[mmengineer]

Hello everyone,

i´m simulating an Open-Channel problem and i´m trying to get Drag values of bridge inside that open channel. The simulations works and i´m getting results for the Drag coefficient. The global courant number of the problem is under 1 with a time step size of 0.005 s and the calculated drag-coefficient is about 0.9.

But when I change the time-step-size to 0.0025 s the drag-coefficient jumps up to about 1.1 and will stay there.

When i change the time-step-size to 0.00005 s the drag-coefficient jumps up to about 30.

When i look at the calculated drag forces the same thing will happen, so i guess it´s not a problem of reference values or something, but a problem inside the simulation. But i can´t figure out what causes the problem, since the courant number is below 1 in every of the simulations.

Can anyone help me with this problem or does anyone at least have an idea what causes this behaviour of the simulation.

Thank you very much