[huangxianbei]

Hi,all
I'm doing a LES simulation. And I want to write the fluctuating velocity, that is:
u'=U-UMean, so how can I implement this? I tried like this

Info<< "Reading field UMean\n" << endl;
    volVectorField UMean
    (
        IOobject
        (
            "UMean",
            runTime.timeName(),
            mesh,
            IOobject::MUST_READ

        ),
        mesh
    );
    volVectorField Ufluc
    (
        IOobject
        (
            "Ufluc",
            runTime.timeName(),
            mesh,
            IOobject::NO_READ,
            IOobject::AUTO_WRITE
        ),
        mesh
    );
    Ufluc=U-UMean;
    Ufluc.write();

However, when calculate, error occurs

NO_READ specified for read-constructor of object Ufluc of class IOobject

    From function regIOobject::readStream()
    in file db/regIOobject/regIOobjectRead.C at line 46.

FOAM aborting

can anyone help?

[huangxianbei]

The innovation to do this is to define the fluctuating field as to do post-process about u', although I know it's possible to do U-UMean in post-process, I still want to know if this can be accomplished directly.

[tomislav_maric]

You have specified the the Ufluc field not to be read from a file, and have failed to provide initial values that are in that case required to construct the field:

volVectorField Ufluc 
(         
    IOobject 
    ( 
        "Ufluc", 
        runTime.timeName(),             
        mesh, 
        IOobject::NO_READ,
        IOobject::AUTO_WRITE 
    ),         
    mesh // Missing initial values
);

If you don't want to provide the field in the '0' directory as a file to be read at run-time, you have to provide the default initialization argument:

volVectorField Ufluc    
(         
     IOobject         
     (             
         "Ufluc",            
         runTime.timeName(),             
         mesh,             
           IOobject::NO_READ,             
         IOobject::AUTO_WRITE         
     ),         
     mesh, 
       dimensionedVector
      (
           "zero", 
           U.dimensions(), // Or Umean.dimensions()
           vector (0,0,0)
      )
 );

Also, don't use the 'regIOobject::write()' inherited member function of a field to do the writing - this will write the field every time step and will probably mess up the case. Writing should be taken care of by the 'Time' class, with:

runTime.write();

This way it won't happen for example that you output 'Ufluc' every time step, and 'U' and 'Umean' every 10th time step.

[huangxianbei]

Originally Posted by tomislav_maric

You have specified the the Ufluc field not to be read from a file, and have failed to provide initial values that are in that case required to construct the field:

volVectorField Ufluc 
(         
    IOobject 
    ( 
        "Ufluc", 
        runTime.timeName(),             
        mesh, 
        IOobject::NO_READ,
        IOobject::AUTO_WRITE 
    ),         
    mesh // Missing initial values
);

If you don't want to provide the field in the '0' directory as a file to be read at run-time, you have to provide the default initialization argument:

volVectorField Ufluc    
(         
     IOobject         
     (             
         "Ufluc",            
         runTime.timeName(),             
         mesh,             
           IOobject::NO_READ,             
         IOobject::AUTO_WRITE         
     ),         
     mesh, 
       dimensionedVector
      (
           "zero", 
           U.dimensions(), // Or Umean.dimensions()
           vector (0,0,0)
      )
 );

Also, don't use the 'regIOobject::write()' inherited member function of a field to do the writing - this will write the field every time step and will probably mess up the case. Writing should be taken care of by the 'Time' class, with:

runTime.write();

This way it won't happen for example that you output 'Ufluc' every time step, and 'U' and 'Umean' every 10th time step.

Hi,Tomislav:
Thank you for your reply. Where should I put the 'runTime.write()' as you say? .H file or in the .C file?

[tomislav_maric]

[QUOTE]
Thank you for your reply. Where should I put the 'runTime.write()' as you say? .H file or in the .C file?
[\QUOTE]

'runTime' is a global object (class 'Foam::Time'), and it's usually used in application (solver) client code - if you open a solver you are interested in, you will find it at the end of the main simulation loop.

If you are doing modifications in createFields.H, you don't have to explicitly write the fields there with '.write()', the solver will take care of the writing of all registered fields.

[huangxianbei]

[QUOTE=tomislav_maric;488832]

Thank you for your reply. Where should I put the 'runTime.write()' as you say? .H file or in the .C file?
[\QUOTE]

'runTime' is a global object (class 'Foam::Time'), and it's usually used in application (solver) client code - if you open a solver you are interested in, you will find it at the end of the main simulation loop.

If you are doing modifications in createFields.H, you don't have to explicitly write the fields there with '.write()', the solver will take care of the writing of all registered fields.

Oh,that's to say, I don't need to do with the '.write' since the solver has already done this. The only thing is to create the filed I need.