| Author | Message | ||
     yi yang (yiyang) New member Username: yiyang Post Number: 1 Registered: 10-2005 |
in a electrostatic problem in fluid Here is my scripts DEFINITIONS eps=79 eps0=8.854e-12 EQUATIONS div(grad(V))= 0 Now I define a surface charge density as BOUNDARIES natural(v)=ChargeDensity/(eps*eps0) Is it right to define charge density like this ? Thank you! | ||
| Robert G. Nelson (rgnelson) Moderator Username: rgnelson Post Number: 525 Registered: 06-2003 |
For your PDE, the Natural BC defines the outward normal component of grad(V) at the boundary. [In any second order divergence term, it will be the outward normal component of the argument of the divergence.] The natural BC you have given therefore says normal(eps*eps0*grad(v)) = ChargeDensity If that's what you want, then you got it right. However, if you ever want to include more than one material, you must put the "eps" inside the divergence. Maxwell's equation says div(D)=rho, and the jump in eps will not be handled correctly unless it is inside the divergence. |