I see the stent axis is along the global Y axis. Create a Cylindrical coordinate system at the center of the stent with the Z axis along the global Y axis.
Pick 3 vertices at the center of the stent, spread around the diameter and apply a Displacement support. Change the Coordinate System to be Cylindrical. Set the Displacement to be Y (tangential) and Z (axial) to 0 and leave X (radial) Free.
Select all the faces at the +Y end of the stent and apply a Remote Displacement, behavior = Deformable, to move the faces using a value in the Y component only and leave all others Free. Repeat with another Remote Displacement at the -Y end of the stent with a negative number in the Y component.
You may get a "not enough constraints" warning, which you can ignore, but you should not get an error.
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