Doctor of Philosophy (PhD), Ohio University, 2007, Electrical Engineering & Computer Science (Engineering and Technology)

Linear impulsive systems are a class of hybrid systems in which the state propagates according to linear continuous-time dynamics except for a countable set of times at which the state can change instantaneously. These systems are useful in representing a number of real world applications, including the problem of drug distribution in the human body, management of renewable resources, spacecraft guidance and control, and sampled-data control systems with consideration of inter-sample behavior. While in general the impulsive effects can be time-driven and/or event-driven, this work focuses on the time-driven case. This study of linear impulsive systems starts by addressing the fundamental concepts of reachability and observability, and shows that these properties depend on whether the impulse times are fixed or free. A geometric characterization of reachable and unobservable sets in terms of invariant subspaces is developed, and algorithms for their construction are established. In particular, the concept of strong reachability, introduced here, enables the formulation of a state-feedback stabilization method for linear impulsive systems that possess these properties. When the open-loop system is strongly reachable, the weighted reachability gramian can be guaranteed to be uniformly positive definite as long as each time interval under consideration contains a sufficient number of impulses, and its inverse can be used to formulate a state feedback law that stabilizes the impulsive system even when the impulse times are not uniformly spaced. An output stabilization problem is formulated and translated into geometric terms starting with the concepts of controlled-invariant and conditioned-invariant subspaces for linear impulsive systems, for which we provide definitions and algorithms for computation. By relating controlled-invariant and conditioned-invariant subspaces of the open-loop impulsive system to invariant subspaces of the corresponding closed-loop system, it (open full item for complete abstract)

Committee: Douglas Lawrence (Advisor) Subjects:

PhD, University of Cincinnati, 2020, Engineering and Applied Science: Aerospace Engineering

This research provides insights on the tilt-rotor quadcopter (TRQ) being a fully actuated system. The tilt-rotor quadcopters are a novel class of quadcopters with the capability of rotating each arm/rotor of the quadcopter to an angle using a servo motor. With the additional servo control inputs, the tilt-rotor quadcopters are fully actuated systems and hence can even hover with a non-zero attitude. Also, this type of a quadcopter can handle external disturbances better than a conventional quadcopter and is fault tolerant. The objective of this dissertation was to design a novel non-linear controller using sliding mode technique that enabled the TRQ to reach desired waypoints, perform robustly under wind disturbances and faults, and hold a commanded attitude and position simultaneously. Four different variants of the tilt rotor quadcopter, namely, TRQ v1, TRQ v2, TCop and TRQ v1H, are studied, and different non-linear control designs using sliding mode technique for each vehicle are presented. Firstly, in this study, the sliding mode control technique is utilized for the pitch, roll and yaw motions for the TRQ v1 while an independent PD controller provides the tilt angles to the servo motors. The dynamic model of the TRQ is presented, based on which sliding surfaces were designed to minimize the tracking errors. Using the control inputs derived from these sliding surfaces, the state variables converge to their desired values in finite-time. Further, the non-linear sliding surface coefficients are obtained by Hurwitz stability analysis. Numerical simulation results are presented that demonstrate the performance and robustness against disturbances using this proposed sliding mode control technique. Secondly, this dissertation studies the fault-tolerant behavior of tilt-rotor platforms. To achieve fault tolerance, the tilt-rotor quadcopter v2 transforms into a T-copter (TCop) design upon motor failure thereby abetting the UAV to cope up with the instabilities ex (open full item for complete abstract)

Committee: Manish Kumar Ph.D. (Committee Chair); Shaaban Abdallah Ph.D. (Committee Member); Kelly Cohen Ph.D. (Committee Member); George T. Black M.S. (Committee Member) Subjects: Aerospace Materials

Doctor of Philosophy, Case Western Reserve University, 2016, EECS - System and Control Engineering

