POLYFLOW - How to define an inverse extrusion case with take-up velocity (draw down) for e.g. fibre spinning?

When defining an inverse extrusion case that involves a take-up velocity, such as in fibre spinning, the solver can encounter difficulties to converge.
In fact, there is a redundancy between the imposed flow rate combined with the take-up velocity and the fixed extrudate cross-section. The most convenient remedy for circumventing the trouble consists of applying a take-up force instead of a take-up velocity. Possibly an evolution can be applied on this force. Throughout the procedure, all solutions are valid, and the user should select the one that involves the requested exit velocity.
From the point of view of the physics, by doing so, each solution involves a specific extensional force, which will produce a given deformation from a predicted die lip to the required extrudate cross section. This usually works for low take-up forces as well as for large ones.

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