UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item Dynamics and Control of Bioinspired Swimming, Schooling, and Pursuit(2023) Thompson, Anthony Allan; Paley, Derek A; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Understanding the benefits of the behaviors of aquatic animals can improve the capabilities of robotic systems. Aquatic species such as the zebrafish swim with discrete motions that alternate between perception and action while avoiding predators and swimming in schools, and other species such as the lionfish use their pectoral fins to herd and trap prey. This work seeks to model these bioinspired behaviors (i.e., schooling, swimming with intermittent sensing and actuation, and pursuit and evasion in a structured environment) and enhance our understanding of their benefits. A hybrid dynamic model is derived with two phases; namely a burst phase during which each particle applies a control input and a coast phase during which each particle performs state estimation. This model provides a way to investigate how having non-overlapping sensing and control affects a multi-agent system's ability to achieve collective behavior such as steering to some desired direction. By evaluating the stability properties of the equilibrium points for the collective behavior, investigators can determine parameter values that exhibit exponentially stable behavior. Aside from swimming intermittently, fish also need to avoid predators. Inspired by observations of predation attempts by lionfish (Pterois sp.), a pursuit-evasion game is derived in a bounded environment to study the interaction of an advanced predator and an intermittently steering prey. The predator tracks the prey with a pure-pursuit strategy while using a bioinspired tactic to minimize the evader's escape routes, i.e, to trap the prey. Specifically, the predator employs symmetric appendages inspired by the large pectoral fins of lionfish, but this expansion increases its drag. The prey employs a bioinspired randomly-directed escape strategy to avoid capture and collisions with the boundary known as the protean strategy. This game investigates the predator's trade-off of minimizing the work to capture the prey and minimizing the prey's escape routes. Using the predator's expected work to capture as a cost function determines when the predator should expand its appendages as a function of the relative distance to the evader and the evader's proximity to the boundary. Prey fish also swim in schools to protect themselves from predators. To drive a school of fish robots into a parallel formation, a nonlinear steering controller is derived and implemented on a robotic fish platform. These robotic fish are actuated with an internal reaction wheel driven by a DC motor. Implementation of the proposed parallel formation control law on an actual school of soft robotic fish is described, including system identification experiments to identify motor dynamics and the design of a motor torque-tracking controller to follow the formation torque control. Experimental results demonstrate a school of four robotic fish achieving parallel formations starting from random initial conditions.Item Reconstruction, Analysis and Synthesis of Collective Motion(2015) Dey, Biswadip; Krishnaprasad, Perinkulam S; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)As collective motion plays a crucial role in modern day robotics and engineering, it seems appealing to seek inspiration from nature, which abounds with examples of collective motion (starling flocks, fish schools etc.). This approach towards understanding and reverse-engineering a particular aspect of nature forms the foundation of this dissertation, and its main contribution is threefold. First we identify the importance of appropriate algorithms to extract parameters of motion from sampled observations of the trajectory, and then by assuming an appropriate generative model we turn this into a regularized inversion problem with the regularization term imposing smoothness of the reconstructed trajectory. First we assume a linear triple-integrator model, and by penalizing high values of the jerk path integral we reconstruct the trajectory through an analytical approach. Alternatively, the evolution of a trajectory can be governed by natural Frenet frame equations. Inadequacy of integrability theory for nonlinear systems poses the utmost challenge in having an analytic solution, and forces us to adopt a numerical optimization approach. However, by noting the fact that the underlying dynamics defines a left invariant vector field on a Lie group, we develop a framework based on Pontryagin's maximum principle. This approach toward data smoothing yields a semi-analytic solution. Equipped with appropriate algorithms for trajectory reconstruction we analyze flight data for biological motions, and this marks the second contribution of this dissertation. By analyzing the flight data of big brown bats in two different settings (chasing a free-flying praying mantis and competing with a conspecific to catch a tethered mealworm), we provide evidence to show the presence of a context specific switch in flight strategy. Moreover, our approach provides a way to estimate the behavioral latency associated with these foraging behaviors. On the other hand, we have also analyzed the flight data of European starling flocks, and it can be concluded from our analysis that the flock-averaged coherence (the average cosine of the angle between the velocities of a focal bird and its neighborhood center of mass, averaged over the entire flock) gets maximized by considering 5-7 nearest neighbors. The analysis also sheds some light into the underlying feedback mechanism for steering control. The third and final contribution of this dissertation lies in the domain of control law synthesis. Drawing inspiration from coherent movement of starling flocks, we introduce a strategy (Topological Velocity Alignment) for collective motion, wherein each agent aligns its velocity along the direction of motion of its neighborhood center of mass. A feedback law has also been proposed for achieving this strategy, and we have analyzed two special cases (two-body system; and an N-body system with cyclic interaction) to show effectiveness of our proposed feedback law. It has been observed through numerical simulation and robotic implementation that this approach towards collective motion can give rise to a splitting behavior.Item A Continuum Model for Flocking: Obstacle Avoidance, Equilibrium, and Stability(2010) Mecholsky, Nicholas Alexander; Ott, Edward; Antonsen, Jr., Thomas M; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The modeling and investigation of the dynamics and configurations of animal groups is a subject of growing attention. In this dissertation, we present a partial-differential-equation based continuum model of flocking and use it to investigate several properties of group dynamics and equilibrium. We analyze the reaction of a flock to an obstacle or an attacking predator. We show that the flock response is in the form of density disturbances that resemble Mach cones whose configuration is determined by the anisotropic propagation of waves through the flock. We investigate the effect of a flock `pressure' and pairwise repulsion on an equilibrium density distribution. We investigate both linear and nonlinear pressures, look at the convergence to a ‘cold’ (T → 0) equilibrium solution, and find regions of parameter space where different models produce the same equilibrium. Finally, we analyze the stability of an equilibrium density distribution to long-wavelength perturbations. Analytic results for the stability of a constant density solution as well as stability regimes for constant density solutions to the equilibrium equations are presented.