Fish Like Aquatic Robot Demonstrates Characteristics of a Linear System (original) (raw)
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An aquatic robot propelled by an internal rotor
IEEE/ASME Transactions on Mechatronics, 2017
Unmanned aquatic vehicles and robots are of tremendous importance in a variety of applications. In this paper we present the model of an underactuated aquatic robot that is propelled by an internal rotor. The propulsion of the robot is based on the exchange of momentum between the body and water that is mediated by the creation of vorticity at the trailing edge of the robot. The robot does not have any external fins, propellers or articulated joints allowing for very easy fabrication. Experimental data on its locomotion and maneuverability are presented.
Swimming performance of a biomimetic compliant fish-like robot
Experiments in Fluids, 2009
Digital particle image velocimetry and fluorescent dye visualization are used to characterize the performance of fish-like swimming robots. During nominal swimming, these robots produce a ‘V’-shaped double wake, with two reverse-Kármán streets in the far wake. The Reynolds number based on swimming speed and body length is approximately 7500, and the Strouhal number based on flapping frequency, flapping amplitude, and swimming speed is 0.86. It is found that swimming speed scales with the strength and geometry of a composite wake, which is constructed by freezing each vortex at the location of its centroid at the time of shedding. Specifically, we find that swimming speed scales linearly with vortex circulation. Also, swimming speed scales linearly with flapping frequency and the width of the composite wake. The thrust produced by the swimming robot is estimated using a simple vortex dynamics model, and we find satisfactory agreement between this estimate and measurements made during static load tests.
Three-dimensional flow structures and vorticity control in fish-like swimming
Journal of Fluid Mechanics, 2002
We employ a three-dimensional, nonlinear inviscid numerical method, in conjunction with experimental data from live fish and from a fish-like robotic mechanism, to establish the three-dimensional features of the flow around a fish-like body swimming in a straight line, and to identify the principal mechanisms of vorticity control employed in fish-like swimming. The computations contain no structural model for the fish and hence no recoil correction. First, we show the near-body flow structure produced by the travelling-wave undulations of the bodies of a tuna and a giant danio. As revealed in cross-sectional planes, for tuna the flow contains dominant features resembling the flow around a two-dimensional oscillating plate over most of the length of the fish body. For the giant danio, on the other hand, a mixed longitudinal–transverse structure appears along the hind part of the body. We also investigate the interaction of the body-generated vortices with the oscillating caudal fin a...
The best known analytical model of swimming was originally developed by Lighthill and is known as large amplitude elongated body theory (LAEBT). Recently, this theory has been improved and adapted to robotics through a series of studies [Boyer et al., 2008, 2010; Candelier et al., 2011] ranging from hydrodynamic modelling to mobile multibody system dynamics. This article marks a further step towards the Lighthill theory. The LAEBT is applied to one of the best bio-inspired swimming robots yet built: the AmphiBot III, a modular anguilliform swimming robot. To that end, we apply a Newton-Euler modelling approach and focus our attention on the model of hydrodynamic forces. This model is numerically integrated in real time by using an extension of the Newton-Euler recursive forward dynamics algorithm for manipulators to a robot without a fixed base. Simulations and experiments are compared on undulatory gaits and turning manoeuvres for a wide range of parameters. The discrepancies between modelling and reality do not exceed 16% for the swimming speed, while requiring only the one-time calibration of a few hydrodynamic parameters. Since the model can be numerically integrated in real time, it has significantly superior accuracy compared with computational speed ratio, and is, to the best of our knowledge, one of the most accurate models that can be used in real-time. It should provide an interesting tool for the design and control of swimming robots. The approach is presented in a self contained manner, with the concern to help the reader not familiar with fluid dynamics to get insight both into the physics of swimming and the mathematical tools that can help its modelling.
