scholarly journals Electromagnetic Scattering Model for Far Wakes of Ship with Wind Waves on Sea Surface

2021 ◽  
Vol 13 (21) ◽  
pp. 4417
Author(s):  
Letian Wang ◽  
Min Zhang ◽  
Jiong Liu
Keyword(s):  
Electromagnetic Scattering ◽  
Wind Waves ◽  
Sea Surface ◽  
Navier Stokes ◽  
Local Wind ◽  
Ship Wake ◽  
Scattering Model ◽  
Ship Wakes ◽  
Modulation Model ◽  
Sar Imagery

A comprehensive electromagnetic scattering model for ship wakes on the sea surface is proposed to study the synthetic aperture radar (SAR) imagery for ship wakes. Our model considers a coupling of various wave systems, including Kelvin wake, turbulent wake, and the ocean ambient waves induced by the local wind. The fluid–structure coupling between the ship and the water surface is considered using the Reynolds–averaged Navier–Stokes (RANS) equation, and the wave–current effect between the ship wake and wind waves is considered using the wave modulation model. The scattering model can better describe the interaction of the ship wakes on sea surface and illustrates well the features of the ship wakes with local wind waves in SAR images.

Near Field Electromagnetic Scattering Model Studying for Coarse Sea Surface

2013 ◽  
Vol 756-759 ◽  
pp. 4586-4590
Author(s):  
Jun Gu ◽  
Kun Cai ◽  
Zi Chang Liang
Keyword(s):  
Electromagnetic Scattering ◽  
Near Field ◽  
Horn Antenna ◽  
Measured Data ◽  
Sea Surface ◽  
Scattering Coefficient ◽  
Distributed Model ◽  
Echo Signal ◽  
Scattering Model ◽  
Rough Sea

The simulated PM-spectrum fractal sea surfaces and the 3-D near-field distributed model of horn antenna are built, the near-field formulas of KA method are deduced. The near-field scattering coefficient and the Doppler echo signal of rough sea surfaces are calculated, the agreement with measured data proved the correctness and validity of the near-field scattering model.

Effect of Ship-Induced Langmuir-Type Circulations on Distribution of Surface-Active Substances and Damping of Short Wind Waves

2019 ◽  
Author(s):  
Ryan Somero ◽  
Andre Basovich ◽  
Eric Paterson
Keyword(s):  
Surface Waves ◽  
Wind Waves ◽  
Sea Surface ◽  
Damping Factor ◽  
Surface Currents ◽  
Ship Wake ◽  
Damping Effect ◽  
Surface Active ◽  
Convergence And Divergence ◽  
Active Substances

It has recently been shown that the interaction of ship-generated nonuniform currents with ambient surface waves can lead to the generation of Langmuir-type circulations (LTCs) (Basovich 2011) and a persistent wake (Somero et al. 2018). Based on this work, it is shown here that the LTC and surface currents of the persistent wake are responsible for the redistribution of surface-active substances (SAS) and a corresponding change in the damping of short surface waves. The persistent wake is a region of the ship wake, where initial ship-generated perturbations have mostly decayed. The LTCs are similar in nature to Langmuir circulations which arise as a result of instability of wind-driven current. LTCs produce a secondary flow with velocity transverse to the direction of the ship, and width significantly larger than the ship beam. Because LTCs are generated in large scale, they persist for a long time after the passage of the ship. Transverse surface currents produced by LTCs in the ship wake redistribute the SAS films at the sea surface. These currents create strong convergence and divergence zones which in turn produce streaks with different concentrations of SAS. The change in concentration of SAS affects the film pressure and the damping effect of SAS on the short surface waves. This effect is represented by a damping factor and is a crucial parameter in determination of the spectral density of short wind waves. Therefore, the damping effect of the film, as represented by the damping factor, is responsible for sea surface roughness modification and is important for prediction of synthetic-aperture RADAR (SAR) imagery of ship wakes on the ocean surface. In this article, we present the mathematical and computational methods, along with simulation results for a naval surface combatant operating in calm, head, and following seas. The simulation results clearly show that the convergence and divergence zones strongly influence the relative SAS concentration and the spatial distribution of the damping factor, the latter of which defines the structure of SAR images of the persistent wake. Comparisons of the magnitude of the damping factor with available SAR data are shown to be in good agreement.