The closed-loop optimal control of multiple model linear systems with unknown parameters is investigated. The Bellman equation is modified to include the discrete random variable of the system mode conditioned on the measurements, and is then used to determine the optimal state feedback or dynamic output feedback controllers. Dynamic programming with the modified Bellman equation is used to calculate the optimal cost with the dual covariance. The dual covariance quantifies the probing aspects of the controller and is demonstrated that the closed-loop state or dynamic output feedback controllers have the dual property for the discrete-time multiple model linear systems with unknown parameters studied in this work. Monte Carlo simulations are used to show that the closed-loop control with state or dynamic output feedback always performs better than controllers such as the Certainty Equivalence or DUL controllers. Finally, the direct discrete-time implementation of the dual dynamic output feedback controller developed in this work is applied to the control of the nonlinear F-16 aircraft. The dual regulator is designed for stability augmentation in the context of reconfigurable control using the multiple model formulation integrated with flight and propulsion to accommodate sensor, actuator, and engine faults. The design process is explained in the context of trim, linearization, calculation of the mode probabilities, and tuning of the Kalman filters and includes the implementation of a six-stage dual regulator with a bank of parallel Kalman filters. The flight simulation results are presented for cases such as speed and pitch rate sensor faults, 1.5% and 3% losses of elevator actuator power, and 4% loss of engine power during steady-state level flight of the nonlinear F-16 aircraft model.

Committee: Kenneth Loparo PhD (Advisor); Marc Buchner PhD (Committee Member); Vira Chankong PhD (Committee Member); Richard Kolacinski PhD (Committee Member) Subjects: Aerospace Engineering; Electrical Engineering

Master of Science, The Ohio State University, 2015, Aero/Astro Engineering

A large number of physical continuous-time systems are controlled using digital controllers. These systems are often referred to as sample data systems or hybrid systems and they have become the norm for many real world applications. With this in mind, the impact of modeling uncertainties and time delay are considered. Maintaining stability in a system is of the upmost importance for any control system but the models which are used to develop the control laws which control the actual system are not perfect, being subject to a variety of uncertainties and errors. The goal of a robust control law is to guarantee the stability despite the uncertainty that may exist in the system while a nominal control law is designed with only single perfectly modeled design point in mind. Despite the drive toward hybrid systems in application, the focus in developing robust control methods for uncertain systems, especially as it applies to input-delayed sample data systems, has been more geared toward strictly continuous-times systems or strictly discrete-time systems. Here a methodology for designing robust digital controllers to stabilize uncertain continuous-time systems when subject to a given range of elemental uncertainty an input-delay is set forth. The inspiration for this research grew out of the challenges of implementing a distributed engine control system for gas turbine engines on aerospace vehicles. As a precursor to the development of the robust control methodology presented in this document, a study was conducted to better understand the impact of uncertainty and time delay on gas turbine engines with a vision toward implementing distributed engine control. Simulation results using linearized models of the GE T700 Turboshaft Engine and the NASA developed generic twin-spool engine model C-MAPSS40k suggest that the gas turbine engine is inherently robust in its ability to maintain stability but still no guarantee of its stability can be made using strictly nominal contr (open full item for complete abstract)

Committee: Rama Yedavalli Dr. (Advisor); Herman Shen Dr. (Committee Member) Subjects: Aerospace Engineering

Doctor of Philosophy, The Ohio State University, 2011, Aero/Astro Engineering

Recently, the idea of using Ecological Sign Stability approach for designing robust controllers for engineering systems has attracted attention with promising results. In this work, continued research on this topic is presented. It is well known that, in the field of control systems, key to a good controller design is the choice of the appropriate nominal system. Since it is assumed that the perturbations are about this nominal, the extent of allowed perturbation to maintain the stability and/or performance very much depends on this ‘nominal' system. Therefore, it is evident that this nominal system must have superior robustness properties. Incorporating certain robustness measures proposed in the literature, control design techniques have been realized in state space framework. However, the variety of controllers in state space framework is not as large as that of robust control design methods in frequency domain. Even these very few methods tend to be complex and demand some specific structure to the real parameter uncertainty (such as matching conditions). Overall, the success of all these methods for application to complex aerospace systems is still a subject of debate. Hence, there is still significant interest in designing robust controllers which can perform better than the existing controllers. Addressing these issues, current research proposes that the stability robustness measures for parameter perturbation are considerably improved if the ‘nominal' system is taken (or driven) to be a ‘sign stable' system. Motivated by this observation, a new method for designing a robust controller for linear uncertain state space systems is proposed. The novelty of this research lies in the incorporation of ecological principles in order to design robust controllers for engineering systems. It is observed that an ecological perspective gives better understanding of the dynamics of the open and closed loop system (nominal) matrices. One of the attractive features of this (open full item for complete abstract)

