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January 3, 2013, 14:21 |
Time step continuity error
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#1 |
Member
Ali Shamooni
Join Date: Oct 2010
Posts: 44
Rep Power: 15 |
Hi
I have some clear questions? I wonder if someone can reply clearly too 1-is time step continuity error really important in steady solvers including energy eq.? 2-what about unsteady ones that use piso? 3-if the answer is yes what should be the order of a-sum local, b-global c-cumulative continuity errors? |
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January 4, 2013, 06:19 |
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#2 |
Senior Member
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January 5, 2013, 11:35 |
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#3 | |
Member
Ali Shamooni
Join Date: Oct 2010
Posts: 44
Rep Power: 15 |
Quote:
as u can see in "rhoPimpleFoam" tutorial case "angleduct"after 10 step it has: sum local=0.000953371, global=0.000776714, cumulative=0.402763 |
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January 5, 2013, 13:00 |
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#4 |
Member
Aathavan
Join Date: Nov 2012
Posts: 70
Rep Power: 13 |
Hi There,
I am also getting the same problem, here is some data. I really dont know how to solve this problem. I am using MRFSimpleFoam Time = 31 time step continuity errors : sum local = 0.00425606, global = 0.000924716, cumulative = 0.0274701 Time = 32 time step continuity errors : sum local = 0.00357216, global = 0.000535369, cumulative = 0.0280054 Time = 33 time step continuity errors : sum local = 0.00360527, global = -0.000591305, cumulative = 0.0274141 Time = 34 time step continuity errors : sum local = 0.00362457, global = -0.000742113, cumulative = 0.026672 Time = 35 time step continuity errors : sum local = 0.00331502, global = -0.000725819, cumulative = 0.0259462 Time = 36 time step continuity errors : sum local = 0.00305899, global = 0.000333275, cumulative = 0.0262795 Time = 37 time step continuity errors : sum local = 0.0030778, global = 0.000586366, cumulative = 0.0268658 I have gone through the link which you have given to alish1984 and so many other post as well. Now I came to know, its is important as well it is something to do with pressure solver. I changed relTol to 0 then there where no problem, but its taking lot of time to solve pressure (for one time step 10 to 15 min) the above data is for relTol = 0.0005 in fvSolution --> pressure adambarfi, if you are able to explain how to solve it, I will be grateful to you. Thanks in advance, Aadhavan |
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March 27, 2018, 03:18 |
time step error cumulative
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#5 |
New Member
Ali Mohammadi
Join Date: Oct 2017
Posts: 15
Rep Power: 8 |
I think the cumulative time step error is the continuity error from the first time step. so if the order of continuity error gets high at the beginning of a run, the cumulative order gets bigger and till the convergence it wont get smaller.
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