I'm creating a model of a line that feeds the convection section of a fired heater. The section is six pass. The heater vendor has provided thermal displacements at the faces of the flanges which connect the external pipe to the convection tubes. The (finned) tubes pass through ferrules in the header box which are 1/2" greater in diameter than the OD of the tubes. Since the tubes themselves rest on the ID of the ferrules - the tubes can move up 1/2" until prevented from moving further by the ferrule. This 1/2" possible movement is a relative movement. I need to input the vendor specified thermal displacement as well as the Y restraint. I thought I could use a CNode and capture all this at one node but of course you can't specify a restraint and displacement at the same node. What's the best way to model this?

A displacement is a restraint - they are both boundary conditions.

If you have a case where you want to impose an X displacement of 1.0, you can define DX1= 1.0. In your load cases, if you include D1 in the list of primitives, the deflection will be applied. In any load case where D1 is not included the X DOF is restrained, the same as DX1=0.

You can add a second CNODE anchor nearby that is CNODED to an otherwise unused node number. Add a displacement to the same element, but apply the displacement on the otherwise unused node number.

Thanks Richard. I didn't explain my problem very well so I'll try again. There are tubes exiting the convection section of a fired heater and the vendor has specified thermal movements at the end of the tubes. Let's focus on the vertical (Y) direction. The deflection they gave is +0.75" - which makes sense - as the unit heats up it grows up from its foundation at grade. Additionally, and here is my difficulty, the support nearest the end of the tube is a tubesheet which will also grow up by an amount close to, if not identical to, +0.75". But the hole which provides support for the tube is oversized - the effect is that the tube can grow up by 0.5" before it is stopped by the hole's top edge. I'm trying to account for both the 0.75" vendor defined displacement at the same time I model a support that will allow a relative vertical movement between the tube and tubesheet of +0.5".

Look in the Application Guide in the restraint section for a "window restraint". I think this is what you want to do, PLUS put a CNODE on the restraint (at the tube) so you can displace that up the desired amount.