Committee: Rama K. Yedavalli PhD (Advisor); Meyer Benzakein PhD (Committee Member); Hooshang Hemami PhD (Committee Member) Subjects: Aerospace Engineering

Doctor of Philosophy, The Ohio State University, 2008, Electrical and Computer Engineering

Hypersonic air-breathing vehicles are a promising and cost-efficient technology for launching low-earth-orbit satellites and providing rapid global-response capabilities. Modeling and control of such vehicles has been an active subject of research in recent years. A first-principle, physics-based model (FPM) of the vehicle's longitudinal dynamics has been developed at the Air Force Research Laboratory, and made available to the academic community for control systems design. This model, while suitable for simulation, is intractable for model-based control, thus requiring further control-oriented modeling. A typical control objective is to track a velocity and altitude reference while maintaining physical feasibility of the control input and the state. Two control strategies are presented in this work. The first is a linear time invariant (LTI) design based on a novel formulation of a robust servo-mechanism using singular perturbation arguments. This approach does not rely on state reconstruction but does require an analysis of a family of linearized models from the FPM. The second design relies on reduced-complexity modeling of the FPM. Intractable expressions of the forces and moment in the FPM are replaced with a curve-fit model (CFM). The CFM is expressed as a linear parameter varying (LPV) system, where the scheduling variables depend on the system output. A novel LPV regulator design methodology is developed, which explicitly addresses the case of over-actuated models (i.e., models with more inputs than performance outputs). This is a non-trivial extension of the analysis and design of output regulators for LTI systems. The LPV regulator separates the control problem into a steady-state controller and a stabilizing controller. The steady-state controller produces a non-unique approximate steady-state using receding horizon constrained optimization, while the stabilizer renders the steady-state attractive. The steady-state controller represents an approach to add (open full item for complete abstract)

Committee: Andrea Serrani PhD (Advisor); Stephen Yurkovich PhD (Committee Member); Kevin Passino PhD (Committee Member) Subjects: Electrical Engineering; Engineering

Doctor of Philosophy, The Ohio State University, 2006, Computer and Information Science

Fluid animation remains one of the most challenging problems in computer graphics. Research on methods using physics-based simulation for animation has recently increased since this method has the capability of producing realistic fluid behavior. However, the primary drawback to using a simulation method is control of the resulting flow field because it is computationally expensive and highly nonlinear. The main goal of this research is to help users produce physically realistic fluid effects along a NURBS curve that can be specified directly or derived from an image or video. A linear-feedback velocity matching method is used to control the fluid flow. A physically realistic smoke flow along a user-specified path is generated by first procedurally producing a target velocity field, and then matching the velocity field obtained from a three-dimensional flow simulation with the target velocity field. The target velocity field can include various effects such as the small scale swirling motion characteristic of turbulent flows. The swirling motion is achieved by incorporating a vortex particle method into the linear feedback loop. The method is flexible in that any procedurally-generated target velocity field may be integrated with the fluid simulation. The efficacy of this approach is demonstrated by generating several three-dimensional flow animations for complex fluid paths, two-dimensional artistic fluid effects, and realistic tornado animations.

Committee: Raghu Machiraju (Advisor) Subjects: Computer Science

Doctor of Philosophy, Case Western Reserve University, 2004, Systems and Control Engineering

