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Animations |
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![]() The interaction of
an oblique plane wave with an interface separating a fluid medium from
an isotropic medium causes a reflected
wave in the fluid medium and two transmitted
waves in the solid medium:
a longitudinal wave L (the particles vibrate in the
propagation
direction of the wave) and a shear vertical wave SV (the
particles
vibrate in the direction perpendicular to the propagation direction of
the wave).
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The
whole field in the fluid medium, which is the summation of the incident
and reflected fields, has always a stationary
character in the direction perpendicular to the interface
(following x3), and a propagative
character in the direction of the interface dans la direction de
l'interface (following x1).
![]() ![]() ![]() ![]() The whole field in the solid medium is the summation of the longitudinal and of the shear fields, each one propagating following its respective propagation direction. |
Generally
speaking, the propagation velocity cf
of the waves in a fluid medium is inferior to that of the waves in a
solid medium, and thus cf<cT<cL
where cL and cT are the
velocities of the longitudinal and shear waves respectively. In this case,
there exist two values for the incident angle, denoted respectively
![]() ![]() ![]() ![]() - When
![]() ![]() ![]() - When
![]() ![]() ![]() - When
![]() ![]() ![]() An evanescent
transmitted wave propagates in a direction parallel to
the interface, while its amplitude has an exponential decreasing with
the depth (when x3 increases), in a direction
perpendicular to the
interface.
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The
cartographies below represent the amplitude of the real part of the
projection on the x3-axis of the stress vector (T33)
which corresponds, in the fluid medium, corresponds to the opposite of
the acoustic pressure; color level (red = maximum, blue = minimum). The oblique black lines represent incident, reflected and transmitted rays, as they are predicted by Snell-Descartes' laws: when the transmitted waves are propagative ( ![]() ![]() ![]() |
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Incident angle inferior to both
critical angles
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Longitudinal transmitted wave,
alone,
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Shear transmitted wave, alone,
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Summation of the longitudinal and
of the shear fields (transmission)
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Incident angle included between
the two critical angles ![]() ![]() ![]() |
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Longitudinal transmitted wave,
alone, ![]() ![]() ![]() ![]() |
Shear transmitted wave, alone, ![]() ![]() ![]() ![]() |
Summation of the longitudinal and
of the shear fields (transmission) ![]() ![]() ![]() ![]() |
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Incident angle superior to both
critical angles
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Summation of the longitudinal and
of the shear fields (transmission) ![]() ![]() ![]() ![]() |