I need to interpolate a vortic
 

I need to interpolate a vorticity vetor field - curl(U) for one of the physical models I'm working on. I'm getting error that reads
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--> FOAM FATAL IO ERROR : keyword (2**skew(grad(U))) is undefined in dictionary "/home/sek/OpenFOAM/sek-1.4.1/applications/solvers/lagrangian/run/bubbleChannel/ constant/bubbleCloudProperties::interpolationSchemes"

file: /home/sek/OpenFOAM/sek-1.4.1/applications/solvers/lagrangian/run/bubbleChannel/c onstant/bubbleCloudProperties::interpolationSchemes from line 83 to line 86.

From function dictionary::lookupEntry(const word& keyword) const
in file db/dictionary/dictionary.C at line 146.

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Is there any workaround?