Detailed meshing guide

Compilation of different meshing projects

Creating a coarse mesh for the Gulf of Mexico + Atlantic Ocean

Script for this example: mesh_test.m

Requirements

Shapefile of the mesh boundary / coastline. This example uses GSHHS: https://www.soest.hawaii.edu/pwessel/gshhg/
DEM in netCDF format. This example uses GEBCO (either of the first two should work): https://www.gebco.net/data_and_products/gridded_bathymetry_data/
Tidal database h_tpxo9.v1.nc

Steps

Set the parameters. These control how fine the mesh will be. Note that "resolution" misleadingly refers to the element size, so the higher the value, the less resolved the mesh will be.

name = 'coarse_1dt';
bbox = [-98 -60;		% lon_min lon_max
        7.9 45.86]; 		% lat_min lat_max
min_el    = 1e3;  		% minimum resolution in meters.
max_el    = 15e3; 		% maximum resolution in meters. 
max_el_ns = 5e3;        % maximum resolution nearshore in meters.
grade     = 0.2; 		% mesh grade in decimal percent.
R         = 2;    		% number of elements to resolve feature width.
slope = 20;

Create the geo and edge objects. I usually use DT = 1 or 2, but in practice you might need to use a smaller timestep.

coastline = 'GSHHS_f_L1';
dem = 'GEBCO_2021.nc';

gdat = geodata('shp',coastline, ...
                'dem',dem, ...
                'bbox',bbox, ...
                'h0',min_el);
%% STEP 3: create an edge function class
fh = edgefx('geodata',gdat,...
            'fs',R, ...
            'max_el',max_el, ...
            'g',grade, ...
            'dt',1);

Triangulate the mesh object and plot it. In this example we use automatic boundary generation. In other cases we will have to manually select boundary segments to designate (see other examples).

% build the mesh...
mshopts = meshgen('ef',fh,'bou',gdat,'plot_on',1,'nscreen',5,'proj','equi');
mshopts = mshopts.build; 

% Get out the msh class and put on nodestrings
coarseMesh = mshopts.grd;
coarseMesh = make_bc(coarseMesh,'auto',gdat); % make the boundary conditions
plot(coarseMesh,'type','bd','proj','equi');

Create bathymetry data by interpolating the DEM. WARNING: if the mesh is large then the system can run out of memory and MATLAB will crash, or worse, Linux will be unresponsive due to the way it handles out-of-memory.
```
coarseMesh = interp(coarseMesh, dem);
```

Create fort.15 with tidal BC and save it to disk, along with the mesh (fort.14).

coarseMesh = Make_f15(coarseMesh, '2012-08-01 00:00', '2012-11-31 00:00', 2, 'const', 'major8','tidal_database','h_tpxo9.v1.nc');

%% Save to fort.14 and fort.15
write(coarseMesh, name, 'f14');
write(coarseMesh, name, 'f15');

Computational Hydraulics Group

Detailed meshing guide

Creating a coarse mesh for the Gulf of Mexico + Atlantic Ocean

Adding levees to a mesh

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