The large displacement certainly sounds as if the two parts are not bonded together, and if the part does not have boundary conditions, it "floated" away. Since you activated the bonded contact, it sounds like the problem is one of these:
1) there may be a gap between the fluid and channel that is larger than the tolerance for matching. (the default tolerance is 5% of the local mesh size)
2) you used a different size mesh or different type of mesh on the two parts, so the meshes do not match. (this makes sense since the mesh for fluid is probably different than that required for the stress analysis)
For item 1), either change the CAD model to remove the gap between the fluid and channel, or change the mesh matching tolerance in Algor Simulation ("Mesh > Model Mesh Settings > Options > Model" and change the "On-surface tolerance based on" and/or the "Tolerance value".
For item 2), you can use the Algor Simulation "smart bonding" which is essentially the same method that Inventor Simulation uses to bond dissimilar meshes between parts. Activate the smart bonding under "Analysis > Parameters > Contact" and set the "Enable smart bonded/welded contact" drop-down. Be sure to click the "Help" button on this dialog and expand the paragraph "Contact Options" to get a better understanding. (Although if the bonded part is very weak like your fluid, then the setting chosen for the smart bonding type should not make a difference.)
If the problem is something else that I have not touched on, please let us know.
John Holtz
Product Design Engineer, Algor Simulation
Autodesk, Inc.
John Holtz, P.E. Global Product Support
Autodesk, Inc. If not provided already, be sure to indicate the version of Inventor Nastran you are using!"The knowledge you seek is at knowledge.autodesk.com" - Confucius 😉