PATCH(NORTHWAL,NWALL,1,NX,NY,NY,1,NZ,1,LSTEP)
IF(NX.GT.1) THEN
 COVAL(NORTHWAL,U1,1.0,0.0)
ENDIF   
IF(NZ.GT.1) THEN
 COVAL(NORTHWAL,W1,1.0,0.0)
ENDIF