Learning PDEs from Scratch in 24 Hours

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Homework Help Overview

The discussion revolves around learning partial differential equations (PDEs) from scratch, with a focus on specific problems and methods such as separation of variables and Fourier series. The original poster expresses a need for guidance on starting these questions, particularly regarding boundary conditions and the application of various mathematical techniques.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning, Problem interpretation, Assumption checking

Approaches and Questions Raised

  • Participants discuss the method of separation of variables and the use of Fourier series. There are questions about boundary conditions and how to apply them, as well as uncertainty regarding the definitions of terms like "complimentary solution." Some participants explore the implications of imaginary roots in the context of ordinary differential equations (ODEs).

Discussion Status

Participants are actively engaging with the problems, offering suggestions and checking each other's reasoning. There is a mix of interpretations regarding the application of methods, and some participants are clarifying their understanding of the mathematical concepts involved. Guidance has been provided on checking solutions and the structure of particular solutions.

Contextual Notes

There is a sense of urgency as the original poster is preparing for a test within a short timeframe. Some participants note the importance of correctly identifying the function f(x) and its relationship to the Fourier expansion, indicating potential confusion in the problem setup.

  • #31
ehh my head's not working, i should go to bed soon.

mVXNF.jpg


question 4. no clue.
H and L are just arbitrary points on the y and x-axis respectively, i presume..
what do each of those initial constraints mean, please?
and how do i know what is insulated?
 
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  • #32
ok found some stuff in my notes.
i think the du/dx (0,y) = 0 line tells you that something is insulated.

i've done some question in my book (obviously lecturer has done it and i was merely copying it, lol), and i have written down:

uxx + uyy = 0
u(0,y) = 0
u(a,y) = 0
u(x,0) = x (maintain temp-profile 'x')
du/dy (x,0) = 0 -> temp gradient perpendicular to side on bottom is zero, ie. no heat can flow across side => INSULATED


i might've missed something because my graph has a 'b', and i see no b's written in the question, but main thing is that from this i can gather that with question 4, the du/dx (0,y) = 0 line tells me that something is insulated :)

now to find out what side is insulated...
 
  • #33
du/dx (0,y) = 0
so, gradient at 0,y is equal to 0?
would this be just the y-axis (up to point H) that is insulated?
 
  • #34
FMJYk.jpg


from there onwards, i simply cannot understand what worked solutions are doing >_<
 
  • #35
in you question i think a=L, b=H as you have
0<x<L, 0<y<H

the insulated side is the one where the derivative is held at zero,
 

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