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A screw fixation can be modelled by using a Nondesign space (red) around the screw as a shell. The Nondesign space is constrained using a clamped fixation.
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To simulate the reality it is also possible to load in import/create an extra volume that’s representing the screw.
However, keep in mind that the screw becomes part of the Design space, so you need the original space without the screw to create a good intersection with the optimization results. Further information regarding the intersection here.
The screw (blue) will be used as a fixation and is clamped. Additionally, there should be a nondesign Nondesign space around the screw (red), which is included in the design space but will not be used as a fixation in the optimization optimisation model. This way the nondesign Nondesign space does not experience an artificial stiffening, which represents the reality much more accurately.
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However, keep in mind that the screw becomes a part of the Design space, so you need the original Design space without the screw to create a good intersection with the optimisation results. Further information regarding the intersection here.