Master of Science, The Ohio State University, 2007, Graduate School

Committee: Not Provided (Other) Subjects:

Master of Science, The Ohio State University, 2007, Graduate School

Committee: Not Provided (Other) Subjects:

Master of Science, The Ohio State University, 2007, Graduate School

Committee: Not Provided (Other) Subjects:

Master of Science, The Ohio State University, 2005, Graduate School

Committee: Not Provided (Other) Subjects:

PhD, University of Cincinnati, 2024, Engineering and Applied Science: Mechanical Engineering

Aligned with the medical device industry's trend of miniaturization, academic and commercial researchers are constantly attempting to reduce device sizes for minimally invasive therapy. Many applications with size constraints require miniature actuators in the millimeter range to perform mechanical work. Here, a millimeter scale robot (called millirobot) is conceptualized for performing diagnostics and therapy such as biopsies and targeted drug delivery in the human body. A 2 mm diameter tethered device equipped with a cutter to traverse through tissue can provide direct access to difficult anatomical locations for the surgeons. Millirobot being a complex system, its development can be decomposed into multiple subsystem problems such as dissection, navigation, drug delivery, biopsy etc. The research presented herein focused on exploring and developing a biocompatible cutting module/actuator for the millirobot. Literature review and initial concepts generated for the cutting module using miniature versions of the traditional hydraulic motors and turbines were presented along with a discussion of their benefits and limitations. Preliminary design, prototyping efforts, numerical modeling and experimental results of a hydraulically driven millirobot cutting module that aims to combine cutting, biopsy and drug delivery were presented. The cutting module was scaled from ~20 mm outside diameter (OD) to the target 2 mm OD. As a challenge, a 1 mm OD micromotor prototype was also fabricated to demonstrate further scaling. As the design was scaled down, the intermediate stage prototypes were tested extensively and numerically modeled to leverage the learnings and go smaller. The 2:1 scale prototype of the cutting module (4 mm OD) established consistent mechanical work from a biocompatible miniature hydraulic motor with output characteristics comparable to motors of different working principles currently available in an equivalent size range. Next, a target sized hydrau (open full item for complete abstract)

Committee: Mark Schulz Ph.D. (Committee Chair); Ashley Paz y Puente Ph.D. (Committee Member); Milind Jog Ph.D. (Committee Member); Kishan Bellur Ph.D. (Committee Member) Subjects: Engineering

Doctor of Philosophy, The Ohio State University, 2024, Mechanical Engineering

The research aims to design, fabricate, and control a new pneumatic soft robot with high load-carrying capacity and motion precision. To achieve this, I design a class of joints/ mechanisms by using compliant mechanisms as backbone coupled with the pneumatic network bending actuators. I break my work into three topics: (1) designing, modeling, and testing a compliant revolute joint, (2) designing, modeling, and testing a compliant translational mechanism, (3) Model joint/mechanisms stiffness under pressurization and external loads by machine learning and apply those models to soft robots' control. The first of these aims to provide rotational motion for soft robots. The second of these gives translational motion to soft robots. The third aim is to predict the proposed mechanisms' motion error under external loads and achieve control of soft robots based on those mechanisms.

Committee: Haijun Su (Advisor); Ayonga Hereid (Committee Member); Anthony Luscher (Committee Member) Subjects: Mechanical Engineering

