Proposed Changes

This pull request addresses a TypeError in the set_ffd_design_var.py script. The change replaces a floating-point division (/) with integer division (//) to ensure that the arguments passed to the range() function are of the correct type.
This change fixes a bug where the script would fail with the error TypeError: 'float' object cannot be interpreted as an integer. This issue occurs in Python 3 environments because the / operator always produces a float, even when the division result is a whole number.

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