225 research outputs found
Volumetric imaging of shark tail hydrodynamics reveals a three-dimensional dual-ring vortex wake structure
Understanding how moving organisms generate locomotor forces is fundamental to the analysis of aerodynamic and hydrodynamic flow patterns that are generated during body and appendage oscillation. In the past, this has been accomplished using two-dimensional planar techniques that require reconstruction of three-dimensional flow patterns. We have applied a new, fully three-dimensional, volumetric imaging technique that allows instantaneous capture of wake flow patterns, to a classic problem in functional vertebrate biology: the function of the asymmetrical (heterocercal) tail of swimming sharks to capture the vorticity field within the volume swept by the tail. These data were used to test a previous three-dimensional reconstruction of the shark vortex wake estimated from two-dimensional flow analyses, and show that the volumetric approach reveals a different vortex wake not previously reconstructed from two-dimensional slices. The hydrodynamic wake consists of one set of dual-linked vortex rings produced per half tail beat. In addition, we use a simple passive shark-tail model under robotic control to show that the three-dimensional wake flows of the robotic tail differ from the active tail motion of a live shark, suggesting that active control of kinematics and tail stiffness plays a substantial role in the production of wake vortical patterns
Improving Swimming Performance and Flow Sensing by Incorporating Passive Mechanisms
As water makes up approximately 70% of the Earth\u27s surface, humans have expanded operations into aquatic environments out of both necessity and a desire to gain potential innate benefits. This expansion into aquatic environments has consequently developed a need for cost-effective and safe underwater monitoring, surveillance, and inspection, which are missions that autonomous underwater vehicles are particularly well suited for. Current autonomous underwater vehicles vastly underperform when compared to biological swimmers, which has prompted researchers to develop robots inspired by natural swimmers. One such robot is designed, built, tested, and numerically simulated in this thesis to gain insight into the benefits of passive mechanisms and the development of reduced-order models.
Using a bio-inspired robot with multiple passive tails I demonstrate herein the relationship between maneuverability and passive appendages. I found that the allowable rotation angle, relative to the main body, of the passive tails corresponds to an increase in maneuverability. Using panel method simulations I determined that the increase in maneuverability was directly related to the change in hydrodynamic moment caused by modulating the circulation sign and location of the shed vortex wake. The identification of this hydrodynamic benefit generalizes the results and applies to a wide range of robots that utilize vortex shedding through tail flapping or body undulations to produce locomotion.
Passive appendages are a form of embodied control, which manipulates the fluid-robot interaction and analogously such interaction can be sensed from the dynamics of the body. Body manipulation is a direct result of pressure fluctuations inherent in the surrounding fluid flow. These pressure fluctuations are unique to specific flow conditions, which may produce distinguishable time series kinematics of the appendage. Using a bio-inspired foil tethered in a water tunnel I classified different vortex wakes with the foil\u27s kinematic data. This form of embodied feedback could be used for the development of control algorithms dedicated to obstacle avoidance, tracking, and station holding.
Mathematical models of autonomous vehicles are necessary to implement advanced control algorithms such as path planning. Models that accurately and efficiently simulate the coupled fluid-body interaction in freely swimming aquatic robots are difficult to determine due, in part, to the complex nature of fluids. My colleagues and I approach this problem by relating the swimming robot to a terrestrial vehicle known as the Chaplygin sleigh. Using our novel technique we determined an analogous Chaplygin sleigh model that accurately represents the steady-state dynamics of our swimming robot. We additionally used the subsequent model for heading and velocity control in panel method simulations. This work was inspired by the similarities in constraints and velocity space limit cycles of the swimmer and the Chaplygin sleigh, which makes this technique universal enough to be extended to other bio-inspired robots
Analysis of underwater snake robot locomotion based on a control-oriented model
This paper presents an analysis of planar underwater snake robot locomotion in the presence of ocean currents. The robot is assumed to be neutrally buoyant and move fully submerged with a planar sinusoidal gait and limited link angles. As a basis for the analysis, an existing, controloriented model is further simplified and extended to general sinusoidal gaits. Averaging theory is then employed to derive the averaged velocity dynamics of the underwater snake robot from that model. It is proven that the averaged velocity converges exponentially to an equilibrium, and an analytical expression for calculating the forward velocity of the robot in steady state is derived. A simulation study that validates both the proposed modelling approach and the theoretical results is presented.Prepint - (c) 2015 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works
Biomimetic and Live Medusae Reveal the Mechanistic Advantages of a Flexible Bell Margin
