Standing waves

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Mechanisms

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Concept

Mechanisms

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Analogy position and time

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Boundary conditions

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The solution to the wave equation

$\displaystyle\frac{\partial^2 u}{\partial t^2}= c ^2\displaystyle\frac{\partial^2 u}{\partial x^2}$



is of the form

$ z = z_0 e^{ i( k s - \omega t )}$



but it must satisfy the conditions of free or fixed edge. In the edge case

- free wave can move but has no support so the stress and thus the deformation must be zero.
- fixed the wave cannot move but it can generate tension and with it deformation

Graphically, we have

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Standing waves

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The equation



It means that there are two solutions.

$\omega = \pm c k$



so the solution is of the form

$x_0 e^{ikx}(e^{i\omega t)}+e^{-i\omega t})$



or with Euler's relation the real part is

$2x_0 \cos(kx)\cos(\omega t)$



In other words, a function of the position oscillates in the same place without moving:

This is called a standing wave.

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Solution modes

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Las condiciones de borde permiten soluciones que tienen mas nodos como se ve en el ejemplo fijo-libre

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Model

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Variables

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Calculations


First, select the equation: to , then, select the variable: to

Calculations

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Equations

#
Equation

$ z = z_0 e^{ i( k s - \omega t )}$

z = z_0 * exp( %i *( k * s - omega * t ))


$\displaystyle\frac{\partial^2 u}{\partial t^2}= c ^2\displaystyle\frac{\partial^2 u}{\partial x^2}$

@DIF( u , t , 2) = c ^2*@DIF( u , x , 2)

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Wave equation

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La ecuación de movimiento

$\displaystyle\frac{\partial^2 u_i}{\partial t^2}=\displaystyle\frac{ E }{ \rho }\displaystyle\frac{\partial^2 u_i}{\partial x^2}$



con la relación

$ c ^2 = \displaystyle\frac{ E }{ \rho }$



representa la ecuación de onda del solido

$\displaystyle\frac{\partial^2 u}{\partial t^2}= c ^2\displaystyle\frac{\partial^2 u}{\partial x^2}$

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General solution of the wave equation

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The general solution of the wave equation

$\displaystyle\frac{\partial^2 u}{\partial t^2}= c ^2\displaystyle\frac{\partial^2 u}{\partial x^2}$



can be written in the complex space as

$ z = z_0 e^{ i( k s - \omega t )}$

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