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Title: Control of systems with hysteresis using servocompensators
Creator: Esbrook, Alexander James
Date: 2012
Collection: Electronic Theses & Dissertations
Description: The tracking problem in systems with hysteresis has become an important topic of research in the past two decades, due in large part to advances in smart material actuators. In particular, applications like Scanning Probe Microscopy require high performance from hysteretic smart material actuators. Servocompensators, or internal model controllers, have been used successfully in many varieties of tracking problems for both linear and nonlinear systems; therefore, their application to systems...
Show moreThe tracking problem in systems with hysteresis has become an important topic of research in the past two decades, due in large part to advances in smart material actuators. In particular, applications like Scanning Probe Microscopy require high performance from hysteretic smart material actuators. Servocompensators, or internal model controllers, have been used successfully in many varieties of tracking problems for both linear and nonlinear systems; therefore, their application to systems with hysteresis is considered in this dissertation. The use of Multi-Harmonic Servocompensators (MHSC) is first proposed to simultaneously compensate for hysteresis and enable high-bandwidth tracking in systems with hysteresis, such as nanopositioners. With the model represented by linear dynamics preceded with a Prandtl-Ishlinskii hysteresis operator, the stability and periodicity of the closed-loop system's solutions are established when hysteresis inversion is included in the controller. Experiments on a commercial nanopositioner show that, with the proposed method, tracking can be achieved for a 200 Hz reference signal with 0.52% mean error and 1.5% peak error over a travel range of 40 μm. Additionally, the proposed method is shown at high frequencies to be superior to Iterative Learning Control (ILC), a common technique in nanopositioning control.The theoretical and practical weaknesses of the proposed approach are then addressed. First, the design of a novel adaptive servocompensator specialized to systems with hysteresis is presented, based on frequency estimation coupled with slow adaptation, and the stability in cases with one, two, or n unknown frequencies are established. Next, a condition in the form of a Linear Matrix Inequality is presented proving the stability of the proposed MHSC when hysteresis inversion is not used. It is then experimentally demonstrated that removing hysteresis inversion further reduces the tracking error achievable by the MHSC. Finally, the properties of self-excited limit cycles are studied for an integral-controlled system containing a play operator. A Newton-Raphson algorithm is formulated to calculate the limit cycles, and linear relationships between the amplitude and period of these limit cycles and system parameters are obtained.
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Title: Artificial lateral line systems for feedback control of underwater robots
Creator: AbdulSadda, Ahmad
Date: 2012
Collection: Electronic Theses & Dissertations
Description: A lateral line system, consisting of arrays of flow-sensing neuromasts, allows fish and amphibians to probe their ambient environment and plays a vital role in their behaviors spanning predator/prey detection, schooling, rheotaxis, courtship and communication. The feats of biological lateral lines have inspired an increasing interest in engineering a similar sensing module for underwater robots and vehicles. Often known as artificial lateral lines, these sensors could potentially enable an...
Show moreA lateral line system, consisting of arrays of flow-sensing neuromasts, allows fish and amphibians to probe their ambient environment and plays a vital role in their behaviors spanning predator/prey detection, schooling, rheotaxis, courtship and communication. The feats of biological lateral lines have inspired an increasing interest in engineering a similar sensing module for underwater robots and vehicles. Often known as artificial lateral lines, these sensors could potentially enable an underwater robot to detect and identify moving or stationary objects, and exploit ambient flow energy for efficient locomotion. Despite the advances made in this area, realizing a practical artificial lateral line still faces significant challenges in both signal processing and flow sensor fabrication.In this dissertation we describe our effort in developing signal processing methods for hydrodynamic object localization and tracking using an artificial lateral line (ALL). We consider two types of objects, a vibrating sphere and a non-vibrating cylinder, both of which are of interest in underwater applications. A vibrating sphere, known as a dipole source, is widely used in the study of biological lateral lines and it emulates the rhythmic body or fin movement. A non-vibrating cylinder (with unknown cross-section shape), on the other hand, represents a general moving or stationary object underwater with a 2D flow profile. First, a novel bio-inspired artificial lateral line system is proposed for underwater robots and vehicles by exploiting the inherent sensing capability of ionic polymer-metal composites (IPMCs). Analogous to its biological counterpart, the IPMC-based lateral line processes the sensor signals through a neural network, and we demonstrate the performance of this approach in the localization of a dipole source. Second, with an assumption of potential flows, we formulate nonlinear estimation problems for the localization and tracking of a dipole source based on analytical flow models, and propose and compare several algorithms for solving the problem. For the case of a moving cylinder, we use conformal mapping to represent a general cross-section profile, and explore the use of Kalman-filtering-type techniques in the tracking and size/shape estimation of the object.We have conducted extensive experiments to validate the developed algorithms with an artificial lateral line prototype made of millimeter-scale IPMC sensors, with sensor-to-sensor separation of 2 cm, which is determined through an optimization process based on the Cramer-Rao bound (CRB) analysis. Finally, we experimentally explore the use of IPMC sensors for estimating the hydrodynamic parameters involved in a Karman vortex street that is created by a stationary cylinder in a flow. We validate that the vortex shedding frequency, which can be extracted from the sensor signal, shows clear correlation with the flow speed and the obstacle size.
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Title: Improving the performance of an under-damped mass spring damper system through switched parameters
Creator: Allafi, Amer Lafi
Date: 2014
Collection: Electronic Theses & Dissertations
Description: In this thesis we propose to improve the performance of the standard single degree-of-freedom under-damped mass-spring-damper (MSD) system using variable structure control. Two controllers are proposed: both of them switch the parameters of the system between their nominal values and their negative values. This approach results in a hybrid system comprised of the nominal system, which is asymptotically stable, and an unstable system. The first controller is based on switched stiffness whereas...
Show moreIn this thesis we propose to improve the performance of the standard single degree-of-freedom under-damped mass-spring-damper (MSD) system using variable structure control. Two controllers are proposed: both of them switch the parameters of the system between their nominal values and their negative values. This approach results in a hybrid system comprised of the nominal system, which is asymptotically stable, and an unstable system. The first controller is based on switched stiffness whereas the second controllers is based on switched stiffness and damping. For both controllers, the parameters are switched based on the location of the system in its configuration space. A phase portrait analysis indicates that the resulting hybrid systems are asymptotically stable although they switch between an asymptotically stable and an unstable system. A comparison of the step response of the hybrid systems with that of the original under-damped system indicates that the switched systems have better performance in terms of rise time, settling time, and reduced or no overshoot. Different designs of the switching logic have been investigated and they provide clues on how the switching logic can be designed to achieve the maximum improvement in performance.
