Theses and Dissertations from UMD

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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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Subject: search.filters.subject.Aeroelasticity

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    EXPERIMENTAL AND COUPLED CFD/CSD INVESTIGATION OF FLEXIBLE MAV-SCALE FLAPPING WINGS IN HOVER
    (2018) Lankford, James; Chopra, Inderjit; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Due to their potential to expand our sensing and mission capabilities in both military and civilian applications, micro air vehicles (MAVs) have recently gained increased recognition. However, man-made MAVs have struggled to meet the aerodynamic performance and maneuvering capabilities of biological flapping wing flyers (small birds and insects) which operate at MAV-scales (Reynolds numbers on the order of 103–104). Several past studies have focused on developing and analyzing flapping-wing MAV designs due to the possibility of achieving the increased lift, performance and flight capabilities seen in biological flapping wing flyers. However, there are still a lack of baseline design principles to follow when constructing a flexible flapping wing for a given set of wing kinematics, target lift values, mission capabilities, etc. This is due to the limited understanding of the complex, unsteady flow and aeroelastic effects intrinsic to flexible flapping wings. In the current research, a computational fluid dynamics (CFD) solver was coupled with a computational structural dynamics (CSD) solver to simulate the aerodynamics and inherent aeroelastic effects of a flexible flapping wing in hover. The coupled aeroelastic solver was validated against experimental test data to assess the predictive capability of the coupled solver. The predicted and experimental results showed good correlation over several different test cases. Experimental tests included particle image velocimetry (PIV) measurements, instantaneous aerodynamic force measurements and dynamic wing deformation recordings via a motion capture system. The aeroelastic solver was able to adequately predict the process of leading edge vortex (LEV) formation and shedding observed during experimentation. Additionally, the instantaneous lift and drag force-time histories as well as passive wing deformations agreed satisfactorily with the experimental measurements. The coupled CFD/CSD solver was used to determine how varied wing structural compliance influences aerodynamic force production, temporal and spatial evolution of the flowfield and overall wing performance. Results showed that for the wings tested, decreasing wing stiffness, especially toward the wing root, increased the time-averaged aerodynamic lift with minimal effect on drag. This is primarily due to prolonged sustainment of the LEVs produced during flapping and suggests that aeroelastic tailoring of flapping wings could improve performance.
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    FLEXIBLE MULTI-BODY DYNAMICS MODEL OF A BIO-INSPIRED ORNITHOPTER WITH EXPERIMENTAL VALIDATION
    (2014) Altenbuchner, Cornelia; Hubbard, James E; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    There is currently a large effort underway to understand the physics of avian-based flapping wing vehicles, known as ornithopters. There is a need for small aerial robots to conduct a variety of civilian and military missions. Efforts to model the flight physics of these vehicles have been complicated by a number of factors, including nonlinear elastic effects, multi-body characteristics, unsteady aerodynamics, and the strong coupling between fluid and structural dynamics. Experimental verification is crucial in order to achieve accurate simulation capabilities. A multi-disciplinary approach to modeling requires the use of tools representing individual disciplines, which must be combined to form a comprehensive model. In the framework of this research a five body flexible vehicle dynamics model and a novel experimental verification methodology is presented. For the model development and verification of the modeling assumptions, a data set providing refined wing kinematics of a test ornithopter research platform in free flight was used. Wing kinematics for the verification was obtained using a Vicon motion capture system. Lagrange equations of motion in terms of a generalized coordinate vector of the rigid and flexible bodies are formulated in order to model the flexible multi-body system. Model development and verification results are presented. The `luff region" and "thrust flap region" of the wing are modeled as flexible bodies. A floating reference frame formulation is used for the ornithopter. Flexible body constraints and modes are implemented using the Craig-Bampton method, which incorporates a semi-physical subspace method. A quasi-steady aerodynamic model using Blade Element Theory was correlated and verified for the problem using the experimental wing kinematics. The aerodynamic model was then formulated in terms of generalized coordinates of the five-body flexible multi-body system and is used in the resulting model in order to account for aero-elasticity. Modeling assumptions were verified and simulation results were compared with experimental free flight test data.
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    AN EXPLICATION OF AIRFOIL SECTION BENDING-TORSION FLUTTER
    (2004-04-30) Wheeler, Philip Curtis; Medina, Ricardo; Civil Engineering
    This thesis examines the dynamic instability known as flutter using a two-degree-of-freedom airfoil section model in both quasi-steady and unsteady flow. It explains the fundamental forces and moments involved in the bending-torsion flutter of an airfoil section, and demonstrates a solution method for determining the critical flutter frequency and speed for both flow cases. Additionally, through the use of a programmed Mathcad 11 worksheet, it evaluates the flutter characteristics of six example sections, illustrating the effects of the elastic, inertial and aerodynamic properties of an airfoil section. For each section, a parametric study of the effect of the section Center of Gravity position along the section chord is performed. The flutter frequency and speed are calculated using both quasi-steady and unsteady aerodynamic forces and moments, and the results compared. Software used was MathSoft Mathcad 11, Microsoft Word and Intergraph Smart Sketch LE.