reset the value for a fixedvalue boundary condition
 

Hi,

I want to reset the value for a fixedvalue BC with uniform value in the OpenFoam code.
Or create a new volscalarField with fixedValue boundary.
I found a way to set the boundary types from another field, like following
volVectorField U
(
IOobject
(
"U",
runTime.timeName(),
runTime,
IOobject::NO_READ,
IOobject::NO_WRITE
),
mesh,
dimensionedVector("zero", dimVelocity, vector::zero),
p.boundaryField().types()
);
However, in this only the boundary type (e.g. fixedvalue) is set. How can I set the value for the fixedvalue BC?
could anyone give some idea?

Best Regards!