Structural dynamics and aerodynamics measurements of biologically inspired flexible flapping wings.

Flapping wing flight as seen in hummingbirds and insects poses an interesting unsteady aerodynamic problem: coupling of wing kinematics, structural dynamics and aerodynamics. There have been numerous studies on the kinematics and aerodynamics in both experimental and computational cases with both natural and artificial wings. These studies tend to ignore wing flexibility; however, observation in nature affirms that passive wing deformation is predominant and may be crucial to the aerodynamic performance. This paper presents a multidisciplinary experimental endeavor in correlating a flapping micro air vehicle wing's aeroelasticity and thrust production, by quantifying and comparing overall thrust, structural deformation and airflow of six pairs of hummingbird-shaped membrane wings of different properties. The results show that for a specific spatial distribution of flexibility, there is an effective frequency range in thrust production. The wing deformation at the thrust-productive frequencies indicates the importance of flexibility: both bending and twisting motion can interact with aerodynamic loads to enhance wing performance under certain conditions, such as the deformation phase and amplitude. By measuring structural deformations under the same aerodynamic conditions, beneficial effects of passive wing deformation can be observed from the visualized airflow and averaged thrust. The measurements and their presentation enable observation and understanding of the required structural properties for a thrust effective flapping wing. The intended passive responses of the different wings follow a particular pattern in correlation to their aerodynamic performance. Consequently, both the experimental technique and data analysis method can lead to further studies to determine the design principles for micro air vehicle flapping wings.

Photoelastic analysis of miniplate osteosynthesis for mandibular angle fractures.

OBJECTIVE: The purpose of this study was to reassess Champy's findings, which were instrumental in justifying the theory of tension band plating for mandibular angle fractures. STUDY DESIGN: Ten anatomically correct mandibles were fabricated with a photoelastic resin. In five mandibles, angle fractures were created and fixed with a superior border miniplate; five uncut mandibles served as controls. Each mandible was loaded in a manner that simulated physiologic conditions. The internal stress patterns were preserved within the models by completing a stress freezing cycle. RESULTS: The stress patterns in the experimental mandibles virtually replicated the patterns seen in the controls. Stress fringes were present surrounding the outer screws, indicating that these screws were subjected to pull-out forces. CONCLUSIONS: There is greater force on the outer screws that may contribute to fixation failure. The theory of tension band plating for mandibular angle fractures is accurate but Champy's model is oversimplified.