DFBI residuals and Initial conditions!
 

Hi All
I am working with VOF waves and dfbi with waves in +ve Z direction and rotation of body in X direction only.
I have chosen proper time step ( implicit unsteady) and number of iterations.
1. Residuals after every timestep seems to be jumping too high especially X and Y momentum and that of Water. Is there anything that can be done?
2. Reverse flow at pressure outlet though my pressure outlet is far off.
3. Do I need to calculate turbulent properties for initialisation or use default values?
I am using Overset mesh for this purpose...

Thanks
Regards,
Muhsin

What does "residuals jump TOO HIGH after every time step" mean? What is too high?
It is nothing special that residuals are jumping up after a time step. And it's no issue as long as they drop in the next time step.

Usually reversed flow doesn't harm. You've got a movement of your 6DOF body, pushing fluid out of your domain. Therefore some fluid needs to re-enter the domain. And fluid entering the domain through a pressure OUTLET is ending in the "reversed flow" message. That's all.

Thanks for your reply sir,
Jumping to to the values of say 5-10. my Sdr and Tke residuals converge well near or below .001, rest all fine.
But when i change time step discretisation to second order my Sdr and Tke residual are too high say 100-500 and dont converge to next time step, but the run goes on.
Also, when i change Turbulent specification to K+omega, free surface distorts and solution diverges soon after that.

Don't worry about the level of the residuals since they are normalized in ccm+. It's just also nothing special that the residuals jump up every time step, it's just important that they drop again during the time step.
For your second issue, I don't have an idea without having more information about your setup. But I would check the usual suspects: Time step, mesh resolution and of course, did you specify proper values for k and omega...

thanks! 1. so i need not to worry about residuals if they converge well every timestep.
2. i can send you my .sim file if u say... time step is .01s for a max velocity of .3m/s and min cell thickess of .005m.
i used both default values and calculated values of K and omega for my set up.
for calculation i used the formulation from fluent manual.

The k-omega model is very sensitive to your turbulence specification. I would enter the values for turbulence intensity and turbulent viscosity ratio. Then Star-CCM+ will calculate proper values for k and omega.
Anyway, when the default values don't work, I would check for a proper mesh resolution. Maybe you can post a picture of a section through your domain...

https://mail-attachment.googleuserco...hPLd4&sadssc=1https://mail-attachment.googleuserco...dZzMs&sadssc=1I am posting picture of my domain. origin is at the base of the body. domain extends from -6m to 20m. http://www.cfd-online.com/Forums/C:%...esktop%5C1.png