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time varying velocity outlet boundary condition

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Old   September 11, 2014, 16:11
Default time varying velocity outlet boundary condition
  #1
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simin
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Dear all,

I am simulating flow inside the pipe considering time varying decrease of outlet velocity. for decreasing outlet velocity by time I used the groovy BC boundary condition for velocity as follows:

velocity::::
boundaryField
{
inlet
{
type zeroGradient;
}
outlet
{
type groovyBC;
variables "U0=0.13;T1=3754;Uout=U0*(1-pow((time()/T1),3));";
valueExpression "(time()<T1) ? vector(Uout,0,0):vector (0,0,0)";

}
axi_symm-f
{
type wedge;
}
axi_symm-r
{
type wedge;
}
wall
{
type fixedValue;
value uniform (0 0 0);
}
defaultFaces
{
type empty;
}
}


pressure:::::

boundaryField
{
inlet
{
type fixedValue;
value uniform 8376;
}
outlet
{
type zeroGradient;
}
axi_symm-f
{
type wedge;
}
axi_symm-r
{
type wedge;
}
wall
{
type zeroGradient;
}
defaultFaces
{
type empty;
}
}


the problem is that after running the case on the terminal page the following message is presented:

--> FOAM Warning :
From function
groovyBCFvPatchField<Type>::groovyBCFvPatchField(c onst fvPatch&
p,const DimensionedField<Type, volMesh>& iF,const dictionary& dict)
in file groovyBCFvPatchField.C at line 131
No value defined for U on outlet therefore using 30{(0 0 0)}

I think it means that the groovy BC is not defined for outlet condition.
But as I have to reduce the outlet velocity by time could any one help me for finding a proper boundary condition.

Many thanks for the help,
Simin
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Old   September 12, 2014, 01:42
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  #2
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simin
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any idea????
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Old   September 12, 2014, 02:09
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  #3
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Mohammad Shakil Ahmmed
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Hi,
From the error message, "No value defined for U on outlet therefore using 30{(0 0 0)}". So, you haven't defined any value,i.e. initial, at the boundary and it's taking some default value. What you can do is that,

outlet
{
type groovyBC;
variables "U0=0.13;T1=3754;Uout=U0*(1-pow((time()/T1),3));";
valueExpression "(time()<T1) ? vector(Uout,0,0):vector (0,0,0)";
value $internalField; Or uniform (0 0 0) if zero.
}
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Old   September 12, 2014, 02:13
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simin
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Hi Ahmmed,

Many thanks for your help
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