clearing oscillations caused by pupms

[woody61]

I can’t clear “Oscillations may require finer routing or smaller dt” error message associated with a node using a pump for an outlet. This is the only error message associated with this node. The routing is set as fine as possible, same with dt. I have modeled the node with the storage volume as close as possible to real conditions, 3-4 minutes of storage volume from incoming watershed prior to pumps starting. The pump outlets to a structure that then gravity drains to a detention pond. The outlet gets submerged briefly, but creating a storage volume in the outlet structure so that it doesn't will not clear the error. The only way I’ve been able to clear the oscillations error message is to make the storage volume of the wet well unrealistically large. Is the oscillation problem typically related to the pumps curved being modeled on a pump that is too large? Any suggestions?

Thanks

 

[psmart]

Oscillations can occur if the pump is improperly sized to the storage and inflow, or the switching points are set incorrectly. Also be sure to resolve any "storage exceeded" condition.

In the mean time, set the finer routing back to the default of 1. And observe the pop-up message about values greater than 3, which can degrade the results. This is a case where bigger is not better.

If you still have problems send the file to HydroCAD support.


Peter Smart
HydroCAD Software

http://www.hydrocad.net