Cruse's model of leg coordination (CCM) was derived to account for gaits and gait transitions in arthropods (analogous to, e.g. walktrotgallop in some quadrupeds). It has also been adapted to control locomotion in a series of hexapod robots. CCM is a systems-level, kinematic model that abstracts key physiological and dynamical properties in favor of tractability. A key feature is that gaits emerge from interaction among pairs of legs as effected by a set of coordination mechanisms acting at discrete points in time. We represent CCM networks as systems of coupled hybrid oscillators. Gaits are quantified by a temporal (discrete) phase vector. System trajectories are polyhedral, hence solvable over finite-time, but the presence of the switching automaton renders infinite horizon properties harder to analyze. Via numerical and symbolic simulations, we have mapped out the synchronization behavior of CCM networks of various topologies parametrically. We have developed a section-map analysis approach that exploits the polyhedral geometry of the hybrid state space. Our approach is constructive. Once switching boundaries are appropriately parameterized, we can extract periodic orbits, their domains of admissibility and stability, as well as expressions for the period of oscillation and relative phase of each cycle, parametrically. Applied to 2-oscillator networks, our approach yields excellent agreement with simulation results. A key emergent concept is that of a virtual periodic orbit (VPO). Distinguished from admissible periodic orbits, VPOs do not correspond to any in the underlying hybrid dynamics. However, when stable and close to being admissible, they are canonical precursors for a class of nonsmooth bifurcations and predictive of long transient behavior. Last, we take into consideration the possibility and difficulties of extending our approach to larger networks and to related oscillator-like hybrid dynamical systems with polyhedral trajectories.

Committee: Randall Beer (Advisor) Subjects:

Master of Science in Electrical Engineering (MSEE), Wright State University, 2023, Electrical Engineering

Stochastic resonance (SR) is a phenomenon that can enhance the detection or transmission of weak signals by adding random noise to a non-linear system. SR introduced into the human motor control system as a subthreshold mechanical vibration has shown promise to improve sensitivity to haptic feedback. SR can be valuable in a laparoscopic surgery application, where haptic feedback is critical. This research sought to find if applying SR to the human motor control system improves performance in a laparoscopic probing task, if the performance differs based on the location of stochastic resonance application, and if there are sustained effects from SR after its removal. Subjects were asked to perform a palpation task using a laparoscopic probe to determine whether a series of simulated tissue samples contained a tumor. Subjects in the treatment groups were presented with a series of samples under the following conditions: Pre-SR, SR applied to the forearm or elbow, and Post-SR. Subjects in the control group did not have SR applied at any point. Performance was measured through the accuracy of tissue assessment, subjects' confidence in their assessment, and assessment time. Data from 27 subjects were analyzed to investigate the application of stochastic resonance and its sustained effects to improve haptic feedback sensitivity in a simulated laparoscopic task. The forearm group was shown to have significant improvement in the accuracy of tissue identification and sensitivity to haptic feedback with the application of SR. Additionally, the forearm group showed a greater improvement in accuracy and sensitivity than the elbow group. Finally, after SR was removed, the forearm group showed sustained significant improvement in accuracy and sensitivity. Therefore, the experiment results supported the hypotheses that stochastic resonance improves subjects' performance and haptic perception, that performance improvement differs based on application location, and that subjec (open full item for complete abstract)

Committee: Luther Palmer III, Ph.D. (Advisor); Caroline Cao Ph.D. (Committee Member); Katherine Lin M.D. (Committee Member) Subjects: Biomedical Engineering; Biomedical Research; Engineering; Health; Health Care; Mechanical Engineering; Surgery

Doctor of Philosophy, The Ohio State University, 2023, Mechanical Engineering

Since its inception in the 1930s, the evolution of the jet engine has largely been dictated by the need to improve propulsion and fuel economy while reducing noise and environmental impact. Although rapid engineering advancements have enabled progress towards these design objectives, they have also yielded increasingly complex air flowpaths, and further improvements have been inhibited by a lack of understanding of the fluid dynamics. This is because the flowfields are typically characterized by interacting turbulent jets, shear layers, boundary layers, and wakes which evolve in the presence of supersonic expansion and shock waves. Additionally, they are rife with fluid dynamic instabilities that may pose a challenge to the structural, thermal and acoustic performance of the engine. To address this knowledge gap, the present work builds upon a collaborative numerical and experimental campaign between The Ohio State University and Syracuse University, that investigates a supersonic, multistream, airframe-integrated, rectangular nozzle architecture that is representative of emerging industry designs. The configuration consists of a contoured, single-sided expansion nozzle on one side, and a flat aft-deck surface representing the airframe on the other. Within the nozzle, two rectangular streams - a supersonic (Mach 1.6) "core" stream and sonic (Mach 1) "deck" stream - interact after being initially separated by a thick splitter plate. The flow conditions and geometry of the nozzle render a complex 3D flowfield which has been extensively examined in previous work. It is also comprised of a shear layer instability which is initiated at the splitter plate trailing edge (SPTE) and is associated with large vortical structures and a strong tone that have a deleterious effect on the acoustic and structural characteristics of the nozzle. Although previous research works attempting to mitigate the instability by thinning out the SPTE have been promising, such (open full item for complete abstract)

