Mechanical Engineering
Permanent URI for this communityhttp://hdl.handle.net/1903/2263
Browse
4 results
Search Results
Item DESIGN, FABRICATION, AND PERFORMANCE CHARACTERIZATION OF MULTIFUNCTIONAL STRUCTURES TO HARVEST SOLAR ENERGY FOR FLAPPING WING AERIAL VEHICLES(2016) Perez-Rosado, Ariel; Bruck, Hugh A; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Flapping Wing Aerial Vehicles (FWAVs) have the capability to combine the benefits of both fixed wing vehicles and rotary vehicles. However, flight time is limited due to limited on-board energy storage capacity. For most Unmanned Aerial Vehicle (UAV) operators, frequent recharging of the batteries is not ideal due to lack of nearby electrical outlets. This imposes serious limitations on FWAV flights. The approach taken to extend the flight time of UAVs was to integrate photovoltaic solar cells onto different structures of the vehicle to harvest and use energy from the sun. Integration of the solar cells can greatly improve the energy capacity of an UAV; however, this integration does effect the performance of the UAV and especially FWAVs. The integration of solar cells affects the ability of the vehicle to produce the aerodynamic forces necessary to maintain flight. This PhD dissertation characterizes the effects of solar cell integration on the performance of a FWAV. Robo Raven, a recently developed FWAV, is used as the platform for this work. An additive manufacturing technique was developed to integrate photovoltaic solar cells into the wing and tail structures of the vehicle. An approach to characterizing the effects of solar cell integration to the wings, tail, and body of the UAV is also described. This approach includes measurement of aerodynamic forces generated by the vehicle and measurements of the wing shape during the flapping cycle using Digital Image Correlation. Various changes to wing, body, and tail design are investigated and changes in performance for each design are measured. The electrical performance from the solar cells is also characterized. A new multifunctional performance model was formulated that describes how integration of solar cells influences the flight performance. Aerodynamic models were developed to describe effects of solar cell integration force production and performance of the FWAV. Thus, performance changes can be predicted depending on changes in design. Sensing capabilities of the solar cells were also discovered and correlated to the deformation of the wing. This demonstrated that the solar cells were capable of: (1) Lightweight and flexible structure to generate aerodynamic forces, (2) Energy harvesting to extend operational time and autonomy, (3) Sensing of an aerodynamic force associated with wing deformation. Finally, different flexible photovoltaic materials with higher efficiencies are investigated, which enable the multifunctional wings to provide enough solar power to keep the FWAV aloft without batteries as long as there is enough sunlight to power the vehicle.Item The Fluid Dynamics of Mayfly Naiads(2014) Abdelziz, Khaled Mohamed-Refaat; Kiger, Kenneth T; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)During their aquatic phase, mayflies Centroptilum triangulifer use a series of tracheal gills to facilitate gas exchange. Recent experimental studies on nymphal mayflies have identified two coupled features associated with the ontogenic progression of their ventilatory kinematics: 1) there is an abrupt shift from a rowing mechanism in small instars to a flapping mechanism in larger instars, and 2) the flapping mechanism is associated with the development of a flexural hinge that permits the passive movement of a distal flap. The primary role of the tracheal gills is tied to ventilation rather than locomotion. As such, it is not yet understood why such a transition happens and which performance metric is improved, if any. Hence, the goal of the current research is to investigate both features using numerical simulations. First, a computational model of the mayfly is built from a dissected animal. Then, a 3-level prescribed kinematic chain is introduced to a previously in-house developed and in-house validated explicit parallel Navier-Stokes solver where both the advective and diffusive terms are advanced explicitly using a third-order, low-storage, Runge-Kutta scheme. Finally, an immersed boundary method based on a moving least squares reconstruction is implemented to enforce the correct moving boundary conditions. Two different parametric spaces are constructed. The first one investigates the transition from rowing to flapping kinematics, the morphological effects on the flow field and on the proposed performance parameters while the second aims to provide an explanation for the hinge development. Two metrics based on control volume analysis are proposed to quantify the performance of each numerical case. The first metric is simply the mechanical efficiency of the energy transfer from the moving gills to the surrounding flow field while the second incorporates the mass flow rate across the control surface. The second metric is promising because it is able to provide a plausible explanation of both features by showing that the rate of work done by the mayfly is diminished throughout ontogeny with respect to the induced mass flow rate.Item Nonlinear Fluid-Structure Interactions in Flapping Wing Systems(2013) Fitzgerald, Timothy; Balachandran, Balakumar; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This work relates to fluid-structure interactions in the context of flapping wing systems. System models of flapping flight are explored by using a coupling scheme to provide communication between a fluid model and a structural model describing a flexible wing. The constructed computational models serve as a tool for investigating complex fluid-structure interactions and characterizing them. Primary goals of this work are construction of models to understand nonlinear phenomena associated with the flexible flapping wing systems, and explore means and methods to enhance their performance characteristics. Several system analysis tools are employed to characterize the coupled fluid-structure system dynamics, including proper orthogonal decomposition, dimension calculations, time histories, and frequency spectra. Results obtained from two-dimensional simulations conducted for a combination of a two-link structural system and a fluid system are presented and discussed. Comparisons are made between the use of direct numerical simulation and the unsteady vortex lattice method as the fluid model in this coupled dynamical system. To enable three-dimensional studies, a novel solid model is formulated from continuum mechanics for geometrically exact finite elements. A new partitioned fluid-structure interaction algorithm based on the Generalized-α method is formulated and implemented in a large scale fluids solver inside the FLASH framework. Consistent boundary conditions are also formulated by using Lagrangian particles. Several examples demonstrating the effectiveness of the methods and implementation are shown, in particular, for flapping flight at low Reynolds numbers. Unique experiments have also been undertaken to determine the first few natural frequencies and mode shapes associated with hawkmoth wings. The computational framework developed in this dissertation and the research findings can be used as a basis to understand the role of flexibility in flapping wing systems, further explore the complex dynamics of flapping wing systems, and also develop design schemes that might make use of nonlinear phenomena for performance enhancement.Item PARAMETRIC INVESTIGATIONS INTO FLUID-STRUCTURE INTERACTIONS IN HOVERING FLAPPING FLIGHT(2013) Maxwell, Jesse R.; Balachandran, Balakumar; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A parametric investigation into flapping flight is presented. For a Reynolds number of 75, harmonically forced flapping dynamics is studied. A wing section is modeled as two rigid links connected by a hinge with a torsion spring-damper combination. This section is wrapped in a smooth aerodynamic surface for immersion in the fluid domain. An immersed boundary method is employed on a two-dimensional structured Cartesian grid to solve the incompressible form of the Navier-Stokes equations for low Reynolds numbers by using a finite difference method. Fully coupled fluid-structure interactions are considered. Performance metrics, which include cycle-averaged lift, drag, power, and their ratios, are used to characterize the effects of different parameters and kinematics. Principal components of flow-field structures are quantified, and the system's response is correlated to performance. The thesis findings can serve as a basis to understand and identify flapping frequencies that provide high performance.