SUMMARYInsect wings demonstrate elaborate three-dimensional deformations and kinematics. These deformations are key to understanding many aspects of insect flight including aerodynamics, structural dynamics and control. In this paper, we propose a template-based subdivision surface reconstruction method that is capable of reconstructing the wing deformations and kinematics of free-flying insects based on the output of a high-speed camera system. The reconstruction method makes no rigid wing assumptions and allows for an arbitrary arrangement of marker points on the interior and edges of each wing. The resulting wing surfaces are projected back into image space and compared with expert segmentations to validate reconstruction accuracy. A least squares plane is then proposed as a universal reference to aid in making repeatable measurements of the reconstructed wing deformations. Using an Eastern pondhawk (Erythimus simplicicollis) dragonfly for demonstration, we quantify and visualize the wing twist and camber in both the chord-wise and span-wise directions, and discuss the implications of the results. In particular, a detailed analysis of the subtle deformation in the dragonflyʼs right hindwing suggests that the muscles near the wing root could be used to induce chord-wise camber in the portion of the wing nearest the specimenʼs body. We conclude by proposing a novel technique for modeling wing corrugation in the reconstructed flapping wings. In this method, displacement mapping is used to combine wing surface details measured from static wings with the reconstructed flapping wings, while not requiring any additional information be tracked in the high speed camera output. Supplementary material available online at

We present the visual analysis of a biologically inspired CFD simulation of the deformable flapping wings of a dragonfly as it takes off and begins to maneuver, using vortex detection and integration-based flow lines. The additional seed placement and perceptual challenges introduced by having multiple dynamically deforming objects in the highly unsteady 3D flow domain are addressed. A brief overview of the high speed photogrammetry setup used to capture the dragonfly takeoff, parametric surfaces used for wing reconstruction, CFD solver and underlying flapping flight theory is presented to clarify the importance of several unsteady flight mechanisms, such as the leading edge vortex, that are captured visually. A novel interactive seed placement method is used to simplify the generation of seed curves that stay in the vicinity of relevant flow phenomena as they move with the flapping wings. This method allows a user to define and evaluate the quality of a seed's trajectory over time while working with a single time step. The seed curves are then used to place particles, streamlines and generalized streak lines. The novel concept of flowing seeds is also introduced in order to add visual context about the instantaneous vector fields surrounding smoothly animate streak lines. Tests show this method to be particularly effective at visually capturing vortices that move quickly or that exist for a very brief period of time. In addition, an automatic camera animation method is used to address occlusion issues caused when animating the immersed wing boundaries alongside many geometric flow lines. Each visualization method is presented at multiple time steps during the up-stroke and down-stroke to highlight the formation, attachment and shedding of the leading edge vortices in pairs of wings. Also, the visualizations show evidence of wake capture at stroke reversal which suggests the existence of previously unknown unsteady lift generation mechanisms that are unique to quad wing insects.

Hovering hinged plates are used to study the effects of passive deflection on aerodynamic performance using two-dimensional Direct Numerical Simulations (DNS) at low Reynolds numbers (Re). The hinge is modeled as a torsional spring at the leading edge, where the prescribed motion is applied. The influence of forced-to-natural frequency ratio (hinge stiffness) is studied, concluding that averaged glide ratio (lift-to-drag) improved as the hinge became stiffer, with a peak performance occurring for ! f ! n = 1 4 . The influences of stroketo-chord ratio on a hovering hinged plate are also investigated, concluding that glide ratio improved as the ratio increased for the frequency ratio that we studied. NomenclatureA x = Amplitude of stroke amplitude in x-direction (m) and orientation angle (deg) C ! , C ! = Lift coefficient and its average over flapping cycles C ! , C ! = Drag coefficient and its average over flapping cycles c, h = Chord and thickness of the plate (m). c is chosen as characteristic length k = Hinge Torsional spring stiffness (N/m) J = Moment of Inertia of plate (m 4 ) ω ! , ω ! = Forced and natural frequency of plate Re = !" ! Reynolds number, ! is kinematic viscosity of fluid (m 2 /s) St = !" ! Strouhal number Glide Ratio = C ! / C !, also known as lift-to-drag ratio U = Characteristic speed (m/s), based on maximum leading edge speed ! = Deflection angle of hinged plate ! ! , ! ! = Density of body and fluid respectively (kg/m 3 ) F ! = Net body force on plate, comprised of gravity and buoyancy (N) F ! = Aerodynamic force on body surface (N) ! ! = Torque generated by gravitational force and buoyancy, with respect to the hinge (Nm) ! ! = Torque with respect to the mass center of hinged body (Nm)