The work presented herein is part of a technical paper co-authored by Maria Mingallon (Arup, Senior Structural Engineer) and Sakthivel Ramaswamy (KRR Engineering, Director), published and presented at ASME 2011. The paper outlines the main findings of a broader biomimetics research study done at the Architectural Association as part of the master program in Emergent Technologies and Design. The aim was to derive the adaptable and performative logics of the dragonfly wing. Digital simulations in GSA were necessary to understand the multiple-pattern and corrugated geometries that give the wings their unique structural behavior and which are responsible for the high performance of dragonflies in passive flight.
The morphology of the dragonfly wing is an optimal natural construction built by a complex patterning process, developed through evolution as a response to force flows and material organisation. The seemingly random variations of quadrangular and polygonal patterns follow multi-hierarchical organisational logics enabling it to alter between rigid and flexible configurations.
How Oasys proved invaluable
As the dragonfly wing is a highly dynamic structure, vibration studies were necessary to obtain realistic deformation patterns and understand the structural behaviour. Ten vibration modes were extracted from the modal analysis performed in GSA. Our eyes have difficulties distinguishing the third, fourth and fifth vibration modes (which occur almost simultaneously) due to the high frequencies exhibited. In our case, slow motion pictures featuring the real flight of the dragonfly allowed us to identify up to the third mode of vibration by comparison with that calculated in the analysis.
The resulting images featuring the different modes of vibration of the wing illustrate the correlation described earlier between the geometrical patterns and the different degrees of flexibility. The rectangular pattern found at the uppermost zone of the wing is designed to withstand load perpendicular to the leading edge taken by the wing during flight, while corrugations help with resisting loads perpendicular to the plane of the wing.
A torsional wave at the trailing edge can be observed throughout the different modes; this is due to the tendency of the elements closer to the wing’s tip to twist ahead of those nearer to the base. The nodus, located at the leading edge, acts as both reinforcement and shock absorber to the wing. The nodus copes with combined torsion and bending stress concentrations at the junction of the rigid concave ante-nodal and the torsionally compliant post-nodal spars. The concentration of stresses and bending moments must have imposed strong selection pressure in the development of the nodus, which combines a stress absorbing strip of soft cuticle with strong, three dimensional cross bars across the entire spar between the costal margin and the leading edge.
The deformed modal shapes demonstrate that the pentagonal-hexagonal pattern is designed to deform and thus provide the thrust necessary to keep the dragonfly in the air. The 120° angle present in these geometries allows for the polygons to reorganise from a single plane to form a concave surface, using much less energy than that of the rectangular pattern.