Generation Of Internal Waves Research Articles

Experimental investigation of elevation internal solitary wave propagation over a ridge

The propagation of elevation internal solitary waves (ISWs) over a large triangular ridge was investigated experimentally in a stratified fluid flume. The propagation characteristics of the elevation ISWs over the ridge were measured by using the real-time wave measuring instrument and particle image velocimetry, respectively. At the front slope of the ridge, the obvious fluid accumulation appeared, the waveform was distorted and broadened, the ISW amplitude increased slightly, the phase velocity decreased suddenly, and the lower layer flow velocity increased significantly. In the region of the ridge top, counterclockwise vortex and bright spots appeared, which signified the occurrence of breaking, the shape of incident wave was transferred to the shape of table-top solitary wave. At the back slope of the ridge, the fission waves became symmetric gradually and restored to normal, the amplitude decreased significantly, and the phase velocity increased slightly. The wave energy decreased consistently during wave propagation and the whole energy loss was about 30%–35% of the incident wave. Due to the wave breaking and fission, the energy loss occurred near the ridge top was the largest and was almost the same at symmetrical positions on the front and back slopes.

Study on prediction of internal solitary waves propagation in the southern Andaman Sea

The prediction of internal solitary waves (ISWs) propagation is a difficult problem in the field of oceanography due to the complexity of its generative mechanism and the lack of in-situ data. In this paper, the simulation data is used to establish a prediction model of ISWs propagation in the southern Andaman Sea by deep learning. The global tidal model TPXO7.2 is used to obtain the semi-diurnal tidal velocity data at the generation source of ISWs. The generation and propagation characteristics of ISWs are obtained by the Massachusetts Institute of Technology General Circulation Model (MITgcm). The generative location, amplitude, and propagation characteristics of the ISWs are calculated based on MITgcm. The database is set up by the extracted data from MITgcm. Then, the prediction model of ISWs propagation is established using long and short-term memory (LSTM) networks. Finally, the accuracy of the model is verified by the ISWs Moderate Resolution Imaging Spectroradiometer (MODIS) images of the southern Andaman Sea and in-situ data. The results demonstrate that, compared with the MODIS images, the average relative error of time predicted by the LSTM model is 17.81%, and the average absolute error is 0.95 h. The average relative error of longitude predicted by the LSTM model is 0.10%, and the average absolute error is 0.10°. The average of the amplitudes predicted by the LSTM model is 56.99 m. The in-situ data of the amplitude of ISWs is 60 m in the previous research. The two amplitudes are relatively close.

Local null controllability of a model system for strong interaction between internal solitary waves

In this paper, we prove the local null controllability property for a nonlinear coupled system of two Korteweg–de Vries equations posed on a bounded interval and with a source term decaying exponentially on [Formula: see text]. The system was introduced by Gear and Grimshaw to model the interactions of two-dimensional, long, internal gravity waves propagation in a stratified fluid. We address the controllability problem by means of a control supported on an interior open subset of the domain and acting on one equation only. The proof consists mainly on proving the controllability of the linearized system, which is done by getting a Carleman estimate for the adjoint system. While doing the Carleman, we improve the techniques for dealing with the fact that the solutions of dispersive and parabolic equations with a source term in [Formula: see text] have a limited regularity. A local inversion theorem is applied to get the result for the nonlinear system.

Non-hydrostatic model for internal wave generations and propagations using immersed boundary method

A non-hydrostatic model is developed to predict internal wave generations and propagations. The model employs a semi-implicit, fractional step algorithm to solve the governing equations based on the Cartesian grid system. Immersed boundary method is incorporated to deal with the complex geometry of uneven bottoms. The combination of the z-level vertical coordinate and the immersed boundary method enables the model to treat uneven bottoms and meanwhile to avoid numerical errors in the calculation of the baroclinic pressure force. To consider the effect of stratification, a variant of the Smagorinsky sub-grid scale model is employed to calculate the eddy viscosity and diffusivity. The capability of the model in resolving internal wave generation by tidal forcing over an idealized Gaussian-shaped topography is firstly validated by comparing the developed model with a terrain-following non-hydrostatic model. Then, two laboratory-scale test cases involving internal solitary wave propagations over variable topographies are considered. It can be found that the model captures the main characteristics of waveform evolution including internal hydraulic jump, wave breaking and waveform inversion. Thus, the proposed model provide an alternative to simulate internal wave generations and propagations.

