TAILIEUCHUNG - Waves in fluids and solids Part 8

Tham khảo tài liệu 'waves in fluids and solids part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 164 Waves in Fluids and Solids bottom right middle right and upper right above the water sediment interface. At all depths the particles follow retrograde elliptical movements. The ellipses are close to circular in this case since the eccentricity is close to zero. For harder sediment the ellipses are more elongated. Figure 4 shows the same plots as in Figure 3 but for the particle displacements in the bottom. The penetration depth in the solid is larger than the wavelength of the Scholte wave. At depth z upper right the particles follow a retrograde elliptical movements while at depth z middle right the particle movement follows a vertical line and at depth z middle right the particle movement is a prograde ellipse. Fig. 3. Particle displacements in the water left and the particle orbits at depth z bottom right middle right and upper right for a Scholte wave at a water sediment interface. Arrows show the directions of the movement. Equations 35 show that all the vertical wave numbers are imaginary and therefore the signal amplitudes decrease exponentially with increasing distance from the interface. A consequence of the imaginary vertical wave numbers is that interface waves cannot be excited by incident plane waves. This can be easily understood by considering the grazing angle of the wave in the uppermost medium. This angle is expressed as k cp0 cos b0 -- 1. cP vp 52 Equation 52 means that the angle 00 must be imaginary and consequently cannot be the incident angle of a propagating plane wave. However the interface waves can be excited by a point source close to the interface that is as a near-field effect. The interface waves are confined to a narrow stratum close to the interface which means that they have cylindrical propagation loss . 1 r rather than spherical spreading loss . 1 r2 as would be true of waves from a point source located in a medium of infinite extent. Cylindrical .

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