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Title: Modelling and control of a turbocharged diesel engine
Creator: Zeng, Tao, (Graduate of Michigan State University)
Date: 2017
Collection: Electronic Theses & Dissertations
Description: The diesel engine is known for its high efficiency, performance, and durability. With stringent fuel economy and emission regulations, diesel engines face increasing challenges. To accommodate emission regulations, fuel economy and performance requirements, modern diesel engines are equipped with the variable geometry turbocharger (VGT) and exhaust gas recirculation (EGR) system. VGT extracts energy from the exhaust gas to drive the compressor to improve transient response, steady-state...
Show moreThe diesel engine is known for its high efficiency, performance, and durability. With stringent fuel economy and emission regulations, diesel engines face increasing challenges. To accommodate emission regulations, fuel economy and performance requirements, modern diesel engines are equipped with the variable geometry turbocharger (VGT) and exhaust gas recirculation (EGR) system. VGT extracts energy from the exhaust gas to drive the compressor to improve transient response, steady-state performance, and fuel efficiency under a wide range of engine flow conditions. Meanwhile, EGR dilutes fresh air with exhaust gas to reduce the formation of mono-nitrogen oxides NO and NO2 (NOx). The VGT and EGR control design is complicated due to the natural coupling between VGT and EGR, and high nonlinearity of diesel engine air-path system. The extra assisted power and regenerative power on the turbocharger shaft further increase the control system complexity. In this dissertation, new approaches for turbocharger system modelling and multivariable control design for the coordinated actuation of the VGT-EGR system are investigated. The control design is further extended to hydraulic regenerative assisted turbocharger system.New modelling approaches for turbocharger system are proposed based on turbomachinery physics. Proposed turbine and compressor models eliminate the interpolation error, and especially, allow smooth extrapolation outside the mapped region. A high fidelity reduced order mean value model of a diesel engine for automotive application is developed based on developed turbocharger model. Further, new models for high-speed hydraulic turbines and centrifugal pumps are developed for hydraulic assisted and regenerative turbochargers.A regenerative hydraulic assisted turbocharger (RHAT) system is investigated in this dissertation. A system level approach based on 1-D simulations is used to understand the assist benefits and design trade-offs. Simulation results show that 3-5% fuel economy improvement for FTP 75 driving cycle, depending on different sub-component sizing. The study also identifies technical challenges for optimal design and control of RHAT systems.A linear controller design approach is proposed in this dissertation for regulating both boost pressure and EGR mass flow rate of the VGT-EGR system. The linear quadratic control with integral action is designed based on the linearized system. Local controllers are scheduled based on engine operational parameter: engine speed and fuel injection quantity. The gain scheduled liner controller is validated against baseline controller based on the nonlinear plant. Results show that designed multi-input and multi-output (MIMO) controller can well manage the trade-offs between boost pressure tracking and EGR mass flow tracking, compared to baseline controller (two single input single output (SISO) controllers). A novel approach is proposed for closed-loop control design with respect to engine performance and engine emission trade-offs. The controller design is further extended to assisted and regenerative turbocharger system with VGT and EGR. The results show that emission reduction, engine performance and fuel economy improvement can be achieved at the same time with external power applied to the turbocharger shaft.
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Title: Reaction-based knock predictive modeling and model-based stochastic knock limit control of spark-ignition engines
Creator: Li, Ruixue
Date: 2020
Collection: Electronic Theses & Dissertations
Description: This dissertation studies the spark-ignition (SI) engine knock phenomenon, abnormal combustion due to the auto-ignition of end-gas ahead of the propagated flame front, resulting in the rapid chemical energy release with aggressive combustion, limiting the further improvement of thermal efficiency and even damaging the engine mechanically. A control-oriented combustion and pressure wave model with satisfactory accuracy and low computational effort is a necessity for the knock control strategy...
Show moreThis dissertation studies the spark-ignition (SI) engine knock phenomenon, abnormal combustion due to the auto-ignition of end-gas ahead of the propagated flame front, resulting in the rapid chemical energy release with aggressive combustion, limiting the further improvement of thermal efficiency and even damaging the engine mechanically. A control-oriented combustion and pressure wave model with satisfactory accuracy and low computational effort is a necessity for the knock control strategy design. This dissertation develops a control-oriented knock predictive model that includes a two-zone reaction-based combustion model and a pressure wave model. This knock predictive model is capable of accurately describing the combustion process of a spark-ignited engine and predict the in-cylinder pressure oscillations under knocking combustion in real-time. Based on this model, a feedforward and feedback stochastic knock limit control strategy is developed to reduce the knock cyclic variability and control the knock mean-intensity below a desired up bound while keeping spark timing as close to engine maximum brake torque (MBT) timing as possible. A control-oriented two-zone reaction-based model to accurately describe the combustion process of a SI engine is first developed. Instead of using the conventional pre-determined Wiebe-based combustion model, a two-step chemical reaction model is utilized to predict the combustion process along with important thermodynamic parameters such as the mass-fraction-burned, in-cylinder pressure, temperatures and individual species mass changes in both zones. Sensitivities of model parameters are analyzed during the model calibration process. As a result, one set of calibration parameters are used to predict combustion characteristics over all engine operating conditions studied in this paper, which is the major advantage of the proposed method. Also, the proposed modeling approach is capable of modeling the combustion process for real-time simulations. As the by-product of the model, engine knock can also be predicted based on the Arrhenius integral in the unburned zone, which is valuable for model-based knock control. The proposed combustion model is intensively validated using the experimental data with a peak relative prediction error of 6.2% for the in-cylinder pressure. Based on this validated combustion model, a control-oriented pressure wave model for SI engines is further developed. This model is capable of predicting the in-cylinder pressure oscillations under knocking combustion in real-time and can be used for the model-based knock prediction and control. A pressure wave equation including the knock deadening behavior is proposed, simplified, and used to calculate the pressure perturbations generated by the knocking combustion. The boundary and initial conditions at knock onset are analyzed and the analytic solution of the pressure wave equation is obtained. The model is calibrated and validated over two different engine operating conditions at knock limit. The chemical kinetic-based Arrhenius integral (ARI) and the KI20 are used as the evaluation methods for knock onset and intensity prediction, and the knock frequency is studied with a fast Fourier transform of the filtered in-cylinder pressure oscillations. Especially, the knock characteristics associated with gas mixture properties at intake valve closing is analyzed based on the experimental data and their effect to knock cycle-to-cycle variation is also studied for the proposed model. In addition, this dissertation studies the correlation between in-cylinder mixture temperature at intake valve closing and the engine knock, along with knock cyclic variability based on the knock predictive model. A strong correlation between the intake temperature and knock intensity has been obtained and validated based on the simulation investigation and experiment data obtained at knock limit. Therefore, a model-based feedforward and feedback stochastic knock limit control strategy is developed to reduce the knock cycle-to-cycle variability and maintain the knock mean-intensity within a desired up bound by controlling the spark timing as close to MBT timing as possible. The control performance is validated with the simulation results to show the capability of the model-based feedforward and feedback stochastic knock limit control in significantly reducing the knock cyclic variability and improving the knock intensity distribution for the best fuel economy.
