[email protected]Dear all,
I am a completely new user with Hec-Ras and am not able to run a 1D/2D model due to instability problem. The model represents a pond area and is built as following :
– a 1D area with the river upstream
– a 2D area with the pond in the middle
– a 1D area with the river downstream.
The aim of the model is to know the discharge and the water level in the river downstream.
A flow hydrograph is defined as a boundary condition in the river upstream and a normal depth as a boundary condition in the river downstream.
The mesh has 20 meters-cells and the calculation timestep is 0.5 second.
After starting the run, the model crashes very quickly and I assume therefore that the problem is due to initial conditions. A realistic water level of the pond is defined in the 2D model as initial condition. In the 1D model, a flow value equal to the discharge at the first timestep of the hydrograph is defined as initial condition in the upstream river too. After reading the Hec-Ras user manual, I guess that an initial condition needs to be defined in the downstream river too. Could you confirm please ? If an initial condition has indeed to be defined here, I wonder how a consistent value can be predicted.
Many things have already been tested in the Unsteady Computation Options and Tolerance window in order to stabilize the model :
– initial conditions times and initial conditions ramp up fraction for the 2D model
– maximum iterations between 1D and 2D
– maximum number of iterations in the General tab
– number of warmup time steps + time step during warm up in the General tab.
Activating the option “keep initial elevations constant during warm up” in the Initial Conditions tab of the Unsteady Flow Data box has been tested too. Reducing and increasing the calculation timestep too.
Unfortunately, nothing seems to work. Would you have any idea how the problem could be solved please ?
In advance, thank you for your advice and have a nice day !