The remarkable maneuverability and aerodynamic efficiency of insects have created an intrinsic interest on learning the mechanisms that govern insect flight and consequently consider their further application in engineered devices, namely micro air vehicles. However, in order to implement such mechanisms into these devices, the wings from micro air vehicles must be optimized, aerodynamically efficient structures. Therefore, a qualitative and quantitative analysis of the structural properties and dynamic response of insect wings is seen as the key element for a successful biomimic implementation. The aforementioned application is the motivation of this study. A crane fly, an insect that has been proven to be aerodynamically efficient at low-speed flight, is chosen to perform a characterization and analysis of its structural dynamic response. The internal and external morphologies of the wing are captured and studied using a micro- computed tomography scan. A finite element model is developed from the reconstructed model of the scan for the natural frequencies and mode shapes of the crane fly forewing in vacuum. Furthermore, a fluid-structure interaction model is developed by coupling a finite element model with a computational fluid dynamics model to investigate the deformations of the crane fly forewing under steady and unsteady airflows. The following conclusions are drawn from this study:
1) Micro-computed tomography proves to be a powerful technique to characterize the internal and external structures of complex specimens. Highly accurate measurements of the wing geometry are determined from the reconstructed 2-D cross-sectional images and the corresponding 3-D model. The structure of the wing is characterized by an uniform thickness membrane attached to a venation system formed by tubular veins of two
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different thicknesses that take into account the stiffness variation along the spanwise y-
direction of the wing.
2) The modal characterization of the crane fly forewing indicates that the natural frequency increases with mode and that the mode shapes are highly dominated by bending and torsional deformation responses. For the crane fly forewing, the first four mode shapes are sufficient to describe the structural response as it is highly unlikely that the wing would naturally experience forces that cause vibrations in the order of magnitude of the frequencies from higher modes. Furthermore, the aforementioned deformation responses provide an insight of the stiffness distribution of the crane fly forewing with slightly more flexible regions at the tip of the wing and at the middle of the leading and trailing edge. 3) The deformation magnitude is highly dominated by the out-of-plane deformation, namely
the z-component of displacement. Furthermore, the deformation along the span of the
wing increases nonlinearly from the root to the tip of the wing as the freestream velocity is increased for both steady and unsteady airflow conditions. Such behavior is due to the stiffness provided at the root of the wing by the fixed constraint and by the thick veins. This stiffness gradually decreases along the span of the wing; therefore, it supports the theory that the veins are indeed more than circulatory medium for the wing but also an important structural feature. Moreover, the presence of a nonlinear deformation
distribution suggests that the stiffness variation along the spanwise y-direction of the
wing plays an important role when generating the desired elastic deformations that are well known to enhance the lift capability of insects. In other words, stiffness variation, accounted by the different thicknesses within the venation pattern, serves as the passive regulatory mechanism for the deformation experienced by insects during flight.
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VITA
Mr. José E. Rubio was born in Tegucigalpa, Honduras. He completed his B.Sc. in Mechanical Engineering at the University of New Orleans in December 2012. Currently, he is about to finish his M.Sc. in Mechanical Engineering in December 2014 while simultaneously being a Ph.D. candidate in Engineering and Applied Sciences program at the University of New Orleans. He holds a Graduate Assistantship through which he conducts research in the areas of fluid-structure interaction and the design of biologically inspired structures.