Master of Science, The Ohio State University, 2024, Aerospace Engineering

Thrust vectoring (TV) is the ability to manipulate the directivity of the primary jet to provide a cross-stream force off the primary jet axis. TV can enable desirable flight regimes such as hyper-maneuverability and short/vertical take-off and landing. Modern conventional TV methods utilize a physical mechanism to mechanically deflect the jet flow and change the thrust direction. This method is both heavy and mechanically complex, especially for an axisymmetric jet. A novel approach to TV is explored in this paper by investigating localized arc filament plasma actuators' (LAFPAs) ability to impart a TV force on a subsonic, axisymmetric jet by attaching the flow to a radially expanding surface (termed “reaction surface”), at the jet exit. LAFPAs will be used to asymmetrically control the entrainment of the jet to provide a deflection of the jet via the conservation of momentum. The deflected jet will then attach to the reaction surface via the Coanda effect. The jet flow was interrogated at baseline and excited cases with a static pressure array located 0.75 jet diameters downstream of the actuators at 70% of the chord of the reaction surface and with cross-stream particle image velocimetry (PIV) located 3 jet diameters downstream of the actuators. Two jet Mach (Mj) values were assessed, Mj = 0.48 and 0.9. The results show that the LAFPAs create a repeatable and significant asymmetric pressure profile trend with respect to excitation frequency. In general, low excitation frequencies provide an asymmetric azimuthal pressure profile that corresponds to a vectored thrust force towards the active actuators, while high excitation frequencies provide an asymmetric azimuthal pressure profile that corresponds to a vectored thrust force away from the active actuators. Cross-stream PIV flow field measurements show that the asymmetry in the azimuthal pressure profile is not as significant as would be desirable for thrust-vectoring applications. However, the PIV results do show (open full item for complete abstract)

Committee: Dr. Nathan Webb (Advisor); Dr. Mo Samimy (Committee Member) Subjects: Aerospace Engineering

Doctor of Philosophy, University of Akron, 2023, Polymer Engineering

One-way shape memory polymers (SMPs) possess the unique ability to remember a programmed 'temporary shape' and revert to its original shape when exposed to an external stimulus. Typically, SMPs contain two structure-spanning, solid networks; a permanent elastic network that is strained during programming to drive shape recovery; and a temporary network that fixes the programmed shape. The shape-shifting features of SMPs make them useful for a wide range of potential applications, including 4D printing, soft robotics, flexible electronics, soft aeronautical engineering, and biomedical devices. An interesting pathway to develop SMPs is by blending an elastomer and a crystalline small molecule, where the elastomer forms the permanent network (that promotes shape recovery), and the small molecule crystal forms the temporary networks (that promotes shape fixity). Typical examples of these systems include crosslinked elastomers (natural rubber) swelled in fatty acids (lauric acid, stearic acid, and palmitic acid), straight-chain alkanes (eicosane, tetracosane) or synthetic waxes (paraffin wax). However, a drawback of this approach is the blooming and expulsion of the small molecule during shape programming and recovery. This dissertation attempts to focus on semi-crystalline shape memory elastomers developed from blends of high cis 1,4 polybutadiene and reactive monomers (octadecyl acrylate and benzyl methacrylate) or molecular crystals (n-eicosane and n-tetracosane) with the aim being reducing the effect of blooming while keeping a simple fabrication route to develop these SMPs. The synthetic, network, mechanical, thermal, and morphological properties of a series of polybutadiene-based semicrystalline or glassy blends were studied to understand the structureproperty relationships between their permanent and reversible networks. Furthermore, it will be shown that thermally annealed high cis 1,4 polybutadiene also demonstrates thermoresponsive actuatio (open full item for complete abstract)

Committee: Kevin Cavichhi (Advisor); Fardin Khabaz (Committee Chair); Qixin Zhou (Committee Member); Li Jia (Committee Member); Weinan Xu (Committee Member) Subjects: Chemistry; Materials Science; Plastics

