- Feb 26 2019
- acaslam.suja

I am a researcher using NAYS2D solver for 2D flood modelling in my research. My study area is around 250km2 and DEM is SRTM 30m. When adjust the settings what is the value can be assigned for relaxation coefficients for water surface calculation, and calculation time step. What will happen when increase the those two values. Your early reply will be highly appreciated.

Thanking you

Suja.

> Forum > Nays2DFlood > Relaxation coefficients for water surface calculation, and calculation time step

## コメント

When dt * v < dx, simulation stops.

Here, dt = time step, v = velocity, dx = grid size.

Please read CFL condition (https://en.wikipedia.org/wiki/Courant%E2%80%93Friedrichs%E2%80%93Lewy_condition)

When the calculation does not converge, decrease relaxation coefficient and increase maximum number of iteration.

Thank you very much for the reply. I could not understand that you said “when dt * v < dx, simulation stops", in this formula we can define time and grid size but how can define velocity?. Is there any range for values that can be assigned to relaxation coefficient and time step if 10m or 15m grid size is used. Your early reply will be highly appreciated.

Thanking you

Suja.

Thank you very much for the reply. I could not understand that you said “when dt * v < dx, simulation stops", in this formula we can define time and grid size but how can define velocity?. Is there any range for values that can be assigned to relaxation coefficient and time step if 10m or 15m grid size is used. Your early reply will be highly appreciated.

Thanking you

Suja.

Please check with trial and error.

Thank you very much for the reply.