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1

Characteristics of internal solitary waves in the Maluku Sea, Indonesia

Purwandana Adi, Cuypers Yannis

Oceanologia

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2023

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Vol. 65 (2)

333--342

EN

The appearance of internal solitary waves (ISWs) in the Maluku Sea is often captured by satellite imagery. However, no study has revealed details on this phenomenon to date. Here, the characteristics of such ISWs were investigated based on their appearance in synthetic aperture radar (SAR) imagery on 20 February 2015. Two different sources of ISW packets were observed: one packet propagating from the Lifamatola Passage and another from the Sangihe Passage. The vertical structure of the waves was constructed using the Korteweg-de Vries (KdV) model, which suggests an average phase speed of ∼2.8 and 2.7 m s−1 for the first and the second sources, respectively. ISWs originating from the first source had a typical amplitude of O(80 m), while those from the second source were characterized by a lower amplitude of O(40 m). The waves generated horizontal and vertical currents with typical magnitudes of O(1 m s−1) and O(10 cm s−1) for the first source and O(0.6 m s−1) and O(4 cm s−1) for the second source, respectively. The mean energy densities of the first and second sources reached 461 MJ m−1 and 185 MJ m−1, respectively. Single leading solitary wave contained a fraction of approximately 20% and 15% of the baroclinic tidal energy generated in the Lifamatola Passage and Sangihe Passage, respectively.

2

Numerical simulations of linearly stratified flow past submerged bodies

Ma W., Li Y., Ding Y., Hu K., Lan L.

Polish Maritime Research

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2018

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S 3

68--77

EN

In this study, a methodology was presented to predict density stratified flows in the near-field of submerged bodies. The energy equation in temperature form was solved coupled with momentum and mass conservation equations. Linear stratification was achieved by the definition of the density as a function of temperature. At first, verifications were performed for the stratified flows passing a submerged horizontal circular cylinder, showing excellent agreement with available experimental data. The ability of the method to cope with variable density was demonstrated. Different turbulence models were used for different Re numbers and flow states. Based on the numerical methods proposed in this paper, the stratified flow was studied for the real scale benchmark DAPRA Suboff submarine. The approach used the VOF method for tracing the free surface. Turbulence was implemented with a k − ω based Detached Eddy Simulation (DES) approach. The effects of submarine speed, depth and density gradient on the free surface wave pattern were quantitatively analyzed. It was shown that, with the increasing of the speed of the submarine, the wavelength and wave height of the free surface wave were gradually increasing. The wave height of the free surface wave was gradually reduced as the submarine’s depth increased. Relative to the speed and submarine depth, the changes of the gradient density gradient have negligible effects on the free surface wave field.

3

Numerical modeling of tsunami wave destruction and turbulent mixing at tsunami wave clash on the shore

Kshevetskii S., Vereshchagina I.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

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2016

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Vol. 20, No 2

157--169

EN

A numerical model of propagation of internal gravity waves in a stratified medium is applied to the problem of tsunami wave run-up onto a shore. In the model, the ocean and the atmosphere are considered as a united continuum in which the density varies with height with a saltus at the water-air interface. The problem solution is sought as a generalized (weak) solution; such a mathematical approach automatically ensures correct conditions of matching of the solutions used on a water-air interlayer. The density stratification in the ocean and in the atmosphere is supposed to be described with an exponential function, but in the ocean a scale of the density stratification takes a large value and the density changes slightly. The initial wave running to a shore is taken in the form of a long solitary wave. The wave evolution is simulated with consideration of the time-varying vertical wave structure. Near the shore, the wave breaks down, and intensive turbulent mixing develops in the water thickness. The wave breakdown effect depends on the bottom shape. In the case when the bottom slope is small and the inshore depth grows slowly with the distance from the shore, mixing happens only in the upper stratum of the fluid due to the formation of a quiet region near the bottom. When the bottom slope takes a sufficiently large value, the depth where fluid mixing takes place goes down up to 50 meters. The developed model shows that the depth of the mixing effects strongly depends on the bottom shape, and the model may be useful for investigation of the impact strong gales and hurricanes on the coastline and beaches.

4

Scattering of internal waves by vertical barrier in a channel of stratified fluid

Dolai P.

International Journal of Applied Mechanics and Engineering

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2015

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Vol. 20, no. 3

471--485

EN

The problem of two dimensional internal wave scattering by a vertical barrier in the form of a submerged plate, or a thin wall with a gap in an exponentially stratified fluid of uniform finite depth bounded by a rigid plane at the top, is considered in this paper. Assuming linear theory and the Boussinesq approximation, the problem is formulated in terms of the stream function. In the regions of the two sides of the vertical barrier, the scattered stream function is represented by appropriate eigen function expansions. By the use of appropriate conditions on the barrier and the gap, a dual series relation involving the unknown elements of the scattering matrix is produced. By defining a function with these unknown elements as its Fourier sine expansion series, it is found that this function satisfies a Carleman type integral equation on the barrier whose solution is immediate. The elements of the scattering matrix are then obtained analytically as well as numerically corresponding to any mode of the incident internal wave train for each barrier configuration. A comparison with earlier results available in the literature shows good agreement. To visualize the effect of the barrier on the fluid motion, the stream lines for an incident internal wave train at the lowest mode are plotted.