Gmsh
Introduction
In this section we brielfy present the procedure for creating a mesh on domains representtive of realistic features like oceans as well as islands. Clealry, the shore borders have to be acqquired from valid sources and created in the Gmsh form otherwise known as the geometry model. The Gmsh is composed of GSHHS plugin (Lambrechts et al, 2008).
Just as it is stated from its name, the plugin applies the Global Self consistent method, high resolution Shoreline Database (Wessel and Smith, 1996) as a basis of shoreline aspect. In precise, the plugins make it possible for the users to choose a region on the globe, and later create aGmsh geometry basis that fits on the spline to the shoreline. The clients are able to create open boundaries so as to create an enclosed domain.
The user is directed to the link http://perso.uclouvain.be/jonathan.lambrechts/
gmsh_ocean/ where the screen shots bring forth the method of how to apply the plugin and create the meshes which are composed of high resolution to the shoreline. Though the clients are able to make a precise descritpion of the plugin choices available and later invoke the plugins from the Gmsh scripts. Hence, a process where the client forms a number of scripts and semi-automates.
Load the Island
The first step is to download the gshhs data from the site
www.soes.hawaii.edu/wessel/gshhs/gshhs.html
Click on tools and select Mesh then fields where a window will open. Click on “new” then box and then convert the corners coordinates in radian form. This can be in longitude and latitude form. Then apply.
Then import the islands data into the gmsh. This is done using the box and lation fields, then a descripton of the value of field using value-1 external of the domain and O inside the domain. Then apply the “GSHHS” plugin. Here you insert the names of the Infiles and Outfile with an iField of 2.
Create a Uniform Mesh
Here you create a comment on the first line of the .geo file to work in the parametric space.
Later create the external boundary and the plane surface using the elementary entity on the geometry option. Then click on split then line where a line to be split is selected.
Tag the surface and the open sea boundary
Decomment the first lines of the file which is in .geo so as to bring the sphere back.
Apply the field to definethe background mesh size in metres
Create 1d and 2d mesh.
Improve the Mesh
First open the domain .geo file using gmsh
Then go to the tools menu and select ”Mesh”. Here you select “new” then on fields where a window will appear. Click on “new” then threshold where the desired figures can be inserted minimum and maximum. Select the option “background mesh size” on a check box then click apply.
Describe the field with regard to the “attractor”; this will give it the distance from the islands
Go the tools option on the menu and select options then mesh followed by advanced ; deselect the “extended from boundary” choice.
Click on general and then the frontal option where then you save.
Choose the “frontal” mesh method which offers a better outcome
Repeat the 1d and 2d mesh. Then save it under the .msh extension.
References
Lambbrechs, J., et al (2008). Multiscale mesh generation on the sphere. Ocean Dynamics. Verlag: Springer.
Wessel, P., and W. H. F. Smith, A. (1996). Global, Self-consistent, Hierarchical, High-Resolution Shoreline Database. J. Geophys. Res., 101, 8741-8743.