Vortex generation due to internal solitary wave propagation past a sidewall constriction

Abstract

Abstract P804: Lopsided Blood-Thinning Drug Increases the Risk of Internal Flow Choking and Shock Wave Generation Causing Asymptomatic Stroke

Introduction: Consequence of lopsided blood-thinning-drug, lowering blood-viscosity (BV), is bleeding and very frequently asymptomatic-hemorrhage (AH) and the acute-heart-failure (AHF) happen. V.R.S.Kumar et al. (2020) reported that such asymptomatic episodes are due to the internal flow choking in the cardiovascular system (CVS) at a critical blood pressure ratio (BPR), which is regulated by biofluid/blood heat capacity ratio (BHCR). Methods: The closed-form-analytical-methodology is used for correlating BV, BPR, BHCR, vessel geometry and ejection fraction (EF). In vitro method is used for the BHCR estimation of healthy subjects. In silico method is used for demonstrating the Sanal flow choking. Results: The analytical models reveal that the relatively high and low BV are risk factors of internal flow choking. In vitro study shows that N 2 , O 2 , CO 2 & Ar gases are predominant in fresh-blood samples of the healthy subjects at a temperature range of 37-40 0 C (98.6-104 0 F), which increases the risk of flow-choking. In silico results demonstrated the Sanal flow choking followed by the shock wave generation and pressure-overshoot in a simulated artery with the divergent/bifurcation region. Conclusions: An overdose of blood-thinning drug reduces BV and increases Reynolds number causing high-turbulence leading to the Sanal flow choking. Asymptomatic stroke could be diminished by concurrently lessening the BV and flow turbulence by rising thermal tolerance level in terms of BHCR or by decreasing the BPR. In conclusion, BPR must always be lower than 1.8257 as dictated by the lowest BHCR of the evolved gas (CO 2 ) for prohibiting asymptomatic stroke.

Robust propagation of internal coastal Kelvin waves in complex domains

Internal coastal Kelvin waves were experimentally generated in a two-layer fluid system on a rotating table. Waves are exponentially localized near the tank boundary and propagate in the same direction as the table rotation along boundaries of complex geometries without being scattered. Our experiments suggest a connection between these unusual wave characteristics and topological properties of the underlying governing equations.

Bäcklund transformation, infinite number of conservation laws and fission properties of an integro-differential model for ocean internal solitary waves

This paper presents an analytical investigation of the propagation of internal solitary waves in the ocean of finite depth. Using the multi-scale analysis and reduced perturbation methods, the integro-differential equation is derived, which is called the intermediate long wave (ILW) equation and can describe the amplitude of internal solitary waves. It can reduce to the Benjamin–Ono equation in the deep-water limit, and to the KdV equation in the shallow-water limit. Little attention has been paid to the features of integro-differential equations, especially for their conservation laws. Here, based on Hirota bilinear method, Bäcklund transformations in bilinear form of ILW equation are derived and infinite number of conservation laws are given. Finally, we analyze the fission phenomenon of internal solitary waves theoretically and verify it through numerical simulation. All of these have potential value for the further research on ocean internal solitary waves.

On the generation of internal waves by river plumes in subcritical initial conditions

Internal waves (IWs) in the ocean span across a wide range of time and spatial scales and are now acknowledged as important sources of turbulence and mixing, with the largest observations having 200 m in amplitude and vertical velocities close to 0.5 m s−1. Their origin is mostly tidal, but an increasing number of non-tidal generation mechanisms have also been observed. For instance, river plumes provide horizontally propagating density fronts, which were observed to generate IWs when transitioning from supercritical to subcritical flow. In this study, satellite imagery and autonomous underwater measurements are combined with numerical modeling to investigate IW generation from an initial subcritical density front originating at the Douro River plume (western Iberian coast). These unprecedented results may have important implications in near-shore dynamics since that suggest that rivers of moderate flow may play an important role in IW generation between fresh riverine and coastal waters.

