When using dynamic time step,what value should the safety factor be? How to judge the safety factor ?Thank you very much!

Thank for your very good questions Binlichen. Here is the response for your question.

Time step in the EFDC can be constant or not depending on the value of “safety factor”. In general this value is in the range of [0,1].

1. Safety factor = 0: Constant time step is used

2. 0 < safety factor < 1: Dynamic time step. This factor is used a factor of the minimum time step then the dynamic time step will increase based on a ratio

3. dH/dT >= 0: This value is used to change the rate of dynamic time step depending on the rate of water depth change.

In general in any cases we can use dynamic time step to speed up the model run, especially when dT is quite small. The common value is within [0.3, 0.8] and the user can change it so that the model run is stable. If the model is not stable with selected value, the user should reduce it until it reaches the stability. So the reasonable value depends on the experience of user. However, after few runs we can recognize a suitable value and this is also a true way to judge its value.

what value should the “#Ramp-Up loops” be? what is it mean? Thanks a lot!

When I use dynamic time step, no matter what low value the time step and safety factor be, my model is unstable. How to set dynamic time ?Thanks a lot! Now,the time step is 1 and safety factor is 0.1.Attachment is the message that jumped out when the model is crashed.