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Packard, Nathan OwenActive Flow Separation Control of a Laminar Airfoil at Low Reynolds Number
Doctor of Philosophy, The Ohio State University, 2012, Aero/Astro Engineering
Detailed investigation of the NACA 643-618 is obtained at a Reynolds number of 6.4x104 and angle of attack sweep of -5° < α < 25°. The baseline flow is characterized by four distinct regimes depending on angle of attack, each exhibiting unique flow behavior. Active flow control is exploited from a row of discrete holes located at five percent chord on the upper surface of the airfoil. Steady normal blowing is employed at four representative angles; blowing ratio is optimized by maximizing the lift coefficient with minimal power requirement. The range of effectiveness of pulsed actuation with varying frequency, duty cycle and blowing ratio is explored. Pulsed blowing successfully reduces separation over a wide range of reduced frequency (0.1-1), blowing ratio (0.5–2), and duty cycle (0.6–50%). A phase-locked investigation, by way of particle image velocimetry, at ten degrees angle of attack illuminates physical mechanisms responsible for separation control of pulsed actuation at a low frequency and duty cycle. Temporal resolution of large structure formation and wake shedding is obtained, revealing a key mechanism for separation control. The Kelvin-Helmholtz instability is identified as responsible for the formation of smaller structures in the separation region which produce favorable momentum transfer, assisting in further thinning the separation region and then fully attaching the boundary layer. Closed-loop separation control of an oscillating NACA 643-618 airfoil at Re = 6.4x104 is investigated in an effort to autonomously minimize control effort while maximizing aerodynamic performance. High response sensing of unsteady flow with on-surface hot-film sensors placed at zero, twenty, and forty percent chord monitors the airfoil performance and determines the necessity of active flow control. Open-loop characterization identified the use of the forty percent sensor as the actuation trigger. Further, the sensor at twenty percent chord is used to distinguish between pre- and post- leading edge stall; this demarcation enables the utilization of optimal blowing parameters for each circumstance. The range of effectiveness of the employed control algorithm is explored, charting the practicality of the closed-loop control algorithm. To further understand the physical mechanisms inherent in the control process, the transients of the aerodynamic response to flow control are investigated. The on-surface hot-film sensor placed at the leading edge is monitored to understand the time delays and response times associated with the initialization of pulsed normal blowing. The effects of angle of attack and pitch rate on these models are investigated. Black-box models are developed to quantify this response. The sensors at twenty and forty percent chord are also monitored for a further understanding of the transient phenomena.

Committee:

Jeffrey Bons, Dr. (Advisor); Mohammad Samimy, Dr. (Committee Member); Jen-Ping Chen, Dr. (Committee Member); Andrea Seranni, Dr. (Committee Member)

Subjects:

Aerospace Engineering; Fluid Dynamics

Keywords:

active flow control; experimental fluid dynamics; closed-loop control

Litter, Jansen J.Mobile robot for search and rescue
Master of Science (MS), Ohio University, 2004, Mechanical Engineering (Engineering)
This thesis presents an overview of search and rescue mobile robots associated with RoboCup and the IGVC. The design of the Ohio University robot that will compete in RoboCup Search and Rescue competitions is explained as well as future work to be done. Solid modeling and FEA analysis of the robot is shown. A stall-torque model is derived as well as the top no-load speed of each tire. These calculations are then compared to real world data. Based on velocity and acceleration data from testing, the robot behaves as was predicted by the calculations. The control of the robot is discussed in the thesis. Open-loop control is the method used for evaluation in this thesis. Closed-loop control and methods to implement it are discussed as well. It was found that the robot can leave marks on concrete and linoleum as well as leave tracks in grass. Recommendations were made to keep this robot from harming any surface it drives on.

Committee:

Robert Williams, II (Advisor)

Keywords:

Mobile Robot; Stall-Torque Model; Open-Loop Control; Closed-Loop Control

WANG, YINGYINGPower Transmitter and Battery Management IC for a Wireless Recharging System
Master of Sciences (Engineering), Case Western Reserve University, 2009, EECS - Electrical Engineering

External and internal circuits for wireless battery recharging have been developed.The external power transmitter operates at 125 kHz, suitable for operation in deeply implanted biomedical devices or in salt water. The power management circuit for the internal device provides efficient charging of Lithium-ion batteries.