Committee: Datta Gaitonde (Advisor); Jen-Ping Chen (Committee Member); Seung Hyun Kim (Committee Member) Subjects: Aerospace Engineering; Mechanical Engineering

Master of Science in Electrical Engineering, University of Dayton, 2022, Electrical Engineering

Despite impressive advancements in the field of robotics, tasks such quick reaching movements, bipedal locomotion, and balance maintenance have shown to be a challenge. A possible reason for this is the predominance of feedback controls in robotics, which provide robust controllers at the expense of a slower response. The part of the human brain responsible for the performance of such tasks is the cerebellum, which functions exclusively in a feedforward way. Prior studies have shown cerebellum inspired controller's capabilities in movement learning, performing quick reaching movements, and functioning in uncertain environments. This thesis focuses on supervised learning cellular-level cerebellum computational models and its capability of performing balance related tasks. Through computer simulations, the innovative design was tested for the first time on the balancing of the inverted pendulum and double inverted pendulum. Another concept investigated in this work is the effect of cerebellum network size on performance, where among four different network sizes, the largest network ever simulated by the EDLUT spiking neural network simulator was created. Lastly, the controller's capability to transfer knowledge to another model performing the same task with different dynamics was evaluated. All controller sizes tested displayed impressive results on the inverted pendulum, quickly learning how to balance the pole. For the double inverted pendulum, all but the smaller sized network were able to achieve learning. The larger networks displayed better performance in both tasks, but the creation of even larger networks might be necessary to properly define the cerebellum network size effect on performance. The bio-inspired design was also shown to be capable of transferring knowledge, with an initially trained controller outperforming an initially naive controller on inverted pendulum models with different dynamics. The findings of this experiment show that cerebellum comp (open full item for complete abstract)

Committee: Raúl Ordóñez (Advisor); Terek Taha (Committee Member); Temesguen Kebede (Committee Member) Subjects: Electrical Engineering

Master of Science (MS), Ohio University, 2021, Mechanical Engineering (Engineering and Technology)

Potential energy savings for small unmanned multirotor copters inside Ground Effects (GE) could be used to increase flight time or mission payload. Operating Inside Ground Effects (IGE) presents non-linear thrust responses potentially introducing instabilities requiring more advanced control than currently present on small autopilot systems. While maximum energy savings are found for rotorcraft hover flight IGE, low altitude forward flight has been shown to offer partial energy saving for small forward velocities compared to hover. The aim of this research was to explore multirotor copter forward flight IGE using an aerodynamics model, such as Blade Element Momentum Theory (BEMT), and quadcopter simulation flights. An existing BEMT method designed to include GE was further modified to consider the impacts forward flight on rotor thrust output for sUAS sized propellers. Thrust results were then adapted to the rotor dynamics of the quadcopter model to simulate low altitude flight of a multirotor sUAS. Non-linear dynamic inversion was used to stabilize the rotorcraft dynamics IGE and maintain specific Height Ratios (HR) during forward flight. GE thrust boosts were compensated for using a GE strength determination method which predicted the rotor GE response by monitoring individual rotor altitudes. Rotor power data collected from quadcopter simulation flights both OGE and IGE were used to identify flight conditions with decreased rotor power and measure the control effort needed multirotor flight IGE. Simulation results found average rotor power to decrease with decreasing HR and forward flight velocity. Increasing forward flight velocity was found to decrease the range of HR where GE energy savings were still present. Flight conditions with decreased power requirements were identified and grouped within an increased rotor efficiency region ranging from HRs of 0.5 to 2 and a forward flight ratios of 0 to 1.5. The increased efficiency region included a range of flight c (open full item for complete abstract)

