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Re: Infinite expression, NDSolve
Posted:
Oct 16, 2012 10:49 PM


Your problem is twofold, I think. One is the obvious numerical singularity at r=0. Here you could try using r=0.00001 or some such to get around it, but care must be taken. The second problem is the inconsistency of the boundary conditions T[1,t]= and T[r,0]==0.
Kevin
On 10/16/2012 3:25 AM, Grasley wrote: > Dear All, > > I am trying to use NDSolve to solve the heat equation for 1D radial flow in cylindrical coordinates, with the initial condition of a spatially constant temperature, and boundary conditions of zero flux at r=0 (axisymmetry) and a constant temperature at a radius of 1. Here is the code: > > NDSolve[{D[T[r, t], t] == 1/r*D[r D[T[r, t], r], r], > Derivative[1, 0][T][0, t] == 0, T[1, t] == 20, T[r, 0] == 0}, T, {r, > 0, 1}, {t, 0, 10}] > > Power::infy: Infinite expression 1/0. encountered. >> > > Infinity::indet: Indeterminate expression 0. ComplexInfinity encountered. >> > > Power::infy: Infinite expression 1/0. encountered. >> > > Infinity::indet: Indeterminate expression 0. ComplexInfinity encountered. >> > > NDSolve::ndnum: Encountered nonnumerical value for a derivative at t == 0.`. >> > > I've tried using nonzero (i.e. very small values) for the initial time and in place of r=0 in the boundary condition, but to no avail. Any ideas? > > Thanks! >



