UMean is not found for acousticDampingSource calculations

Summary

I am currently trying to apply acoustic Damping source to a part of the computational domain surrounding aerofoil. I am using rhoPimpleFoam solver for a 3-D computational domain with cyclic boundary conditions in the span-wise direction (Z-direction).

The following Lines are added in the fvOptions

acousticDampingSource
 {
    type      acousticDampingSource;
    active    yes;
    acousticDampingSourceCoeffs
    {
      //  timeStart      0.004;
        duration       1000.0;
        selectionMode        all;
      //  selectionMode        cellZone;
      //  cellZone            selectedCells;
        origin         (0.2 0 0);
        radius1         0.5;
        radius2         0.54;
        frequency       1000;
        U               U;
        URef            UMean;
    }

The error message produced is that indicating that the UMean is not found although they are present in the time history data

#0  Foam::error::printStack(Foam::Ostream&)[3] 
[3] 
[3] --> FOAM FATAL ERROR: 
[3] 
    request for volVectorField UMean from objectRegistry region0 failed
    available objects of type volVectorField are
4(wallShearStress U_0 U U_0_0)
[3] 
[3]     From function const Type& Foam::objectRegistry::lookupObject(const Foam::word&, bool) const [with Type = Foam::GeometricField<Foam::Vector<double>, Foam::fvPatchField, Foam::volMesh>]
[3]     in file /data/openFOAM/OpenFOAM-v1906/src/OpenFOAM/lnInclude/objectRegistryTemplates.C at line 464.
[3] 

I do not know why the ONLY seen vectorFields are only (wallShearStress U_0 U U_0_0), although, there are other vectorFields like wallShearStressMean,UMean,vorticity,vorticityMean?