Hi,

I noticed a difference between the result given by the SOP output of simple *SOILS analysis and what one would expect analytically.

The model in question is a cylinder with a surface pore fluid load applied to the bottom surface (of 1, in the vertical (z) direction) and a pore pressure boundary condition of 0 applied to the top surface. A displacement boundary condition is applied to the whole model (i.e. nodes are not permitted to move). Hence there is only constant, uniform flow of pore fluid through the cylinder.

An integrated output section (for SOP) was created from a cross-section perpendicular to the flow direction vector (normal vector in the -z direction). 

However, the value output for SOP differs from what is expected analytically (i.e. integrating the dot product of the (effective) fluid velocity with the surface normal over the surface; in this case it simplifies to just the (negative) area of the surface since f.n = -1 in this case); the SOP differs by a factor of 5.0.

What is the cause of this difference?