Doctor of Philosophy, The Ohio State University, 2022, Aerospace Engineering

The propulsion/airframe integration benefits of non-axisymmetric nozzles have led to renewed interest in their integration into future generations of aircraft design. Rectangular nozzles can offer significant benefits in terms of drag reduction, improved mixing for heat signature reduction and ease of implementing thrust vectoring. Aircraft with high- and low-aspect-ratio rectangular nozzles have already been operational for years and the recent interest in developing manned and unmanned platforms with such nozzles integrated with the airframe underscores the need for further development and understanding the physics of flow in such geometries. Jet noise emitted from the hot, high-speed jet plumes of high-performance tactical fighters severely affects the crew and communities exposed to it. Furthermore, interaction and coupling of jet plumes in twin-engine tactical aircraft has the potential to cause structural fatigue and failure due to elevated near-field pressure fluctuations. This work seeks to address these issues by studying the physics of flow and acoustics in low aspect ratio rectangular twin jets (RTJs) and implementing active flow control to alleviate near-field pressure fluctuations and far-field noise. One of the major contributions of the present work is the extensive characterization of baseline RTJs in a wide range of operation conditions (jet Mach number, Mj, or nozzle pressure ration, NPR) to better understand the underlying processes that drive flow and acoustic behavior of these jets. The second contribution of this work is to implement active flow control with localized arc filament plasma actuators (LAFPAs), the control authority of which has been demonstrated in a wide range of high-speed flows. In the present work, LAFPAs have been used to manipulate the growth and development of large-scale structures (LSS) in jet shear layers and thus affect the flow-field and acoustics of RTJs. The twin jet setup studied in this work consists of two milit (open full item for complete abstract)

Committee: Mo Samimy (Advisor); Lian Duan (Committee Member); Datta Gaitonde (Committee Member); Nathan Webb (Committee Member) Subjects: Aerospace Engineering

PHD, Kent State University, 2022, College of Arts and Sciences / Department of Physics

Over the past few decades, there has been tremendous development on soft materials in soft robotics, energy generation and sensing applications. These soft materials are mostly polymers. Their compliant elasticity, good adaptability to external constraints, and biocompatibility make them suitable for those applications. Further, polymers that respond by changing their shape or size to an external stimulus such as electric field, magnetic field, heat, pressure, pH, and light have great potential for these applications. Among these stimuli responsive materials, electro responsive polymers (electroactive polymers (EAPs)) acquires great attention. Organic electrochemical transistors (OECTs) have attracted great attention since their discovery in 1984 due to their flexibility, biocompatibility, easy fabrication and tunability through synthetic chemistry. As OECTs conduct both electronic and ionic charge, they are suitable for bioelectronic applications, such as recording electric activity of cells and tissues, detection of ions, metabolites, antigens related with various diseases, hormones, DNA, enzymes and neurotransmitter. In my dissertation, I will describe how we developed ionic electroactive polymers (iEAPs) and ionic liquid crystal elastomers (iLCEs) for the applications of soft robotics, energy harvesting (flexo-ionic effect), sensing and organic electrochemical transistors. Firstly, we engineered poly (ethylene glycol) diacrylate based iEAPs for soft robotics application. Here, low voltage induced bending (converse flexoelectricity) of crosslinked poly (ethylene glycol) diacrylate (PEGDA), modified with thiosi-loxane (TS) and ionic liquid (1-hexyl-3-methylimidazolium hexafluorophos-phate) (IL) is studied. In between 2μm PEDOT:PSS electrodes at 1 V, it provides durable (95% retention under 5000 cycles) and relatively fast (2 s switching time) actuation with the second largest strain observed so far in iEAPs. In between 40 nm gold electrodes under 8 V DC volt (open full item for complete abstract)

Committee: Antal Jákli (Advisor); Björn Lüssem (Committee Member); Songping Huang (Committee Member); John West (Committee Member); Robin Selinger (Committee Member) Subjects: Physics

