Heat flow in semi inifinite wall: Dirichlet problem or separate variables?

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SUMMARY

The discussion centers on solving the two-dimensional heat equation for a semi-infinite wall defined by the region \(A = \{(x,y) | 0 < x < 1, 0 < y < \infty\}\). The problem is approached using two methods: separation of variables with Fourier Series and the Dirichlet problem, which simplifies to Laplace's equation in a stationary regime. The participant explores conformal transformations to adjust the boundary conditions and attempts to express the solution in polar coordinates, ultimately seeking guidance on determining constants A and B under the given contour conditions.

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  • Understanding of the two-dimensional heat equation
  • Familiarity with Fourier Series and separation of variables
  • Knowledge of Laplace's equation and Dirichlet boundary conditions
  • Experience with conformal transformations and polar coordinates
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  • Study the application of Fourier Series in solving boundary value problems
  • Research methods for solving Laplace's equation in semi-infinite domains
  • Learn about conformal mapping techniques in mathematical physics
  • Explore the use of contour conditions in determining constants in differential equations
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Students and professionals in applied mathematics, physics, and engineering who are dealing with heat transfer problems, particularly those involving boundary value problems and differential equations.

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Homework Statement



The plane region defined by [tex]\[A = \left\{ {(x,y)/0 < x < 1,0 < y < \infty } \right\}\][/tex] defines the profile of a semi infinite wall, where there's a stationary regime heat flow. The left and right sides are isolated at 15º, and the base is isolated at 0º. Find T(x,y) in each point of the wall.

Homework Equations



Two-dimensional Heat equation: [tex]\[\frac{{{\partial ^2}T}}{{\partial {x^2}}} + \frac{{{\partial ^2}T}}{{\partial {y^2}}} = \frac{{\partial T}}{{\partial t}}\][/tex]

Image

ico65l.jpg


The Attempt at a Solution



This problem got me thinking, because it's done either one of two ways: either I treat it as a problem of separate variables and use Fourier Series, or I treat it as a differential geometry problem (Dirichlet problem, since in stationary regime the heat equation becomes Laplace's equation). I tried thinking of it as a Dirichlet problem.

If I treat it as a differential geometry problem, I have to use conform transformations. First I have to multiply the whole thing by [tex]\[\pi \][/tex], so that then the wall has its sides at x = 0 and x = [tex]\[\pi \][/tex] (the base remains at y = 0, and it remains semi infinite). Then I have to traslate it [tex]\[ - \frac{\pi }{2}\][/tex], so that now the sides are at x = [tex]\[ - \frac{\pi }{2}\][/tex] and x = [tex]\[\frac{\pi }{2}\][/tex].

So far, I transformed [tex]\[x + iy\][/tex] into [tex]\[\left( {\frac{\pi }{2}x - \frac{\pi }{2}} \right) + i\frac{\pi }{2}y\][/tex]. Now, I've only seen this kind of problem in which there are 3 contour conditions being solved by applying the transform sin(z). If I do that, then I transform the strip into Im(z) > 0, now I have transformed [tex]\[x + iy\][/tex] into [tex]\[\sin \left( {\frac{\pi }{2}x - \frac{\pi }{2}} \right)\cosh \left( {\frac{\pi }{2}y} \right) + i\cos \left( {\frac{\pi }{2}x - \frac{\pi }{2}} \right)\sinh \left( {\frac{\pi }{2}y} \right)\][/tex].

The image is then transformed into:

242y9mp.jpg


Now, using polar coordinates, T doesn't depend of the radius, [tex]\rho \[/tex], so [tex]\[{\nabla ^2}T = \frac{1}{\rho }\frac{{{\partial ^2}T}}{{\partial {\varphi ^2}}}\][/tex]. This means that [tex]\[T(x,y) = A\theta + B\][/tex].

But I can't go pass that. I don't know how to find A and B using the countour conditions.

Any ideas?
 
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Homework Statement



The plane region defined by [tex]\[A = \left\{ {(x,y)/0 < x < 1,0 < y < \infty } \right\}\][/tex] defines the profile of a semi infinite wall, where there's a stationary regime heat flow. The left and right sides are isolated at 15º, and the base is isolated at 0º. Find T(x,y) in each point of the wall.

Homework Equations



Two-dimensional Heat equation: [tex]\[\frac{{{\partial ^2}T}}{{\partial {x^2}}} + \frac{{{\partial ^2}T}}{{\partial {y^2}}} = \frac{{\partial T}}{{\partial t}}\][/tex]

Image

ico65l.jpg


The Attempt at a Solution



This problem got me thinking, because it's done either one of two ways: either I treat it as a problem of separate variables and use Fourier Series, or I treat it as a differential geometry problem (Dirichlet problem, since in stationary regime the heat equation becomes Laplace's equation). I tried thinking of it as a Dirichlet problem.

If I treat it as a differential geometry problem, I have to use conform transformations. First I have to multiply the whole thing by [tex]\[\pi \][/tex], so that then the wall has its sides at x = 0 and x = [tex]\[\pi \][/tex] (the base remains at y = 0, and it remains semi infinite). Then I have to traslate it [tex]\[ - \frac{\pi }{2}\][/tex], so that now the sides are at x = [tex]\[ - \frac{\pi }{2}\][/tex] and x = [tex]\[\frac{\pi }{2}\][/tex].

So far, I transformed [tex]\[x + iy\][/tex] into [tex]\[\left( {\frac{\pi }{2}x - \frac{\pi }{2}} \right) + i\frac{\pi }{2}y\][/tex]. Now, I've only seen this kind of problem in which there are 3 contour conditions being solved by applying the transform sin(z). If I do that, then I transform the strip into Im(z) > 0, now I have transformed [tex]\[x + iy\][/tex] into [tex]\[\sin \left( {\frac{\pi }{2}x - \frac{\pi }{2}} \right)\cosh \left( {\frac{\pi }{2}y} \right) + i\cos \left( {\frac{\pi }{2}x - \frac{\pi }{2}} \right)\sinh \left( {\frac{\pi }{2}y} \right)\][/tex].

The image is then transformed into:

242y9mp.jpg


Now, using polar coordinates, T doesn't depend of [tex]\rho[/tex], so then [tex]\[{\nabla ^2}T = \frac{1}{\rho }\frac{{{\partial ^2}T}}{{\partial {\varphi ^2}}}\][/tex]. This means that [tex]\[T(x,y) = A\theta + B\][/tex].

But I can't go pass that. I don't know how to find A and B using the countour conditions.

Any ideas?
 

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