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Help with nonlinear PDE

  1. Nov 7, 2015 #1
    Hello. I was wondering if anyone here had come across an equation similar to this one:
    [itex] \alpha(uu_x)_x= u_t [/itex]

    Any info regarding this equation or tips on how to solve this would be appreciated :)

    I came across these solutions: http://eqworld.ipmnet.ru/en/solutions/npde/npde1201.pdf, but how do I choose which one to use? I am looking at a initial value problem. And u > 0.
    Last edited: Nov 7, 2015
  2. jcsd
  3. Nov 7, 2015 #2


    Staff: Mentor

    I don't think the equation given in the link you posted will be helpful. The equation there is equivalent to ##a(w^m w_x)_x = w_t##.
    The only thing that comes to mind in your equation is to take the partial w.r.t x of the left side (using the product rule). That would leave you with ##\alpha[(u_x)^2 + uu_{xx}] = u_t##, although I'm not sure that gets you anywhere.
  4. Nov 7, 2015 #3


    User Avatar
    Homework Helper

    For [itex]\alpha > 0[/itex] this is a one-dimensional diffusion equation [tex]
    u_t - (Du_x)_x = 0
    [/tex] where the diffusivity [itex]D[/itex] is not constant, but is instead proportional to the density [itex]u[/itex] of the diffused quantity: [itex]D = \alpha u[/itex].

    You seem to be dealing with the case [itex]m = 1[/itex]. I don't think the given analytic solutions will help you, except for particular special cases of the initial condition. For generic initial conditions you must fall back on numerical methods.
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