A. James Clark School of Engineering
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The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item Electroosmotic Soft Actuators(2017) Sritharan, Deepa; Smela, Elisabeth; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation details the research involved in creating the first paper-based soft actuator driven by electroosmosis. To accomplish this, research breakthroughs were made in the fields of electrokinetic pumping and device manufacturing using soft materials. Electroosmosis is an electrically induced microfluidic flow phenomenon. When an electric field is applied to the fluid, across the microchannels, electroosmotic flow occurs in the direction of the applied electric field. In this work, liquid was electroosmotically displaced within a flexible microfluidic device to actuate an elastomeric membrane. The goal of this work was to create a fully sealed fluidic actuator. It was therefore necessary to encapsulate the pumping fluid within the device, and to maximize pressure it was necessary to eliminate compliance caused by trapped gases. Electrolytic gas formation is well known to disrupt pumping in DC electroosmotic systems that use water as the pumping liquid. In this work, electrolysis was eliminated by replacing water with propylene carbonate (PC): PC was determined to be electrochemically stable up to at least 10 kV, in the absence of moisture or salt contaminants. Bubble-free electroosmotic pumping with PC was achieved within sealed miniature actuators, which could be continuously operated for at least one hour. Benchtop fabrication techniques were developed to build encapsulated fluidic actuators composed entirely of soft, flexible materials. Stretchable electrochemically stable electrodes were made using a conductive paint made by mixing carbon nanoparticles into a silicone base. High-density microchannel networks were incorporated by using paper and other flexible porous materials, instead of conventional planar replica-molded microchannels. The device was filled with pumping fluid without the use of external tubing, and then encapsulated by casting a film of elastomer over the filled reservoir to form the actuating membrane. The resulting actuators were flexible and stretchable, demonstrating significant membrane deformations (hundreds of micrometers) within seconds of applying the electric field and ability to lift large loads (tens of grams). These polymeric electroosmotic actuators are unique among electroactive polymer actuators because they are able to simultaneously generate high force as well as large stroke. It is envisioned that this research will pave the way for the creation of artificial muscles and smart shape-changing materials that can be actuated by electroosmosis.Item Flight Dynamics Simulation Modeling and Control of a Large Flexible Tiltrotor Aircraft(2014) Juhasz, Ondrej; Celi, Roberto; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A high order rotorcraft mathematical model is developed and validated against the XV-15 and a Large Civil Tiltrotor (LCTR) concept. The mathematical model is generic and allows for any rotorcraft configuration, from single main rotor helicopters to coaxial and tiltrotor aircraft. Rigid-body and inflow states, as well as flexible wing and blade states are used in the analysis. The separate modeling of each rotorcraft component allows for structural flexibility to be included, which is important when modeling large aircraft where structural modes affect the flight dynamics frequency ranges of interest, generally 1 to 20 rad/sec. Details of the formulation of the mathematical model are given, including derivations of structural, aerodynamic, and inertial loads. The linking of the components of the aircraft is developed using an approach similar to multibody analyses by exploiting a tree topology, but without equations of constraints. Assessments of the effects of wing flexibility are given. Flexibility effects are evaluated by looking at the nature of the couplings between rigid-body modes and wing structural modes and vice versa. The effects of various different forms of structural feedback on aircraft dynamics are analyzed. A proportional-integral feedback on the structural acceleration is deemed to be most effective at both improving the damping and reducing the overall excitation of a structural mode. A model following control architecture is then implemented on full order flexible LCTR models. For this aircraft, the four lowest frequency structural modes are below 20 rad/sec, and are thus needed for control law development and analysis. The impact of structural feedback on both Attitude-Command, Attitude-Hold (ACAH) and Translational Rate Command (TRC) response types are investigated. A rigid aircraft model has optimistic performance characteristics, and a control system designed for a rigid aircraft could potentially destabilize a flexible one. The various control systems are flown in a fixed-base simulator. Pilot inputs and aircraft performance are recorded and analyzed.