[vinz]

Ok I see, not straight forward but brilliant!

I manage to get something which looks interesting with the following lines:

    mask
    {
        type swakExpression;
	valueType internalField;
        variables (
            "maskField=(vorticity.z>0 || pos().y<0.3) ? 0 : 1;"
	);
        storedVariables (
            {
                name maskField;
                initialValue "0";
            }
        );
        expression "maskField";
	accumulations ( 
	   max
	);
        verbose true;        
    } 


    maxVortPos
    {
        type swakExpression;
	valueType internalField;
        variables (
	    "vortPos2= maxPosition((maskField>0) ? magVorticity : -1000);"
        );
        storedVariables (
            {
                name vortPos2;
                initialValue "vector(-0.4,1,0)";
            }
        );
        expression "vortPos2";
	accumulations ( 
	   max
	);
        verbose true;        
    } 

    maxVortPosY
    {
        type swakExpression;
	valueType internalField;
        expression "vortPos2.y";
	accumulations ( 
	   max
	);
        verbose true;        
    } 

    maxVortPosX
    {
        type swakExpression;
	valueType internalField;
        expression "vortPos2.x";
	accumulations ( 
	   max
	);
        verbose true;        
    }

Now I would like to compute the integral of U on a surface which would be a sphere centered on my vortex.
I tried the following to create such a sphere :

    distField
    {
        type expressionField;
        outputControl timeStep;
        outputInterval 1;
        fieldName distanceFromVortex;
        expression "mag(pos()-vortPos2)";
        autowrite true;        
    } 

    surfaceIsoDist
    {
        type swakExpression;
        valueType surface;
        surfaceName isoVortexDist;
        surface {
            type isoSurface;
            isoField distanceFromVortex;
            isoValue 0.15;
            interpolate true;
        }
        verbose true;
        expression "mag(U)";
        accumulations (
            min
            max
	    average
        );
    }

but it crashes complaining that vortPos2 does not exist or is of wrong type although I use it earlier to get vortPos2.x for instance.

Then I am wondering what type is expected at this place? Any idea?