Computational Investigation of Staggered Vegetation Barriers for Coastal Defense Systems using VOF

Abstract

In coastal areas, the threat of tsunamis always remains, and these areas are highly affected by tsunamis. After the 2011 earthquake and tsunami in Japan, researchers were prompted to recognize that engineered hard elements like embankments alone are not sufficient, so they shifted their focus to using vegetation as a natural protection system with engineered elements to reduce tsunami energy. Trees not only reduce energy but also help in reducing the depth of flowing water, and they are economically feasible and environmentally friendly. In this study, we placed vegetation in a numerical model in a staggered arrangement. We performed simulations in ANSYS FLUENT using the VOF model, and after the water passed through the vegetative zone, the percentage of energy reduction and the changes in velocity were observed. We set the domain under subcritical conditions (Fr=0.66), which represents a small-scale tsunami flow. From the model, we observed a noticeable 25% reduction in energy as the flow passed through the vegetative region. When flowing water struck the stem, there was a sudden loss of velocity, and at that point, the velocity became approximately equal to 0. After passing through the vegetation, the depth also reduced by 55.2%. These results show that even small vegetation can affect the flow behavior of water. This study adds support for including vegetation in hybrid coastal protection strategies and may help guide future improvements.