Committee: Jay Wilhelm (Advisor); Sergio Ulloa (Committee Member); Douglas Lawrence (Committee Member); Robert Williams (Committee Member) Subjects: Aerospace Engineering; Energy; Engineering

Master of Science, The Ohio State University, 2017, Mechanical Engineering

This thesis presents the development details of a human safety robotic arm design with variable stiffness, starting from an initial conceptual design to prototype validations. Instead of changing the compliance of the joint, this design concept introduces compliance to the robotic link itself. The mechanism of the design is a parallel guided beam with a slider linear actuated by a power screw and a DC motor. By controlling the slider position, the effective length of the robotic arm link can be adjusted to achieve necessary stiffness change. The stiffness variation capability of the effective length concept was first validated on a physical conceptual model by experiments. For comparison, a simulation model was also created for the structure of the robotic arm in Abaqus using finite element methods. All the analysis, simulation and tests performed in this research were based on small beam bending deflections. A prototype was developed based on the conceptual model, having transmission and actuation module integrated. Simple and accurate PID position control using Arduino for rapid prototyping is also demonstrated in this thesis. The performance of the prototype was evaluated by two categories of experiments: stiffness tests and PID position calibration. The overall stiffness change ratio achieved was around 20 times by static stiffness test results. The position steady state error and the overshoot of the system was within 0.5mm.

Committee: Haijun Su (Advisor); Junmin Wang (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2015, Aero/Astro Engineering

Secondary flows in turbomachinery and similar engineering applications are often dominated by a single streamwise vortex structure. Investigations into the control of these flows using periodic forcing have shown a discrete range of forcing frequency where the vortex is particularly receptive. Forcing in this frequency range results in increased movement of the vortex and decreased total pressure losses. Based on the hypothesis that this occurs due to a linear instability associated with the Crow instability, a fundamental study of instabilities in streamwise vortex-wall interactions is performed. In the first part of this study a three-dimensional vortex-wall interaction is computed and analyzed for the presence of convective instabilities. It is shown that the Crow instability and a range of elliptic instabilities exist in a similar form as to what has been studied in counter-rotating vortex pairs. The Crow instability is particularly affected by the presence of a solid no-slip wall. Differences in the amplification rate, oscillation angle, Reynolds number sensitivity, and transient growth are each discussed. The spatial development of the vortex-wall interaction is shown to have a further stabilizing effect on the Crow instability due to a “lift-off” behavior. Despite these discoveries, it is still shown that amplitude growth on the order of 20% is possible and transient growth mechanisms might result in an order-of-magnitude of further growth if properly initiated. With these results in mind, an experiment is developed to isolate the streamwise vortex-wall interaction. Through the use of a vortex generating wing section and a suspended splitter plate, a stable interaction is created that agrees favorably in structure to the three-dimensional computations. A small synthetic jet actuator is mounted on the splitter plate below the vortex. Phase-locked stereo-PIV velocity data and surface pressure taps both show spatial amplification of the disturbance in a frequenc (open full item for complete abstract)

Committee: Jeffrey Bons Ph.D. (Advisor); Mohammad Samimy Ph.D. (Committee Member); James Gregory Ph.D. (Committee Member); Jen-Ping Chen Ph.D. (Committee Member) Subjects: Aerospace Engineering; Fluid Dynamics

MS, University of Cincinnati, 2014, Engineering and Applied Science: Aerospace Engineering

Air-breathing hypersonic vehicles have the potential to provide global reach and affordable access to space. Recent technological advancements have made scramjet-powered flight achievable, as evidenced by the successes of the X-43A and X-51A flight test programs over the last decade. Air-breathing hypersonic vehicles present unique modeling and control challenges in large part due to the fact that scramjet propulsion systems are highly integrated into the airframe, resulting in strongly coupled and often unstable dynamics. Additionally, the extreme flight conditions and inability to test fully integrated vehicle systems larger than X-51 before flight leads to inherent uncertainty in hypersonic flight. This thesis presents a means to design vehicle geometries, simulate vehicle dynamics, and develop and analyze control systems for hypersonic vehicles. First, a software tool for generating three-dimensional watertight vehicle surface meshes from simple design parameters is developed. These surface meshes are compatible with existing vehicle analysis tools, with which databases of aerodynamic and propulsive forces and moments can be constructed. A six-degree-of-freedom nonlinear dynamics simulation model which incorporates this data is presented. Inner-loop longitudinal and lateral control systems are designed and analyzed utilizing the simulation model. The first is an output feedback proportional-integral linear controller designed using linear quadratic regulator techniques. The second is a model reference adaptive controller (MRAC) which augments this baseline linear controller with an adaptive element. The performance and robustness of each controller are analyzed through simulated time responses to angle-of-attack and bank angle commands, while various uncertainties are introduced. The MRAC architecture enables the controller to adapt in a nonlinear fashion to deviations from the desired response, allowing for improved tracking performance, stabili (open full item for complete abstract)