Flexible bell margins are characteristic components of rowing medusan morphologies and are expected to contribute towards their high propulsive efficiency. However, the mechanistic basis of thrust augmentation by flexible propulsors remained unresolved, so the impact of bell margin flexibility on medusan swimming has also remained unresolved. We used biomimetic robotic jellyfish vehicles to elucidate that propulsive thrust enhancement by flexible medusan bell margins relies upon fluid dynamic interactions between entrained flows at the inflexion point of the exumbrella and flows expelled from under the bell. Coalescence of flows from these two regions resulted in enhanced fluid circulation and, therefore, thrust augmentation for flexible margins of both medusan vehicles and living medusae. Using particle image velocimetry (PIV) data we estimated pressure fields to demonstrate a mechanistic basis of enhanced flows associated with the flexible bell margin. Performance of vehicles with flexible margins was further enhanced by vortex interactions that occur during bell expansion. Hydrodynamic and performance similarities between robotic vehicles and live animals demonstrated that the propulsive advantages of flexible margins found in nature can be emulated by human-engineered propulsors. Although medusae are simple animal models for description of this process, these results may contribute towards understanding the performance of flexible margins among other animal lineages
Modeling, Control and Energy Efficiency of Underwater Snake Robots
This thesis is mainly motivated by the attribute of the snake robots that they
are able to move over land as well as underwater while the physiology of the robot
remains the same. This adaptability to different motion demands depending on the
environment is one of the main characteristics of the snake robots. In particular,
this thesis targets several interesting aspects regarding the modeling, control and
energy efficiency of the underwater snake robots.
This thesis addresses the problem of modeling the hydrodynamic effects with
an analytical perspective and a primary objective to conclude in a closed-form
solution for the dynamic model of an underwater snake robot. Two mathematical
models of the kinematics and dynamics of underwater snake robots swimming in
virtual horizontal and vertical planes aimed at control design are presented. The
presented models are derived in a closed-form and can be utilized in modern modelbased
control schemes. In addition, these proposed models comprise snake robots
moving both on land and in water which makes the model applicable for unified
control methods for amphibious snake robots moving both on land and in water.
The third model presented in this thesis is based on simplifying assumptions in
order to derive a control-oriented model of an underwater snake robot moving in a
virtual horizontal plane that is well-suited for control design and stability analysis.
The models are analysed using several techniques. An extensive analysis of the
model of a fully immersed underwater snake robot moving in a virtual horizontal
plane is conducted. Based on this analysis, a set of essential properties that characterize
the overall motion of underwater snake robots is derived. An averaging
analysis reveals new fundamental properties of underwater snake robot locomotion
that are useful from a motion planning perspective.
In this thesis, both the motion analysis and control strategies are conducted
based on a general sinusoidal motion pattern which can be used for a broad class
of motion patterns including lateral undulation and eel-like motion. This thesis
proposes and experimentally validates solutions to the path following control problem
for biologically inspired swimming snake robots. In particular, line-of-sight
(LOS) and integral line-of-sight (I-LOS) guidance laws, which are combined with
a sinusoidal gait pattern and a directional controller that steers the robot towards
and along the desired path are proposed. An I-LOS path following controller for
steering an underwater snake robot along a straight line path in the presence of
ocean currents of unknown direction and magnitude is presented and by using a
Poincaré map, it is shown that all state variables of an underwater snake robot,
except for the position along the desired path, trace out an exponentially stable periodic orbit. Moreover, this thesis presents the combined use of an artificial potential
fields-based path planner with a new waypoint guidance strategy for steering
an underwater snake robot along a path defined by waypoints interconnected by
straight lines. The waypoints are derived by using a path planner based on the
artificial potential field method in order to also address the obstacle avoidance
problem.
Furthermore, this thesis considers the energy efficiency of underwater snake
robots. In particular, the relationship between the parameters of the gait patterns,
the forward velocity and the energy consumption for the different motion patterns
for underwater snake robots is investigated. Based on simulation results, this thesis
presents empirical rules to choose the values for the parameters of the motion
gait pattern of underwater snake robots. The experimental results support the derived
properties regarding the relationship between the gait parameters and the
power consumption both for lateral undulation and eel-like motion patterns. Moreover,
comparison results are obtained for the total energy consumption and the
cost of transportation of underwater snake robots and remotely operated vehicles
(ROVs). Furthermore, in this thesis a multi-objective optimization problem is developed
with the aim of maximizing the achieved forward velocity of the robot and
minimizing the corresponding average power consumption of the system
A numerical study of fin and jet propulsions involving fluid-structure interactions
Fish swimming is elegant and efficient, which inspires humans to learn from them to design
high-performance artificial underwater vehicles. Research on aquatic locomotion has made
extensive progress towards a better understanding of how aquatic animals control their
flexible body and fin for propulsion. Although the structural flexibility and deformation of
the body and fin are believed to be important features to achieve optimal swimming
performance, studies on high-fidelity deformable body and fin with complex material
behavior, such as non-uniform stiffness distributions, are rare.
