Error : Kiwi 3D cannot refine periodic surface. Refinement. u is set to 1

I am getting following error while assigning surface refinement to the shell element to the baked geometry.

error : Kiwi 3D cannot refine periodic surface.

Where as when I am assigning the same berp and surface refinement (without baking) to the shell element showing following error.

Solution exception: Object reference not set to an instance of an object.

How to solve the errors ?

Please find the attached file. I am new to paramteric structures, hope so you won’t mind my silly questions. Awaiting your response & thanking in advance


I don’t have time to look at your file today but here’s a short hint: you could try to make your structure nonperiodic. There is a command in Rhino, most probably also in Grasshopper.

Thanks it works but what’s the solution for the another error which I get while assigning berp a shell element.

If it is the same error as in the initial file, you cannot input null objects into the shell component. You have to filter them.

there is afaik no native component for makenonperiodic in GH but you can use e.g. a c# component with the following code:
private void RunScript(Surface N, ref object A)

var nurbs = N.ToNurbsSurface();

if (nurbs.IsPeriodic(0) )
  nurbs.KnotsU.InsertKnot(nurbs.KnotsU[nurbs.Degree(0) - 1], nurbs.Degree(0));
  nurbs.KnotsU.InsertKnot(nurbs.KnotsU[nurbs.KnotsU.Count - nurbs.Degree(0)], nurbs.Degree(0));

if (nurbs.IsPeriodic(1) )
  nurbs.KnotsV.InsertKnot(nurbs.KnotsV[nurbs.Degree(1) - 1], nurbs.Degree(1));
  nurbs.KnotsV.InsertKnot(nurbs.KnotsV[nurbs.KnotsV.Count - nurbs.Degree(1)], nurbs.Degree(1));
A = nurbs;


Thank you so much Anna… It’s working…

I have one more doubt, can the analysis of whole structure (in this particular case, cable, shell, beam, column) can be done by using single command (linear & no linear analysis & IGA solver) or we have to analyse each component separately ?

Sorry to disturb you again :grimacing:

Thank you

Not sure if I understand the question but yes you can (and should) do formfinding and structural analysis with the whole system.