Committee: Kelly Cohen Ph.D. (Committee Chair); Michael Bolender Ph.D. (Committee Member); Elad Kivelevitch Ph.D. (Committee Member) Subjects: Aerospace Materials

Master of Science, The Ohio State University, 2013, Entomology

Pumpkins (Cucurbita pepo) rely on insect-mediated pollination, and host a distinct community of pests, natural enemies and pollinators. My goal was to determine if biocontrol and pollination services in pumpkins were affected by local habitat management and landscape composition in Ohio. I measured biocontrol through predation and parasitism rates of sentinel egg cards of squash bug (Anasa tristis) and the spotted cucumber beetle (Diabrotica undecimpunctata howardii), and collected adults of striped cucumber beetle (Acalymma vittatum) to determine parasitism activity in 2011-2012. I used pitfall traps to determine the activity density of ground-dwelling predators per field per sample period, and video cameras to determine the taxa responsible for egg mortality. I measured visitation frequency and duration of Apis mellifera, Bombus spp., and Peponapis pruinosa in male and female flowers of pumpkins in 2011-2012, and pollen deposition across the pollination window (0600-1200 hr) in 2012. I tested the Intermediate Landscape-Complexity Hypothesis in one year by determining the combined effects of surrounding landscape composition and local habitat management on the relative visit frequency of pollinators, activity density of predators, and rates of predation and parasitism services by ranking general linear mixed models. I found that only D. undecimpunctata experienced a significant amount of egg predation, which was positively correlated to the percentage of field crops within a 1500 m radius of pumpkin fields. The parasitism of A. vittatum and the visitation frequency of A. mellifera was diluted in the presence of fruit and vegetable habitats within a 1500 m radius, and P. pruinosa visit frequency was diluted within a 500 m radius. Parasitism of A. vittatum was positively associated with urban habitats within a 500 m radius, and the visit frequency of P. pruinosa was positively associated with urban habitats within a 1500 m radii. Predation of A. tristis and D. undeci (open full item for complete abstract)

Committee: Mary Gardiner (Advisor); Karen Goodell (Committee Member); Robin Taylor (Committee Member); Celeste Welty (Committee Member) Subjects: Agriculture; Ecology; Entomology

Master of Science, The Ohio State University, 2013, Aero/Astro Engineering

This thesis addresses the importance and issues of the robust control design of linear time-invariant (LTI) systems with real-time parameter uncertainties. It is known that most of the existing robust control techniques are fairly conservative when dealing with real time parameter uncertainty. Also, majority of these existing techniques use control gains that are essentially functions of the perturbation information. The robust control design algorithm proposed in this thesis differs from these traditional techniques by focusing on the control design in achieving a specific structure of the closed loop system matrix that guarantees a maximum stability robustness index as possible without the using any of the perturbation information. The determination of this specific desired structure of closed loop system matrix forms the focal point of this algoithm and is inspired by already existing principles in the field of ecology. Using this ecological backdrop, the desired closed loop matrix is determined to contain self regulated species with predator-prey interactions among these species. In matrix nomenclature, such a set of matrices are labelled as Target Pseudo-Symmetric (TPS) matrices and hence form the class of desirable closed-loop system matrices. Based on these TPS matrices, which capture the maximum robustness index for any LTI system, a robust control design is carried out such that the final closed loop system possesses a robustness index as close to this maximum as possible. The robust control design algorithm presented is based on minimizing the norm of an implicit error and is supported with several illustrative examples. This eco-inspired robust control algorithm exemplifies the strong correlation that exists between natural systems and engineering systems. Hence, the main goal of this thesis is to aid in the revival of research in the field of robust control using insights from ecological principles.

