# small Diffusion Coefficient leads to divergence

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 November 28, 2020, 11:26 small Diffusion Coefficient leads to divergence #1 Member   Deutschland Join Date: Jun 2020 Location: https://t.me/pump_upp Posts: 43 Rep Power: 4 Hi all, I figured out, that divergence in my case starts because of the small diffusion coefficient I use. For UDS0 = 3e-5, for UDS1=1e-10. Does someone know how to avoid this problem? When I use Diffusion coefficient= 0 the solution converges. Also I notice that my UDS Value go towards infinite when I disable the Flux term ans use the specific diffusion coefficient. So I am not sure if only the Diffusion Coefficient is the problem. Urgent help would be nice Deadline for thesis is in 1 week :/ Ideas I could find: do a linearization for Source Term. But I do not understand it completely and I am not sure if this will help. Could be the mesh a problem, if it works already with diffusion coefficient = 0? This is my Source Term for UDS1 and 2: C is scalar from UDS 1, M is scalar of UDS2 ast. adyn, gst, gdy, C_sat, M_sat are coefficients, c_vel = velocity. source (C)= -c_density * ((ast + adyn * c_vel) * (1 - M / M_sat) * C + (gst + gdyn * c_vel) * (1 - C / C_sat) * M); dS[eqn] = -c_density * ((ast + adyn * c_vel) * (1 - M / M_sat) - (gst + gdyn * c_vel)*M/C_sat); source (M)= c_density * ((ast + adyn * c_vel) * (1 - M / M_sat) * C + (gst + gdyn * c_vel) * (1 - C / C_sat) * M); dS[eqn2] = -c_density*((gst + gdyn * c_vel) * (1 - C / C_sat)+(ast + adyn * c_vel)*C/M_sat); Last edited by schwaral; November 29, 2020 at 03:31.

 Tags diffusion coef., divergence