterior part of swimmers towards the thrust direction. Specifically, when a variable body stiffness scenario is considered, the bionic body stiffness profile results in better performance in most cases studied herein compared with a uniform stiffness commonly investigated in previous studies. Given the second scenario, where the stiffness is varied only in the spanwise direction of the tail, similar tail kinematics to that of the live scombrid fish only occurs in association with the heterocercal flexural rigidity profile. The resulting asymmetric tail conformation also yields performance improvement at intermediate stiffness in comparison to the cupping and uniform stiffness.
03 May 2021-Physics of Fluids
TL;DR: In this article, the authors employed a body-conforming fluid-structure interaction solver for a high-fidelity numerical study of three-dimensional pitching flexible plates with varying flexibility and trailing edge shapes.
Abstract: In this paper, we numerically investigate the propulsive performance of three-dimensional pitching flexible plates with varying flexibility and trailing edge shapes. We employ our recently developed body-conforming fluid-structure interaction solver for our high-fidelity numerical study. To eliminate the effect of other geometric parameters, only the trailing edge angle is varied from 45 ° (concave plate), 90 ° (rectangular plate) to 135 ° (convex plate) while maintaining the constant area of the flexible plate. For a wide range of flexibility, three distinctive flapping motion regimes are classified based on the variation of the flapping dynamics: (i) low bending stiffness K B low, (ii) moderate bending stiffness K B moderate near resonance, and (iii) high bending stiffness K B high. We examine the impact of the frequency ratio f * defined as the ratio of the natural frequency of the flexible plate to the actuated pitching frequency. Through our numerical simulations, we find that the global maximum mean thrust occurs near f * ≈ 1 corresponding to the resonance condition. However, the optimal propulsive efficiency is achieved around f * = 1.54 instead of the resonance condition. While the convex plate with low and high bending stiffness values shows the best performance, the rectangular plate with moderate K B moderate is the most efficient propulsion configuration. To examine the flow features and the correlated structural motions, we employ the sparsity-promoting dynamic mode decomposition. We find that the passive deformation induced by the flexibility effect can help in redistributing the pressure gradient, thus, improving the efficiency and the thrust production. A momentum-based thrust evaluation approach is adopted to link the temporal and spatial evolution of the vortical structures with the time-dependent thrust. When the vortices detach from the trailing edge, the instantaneous thrust shows the largest values due to the strong momentum change and convection process. Moderate flexibility and convex shape help to transfer momentum to the fluid, thereby improving the thrust generation and promoting the transition from drag to thrust. The increase in the trailing edge angle can broaden the range of flexibility that produces positive mean thrust. The role of added mass effect on the thrust generation is quantified for different pitching plates and the bending stiffness. These findings are of great significance to the optimal design of propulsion systems with flexible wings.