A Machine-Learning Model for Forecasting Internal Wave Propagation in the Andaman Sea

Internal waves (IWs) are broadly distributed globally and have significant impacts on offshore engineering and underwater navigation. The prediction of IW propagation is a challenging task because of the complex factors involved. In this study, a machine-learning model was developed to predict IW propagation in the Andaman Sea. The model is based on a back-propagation neural network trained by 1189 IW samples, including the crest length and the peak-to-peak distance of IWs, extracted from 123 Moderate-Resolution Imaging Spectroradiometer (MODIS) images and 33 Ocean Land Color Instrument (OLCI) images acquired from 2015 to 2019 and corresponding ocean environment parameters. Using the leading wave crest within an IW packet as input, we ran the model to forecast the IW locations and compare them with satellite observations. The average root-mean-square difference between the model-forecasted and satellite-observed IW leading crest after one tidal cycle was 3.21 km. The corresponding averaged correlation coefficient was 0.95 and the average Fréchet Distance was 11.46 km. We reiterated the model run over two tidal periods and obtained similar statistical results, indicating the robustness of forecasting IW packets. We find that reducing the time step helped to improve forecasting accuracy. The influence of input errors and seasonal variations on model results are discussed and an analysis shows that the initial propagation direction introduced to the model is necessary for cross-propagating IW patterns. Comparisons with the Korteweg-de Vries equation results show that the developed model has better performance and is more robust.

Research on the modal intensity fluctuation during the dynamic propagation of internal solitary waves in the shallow water

内孤立波是一种常见于浅海海域的非线性内波, 具有振幅大、周期短和流速强等特点, 它通过扰动水体中的温盐分布使声速剖面产生明显的距离依赖性, 进而影响水下声传播特性. 内波自生成后通常以 O(1) m/s 量级的速度传播, 运动的内波使声传播路径上声波模态能量在空间和时间上剧烈起伏. 本文定义模态强度为模态系数模值(模态幅度)的平方, 并用其衡量各阶模态所含声能量的大小. 文中基于耦合简正波理论, 推导了内波运动时声波模态强度起伏的表达式, 将模态强度表征为振荡项和趋势项的线性叠加. 以往的工作大多局限于单独从时域或频域研究内波运动时声波模态强度的时变规律, 本文则结合短时傅里叶变换在时频平面上揭示了模态强度的起伏机理. 理论推导和数值仿真均表明内孤立波使各阶声波模态之间发生能量交换, 即模态耦合. 内波的动态传播进一步引起模态干涉, 这种干涉效应表现为模态强度中的振荡项并使模态强度随时间快速起伏. 受模态剥离效应(不同阶模态之间衰减系数的差异)的影响, 趋势项的幅度随时间不断变化, 进而对模态干涉引起的振荡叠加了时变的偏置. 模态强度的整体走势和振荡项中各频率分量振幅的时变特征均与模态衰减密切相关. 同时, 本文使用深度积分声强作为总接收声场强度的度量, 研究了内波运动时模态强度起伏对接收阵位置处声能量的影响. 结果表明, 能量较大且起伏剧烈的模态强度将主导总接收声强的变化.

Современные исследования динамики вод в северо-западной части Черного моря по данным LADCP

In this work a result of preliminary analysis of current measurements collected in fourteen large-scale expeditions of the Marine Hydrophysical Institute in 2016–2019 in the north-eastern part of the Black Sea is presented. It is shown that the use of the Lowered Acoustic Doppler Current Profiler (LADCP) significantly increases the information content of the expedition materials, opening up new opportunities in the experimental study of water dynamics. Based on the materials of the expeditions, it was found that the upper layer of shear baroclinic currents in the measurement area is limited by the isopycnic depth with a potential density of ~16.75 kg/m3 (~350 m). At this depth, the variability of the buoyancy frequency with the depth changes from a power-law to an exponential dependence. The same depth limits the penetration of seasonal variations of the average kinetic energy into the water column. The highest values of the average kinetic energy are observed in April-May and November–December, the lowest—in June–August. The ratio of the maximum energy values (summer) to its minimum values (spring, late autumn, winter) was ~3. The Rim Black Sea Current is most pronounced near the Crimean Peninsula in the spring and winter seasons. In summer and autumn, the horizontal distribution of the current velocity in depths of 30–80 m is less structured, which is caused by the seasonal intensification of mesoscale processes. At a number of stations, the current velocity profiles contain fragments with a well-defined harmonic variability of the current velocity components with depth, which can be interpreted as the manifestation of near-inertial internal waves. In most cases, the rotation of the current velocity vector with depth occurs clockwise, which determines the main direction of propagation of the inertial internal waves into the water column. The example of one of the stations shows the significant contribution of such waves to the value of shear. This fact suggests a significant influence of near-inertial internal waves on the processes of vertical turbulent exchange in the water column.

