Discussion Forum

Hello,
Currently, I am modeling the transport of diluted species under concentration gradient and pressure differential in the soil which enters the building through foundation cracks. I am using two modules, darcy’s law and transport of diluted species. I have to define a relationship for flux through the crack and the full expression for flux is as below. The dl.w is the q (velocity in z direction from darcy law) :

JT = -c*q*[exp(q*tck/Deff) / (1 - exp(q*tck/Deff))]

After substituting constant values, I am entering it to comsol as:

-dl.w*c*(exp(dl.w*0.156/7.2*10^6)/(1 - exp(dl.w*0.156/7.2*10^6)))

c: concentration of gas, given by comsol
tck: crack thickness
Deff : diffusion coefficient of gas

But the problem is that, the whole expression turns brown and when I run the model, it gives me an error which says in 4000 degrees of freedom has undefined NaN/Inf value. The coordinates for these nodes are exactly located across the crack. The above expression accounts for both advective and diffusive fluxes through the crack. When I neglect the diffusive flux and just use the term: dl.w*c, the solution converges and I can get the average value for flux but this is not the exact value. I am interested in calculating the exact value. I hope you could help me.

Thanks
Ali