Laplace equation with irregular boundaries

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Discussion Overview

The discussion revolves around the possibility of solving Laplace's Equation on irregular domains, specifically in the context of a 2D parabolic plate. Participants explore the existence of analytical methods, the applicability of separation of variables, and the prevalence of irregular geometries in real-life problems.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant inquires about analytical methods for solving Laplace's Equation on irregular domains, questioning the feasibility of such solutions and the reasons behind any limitations.
  • Another participant suggests that solutions can often be found using coordinates where the Laplacian separates, and mentions the use of orthogonal function systems and generalized Fourier series.
  • There is a discussion about the special nature of the 2D case, where complex functions and conformal mappings may provide elegant solutions.
  • A participant asks whether separation of variables can be applied to irregular boundaries defined by functions and seeks clarification on the frequency of encountering irregular geometries in practical scenarios.
  • It is noted that separation of variables is typically applicable only when boundaries are constant in one of the coordinates, with specific examples provided for Cartesian and cylindrical coordinates.
  • Another participant emphasizes that irregular boundaries are common in real life, often necessitating the use of numerical techniques, while also highlighting the value of solving simpler textbook problems for gaining insights.

Areas of Agreement / Disagreement

Participants express differing views on the applicability of analytical methods for irregular domains, with some suggesting that numerical techniques are often required. The discussion remains unresolved regarding the potential for analytical solutions in such cases.

Contextual Notes

Limitations include the dependence on specific coordinate systems for the separation of variables and the unresolved nature of whether analytical methods can be effectively applied to irregular boundaries.

physwiz222
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TL;DR
We can solve Laplace’a Equation on regular shapes like squares and circles but what if we have an irregular shape can it still be solved
Is there a way to solve Laplace’s Equation on irregular domains if the domain’s shape is given by a function for example a 2D parabolic plate. I keep seeing numerical methods but I want to know is there an ANALYTICAL method to solve it on an irregular domain. If there isn't are there approximate analytical methods to solve it. If it isn't solvable why not.
 
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Usually you need coordinates, where the Laplacian "separates". Then you can find solutions of boundary-value problems by expansion in terms of the corresponding orthogonal function systems (generalized Fourier series).

The 2D case is special since there you can apply the very elegant formulation in terms of complex functions and conformal mappings.

A good book about all this is

P. M. Morse, H. Feshbach, Methods of Theoretical Physics, 2 Vols., McGraw-Hill (1953)
 
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vanhees71 said:
Usually you need coordinates, where the Laplacian "separates". Then you can find solutions of boundary-value problems by expansion in terms of the corresponding orthogonal function systems (generalized Fourier series).

The 2D case is special since there you can apply the very elegant formulation in terms of complex functions and conformal mappings.

A good book about all this is

P. M. Morse, H. Feshbach, Methods of Theoretical Physics, 2 Vols., McGraw-Hill (1953)
Interesting but one more question can separation of variables be used for a solution on an irregular boundary given by a function. And how common are irregular geometries encountered in real life problems
 
Last edited:
vanhees71 said:
Usually you need coordinates, where the Laplacian "separates". Then you can find solutions of boundary-value problems by expansion in terms of the corresponding orthogonal function systems (generalized Fourier series).

The 2D case is special since there you can apply the very elegant formulation in terms of complex functions and conformal mappings.

A good book about all this is

P. M. Morse, H. Feshbach, Methods of Theoretical Physics, 2 Vols., McGraw-Hill (1953)
How about the 3D case
 
physwiz222 said:
Interesting but one more question can separation of variables be used for a solution on an irregular boundary given by a function. And how common are irregular geometries encountered in real life problems
For The Laplace equation you can only use separation of variables when the boundaries are on surfaces where one of the coordinates is a constant. In Cartesian coordinates, the boundaries must be x=constant or y=constant or z=constant. In cylindrical coordinates the boundaries must be r=constant, z=constant or theta=constant. Etc.

In real life it is common to have irregular boundaries, and we usually must resort to numerical techniques. However, solving the simple problems in textbooks and examining properties of the solutions often yields a lot of insight to help with understanding those real-life cases.
 
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