AN INTERNAL WAVE GENERATION METHOD FOR THE NON-HYDROSTATIC MODEL SWASH

Numerical wave propagation models are commonly used as engineering tools for the study of wave transformation in coastal areas. In order to simulate waves in the nearshore zone correctly, the generation and absorption of waves at the boundaries of the models need to be modelled accurately. In numerical models, incident waves are usually generated by prescribing their horizontal velocity component at the boundary of the computational domain over the vertical direction. Additionally, in order to absorb and to prevent re-reflections in front of the numerical wave generator, a weakly reflective wave generation boundary condition is applied in which the total velocity signal is a superposition of the incident velocity signal and a velocity signal of the reflected waves. However, this method is based on the assumption that the reflected waves are small amplitude shallow water waves propagating perpendicular to the boundary of the computational domain and hence this method is weakly reflective for directional and dispersive waves. Within the present study, an internal wave generation method combined with sponge layers is applied in the non-hydrostatic model SWASH, in order to more accurately generate waves and avoid re-reflections at the boundaries.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/5M3aU03XJvI

On the influence of magnetic topology on the propagation of internal gravity waves in the solar atmosphere.

The solar surface is a continuous source of internal gravity waves (IGWs). IGWs are believed to supply the bulk of the wave energy for the lower solar atmosphere, but their existence and role for the energy balance of the upper layers is still unclear, largely due to the lack of knowledge about the influence of the Sun's magnetic fields on their propagation. In this work, we look at naturally excited IGWs in realistic models of the solar atmosphere and study the effect of different magnetic field topographies on their propagation. We carry out radiation-magnetohydrodynamic simulations of a magnetic field free and two magnetic models-one with an initial, homogeneous, vertical field of 100 G magnetic flux density and one with an initial horizontal field of 100 G flux density. The propagation properties of IGWs are studied by examining the phase-difference and coherence spectra in the kh - ω diagnostic diagram. We find that IGWs in the upper solar atmosphere show upward propagation in the model with predominantly horizontal field similar to the model without magnetic field. In contrast to that the model with predominantly vertical fields show downward propagation. This crucial difference in the propagation direction is also revealed in the difference in energy transported by waves for heights below 0.8 Mm. Higher up, the propagation properties show a peculiar behaviour, which require further study. Our analysis suggests that IGWs may play a significant role in the heating of the chromospheric layers of the internetwork region where horizontal fields are thought to be prevalent. This article is part of the Theo Murphy meeting issue 'High-resolution wave dynamics in the lower solar atmosphere'.

Determination of Internal Waves Off the Coast of Morocco According to Earth Remote Sensing Data

This paper presents the results of a study of the internal wave isolation of the Northern coast of Morocco using synthetic aperture radar (SAR) images. A filter is applied to the remote sensing data to reduce the image grain, after which the direction of propagation of the wave is determined and its length is calculated. In most cases, internal waves appear on satellite images as quasi-periodic linear structures whose brightness is lower or higher than the background, which is well registered in the visible range and by synthetic aperture radar. When analyzing images off the coast of Morocco, internal waves were detected, the wave packet propagates in the direction from West to East. When comparing the obtained images with the bottom relief map, it can be assumed that the generation of internal waves is caused by the roughness of the bottom near the Northern coast of Morocco. The maximum wave length in the wave packet is almost 0.7 km, consists of at least 5 solitons, the prints of these solitons in the sea roughness area are visible in the images mainly in the Central part of a wave packet, the distance between a wave packet solitons is different. The wavelength decreases when moving to the back of a wave packet, which can be traced by changing the contrast on the site. As a result, internal waves were detected off the Northern coast of Morocco in rads images with a synthesized aperture, and the main characteristics of these waves were determined.