Doctor of Philosophy, The Ohio State University, 2020, Mechanical Engineering

High injury severity occurs when a stiff robotic system hits an operator. Introducing compliance into robotic components including joints, links, and grippers reduces the severity of impact and enables safe human-robot interaction. The two aims of this research are to develop variable-stiffness mechanisms for safe co-robot links, and develop and model soft actuators and grippers based on these mechanisms. A discrete layer jamming mechanism is developed that is composed of a multilayered beam and multiple discrete variable pressure clamps placed along the beam; system stiffness can be varied by changing the pressure applied by the clamps. In comparison to continuous layer jamming, discrete layer jamming offers advantages of simplicity with implementation of dynamic variable pressure actuators for faster control, better portability, and no sealing issues due to no need for an air supply. This research provides a full characterization of discrete layer jamming based on computational case studies using finite element analysis, which has been experimentally validated for five key parameters, including clamp location, clamp width, number of laminates, friction coefficient, and number of clamps. Pneumatically-actuated variable-stiffness mechanisms are developed that are composed of a multilayered beam and an air bag placed inside the beam; system stiffness can be varied by changing the pressure applied to the air bag. One variable-stiffness mechanism is based on pure anisotropic effects generated between the inflated air bag and the outer constraint layer. The other one combines two variable-stiffness mechanisms including the air introduced anistropic effects and shape morphing. This research provides a full characterization of the stiffness performance based on experimental studies. Fluidic prestressed composite (FPC) actuators can be used for soft grippers to achieve continuous control of shape and stiffness. Due to their highly deformable features, it is diffi (open full item for complete abstract)

Committee: Marcelo Dapino (Advisor); Robert Siston (Committee Member); Haijun Su (Committee Member); Manoj Srinivasan (Committee Member) Subjects: Mechanical Engineering; Robotics

Master of Science, The Ohio State University, 2020, Aero/Astro Engineering

Integrated propulsion systems, which are becoming increasingly common in designs of next-generation aircraft, require compact inlets with large vertical offsets in the duct centerline. These offset inlets and the integrated propulsion systems they permit provide a variety of benefits. For example, due to the offset, similar diffusion can be achieved in less overall length. This allows for a smaller overall propulsion system and therefore a smaller, lighter, more maneuverable aircraft. The offset also hides the engine fan face as a source of radar return. This significantly increases the stealth capability of the aircraft. The benefits provided by the inlet offset are accompanied by some significant drawbacks. At each duct turn, fluid in the boundary layer experiences an imbalance between pressure forces and centrifugal forces. This results in the boundary layer fluid migrating towards the interior of each duct turn. This crossflow within the diffuser creates a pair of counter-rotating streamwise vortices at each duct turn. In addition to the streamwise vortices, the flow through the inlet can experience separation at the duct turns. The streamwise vortices advect low momentum fluid created by the separation towards the duct centerline. This low momentum fluid creates distinct regions of total pressure loss at the plane where the inlet interfaces with the compressor fan face (the aerodynamic interface plane (AIP)). The concentrated regions of total pressure loss at the AIP generate unsteady loading on the compressor fan blades that can significantly reduce their performance and lifespan. Therefore, it is desirable to reduce the secondary flow structures and separation that lead to this unsteady loading. This can be accomplished through the use of flow control methods. 4 A class of plasma actuators called localized arc-filament actuators (LAFPAs) have been shown to be successful in controlling flows similar to that t (open full item for complete abstract)

Committee: Mo Samimy (Advisor); Kiran D'Souza (Committee Member); Nathan Webb (Committee Member) Subjects: Aerospace Engineering

Doctor of Philosophy, University of Akron, 2019, Polymer Engineering Specialization

