Hi Sandeep, Is your self-defined udiiff a non-dimensional one? If not, maybe you can try to set dimensionless properties in uservp subroutine, then the non-positive error may disappear. Cheers, Bolun ---------------------------------------------------------------- Bolun Xu University of Science and Technology of China Department of Modern Mechanics Hefei, Anhui, China -----邮件原件----- 发件人: [email protected] [mailto:[email protected]] 代表 [email protected] 发送时间: 2016年12月2日 4:18 收件人: [email protected] 主题: Nek5000-users Digest, Vol 94, Issue 1 Send Nek5000-users mailing list submissions to [email protected] To subscribe or unsubscribe via the World Wide Web, visit https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users or, via email, send a message with subject or body 'help' to [email protected] You can reach the person managing the list at [email protected] When replying, please edit your Subject line so it is more specific than "Re: Contents of Nek5000-users digest..." Today's Topics: 1. uservp MHD error ([email protected]) ---------------------------------------------------------------------- Message: 1 Date: Thu, 1 Dec 2016 18:31:45 +0100 From: [email protected] To: [email protected] Subject: [Nek5000-users] uservp MHD error Message-ID: <[email protected]> Content-Type: text/plain; charset="utf-8" Hello All, I want to run MHD case with different magnetic diffusivities in different region of the domain. Can we run MHD run with different magnetic diffusivities? Assuming that udiff=magnetic diffusivity (eta), in the uservp file I added the following 1.0000000E+00 p30 > 0 ==> properties set in uservp() subroutine uservp (ix,iy,iz,ieg) include 'SIZE' include 'TOTAL' include 'NEKUSE' if (ifield.eq.1) then ! velocity utrans = param(1) udiff = param(2) elseif (ifield.eq.ifldmhd) then ! B-field utrans = 1.0 R1 = sqrt(x*x+y*y); if(R1 .le. 2.0) then udiff= param(29) else udiff= 1000.0D0*param(29) endif endif return end I get an error done :: set initial conditions ERROR: Non-positive diffusivity ( 0.00 ) specified for field 2, group 0 element ERROR: Non-positive diffusivity ( 0.00 ) specified for field 2, group 0 element Attached are the .usr, .rea and the logfile When I set the p30=0.000 and just utrans=0.0 udiff=0.0 in the uservp, the simulation is running fine. Thank you in advance. Cheers, Sandeep