Periodic Head Flow

It looks like the help documentation does a pretty good job here if you look at the help document titled,  "Periodic Head-Flow Elements".

Here is what it states:

The Periodic Head-Flow element represents a versatile hydraulic boundary condition which allows you to specify a constant head (pressure), flow, or any time-dependent variation, including periodic changes that repeat indefinitely until the end of the simulation.

Note:  The Periodic Head/Flow element supports a single branch connection only. If there is more than one branch connected to it, the transient run will fail and an error message may appear, such as:  

"Only one active pipe may be connected to this type of node in its current configuration."  

This element is used to prescribe a boundary condition at a hydraulic element where flow can either enter or leave the system as a function of time. It can be defined either in terms of Head (for example, the water level of a clear well or process tank) or Flow (for example, a time-varying industrial demand). The periodic nature of variation of head/flow can be of sinusoidal or of any other shape that can be approximated as a series of straight lines.

Note:  During a Steady State of EPS run (used to determine the initial conditions for a transient analysis), the head/flow for this element is held constant at the initial head/flow value on the sinusoidal or user-defined pattern. The head/flow only varies during a transient analysis.  

It looks like both of your questions are answered in the second blue note.

I hope that helps,

Mark

In additional to what Mark said, I'll add some background and suggestions.

The periodic head-flow element was introduced into WaterCAD and WaterGEMS in 2007, along with the first release of HAMMER V8 XM. It is only useful during a transient simulation in Bentley HAMMER, where it allows the user to directly control the head or flow at that point in the network.

If you are trying to control the head or flow during an EPS in WaterGEMS, other elements can be used. To control the boundary hydraulic grade (head) over time, set up a pattern under Components > Patterns > Reservoir, then select it in the properties of a reservoir.

If you're trying to control the inflow over time, use a negative demand on a junction with corresponding pattern (Components > Patterns > Hydraulic).

Note that if you're trying to do this to represent a connection to an existing system, it may be better to model at least a skeletonized version of the system all the way back to the source, or use the reservoir/pump approach (based on hydrant flow tests) described in the below Support Solution:

communities.bentley.com/.../9293.modeling-a-connection-to-an-existing-system.aspx

That's mean I could use this function under normal operation which is demand driven analysis?

Jesse, I did used function as you describe above, but could I use periodic head flow if I don't have flow at inlet?

Or this function is only for transient analysis?

Thank you.

The pattern functionality of the periodic head-flow element is for transient analysis only (in Bentley HAMMER). In other words, you cannot use that element to force the head or flow to change over time during an Extended Period simulation (EPS) in WaterCAD or WaterGEMS.

If this doesn't help, please elaborate on exactly what you're trying to do.

The pattern functionality of the periodic head-flow element is for transient analysis only (in Bentley HAMMER). In other words, you cannot use that element to force the head or flow to change over time during an Extended Period simulation (EPS) in WaterCAD or WaterGEMS.

If this doesn't help, please elaborate on exactly what you're trying to do.