One type of stimuli-responsive actuator is a bending actuator, which is typically constructed by bonding together two materials with differential volumetric expansion or contraction under a stimulus e.g.solvent quality and temperature. In this dissertation, solvent and temperature sensitive polymer bilayer bending actuators were created in a facile and universal fabrication to scaling up without complicated synthesis and delicate technology. Solvent-responsive bilayer was produced by crosslinking poly(dimethylsiloxane) (PDMS) oligomers in terms of variable fabrication parameters through hydrosilylation. Before vulcanization, the base-tocrosslinker weight ratios determined a crosslinking extent or gel fraction and subsequently, dominated the equilibrium swelling ratio and linear swelling expansion ratio of PDMS rubbers. Except for the base-tocrosslinker weight ratios, the gel fraction of the bottom layer has a predominant impact of the bending extent of the bilayer in terms of the curing time of the bottom layer and deposition order of PDMS layers. The optimum bending degree of the bilayer was estimated by using a simulation model derived from Timoshenko's equation in the case of bimetallic thermostat. Ultimately, the calculated base-to-crosslinker weight ratio of the top layer of the bilayer was significantly corresponded to the experimental data. A different type of bilayer bending actuators with respect to temperature was presented. These temperature-activated actuators containing the phase-change materials would make it potential to detect latent heat in the nature and conduct the thermal-management. A self-contained thermal bending actuator based on a polymer bilayer where the actuation is driven by the expansion and contraction of paraffin wax undergoing solid-to-liquid phase transition. Bilayer films consisting of active, wax-containing polymer layer and passive, wax-free polymer layer were fabricated using commercially available polymers and a commercially (open full item for complete abstract)

Committee: Kevin Cavicchi (Advisor); Mark Soucek (Committee Member); Nicole Zacharia (Committee Member); Li Jia (Committee Member); Alper Buldum (Committee Member) Subjects: Materials Science; Polymer Chemistry; Polymers

Doctor of Philosophy, The Ohio State University, 2019, Electrical and Computer Engineering

Polypyrrole (PPy) as a versatile conducting polymer (CP) has been widely employed in flexible electronics, anti-static coatings, and soft ionic actuators. While prior studies have focused on the exploration of novel counterions (or dopants), this work aims to achieve demanding functions by systematic structural designs combined with precise fabrication techniques. Toward higher conductivity and electroactivity, I show that a network structure of conjugated chains maintains high macroscopic conductivity even at nanoscale thickness, an intrinsically preserved bilayer structure brings power-efficient single-side-passivation, and a laser-patterned configuration achieves diversely alterable deformation forms, such as squeezing, gripping, waving, lifting and rotation. I further demonstrate that the link from structure to function is deterministic and repeatable, and these geometrically enabled actuators are both electrochemically and mechanically robust. Such features have inspired the development of a wirelessly powered lightweight insulin pump for easily controllable microinjection. From materials to devices, this thesis highlights, although still a small portion of, the enormous potential of geometrically enabled CPs for advanced robotics and soft biomedical devices.

Committee: Liang Guo (Advisor); Wu Lu (Committee Member); Asimina Kiourti (Committee Member); Nan Hu (Committee Member); Alexander Lindsey (Committee Member) Subjects: Electrical Engineering; Materials Science; Robotics

Master of Science, University of Toledo, 2018, Mechanical Engineering

This thesis work elaborates a facile technique for fabrication of functionally graded all graphene films using a one-step film coating process. The film coating consists of inter-facial reduction and self-assembly of a graphene oxide (GO) precursor on an active metal substrate. Processing parameters such as the underlying substrate metal and the film drying environment are controlled in order to tailor the internal architecture of the films and to achieve functionally graded structure during the reduction of GO. The self-assembly and functional grading of the films, where one side is electrically conductive reduced GO (rGO) and the opposite side is insulating GO, was confirmed by SEM, Raman, XRD, FTIR, and XPS characterization studies. All graphene based free standing films with selectively reduced GO were used in transient electronics application as flexible circuitry and RFID tag antenna where their decommissioning was easily achieved by capitalizing on GO's ability to readily dissociate and create a stable suspension in water. Furthermore, the functionally graded structure was found to exhibit differential swelling behavior and its potential applications in graphene-based actuators were outlined.

