How to apply divergence free (∇.v=0) in nodal finite element method?

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Discussion Overview

The discussion revolves around the application of the divergence-free condition (∇·v=0) in the nodal finite element method, particularly in the context of Maxwell's and Stokes equations. Participants explore methods to enforce this condition without resorting to edge elements, focusing on theoretical and practical aspects of implementation.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant expresses familiarity with boundary conditions but struggles with applying the divergence-free condition in nodal finite element methods, preferring not to use edge elements.
  • Another participant clarifies that divergence-free is not typically a boundary condition but a condition that must hold throughout the domain, suggesting that vector fields can be expressed to satisfy this condition automatically.
  • For 2D problems, the use of a stream function is proposed as a solution.
  • For 3D problems, a toroidal-poloidal decomposition is suggested as a method to enforce the divergence-free condition.
  • A participant inquires about the applicability of potential formulations for the curl-curl equations of Maxwell or Navier-Stokes equations in fluid flow.
  • Another participant requests an example of the Navier-Stokes equation using a stream function in finite element methods.

Areas of Agreement / Disagreement

Participants present multiple competing views on how to enforce the divergence-free condition, with no consensus reached on a singular method or approach.

Contextual Notes

The discussion does not resolve the specific mathematical steps or assumptions required for implementing the proposed methods, leaving these aspects open for further exploration.

Who May Find This Useful

Researchers and practitioners in computational fluid dynamics, finite element analysis, and those interested in the mathematical foundations of divergence-free conditions in physical equations.

mdn
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I know how to apply boundary condition like Dirichlet, Neumann and Robin but i have been struggling to apply divergence free condition for Maxwells or Stokes equations in nodal finite element method. to overcome this difficulties a special element was developed called as edge element but i don't want to use this element because my complete programming depends on the nodal base element.
 
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Divergence free is not usually a boundary condition; it is, certainly in both the examples you give, a condition which is true throughout the domain. The way to enforce it is to express your vector field in a manner which satisfies the condition automatically.

For 2D problems, use a stream function.

For 3D problems, you can use a toroidal-poloidal decomposition.
 
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Can I use such potential formulation for curl, curl equation of Maxwell or Navier- Stokes equation in fluid flow?
 
Would you give me the example of NS equation using stream function in fem?
 

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