On 3/10/20 12:59 PM, Krishnakumar Gopalakrishnan wrote:
Step-22 has a strong-sounding stub-like statement:/"In practice, one wants to impose as little regularity on the pressure variable as possible".
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The above one-liner (fairly enough) assumes domain knowledge. As a new entrant to deal.ii (haven't studied fluid mechanics before), may I ask the following?

 1. Why do we impose as little regularity on the pressure as possible?

We do the same on the velocity. That's why we integrate by parts the form
  \int v (-Delta u)
to
  \int \nabla v . \nabla u


 2. When I attempt to solve my own PDE (outside traditional areas such
    as fluid or structural mechanics), what properties should I know
    about the field variable to correctly apply the procedure and
    learnings from this tutorial, i.e. what exactly is the regularity
    condition mentioned here?

You'll have to take a second course on PDEs, and most importantly learn a bit about the theory of weak solutions. Here's a patch that explains this in about as much detail as I would like to go into:
  https://github.com/dealii/dealii/pull/9652/files

Best
 W.


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Wolfgang Bangerth          email:                 bange...@colostate.edu
                           www: http://www.math.colostate.edu/~bangerth/

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