scholarly journals Ship Wakes and Their Potential Impacts on Salt Marshes in Jamaica Bay, New York

2020 ◽  
Vol 8 (5) ◽  
pp. 325
Author(s):  
Hoda El Safty ◽  
Reza Marsooli
Keyword(s):  
New York ◽  
Salt Marsh ◽  
Salt Marshes ◽  
Morphological Changes ◽  
Wind Waves ◽  
Sediment Supply ◽  
Aerial Photographs ◽  
Ship Wake ◽  
Jamaica Bay ◽  
Ship Wakes

Aerial photographs and field studies have revealed a rapid deterioration of salt marshes in Jamaica Bay, New York. Past studies have linked marsh deterioration to sediment supply, water quality, storms, and sea level rise. Yet ship wakes and their potential impacts on marsh edge erosion are not understood. Here, we study ship wake transformation in Jamaica Bay and their potential impacts on salt marsh erosion. We apply short-time, Fourier transform (spectrogram) on existing water level measurements collected during 2015 and 2016. Our analysis reveals the existence of typical wake components. Among the observed wake components is a long wave component which propagates over shallow areas where short wind waves do not reach. We further implement a phase-resolving wave model to study wake transformation in the vicinity of salt marsh islands Little Egg and Big Egg and the consequent morphological changes. The selected marshes are located near a deep shipping channel and a ferry station, making them exposed to wakes of vessels with different size and sailing speed. A series of numerical experiments show that ship wakes can result in erosion spots near the border of deep shipping channels and their banks, i.e., edges of mudflats and marsh substrates. We show that the cumulative erosion increases rapidly with the number of vessels that pass through the study area. For instance, the magnitude of final bed erosion after the passage of 10 vessels is two to three times larger than that after the passage of five vessels.

scholarly journals BOUSSINESQ MODELING OF SHIP-WAKES AND THEIR CONTRIBUTION TO COASTAL EROSION IN AN ADAPTIVE MESH REFINEMENT SYSTEM

2018 ◽  
pp. 25
Author(s):  
Fengyan Shi ◽  
Young-Kwang Choi ◽  
Matt Malej ◽  
Jane M. Smith ◽  
James T. Kirby
Keyword(s):  
Adaptive Mesh Refinement ◽  
High Speed ◽  
Large Scale ◽  
Wind Waves ◽  
Adaptive Mesh ◽  
Wave Generation ◽  
Physical Processes ◽  
Model Framework ◽  
Ship Wake ◽  
Ship Wakes

Heavy ship traffic causes a growing concern with respect to public safety, potential damage of coastal structures, and corresponding environmental impacts. High-speed ship-generated wakes such as solitons, undular bores, and breaking bores behave differently compared to wind waves and have a great potential for damage in vulnerable areas such as low-energy coasts and wetlands. In this study, we are developing a multi-grid model framework for the Fully Nonlinear Boussinesq Wave Model, FUNWAVE-TVD (Shi et al., 2012), for simulating ship-wakes in both the operational scale and refined process scales using full two-way coupling. Physical processes in areas of interest requiring higher model resolution, such as the ship-wake generation region, wave breaking in the near-field, and wave evolution with wave-structure interaction in the nearshore field, will be modeled in refined grids embedded in the operational-scale domain. A dynamically adaptive grid algorithm is implemented in order to track a vessel and calculate the physical processes precisely in the wave generation and breaking region in the vicinity of the vessel. Both pressure source and panel source methods for ship wave generation will be tested in the model framework. A concept of nesting layers based on the hierarchical basis, and an efficient parallelization method in the context of the full domain partition are utilized to allow the model to deal with a large-scale computation efficiently in a High Performance Computing (HPC) system.

