Converting surface integral to line

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SUMMARY

The discussion focuses on converting a surface integral involving a velocity vector \(\mathbf{v}\) and a function \(f_i\) over a triangular area ABC into a line integral using Stokes' theorem. The integral is expressed as \(\mathbf{v}\cdot \int_{AB}{f_id\mathbf{l}} + I_s\), where \(I_s\) represents the flux across the edges BC and AC. The key challenge is understanding how to apply Stokes' theorem, which relates the line integral around the boundary of a surface to the curl of a vector field over that surface.

PREREQUISITES
  • Understanding of vector calculus, specifically Stokes' theorem.
  • Familiarity with surface integrals and line integrals.
  • Knowledge of gradient and curl operators in vector fields.
  • Basic concepts of flux in the context of vector fields.
NEXT STEPS
  • Study Stokes' theorem in detail, including its applications in vector calculus.
  • Learn how to compute line integrals and surface integrals for vector fields.
  • Investigate the properties of curl and gradient operators in three-dimensional space.
  • Explore examples of converting surface integrals to line integrals in physics and engineering contexts.
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Students and professionals in mathematics, physics, and engineering who are working with vector calculus, particularly those dealing with fluid dynamics and electromagnetism.

Niles
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Homework Statement


I have the following integral
<br /> \int_{ABC}{\mathbf{v}\cdot \nabla f_id\sigma}<br />
where $d\sigma$ is an area element, $\mathbf v$ is a velocity vector and f_i some function. The integral is performed across a triangle ABC and it is assumed that f is linear.

In my book this integral becomes
<br /> \mathbf v\cdot \int_{AB}{f_id\mathbf l} + I_s,<br />
where I_s is the flux across BC and AC. Can someone explain to me how this integral is solved?
 
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Use "Stoke's theorem" that you should remember from Calculus:
\oint_C \vec{f}\cdot d\vec{r}= \int_\sigma\int \nabla\times\vec{f}dS
where C is the boundary of surface \sigma.
 
HallsofIvy said:
Use "Stoke's theorem" that you should remember from Calculus:
\oint_C \vec{f}\cdot d\vec{r}= \int_\sigma\int \nabla\times\vec{f}dS
where C is the boundary of surface \sigma.

Hi HallsofIvy

Thanks, I remember that. But the RHS is in terms of a rotation operatir, not the gradient as I have.
 

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