Distance-Based Formation Control of Multi-Agent Systems

This Ph.D. dissertation studies the distance-based formation control of multi-agent systems. A new approach to the distance-based formation control problem is proposed in this thesis. We formulated distance-based formation in a nonlinear optimal control framework and used the state-dependent Riccati equation (SDRE) technique as the primary tool for solving the optimal control problem. In general, a distance-based formation can be undirected, where distance constraints between pairs of agents are actively controlled by both adjacent agents, or directed, where just one of the neighboring agents is responsible for maintaining the desired distance. This thesis presents both, undirected and directed formations, and provides extensive simulations to verify the theoretical results. For undirected topologies, we studied the formation control problem where we showed that the proposed control law results in the global asymptotic stability of the closed-loop system under certain conditions. The formation tracking problem was studied, and the uniform ultimate boundedness of the solutions is rigorously proven. The proposed method guarantees collision avoidance among neighboring agents and prevents depletion of the agents' energy. In the directed distance-based formation control case, we developed a distributed, hierarchical control scheme for a particular class of directed graphs, namely directed triangulated and trilateral Laman graphs. The proposed controller ensures the global asymptotic stability of the desired formation. Rigorous stability analyses are carried out in all cases. Moreover, we addressed the flip-ambiguity issue by using the signed area and signed volume constraints. Additionally, we introduced a performance index for a formation mission that can indicate the controller's overall performance. We also studied the distance-based formation control of nonlinear agents. We proposed a method that can guarantee asymptotic stability of the distance-based formation for a broad category of nonlinear systems. Furthermore, we studied a distance-based formation control of uncertain nonlinear agents. Based on the combination of integral sliding mode control (ISMC) theory with the SDRE method, we developed a robust optimal formation control scheme that guarantees asymptotic stability of the desired distance-based formation in the presence of bounded uncertainties. We have shown that the proposed controller can compensate for the effect of uncertainties in individual agents on the overall formation

Control of Formations with Non-rigid and Hybrid Graphs

This thesis studies the problem of control of multi-agent formations, of which the interaction architectures can be modeled by undirected and directed graphs or a mixture of the two (hybrid graphs). The algorithms proposed in this thesis can be applied to control the architectures of multi-agent systems or sensor networks, and the developed control laws can be employed in the autonomous agents of various types within multi-agent systems. This thesis discusses two major issues. The first tackles formations with undirected and directed underlying graphs, more specifically, the problems of rigidity restoration and persistence verification for multi-agent formations are studied. The second discusses the control of formations with both undirected and directed interaction architectures (hybrid formations) by distance-based control methods. The main contributions of this thesis are: definition of spindle agent and basic graphs for non-rigid undirected graphs, development of new operations for the constructions of undirected and directed graphs, design of graph rigidity restoration strategy by merging two or more non-rigid graphs, development of new persistence analysis strategy for arbitrary directed graphs, definition and investigation of hybrid formations and the underlying hybrid graphs, verification of persistence and minimal persistence for hybrid graphs, as well as the control of persistent hybrid formations by distance-based approaches

