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Ocean Acoustics and Helmholtz Equation
Published in Prem K. Kythe, An introduction to BOUNDARY ELEMENT METHODS, 2020
Internal waves, generated inside the ocean medium, are similar to surface waves, except that they are gravity waves with varying vertical displacement depending on variations in density with depth and temperature or between two water masses of different densities. The motion of internal waves can be noticed both below and above this interface. The material velocity variations in these waves have, in general, a lesser acoustic effect than temperature variations. The vertical and horizontal components of the material velocity for a long–crested wave in deep water are usually totally orbital near the water surface (Fig. 7.1). The depth dependence of the displacement amplitude a is given by a=a0e−2πz/λ, where a0 is the incident wave amplitude at the surface, z the depth, and λ the surface wavelength. Besides this type of well defined underwater motion, there always is the turbulent motion which is non-isotropic (independent of direction). There also exists an isotropic turbulent motion which depends on depth and surface conditions. We shall, however, not study turbulent motion at all.
The offshore environment
Published in White David, Cassidy Mark, Offshore Geotechnical Engineering, 2017
Another class of gravity waves present in the oceans are internal waves. Internal waves oscillate within, rather than on the surface of, a fluid medium. Internal ocean waves typically act along the interface between the warm upper ocean waters and the colder, saltier, therefore denser and deeper ocean waters. The so-called thermocline typically occurs between water depths of 100–200 m but internal waves have been measured at water depths of 1,000 m with a wave height of 60 m (Gerwick 2007). The density variation in the layers of water adjacent to the thermocline is considerably less than the density variation at the air–water interface; therefore, the restoring force and hence the energy to initiate and propagate internal waves is less than for surface waves. Internal waves travel slower than surface waves, with typical periods of several minutes (although periods of several hours have been measured in the open ocean), compared with typical wind wave periods of 5–15 seconds and typical swell periods of 20–30 seconds.
Chapter 1: Physical Processes
Published in Gunnar Kullenberg, Pollutant Transfer and Transport in the Sea, 1982
Gunnar Kullenberg, Gunnar Kullenberg
Internal waves are very prominent features of the oceanic motion and manifest themselves by considerable vertical oscillations of the density profile (Figure 6). The waves are influenced by vertical variations of the stratification and by horizontal currents. Phillips42 summarized recent observations and showed that the frequency and wave number spectra had slopes near –2 over a fairly large range. The frequency ω is limited to the range f ≤ ω ≤ N, where f is the Coriolis parameter and N the Brunt Väisälä frequency. The amplitude can be considerable, up to several tens of meters. Internal waves can be generated by slowly moving atmospheric pressure disturbances, by an advecting pattern of surface stress, by flow over an irregular bottom topography, and by an oscillating current (e.g., due to tides), encountering the continental slope. On the basis of available observations, Garrett and Munk43,44 suggested a universal internal wave spectrum for the deep water.
Safety analysis of deep-sea mining pipeline deployment operations considering internal solitary waves
Published in Marine Georesources & Geotechnology, 2022
Rongyao Wang, Guoming Chen, Xiuquan Liu, Nan Zhang, Wei Liu
With the increasing shortage of land resources and the continuous progress of deep-sea engineering technology, seabed mineral resources have become a hot topic. Underwater transportation pipeline is a vulnerable component in deep-sea mining system and easily affected by marine environmental loads. Internal solitary waves (also called internal waves) is a crucial risk factor for offshore operation. In 2006, the Discoverer 534 platform encountered internal waves during its drilling operation in the South China Sea, resulting in excessive platform offset and thus cementing failure (Wang et al. 2015). In 2011, the West Aquarius platform experienced a strong internal wave of 4.1 m/s during the oil & water refilling operation of a well in the South China Sea, leading to the fracture of the transmission pipeline (Hu, Liu, and Chen 2015). In May 2013, Nanhai No.8 platform confronted an internal wave of more than 2 m/s during its drilling operation in the South China Sea, causing structural damage to the tension rope and telescopic joint of the platform (Liu and Hu 2015).
A dynamic model of deep water riser and its global response characteristics induced by ocean internal wave and floating platform
Published in Ships and Offshore Structures, 2021
Lei Guo, Menglan Duan, Zongming Zhu
Internal wave is a kind of underwater wave which usually occurs in layered media, and it has a wave process like surface wave along the water interface of different densities. If the stratified flow meets a sudden change of seabed topography, the steady-state stratified water has a large vertical fluctuation, and then a large downward trough (internal wave) is formed (Ali et al. 2020). The formation of heterogeneous water layer in the ocean is usually due to the stratification of seawater temperature (Rudnick et al. 2013). When the main thermocline in the ocean medium is driven by strong wind, tide and current, an internal wave is also formed (see Figure 1). So, the generation of internal waves is related to the temperature fluctuation of the main thermocline in most cases (Haren and Puig 2017).
Synthetic aperture radar image simulation of the internal waves excited by a submerged object in a stratified ocean
Published in Waves in Random and Complex Media, 2020
Letian Wang, Min Zhang, Jiakun Wang
As a submerged object moves in a stratified ocean, internal waves are generated. The waves could impact the sea surface by altering its elevation and velocity field on the surface. The wakes can spread far beyond the ocean with long wavelength and lasting duration, which makes it able to be observed in synthetic aperture radar (SAR) images [1,2]. The wake patterns are quite important for target detection that can be used to calculate the travel speed, submerged depth and direction of the object, thus the remote sensing of submarine wakes is a crucial technology in submerged target nonacoustic detection.