At the end of the menu tree you will find a feature called Edit Script, when we click on it we a text editor pops up with the script that describes the geometry you have just created. This last step finalizes the creation of a circle using Gmsh’s GUI. In our case we have a solid surface, so we can press ‘e’ to end the selection. First we need to select the surrounding boundary, and then if any, the boundaries of the holes within the surface. The Plane surface feature enables you to create solid surfaces or with holes. Since the face of our geometry is flat, we can use the Plane Surface feature to define the circle. Once we have connected all the dots, we have identified the circumference of the circle, hence, only its boundary line. Note that Line 1 connects Point 2 and Point 3 with center in Point 1, Line 2 connects Point 3 and 4 with center in Point 1, and so on. To generate a circle you will need to connect the points created using the Circle arc feature in the tree, first choosing the starting point, the center of the circular arc and the end point as shown below. By selecting Point a new window pops up, enabling you to select the rectangular coordinates where the points will be located. In the image below we show how to expand the Geometry tree and create points within the interface. A circle is a 2D geometrical entity and we will need to define three characteristics: the points that define our plane (at least three), the lines that connect our points and the surface itself. There is a consistent workflow in the generation of geometries in Gmsh. For this reason I will compare the workflow shown on the GUI to the text file generated, for you to see their similarities. I personally like using a combination of both: GUI and text editor in parallel, as some things are done quicker one way rather than the other. This will ramp up the learning curve and allows you to learn Gmsh’s syntax. Generally, it is appropriate to start working with the GUI at the beginning, if you have never used Gmsh before. The latter one will be quite useful for more complex or parametrized geometries, and we’ll touch on it at the end of this post. There are two ways of constructing geometries using Gmsh: using the Graphical User Interface (GUI) or simply by creating a text file (.geo) in a text editor, using Gmsh’s syntax. This post addresses the very basics of geometry generation using a circle as an example. In case you want to keep the two domains separate you should handle the boundary conditions as indicated in the previous tip.The creation of geometries using Gmsh can be tricky at times. Rectangles = (,, tag=3, removeObject=True, removeTool=True) # link both domains and remove old rectangles The gmsh part of the code could look like this: # initialise gmsh engine Applying a boundary condition is then easily done via bc = DirichletBC(V, u0, mf_1d, Your_Boundary_Index)Īnother possible solution in case you don’t need the line linking the two domains is to use the gmsh command: I would define all boundaries in gmsh (name lines in your mesh) and create a 1d-MeshFunction in Fenics representing the boundaries. However I assume my quick solution is not very practical to use for you as it’s kind of dirty (at least in my opinion). # Define Dirichlet boundaryīc2 = DirichletBC(V, u0, boundary_Bottom) If I create 4 different boundary conditions like this, then it works. I think the problem is due to your boundary condition (I assume, that the parameter on_boundary) is also true for boudnaries between subdomains). Pyplot.title ("Cahn - Hilliard solution ") Mf_2d = (mesh, mvc_2d)ĭx = Measure("dx", domain=mesh, subdomain_data=mf_2d) Mvc_2d = MeshValueCollection("size_t", mesh, 2) # gnerate 2D mesh, write mesh and convert to xdmfĪrea_mesh = meshio.Mesh(points=msh.points, cells=) Hi 3200×2400 215 KB from matplotlib import pyplot
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