Constitutive Modeling and Coupled Computational Simulations for Biologically Active Wing Skins.

Natural flyers including bats have been the subject of increasing interest for researchers to understand physical flight-enabling mechanisms, and to leverage flight mechanisms for micro-aerial vehicles. Several studies have investigated the aerodynamics and kinematics of bats. However, the relationship between the constitutive properties of the highly compliant and active wing membrane and its flight functionality is not well understood. In this dissertation experimental and modeling techniques are used to analyze the mechanical behavior of bat wing skin, and examine the relationships between material properties, mechanical response, and flight performance for active anisotropic aerodynamic membranes inspired by bats. A novel polarizing image correlation technique is developed for determining full field material strains and fiber kinematics of mesoscopically resolved birefringent fibrous tissue during biaxial mechanical testing. Biaxial tension experiments are performed on samples of wing skin with the in-house test frame to generate the first biaxial characterization of the tissue. A new constitutive model for the active viscoelastic and anisotropic behavior of a biological membrane with embedded skeletal muscle fibers is constructed that captures characteristic isometric (constant length) and isotonic (constant load) behavior of active skeletal muscle. An iterative coupling framework for fluid-structure interactions (FSI) is presented that captures the complexity of the wing skin with a commercial finite element solver incorporating a user material subroutine for the active viscoelastic constitutive model, and viscous flow behavior with a Reynolds Averaged Navier-Stokes fluids solver. This work is the first in-depth FSI analysis of highly compliant nonlinear anisotropic passive and active membranes in low Reynolds number flow. Results demonstrate muscle-induced camber control, and enhanced lift performance and flight efficiency (lift-to-drag ratio) in active compliant membranes over rigid airfoils of up to 36% and 20%, respectively. Detailed analysis of in-plane kinematics and muscle activation of an M-shaped plagiopatagium membrane highlights a large range of deformed membrane conformations and aerodynamic performance. Results demonstrate that a trailing edge muscle fiber is more effective for modifying lift performance, while membrane musculature is more effective for providing stable conditions for steady flow over the wing. These results are useful for informing design choices of engineered wing membranes.PHDAerospace EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/135938/1/skulbors_1.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/135938/2/skulbors_2.pd