arXiv (Cornell University), 2021
In this work we developed a mathematical model and a simulation platform for a fish-inspired robotic template, namely Magnetic, Modular, Undulatory Robotics (µBots). Through this platform, we systematically explored the effects of design and fluid parameters on the swimming performance via reinforcement learning. The mathematical model was composed of two interacting subsystems, the robot dynamics and the hydrodynamics, and the hydrodynamic model consisted of reactive components (added-mass and pressure forces) and resistive components (drag and friction forces), which were then nondimensionalized for deriving key "control parameters" of robot-fluid interaction. The µBot was actuated via magnetic actuators controlled with harmonic voltage signals, which were optimized via EM-based Policy Hyper Parameter Exploration (EPHE) to maximize swimming speed. By varying the control parameters, total 36 cases with different robot template variations (Number of Actuation (NoA) and stiffness) and hydrodynamic parameters were simulated and optimized via EPHE. Results showed that wavelength of optimized gaits (i.e., traveling wave along body) was independent of template variations and hydrodynamic parameters. Higher NoA yielded higher speed but lower speed per body length however with diminishing gain and lower speed per body length. Body and caudal-fin gait dynamics were dominated by the interaction among fluid added-mass, spring, and actuation torque, with negligible contribution from fluid resistive drag. In contrast, thrust generation was dominated by pressure force acting on caudal fin, as steady swimming resulted from a balance between resistive force and pressure force, with minor contributions from added-mass and body drag forces. Therefore, added-mass force only indirectly affected the thrust generation and swimming speed via the caudal fin dynamics.
Hydrodynamics of Fishlike Swimming
Annual Review of Fluid Mechanics, 2000
Interest in novel forms of marine propulsion and maneuvering has sparked a number of studies on unsteadily operating propulsors. We review recent experimental and theoretical work identifying the principal mechanism for producing propulsive and transient forces in oscillating flexible bodies and fins in water, the formation and control of large-scale vortices. Connection with studies on live fish is made, explaining the observed outstanding fish agility. Annu. Rev. Fluid Mech. 2000.32:33-53. Downloaded from arjournals.annualreviews.org by UNIVERSITY OF MAINE -ORONO on 04/13/08. For personal use only. Annu. Rev. Fluid Mech. 2000.32:33-53. Downloaded from arjournals.annualreviews.org by UNIVERSITY OF MAINE -ORONO on 04/13/08. For personal use only. Annu. Rev. Fluid Mech. 2000.32:33-53. Downloaded from arjournals.annualreviews.org by UNIVERSITY OF MAINE -ORONO on 04/13/08. For personal use only.
Vorticity Control in Fish-like Propulsion and Maneuvering
Integrative and Comparative Biology, 2002
SYNOPSIS. Vorticity control is employed by marine animals to enhance performance in maneuvering and propulsion. Studies on fish-like robots and experimental apparatus modelling rigid and flexible fins provide some of the basic mechanisms employed for controlling vorticity.
3D hydrodynamic analysis of a biomimetic robot fish
2010 11th International Conference on Control Automation Robotics Vision, 2010
This paper presents a three-dimensional (3D) computational fluid dynamic simulation of a biomimetic robot fish. Fluent and user-defined function (UDF) is used to define the movement of the robot fish and the Dynamic Mesh is used to mimic the fish swimming in water. Hydrodynamic analysis is done in this paper too. The aim of this study is to get comparative data about hydrodynamic properties of those guidelines to improve the design, remote control and flexibility of the underwater robot fish.
