AFTER the system is "buried" in CAESAR II, break the pipe at the location of the coupling. For example, break 90-100 by adding node 95. This will create two element: 90-95 & 95-100. Change 95-100 to 96-100. Now you can model your coupling as restraints between 95 and 96 - restraint at 95 and a CNODE 96. CNODE is the CAESAR II "connecting node"; you are defining a restraint between two nodes rather than typically between the node and "earth". (I don't mean earth as in soil but earth as in the planet - you can't move earth.) Consider all 6 degrees of freedom when defining these restraints with CNodes.
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Dave Diehl