The power transmitter is an efficient Class-E amplifier to transmit power, and commands can be sent by modulating the gate drive of the power transistor. A novel microprocessor-based closed-loop controller is used to optimize frequency and duty factor of the gate drive in real time. Experimental results indicate a dc-to-ac conversion gain of 3.5 for the drain-to-source voltage of the transistor, and 21.9 times for the load inductor, with low power consumption in the switch.

By employing current sense and control loops, a novel charge management integrated circuit realizes a smooth transition from constant-current (C-I) mode to constant-voltage (C-V) mode, and provides accurate switching from C-I to C-V to end-of-charge. SPICE simulations in a 0.5-μm bulk CMOS process indicate that the proposed circuitry can provide an accurate voltage/current profile with a C-I charging current of 1.5 mA, while drawing 140 μA from a 4.2-V supply. Die area is just 300 μm by 56 μm. A prototype IC is being sent for fabrication.

Committee:

Steven Garverick (Advisor); Darrin Young (Committee Member); Swarup Bhunia (Committee Member)

Subjects:

Electrical Engineering

Keywords:

Power transmitter; optimal Class-E working condition; closed-loop control; power efficiency.

Wenzel, Brian JeffreyCLOSED-LOOP ELECTRICAL CONTROL OF URINARY CONTINENCE
Doctor of Philosophy, Case Western Reserve University, 2005, Biomedical Engineering
Individuals with spinal cord injury or neurological disorders may develop involuntary bladder contractions at low volumes (bladder hyper-reflexia) that cause incontinence and can lead to significant health problems. Bladder contractions can be suppressed by electrical stimulation of inhibitory pathways, but continuous activation may lead to habituation of the inhibitory reflex and loss of continence. Conditional stimulation, with stimulation of inhibitory pathways applied only at the onset of nascent bladder contractions, should reduce habituation. Conditional stimulation needs methods of detecting the onset of bladder contractions to trigger inhibitory electrical stimulation. The objectives of this study were to determine if the electrical activity of the pudendal nerve could serve as a control signal for conditional stimulation, to determine whether conditional stimulation allowed the bladder to fill to a greater volume before continence was lost than did continuous stimulation, and to determine whether the techniques developed to detect bladder contractions could be transferred to individuals with a spinal cord injury (SCI). The electrical activity of the pudendal nerve was modulated during bladder contractions and recordings of the pudendal nerve electroneurogram enabled detection of the onset of reflexive bladder contractions within 2 seconds of the start of the bladder contractions in 9 anesthetized male cats. Conditional electrical stimulation based on the electrical activity of the pudendal nerve allowed the bladder to fill to greater capacity before continence was lost than either continuous stimulation or no stimulation. The techniques developed in preclinical studies were tested on a retrospective clinical data set of 81 subjects with SCI. The activity of the external anal sphincter was modulated in individuals with SCI and enabled detection of the hyper-reflexive bladder contraction. These results indicate that the electrical activity of pudendal nerve can serve as a control signal for conditional inhibitory stimulation, conditional stimulation is more effective at maintaining continence than continuous inhibitory stimulation or no stimulation, and these techniques are transferable to humans with SCI.

Committee:

Warren Grill (Advisor)

Subjects:

Engineering, Biomedical

Keywords:

Urinary Continence; Neural Prosthesis; Electrical Stimulation; Closed-Loop Control

Botha, Hermanus Van NiekerkA Closed Loop Research Platform That Enables Dynamic Control Of Wing Gait Patterns In A Vertically Constrained Flapping Wing - Micro Air Vehicle
Master of Science in Computer Engineering (MSCE), Wright State University, 2016, Computer Engineering
Research in Flapping Wing - Micro Air Vehicles(FW-MAVs) has been growing in recent years. Work ranging from mechanical designs to adaptive control algorithms are being developed in pursuit of mimicking natural flight. FW-MAV technology can be applied in a variety of use cases such a military application and surveillance, studying natural ecological systems, and hobbyist commercialization. Recent work has produced small scale FW-MAVs that are capable of hovering and maneuvering. Researchers control maneuvering in various ways, some of which involve making small adjustments to the core wing motion patterns (wing gaits) which determine how the wings flap. Adaptive control algorithms can be implemented to dynamically change these wing motion patterns to allow one to use gait based modification controllers even after damage to a vehicle or its wings occur. This thesis will create and present a hardware research platform that enables hardware-in-the-loop experimentation with core wing gait adaptation methods.

