Nozzle FEM analysis for LNG tank

To verify the integrity of the LNG tank's nozzles on the roof against external piping load, I am attempting to conduct a FEM analysis. The nozzles are approximately 3 to 4 meters long, and their ends will be secured by the platform structure. I have a few questions regarding this analysis.

- Where I need to put the external piping load A or B otherwise the end of nozzle?
- The end of nozzles shall be modeled as fixed at platform or free?


Thank you so much.