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Title: Smooth switching LPV control and its applications
Creator: He, Tianyi
Date: 2019
Collection: Electronic Theses & Dissertations
Description: This dissertation studies the smooth switching LPV (Linear Parameter-Varying) system and control, as well as its applications in mechanical systems, aerospace systems to achieve the smooth transition between switching LPV controllers. Both state-feedback and dynamic output-feedback cases are addressed by the simultaneous design approach of smooth switching LPV control, and the proposed method has been applied to active vibration control of BWB (Blended-Wing-Body) aircraft flexible wing and...
Show moreThis dissertation studies the smooth switching LPV (Linear Parameter-Varying) system and control, as well as its applications in mechanical systems, aerospace systems to achieve the smooth transition between switching LPV controllers. Both state-feedback and dynamic output-feedback cases are addressed by the simultaneous design approach of smooth switching LPV control, and the proposed method has been applied to active vibration control of BWB (Blended-Wing-Body) aircraft flexible wing and the AMB (Active Magnetic Bearing) system. Moreover, a sequential design approach is developed to design smooth switching LPV controllers, where the high-dimensional optimization in the simultaneous design approach can be relaxed.In conventional switching LPV control, switching controllers are designed on each subregion while guaranteeing safe switching, but without considering the smoothness during switching events. The abruptly varying control signal can exceed actuator authority; moreover, abrupt changes in system responses caused by unsmooth controller gains will be harmful to system components and hardware. The simultaneous design of smooth switching LPV control minimizes a combined cost of system output H2 performance and smooth-switching index subject to H2 constraints on control inputs and Hinf constraint on bounded model uncertainty. These stability and performance criteria are then formulated using a set of Parametric Linear Matrix Inequalities (PLMIs). Besides, a tunable weighting coefficient is introduced to provide an optimal trade-off design between system H2 performance and switching smoothness. Simulation results with the AMB model and BWB aircraft wing model are provided to demonstrate the effectiveness of the proposed smooth switching control. In the above approach, switching controllers are synthesized by controller variables that simultaneously satisfy PLMIs on all subregions and switching stability conditions on all switching surfaces. When the number of subregions goes large, simultaneous design approach leads to a high-dimensional optimization problem, with a high number of LMI constraints, decision variables, online computational load, and memory requirement. As a result, these drawbacks make simultaneous design practically infeasible for high-order systems with many divided subregions. An innovative sequential design approach is proposed by introducing interpolated controller decision variables and formulating independent PLMI conditions on each subregion such that system performances on overlapped subregions are guaranteed as well. In this way, the switching controller synthesis conditions are formulated as independent optimization problems and can be well solved sequentially. Besides, this dissertation also utilizes the LPV framework to investigate optimal sensor placement to achieve optimal vibration suppression for a flexible BWB airplane wing. For a given flight speed range, vibration behaviors of the wing structure are evaluated by the guaranteed H2 performance with the H2 LPV controller. Candidate sensor locations are identified on each wing, and the optimal sensor placements can be found among these candidate sensor locations by the greedy algorithm. The searched optimal results are validated by globally searching through all possible combinations. With the LPV model of a flexible wing and H2 controller synthesisconditions, search results provide the optimal sensor locations, and besides, the trade-off between optimal system performance and the number of sensors can also be obtained.
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Title: Teleoperation of mobile manipulators
Creator: Jia, Yunyi
Date: 2014
Collection: Electronic Theses & Dissertations
Description: Mobile manipulators provide larger working spaces and more flexibility than standard manipulators by introducing mobility. Through teleoperation, they can be applied to a variety of areas such as hazardous material handling, outer space exploration, searching and rescue, etc.Inspired by application requirements, there are four major challenges in the teleoperation of mobile manipulators including the modeling and control of mobile manipulators, teleoperation of multiple mobile manipulators,...
Show moreMobile manipulators provide larger working spaces and more flexibility than standard manipulators by introducing mobility. Through teleoperation, they can be applied to a variety of areas such as hazardous material handling, outer space exploration, searching and rescue, etc.Inspired by application requirements, there are four major challenges in the teleoperation of mobile manipulators including the modeling and control of mobile manipulators, teleoperation of multiple mobile manipulators, modeling the human teleoperator in teleoperation system and communications between the human teleoperator and mobile manipulators. Therefore, this study aims to address these challenges.For the modeling and control of mobile manipulators, the motion accuracy of the end-effector is a problem for the existing methods due to the system performance differences. To address this issue, we introduce a new control method with online motion distribution and coordination to improve the accuracy. In addition, a sensor-based redundancy resolution scheme is proposed to further improve the teleoperation efficiency.For the teleoperation of multiple mobile manipulators, the system stability under random communication delays and unexpected events is a major problem for the existing methods. To address this issue, we propose a non-time based teleoperation and coordination method. A non-time perceptive reference is designed as the new reference to replace the time in the system modeling and control. Through this design, the system stability under random communication delays and unexpected events could be ensured.For modeling the human teleoperator in teleoperation system, there are no existing models and the teleoperation efficiency and safety are always subject to the operation status of the teleoperator. To address this issue, we propose a concept named quality of teleoperator (QoT) to represent the teleoperator and incorporate it into the modeling and control of the teleoperation system. Through this design, the teleoperation efficiency and safety could be improved under various operation status of the teleoperator.For the communications between the human teleoperator and mobile manipulators, the existing methods of using joysticks are neither efficient nor intuitive. Therefore, we introduce the natural language as a new communication manner. However, the existing natural language control methods could not online handle unexpected events in the environment and robotic system. To address this issue, a new systematic natural language modeling and control method is designed to online handle such unexpected events.Finally, the proposed methods are all implemented on our developed mobile manipulators and the experimental results illustrate their effectiveness and advantages.
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Title: Exploiting impulsive inputs for stabilization of underactuated robotic systems : theory and experiments
Creator: Kant, Nilay
Date: 2020
Collection: Electronic Theses & Dissertations
Description: Robots have become increasingly popular due to their ability to perform complex tasks and operate in unknown and hazardous environments. Many robotic systems are underactuated i.e., they have fewer control inputs than their degrees-of-freedom (DOF). Common examples of underactuated robotic systems are legged robots such as bipeds, flying robots such as quadrotors, and swimming robots. Due to limited control authority, underactuated systems are prone to instability. This work includes...
