Using Variable Surface Load with a Cylindrical Coordinate System

[andrewdroth]

I'm trying to figure out how surface variable loads are defined by functions in a cylindrical coordinate system.

I tried a simple test. Make a cylindrical coordinate system with the origin at the top of the tank, and the positive Z pointing to the bottom.

I then applied a surface variable load to the shell wall. The function is R = s, therefor the pressure should increase from 0 to 6.3 as it goes around the tank.

The Variable Load Viewer confirms what I want to achieve. 

But when I run the model, the pressure increases to pi radians (180 deg) in the positive and negative directions.

I was expecting it to steadily increase positively all around the tank.

Anybody have an Idea why it splits?

[andrewdroth]

By changing the equations to ABS(s) I can get it positive both ways. But I'm still not sure why it counts up to pi radians in each direction.