Committee: Reza Rizvi (Committee Chair); Hossein Sojoudi (Committee Member); Ahalapitiya Jayatissa (Committee Member) Subjects: Chemistry; Materials Science; Mechanical Engineering; Nanotechnology

Master of Science, Miami University, 2018, Mechanical and Manufacturing Engineering

Haptic feedback is a highly beneficial feature of touch screens. Due to the limitations of current haptic technologies, devices with large touch screens are unable to provide haptic feedback to users. This study proposes and investigates an electrostatic actuator utilizing frequency beating phenomenon with the goal of generating haptic feedback in devices with large touch screens. A prototype device was fabricated and through experimentation, two unique high intensity vibration patterns were found at each beat frequency. An analytical model of the prototype was developed to. The model produced a peak vibration intensity distribution closely resembling that of the experimental data. The possibility of three input signals was investigated. Variations in beating patterns could be seen, but this provides little benefit in application. A multiphysics model was developed to provide a more accurate representation of the operation of the actuator. This model was also used do investigate the effects of the coupling of displacement and electrostatic force. The multiphysics model was able to produce accurate results but was unstable when using certain input conditions. The displacement coupling creates changes in the computed displacement and intensity response. The model produced the same peak intensity distribution as the experimental data. Improvements can be made to both models to improve accuracy and stability. The models are intended to aid in the refinement of the design of future prototypes.

Committee: Jeong-Hoi Koo Ph. D. (Advisor); Jens Mueller Ph. D (Committee Member); Kumar Singh Ph. D. (Committee Member) Subjects: Design; Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2018, Materials Science and Engineering

Electrically vaporized foil actuators (VFA) have several potential impulse manufacturing applications, the most important of which are impact welding of dissimilar-material structures and impulse forming of high-strength materials. For all impulse manufacturing applications, it is necessary to control the distribution and magnitude of the force acting on the workpiece. Therefore, to effectively and efficiently apply the VFA process to manufacturing, it is first necessary to understand how to tailor the input parameters to consistently produce the desired output pressure. In the VFA process, a high-current electrical discharge rapidly vaporizes a thin metallic conductor, resulting in a high-pressure pulse due to the vaporized metal expanding outward from its initial volume. The controlling parameter of the VFA process is the specific energy deposited into the actuator through resistive heating up to the point of vaporization. It is shown here that above a critical threshold, there is a positive linear relationship between the “deposited energy ratio” (DER) – the ratio of deposited energy/energy to sublimate the actuator – and the pressure output from the vaporization. However, while the pressure magnitude depends on the total energy deposition into the actuator, the uniformity of the pressure is shown to depend on the rate of energy input into the actuator. The temporal nature of the vaporization is also investigated, revealing an initial very high-pressure, very brief shock wave, followed by the sustained push of the expanding vapor. The specific avenues which can be taken to improve the energy deposition rate into the actuator and the DER, as well as the limitations of the process, are investigated and explained. The key to higher DER is shown to be increasing the rate of current rise, either by increasing the discharge rate of the capacitor bank discharge into the actuator, or by increasing the charging voltage for a given capacitor bank; the limitati (open full item for complete abstract)

Committee: Glenn Daehn (Advisor); Alan Luo (Committee Member); Stephen Niezgoda (Committee Member) Subjects: Engineering; Materials Science

Master of Science (M.S.), University of Dayton, 2017, Mechanical Engineering

Electromechanical actuators (EMAs) are seen as the future actuation technology for next-generation, energy-optimized aircraft. Implementation into primary flight control entails many challenges and requires much research, development, and experience to prove the technology's robustness and maturity. Operation of multiple actuators on a control surface introduces a phenomenon known as force fight, where instead of equally sharing load they behave unequally or oppose each other. Force fight is well studied for hydraulic actuation systems, but limited research has been done on EMAs. The purpose of this thesis is to study force fight experimentally between two X-38 EMAs in a passive spring loaded dual EMA test rig. Static and dynamic analytical models of the test setup were created to assist the force fight study. The command to both EMAs was a 1-Hz, 5-degree-amplitude sine wave of ten cycles. Known force fight conditions of position lag, gain, and offset errors were introduced to each EMA in turn and the impacts of each condition were examined in terms of force difference and energy consumption. Torque, rotation, voltage, current, and power were measured from the test stand along with EMA controller position and current monitors for data analysis. Energy demand of the EMAs was calculated from the integral of the mechanical and electrical power. The force difference impact also was analyzed utilizing the maximum and minimum force difference as recorded on the torque cells. It was shown that all three cases, lag, gain, and offset, resulted in significant force fight between the two EMAs expressed as force difference. The magnitude of force fight was a linear function of the magnitude of the errors. In addition, both the gain and offset errors caused significant increase in total electrical energy demand, the larger the gain or offset, the higher the electrical energy demand, while the lag errors showed slight electrical energy increase. It also was shown that mechanical (open full item for complete abstract)

