Theses and Dissertations from UMD

Permanent URI for this communityhttp://hdl.handle.net/1903/2

New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM

More information is available at Theses and Dissertations at University of Maryland Libraries.

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    Reduced Order Modeling of Flapping Wing Flight Dynamics
    (2017) MacFarlane, Kenneth Foster; Humbert, James S; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Flapping wing vehicles have become a compelling alternative to classical fixed or rotary wing aircraft, especially as unmanned aircraft technology focuses on smaller, more agile platforms. Flying insects provide an inspiration for the control of flapping wing platforms, using limited computational resources in their specialized neural pathways to generate robust, agile performance. The flapping wing design is less studied, and the underlying physical principles are often more complex – non-linear time varying dynamics are dominated by forcing due to complex, unsteady aerodynamics. Reduced order models are critical to formulating tractable sensing and control concepts from the complex physics of flapping wing flight. Previous research has focused on a single methodology for the estimation of flight dynamics. This dissertation investigates the reduced order modeling of flapping wing flight dynamics for the purposes of tractable simulation and control, comparing multiple methodologies. Simplification of rigid body vehicle dynamics due to both linearization and time-invariance is discussed, and computational and experimental verification is presented for a simplified model of flapping wing aerodynamics. Additionally, a novel method is presented to maximize the agility and performance of a flapping wing vehicle when reducing the number of control inputs. These reduced order modeling techniques are applied to both a model of a small flying insect and to a flapping wing micro air vehicle.
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    LARGE MOTION VISUALIZATION AND ESTIMATION FOR FLAPPING WING SYSTEMS
    (2015) Hsu, Tzu-Sheng; Balachandran, Balakumar; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Studies of fluid-structure interactions associated with flexible structures such as flapping wings require the capture and quantification of large motions of bodies that may be opaque. Motion capture of a free flying insect is considered by using three synchronized high-speed cameras. A solid finite element representation is used as a reference body and successive snapshots in time of the displacement fields are reconstructed via an optimization procedure. An objective function is formulated, and various shape difference definitions are considered. The proposed methodology is first studied for a synthetic case of a flexible cantilever structure undergoing large deformations, and then applied to a Manduca Sexta (hawkmoth) in free flight. The three-dimensional motions of this flapping system are reconstructed from image date collected by using three cameras. The complete deformation geometry of this system is analyzed. Finally, a computational investigation is carried out to understand the flow physics and aerodynamic performance by prescribing the body and wing motions in a fluid-body code. This thesis work contains one of the first set of such motion visualization and deformation analyses carried out for a hawkmoth in free flight. The tools and procedures used in this work are widely applicable to the studies of other flying animals with flexible wings as well as synthetic systems with flexible body elements.
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    Analysis of Factors Affecting the Aerodynamics of Low Reynolds Number Rotating Wings
    (2013) Schlueter, Kristy Lynn; Jones, Anya R; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    A computational analysis was performed to address the effects of walls on wings rotating at a Reynolds number of 120. For rotation angles less than one revolution, a tip clearance of 0.5 chord-lengths is sufficient to approximate a wing rotating in an infinitely large volume of fluid. However, for a maximum rotation of two revolutions, a tip clearance of 5.0 chords is necessary. At the start of the second revolution, the wing encounters its wake, and the wake structure is significantly affected by low tip clearances. Lift and drag forces were measured experimentally for wings rotating at a Reynolds number of 10,000 while parameters including root cutout were varied. Root cutout significantly alters the lift and drag coefficients, including the location of a second local maximum in both lift and drag. The root-relative method of force non-dimensionalization provided the best comparison of force coefficients between cases with different root cutouts.