All Rights Reserved iv ÖZET Yüzebilen mikro robotik sistemler, gelecekteki minimal invaziv cerrahi uygulamalar için alternatif oluşturmaktadır. Mikro boyutlardaki robotların canlı dokular içerisindeki sıvı dolu boşluk ve kanallarda verimli bir şekilde hareket edebilmesi için bakteri hücreleri gibi doğal mikro yüzücüleri taklit etmeleri gerekmektedir. Buna bağlı olarak, bakteri hücrelerinin mikro boyutlarda hidrodinamik modellemelerinin yapılması kontrol ve optimizasyon çalışmaları açısından önem taşımaktadır. Bu çalışmada, bakterileri taklit eden santimetre boyutundaki robotik prototiplerin düzgün silindirik kanallar içerisindeki yüzme hareketleri incelenmiştir. Söz konusu prototipler taşıdıkları batarya ve kontrol devreleri ile döner sarmal kuyruklarını tahrik ederek kendilerini yüksek viskoziteli sıvılar içerisinde sevk etmektedirler. Deneylerde, yüzme hızı ile değişken kuyruk geometrisi, değişken kanal çapı ve dikey/yatay konumlarda kanal duvarlarına yakınlık ilişkileri incelenmiştir. Daha sonra, hesaplamalı akışkanlar mekaniği metoduna dayanan benzeşim çalışmaları yapılmıştır. Benzeşim çalışmalarında, dar ve geniş kanallar içerisinde hareket eden bu yüzücü robotlar modellenmiş, ve deney sonuçları ile model doğrulamaları yapılmıştır. Doğrulanmış modeller ile sınırlandırılmamış yüksek viskoziteli sıvılar içerisinde duvar etkilerinden bağımsız olarak yüzen bakteri tipi robotların gövde ve kuyrukları arasındaki hidrodinamik etkileşim incelenmiştir. Ayrıca, değişken kanal çapının ve de kuyruk geometrisinin yüzme hızı üzerindeki etkileri de incelenmiştir. Son olarak, direnç-kuvveti-teorisi tabanlı, zamana-bağlı altı-serbestlik-dereceli bir mikrohidrodinamik model geliştirilmiştir. Bu modelde, viskoz kuvvetler göz önüne alınarak tüm katı-cisim ve akışkan ivmeleri sıfır kabul edilmiştir. Robotun yüzme hızları sıfırkuvvetle-yüzme kısıtlaması kullanılarak birinci dereceden bir denklemler sistemi ile hesaplanmaktadır. Mikrohidrodinamik model, dikey/yatay kanal deneyleri ve hesaplamalı akışkanlar mekaniği benzeşim sonuçları ile ayrı ayrı doğrulanmıştır. Doğrulanan mikrohidrodinamik model, örnek model-tabanlı kontrol çalışmalarında ve enerji verimliliği ile yüksek hız için gerekli sarmal kuyruk taslaklarının bulunmasında kullanılmıştır. v ABSTRACT Modeling and control of swimming untethered micro robots are important for future therapeutic medical applications. Bio-inspired propulsion methods emerge as realistic substitutes for hydrodynamic thrust generation in micro realm. Accurate modeling, power supply, and propulsion-means directly affect the mobility and maneuverability of swimming micro robots with helical or planar wave propagation. Flow field around a bio-inspired micro swimmer comprised of a spherical body and a rotating helical tail is studied with time-dependent three-dimensional computational fluid dynamics (CFD) model. Analytical hydrodynamic studies on the bodies of well known geometries submerged in viscous flows reported in literature do not address the effect of hydrodynamic interactions between the body and the tail of the robot in unbounded viscous fluids. Hydrodynamic interactions are explained qualitatively and quantitatively with the help of CFD-model. A cm-scale powered bio-inspired swimmer robot with helical tails is manufactured including a payload and a replaceable rigid helical tail. The payload includes on-board power supply and remote-control circuitry. A number of helical tails with parameterized wave geometry are used. Swimmer performed in cylindrical channels of different diameters while fully submerged in an oil-bath of high viscosity. A real-time six degrees-of-freedom microhydrodynamic model is developed and implemented to predict the rigid-body motion of the swimming robots with helical and traveling-plane-wave tails. Results of microhydrodynamic models with alternative resistance coefficients are compared against CFD simulations and in-channel swimming experiments with different tails. Validated microhydrodynamic model is further employed to study efficient geometric designs with different wave propagation methods within a predefined design space. vi ACKNOWLEDGEMENTS
Study of the thrust–drag balance with a swimming robotic fish
Physics of Fluids, 2018
A robotic fish is used to test the validity of a simplification made in the context of fish locomotion. With this artificial aquatic swimmer, we verify that the momentum equation results from a simple balance between a thrust and a drag that can be treated independently in the small amplitude regime. The thrust produced by the flexible robot is proportional to A2f2, where A and f are the respective tail-beat amplitude and oscillation frequency, irrespective of whether or not f coincides with the resonant frequency of the fish. The drag is proportional to U02, where U0 is the swimming velocity. These three physical quantities set the value of the Strouhal number in this regime. For larger amplitudes, we found that the drag coefficient is not constant but increases quadratically with the fin amplitude. As a consequence, the achieved locomotion velocity decreases, or the Strouhal number increases, as a function of the fin amplitude.