scholarly journals Generation of internal solitary waves in a pycnocline by an internal wave beam: a numerical study

2011 ◽  
Vol 676 ◽  
pp. 491-513 ◽  
Author(s):  
N. GRISOUARD ◽  
C. STAQUET ◽  
T. GERKEMA
Keyword(s):  
Solitary Waves ◽  
Western Europe ◽  
Numerical Study ◽  
Western Indian Ocean ◽  
Internal Solitary Waves ◽  
Generation Process ◽  
Hydrostatic Model ◽  
Direct Generation ◽  
Local Generation ◽  
Selection Of

Oceanic observations from western Europe and the south-western Indian ocean have provided evidence of the generation of internal solitary waves due to an internal tidal beam impinging on the pycnocline from below – a process referred to as ‘local generation’ (as opposed to the more direct generation over topography). Here we present the first direct numerical simulations of such a generation process with a fully nonlinear non-hydrostatic model for an idealised configuration. We show that, depending on the parameters, different modes can be excited and we provide examples of internal solitary waves as first, second and third modes, trapped in the pycnocline. A criterion for the selection of a particular mode is put forward, in terms of phase speeds. In addition, another simpler geometrical criterion is presented to explain the selection of modes in a more intuitive way. Finally, results are discussed and compared with the configuration of the Bay of Biscay.

scholarly journals Internal solitary wave generation by tidal flow over topography

2018 ◽  
Vol 839 ◽  
pp. 387-407 ◽  
Author(s):  
R. Grimshaw ◽  
K. R. Helfrich
Keyword(s):  
Froude Number ◽  
Solitary Waves ◽  
Vries Equation ◽  
Tidal Flow ◽  
Phase Speed ◽  
Wave Generation ◽  
Equation Model ◽  
Internal Solitary Waves ◽  
Generation Process ◽  
De Vries

Oceanic internal solitary waves are typically generated by barotropic tidal flow over localised topography. Wave generation can be characterised by the Froude number $F=U/c_{0}$, where $U$ is the tidal flow amplitude and $c_{0}$ is the intrinsic linear long wave phase speed, that is the speed in the absence of the tidal current. For steady tidal flow in the resonant regime, $\unicode[STIX]{x1D6E5}_{m}<F-1<\unicode[STIX]{x1D6E5}_{M}$, a theory based on the forced Korteweg–de Vries equation shows that upstream and downstream propagating undular bores are produced. The bandwidth limits $\unicode[STIX]{x1D6E5}_{m,M}$ depend on the height (or depth) of the topographic forcing term, which can be either positive or negative depending on whether the topography is equivalent to a hole or a sill. Here the wave generation process is studied numerically using a forced Korteweg–de Vries equation model with time-dependent Froude number, $F(t)$, representative of realistic tidal flow. The response depends on $\unicode[STIX]{x1D6E5}_{max}=F_{max}-1$, where $F_{max}$ is the maximum of $F(t)$ over half of a tidal cycle. When $\unicode[STIX]{x1D6E5}_{max}<\unicode[STIX]{x1D6E5}_{m}$ the flow is always subcritical and internal solitary waves appear after release of the downstream disturbance. When $\unicode[STIX]{x1D6E5}_{m}<\unicode[STIX]{x1D6E5}_{max}<\unicode[STIX]{x1D6E5}_{M}$ the flow reaches criticality at its peak, producing upstream and downstream undular bores that are released as the tide slackens. When $\unicode[STIX]{x1D6E5}_{max}>\unicode[STIX]{x1D6E5}_{M}$ the tidal flow goes through the resonant regime twice, producing undular bores with each passage. The numerical simulations are for both symmetrical topography, and for asymmetric topography representative of Stellwagen Bank and Knight Inlet.

scholarly journals Source site of internal solitary waves in the northern South China of westward shoaling thermocline

2017 ◽  
Author(s):  
Gang Wang ◽  
Yuanling Zhang ◽  
Chang Zhao ◽  
Dejun Dai ◽  
Min Zhang ◽  
...  
Keyword(s):  
Solitary Waves ◽  
South China ◽  
General Circulation ◽  
Northern South China Sea ◽  
Three Dimensional ◽  
Circulation Model ◽  
Internal Solitary Waves ◽  
Generation Process ◽  
The West ◽  
Source Site

Abstract. This study use a three dimensional general circulation model, MITgcm with non-hydrostatic option, to study the source site of internal solitary waves (ISWs) observed in the northern South China Sea. Simulation reveals that besides Luzon Strait, ISWs in the northern SCS are also generated around Dongsha Islands and near the continental shelf break. It is one of the reasons that there are more wave package to the west of 120° E in SAR images, and even more to the west of 118° E. The generation process and propagation feature of ISWs in these source sites are described.

scholarly journals NONLINEAR OBLIQUE INTERACTION OF LARGE AMPLITUDE INTERNAL SOLITARY WAVES