Numerical study on the interaction between the internal and surface waves by a 2D hydrofoil moving in two-layer stratified fluid

The water temperature in the ocean varies according to its depth and generates a thermocline layer. An internal wave can be excited by an object moving near the thermocline layer because the density changes owing to the water temperature. The internal wave propagates and interacts with the surface wave. This study aims to investigate the internal wave propagation in a two-layer stratified flow, generated by 2D hydrofoil (NACA0012) using a RANS based CFD model. Eulerian multiphase methods were used for the modeling of the two-layer stratified flow; Volume of Fluid (VOF) model and mixture model. A two-layer stratified fluid consisting of air(ρair)-water1(ρw1)-water2(ρw2) is considered instead of the thermocline layer to simplify the numerical simulations. The generation and propagation of the internal wave were investigated, with different configurations of the speed and submergence depth of the hydrofoil. The result suggested that the VOF model shows better agreement with the experimental data compared to the mixture model.

Generation of Internal Gravity Waves Far from Moving Non-Local Source

We consider analytical solutions describing the generation of internal gravity waves far from a non-local source of disturbances. We suppose that the source moves on the surface of stratified medium of a finite depth. A model distribution of the non-local source shape with radial symmetry is used. This approximation correctly describes (qualitatively) the main spatiotemporal characteristics of natural sources of generation of internal gravity waves in the ocean. The resulting solution is the sum of wave modes. The solution is presented as a series of eigenfunctions of the spectral problem of internal gravity waves. The results of numerical calculations of internal gravity waves components at different depths are presented and discussed.

On the accuracy of internal wave generation method in a non-hydrostatic wave model to generate and absorb dispersive and directional waves

The weakly reflective wave generation is a wave generation and absorption method in phase-resolving models, based on the assumption that the waves propagating towards the wave generation boundary are small amplitude shallow water waves with direction perpendicular to the boundary. This assumption makes the method weakly reflective for dispersive and directional waves. The internal wave generation method was proposed by Vasarmidis et al. (2019b) as an alternative, for the non-hydrostatic wave model, SWASH, to avoid reflections. In this study, a comparison is made between the performance of the new internal wave generation method and the weakly reflective wave generation method. It is shown that using the internal wave generation leads to a significantly more accurate prediction of the resulting wave field in case of waves reflected back to the numerical boundary. Additionally, the internal wave generation method is extended to short-crested waves and SWASH is validated for the first time with experimental data for the cases of wave propagation over a shoal and wave diffraction around a wall. The proposed extended internal wave generation method increases the capability of SWASH towards the study of wave propagation of highly dispersive short-crested waves in coastal environments with minimal reflection from the boundaries.

Internal Waves Formation and Propagation in the Persian Gulf

The Persian Gulf (PG), as a semi-enclosed water basin extends in[47-57] E, [24-30] N, geographic domain. Particularly, northern part of the PG shows more baroclinicity and turbulence because of the river inflow from the Arvand, bottom and costalstresses.Furthermore, wind stress has many effects rather than in mid deep domain of the PG. Thermocline development in the PG is observed because of studying the data measured in the Mt. Mitchell cruise in 1992 by different models from winter to summer. The studied turbulence in the northern part of the PG is navigated from winter to summer due to the internal wave’s activity and stability intensified through water column.

Generation of Internal Gravity Waves in the Thermosphere during Operation of the SURA Facility under Parametric Resonance Conditions

The problem of excitation of internal gravity waves (IGWs) in the upper atmosphere by an external source of a limited duration of operation is investigated. An isothermal atmosphere was chosen as the propagation environment of IGWs in the presence of a uniform wind that changes over time according to the harmonic law. For the vertical component of the displacement of an environment, the Mathieu equation with zero initial conditions was solved with the right part simulating the effect of a powerful heating facility on the ionosphere. In the case of a small amplitude of the variable component of the wind, the time dependence of the vertical displacement under parametric resonance conditions using the perturbation method is obtained. The obtained dependence of the solution of the differential equation on the parameters allows us to perform a numerical analysis of the problem in the case of variable wind of arbitrary amplitude. For practical estimations of the obtained values, data on the operating modes of the SURA heating facility (56.15° N, 46.11° E) with periodic (15–30 min) switching on during of 2–3 h for ionosphere impact were used.