Significance of C-node while evaluating effects of ship displacements in piping 1

[paddy1385]

Hi, I am doing piping stress analysis for one of our FPSO skids. Customer have told us a scenario that due to sagging & hogging of the ship, there are displacements in ship deck & hence those displacements should be taken into account while doing this analysis.
These displacements are interpolable & so I can calculate the displacements at each restraints in X, Y & Z directions. Now I have been told that I can assign these displacement values to a C-node given to the restraints. For e.g. if my restraint node is 100 in element 90-100, I can create C-node as 99 & provide displacement to this node.
So I have below questions.
1. What is the significance of C-node.
2. Will it be a correct method to actually analyze the displacements of ship.

Please advise.

 

[bimr]

You need to know the type of ship and design guidelines for the ship that you skid will be installed on. Also need to know the size of skids.

https://www.youtube.com/watch?v=NE_ri8PkihE&feature=related

 

[nickcaiyh]

Paddy1385,

To use the Cnode in CAESAR II is a correct solution to deal with deck deflection such as hogging and sagging.
When you have a restrain on node 100 as a +-Y maybe with guide or axial stops(assume Y is Elevation), you can have a Cnode of 101, and then fill your displacement data on 101. Maybe D4 for hogging and D5 for sagging. You can simply imagin the root of the supports based on the structure moving together with the ship movment and deck deflection.

However, your topside skid may supported by the stools, so the structure should have ability to absorb the deflection of the deck, normally, the topside skid is not all fixed on stools, there are some anchor stools and others were sliding or guided. So I suggest you find some design input from structure calculation to obtain the "real" displacements for each restrain, and pay much attention for those pipe restrain exit from one skid and enter to another.