1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Green's theorem or divergence theorem?

  1. Nov 30, 2011 #1
    Hi,

    I want to calculate the total flux but I'm not sure if I have to use Green's theorem (2D) or the divergence theorem (3D). The equation below is a modified Reynolds equation describing the air flow in the clearance of porous air bearing.

    [itex]\frac{\partial}{\partial\theta}(PH^3 \frac{\partial P}{\partial\theta}) +(\frac{R}{L})^2 \frac{\partial}{\partial Y}(PH^3 \frac{\partial P}{\partial Y}) - \Lambda \frac{\partial}{\partial\theta}PH + \Psi P (\frac{\partial P'}{\partial Z})_{Z=1} = 0[/itex]

    P is the pressure in the clearance of the air bearing, P' is the pressure in the porous media. However, at Z=1 P' must be equal to P for continuity.

    This equation can be rewritten using the divergence vector operation:

    [itex]\nabla\bullet\left[PH^3 \frac{\partial P}{\partial\theta} + (\frac{R}{L})^2 PH^3 \frac{\partial P}{\partial Y} - \Lambda PH + \Psi P P'\right] = 0[/itex]

    Solving this equation with a numerical method (i.e. finite difference) can be done by first simplifying the equation with Green's theorem for flux or the divergence theorem. Because I'm interested in the flow in the [math]\theta[/math] - Y direction I want to solve the equation applying Green's theorem (2D). However, in the first equation there is also a gradient in the Z-direction namely [itex]\Psi P (\frac{\partial P'}{\partial Z})_{Z=1}[/itex]. So my question is: Can I calculate the flux with Green's theorem or do I have to use the divergence theorem because of the pressure gradient in the Z-direction?
     
  2. jcsd
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Can you offer guidance or do you also need help?
Draft saved Draft deleted



Similar Discussions: Green's theorem or divergence theorem?
  1. Virial Theorem (Replies: 1)

  2. Physics Theorem? (Replies: 6)

  3. Noether's Theorem (Replies: 1)

  4. Uniqueness theorem (Replies: 1)

Loading...