Hi Experts,
I need a piece of information, please.



Input data are:

Vertical pipe from node 10 (lower node) to node 20 (upper node);

Distance between node 10 and node 20 (pipe length): 1000mm;

Pipe diameter, thickness and material: 1"-STD schedule-A106B
(but is not relevant for this example);

Reference system: X axis and Z axis are horizontal, Y axis is vertical;

Restraints at node 10 only: Guide (along X and Z) and Y (this Y is the restraint, not vertical axis);

Imposed displacement at node 20 only: 1000mm along X axis (other displacements and rotations are left blank);

Installation and working temperature are the same (21.1111°C).



Displacements report:

CASE 1 (OPE) W+D1

Node 10
DX 0.000mm
DY 0.000mm
DZ 0.000mm
RX 0.000deg
RY 0.000deg
RZ -57.296deg


Node 20
DX 1000.000mm
DY 0.000mm
DZ 0.000mm
RX 0.000deg
RY 0.000deg
RZ -57.296deg


So, RZ at node 20 is 57.296deg therefore DX is not a linear displacement but is the length of a circumference arc (OK, even if I think that the displacement I imposed was horizontal);

DY at node 20 is zero!!!

Please, can You explain me why DY at node 20 is zero?
I think that it should be -158.527mm if I consider that RZ!

Thanks.
Best regards.

The system (and boundary condition) stiffness is set by the initial model layout. As the piping may change its position under load, there are no matching changes in piping layout stiffness matrix to reflect these changes. Nonlinear boundary conditions are the exception.
Your situation is more like a linkage system where position is controlled by geometry. This is not the forte of CAESAR II. You cannot use CAESAR II to analyze a slack rope between two anchors. It's not built for that.
(You can force a better response. Search our web site for the old newsletter article on modeling large rotation ball joints.)
Your situation is not common in piping. Piping usually shows very small rotation so this problem is seldom seen.

Dear Mr. Diehl,
thanks for Your reply.
I noticed this behaviour because I modeled a lateral universal tied expansion joint but I didn't find vertical displacement of its upper end when this end moves in parallel from the other.

Best regards.