Hi Yasemin,

Have you tried increasing the Weight of the MNCA operand? If not try doing it gradually. The default weight is 1 I believe and you could try 5, 10, etc. Remember that if you keep MNCA under the DMFS operand, its weight will be reset whenever you regenerate the default Merit function with the wizard. Increasing the weight of an operand makes its contribution to the Merit function more important and less likely to be violated. However, it comes at the cost that other operands may start to be violated.

If it keeps becoming negative despite the weight being increased, perhaps your system lacks the degrees of freedom to come up with a realistic design. It would help if you could share more details about said system if you want to get more specific answers to your question.

I hope this helps, take care,

David

Hi Yasemin,

I just wanted to chime in here as I agree with David’s comments. I think the only detail I would add is that if your system currently has some negative airspace thicknesses, it may be in a pretty rough spot in the solution space and local optimization may stagnate without some modifications to your system. One approach would be to, as David shared, increase the MNCA weights (and potentially just manually increase the distance between the offending surfaces and let optimization keep them positive with the increased MNCA weights). Additionally, you may also want to see if you have any earlier iterations of your design that do not yet have these negative airspaces, and use those as an intermediate “starting point” with increased MNCA operand weights.

Lastly, you could also always try one of the global optimizer routines -- probably the Hammer optimization is what you’d want (as Global Search will provide several starting points and is meant to generate initial ideas that you iterate further upon). Hammer Optimization won’t be limited by the local merit function minima (which local optimization may be finding with the negative airspace solution), but rather it will try to expand its search the longer you let it run.

Thanks, and good luck!