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-   -   CrankNicholson errors (http://www.cfd-online.com/Forums/openfoam-solving/60200-cranknicholson-errors.html)

lr103476 October 21, 2005 10:40

Consider the movingCone case w
 
Consider the movingCone case with the solver icoFoamAutoMotion.

When using the second order CrankNicholson time integration I get an error message after the first mesh update.

FOAM FATAL IO ERROR : attempt to read beyond EOF

From function ITstream::read(token& t)
in file db/IOstreams/Tstreams/ITread.C at line 70.

Later I also tried this scheme in the cavity problems, but with no succes.

Is someone actually using this scheme, or am I doing something wrong.

Frank

hjasak October 21, 2005 10:47

There has been a change in the
 
There has been a change in the format that is not reflected in the config files. Add 0.5 after CrankNicholson (now the factor is run-time selectable):

ddtSchemes
{
default CrankNicholson 0.5;
}

Enjoy,

Hrv

maka May 21, 2006 13:07

shouldn't be CrankNicholson 1?
 
shouldn't be CrankNicholson 1?

in the user guide:

4.4.6 Time schemeshttp://www.opencfd.co.uk/openfoam/do...#x20-1050004.4

it says:

There is an off-centering coefficient y with the CrankNicholson scheme that blends it with the the Euler scheme. A coefficient of y = 1 corresponds to pure CrankNicholson and and y = 0 corresponds to pure Euler. The blending coefficient can help to improve stability in cases where pure CrankNicholson are unstable.

best regards,
Maka

mattijs May 22, 2006 07:01

Sorry, I don't understand. Wha
 
Sorry, I don't understand. What shouldn't be 1?

(I only see some duplicate 'the the' and 'and and' in that section)

maka May 22, 2006 09:46

I mean that the previous messa
 
I mean that the previous message seemed to suggest that: a pure CrankNicholson scheme is applied in OpenFOAM by setting:

ddtSchemes
{
default CrankNicholson 0.5;
}

while the help in the user guide seems to says that it is:

ddtSchemes
{
default CrankNicholson 1;
}

which is right?

Many thanks,
Maka

hjasak May 22, 2006 21:00

You should be able to find thi
 
You should be able to find this out by looking at the source code:

/finiteVolume/ddtSchemes/CrankNicholsonDdtScheme/CrankNicholsonDdtScheme.H

//- Off-centering coefficient, 1 -> CN, less than one blends with EI
scalar ocCoeff_;


Need I say more? :-)

Hrv

lr103476 May 23, 2006 03:21

So a factor of 1 corresponds t
 
So a factor of 1 corresponds to fully second order Crank-Nicholson? I thought it should be 0.5?

Is this changed in OpenFOAM version 1.3

Frank

maka May 23, 2006 06:17

CrankNicholsonDdtScheme.C chan
 
CrankNicholsonDdtScheme.C changed between V 1.2 and 1.3 but I have no clue if the behavior changed. I'm still using V 1.2 and have been running a one-month simulation assuming it should be CrankNicholson 0.5 as the early post suggested. Do not ask me what is right and what is wrong. All I can say, enjoy :-)

/Maka

lr103476 May 24, 2006 10:23

Could someone please explain t
 
Could someone please explain the differences (if any) between v1.2 and v1.3.

Conform the theory books, a value of 0.5 would makes more sense then 1.0.

Frank

mattijs May 25, 2006 05:22

No basic differences between 1
 
No basic differences between 1.2 and 1.3.

//- Off-centering coefficient, 1 -> CN, less than one blends with EI

maka May 26, 2006 03:14

Many thanks Mattijs for your c
 
Many thanks Mattijs for your clear reply.
/Maka.

lr103476 May 29, 2006 03:58

So for the record, Crank Nicho
 
So for the record, Crank Nicholson 1.0 corresponds to fully second order accuracy, while a value less then 1.0 is less accurate.

Sorry to bother you again, but I am not really into the theory at this moment.

Frank

openfoammaofnepo October 20, 2013 06:21

Hi All,

When I choose CN, but set the factor to 1. The pressure is very prone to blow up, which lead to the simulation failure. Could anyone tell me what is the reason for this problem? Thank you very much.

Quote:

Originally Posted by hjasak (Post 195677)
You should be able to find this out by looking at the source code:

/finiteVolume/ddtSchemes/CrankNicholsonDdtScheme/CrankNicholsonDdtScheme.H

//- Off-centering coefficient, 1 -> CN, less than one blends with EI
scalar ocCoeff_;


Need I say more? :-)

Hrv



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