Committee:

John Gallagher, Ph.D (Advisor); Travis Doom, Ph.D (Committee Member); Mateen Rizki, Ph.D (Committee Member)

Subjects:

Computer Engineering

Keywords:

FW-MAV, Closed Loop Control, Machine Learning, Autonomy, Control

To, Curtis Sai-HayClosed-Loop Control and Variable Constraint Mechanisms of a Hybrid Neuroprosthesis to Restore Gait after Spinal Cord Injury
Doctor of Philosophy, Case Western Reserve University, 2010, Biomedical Engineering

A hybrid neuroprosthesis (HNP) was developed with the goal of providing improved gait to individuals with paraplegia relative to existing assistive gait systems. The HNP is an approach to restoring gait by combining a lower extremity exoskeleton with functional neuromuscular stimulation (FNS). Individually, exoskeletons apply constraints for support, but provide limited step length and depend on upper extremity actions on a walker for forward propulsion. Conversely, FNS mobilizes the limbs through electrical pulses to paralyzed muscles. However, muscles targeted for stimulation quickly fatigue and provide inadequate postural support. The HNP was designed to functionally combine the supportive features of the exoskeleton and joint mobility of FNS. Controllable knee and hip joint mechanisms were developed to support the user while allowing for functional motion from FNS for forward progression. These mechanisms were optimized for maximal torque when supporting a joint and minimal resistance when driven by FNS. A closed-loop controller based on sensor measurements of joint dynamics was developed to synchronize exoskeletal operation with muscle stimulus activity. The objectives were to modulate joint constraints to provide continual support to the user while minimizing the deleterious effects of the constraints on joint mobility, deactivate stimulus to target muscles when certain exoskeletal constraints are engaged to allow the target muscles to rest, and modulate FNS from baseline levels to achieve functional joint positions.

The operational response of the controller and mechanisms were characterized through simulation, bench, and able-bodied testing. Implementation of the HNP with an individual with paraplegia respectively showed a 40 % and 16 % reduction in maximum exerted upper extremity forces relative to exoskeleton-only and FNS-only gait. Step lengths were shown to be comparable between HNP and FNS-only gait. When comparing the HNP with and without the FNS modulation, the average gait speed was increased by 16 % with FNS modulation due to a 10 % increase in the hip range of motion. Reductions in muscle activity were feasible when the exoskeletal constraints were enabled.

Future work to optimize joint coordination or apply an active mechanism to the exoskeleton to assist hip extension may improve postural control and forward progression.

Committee:

Robert Kirsch, PhD (Committee Chair); Ronald Triolo, PhD (Committee Member); Roger Quinn, PhD (Committee Member); Patrick Crago, PhD (Committee Member); Musa Audu, PhD (Advisor)

Subjects:

Biomedical Research; Design; Engineering; Health Care; Mechanical Engineering; Rehabilitation; Technology

Keywords:

hybrid neuroprosthesis; exoskeleton; functional neuromuscular stimulation; gait restoration; assistive gait systems; spinal cord injury; paraplegia; portable/wearable hydraulic constraint mechanisms; closed-loop control of gait; real-time control

Garimella, SureshActuator Modeling and Control For a Three Degrees of Freedom Differential Thrust Control Testbed
Master of Science (MS), Ohio University, 2007, Electrical Engineering & Computer Science (Engineering and Technology)
This thesis presents an improvement in the performance of a three degrees of freedom differential thrust control testbed by considering the actuator dynamics. The testbed consists of three propellers that are used to produce thrust as well as attitude control for vertical takeoff and landing flight. Actuator dynamics consist of the motor-propeller dynamics and the nonlinear mapping relating the aerodynamic torques to the propeller speed. A previous controller was designed by neglecting the motor-propeller dynamics and the control allocation was done assuming a linear static relationship between aerodynamic torques and motor voltages. This work will determine the nonlinear control allocation mapping and model the motor-propeller dynamics as a first-order linear system. Simulation and real-time results showing an improvement in the performance of the testbed are presented by replacing the linear control allocation with nonlinear control allocation and by compensating for the motor-propeller dynamics. Further, the existing controller is redesigned considering the gyroscopic effects produced due to the spinning propellers.

Committee:

Jianchao Zhu (Advisor)

Keywords:

Nonlinear Control Allocation; Actuator Dynamics; DC Motor-propeller dynamics; Differential thrust control testbed; Trajectory Linearization Control; MATLAB/Simulink; Open-loop control; Closed-loop control