- text description to 3D geometry gap: you can't easily describe complex geometry in a language that's common and convenient to both humans and machines

- 3D geometry to physical model gap: material , geometrical constraints induced by manufacturing (machines, tools, costs, …)

- physical model to model fit for simulation gap: meshing, constraints, stress modelling, …

- simulation outcome to fitness assessment gap: now you have a high-dimensional and numerically heavy simulation to weigh against a non-rigorously defined acceptance criteria

- simulation outcome to geometry profiling gap: how do you even start to guide the LLM into the vast space of possible changes to apply to the 3D geometry and reboot that loop?

LLMs don't strike me as a particularly relevant technique to apply here, to be honest.