Physics of Biology

Aeroelastic Similarity in Trees

Authors: Brian Scannell
Comments: 17 Pages. (Note by viXra Admin: Please submit article written with AI assistance to ai.viXra.org)

Trees are dynamically complex branched structures in which trunks, branches and higher ordercrown elements possess characteristic motions and are mechanically coupled. In a doctoral thesis completed in 1983 and formally awarded in 1984, Scannell proposed a qualitative mechanical principle termed aeroelastic similarity. Measurements on Sitka spruce suggested approximate relationships between modal frequencies at successive structurallevels, together with direct evidence of coupled branch motion. The original interpretationproposed that overlapping frequency ranges could permit wind-induced mechanical energyto be redistributed through the crown and dissipated, thereby restricting large-amplituderesonant motion. This paper reassesses that hypothesis against four decades of subsequent tree biomechanics research. Later work explicitly tested the named aeroelastic-similarity theory and subsequently developed mass damping, multiple resonance damping and damping by branching.The evidence does not support a universal hierarchy of exact modal equivalence. It does,however, support a broader principle in which frequency-compatible, mechanically coupled treemotions can exchange energy and thereby provide access to distributed dissipative mechanisms.We formulate this surviving idea as dynamically coupled modal compatibility, not modalidentity. A reduced coupled-oscillator model separates conservative energy redistribution fromdissipation, introduces descriptive measures of spectral separation and mode hybridisation,and motivates a hierarchical modal-network interpretation. We then propose a falsifiableexperimental programme based on controlled detuning in numerical models, laboratorybranched structures and living trees. Aeroelastic Similarity is therefore retained not asan exact frequency-scaling law, but as a testable hypothesis concerning the dynamicalorganisation of branched structures.
Category: Physics of Biology