Discussion Forum

So, I'm using heat transfer and laminar flow to simulate convection. Everything works fine if initial values in the laminar flow module are set zero and there's only movement due to convection. However, if I want to include some general movement of air, I'll get the error message "failed to find consistent initial values. last time step not converged".

I was told that it is because the velocity from laminar flow comes too sharply and produces a change too big in the time domain and solver can't take sufficiently small steps quickly enough. I was told to use the ramp function so that it would take some time for velocity to change from 0 to some v_0. If I have this ramp function, I can write v_0*rm1(t) as the initial value of velocity.

Well that is clear enough, but I just don't get this ramp function. I can only set location, slope and cut-off. Where should v_0 come in and where can I define the time during which velocity changes from 0 to this v_0?