[ff3d-users] diffusion eqn and Reflecting Boundary condition.

[Debasis Dan]

Hello !
   I am trying to solve a simple time dependent chemical diffusion 
equation inside a box containing an opaque object (no chemical can diffuse 
inside) say a small sphere. The boundary condition is d/dn (c) = 0 on all
boundary surface including the outer bounding box. My initial condition is 
a sharp gaussian ditribution at an arbitrary point. 
 d/dt (theta) = div(grad(theta))
   So I use the definition domain(S,outside(<1,0,0>)); where <1,0,0> is my 
embedded sphere.   
Then I loop this small code :

 solve(theta) in Omega by M 
   {
      pde(theta)
      theta-div(dt*grad(theta)) = theta0;
      dnu(theta) = 0 on <1,0,0> ;
      dnu(theta) = 0 on M ;
   };

   theta0 = theta ;

But I find that chemical is diffusing inside my embedded object. Can you 
please tell me how to overcome this problem.  

Regards,
Debasis Dan

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                                Debasis Dan
                             Swain Hall West 117
                            Department of Physics 
                             Indiana University
                           Bloomington, IN 47405
                           Phone:      812-855-2441
                           Fax  :      812-855-5533
                           Email : address@hidden
    
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