Development of Robust Control Strategies for Autonomous Underwater Vehicles

The resources of the energy and chemical balance in the ocean sustain mankind in many ways. Therefore, ocean exploration is an essential task that is accomplished by deploying Underwater Vehicles. An Underwater Vehicle with autonomy feature for its navigation and control is called Autonomous Underwater Vehicle (AUV). Among the task handled by an AUV, accurately positioning itself at a desired position with respect to the reference objects is called set-point control. Similarly, tracking of the reference trajectory is also another important task. Battery recharging of AUV, positioning with respect to underwater structure, cable, seabed, tracking of reference trajectory with desired accuracy and speed to avoid collision with the guiding vehicle in the last phase of docking are some significant applications where an AUV needs to perform the above tasks. Parametric uncertainties in AUV dynamics and actuator torque limitation necessitate to design robust control algorithms to achieve motion control objectives in the face of uncertainties. Sliding Mode Controller (SMC), H / μ synthesis, model based PID group controllers are some of the robust controllers which have been applied to AUV. But SMC suffers from less efficient tuning of its switching gains due to model parameters and noisy estimated acceleration states appearing in its control law. In addition, demand of high control effort due to high frequency chattering is another drawback of SMC. Furthermore, real-time implementation of H / μ synthesis controller based on its stability study is restricted due to use of linearly approximated dynamic model of an AUV, which hinders achieving robustness. Moreover, model based PID group controllers suffer from implementation complexities and exhibit poor transient and steady-state performances under parametric uncertainties. On the other hand model free Linear PID (LPID) has inherent problem of narrow convergence region, i.e.it can not ensure convergence of large initial error to zero. Additionally, it suffers from integrator-wind-up and subsequent saturation of actuator during the occurrence of large initial error. But LPID controller has inherent capability to cope up with the uncertainties. In view of addressing the above said problem, this work proposes wind-up free Nonlinear PID with Bounded Integral (BI) and Bounded Derivative (BD) for set-point control and combination of continuous SMC with Nonlinear PID with BI and BD namely SM-N-PID with BI and BD for trajectory tracking. Nonlinear functions are used for all P,I and D controllers (for both of set-point and tracking control) in addition to use of nonlinear tan hyperbolic function in SMC(for tracking only) such that torque demand from the controller can be kept within a limit. A direct Lyapunov analysis is pursued to prove stable motion of AUV. The efficacies of the proposed controllers are compared with other two controllers namely PD and N-PID without BI and BD for set-point control and PD plus Feedforward Compensation (FC) and SM-NPID without BI and BD for tracking control. Multiple AUVs cooperatively performing a mission offers several advantages over a single AUV in a non-cooperative manner; such as reliability and increased work efficiency, etc. Bandwidth limitation in acoustic medium possess challenges in designing cooperative motion control algorithm for multiple AUVs owing to the necessity of communication of sensors and actuator signals among AUVs. In literature, undirected graph based approach is used for control design under communication constraints and thus it is not suitable for large number of AUVs participating in a cooperative motion plan. Formation control is a popular cooperative motion control paradigm. This thesis models the formation as a minimally persistent directed graph and proposes control schemes for maintaining the distance constraints during the course of motion of entire formation. For formation control each AUV uses Sliding Mode Nonlinear PID controller with Bounded Integrator and Bounded Derivative. Direct Lyapunov stability analysis in the framework of input-to-state stability ensures the stable motion of formation while maintaining the desired distance constraints among the AUVs

Race, Nature, and Accumulation: A Decolonial World-Ecological Analysis of Indian Land Grabbing in the Gambella Province of Ethiopia

This dissertation situates the post-crisis phenomenon of large-scale agricultural land acquisition, otherwise known as the global land grab, within the longue duree of the capitalist world-ecology. It does so by advancing a theoretical and historical framework, which I call the decolonial world-ecological agrarian question, that clarifies the key role played by the co-production of race and nature in provisioning the ecological surplus of cheap food that has historically secured the emergence and reproduction of capitalist development. This framework specifically foregrounds the racialized denial of indigenous human presence as the necessary condition of possibility for the reduction of the colonial frontier to a state of unused nature. While the racialized denial of the reproductive conditions of the colonial frontiers fertile soils ultimately exhausts the latters surplus provisioning capacity, the longue duree of the capitalist world-ecology has been marked by successive attempts to overcome such exhaustion by forging, through technologies of racialization, new frontiers of unused externalized natures. The key premise of this dissertation is that, in light of the food price crisis indexing the exhaustion of the accumulation capacity of the neoliberal epoch of the capitalist world-ecology, the global land grab constitutes another such attempted moment of re-securing the cheap food premise through racialized frontier appropriation. This dissertation highlights the distinctive South-South dimensions of the contemporary global land grab by taking as its empirical site of investigation the case of Indian land grabbing in the Gambella province of Ethiopia. The central argument advanced here is that, within the neoliberal crisis conjuncture, the hegemonic resolution of the agrarian question in the core national space of India calls forth, through the practice of global primitive accumulation, the racialized construction of frontiers of unused nature in an emergent African zone of appropriation. Specifically, the cheap food imperative of Indian capitalist development constructs the fertile soils and abundant waters of Gambella as unused natures hitherto wasted by the primitive practices of the indigenous Anywaa people. Indian state and capital thus simultaneously appropriate and erase the indigenous practice and knowledge which has been historically integral to the socio-ecological foundation of Gambellas natural abundance

