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Re: [Libmesh-users] oscillations boundary conditions example code 9

 Re: [Libmesh-users] oscillations boundary conditions example code 9 From: John Peterson - 2010-12-08 16:45:15 ```On Wed, Dec 8, 2010 at 10:13 AM, robert wrote: > after the solve, the initial data are all set to one. I only played with > the boundary conditions. So you are solving ex9 (convection-diffusion) with discontinuous data near the boundaries, and you are surprised there are oscillations? AFAIK even pure diffusion can display "ringing" when using Crank-Nicolson and discontinuous data... -- John ```

 [Libmesh-users] oscillations boundary conditions example code 9 From: robert - 2010-12-08 15:54:36 ```Hi, I have tried to modify example code 9. I am using a starting concentration of one everywhere but want to set the condition for one (or more) boundary to zero. for (unsigned int qp=0; qp
 Re: [Libmesh-users] oscillations boundary conditions example code 9 From: John Peterson - 2010-12-08 16:08:35 ```On Wed, Dec 8, 2010 at 9:53 AM, robert wrote: > Hi, > > I have tried to modify example code 9. I am using a starting > concentration of one everywhere but want to set the condition for one > (or more) boundary to zero. > > for (unsigned int qp=0; qp                { >                  //const Number value = exact_solution > (qface_points[qp](0), >                    // > qface_points[qp](1), >                      //                                 time); > >                  // RHS contribution >                  for (unsigned int i=0; i                    Fe(i) += 0.;//penalty*JxW_face[qp]*value*psi[i][qp]; > >                  // Matrix contribution >                  for (unsigned int i=0; i                    for (unsigned int j=0; j                      Ke(i,j) += > penalty*JxW_face[qp]*psi[i][qp]*psi[j][qp]; >                } > > > Well, at the boundaries I get the values which I want to have. However, > I also get strong oscillations. > I have also tried to just put the initial concentration to zero for a > small region within the domain. Again, I got oscillations (but less > intense). > What am I doing wrong here? You got oscillations... after a solve? In the initial data? -- John ```
 Re: [Libmesh-users] oscillations boundary conditions example code 9 From: John Peterson - 2010-12-08 16:45:15 ```On Wed, Dec 8, 2010 at 10:13 AM, robert wrote: > after the solve, the initial data are all set to one. I only played with > the boundary conditions. So you are solving ex9 (convection-diffusion) with discontinuous data near the boundaries, and you are surprised there are oscillations? AFAIK even pure diffusion can display "ringing" when using Crank-Nicolson and discontinuous data... -- John ```