If your Nondesign spaces are tearing off, your result looks something like the picture below
Reasons why the Nondesign spaces are tearing off:
either no force or displacement is applied → no stresses are available for the stress optimization
or the force applied is too small
the additional fixation is not needed for the defined boundary conditions and optimization constraints
Steps to prevent this behaviour:
Either it is a design proposal you can accept/want to achieve in order to reduce the number of fixation points
Or prevent the tearing off by:
increasing the complexity → more elements are available and a finer model is possible (calculation effort increases!)
reducing the optimization stress goal
increasing the applied force so that the stresses and therefore the relevance of the nondesign space is increased
creating an extra load case in which fixations and loads are switched
If you are using the symmetry function with the whole model, the optimizer won't use the symmetrical nondesign spaces and will notify you thereof - don’t worry everything is just as it is supposed to be