Show moreRobots have become increasingly popular due to their ability to perform complex tasks and operate in unknown and hazardous environments. Many robotic systems are underactuated i.e., they have fewer control inputs than their degrees-of-freedom (DOF). Common examples of underactuated robotic systems are legged robots such as bipeds, flying robots such as quadrotors, and swimming robots. Due to limited control authority, underactuated systems are prone to instability. This work includes impulsive inputs in the set of admissible controls to address several challenging control problems. It has already been shown that continuous-time approximation of impulsive inputs can be realized in physical hardware using high-gain feedback.Stabilization of an equilibrium point is an important control problem for underactuated systems. The ability of the system to remain stable in the presence of disturbances depends on the size of the region of attraction of the stabilized equilibrium. The sum of squares and trajectory reversing methods are combined to generate a large estimate of the region of attraction. This estimate is then effectively enlarged by applying the impulse manifold method to stabilize equilibria from points lying outside the estimated region of attraction. Simulation results are provided for a three-DOF tiptoebot and experimental validation is carried out on a two-DOF pendubot. Impulsive inputs are also utilized to control the underactuated inertia-wheel pendulum (IWP). When subjected to impulsive inputs, the dynamics of the IWP can be described by algebraic equations. Optimal sequences of inputs are designed to achieve rest-to-rest maneuvers and the results are applied to the swing-up control problem. The novel problem of juggling a devil-stick using impulsive inputs is also investigated. Impulsive forces are applied to the stick intermittently and the impulse of the force and its point of application are modeled as inputs to the system. A dead-beat design for one of the inputs simplifies the control problem and results in a discrete linear time invariant system. To achieve symmetric juggling, linear quadratic regulator (LQR) and model predictive control (MPC) based designs are proposed and validated through simulations.A repetitive motion is described by closed orbits and therefore, stabilization of closed orbits is important for many applications such as bipedal walking and steady swimming. We first investigate the problem of energy-based orbital stabilization using continuous inputs and intermittent impulsive braking. The orbit is a manifold where the active generalized coordinates are fixed and the total mechanical energy of the system is equal to some desired value. Simulation and experimental results are provided for the tiptoebot and the rotary pendulum, respectively. The problem of orbital stabilization using virtual holonomic constraints (VHC) is also investigated. VHCs are enforced using a continuous controller which guarantees existence of closed orbits. A Poincare section is constructed on the desired orbit and the orbit is stabilized using impulsive inputs which are applied intermittently when the system trajectory crosses the Poincare section. This approach to orbital stabilization is general, and has lower complexity and computational cost than control designs proposed earlier.
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Title: Stability investigations of non-conservative dynamic systems
Creator: Abdullatif, Mahmoud Nabil
Date: 2020
Collection: Electronic Theses & Dissertations
Description: Elastic stability continues to be a subject of considerable interest due to the increasing demands of lightweight structures. It is well known that structures may lose stability through divergence or flutter and the nature of the instability depends on the type of loading. A structure may lose stability through divergence when the loading is conservative but may lose stability through divergence or flutter when the loading is non-conservative. In this work, we investigate stability...
Show moreElastic stability continues to be a subject of considerable interest due to the increasing demands of lightweight structures. It is well known that structures may lose stability through divergence or flutter and the nature of the instability depends on the type of loading. A structure may lose stability through divergence when the loading is conservative but may lose stability through divergence or flutter when the loading is non-conservative. In this work, we investigate stability transitions in structures due to: damping in the presence of non-conservative loading, terminal dynamic moment with and without intermediate support, and external flow with dynamic moment. The role of damping on non-conservative systems, which was first investigated by Ziegler, is revisited here. It is shown that increasing the level of damping can cause an unstable non-conservative system to become stable, then unstable, then stable again at the same value of the non-conservative load. This sequence of stability transitions, which has not been reported in the literature, is found to exist for several non-conservative systems, including articulated linkages with follower end forces and fluid-conveying pipes. The stability transitions were investigated by applying the Routh-Hurwitz criterion twice: once for the characteristic polynomial and the second time for the polynomial that guarantees the existence of a second-order auxiliary polynomial in the Routh array. Nonconservative loading in elastic structures has previously been limited to follower forces and forces generated by a fluid jet exiting a fluid-conveying pipe. A new type of non-conservative loading is introduced here in the form of a terminal dynamic moment. The terminal moment is dynamic in the sense that it is proportional to the slope or curvature of a point along the structure. Irrespective of whether the moment is slope-dependent or curvature-dependent, stability is lost in a beam through divergence when the constant of proportionality is positive, and through flutter when the constant of proportionality is negative. Some of the theoretical investigations are supported by experiments with a cantilever beam. In non-conservative systems, the introduction of an intermediate support is known to result in stability transitions between flutter and divergence. This result was confirmed for the new type of non-conservative loading, namely, the terminal dynamic moment. For a cantilever beam with terminal dynamic moment, a rich set of stability transitions were observed for the first time. This includes multiple stability transitions between divergence and flutter and between different modes of flutter. In some cases, the transitions are accompanied by an abrupt change in the critical load, which is commonly referred to as the 03000300jump phenomenon" in the literature. External flow is known to result in non-conservative loading and, therefore, stability transitions are investigated in a hinged beam in external flow. A dynamic moment, proportional to the curvature of the beam at some point along its length, is applied at the hinge. The combined effect of non-conservative loading due to both dynamic moment and external flow is investigated with the objective of developing a mechanism for energy harvesting from flow fields.
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Title: Control of multi-link one-legged hopping locomotion
Creator: Allafi, Amer
Date: 2020
Collection: Electronic Theses & Dissertations
Description: Controlling one-legged hopping locomotion is a challenging problem due to the hybrid dynamics of the hopper and the interaction with ground. The hybrid dynamics of the one-legged hopper consists of mainly two sub-dynamics, one when the hopper is in contact with ground, and the other when there is no contact. The ground model can effect the hopper behavior since the hopper interact with ground when the hopper in contact with ground. Here we investigate the locomotion behavior of the one-legged...
Show moreControlling one-legged hopping locomotion is a challenging problem due to the hybrid dynamics of the hopper and the interaction with ground. The hybrid dynamics of the one-legged hopper consists of mainly two sub-dynamics, one when the hopper is in contact with ground, and the other when there is no contact. The ground model can effect the hopper behavior since the hopper interact with ground when the hopper in contact with ground. Here we investigate the locomotion behavior of the one-legged multi-link hopper hopes on three different ground models, namely, rigid, elastic, and viscoelastic ground. The rigid ground apply an impulsive force to the hopper when the hopper came in contact with ground resulting energy losses. A partial feedback linearization is used to control the internal dynamics of the hopper. A Poincar\\'e map is used to construct a discrete-time system and a controller with integral action is designed to achieve the control objectives. The elastic ground, the ground modeled as massless spring, the spring in the ground store some of the energy of the hopper during the contact. A continuous backstepping controller is designed to control the energy level and internal dynamics of the hopper. A Poincar\\'e map is used to construct a discrete-time system and a controller with integral action is designed to achieve the control objectives. The viscoelastic ground, the ground modeled as an under-damped mass-spring-damper system, the damper and the impact with ground mass resulting in energy losses and the ground spring store some of the energy of the hopper during the contact. A continuous backstepping controller is designed to control the energy level and internal dynamics of the hopper. A Poincar\\'e map is used to construct a discrete-time system and a controller with integral action is designed to achieve the control objectives. We considered multiple versions of one-legged hoppers, namely, two-DOF two-mass, two-DOF ankle-knee-hip, and four-link hopper. Simulation results are presented to demonstrate the efficacy of the controllers.
