Engineering Acoustics/Time-Domain Solutions

d'Alembert Solutions
In 1747, Jean Le Rond d'Alembert published a solution to the one-dimensional wave equation.

The general solution, now known as the d'Alembert method, can be found by introducing two new variables:

$$\xi=ct-x\,$$ and $$\eta=ct+x\,$$

and then applying the chain rule to the general form of the wave equation.

From this, the solution can be written in the form:

$$y(\xi,\eta)= f(\xi)+g(\eta)\,=f(x+ct)+g(x-ct)$$

where f and g are arbitrary functions, that represent two waves traveling in opposing directions.

A more detailed look into the proof of the d'Alembert solution can be found [http://mathworld.wolfram.com/dAlembertsSolution.html here. ]

Example of Time Domain Solution
If f(ct-x) is plotted vs. x for two instants in time, the two waves are the same shape but the second displaced by a distance of c(t2-t1) to the right.

The two arbitrary functions could be determined from initial conditions or boundary values.

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