Drag reduction by reconfiguration of highly flexible structures subjected to fluid flow

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In most traditional engineering applications, structures are designed to be stiff such that the loads they must bear do not deform them substantially. In nature, the contrary is true. Especially when it comes to fluid loading, natural structures tend to be compliant and flexible whereas man-made structures are rigid and unyielding. Plants, which seek to maximize their surface area to capture the most sunlight, make use of their flexibility by changing their shape when they are subjected to a fluid loading, whether water flow or wind. We say that they reconfigure.By bending and twisting under fluid loading, plants reduce their projected area perpendicular to the flow, and also become more streamlined. Through these two primary mechanisms of reconfiguration, the drag load that plants must support does not grow with the square of the velocity of the flow they are subjected to - as it would on a rigid bluff body at a high Reynolds number - but rather in a less pronounced way. Experimental measurements on the reconfiguration of aquatic and terrestrial plants are abundant in the literature, and a large interest exists for an understanding of the scaling of drag of plants with flow velocity. However, theoretical interpretation is difficult to obtain from real plants because of their complex geometries and materials as well as the significant variations between specimens. It is for this reason that a fundamental understanding of reconfiguration is sought by studying simple structures such as beams and plates subjected to flow. We seek to gain a fundamental understanding of the reconfiguration of simple elastic structures via wind tunnel experiments and numerical simulations. Our goal is to paint a complete picture of the mechanical aspects of plant reconfiguration with all its mechanisms and their effects on drag scaling.It is essential to understand the fluid loadings on vegetation in order to devise better models to comprehend and predict wind damages to forests, crops and shore vegetation, as well as to study the adaptation of aquatic and terrestrial plants to their environment.