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Title: Gliding robotic fish : design, collaborative estimation, and application to underwater sensing
Creator: Ennasr, Osama Nasr
Date: 2020
Collection: Electronic Theses & Dissertations
Description: Autonomous underwater robots have received significant attention over the past two decades due to the increasing demand for environmental sustainability. Recently, gliding robotic fish has emerged as a promising mobile sensing platform in versatile aquatic environments. Such robots, inspired by underwater gliders and robotic fish, combine buoyancy-driven gliding and fin-actuated swimming to realize both energy-efficient locomotion and high maneuverability. In this dissertation, we first...
Show moreAutonomous underwater robots have received significant attention over the past two decades due to the increasing demand for environmental sustainability. Recently, gliding robotic fish has emerged as a promising mobile sensing platform in versatile aquatic environments. Such robots, inspired by underwater gliders and robotic fish, combine buoyancy-driven gliding and fin-actuated swimming to realize both energy-efficient locomotion and high maneuverability. In this dissertation, we first discuss the design improvements for the second-generation gliding robotic fish "Grace 2". These improvements have transformed the robots to underwater sensing platforms that can be modified to fit the requirements of a specific application with relative ease.We focus on the application of detecting and tracking live fish underwater, which is an important part of fishery research, as it helps scientists understands habitat use, migratory patterns, and spawning behavior of fishes. The gliding robotic fish has demonstrated its ability to detect special acoustic signals emulating tagged fish through a series of trials in Higgins Lake, Michigan. These tests have also validated a gliding-based strategy for navigating to a GPS waypoint, and offered insight into the limitations of the current design. Additional improvements are proposed to allow these robots to glide at larger depths and perform more interesting working patterns underwater.Motivated by the problem of tracking real fish, we consider the case where multiple robots localize and track a moving target without the need for a centralized node. We present theoretical treatment on how a network of robots can infer the location of an emitter (or target), and then track it, through a time-difference-of-arrival (TDOA) localization scheme in a fully distributed manner. In particular, we utilize a networked extended Kalman filter to estimate the target's location in a distributed manner, and establish that successful localization can be achieved under fixed and time-varying undirected communication topologies if every agent is part of a network with a minimum of 4 connected, non-coplanar agents. We further propose a movement control strategy based on the norm of the estimation covariance matrices, with a tuning parameter to balance the trade-off between estimation performance and the total distance traveled by the robots.Finally, motivated by the distributed localization problem, we investigate a more general problem of distributed estimation by a network of sensors. Specifically, we consider the class of consensus-based distributed linear filters (CBDLF) where each sensor updates its estimate in two steps: a consensus step dictated by a weighted and directed communication graph, followed by a local Luenberger filtering step. We show that the sub-optimal filtering gains that minimize an upper bound of a quadratic filtering cost are related to the convergence of a set of coupled Riccati equations. Then we show that the convergence of these coupled Riccati equations depends on the notion of squared detectability for the networked system, and proceed to provide necessary conditions that link the convergence of the coupled Riccati equations to the network topology and consensus weights of the communication graph.
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Title: Integrated modeling and control of flexible aircraft wings
Creator: Wehr, Dagmara Anna
Date: 2014
Collection: Electronic Theses & Dissertations
Description: Structural control for vibration reduction has important applications in many research areas, including the effect of earthquakes on buildings and aerodynamic forces on aircraft stability and performance. Both passive and active control techniques have been implemented, with the best solution usually involving a passive approach followed by an active one. This thesis presents an integrated modeling and controller design approach. Modal Cost Analysis (MCA) and Output Covariance Constraint (OCC...
Show moreStructural control for vibration reduction has important applications in many research areas, including the effect of earthquakes on buildings and aerodynamic forces on aircraft stability and performance. Both passive and active control techniques have been implemented, with the best solution usually involving a passive approach followed by an active one. This thesis presents an integrated modeling and controller design approach. Modal Cost Analysis (MCA) and Output Covariance Constraint (OCC) control are used to reduce a high-order aeroelastic wing model to establish the best controller for the reduced-order model, with a constraint on the covariance of the vibration outputs. MCA seeks to keep the modes that have the highest contribution to a given cost function. Using iterations on the two processes will allow a lower-order controller to be designed and result in the same performance.The OCC and MCA methods and their respective algorithms are presented, and an approach to integrate the two procedures is given. NASA's model used in this thesis is applied to the MCA and OCC algorithms using MATLAB. A 40th-order wing model is derived. The model reduction technique initially reduces the system to a 12th order one. A simulation of the OCC algorithm is performed on the reduced-order model and applied to the full-order model. The controller resulting in the best closed-loop performance is shown to significantly reduce the vibrations due to wind. A corresponding weighting matrix used in OCC is then used for a second round of MCA to further reduce the model to an 8th order model. A lower-order controller designed for this second model is shown to similarly reduce the output vibrations.
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Title: Nonlinear Control of Robotic Fish
Creator: Castaño, Maria L.
Date: 2021
Collection: Electronic Theses & Dissertations
Description: In the past few decades, robots that propel and maneuver themselves like fish, known as robotic fish, have received substantial attention due to their efficiency, maneuverability, and lifelike features. Their agile locomotion can be partially attributed to their bio-inspired propulsion methods, which range from tail (caudal) and dorsal to paired pectoral fins. While these characteristics make robotic fish an attractive choice for a myriad of aquatic applications, their highly nonlinear, often...
