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Old   September 23, 2019, 14:40
Default Transient Convergence
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Soumitra Vadnerkar
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If after sometime, every subsequent timestep is converging in mere 2-3 iterations (i.e. very quickly), can we say the solution not variables are not drastically changing, meaning the solution is nearly converged already?
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Old   September 23, 2019, 14:42
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Originally Posted by soumitra2102 View Post
If after sometime, every subsequent timestep is converging in mere 2-3 iterations (i.e. very quickly), can we say the solution not variables are not drastically changing, meaning the solution is nearly converged already?



No, the convergence to a steady state solution must be confirmed by the residuals on the equations, that is the time derivatives magnitude.
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Old   September 23, 2019, 15:13
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I have kept the residual criteria for all equations--continuity, velocity, energy, etc. in my transient simulation as same as they are for a typical steady-state simulation.
And with these set targets, each of the residual criteria is satisfying for every time-step within no more than 2-3 iteration calculation per time-step; and this is happening for almost all subsequent time-steps.
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Old   September 23, 2019, 15:24
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Originally Posted by soumitra2102 View Post
I have kept the residual criteria for all equations--continuity, velocity, energy, etc. in my transient simulation as same as they are for a typical steady-state simulation.
And with these set targets, each of the residual criteria is satisfying for every time-step within no more than 2-3 iteration calculation per time-step; and this is happening for almost all subsequent time-steps.



If the residuals correspond to the time derivatives and the thresholds for the convergence criteria is adequate, you can assume that the computed solution is steady.
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Old   September 24, 2019, 00:04
Default Residual plot for a transient simulation
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Soumitra Vadnerkar
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Sorry to ask again, but, just to be clear,


Can we say about the attached image of residual plots of a transient simulation indicate that the solution is nothing but a converged steady-state solution?tube_fluid-1-01001.png


In other words, is it so that, maybe if a converged steady-state solution (with same residual target criteria) was available would seem no different than this transient simulation ?
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