In this thesis, a fully coupled three-dimensional high-fidelity fluid-structure interaction (FSI)
solver is developed to investigate the flow field evolution and propulsion performance of
caudal fin and jet propulsion involving body and/or fin deformation. Within this FSI solver,
the fluid is resolved by solving unsteady and viscous Navier-Stokes equations based on the
finite volume method with a multi-block grid system. The solid dynamics are solved by a
nonlinear finite element method. The coupling between the two solvers is achieved in a
partitioned approach in which convergence check and sub-iteration are implemented to
ensure numerical stability and accuracy. Validations are conducted by comparing the
simulation results of classical benchmarks with previous data in the literature, and good
agreements between them are obtained.
The developed FSI solver is then applied to study the bio-inspired fin and jet propulsion
involving body deformation. Specifically, the effect of non-uniform stiffness distributions of
fish body and/or fin, key features of fish swimming which have been excluded in most
previous studies, on the propulsive performance is first investigated. Simulation results of a
sunfish-like caudal fin model and a tuna-inspired swimmer model both show that larger
thrust and propulsion efficiency can be achieved by a non-uniform stiffness distribution (e.g.,
increased by 11.2% and 9.9%, respectively, for the sunfish-like model) compared with a
uniform stiffness profile. Despite the improved propulsive e performance, a bionic variable
fish body stiffness does not yield fish-like midline kinematics observed in real fish,
suggesting that fish movement involves significant active control that cannot be replicated
purely by passive deformations.
Subsequent studies focus on the jet propulsion inspired by squid locomotion using the
developed numerical solver. Simulation results of a two-dimensional inflation-deflation jet
propulsion system, whose inflation is actuated by an added external force that mimics the
muscle constriction of the mantle and deflation is caused by the release of elastic energy of
the structure, suggest larger mean thrust production and higher efficiency in high Reynolds
number scenarios compared with the cases in laminar flow. A unique symmetry-breaking
instability in turbulent flow is found to stem from irregular internal body vortices, which
cause symmetry breaking in the wake. Besides, a three-dimensional squid-like jet propulsion
system in the presence of background flow is studied by prescribing the body deformation
and jet velocity profiles. The effect of the background flow on the leading vortex ring
formation and jet propulsion is investigated, and the thrust sources of the overall pulsed jet
are revealed as well.
Finally, FSI analysis on motion control of a self-propelled flexible swimmer in front of a
cylinder utilizing proportional-derivative (PD) control is conducted. The amplitude of the
actuation force, which is applied to the swimmer to bend it to produce thrust, is dynamically
tuned by a feedback PD controller to instruct the swimmer to swim the desired distance from
an initial position to a target location and then hold the station there. Despite the same
swimming distance, a swimmer whose departure location is closer to the cylinder requires
less energy consumption to reach the target and hold the position there.Fish swimming is elegant and efficient, which inspires humans to learn from them to design
high-performance artificial underwater vehicles. Research on aquatic locomotion has made
extensive progress towards a better understanding of how aquatic animals control their
flexible body and fin for propulsion. Although the structural flexibility and deformation of
the body and fin are believed to be important features to achieve optimal swimming
performance, studies on high-fidelity deformable body and fin with complex material
behavior, such as non-uniform stiffness distributions, are rare.
In this thesis, a fully coupled three-dimensional high-fidelity fluid-structure interaction (FSI)
solver is developed to investigate the flow field evolution and propulsion performance of
caudal fin and jet propulsion involving body and/or fin deformation. Within this FSI solver,
the fluid is resolved by solving unsteady and viscous Navier-Stokes equations based on the
finite volume method with a multi-block grid system. The solid dynamics are solved by a
nonlinear finite element method. The coupling between the two solvers is achieved in a
partitioned approach in which convergence check and sub-iteration are implemented to
ensure numerical stability and accuracy. Validations are conducted by comparing the
simulation results of classical benchmarks with previous data in the literature, and good
agreements between them are obtained.