Show moreIn the past few decades, robots that propel and maneuver themselves like fish, known as robotic fish, have received substantial attention due to their efficiency, maneuverability, and lifelike features. Their agile locomotion can be partially attributed to their bio-inspired propulsion methods, which range from tail (caudal) and dorsal to paired pectoral fins. While these characteristics make robotic fish an attractive choice for a myriad of aquatic applications, their highly nonlinear, often under-actuated dynamics and actuator constraints present significant challenges in control design. The goal of this dissertation is to develop systematic model-based control approaches that guarantee closed-loop system stability, accommodate input constraints, and are computationally viable for robotic fish.We first propose a nonlinear model predictive control (NMPC) approach for path-following of a tail-actuated robotic fish, where the control design is based on an averaged dynamic model. The bias and the amplitude of the tail oscillation are treated as physical variables to be manipulated and are related to the control inputs via a nonlinear map. A control projection method is introduced to accommodate the inputs constraints while minimizing the optimization complexity in solving the NMPC problem. Both simulation and experimental results on a tail-actuated robotic fish support the efficacy of the proposed approach and its advantages over alternative approaches. Although NMPC is a promising candidate for tracking control, its computational complexity poses significant challenges in its implementation on resource-constrained robotic fish. We thus propose a backstepping-based trajectory tracking control scheme that is computationally inexpensive and guarantees closed-loop stability. We demonstrate how the control scheme can be synthesized to handle input constraints and establish via singular perturbation analysis the ultimate boundedness of three tracking errors (2D-position and orientation) despite the under-actuated nature of the robot. The effectiveness of this approach is supported by both simulation and experimental results on a tail-actuated robotic fish. We then turn our attention to pectoral fin-actuated robotic fish. Despite its benefits in achieving agile maneuvering at low swimming speeds, the range constraint of pectoral fin movement presents challenges in control. To overcome these challenges, we propose two different backstepping-based control approaches to achieve trajectory tracking and quick-maneuvering control, respectively. We first propose a scaling-based approach to develop a control-affine nonlinear dynamic average model for a pectoral fin-actuated robotic fish, which is validated via both simulation and experiments. The utility of the developed average dynamic model is then demonstrated via the synthesis of a dual-loop backstepping-based trajectory tracking controller. Cyclic actuation can often limit precise manipulation of the fin movements and the full exploitation of the maneuverability of pectoral fin-actuated robotic fish. To achieve quick velocity maneuvering control, we propose a dual-loop control approach composed of a backstepping-based controller in the outer loop and a fin movement-planning algorithm in the inner loop. Simulation results are presented to demonstrate the performance of the proposed scheme via comparison with a nonlinear model predictive controller.
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Title: Transient dynamics of nonlinear oscillators with applications to centrifugal pendulum vibration absorbers
Creator: Monroe, Ryan James
Date: 2011
Collection: Electronic Theses & Dissertations
Description: We consider the transient behavior of centrifugal pendulum vibration absorbers (CPVAs), specifically, the overshoot problem encountered when these absorbers are suddenly activated. CPVAs are passive devices used to address torsional vibrations in rotating systems, for example, helicopter rotors and crankshafts of internal combustion engines. They consist of pendulums mounted on a rotor, driven by system rotation, and tuned in such a manner that in steady-state operation they counteract engine...
Show moreWe consider the transient behavior of centrifugal pendulum vibration absorbers (CPVAs), specifically, the overshoot problem encountered when these absorbers are suddenly activated. CPVAs are passive devices used to address torsional vibrations in rotating systems, for example, helicopter rotors and crankshafts of internal combustion engines. They consist of pendulums mounted on a rotor, driven by system rotation, and tuned in such a manner that in steady-state operation they counteract engine-order fluctuating torques acting on the rotor, thereby smoothing vibrations. The primary feature of these devices is that they are order tuned, that is, tuned to a given multiple of the rotation rate, as opposed to the more common frequency tuned absorbers. Recently these absorbers have been proposed to expand the operating envelope for cylinder deactivation in variable displacement engines, in order to improve fuel economy. In these applications, the system encounters conditions in which the absorbers are suddenly activated and undergo a beating-type transient motion, resulting in overshoot of the absorber amplitude before it reaches steady-state. This overshoot depends on a number of parameters, including the difference between the absorber's natural frequency and the frequency of excitation, the ratio of absorber inertia to rotor inertia, the system damping, and system nonlinearities. An approximate analytical model is developed, using perturbation methods, that predicts the overshoot in terms of these parameters, and the model results are verified by simulations of the equations of motion and by experiments using a fully instrumented spin rig. The predictive results are found to provide a useful bound on the overshoot, and will be of use when designing absorber systems so that they do not exceed rattle space constraints during startup. It is found that absorbers with near tautochronic paths behave much like linear absorbers, and when lightly damped and start from small initial conditions, they have an overshoot close to 100%. For absorbers with softening paths, such as the commonly used circular path absorbers, the overshoot can reach up to 173%, depending on system and input parameters.
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Title: Alignment Control for Optical Communication between Underwater Robots
Creator: Solanki, Pratap Bhanu
Date: 2021
Collection: Electronic Theses & Dissertations
Description: Light-emitting diode (LED)-based optical communication is emerging as a promising low-power, low-cost, and high-data-rate alternative to acoustic communication for underwater applications. However, it requires a close-to-line-of-sight (LOS) link between the communicating parties.Achieving and maintaining the LOS is challenging due to the constant movement of underlying mobile platforms caused by propulsion and unwanted disturbances. In this dissertation, a novel, compact LED-based wireless...
Show moreLight-emitting diode (LED)-based optical communication is emerging as a promising low-power, low-cost, and high-data-rate alternative to acoustic communication for underwater applications. However, it requires a close-to-line-of-sight (LOS) link between the communicating parties.Achieving and maintaining the LOS is challenging due to the constant movement of underlying mobile platforms caused by propulsion and unwanted disturbances. In this dissertation, a novel, compact LED-based wireless communication system with active alignment control is presented that maintains the LOS despite the movement of the underlying platform. Multiple alignment control algorithms are developed for scenarios that range from a simple one-way two-dimensional (2D) setting to a practical three-dimensional (3D) bi-directional underwater setting. An extended Kalman filter (EKF)-based approach is first proposed to estimate the relative orientation between the heading angle and the LOS direction, which is subsequently used for alignment control. The EKF uses only the measurement of light intensity from a single photo-diode, where successive measurements are obtained via a scanning technique that ensures the full observability of the underlying system. The approach is first examined in a 2D setting, and then extended to the 3D scenario with improvements in both the hardware and the algorithm. The amplitude of the scanning is modulated according to the alignment performance to achieve a sound trade-off between estimation accuracy, signal strength, and energy consumption. The efficacy of the approach is tested and verified via simulation and on an experimental setup involving two robots with relative 3D motion. The EKF approach uses an assumption that the relative motion between the robots is small, and consequently, requires the communicating robots to take the scanning in an alternating fashion for the convergence of the estimator. An alternative approach, first explored in the 2D setting, is developed that allows simultaneous, bi-directional alignment control for both parties. Because of the convex nature of the measured intensity functions, model-free approaches, including both hill-climbing (HC) and extremum-seeking (ES), are explored. The hill-climbing approach is found to be superior to the ES approach in terms of convergence time and computational efficiency. Theoretical analysis is provided for the hill-climbing approach that guarantees finite time convergence to an $O(\delta)$ neighborhood of the LOS, for control step size $\delta$.Finally, a model-free approach for the 3D setting is proposed that maximizes light intensity based on three consecutive intensity measurements from an equilateral triangle configuration. The efficacy of the approach is demonstrated experimentally, first with an underwater robot controlled by a joystick via LED communication and then with two robots performing bi-directional communication and tracking in an underwater setting.
