![]() ![]() I have written a basic script, available here, which converts the GMSH mesh file to 2 XDMF files, tetrahedral and physical boundary mesh. The XDMF format avoids some incompatibility issues, often more memory efficient as well as splitting the mesh into the tetrahedral mesh and physical boundary mesh.įortunately, the conversion is very simple using Meshio. We need to convert the GMSH MSH file to an XDMF, the preferred format for FEniCS. Meshio is software which converts the GMSH “.msh” file to “.XDMF” which has better file size in comparison to other mesh formats as well as working well within BERNAISE. The MSH file format should be “Version 4 ASCII” but “Version 2 ASCII” should work due to the wide support within Meshio. Once generated, the mesh can be exported by File > Export menu and choosing “Mesh – Gmsh MSH – (*.msh)” format from the file type drop down menu and saved with an appropriate name. If we wanted 2D, we could select 2D from the left hand menu. The mesh can be created by selecting 3D from the left hand menu, for example Modules > Mesh > 3D.If we do not label the surfaces and volume, we cannot set inlet, outlet and wall boundary conditions later. Next we must label each “Surface” and the “Volume” using the “Physical Groups”.For example, if the mesh is in millimetres, 0.01 will be 0.01 millimetres. The element size is relative to the mesh size. Select the “General” tab and min/max element size can be set. Within GMSH, open the Tools > Option and select “Mesh” from the left hand side.Open GMSH and load the “.STEP” file we created in AutoDesk Fusion.I personally use GMSH as we can create 2D and 3D meshes as well as having control over the element arrangement. To create a mesh, we need meshing software such as GMSH. Now we have our CAD, we need to turn it into a mesh we can use in BERNAISE. Select your sketch and extrude, for example 0.2 mm which is 200 μm. Exit the 2D sketch and select the extrude tool. Now we need to extrude the 2D sketch into 3D. ![]() The straight line, channel width, should be 500 μm assuming both circles are centred. Then draw straight lines on the axis and crop one side of the circle. ![]() Select the circle tool and draw a circle with a radius of 5 mm and a smaller circle with a 4.5 mm radius, 0.5 mm smaller. For simplicity, let’s create a 2D sketch. Once the document is set up correctly, we need to create a sketch.I personally set the document settings to milli-metres. We need to ensure we set the units for the document up correctly so that when we draw our model, it is represented correctly.The CAD program I use is AutoDesk Fusion as it is free to use for personal and hobby use. For this tutorial, we are going to use a curved channel for simplicity, created in a CAD program as well as labelling the boundaries later. We need a model to simulate our CFD where computer-aided design (CAD) allows for particular control of structures and features in the flow path. Creating a Microfluidic Computer-Aided Design (CAD) However, the layout in BERNAISE is straight forward with the definitions that novice users can implement problems. This process is without a graphical user interface unlike other popular CFD simulation programs. Here we are going to use a CFD template and add the values of the mesh and parameters of the CFD problem using BERNAISE. ![]() Currently this blog has investigated Navier-Stokes problems with Understanding The Navier-Stokes Solvers and Phase-Field problems with Microfluidic Dro plet Formation using BERNAISE, Binary ElectRohydrodyNAmIc SolvEr, which runs on FEniCS, Finite Element Computational Software. These settings can differ greatly between CFD programs and may differ in the units used to define the problems. Setting up a computational fluid dynamic (CFD) problem can be daunting with all the different parameters and solvers available. ![]()
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