The Watchmaker's guide to Artificial Life: On the Role of Death, Modularity and Physicality in Evolutionary Robotics

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Biorobotics: Using robots to emulate and investigate agile animal locomotion

The graceful and agile movements of animals are difficult to analyze and emulate because locomotion is the result of a complex interplay of many components: the central and peripheral nervous systems, the musculoskeletal system, and the environment. The goals of biorobotics are to take inspiration from biological principles to design robots that match the agility of animals, and to use robots as scientific tools to investigate animal adaptive behavior. Used as physical models, biorobots contribute to hypothesis testing in fields such as hydrodynamics, biomechanics, neuroscience, and prosthetics. Their use may contribute to the design of prosthetic devices that more closely take human locomotion principles into account

Modeling Complex Biological and Mechanical Movements: Applications to Animal Locomotion and Gesture Classification in Robotic Surgery

Mutual interaction between biology and robots can significantly benefit both fields. The richness and diversity in animal locomotion and movement provides an extensive resource for inspiration in engineering design of robots. On the other hand, bio-mimetic and bio-inspired robots play a critical role in testing hypotheses in biology and neuromechanics. Modeling complex biological and mechanical movements is at the core of this mutual interaction. Models and analytical tools are required for decoding and analysis of behavior in biological and mechanical systems, both at low level (sensory systems and control) and high level (activity recognition). This dissertation is focused on modeling approaches for biological and mechanical movements. We first primarily focus on physics-based template modeling to answer a long-standing question in animal locomotion: why do animals often produce substantial forces in directions that do not directly contribute to movement? We examine the weakly electric knifefish, a well-suited model system to investigate the relationship between mutually opposing forces and locomotor control. We use slow-motion videography to study the ribbon-fin motion and develop a physics-based template model at the task-level for tracking behavior. Using the developed physics-based model integrated with experiments with a biomimetic robot, we demonstrate that the production and differential control of mutually opposing forces is a strategy that generates passive stabilization while simultaneously enhancing maneuverability, thereby simplifies neural control. The second part of this work aims to propose a more general data-driven system-theoretic framework for decoding complex behaviors. Specifically we introduce a new class of linear time-invariant dynamical systems with sparse inputs (LDS-SI). In the proposed framework, at each time instant, the input to the system is sparse with respect to a dictionary of inputs. In the context of complex behaviors, the dictionary may represent the dictionary of inputs for all possible simple behaviors. We propose a convex optimization formulation for the state estimation with unknown inputs in LDS-SI. We derive sufficient conditions for the perfect joint recovery and explore the results with simulation. We demonstrate the power of the proposed framework in the analysis of complex gestures in robotic surgery. Results are better than state-of-the-art methods in joint segmentation and classification of surgical gestures in a dataset of suturing task trials performed by different surgeons

INVESTIGATING DORSAL FIN HYDRODYNAMIC FUNCTION OF THE LEMON SHARK, NEGAPRION BREVIROSTRIS

Many sharks are considered highly efficient swimmers. Their swimming efficiency is partially governed by their morphological features such as dorsal fins, which play a role in their hydrodynamics. Most sharks feature two dorsal fins that can vary in size and location over the body. The first dorsal fin has been shown to improve stabilization, maneuverability, and increase thrust production during swimming, whilst the hydrodynamic role of the second dorsal fin is largely unknown. An understanding of the hydrodynamic function of the dorsal fins can be utilized in engineering applications, e.g., to replicate fins on underwater autonomous vehicles to increase energy efficiency during locomotion. To explore the hydrodynamics of the second dorsal fin and seek solutions applicable to the biomimetic world, we selected a species with a second dorsal fin that is almost as large as its first dorsal fin: the Lemon Shark. An enlarged second dorsal fin is an uncommon characteristic among sharks. Here, we performed a comparative study between the Lemon Shark and another shark species that has a small 2nd dorsal fin compared to the first: the Spinner Shark. We experimentally investigated the hydrodynamic role of the 2nd dorsal fin of the Lemon Shark and used particle image velocimetry to measure the fluid dynamics in its wake. Measurements were collected in the streamwise-spanwise plane behind the 1st and 2nd dorsal fins, as well as the caudal fin for deceased sharks of both species (Spinner Shark and Lemon Shark). In addition, a 3D flexible Lemon Shark model was also used to compare with the deceased specimens. Using the measured data, we: i) evaluated the characteristics of the specimens\u27 and model\u27s wake and ii) examined what effect these characteristics have on the hydrodynamic forces acting on the sharks. The presence of a vortex street in the wake was identified using proper orthogonal decomposition (POD). Based on the POD, the vortex street characteristics such as: wavelength, cross-stream distance, spacing ratio, Kronauer stability, von-Karman stability, and Strouhal number were computed. These wake characteristics were used to compute the thrust, and the drag was computed based on the momentum deficit in the wake. Results showed a stable vortex street developed in the wake behind the 1st dorsal fin for both species. Although the Lemon Shark had two dorsal fins similar in size, the Lemon Shark\u27s 2nd dorsal fin did not feature a vortex street in the wake. The size of the wake was larger than that of the 1st dorsal fin, which resulted in higher drag behind the second dorsal fin compared to the first dorsal fin. It was also found that the flow behind the 2nd dorsal fin did not fully recover prior to reaching the caudal fin, which indicated some interaction with the wake formation behind the caudal fin. It appeared that this interaction reduced the size of the overall wake for the Lemon Shark. Ultimately, this smaller wake resulted in lower drag behind the caudal fin compared to a species with only one large dorsal fin, like the Spinner Shark

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