Thanks for the feedback, kotten!
I do not have your model here, so try this:
Cut the object, Split enabled, with the knife. Visible Only: off. You will get two parts (A and B). You can select a single polygon and then “Select Connected”, move that part 20cm in X (or whatever fits your cut best). Store that selection, Use U~I to invert the selection and store that as well
Use the outline Selection and create via “Edge to Spline” a Spline object. Extrude this about 20cm to have it connect both parts. Set the Subdivision to 2.
At the moment, it fits the two “shells,” great. Make it editable [C].
Select both parts and use the “Connect and Delete”. Select the middle Edge Loop of the patch, and store that selection.
Select all points, and use the Optimize functions. Check your model how close points are, and set the tolerance not smaller or equal.
Select the previous moved Shell [B] back 20 cm.
Select the edge loop, move it and scale it down slightly.
Your model is ready for animation.
With the selections stored before, and a PoseMorph set to Points, you can shape your effect as needed, then animate as shown before.
(I have not suggested the Bridge Tool, perhaps that could be a way to create the ‘geo’ for the gap faster, but I don’t know your model. Also: Perhaps a cut with a zero bevel…)
Example
https://www.amazon.com/clouddrive/share/P6Kc0GhOFcjutW9yXt12xL9QIM7ayEqAkYj84TjGme3
All the best
