Thresholds of Deflection For Flexible Conical Vegetation Under Wave Flow

Abstract

This work seeks to expand on the research done previously by the WOODY group on the ability of vegetation as a form of wave damping. Specifically in this work, we are looking at pollard willow trees (Salix Alba) and the relationship between the motion of the object and the forces it can induce on the wave flow. This was done by testing a range of stiff and flexible conical mimics of three different sizes and varying moduli of elasticity across multiple water levels. The results were compared to commonly used relationships for predicting object motion such as Cauchy, KC, and CAL/KC (Jacobson). Due to the non-constant cross-sectional area of a conical object. However, the relationships could not fully capture the motion. As such a new equation was fitted and derived from the relationships that better captured the motion of the mimics under wave flow. This equation relates the peak forces felt by the objects to the peak deflection. Which can be used as an indicator of wave damping. Along with this number thresholds for motion were also derived from the data. It was found that when an object tip has deflected 2 degrees or less it can be considered completely stiff. If deflecting between 2 and 5 degrees it can be considered relatively stiff, however, high-frequency flow effects can cause discrepancies in the forces between tests.