Experimental study on wave attenuation by vegetation by means of particle imaging velocimetry

TL;DR

This study experimentally investigates how coastal vegetation attenuates waves using particle imaging velocimetry, introduces a new method for accurately measuring drag coefficients, and models the flow and energy dissipation mechanisms involved.

Contribution

It proposes a modified direct measurement method for vegetation drag coefficient and analyzes flow fields and energy dissipation mechanisms during wave attenuation.

Findings

Drag coefficient correlates with Reynolds number.

Flow field analysis reveals wave energy dissipation mechanisms.

A predictive model for turbulent kinetic energy was developed.

Abstract

Coastal vegetation serves as an ecological defense and plays an important role when facing marine disaster such as storm surge. In this study, we investigated experimentally the wave attenuation, including wave height and wave force decay, and flow field within rigid vegetation by means of particle imaging velocimetry (PIV). Drag coefficient of vegetation is closely related the wave attenuation by vegetation. Based on Morison equation, a new modified direct measurement method to derive the drag coefficient of vegetation was proposed in this study. This method can eliminate the potential errors and obtain more accurate drag coefficient to have a well-fitted relationship with Reynolds number compared with the previous methods. More importantly, we showed the flow field including instantaneous velocity filed in different wave phase within the vegetation and turbulent kinetic energy (TKE) field to describe the mechanisms of wave energy dissipation. In addition, a prediction model to reproduce the instantaneous TKE was proposed by the work input of vegetation. The results illustrated that all these characteristics of parameters can help us understand the effect of the coastal vegetation on wave attenuation better.