Water Surface Elevation in Buoyancy Input

I have modeled a free span submerged pipeline system in AUTOPIPE V8i version 09.06.00.15, but I'm still confused about water surface elevation origin point in buoyancy input. I have a pipeline system that submerged in 12 meters depth (you can see the details in the picture).

my model first point is "ANC1" and has 0 mm,-12000 mm, 0 mm x,y,z offset respectively. what I want to ask is, in buoyancy water surface elevation, what should I input? 12000 mm or -12000 mm or 0 mm? 

I also uploaded my AUTOPIPE model, and is listed below 


FP-FRESPAN-01-SOIL NO SEGMENT.dat

  • From the AutoPIPE Help:

    Water surface elevation

    Enter the elevation of the fluid surface. Elevation is measured from the origin of the global coordinate system. All points with a vertical coordinate value less than the elevation specified in this field will be considered submerged.

    In your current model, since all of your Global DY values ares -12000 mm, if you enter any value in the "buoyancy water surface elevation" of -12000 mm or greater, the buoyancy load would be applied to the piping in this model.  Therefore, if you enter in -12000 mm or 0 mm in the "buoyancy water surface elevation", you will notice the same results.  If you enter in any value less than -12000 mm in the "buoyancy water surface elevation", you will notice the different results.  

    To be correct, in this model, the value entered n the "buoyancy water surface elevation" should be 0, since the first point Global DY value is -12000 mm and you mention that Point ANC1 is submerged 12 meters deep.

       
    This is a test