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Despite the high accuracy of conventional acoustic hydrographic systems, measurement of the seabed along coastal belts is still a complex problem due to the limitations arising from shallow water. In addition to traditional echo sounders, airborne LiDAR also suffers from high application costs, low efficiency, and limited coverage. On the other hand, remote sensing offers a practical alternative for the extraction of depth information, providing fast, reproducible, low-cost mapping over large areas to optimize and minimize fieldwork. Satellite-derived bathymetry (SDB) techniques have proven to be a promising alternative to supply shallow-water bathymetry data. However, this methodology is still limited since it usually requires in situ observations as control points for multispectral imagery calibration and bathymetric validation. In this context, this paper illustrates the potential for bathymetric derivation conducted entirely from open satellite data, without relying on in situ data collected using traditional methods. The SDB was performed using multispectral images from Sentinel-2 and bathymetric data collected by NASA's ICESat-2 on two areas of relevant interest. To assess outcomes' reliability, bathymetries extracted from ICESat-2 and derived from Sentinel-2 were compared with the updated and reliable data from the BathyDataBase of the Italian Hydrographic Institute. [ABSTRACT FROM AUTHOR]

Ship–seabed interaction is highly critical to ship safety and ship performance when ship operates over shallow water with uneven seabed. However, the prediction method for ship reaction is still yet to be fully developed. In this paper, a high-fidelity transient numerical simulation method with sliding mesh is developed based on computational fluid dynamics to model a vessel passing a step bank, demonstrating to be a computational cost economical solution. The comprehensive numerical model is validated and verified against benchmarked experimental and numerical studies, which is proved to be highly accurate in predicting force characteristics and wave development. Meanwhile, during the research the impulse effect generated by the step bank was found to have striking effects on the wave elevation, wake development and vessel sinkage. Five regions on the behaviour of vessel sinkage are defined in the present work. According to the result, the vessel will encounter the extreme sinkage after a relatively long distance (12 L pp at F h 2 = 0.519 ) passing the step bank instead of immediately. [ABSTRACT FROM AUTHOR]

The marine transient electromagnetic method is a valuable means for locating mineral resources because of its higher detection resolution as well as other advantages. However, this method is easily affected by the air layer and complex terrain, which significantly increase its calculation times. We addressed this problem by developing a three-dimensional finite-difference method based on the principle of correspondence between the diffusive and fictitious wave fields. Using a fast-iteration formula appropriate for a large time step, solving the Maxwell equations in a fictitious wave field, and the effects of air and seawater parameters on the electromagnetic response in shallow water are discussed. Choosing the first derivative of a Gaussian as a source, the 3D numerical simulation of transient electromagnetics in a shallow water area is realized. Comparing to the existing methods, the effectiveness of the proposed method is verified. The results show that this method enables fast and high-precision numerical calculations for 3D models and provides theoretical guidance for detecting seabed mineral resources in complex geological environments in shallow water. [ABSTRACT FROM AUTHOR]

Underwater acoustic power around a submerged body in shallow water was investigated using the Boundary Element Method (BEM). The model domain simulated a nearshore environment with shallow water conditions. The seabed was assumed flat and sound velocity was constant over depth. The boundary element method was combined with eigen function expansion to model radiation boundary conditions. Underwater acoustic power was calculated from the underwater acoustic potential in the domain. Several cases were investigated in this study: cases with variation of submerged body distance from the seabed, variation of submerged body location from the underwater acoustic source, and variation of submerged body length. [ABSTRACT FROM AUTHOR]

Regular surveys of coastal zone seabed deliver important information about geomorphologic processes such as silting of waterways. The recent introduction of the Sentinel series of sensors has allowed for the use of satellite sensing for shallow bathymetry morphology monitoring. In this context, this article presents a dedicated Geographic Information System for Baltic Sea shallow water depth monitoring on the basis of Sentinel-2 imagery. The system employs Geovisual Analytics for differential analysis of bathymetry changes as well as monitoring the visibility of known wrecks in the coastal waters of Southern Baltic Sea. Results are verified with regard to known changes in shallow water bathymetry between 28 June 2015 and 3 March 2017. [ABSTRACT FROM AUTHOR]

