BE104 Lab 6b - CAD import

BE104 Lab 6b - CAD import - BE104 Lab 6b (OPTIONAL) ...

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Unformatted text preview: BE104 Lab 6b (OPTIONAL) The purpose of this lab is to model cerebrospinal fluid flow in the cerebral ventricular system. This system has a complex geometry which differs from patient to patient, so we will import a CAD file that was generated from MRIs of a former BioE 104 student’s brain (with his permission, of course). Thanks also to Dr. Colin Studholme and UCSF’s Biomedical Image Computing Group. During this lab you should focus on learning the following lessons: • Importing geometries – how to import complex shapes created in other programs into COMSOL. • Interpreting warnings – complex shapes can often mesh poorly, generating error or warning messages. • Differentiating models from reality – by this point you should start questioning how these models differ from the physical system. What has been left out of the model, and how might the model be affected by its absence? Modeling cerebrospinal fluid flow in the cerebral ventricular system using COMSOL: (1) Open COMSOL. The Model Navigator window will open. (2) Select Space Dimension > 3D and click OK. (3) Go to File > Import > CAD Data from file and import BioE 104 Lab 06b.stl. To scale the model properly, it should be shrunk by a factor of 1,000 in all directions. (4) (5) (6) Add Navier ­Stokes (Steady ­State) from the multiphysics menu, and include the viscosity and density of water in the subdomain settings. Mesh as usual. A free mesh with a normal size element should be adequate. A person makes ~500 mL/day of cerebrospinal fluid, which is emitted from the walls of the ventricles (which make up almost all of the area of the subdomain). Go to Draw>Geometric properties and note the area of your ventricular system. Calculate the flow rate being emitted by that area (in m/s) to equal 500 mL/day. There should be two different boundary settings. An inlet with an Normal Inflow Velocity that you calculated in the last step, and an outlet at the “bottom” of the fourth ventricle (pictured below in pink). Everything that isn’t an outlet should be an inlet. This is an anatomic simplification but is adequate for our purposes. (7) (8) (9) Click Solve. Note the warning messages. COMSOL has made some adjustments to avoid problems solving your complicated geometry. (10) Visualize the flow with streamlines or arrows and export an image of your model to turn in with your homework. (11) List three significant simplifications we made with this model that differ from reality. (This may take a bit of research.) ...
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