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Pol Grasland-Mongrain edited The_absorption_of_the_laser__.tex
over 8 years ago
Commit id: 2115cdd8897f2d8b6bb43f1047ab4edac49ed3b4
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To calculate the propagation of the displacement along space and time, we have to take into account the dilatation along X and Y axis which lead to stronger displacements than along Z. We modeled thus the thermoelastic regime as two opposite forces during 100 $\mu$s directed along Y axis with a depth of 100 $\mu$m and decreasing linearly from 2.5 to 0 mm (respectively -2.5 to 0 mm) \cite{Davies_1993}. Propagation as a shear wave along Z axis was calculated using Green operators $G_{yz}$ as calculated by Aki Richards \cite{aki1980quantitative}:
\begin{equation}
G_{yz} (r,\theta,z,t)= \frac{\cos \theta \sin \theta}{4\pi \rho c_p^2 r} f(t-\frac{r}{c_p}) - \frac{\sin \theta \cos \theta}{4\pi \rho c_s^2 r} f(t-\frac{r}{c_s}) + \frac{3\cos \theta \sin \theta}{4\pi \rho r^3} \int_{r/c_p}^{r/c_s}{\tau
f_{NF}} f_{NF}(t) dt}
\label{eq:Gyz}
\end{equation}
where $\theta$ is the angle between the applied force and the considered point (r,$\theta$,z), $c_p$ and $c_s$ the compression and shear wave speed respectively, $\tau$ the time and
$f_{NF}$ $f_{NF}(t)$ representing near-field effects. The three terms correspond respectively to the far-field compression wave, the far-field shear wave and the near-field component.
Displacements are then computed by convoluting $G_{yz}$ with time and spatial extent of the force $H_y$ : $u_z=G_{yz}*H_y$.