| Summary: | 碩士 === 國立中山大學 === 海下科技暨應用海洋物理研究所 === 101 === Internal waves occur in the interface between two layers of fluids with density
stratification. In order to better understand the characteristics of continuous internal
waves, a series of experiments were conducted in a laboratory tank. The upper and
lower layers are fresh water of 15 cm thick and salt water of 30 cm thick, respectively.
The periods of internal waves are 2.5, 5.5 and 6.6 sec. A micro-ADV is used to
measure velocity profiles. Wave profiles at the density interface and the free surface
are monitored respectively by an ultrasonic and capacitance wave gauges. Our results
indicate that particle velocities (u and w) above and below the density interface have
opposite directions. The speed is peaked near the density interface and it becomes
weaker further away from the interface. Empirical Mode Decomposition is used to
remove noise from the observed particle velocities, and the period is consistent with
those derived from the interface elevations. The observed particle velocities also
compare favorably with the theoretical results.
When internal waves propagate without the interference of a sloping bottom, the
turbulence induced is rather insignificant. The turbulence is more significant only near
the density interface. With the existence of a sloping bottom, the internal waves
gradually shoal and deform, the crest becomes sharp and steep, finally the waves
become unstable, break and overturn. In this study the effect of bottom slope and the
steepness of internal waves on the reflectivity of incoming waves are investigated.
The reflectivity is smaller with gentler slope, and it increases and reaches a constant
value with steeper slopes. The observed energy dissipation rateεis higher near the
slope. Three methods were used to estimate the energy dissipation rate and shear
stress; namely, the inertial dissipation, the TKE and auto-correlation method. Theε
estimated from the auto-correlation method is larger than that from the other two
methods, but their trend is similar. The energy dissipation rate is found to increase
with a gentler sloping bottom.
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