# what can cause divergence?

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 August 31, 2004, 10:51 what can cause divergence? #1 Jeffery Guest   Posts: n/a Sponsored Links My model is simple,(a cylinder, two opening(top and bottom).Gas come from a a opening(velocity inlet) and out from another(pressure outlet).I take gas as incompressible idea gas. And this is transient model. My question is that in my model, continue equation does't converge(5e-2), even iterating over 1000 time. So I want to know what may be wrong in my model. Appreciate !!!

 September 1, 2004, 11:44 Re: what can cause divergence? #2 SAM Guest   Posts: n/a it is also convergence. if ur residuale line contiue to be on same value then it is convergene by defintion.

 September 1, 2004, 11:59 Re: what can cause divergence? #3 Jeffery Guest   Posts: n/a Thanks, but I am still not confident about this result.Is there any way to make this value down(such as less than 1e-3)? Meshing the grid fine will help?

 September 1, 2004, 12:28 Re: what can cause divergence? #4 Jason Guest   Posts: n/a The residuals you are looking at aren't the actual residuals. They are the average residuals normalized based on the initial residuals. Which means if your initial guess is close, and there isn't much change from the initialized solution, then you're residuals won't drop 3 orders of magnitude. You shouldn't judge convergence just on the residuals though. You should monitor any important characteristics, such as lift coefficient, drag coefficient, pressure at a point, maximum velocity magnitude over the domain... Think about what you are trying to get out of the solution and monitor those values to make sure they are converging. The residuals help you understand what your model is having problems with, and help you to adjust your model to make it solve better, but convergence shouldn't be judged by residuals alone. If the residuals are flat-lined, and your monitors are too, then you have a converged solution you can be confident in (assuming you didn't screw up the model ) Good luck, Jason kaktus10 likes this.

 September 1, 2004, 14:40 Re: what can cause divergence? #5 Jeffery Guest   Posts: n/a Jason,thanks a lot, you suggestion is very helpful for me.

 September 16, 2004, 12:54 Re: what can cause divergence? #6 ppaitt Guest   Posts: n/a Try to mesh the model again. And make more denser grid as you can. The mesh quality plays an important role on convergent. kaktus10 likes this.

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