Fourier sine series for a triangular wave on a finite string

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Homework Help Overview

The discussion revolves around finding the Fourier coefficient Bn for a triangular wave on a finite string of length L = 8, which is fixed at both ends and initially displaced. Participants are exploring the appropriate mathematical representation for the initial displacement function U0(x).

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the form of the triangular displacement function, with suggestions for defining U0(x) in terms of linear equations over specified intervals. There are questions regarding the significance of the displacement's magnitude and its impact on the Fourier coefficient calculation.

Discussion Status

Some guidance has been offered regarding the representation of the triangular wave, with participants questioning the validity of previous suggestions and clarifying the correct form of the displacement function. Multiple interpretations of the displacement function are being explored without a clear consensus.

Contextual Notes

There is an emphasis on the constraints of the problem, particularly the fixed endpoints of the string and the nature of the initial displacement. Participants are also navigating the limitations of their responses in relation to homework policies.

nazmus sakib
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Homework Statement


A string of length L =8 is fixed at both ends. It is given a small triangular displacement and released from rest at t=0. Find out Fourier coefficient Bn.

Homework Equations



what should i use for U0(x) ?

The Attempt at a Solution


fourier sin.png
 
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Hello nazmus, :welcome:

ax from 0 to L/2 and x(1-x) from L/2 to L . Oops :nb), I'm not supposed/allowed to give direct answers !
 
nazmus sakib said:

Homework Statement


A string of length L =8 is fixed at both ends. It is given a small triangular displacement and released from rest at t=0. Find out Fourier coefficient Bn.

Homework Equations



what should i use for U0(x) ?
First, you need to know what the "small" displacement is. Let's say you lift the center by an amount ##h##, so the center of the string is at ##(\frac L 2,h)##. Now just find the equation of the two straight line segments forming the triangular displacement. Also, I would ignore BvU's answer which is a) discontinuous and b) partially parabolic.
 
LCKurtz said:
Also, I would ignore BvU's answer which is a) discontinuous and b) partially parabolic.
No, it was just a typo. I (of course) meant

ax from 0 to L/2 and a(L-x) from L/2 to L
And for the Fourier coefficient calculation it really doesn't matter how big a (or h) is.

All lin good spirit :smile:

Cheap, fast, and reliable. Pick any two.
 
Last edited:

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