The Simulation Options dialog box is used to adjust some facets of a model prior to running it. Simulation options are usually associated with specific scenarios.

For example, suppose you would like to specify a global bulk chlorine decay of -0.5 for one simulation and have another simulation with a decay of -0.7. This can be accomplished through the Simulation Options, where one option can be tied to one scenario while another set of options is specified for a different scenario.

The Simulation Options dialog box, used to modify sets or instances of simulation options, can be accessed from the Operation tab of the Model Explorer or from the Simulation Options' Browse button in the Run Manager.

General Options

ID and Description

The Simulation Options ID and Description area shows the name and description of the defined options. The green tic on the ID folder indicates which set of options is currently active. 

General Tab

Demand Options

Quality Options

Energy Options

In order to run an Energy Management Simulation, you would need to check the Run Energy Management Simulation check box.

Advanced Options

Note: The role of relaxation factor.

The new solution (flow rate) at each iteration of the solution engine is:

New Q = Previous Q + Relaxation Factor * Delta Q (Q increment).

Based on the Newton-Raphson (NR) solution method, this is exactly same idea with relaxation factor = 1. On comparison to the other numerical method, the main advantage of NR method is its speed and efficiency to converge upon a solution. However, it also has a disadvantage of a high level of divergence (where it can not find a solution). As a numerical aid to reduce the chance of divergence, we can add a relaxation factor (usually 0.6 to 1). This simply decreases the Delta Q (increment). By adding a small relaxation factor (decreasing Q increment), the model tends to provide a more stable solution, but, obviously, with a slower computational speed. Therefore, the relaxation factor is a trade off between computation speed and model stability. The reason we changed the default of relaxation factor as 1 is to provide faster computation times. However, it may increase the chance of reaching a simulation failure (in most cases, it should be fine). Currently, the EPANET engine uses 0.6 as a relaxation factor.

To summarize, if you have a simulation failure that used to run in a previous version, please consider changing the relaxation factor into 0.6. Also, consider doubling the Status Check Frequency to four and change the Maximum Status Check Iteration to a value between 4 and 20 to reach a solution.

Example: Check Frequency = 2, Max Status Check = 10, Damping Limit = 0

Example: Check Frequency = 10, Max Status Check = 100, Damping Limit = 0.01

Example: Check Frequency = Max trials, Max Status Check = Max Trials, Damping Limit = Convergence Accuracy