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mesh study with high residuals - redo?

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Old   December 7, 2014, 13:54
Default mesh study with high residuals - redo?
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I've done a mesh study and taken significant time/money to come up with an answer. but i later found out my model was not convereged due to higher residual values and needing more inner iterations. When i had done the study, i had good agreement between my drag coefficient to a max difference of .003 between meshs 7 mil and 12 mil.

even though my drag values were off from the expected values from the physical test. can i consider the mesh study conclusive or would i have to redo the test with a more converged solution to prove the values don't change.

currently i'm working to refine the timestep and inner iteration count, but i would rather not have to redo the mesh study if i can assume the solution remains conclusive, but only more accurate with the decreased residual values.
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Old   December 7, 2014, 14:10
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Originally Posted by SB123 View Post
I've done a mesh study and taken significant time/money to come up with an answer. but i later found out my model was not convereged due to higher residual values and needing more inner iterations. When i had done the study, i had good agreement between my drag coefficient to a max difference of .003 between meshs 7 mil and 12 mil.

even though my drag values were off from the expected values from the physical test. can i consider the mesh study conclusive or would i have to redo the test with a more converged solution to prove the values don't change.

currently i'm working to refine the timestep and inner iteration count, but i would rather not have to redo the mesh study if i can assume the solution remains conclusive, but only more accurate with the decreased residual values.

Use of residuals is only one measure of solution convergence. It is a measure of how well the discretized PDEs are satisfied. However, as you are concerned with drag, you should monitor drag during your computations as well. The solution could then be considered converged when the residuals fall below some tolerance (say 10e-3 for continuity and 10e-4 for momentum) and the drag value is also converged within a tolerance acceptable for you particular problem.

The mesh study is not conclusive if the solutions on each mesh are not converged based on the above criteria.
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Old   December 7, 2014, 16:10
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so converged within a tolerance acceptable for you particular problem.

The mesh study is not conclusive if the solutions on each mesh are not converged based on the above criteria.
so with a higher accuracy of solution to PDE's (lower residual values), can affect the spatial solution convergence ie mesh relationship solution?
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Old   December 7, 2014, 16:23
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so with a higher accuracy of solution to PDE's (lower residual values), can affect the spatial solution convergence ie mesh relationship solution?
Correct. Any conclusions you draw in moving from a coarse mesh to a finer mesh may be erroneous if the individual solutions are not "converged".
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Old   December 7, 2014, 16:29
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aww shucks... thanks for the help though!
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