Model Instability

[Nisha]

Hello,
I’m simulating 1D/2D model an it become unstable at first time step. Initially, spacing between CS was 50 m. as the model become unstable at the first time step, I thought the error must be in geometry and changed the CS spacing to 5 m. Yet I’m getting the error. I have set initial flow (and set the same flow in first few time steps in each BC hydro graphs). I have tried to run without 2D, yet getting the error.

Any advice to get rid of this? Thanks..!

[Scott Miller]

Flow across a 1D/2D boundary at initial conditions can throw an otherwise stable 1D model. Is the initial 1D flow high enough to pass into the 2D area? Is there an initial wse in the 2D flow area that drops into the 1D reach? It may be necessary to balance the initial conditions, by trial and error, to get inundation in the 2D flow area into a realistic distribution.

With lateral structures passing 1D/2D flow, you can allow the calculations to iterate. Unsteady Flow – Options >> Calculation Options and Tolerances >> 1D/2D Options tab. (The default is no iterations, so try this.) Choose a minimum flow tolerance that works for the scale of your model. The 1D/2D flow errors during a run give you an idea where to set the tolerance.

[Nisha]

Thanks Scott for the reply. As you said issue was with the initial condition of the 2D area.

[Author]

Posts