Problem

In HAMMER, what is the purpose of "Specify initial conditions" in the Transient Solver calculation options?

What is the purpose of the various fields that sometimes show up in the properties of elements, under the "Transient (Initial)" section of the properties. For example for a junction, "Pressure Drop (Typical)" and "Flow (Typical)" or for a pipe, "Flow (Initial)", "Hydraulic Grade (Initial Start)", etc.

Problem Number 30664

Solution

In the Transient calculation options, if "Specify Initial Conditions" is set to true, then the program will use the values shown in the "Transient (initial)" section of the element properties, NOT the values in the "results" section, when running a transient analysis. So, you would set this to "true" if you wanted to override some computed steadystate/eps values with user defined values. If you set this to "false" (the default), then the transient analysis will be using the computed steadystate/eps results from the "results" section of the properties. If this is an EPS simulation, you should specify a particular timestep from that analysis for the transient run to use as the initial conditions. This is specified in the field of the calculation options called "Initialize Transient run at time ..."

In almost all cases, you would leave this setting as "False" and let the program compute the initial conditions for you, based on the physical parameters and boundary conditions that you enter in the model. The ability to specify custom initial conditions is primarily a legacy feature carried over from very old versions of HAMMER. There are however some rare cases where you might want to force custom initial conditions, and this option allows you to do it. One potential problem with this feature is if you are working with a model created by someone else who happened to have it set to "true" - it could cause confusion if you do not realize that changes to physical parameters are not having an impact on the transient results, since the transient simulation would still be using the custom initial conditions.

See Also

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