2012 ◽  
Vol 1 (33) ◽  
pp. 19
Author(s):  
Keisuke Nakayama ◽  
Taro Kakinuma ◽  
Hidekazu Tsuji ◽  
Masayuki Oikawa
Keyword(s):  
Solitary Waves ◽  
Water Waves ◽  
Large Amplitude ◽  
Numerical Study ◽  
Incident Angle ◽  
Resonant Interaction ◽  
Internal Solitary Waves ◽  
Weakly Nonlinear ◽  
Wave Angle ◽  
The One

Solitary waves are typical nonlinear long waves in the ocean. The two-dimensional interaction of solitary waves has been shown to be essentially different from the one-dimensional case and can be related to generation of large amplitude waves (including ‘freak waves’). Concerning surface-water waves, Miles (1977) theoretically analyzed interaction of three solitary waves, which is called “resonant interaction” because of the relation among parameters of each wave. Weakly-nonlinear numerical study (Funakoshi, 1980) and fully-nonlinear one (Tanaka, 1993) both clarified the formation of large amplitude wave due to the interaction (“stem” wave) at the wall and its dependency of incident angle. For the case of internal waves, analyses using weakly nonlinear model equation (ex. Tsuji and Oikawa, 2006) suggest also qualitatively similar result. Therefore, the aim of this study is to investigate the strongly nonlinear interaction of internal solitary waves; especially whether the resonant behavior is found or not. As a result, it is found that the amplified internal wave amplitude becomes about three times as much as the original amplitude. In contrast, a "stem" was not found to occur when the incident wave angle was more than the critical angle, which has been demonstrated in the previous studies.

scholarly journals Reflecting tidal wave beams and local generation of solitary waves in the ocean thermocline

2007 ◽  
Vol 593 ◽  
pp. 297-313 ◽  
Author(s):  
T. R. AKYLAS ◽  
R. H. J. GRIMSHAW ◽  
S. R. CLARKE ◽  
ALI TABAEI
Keyword(s):  
Continental Shelf ◽  
Solitary Waves ◽  
Numerical Solutions ◽  
Wave Beam ◽  
Incident Beam ◽  
Tidal Wave ◽  
Internal Solitary Waves ◽  
Long Wave ◽  
Lower Fluid ◽  
Local Generation

It is generally accepted that ocean internal solitary waves can arise from the interaction of the barotropic tide with the continental shelf, which generates an internal tide that in turn steepens and forms solitary waves as it propagates shorewards. Some field observations, however, reveal large-amplitude internal solitary waves in deep water, hundreds of kilometres away from the continental shelf, suggesting an alternative generation mechanism: tidal flow over steep topography forces a propagating beam of internal tidal wave energy which impacts the thermocline at a considerable distance from the forcing site and gives rise to internal solitary waves there. Motivated by this possibility, a simple nonlinear long-wave model is proposed for the interaction of a tidal wave beam with the thermocline and the ensuing local generation of solitary waves. The thermocline is modelled as a density jump across the interface of a shallow homogeneous fluid layer on top of a deep uniformly stratified fluid, and a finite-amplitude propagating internal wave beam of tidal frequency in the lower fluid is assumed to be incident and reflected at the interface. The induced weakly nonlinear long-wave disturbance on the interface is governed in the far field by an integral-differential equation which accounts for nonlinear and dispersive effects as well as energy loss owing to radiation into the lower fluid. Depending on the strength of the thermocline and the intensity of the incident beam, nonlinear wave steepening can overcome radiation damping so a series of solitary waves may arise in the thermocline. Sample numerical solutions of the governing evolution equation suggest that this mechanism is quite robust for typical oceanic conditions.

An Iterative Updating Method for Dynamic Responses of a Floating Platform Under Action of Internal Solitary Waves

2019 ◽  
Author(s):  
Wang Junrong ◽  
Du Junfeng ◽  
Zhang Min ◽  
Chang Anteng
Keyword(s):  
South China Sea ◽  
Solitary Waves ◽  
South China ◽  
Numerical Study ◽  
Ocean Current ◽  
Internal Solitary Waves ◽  
Floating Structures ◽  
Oil Companies ◽  
China Sea ◽  
Fluid Body

Abstract The internal solitary waves, have properties of two-way shear profile, significant velocity and acceleration, etc., which threaten the safety of deepwater floating systems in South China Sea (SCS), for the frequent occurrence and the high intensity of internal solitary waves in SCS. In recent years, offshore oil companies of China encountered many strong internal waves during its deepwater oil and gas exploration and development activities in South China Sea. However, the action mechanism of ISWs to floating structures is not understood clearly, and the internal solitary waves are classified as ocean current in API RP 2SK (3rd edition), therefore engineers ignore the velocity variance and long period “wave” characteristics in the design of floating structures. Furthermore, the offshore floating structures is oscillating under the action of environmental forces, due to the horizontal velocity of the platform is comparative to that of ISWs, thus fluid-body coupling is significant that one cannot analyse it by simply adding a specified ISW force time history to the floater. This paper proposes a new iterative updating method for ISW loading calculation considering the fluid-body coupling, and applied this method to a semi MODU, numerical study shows the iteration is efficient and the result is more reasonable compared to conventional method, and it is found that the maximal offset decreases significantly.

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