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Transport due to internal waves in the coastal ocean

PhD Student: Goncalo Gil

This project focuses on the potential for transport of polutants due to internal tides in the coastal ocean. Non-linear effects associated with internal waves include the advection of fluid particles along with suspended mass such as sediment, nutrients, larvae, as well as contaminants in the direction of wave propagation. Studies have shown that internal tides play an important role in the advection of larvae and other organisms to the near shore including the development of benthic communities. Moreover, high-frequency internal waves have been shown to influence the spatial distribution of plankton, effectively controlling nutrient dispersal in coastal regions. Other studies have shown that large solitary internal waves containing a recirculating core are able to trap and advect pollutants over large distances through a stratification generated waveguide.

 
To quantify the advection of fluid via internal waves, simulations using a Navier-Stokes code developed at the EFML by Zang et al. are employed. The code is a widely tested and validated large-eddy simulation solver which uses a fractional time step method to solve the Navier-Stokes and scalar transport equations using a finite-volume formulation on a generalized curvilinear coordinate non-staggered grid. The method is second order accurate in time and space.
 
Figure 1 depicts Lagrangian particle trajectories for a first-mode internal wave in a linearly stratified fluid with a Froude number of 0.48 defined by the ratio of the maximum fluid velocity divided by the linear wave speed. Since wave propagation is from left to right, the classic profile of transport in the direction of wave propagation is exhibited in the upper and lower parts of the water column, while transport is directed in the opposite sense in the middle of the water column. Trajectories are computed using the Navier Stokes solver and compared to those computed using the linear theoretical velocity profiles, showing that even at high Fr the agreement is surprisingly close.

Figure 1: Lagrangian particle trajectories in a first-mode internal wave in linear stratification over three wave periods with Fr=0.48, comparing the result of using a Navier-Stokes solver (solid line) with trajectories computed using the velocity from linear wave theory (dashed line).

This project is funded by the Leavell Family Faculty Scholarship and a Ph.D. fellowship from the Portuguese Ministry of Science.

For more information please visit Zo's web page.

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Last updated: 11/11/09