Document Type
Dissertation
Date of Award
5-31-2023
Degree Name
Doctor of Philosophy in Mechanical Engineering - (Ph.D.)
Department
Mechanical and Industrial Engineering
First Advisor
Simone Marras
Second Advisor
Juan Carlos Cajas
Third Advisor
Chao Zhu
Fourth Advisor
Samaneh Farokhirad
Fifth Advisor
Kyle T. Mandli
Abstract
Communities worldwide are increasingly interested in nature-based solutions like coastal forests for the mitigation of coastal risks. Still, it remains unclear how much protective benefit vegetation provides, particularly in the limit of highly energetic flows after tsunami impact. The present thesis, using a three-dimensional incompressible computational fluid dynamics model with a fluid-structure interaction approach, aims to quantify how energy reflection and dissipation vary with different degrees of rigidity and vegetation density of a coastal forest.
In this study, tree trunks are represented as cylinders, and the elastic modulus of hardwood trees such as pine or oak is used to characterize the rigidity of these cylinders. To capture tsunami bore propagation in onshore, dam break flow is used over the wet surface in the numerical studies. After validating numerical code against experimental studies, multi-cylinder configurations are incorporated and Froude Number is used to scale the flow parameters and vegetation flow parameter (VFP) to scale the tree parameters such as elastic modulus, the diameter of the trunk, etc. Numerical tests are conducted for different cylinder diameters, densities, and elastic moduli.
The numerical results show that energy reflection increases with rigidity only for a single cylinder. In the presence of multiple cylinders, the difference in energy reflection created by varying rigidity diminishes as the number of cylinders increases. Instead of rigidity, the blockage area created by the presence of multiple tree trunks is found to dominate energy reflection.
As tree trunks are deformed by the hydrodynamic forces, they alter the flow field around them, causing turbulent kinetic energy generation in the wake region. As a consequence, trees dissipate flow energy, highlighting the importance of coastal forests in reducing the onshore energy flux of tsunamis by means of both reflection and dissipation.
Recommended Citation
Mukherjee, Abhishek, "Importance of vegetation in tsunami mitigation: evidence from large eddy simulations with fluid-structure interactions" (2023). Dissertations. 1668.
https://digitalcommons.njit.edu/dissertations/1668
Included in
Fluid Dynamics Commons, Ocean Engineering Commons, Oceanography and Atmospheric Sciences and Meteorology Commons
