CFD Modelling of experiments with artificial reefs

Coral reefs, often likened to natural breakwaters, exhibit remarkable efficiency in dissipating wave energy. Accurately modelling the hydrodynamics of these complex ecosystems, both physically and numerically, pose many challenges.

In this three-dimensional numerical model, we firstly replicate the results of a flume experiment focusing on key features such as coral reef length, depth, rugosity, and the characteristics of the incident wave, namely the wave height and period. Using the advanced Computational Fluid Dynamics (CFD) capabilities of the StarCCM+ software, we simulated the complex interactions between these parameters to comprehensively understand their influence on wave hydrodynamics. Through this approach, we seek to provide a robust analysis of how variations in depth, reef length, and rugosity impact wave height attenuation, energy dissipation and the nearbed velocities. The numerical model is also aimed at addressing limitations of the physical model by accounting for the reflection in the flume and enabling easy variation of reef properties. As such, we can then augment the datasets using the validated numerical model to expand the parameter ranges.

The results obtained from this three-dimensional numerical model are expected to offer valuable insights for the assessment and implementation of coastal engineering and management strategies, with the aim to support sustainable coastal development.

Numerical Modelling of coral reefs at a field scale

This is a short video showing the output of a coupled numerical model using DHI’s 2D modelling suite MIKE 21 where only the Spectral Wave (SW) and Hydrodynamic (HD) modules are included. The SW Module is able to simulate the waves in the nearshore, while the HD module is used to simulate the water levels and currents. The coupled model can interactively model these various processes in coastal regions.

The numerical simulation aims to capture the hydrodynamic effects of the Buccoo Reef system located off the southwestern coast of the island of Tobago, and quantify the coral reef’s impact on the waves and currents near the shore. The northwest boundary of the simulation domain, which represents the offshore boundary, is located at the nearest WaveWatch 3 point off the Buccoo Bay/Bon Accord region of Tobago. WaveWatch 3 is a wave model developed at NOAA/NCEP and this output is freely available. The wave parameters from WaveWatch 3 are used as input for the offshore boundary of the model simulation domain. As part of the input parameters of the hydrodynamic forcing, the model also incorporates tides generated from MIKE’s Tide Generator for all non-land boundaries, HYbrid Coordinate Ocean Model (HYCOM) currents at the northwest boundary and Global Forecast System (GFS) winds across the model domain. The bathymetry is a compilation of digitized data from relevant UK Hydrographic Office (UKHO) maps and primary data collected in during a data collection campaign in 2016.

The numerical model was calibrated and validated using wave and current data from the same campaign in 2016, but the model will be re-assessed using data collected from this ongoing project.