Discussion Forum

Hi,

Im new to comsol and i want to simulate shear induced migration of particles in a suspension at low reynolds number. I tried to implement it in the mixture model laminar flow but the model had some extra terms which I cant seem to get out of the model equations.

In 2d, I have two concentric circles, in which the inner one moves, I have pics of my model attatched

Using creeping flow model, (spf)
rho*du/dt= del.[-pI+mu( del u + (del u)^T)] +F

Here i express the viscosity mu equal to a variable I defined as
eta_f=((1-(phi/phid_max))^(-1.82))*eta_f0

Where phid_max and eta_f0 are parameters = 0.68 and 4.95.

phi I define via a coefficient for pde:
d phi/dt+ del.(-(D1*phi*spf.sr+D2*spf.sr*phi*phi*d(eta_f,phi)/eta_f)- alpha*phi) +u. del phi=0

alpha= D1*phi*phi*d(spf.sr,x) .........in x
D1*phi*phi*d(spf.sr,y).....in y

For the creeping flow I have initial values u,v =0 ,p=1, outer circle as wall, inner circle as inlet,
u0= ay in x
-ax in y

for the pde I have no flux on all walls and initial value 0.5.

when i run it, it always says last time step not converged. Inconsistent initial values. should I make any changes in the solver to make it converge. I also tried to remove viscosity from the variables and tried to implement it as a pde with only f as the function and all others zero (where it did run once but Couldnt run it again after tweaking it a bit, cant seem too get back the earlier run)

Do i have to add any weak constraint or change any discretization or anything?? I am using the fully coupled solver, ill also try the segregated solver now.

I would be very grateful on any help on this to converge. I have pics attatched of my model.

Thank you
Nikhil