Adaptive Formation Control of Cooperative Multi-Vehicle Systems

The literature comprises many approaches and results for the formation control of multi-vehicle systems; however, the results established for the cases where the vehicles contain parametric uncertainties are limited. Motivated by the need for explicit characterization of the effects of uncertainties on multi-vehicle formation motions, we study distributed adaptive formation control of multi-vehicle systems in this thesis, focusing on different interrelated sub-objectives. We first examine the cohesive motion control problem of minimally persistent formations of autonomous vehicles. Later, we consider parametric uncertainties in vehicle dynamics in such autonomous vehicle formations. Following an indirect adaptive control approach and exploiting the features of the certainty equivalence principle, we propose control laws to solve maneuvering problem of the formations, robust to parametric modeling uncertainties. Next, as a formation acquisition/closing ranks problem, we study the adaptive station keeping problem, which is defined as positioning an autonomous mobile vehicle $A$ inside a multi-vehicle network, having specified distances from the existing vehicles of the network. In this setting, a single-integrator model is assumed for the kinematics for the vehicle $A$, and $A$ is assumed to have access to only its own position and its continuous distance measurements to the vehicles of the network. We partition the problem into two sub-problems; localization of the existing vehicles of the network using range-only measurements and motion control of $A$ to its desired location within the network with respect to other vehicles. We design an indirect adaptive control scheme, provide formal stability and convergence analysis and numerical simulation results, demonstrating the characteristics and performance of the design. Finally, we study re-design of the proposed station keeping scheme for the more challenging case where the vehicle $A$ has non-holonomic motion dynamics and does not have access to its self-location information. Overall, the thesis comprises methods and solutions to four correlated formation control problems in the direction of achieving a unified distributed adaptive formation control framework for multi-vehicle systems

Gifts of Sovereignty: Settler Colonial Capitalism and the Kanaka ʻŌiwi Politics of Ea

This dissertation examines Hawaiian sovereignty in history, law, and activism. The project tracks Indigenous claims, negotiations, and articulations of sovereignty in Hawai‘i. Using a critically Indigenous approach to Hawaiian studies, I advance two main theses. First, Kānaka Maoli (Native Hawaiians) are discussed as a community divided on Hawaiian sovereignty. However, I contend that Kānaka Maoli exercise a diversity of strategies and tactics for Hawaiian sovereignty. I show how Kānaka Maoli practice multiple modalities of sovereignty that cumulatively produce the Kanaka ‘Ōiwi (Indigenous Hawaiian) politics of ea (life and sovereignty). Second, the historical development of settler colonial capitalism operationalized the US settler-state in Hawai‘i and fuels its management of Kānaka Maoli in contemporary struggles with federal recognition, nation-building, and astronomy industry development. Yet, Kanaka ‘Ōiwi artists and activists engage in geontologies of aloha ‘āina—a geographic way of being in the ‘āina (land and that which feeds)—that seek to overturn settler colonial capitalism and its champion the US settler-state. I argue that these practices issue gifts that disidentify with dominant ideologies of sovereignty as a way of reimagining ea for a decolonized then and deoccupied there. Therefore, my project explains the nefarious ways that the settler-state attempts to cohere territorial control to juridical authority and how Kānaka Maoli antagonize and disrupt the precariousness of settler sovereignty in Hawai‘i. Intervening into Indigenous Studies, Hawaiian Studies, and critical theories, the study offers new insights on the complex relationship between settler colonial capitalism and Hawaiian sovereignty

Computational phenotypes : where the theory of computation meets evo-devo

This article argues that the Chomsky Hierarchy can be reinterpreted as a developmental morphospace constraining the evolution of a discrete and finite series of computational phenotypes. In doing so, the theory of Morphological Evolution as stated by Pere Alberch, a pioneering figure of Evo-Devo thinking, is adhered to

Symposium Internationale Quartum Anatomiae Clinicae

Proceedings from the Symposium