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Currently, the creation of displacement constraints with RBE2 ties and rotational degrees of freedom isn’t supported from the graphical user interface. To realize it, dummy loads are created and modified with by the Advanced User Settings.
On the outer cylindric surfaces two dummy loads are created. These dummy loads need to have a load value in a the direction which will be constraint afterwards.
Name | Force/Moment/Pressure/Gravity | Direction | Value in N/Nmm |
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Force 2 | Force on faces | x | 1 |
Force 3 | Force on faces | x | 1 |
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In Step 6 the dummy loads will be modified to displacement constraints with a RBE2 tie and unconstraint rotational degrees of freedom. |
Step 4: Interface Creation
Interfaces have to be created for every functional surface - so every surface where a boundary condition is applied to. With this Tool an offset to the inside with the input “Non-Design Space Thickness” and an offset to the outside with the input “Machining Allowance” is created. The Offset Distance is expanding the Interface to the set value to create material on front faces.
All surfaces on which a boundary condition is applied can be selected directly as an interface with the “Select Faces from Loads and Boundary Conditions” button. The Boundary Condition surfaces will be highlighted and can be selected/deselected. With “Apply” the Non-Design Space Thickness, Machining Allowance and if available Offset Distance values will be applied to the selected surfaces.
In this case for the outer, bigger cylinders and the middle cylinder inclusive the front faces are manually selected. A a Non-Design Space Thickness of 3 mm and , a Machining Allowance of 1 mm and an Offset Distance of 3 mm is entered. Via “Automatically create interfaces from Loads and Boundary conditions” the interfaces are created automatically for all 3 cylinders.
Note: the Interface Offset (usually displayed in red) is not visualized due to a limitation. The correct value will be considered in the optimisation.
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On the smaller outer cylinders a Non-Design Space Thickness of 1mm and a Machining Allowance of 0.5 mm is applied. For these cylinders the “automatically create interface” option can be used by selecting the corresponding boundary conditions on these surfaces.
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Step 5: Definition of load cases
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Event 1: Force 1, Force 2, Constraint 1Event 2: Force 3, Force 4, Force 5, Force 6, Force 7, Force 8, Force 9, Force 10, Constraint 2, Constraint 3
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Step 6:
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To change the Manufacturing Method to Casting the Advanced User Settings have to be used.
The following commands are added to the scenario:
configuration.strategy=Casting tool.tool0.draft=5 tool.tool1.draft=5 |
With the first command the optimisation strategy is set to Casting. The following commands defining tools. Each tool is one draw direction for the manufacturing process. The actual draw direction is set as a vector. For each draw direction a draft angle can be set. The draft angle (specified in degrees) is the tapering angle for walls/ribs regarding the draw directions.
In this case two draw directions are defined in positive and negative z-direction and a tapering angle of 5°.
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Modifying the dummy loads to displacement constraints (with RBE2 ties)
With the Advanced User Settings the dummy loads (Load 2, Load 3) are modified to displacement constraints.
Dummy load Force 2 is changed to a RBE2 discrete tie. Furthermore, the translational degrees of freedom in all 3 directions and the rotational degrees of freedom around the y- and z-axis are constraint. The rotation around the x-axis is free.
The same is done for the second dummy load. For this, the translational displacement in x-direction is free as well.
boundaryCondition.ModelLoadEvent_Force_2_Force.tyingMode=RBE2 boundaryCondition.ModelLoadEvent_Force_3_Force.tyingMode=RBE2 |
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Step 7: Definition of optimisation parameters and Generative Design Settings
The optimisation parameters are selected in the Studies Area as well.
Manufacturing Method: Generic AM
Failure Criteria: Von Mises
Safety Factor: 2535
Strut Density: Medium
Shape Quality: Balanced
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Step 8: Starting the optimisation in the command line and visualize the results
If all data is correctBecause the graphical user interface does not support the displacement constraints with rotational degrees of freedom yet, the optimisation can be started and tracked in the Post Processing. The Analysis Readiness function checks if all information is provided and the optimisation can start.
All result iterations are displayed as soon as they are available. Furthermore, you are able to stop the optimisation in this selection area. However, a Restart is not directly possible.
The optimisation is finished after 64 iterations (Shape Quality: Balanced).
You can check the status of the optimisation in the GD Status and get more information on Warning and Error messages. This can be done directly in the Post-Processing as well as in the Studies tab for an optimisation that has already run.
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has to be executed in the command line.
Therefore, the optimisation scenario is exported by a right click on the scenario to a freely selectable folder.
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Inside the exported folder, all geometry information and the input configuration file for the optimisation are stored. A PowerShell or command line has to be opened here.
Inside the installation folder of MSC Apex the “runGD_Engine-bat” has to be executed with the additional command (-c) for the configuration file.
& 'C:\Program Files\MSC.Software\MSC Apex\...\runGD_Engine.bat' -c .\RotationalDoF.json
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The optimisation starts and all optimisation results will be saved in a subfolder.
Step 8: Importing the results back & visualisation
The optimisation results can be imported back into the graphical user interface. Therefore, the Import Generative Design Results option is used. The post processing can be accessed over the new imported scenario.
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Inside the Post-Processing the von Mises stress and the displacements are visible for all iterations and for every Event
The Scale can be influenced individually
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You can go back to the model setup by clicking the Exit button in the right bottom corner.
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In the picture below the displacement in z-direction is displayed
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With the Mission Switch the optimised result can be analysed with MSC Apex / Nastran. The following gif shows the rotation in the created displacement constraints.
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The complete MSC Apex Generative Design project with all results can be downloaded here:
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