Committee: Quinn Leland Ph.D. (Committee Chair); Steven Fuchs M.S., P.E. (Committee Member); Bang-Hung Tsao Ph.D. (Committee Member); Jamie Ervin Ph.D. (Committee Member) Subjects: Engineering; Mechanical Engineering

Doctor of Philosophy, University of Akron, 2017, Civil Engineering

The effective utilization of shape memory alloys (SMAs) rests on the comprehensive understanding of the factors which influence their performance under various practical thermomechanical loading conditions. In this study, computational efforts needed to complement existing experimental tests have been made towards studying the unique behaviors exhibited by shape memory alloys, with an eye towards their application in the various engineering fields. To this end, a newly developed three-dimensional general model was used. A characterization procedure, involving systematic classification of the model parameters into fixed and temperature and /or state-dependent parameters was given, which allowed easy calibration and application of the SMA mathematical model. In particular, with its implementation in a commercial finite element code, SMA devices, such as aerospace actuators, biomedical stents, bone staples, and earthquake dampers, under variable geometries and boundary loading conditions were simulated. The numerical results obtained from the model matched most of the experimental or test results. The practical significance offered by the developed model in this study included: (a) its ability to guide material users on the optimum conditions at which the alloys can be used, as well as (b) provide important information regarding the immediate and long-term performances of devices designed with SMAs, knowing that such information can be extremely costly to obtain from the physical experiments.

Committee: Atef Saleeb Dr (Advisor); Anil Patnaik Dr (Committee Member); Michelle Hoo Fatt Dr (Committee Member); Qindan Huang Dr (Committee Member); Kevin Kreider Dr (Committee Member) Subjects: Aerospace Materials; Biomechanics; Engineering

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

Flow field surrounding a moving body is often unsteady. This motion can be linear or rotary, but the latter will be the primary focus of this thesis. Unsteady flows are found in numerous applications, including sharp maneuvers of fixed wing aircraft, biomimetics, wind turbines, and most notably, rotorcraft. Unsteady flows cause unsteady loads on the immersed bodies. This can lead to aerodynamic flutter and mechanical failure in the body. Flow control is hypothesized to reduce the load hysteresis, and is achieved in the present work via nanosecond pulse driven dielectric barrier discharge (NS-DBD) plasma actuators. These actuators have been effective in the delay or mitigation of static stall. The flow parameters were varied by Reynolds number (Re=167,000-500,000), reduced frequency (k=0.025-0.075), and excitation Strouhal number (Ste=0-10). It was observed that the trends of Ste were similar for all combinations of Re and k, and three major conclusions were drawn. It was first observed that low Strouhal number excitation (Ste<0.5) results in oscillatory aerodynamic loading in the stalled stage of dynamic stall. At high Strouhal number excitation (Ste>2), this behavior is not observed, as in the static stall cases. Second, all excitation resulted in earlier flow reattachment. Lastly, it was shown that excitation resulted in reduced aerodynamic hysteresis and dynamic stall vortex strength. The decrease in the strength of the dynamic stall vortex is achieved by the formation of excited structures that bleed the leading edge vorticity prior to the ejection of the dynamic stall vortex. At sufficiently high excitation Strouhal numbers (Ste˜10), the dynamic stall vortex was suppressed.

Committee: Mo Samimy (Advisor); Datta Gaitonde (Committee Member); James Gregory (Committee Member) Subjects: Aerospace Engineering