scholarly journals Polarimetric Scattering from Two-Dimensional Dielectric Rough Sea Surface with a Ship-Induced Kelvin Wake

2016 ◽  
Vol 2016 ◽  
pp. 1-14 ◽  
Author(s):  
Pengju Yang ◽  
Lixin Guo
Keyword(s):  
Electromagnetic Scattering ◽  
Sea Surface ◽  
Two Dimensional ◽  
Ship Wake ◽  
Enhanced Backscattering ◽  
Rough Sea Surface ◽  
Configuration Simulation ◽  
Depolarized Scattering ◽  
Limited Surface ◽  
Rough Sea

Based on the polarimetric scattering model of second-order small-slope approximation (SSA-II) with tapered wave incidence for reducing the edge effect caused by limited surface size, monostatic and bistatic polarimetric scattering signatures of two-dimensional dielectric rough sea surface with a ship-induced Kelvin wake is investigated in detail by comparison with those of sea surface without ship wake. The emphasis of this paper is on an investigation of depolarized scattering and enhanced backscattering of sea surface with a ship wake that changes the sea surface geometric structure especially for low wind conditions. Numerical simulations show that in the plane of incidence rough sea surface scattering is dominated by copolarized scattering rather than cross-polarized scattering and that under low wind conditions a larger ship speed gives rise to stronger enhanced backscattering and enhanced depolarized scattering. For both monostatic and bistatic configuration, simulation results indicate that electromagnetic scattering signatures in the presence of a ship wake dramatically differ from those without ship wake, which may serve as a basis for the detection of ships in marine environment.

scholarly journals Non-Linear Modeling of Detectability of Ship Wake Components in Dependency to Influencing Parameters Using Spaceborne X-Band SAR

2021 ◽  
Vol 13 (2) ◽  
pp. 165
Author(s):  
Björn Tings
Keyword(s):  
Incidence Angle ◽  
Support Vector ◽  
Wave Direction ◽  
Linear Modeling ◽  
Movement Velocity ◽  
Transverse Waves ◽  
Ship Wake ◽  
Ship Wakes ◽  
Wake Detection ◽  
Sar Imagery

The detection of the wakes of moving ships in Synthetic Aperture Radar (SAR) imagery requires the presence of wake signatures, which are sufficiently distinctive from the ocean background. Various wake components exist, which constitute the SAR signatures of ship wakes. For successful wake detection, the contrast between the detectable wake components and the background is crucial. The detectability of those wake components is affected by a number of parameters, which represent the image acquisition settings, environmental conditions or ship properties including voyage information. In this study the dependency of the detectability of individual wake components to these parameters is characterized. For each wake component a detectability model is built, which takes the influence of incidence angle, polarization, wind speed, wind direction, sea state (significant wave height, wavelength, wave direction), vessel’s velocity, vessel’s course over ground and vessel’s length into account. The presented detectability models are based on regression or classification using Support Vector Machines and a dataset of manually labelled TerraSAR‑X wake samples. The considered wake components are: near‑hull turbulences, turbulent wakes, Kelvin wake arms, Kelvin wake’s transverse waves, Kelvin wake’s divergent waves, V‑narrow wakes and ship‑generated internal waves. The statements derived about wake component detectability are mainly in good agreement with statements from previous research, but also some new assumptions are provided. The most expressive influencing parameter is the movement velocity of the vessels, as all wake components are more detectable the faster vessels move.

