	Applies To
	Product(s):	HAMMER
	Version(s):	08.11.XX.XX and higher

Problem

How do you define the starting conditions (starting steady state) of a transient simulation?

Solution

A transient is a transition from one steady state to another. In HAMMER you must establish the starting steady state, along with the trigger of the transition (such as a pump shutting down).

Typically, you would use the steady state solver (Analysis > Compute initial conditions) to calculate them the starting steady state condition. This will be based on the demands, boundary conditions, and other element attributes. This is the same solver that WaterCAD and WaterGEMS use. The transient solver then uses those computed flows and hydraulic grades as the starting conditions.

There can be times when your model uses demand patterns that you want applied to the system, or cases where your initial conditions is a Extended Period Simulation. In these situations, there are a few options for you.

When you have a steady state run but you want to apply a demand pattern, you can use the EPS Snapshot feature. In the Steady State/EPS calculation options, you would set "Is EPS Snapshot?" to True and set the appropriate starting time. The program will still compute a steady state run, but it will also use your demand patterns.

If your initial conditions calculation is an EPS run, you can set the starting time for the transient calculation in the Transient calculation options. In the Transient Calculation options, find the field "Initial Transient Run at Time" and set this to the time step of your EPS initial conditions calculation you want to use.

You can also define your own starting conditions (flow and head) by setting the Transient calculation options field "Specify initial conditions?" to True. This is rarely needed and primarily a legacy feature carried over from older versions of HAMMER, and typically not recommended in most modeling cases. The steady state initial conditions calculation is typically sufficient for this instead. When using this feature, the transient solver will no longer use the head/flow computed by the "Compute initial conditions", but instead will use the head and flow values that you must enter in the "Transient (Initial)" section of each element's properties. Note that if you want to slightly modify some computed initial conditions, you can copy them over to the user defined initial conditions fields first by using the "copy initial conditions" tool (under the Tools menu) and then alter them as you see fit.

How do you define the starting conditions of the transient simulation?

Problem

Solution

See Also