To avoid loss of persistence in the Mechanical application, it is a good idea to either use the parts obtained from CAD import and/or form new parts in the DesignModeler application before assigning loads and boundary conditions in the Mechanical application.
When forming new parts in the DesignModeler application using the Form New Part operation, the DesignModeler application will attempt to preserve Part IDs as best it can. For the resultant part, it will choose the Part ID that minimizes the number of bodies that must switch their Part IDs. However, it is inevitable that when forming new parts some bodies will have their Part ID changed.
When destructing a part using the Explode Part operation, nearly all the bodies involved in the operation will change their Part ID, since they will now belong to separate, single-body parts.
Below are some suggestions you can use to help avoid loss of persistence for your loads and boundary conditions in the Mechanical application when working with multibody part models:
Form your parts in the DesignModeler application before assigning loads and boundary conditions in the Mechanical application. Doing so will reduce the likelihood that you will need to redefine them later.
If you need to perform slicing in your model, it is better to do it before assigning loads and boundary conditions in the Mechanical application. When slicing, the DesignModeler application will automatically group the new sliced bodies into the same part as their source bodies so that their Part ID is maintained. However, you may need to redefine selections in the Mechanical application if your original selection was in a region that got sliced.
If you scope a load or boundary condition in the Mechanical application to a Named Selection that was defined in the DesignModeler application, it will remain persistent even if a body’s Part ID has changed. This is because Named Selections from the DesignModeler application are refreshed during each geometry update and can adapt to part changes in its selection.
Avoid exploding parts unnecessarily. For example, if you wish to remove a small number of bodies from a large part, it is better to select only those bodies and perform a Form New Part operation on them. This will pull out the bodies into their own separate part, which you can then explode. More importantly, it leaves the original large part intact.
Save the DesignModeler model with the Share Topology feature applied. Doing so allows the model to be read downstream in subsequent Workbench sessions, without your having to reapply the topology sharing each time (as long as there are no design parameter changes to be applied).