Kratos Multi-Physics 3D Fluid Analysis Tutorial Pooyan Dadvand Jordi Cotela Kratos Team
Kratos 3D Fluid Tutorial In this tutorial we will solve a simple example using GiD and Kratos Geometry Input data and conditions PostProcess
DEFINING THE GEOMETRY
Geometry Rotate the view to plane XZ View > Rotate > Plane XZ Create domain and beam base Geometry > Create > Point Introduce the following points in the command line Press Enter after each point Beam Boundary box 0.0, 0.0, 0.0-2.0, 0.0, -0.5 0.2, 0.0, 0.0-2.0, 0.0, 0.7 0.0, 0.0, 0.2 6.2, 0.0, -0.5 0.2, 0.0, 0.2 6.2, 0.0, 0.7
Geometry
Geometry Now define the lines Geometry > Create > Straight line Ctrl + a Join the points of the beam base
Geometry Once finished, press Esc Create additional lines to define the boundary
Geometry Now we add the third dimension Utilities > Copy In the copy window, select Entities type: Lines Transformation: Translation First point: One of the beam corners Second point: Enter the same point but set y coordinate = 2 Do extrude: Lines Don t change the other options Press Select and mark the beam base
Geometry
Geometry Do the same for the boundary First point: (-2.0, 0.0, 0.7) Second point: (-2.0, 2.5, 0.7) You can rotate the view to check that the transformation worked
Geometry You can see that we are still missing some surfaces Geometry > Create > NURBS surfaces > By contour Select the top 4 lines of the beam and press Esc
Geometry Do the same for the top of the domain Geometry > Create > NURBS surfaces > By contour For the bottom of the domain, select the bases of the domain and the beam to take the hole into account
Geometry The final step is defining the volume Geometry > Create > Volume > By contour Select all surfaces and press Esc You can select all surfaces by drawing a box around the entire model
PROBLEM INPUT
Input data Load the Kratos problem type Data > Problem type > Kratos A new icon bar will appear
Define entity groups Click the Groups button to open the group window Each group will define a part of the model Fluid body Inlet surface Outlet surface Solid boundary Create a new group Click the New button Assign entities to a group Click the Assign button Choose an entity type
Define entity groups Fluid group Select the volume Inlet group Select the front surface Outlet Outlet group Select the back surface Fluid Wall group Select all remaining surfaces Inlet
Model Properties window Click the Properties button to open the properties window The tree contains all information about the model
Basic properties Path to your Kratos installation Set Fluid to Yes to run fluid simulations Choose the Fractional step solver You can use this option to choose a different solution algorithm
Solver properties Select an Iterative solver for velocity and pressure Set the analysis times: Start time: 0.0 End time: 2.0 Time step: 0.01
Fluid properties Create a new property for your fluid by selecting Properties Define a name for your property Assign a material (use default Water) Click Ok You can add or modify materials from the Materials tab
Element type Define the finite elements that will be used to mesh the domain Select Fluid elements A box that appears at the bottom Set the type to Tetrahedra Assign them the property defined in the previous step Assign the elements to the Fluid entity group we created earlier Click Ok
Boundary conditions Assign the boundary conditions using the surface entity groups First, assign the inlet condition Choose the Inlet velocity condition Assign it to the Inlet surface group The Activation tab is used to choose which velocity components we want to fix The Values tab is used to set the prescribed values Set the X value to 10.0
Boundary conditions Now assign the Outlet Pressure condition Set the pressure of the Outlet entity group to 0.0 Finally, assign a No-Slip condition to the solid boundary Select the Wall entity group Leave the three components active Leave all values at 0.0
Mesh the domain Mesh by selecting the menu option Mesh > Generate mesh On the box that appears, set size to 0.25 You can view the mesh using the View mesh button
Solve the problem Save your model Files > Save Launch Kratos with Calculate > Calculate The input data will be checked for errors A warning window will appear, as we didn t introduce some additional information. In this case, you can ignore it
Solve the problem You can check that the solution process is running properly using Calculate > View process info A window will pop up once the solution process finishes Click on Postprocess to view the results
SOLUTION POSTPROCESS
Post Processing Once the solution finishes, GiD will switch to Postprocess mode Alternatively, you can switch manually with View > Mode > Post Process By default, the results for your model will be loaded You can open other results with File > Open Common result formats are.post.bin binary results.post.res ASCII results.post.lst A list file pointing to multiple result files
Post Processing View the Pressure results with View results > Contour Fill > Pressure To view the interior of the model Windows > View Style In the View Style window, select Front Face culling
Post Processing Using Ctrl+m you see an animation of the results This is equivalent to Windows > Animate
Using cuts View the a result on an arbitrary plane using a cut Display velocity results with View results > Contour Fill > Velocity Define a cut using Do cuts > Cut plane > 3 points Use these points: -2.0, 1.25, 0.7-2.0, 1.25, -0.5 6.2, 1.25, 0.7
Using cuts To view just the cut Open the view style window Windows > View Style Turn off the light bulb next to Kratos View the time evolution with Ctrl+m
Thanks More Kratos at: Kratos webpage: http://www.cimne.com/kratos/ Kratos wiki: http://kratos.cimne.upc.es/kratoswiki/ Kratos tutorials: http://kratos.cimne.upc.es/index.php/kratos_tutorials/