Reply To: Could not addVelocityBoundary
Warnings of this kind are printed when the boundary setter (the addVelocityBoundary method in this case) fails to instantiate the necessary dynamics / post processors for a particular cell. This means that the boundary for this cell is not well defined. However in practice this is frequently overlooked as single erroneous populations don’t necessarily impact the overall simulation in a noticeable fashion. This seems to also be the case here?
Of course it is good practice to keep an eye on such messages and to fix the underlying geometry problem. In this case I suspect that the discrete wall normal could not be recovered correctly / the wall normal can not be handled by the specific velocity condition.
Did you already verify the material number setup in ParaView?
w.r.t. your second question: Depending on what you mean, this is either an artifact of the specific geometry setup (rounding or otherwise) or the overlap area around each block that is used for communication.