Committee: Rama Yedavalli Dr. (Advisor); Chia-Hsiang Menq Dr. (Committee Member) Subjects: Aerospace Engineering; Applied Mathematics; Automotive Engineering; Ecology; Engineering; Mathematics Education; Mechanical Engineering

MS, University of Cincinnati, 2001, Engineering : Mechanical Engineering

Stability is imperative in the design of hydraulic systems. Servo-hydraulic systems are inherently non-linear creating various nuances when analyzing the stability of the system. Friction, port flow, saturation, impact loading, line dynamics, and boundary conditions are a few of the many non-linearities found in servo-hydraulic systems which are to be analyzed using advanced non-linear stability analysis techniques. Some effects of instabilities induced by non-linearities such as pressure oscillations, noise, etc., can be detrimental to the stability or operation of hydraulic systems especially when the design is near the envelope of stability. This thesis presents preliminary research on the various non-linearities found in hydraulic systems. A test stand has been developed to test the hydraulic cylinder system dynamics, with the inclusion of a mass-spring-damper system. An experimental modal analysis was performed on the hydraulic test stand to provide helpful information regarding the natural frequencies of the structure to insure that these frequencies do not lie near the natural frequencies of the hydraulic systems. Initial non-linear dynamic testing was completed on two hydraulic cylinders, consisting of finding the breakaway friction forces of the hydraulic cylinders.

Committee: Dr. David Thompson (Advisor) Subjects: Engineering, Mechanical

MS, University of Cincinnati, 2003, Engineering : Mechanical Engineering

Hydraulic power systems find a wide range of applications varying from high power transmission as in heavy machinery to accurate control as in robotics and flight control actuators, and in mobile systems like agricultural machines. Hydraulic systems have many advantages. They have a high power to weight ratio and the system can be controlled electronically. Therefore they are flexible and are efficient in transferring and controlling power. Hydraulic systems are highly nonlinear in nature and exhibit dynamic fluctuations in parameters such as pressure and velocity. These effects, if not controlled, would lead to large scale oscillations that would damage system components. This work is focused on the robust parametric stability analysis a servo-hydraulic system in two-parameter space. A higher order linear controller and a nonlinear controller using feedback linearization technique are designed. State and input/output transformation were used to reduce the order of the inner-loop feedback linearized plant. In this thesis, the stable-unstable boundary for two-parameter variations is obtained by non-linear analysis and is verified by experimentation. These stability boundaries are used as a tool to study the robustness of the system by measure of distance to instability from the nominal parameters. The control strategies were implemented using Matlab/Simulink and the real time control was implemented using WinCon software developed by Quanser.

Committee: Dr. David F. Thompson (Advisor) Subjects: Engineering, Mechanical

Master of Science, The Ohio State University, 2012, Electrical and Computer Engineering

Robust control of linear state space systems is an important area since uncertainties in the system can result in unacceptable system behavior. Before starting actual control design, analyzing the system to obtain detailed information about its characteristics always helps in achieving better results. This research is an attempt into understanding more about the robustness of linear uncertain systems based on their feedback structure. One of the basic reason for introducing feedback in control design is uncertainty and hence, understanding the feedback structure of a system can give useful insights in its robustness properties. Individual elements in a system interact with each other to form feedback cycles, thus forming feedback structure of the system. Ecological systems are shown to have robustness properties since they tend to be stable under the influence of external perturbations. It would be interesting to see if such principles in ecology could be useful in designing robust engineering control systems. To address these topics, the current research investigates applicability of an ecological method of finding out sensitivity of a system to its model structure into robustness analysis of engineering systems. This method has been modified and improved to address the robustness issue in linear uncertain systems. Moreover, new robustness indices have been proposed that measure the robustness of a system based on sensitivity of elements in it to its stability. Thus, this research finds ecological principles to be very helpful in designing robust control systems and stresses the importance of research to further investigate this idea.

Committee: Hooshang Hemami PhD (Advisor); Rama Yedavalli PhD (Advisor) Subjects: Electrical Engineering