Discussion Forum

Hello,

I am working on the design of a 3D Comsol model which mimics the setup of a 7cm x 10 cm dish filled with porous medium and nanoparticles located at the top of the dish which are then dragged down by a magnet of 0.8 T. The equations I used to design the model are the Magnetostatics (emqa), Convection and Diffusion (cd) and Brinkman Equations (chns). The model runs with the Magnetostatics and Convection and Diffusion equations, however, the Brinkman equations return the following error:

Messages:
Failed to evaluate variable jacobian
- Variable: Azyy
- Geometry: 1
- Subdomain: 4

The second derivative of the magnetic potential vector, Azyy, is a component of the force acting upon the nanoparticles and is part of the following equation:

F_ffx = K1*c*((Azy-Ayz)*(Azyx-Ayzx)+(Axz-Azx)*(Azyy-Ayzy)+(Ayx-Axy)*(Azyz-Ayzz))*chi_ff/(mu0*(1+chi_ff)^2) (N/m^3) where
F_ffx is the nanoparticle volume force in the x direction
K1, c, chi_ff, muo are constrants

I have built a similar model in 2D and my equations were similar but a lot more simplistic. Interestingly, I was able to run the 2D model for all equations including Brinkman's equations. I tried changing the geometry of the model as well as refining the mesh. I also checked the force equations (F_ffx, F_ffy and F_ffz) with my instructor. I am not sure what the problem is and I have tried to troubleshoot for the past few weeks. Any suggestions are welcome.

Sincerely,

Madelaine Daianu

PS: I attached two images illustrating the model setup and the magnetic flux density slide plots after solving for the Magnetostatics eqautions.