A Caution message in AFT Impulse.

Full message is:

Constant friction factors from the steady-state calculations were used during the transient analysis. The pipes listed below appear to have a wide range of actual friction factors and the predicted results may not be reliable. If a pipe is listed as closed, then the friction factor was estimated using a velocity of 5 feet/sec (1.52 meters/sec). It is recommended to use a Time Varying friction model which is defined in the Transient Friction panel.

This caution message is intended to alert users that the model results may not be reliable, as the transient analysis is using the initial steady-state friction factors. In some cases, this estimate may be appropriate, while in others it may not. Below the text of the caution, the steady-state friction factor being used and the potential maximum transient friction factor are listed. This can help give users an idea of how well this transient friction model fits their system. In the case that a pipe is closed or has no flow through it in the steady state, the friction factor is estimated using a velocity of 5 feet/sec (1.52 meters/sec).

When this message is shown, it is recommended that a Time Varying friction model is used for the transient simulation. This option can be specified in the Transient Friction Panel.