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Title: Impulsive control of underactuated mechanical systems
Creator: Jafari Tafti, Sayyed Rouhollah
Date: 2012
Collection: Electronic Theses & Dissertations
Description: Although there has been a significant amount of research in designing and analyzing impulsive control systems, there are very few applications of impulsive control in mechanical systems. In the first part of this dissertation, we investigate new control strategies for underactuated mechanical systems based on impulsive inputs. The control problem of underactuated systems is more challenging since such systems have fewer actuators than the number of their degrees of freedom. We first address...
Show moreAlthough there has been a significant amount of research in designing and analyzing impulsive control systems, there are very few applications of impulsive control in mechanical systems. In the first part of this dissertation, we investigate new control strategies for underactuated mechanical systems based on impulsive inputs. The control problem of underactuated systems is more challenging since such systems have fewer actuators than the number of their degrees of freedom. We first address the important concern related to application of impulsive control in mechanical systems, namely, implementation of impulse-like control inputs using standard hardware. This is done through experimental verification of an impulsive control algorithm for swing-up control of the Pendubot; the control algorithm was developed earlier in our research group. Showing the effectiveness of the impulsive control algorithm in experiments, we develop impulsive control algorithms for swing-up control of the Acrobot; the impulsive control algorithms have distinct advantages over existing algorithms in terms of the time required for swing-up and maximum control torque used by the continuous controller. Impulsive inputs cause jumps in velocity states of mechanical systems, and consequently, produce jumps in Lyapunov function candidates used in control design. This attribute is used to enlarge the region of attraction of equilibria using impulsive inputs at discrete instants of time. Several case studies of underactuated mechanical systems have been presented to demonstrate this benefit of using impulsive control. Another advantage of using impulsive inputs is that such inputs can significantly alter the dynamics of the system in a very short period of time. This property is used to design a safe fall algorithm for humanoid robots undergoing a fall, i.e., after the continuous controller has failed to keep the system trajectories confined to a fixed region around the equilibrium. The algorithm uses impulsive inputs to change the fall direction of the robot to minimize the damage to people and objects in the vicinity, as well as to its own self. In many instances, external disturbances or impact from interaction with the environment can have an adverse effect on system performance. In the second part of this dissertation, we develop control algorithms to mitigate these effects in underactuated biped robots. We first develop a disturbance rejection algorithm for the synthetic-wheel biped to mitigate the effects of external disturbances. A continuous controller is then designed for the synthetic-wheel biped to generate an impact-free walking gait. This gait consumes zero energy in the ideal case and the necessary conditions to achieve this gait are shown to be general and applicable to a range of bipedal robotic systems. An underactuated mechanical system can be non-minimum-phase if its zero dynamics is unstable. We finally investigate the output-tracking problem for linear non-minimum-phase systems. Intermittent output tracking is achieved under the condition of finite preview of the reference trajectory; the control algorithm uses switched inputs, which can be approximated by impulsive inputs in the limit.
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Title: Real-time multimodal sensing in nano/bio environment
Creator: Song, Bo
Date: 2016
Collection: Electronic Theses & Dissertations
Description: As a sensing device in nano-scale, scanning probe microscopy (SPM) is a powerful tool for exploring nano world. Nevertheless two fundamental problems tackle the development and application of SPM based imaging and measurement: slow imaging/measurement speed and inaccuracy of motion or position control. Usually, SPM imaging/properties measuring speed is too slow to capture a dynamic observation on sample surface. In addition, Both SPM imaging and properties measurement always experience...
Show moreAs a sensing device in nano-scale, scanning probe microscopy (SPM) is a powerful tool for exploring nano world. Nevertheless two fundamental problems tackle the development and application of SPM based imaging and measurement: slow imaging/measurement speed and inaccuracy of motion or position control. Usually, SPM imaging/properties measuring speed is too slow to capture a dynamic observation on sample surface. In addition, Both SPM imaging and properties measurement always experience positioning inaccuracy problems caused by hysteresis and creep of the piezo scanner. This dissertation will try to solve these issues and proposed a SPM based real-time multimodal sensing system which can be used in nano/bio environment. First, a compressive sensing based video rate fast SPM imaging system is shown as an efficient method to dynamically capture the sample surface change with the imaging speed 1.5 frame/s with the scan size of 500 nm * 500 nm. Besides topography imaging, a new additional modal of SPM: vibration mode, will be introduced, and it is developed by us to investigate the subsurface mechanical properties of the elastic sample such as cells and bacteria. A followed up study of enzymatic hydrolysis will demonstrate the ability of in situ observation of single molecule event using video rate SPM. After that we will introduce another modal of this SPM sensing system: accurate electrical properties measurement. In this electrical properties measurement mode, a compressive feedbacks based non-vector space control approach is proposed in order to improve the accuracy of SPM based nanomanipulations. Instead of sensors, the local images are used as both the input and feedback of a non-vector space closed-loop controller. A followed up study will also be introduced to shown the important role of non-vector space control in the study of conductivity distribution of multi-wall carbon nanotubes. At the end of this dissertation, some future work will be also proposed to fulfill the development and validation of this real-time multimodal sensing system.
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Title: Defense against primary user emulation attacks in cognitive radio networks using advanced encryption standard
Creator: Alahmadi, Ahmed Salah
Date: 2014
Collection: Electronic Theses & Dissertations
Description: This thesis considers primary user emulation attacks (PUEA) in cognitive radio networks operating in the white spaces of the digital TV (DTV) band. We propose a reliable AES-assisted DTV scheme, in which an AES-encrypted reference signal is generated at the TV transmitter and used as the sync bits of the DTV data frames. By allowing a shared secret between the transmitter and the receiver, the reference signal can be regenerated at the receiver and used to achieve accurate identification of...
Show moreThis thesis considers primary user emulation attacks (PUEA) in cognitive radio networks operating in the white spaces of the digital TV (DTV) band. We propose a reliable AES-assisted DTV scheme, in which an AES-encrypted reference signal is generated at the TV transmitter and used as the sync bits of the DTV data frames. By allowing a shared secret between the transmitter and the receiver, the reference signal can be regenerated at the receiver and used to achieve accurate identification of the authorized primary users. Moreover, when combined with the analysis on the auto-correlation of the received signal, the presence of the malicious user can be detected accurately no matter the primary user is present or not. We analyze the effectiveness of the proposed approach through both theoretical analysis and simulation examples. It is shown that with the AES-assisted DTV scheme, the primary user, as well as malicious user, can be detected with high accuracy under primary user emulation attacks. It should be emphasized that the proposed scheme requires no changes in hardware or system structure except of a plug-in AES chip. Potentially, it can be applied directly to today's DTV system under primary user emulation attacks for more efficient spectrum sharing.