ИССЛЕДОВАНИЯ АКУСТИЧЕСКИХ ХАРАКТЕРИСТИК ВЕРХНЕГО СЛОЯ МОРЯ МЕТОДОМ МНОГОЧАСТОТНОГО АКУСТИЧЕСКОГО ЗОНДИРОВАНИЯ

2020 ◽  
Author(s):  
V.A. Bulanov ◽  
I.V. Korskov ◽  
A.V. Storozhenko ◽  
S.N. Sosedko
Keyword(s):  
High Frequency ◽  
Wave Motion ◽  
High Spatial Resolution ◽  
Wind Waves ◽  
Acoustic Parameter ◽  
Sea Surface ◽  
Near Surface ◽  
Acoustical Properties ◽  
Acoustic Spectroscopy ◽  
Sea Bottom

Описано применение акустического зондирования для исследования акустических характеристик верхнего слоя моря с использованием широкополосных остронаправленных инвертированных излучателей,устанавливаемых на дно. В основу метода положен принцип регистрации обратного рассеяния и отраженияот поверхности моря акустических импульсов с различной частотой, позволяющий одновременно измерятьрассеяние и поглощение звука и нелинейный акустический параметр морской воды. Многочастотное зондирование позволяет реализовать акустическую спектроскопию пузырьков в приповерхностных слоях моря,проводить оценку газосодержания и получать данные о спектре поверхностного волнения при различных состояниях моря вплоть до штормовых. Применение остронаправленных высокочастотных пучков ультразвукапозволяет разделить информацию о планктоне и пузырьках и определить с высоким пространственным разрешением структуру пузырьковых облаков, образующихся при обрушении ветровых волн, и структуру планктонных сообществ. Участие планктона в волновом движении в толще морской воды позволяет определитьпараметры внутренних волн спектр и распределение по амплитудам в различное время.This paper represents the application of acoustic probingfor the investigation of acoustical properties of the upperlayer of the sea using broadband narrow-beam invertedtransducers that are mounted on the sea bottom. Thismethod is based on the principle of the recording of thebackscattering and reflections of acoustic pulses of differentfrequencies from the sea surface. That simultaneouslyallows measuring scattering and absorption of the soundand non-linear acoustic parameter of seawater. Multifrequencyprobing allows performing acoustic spectroscopy ofbubbles in the near-surface layer of the sea, estimating gascontent, and obtaining data on the spectrum of the surfacewaves in various states of the sea up to a storm. Utilizationof the high-frequency narrow ultrasound beams allows us toseparate the information about plankton and bubbles and todetermine the structure of bubble clouds, created during thebreaking of wind waves, along with the structure of planktoncommunities with high spatial resolution. The participationof plankton in the wave motion in the seawater columnallows determining parameters of internal waves, such asspectrum and distribution of amplitudes at different times.

Kelvin and V-like Ship Wakes Affected by Surfactants

2001 ◽  
Vol 45 (02) ◽  
pp. 150-163
Author(s):  
Gregory Zilman ◽  
Touvia Miloh
Keyword(s):  
Cross Section ◽  
Single Layer ◽  
Ship Wake ◽  
Backscattering Cross Section ◽  
Alternative Approach ◽  
Ship Wakes ◽  
Half Angle ◽  
Radar Backscattering ◽  
The Green Function ◽  
Theoretical Results

Synthetic aperture radar (SAR) ship wake images in light wind and calm sea conditions frequently appear in the form of a bright V with a half-angle of 2 to 3 deg. Sophisticated and conflicting explanations of this phenomenon, based on the Bragg scattering mechanism, have been proposed. There is a belief that the narrow V-wake is not a part of the Kelvin wake. An alternative approach, which is not generally accepted, suggests that short divergent Kelvin waves may contribute to the V-wake imaging although these waves are mixed with unsteady surface waves generated by the ship-induced turbulence. Ship-generated divergent waves contaminated by surfactants and their radar backscattering cross section are studied. The hull of the ship is represented by a single layer of hydrodynamic singularities. The Green function of a point source moving below a free surface covered by surfactants is derived. A closed-form asymptotic solution for the far ship wave wake is obtained. It is used to calculate analytically the corresponding radar backscattering cross section. The radiative, viscous, and surfactant-induced decay of the V-wake brightness along the V-arms is discussed. The theoretical results are compared against available experimental data.

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