The developed FSI solver is then applied to study the bio-inspired fin and jet propulsion
involving body deformation. Specifically, the effect of non-uniform stiffness distributions of
fish body and/or fin, key features of fish swimming which have been excluded in most
previous studies, on the propulsive performance is first investigated. Simulation results of a
sunfish-like caudal fin model and a tuna-inspired swimmer model both show that larger
thrust and propulsion efficiency can be achieved by a non-uniform stiffness distribution (e.g.,
increased by 11.2% and 9.9%, respectively, for the sunfish-like model) compared with a
uniform stiffness profile. Despite the improved propulsive e performance, a bionic variable
fish body stiffness does not yield fish-like midline kinematics observed in real fish,
suggesting that fish movement involves significant active control that cannot be replicated
purely by passive deformations.
Subsequent studies focus on the jet propulsion inspired by squid locomotion using the
developed numerical solver. Simulation results of a two-dimensional inflation-deflation jet
propulsion system, whose inflation is actuated by an added external force that mimics the
muscle constriction of the mantle and deflation is caused by the release of elastic energy of
the structure, suggest larger mean thrust production and higher efficiency in high Reynolds
number scenarios compared with the cases in laminar flow. A unique symmetry-breaking
instability in turbulent flow is found to stem from irregular internal body vortices, which
cause symmetry breaking in the wake. Besides, a three-dimensional squid-like jet propulsion
system in the presence of background flow is studied by prescribing the body deformation
and jet velocity profiles. The effect of the background flow on the leading vortex ring
formation and jet propulsion is investigated, and the thrust sources of the overall pulsed jet
are revealed as well.
Finally, FSI analysis on motion control of a self-propelled flexible swimmer in front of a
cylinder utilizing proportional-derivative (PD) control is conducted. The amplitude of the
actuation force, which is applied to the swimmer to bend it to produce thrust, is dynamically
tuned by a feedback PD controller to instruct the swimmer to swim the desired distance from
an initial position to a target location and then hold the station there. Despite the same
swimming distance, a swimmer whose departure location is closer to the cylinder requires
less energy consumption to reach the target and hold the position there
Bio-Inspired Robotics
Modern robotic technologies have enabled robots to operate in a variety of unstructured and dynamically-changing environments, in addition to traditional structured environments. Robots have, thus, become an important element in our everyday lives. One key approach to develop such intelligent and autonomous robots is to draw inspiration from biological systems. Biological structure, mechanisms, and underlying principles have the potential to provide new ideas to support the improvement of conventional robotic designs and control. Such biological principles usually originate from animal or even plant models, for robots, which can sense, think, walk, swim, crawl, jump or even fly. Thus, it is believed that these bio-inspired methods are becoming increasingly important in the face of complex applications. Bio-inspired robotics is leading to the study of innovative structures and computing with sensory–motor coordination and learning to achieve intelligence, flexibility, stability, and adaptation for emergent robotic applications, such as manipulation, learning, and control. This Special Issue invites original papers of innovative ideas and concepts, new discoveries and improvements, and novel applications and business models relevant to the selected topics of ``Bio-Inspired Robotics''. Bio-Inspired Robotics is a broad topic and an ongoing expanding field. This Special Issue collates 30 papers that address some of the important challenges and opportunities in this broad and expanding field
Evolving soft locomotion in aquatic and terrestrial environments: effects of material properties and environmental transitions
Designing soft robots poses considerable challenges: automated design
approaches may be particularly appealing in this field, as they promise to
optimize complex multi-material machines with very little or no human
intervention. Evolutionary soft robotics is concerned with the application of
optimization algorithms inspired by natural evolution in order to let soft
robots (both morphologies and controllers) spontaneously evolve within
physically-realistic simulated environments, figuring out how to satisfy a set
of objectives defined by human designers. In this paper a powerful evolutionary
system is put in place in order to perform a broad investigation on the
free-form evolution of walking and swimming soft robots in different
environments. Three sets of experiments are reported, tackling different
aspects of the evolution of soft locomotion. The first two sets explore the
effects of different material properties on the evolution of terrestrial and
aquatic soft locomotion: particularly, we show how different materials lead to
the evolution of different morphologies, behaviors, and energy-performance
tradeoffs. It is found that within our simplified physics world stiffer robots
evolve more sophisticated and effective gaits and morphologies on land, while
softer ones tend to perform better in water. The third set of experiments
starts investigating the effect and potential benefits of major environmental
transitions (land - water) during evolution. Results provide interesting
morphological exaptation phenomena, and point out a potential asymmetry between
land-water and water-land transitions: while the first type of transition
appears to be detrimental, the second one seems to have some beneficial
effects.Comment: 37 pages, 22 figures, currently under review (journal
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