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Title: Robotic fish : development, modeling, and application to mobile sensing
Creator: Wang, Jianxun (Mechatronic engineer)
Date: 2014
Collection: Electronic Theses & Dissertations
Description: Robotic fish are underwater robots that emulate locomotion of live fish through actuated fin and/or body movements. They are of increasing interest due to their potential applications such as aquatic environmental monitoring and robot-animal interactions.In this work, several bio-inspired robotic fish prototypes have been developed that make use of periodic tail motions. A dynamic model for a tail-actuated robotic fish is presented by merging rigid-body dynamics with Lighthill's large...
Show moreRobotic fish are underwater robots that emulate locomotion of live fish through actuated fin and/or body movements. They are of increasing interest due to their potential applications such as aquatic environmental monitoring and robot-animal interactions.In this work, several bio-inspired robotic fish prototypes have been developed that make use of periodic tail motions. A dynamic model for a tail-actuated robotic fish is presented by merging rigid-body dynamics with Lighthill's large-amplitude elongated-body theory. The model is validated with extensive experiments conducted on a robotic fish prototype. The role of incorporating the body motion in evaluating the tail-generated hydrodynamic forces is assessed, which shows that ignoring the body motion (as often done in the literature) results in significant overestimate of the thrust force and robot speed. By exploiting the strong correlation between the angle of attack and the tail-beat bias, a computationally efficient approach is further proposed to adapt the drag coefficients of the robotic fish.It has been recognized that the flexibility of the body and fin structures has a pronounced impact on the swimming performance of biological and robotic fish. To analyze and utilize this trait, a novel dynamic model is developed for a robotic fish propelled by a flexible tail actuated at the base. The tail is modeled with multiple rigid segments connected in series through rotational springs and dampers. For comparison, a model using linear beam theory is created to capture the beam dynamics. Experimental result show that the two models have almost identical predictions when the tail undergoes small deformation, but only the proposed multi-segment model matches the experimental measurement closely for all tail motions.Motivated by the need for system analysis and efficient control of robotic fish, averaging of robots' dynamics is of interest. For dynamic models of robotic fish, however, classical or geometric averaging typically cannot produce an average model that is accurate and the in the meantime amenable to analysis or control design. In this work, a novel averaging approach for tail-actuated robotic fish dynamics is proposed. The approach consists of scaling the force and moment terms and then conducting classical averaging. Numerical investigation reveals that the scaling function for the force terms is a constant independent of tail-beat patterns, while the scaling function for the moment term depends linearly on the tail-beat bias. Existence and local stability of the equilibria for the average model are further analyzed. Finally, as an illustration of the utility of the average model, a semi-analytical framework is presented for obtaining steady turning parameters.Sampling and reconstruction of a physical field using mobile sensor networks have recently received significant interest. In this work, an adaptive sampling framework is proposed to reconstruct aquatic environmental fields (e.g., temperature, or biomass of harmful algal blooms) using schools of robotic sensor platforms. In particular, it is assumed that the field of interest can be approximated by a low rank matrix, which is exploited for successive expansion of sampling area and analytical reconstruction of the field. For comparison, an Augmented Lagrange Multiplier optimization approach is also taken to complete the matrix reconstruction using a limited number of samples. Simulation results show that the proposed approach is more computationally efficient and requires shorter travel distances for the robots.
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Title: Modeling, design and control of gliding robotic fish
Creator: Zhang, Feitian
Date: 2014
Collection: Electronic Theses & Dissertations
Description: Autonomous underwater robots have been studied by researchers for the past half century. In particular, for the past two decades, due to the increasing demand for environmental sustainability, significant attention has been paid to aquatic environmental monitoring using autonomous underwater robots. In this dissertation, a new type of underwater robots, gliding robotic fish, is proposed for mobile sensing in versatile aquatic environments. Such a robot combines buoyancy-driven gliding and fin...
Show moreAutonomous underwater robots have been studied by researchers for the past half century. In particular, for the past two decades, due to the increasing demand for environmental sustainability, significant attention has been paid to aquatic environmental monitoring using autonomous underwater robots. In this dissertation, a new type of underwater robots, gliding robotic fish, is proposed for mobile sensing in versatile aquatic environments. Such a robot combines buoyancy-driven gliding and fin-actuated swimming, inspired by underwater gliders and robotic fish, to realize both energy-efficient locomotion and high maneuverability. Two prototypes, a preliminary miniature underwater glider and a fully functioning gliding robotic fish, are presented. The actuation system and the sensing system are introduced. Dynamic model of a gliding robotic fish is derived by integrating the dynamics of miniature underwater glider and the influence of an actively-controlled tail. Hydrodynamic model is established where hydrodynamic forces and moments are dependent on the angle of attack and the sideslip angle. Using the technique of computational fluid dynamics (CFD) water-tunnel simulation is carried out for evaluating the hydrodynamic coefficients. Scaling analysis is provided to shed light on the dimension design. Two operational modes of gliding robotic fish, steady gliding in the sagittal plane and tail-enabled spiraling in the three-dimensional space, are discussed. Steady-state equations for both motions are derived and solved numerically. In particular, for spiral motion, recursive Newton's method is adopted and the region of convergence for this method is numerically examined. The local asymptotic stability of the computed equilibria is established through checking the Jacobian matrix, and the basins of attraction are further numerically explored. Simulation and experiments are conducted to validate steady-state models and calculated equilibria for both motions.Tail-enabled feedback control strategies are studied in both sagittal-plane glide stabilization and three-dimensional heading maintenance. A passivity-based controller and a sliding mode controller are designed and tested in experiments for those two problems, respectively. In sagittal-plane glide stabilization, a nonlinear observer is designed and implemented to estimate velocity-related states. A three-dimensional curve tracking problem is also discussed and a two-degree-of-freedom control scheme is proposed by integrating static inverse mapping and H_&infin control technique. The differential geometric features, such as the torsion and curvature, are explored for planning the trajectory.Finally, the field tests with the lab-developed prototype of gliding robotic fish are conducted in the Kalamazoo River, Michigan and the Wintergreen Lake, Michigan for detecting oil spill and sampling harmful algal blooms, respectively. Both gliding and spiraling motions are tested in the experiments as well as the fish-like swimming. The field test results are presented to show the effectiveness of the designed robot in environmental monitoring tasks.
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