Dear all, in a 3D turbulent channel flow simulation with Fourier expansions in one direction, I want to add some small wall imperfections using Robin boundary conditions. To this end, I specified the following simple cos disturbances into wall boundary: <R VAR="u" VALUE="0" PRIMCOEFF="(pertAmp*cos(2.0*PI/LZ*2*z+2.0*PI/LX*4*x))^(-1)"/> <R VAR="v" VALUE="0" PRIMCOEFF="(pertAmp*cos(2.0*PI/LZ*2*z+2.0*PI/LX*4*x))^(-1)"/> <R VAR="w" VALUE="0" PRIMCOEFF="(pertAmp*cos(2.0*PI/LZ*2*z+2.0*PI/LX*4*x))^(-1)"/> When I checked the data, it seems like the terms multiplied by z remains alway zero while x-related terms have no problem. In this regard, I was wondering whether 3D1H case does support functional expansions in the Fourier direction for Robin BC. Any feedback would be appreciated. Thanks, Asim