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Unstructured mesh generation

High quality meshes adjusted to the simulations’ needs are essential to take advantage of the finite element method. That’s why the mesh generation tool constitutes a crucial part of this model. SLIM relies on the state-of-the-art mesh-generation software GMSH to build meshes whose resolution can depend on a number of different criteria such as:

  • the distance from coastlines,
  • the square root of the bathymetry,
  • the curvature of the bathymetry,
  • the curvature of the coastlines,
  • the location of a specific region of interest,
  • the error measured from a previous simulation.

These different criteria are blended together to create a unique mesh resolution map.

Mesh of the Great Barrier Reef (Australia) refined along the coastlines and in shallow regions. It contain 8e5 triangles and its resolution ranges from 200m to 5km.

The quality of the simulation strongly depends on the quality of the mesh. By locally increasing the mesh resolution, we can capture small-scale flow features and accurately describe the topography. The animation below shows the impact of the mesh resolution on the representation of the topography, which in turn influences the flow. The coarsest mesh has a 4km resolution that cannot represent all the small islands present in that area. As a result, they are all merged together in a continuous piece of land. By increasing the resolution to 2km, 1km, 500m and finally 250m, we can see how small-scale topographic features start to appear in the mesh and how they influence the flow. In particular, recirculation eddies are only present with a resolution of at least 500m.

To learn more…

Remacle, J.-F., & Lambrechts, J. (2018). Fast and robust mesh generation on the sphere—Application to coastal domains. Computer-Aided Design, 103, 14–23.
Lambrechts, J., Comblen, R., Legat, V., Geuzaine, C., & Remacle, J.-F. (2008). Multiscale mesh generation on the sphere. Ocean Dynamics, 58(5–6), 461–473.
Legrand, S., Deleersnijder, E., Delhez, E., & Legat, V. (2007). Unstructured, anisotropic mesh generation for the Northwestern European continental shelf, the continental slope and the neighbouring ocean. Continental Shelf Research, 27(9), 1344–1356.
Legrand, S., Deleersnijder, E., Hanert, E., Legat, V., & Wolanski, E. (2006). High-resolution, unstructured meshes for hydrodynamic models of the Great Barrier Reef, Australia. Estuarine, Coastal and Shelf Science, 68(1–2), 36–46.
Legrand, S., Legat, V., & Deleersnijder, E. (2000). Delaunay mesh generation for an unstructured-grid ocean general circulation model. Ocean Modelling, 2(1–2), 17–28.