This paper aims at investigating the effect of bottom slope to the nonlinear triad interactions for irregular waves propagating in shallow water. The physical experiments are conducted in a wave flume with respect to the transformation of waves propagating on three bottom slopes (β = 1/15, 1/30, and 1/45). Irregular waves with different type of breaking that are mechanically generated based on JONSWAP spectra are used for the test. The obviously different variations of spectra measured on each bottom reveal a crucial role of slope effect in the energy transfer between harmonics. The wavelet-based bispectrum were used to examine the bottom slope effect on the nonlinear triad interactions. Results show that the different bottom slopes which waves are propagated on will cause a significant discrepancy of triad interactions. Then, the discussions on the summed bicoherence which denote the distribution of phase coupling on each frequency further clarify the effect of bottom slope. Furthermore, the summed of the real and imaginary parts of bispectrum which could reflect the intensity of frequency components participating in the wave skewness and asymmetry were also investigated. Results indicate that the value of these parameters will increase as the bottom slope gets steeper. [ABSTRACT FROM AUTHOR]

The free flexural vibration of a cylindrical shell horizontally immersed in shallow water is analyzed in low frequency range using the wave propagation approach. The effects of both the upper and lower fluid boundaries, i.e. , free surface and seabed, are considered with the image method, and the scattering effect of cylindrical shell is neglected. Motions of cylindrical shell and fluid are modeled with the Flügge shell theory and wave equation, respectively. The accuracy of present method is verified through comparison with available experimental works. The modal added mass is introduced to show the influence of shallow water on coupled modal frequency. The influence of shallow water is significant in the case of small water depth and it's the contributions from fluid boundaries. The presence of free surface (seabed) will make negative (positive) contribution to the modal added mass and finally result in the increase (reduction) of coupled modal frequency. But the individual fluid boundary effect will be reduced gradually and finally negligible when the distance between cylindrical shell and fluid boundary increases. The influence of shallow water can not be negligible when the water depth is less than 8 times of shell radius. This work will help to select proper test environment for submerged cylindrical shell. [ABSTRACT FROM AUTHOR]

In order to ensure the safe operation of a VLFS, a combination of mooring, breakwater and other motion reducing systems is employed. In the present work, the transient hydroelastic response of a floating, thin elastic plate, elastically connected to the seabed, is examined. The plate is modelled as an Euler-Bernoulli strip, while the linearized shallow water equations are used for the hydrodynamic modelling. Elastic connectors are approximated by a series of simple spring-dashpot systems positioned along the strip. A higher order finite element scheme is employed for the calculation of the hydroelastic response of the strip-connector configuration over the shallow bathymetry. After the definition of the initial-boundary value problem, its variational form is derived and discussed. Next, on the basis of the aforementioned formulation, an energy balance expression is obtained. The effect of variable bathymetry on the response of a two connector-strip system is examined by means of three seabed profiles featuring a flat bottom, an upslope and a downslope environment. For the flat bottom case, the strip response mitigating effect exerted by the employment of two and three elastic connectors is considered. Finally, by means of the derived energy balance equation, the energy exchange is monitored, providing a valuable insight into the transient phenomena that take place in the studied configurations. [ABSTRACT FROM AUTHOR]

• The importance of proper understanding of ship manoeuvrability in shallow water was discussed. • Ship manoeuvring behaviours were determined in various finite depth conditions in free running CFD platform. • The ratio of water depth to draft was identified as a key parameter to determine turning manoeuvring indices and trajectories. • It is highly believed to offer a practical insight into enhancing the ship manoeuvrability in a reliable way. The manoeuvring performance of a ship in shallow water is substantially different from its performance in deep water, attributed to shallow water effects caused by the presence of a finite water depth. Without a doubt a ship will navigate in areas of shallow water at various times during its operational life (such as when approaching harbours or ports), which underscores the importance of understanding the shallow water effects on ship manoeuvrability. In the present paper, the manoeuvrability of the KRISO Container Ship (KCS) model in different shallow water conditions was comprehensively analysed by means of the unsteady Reynolds-Averaged Navier-Stokes (URANS) computations coupled with the equations of rigid body motion with full six degrees of freedom (6DOF). A dynamic overset grid approach was implemented to allow the ship hull to move in 6DOF in a computational domain and to enable the rudder to be deflected according to a rudder controller for free-running manoeuvres. A series of manoeuvring simulations were performed in shallow waters with water depth to draft ratios varying between 1.2 and 4.0, and partially validated with the available experimental data from a free running test. The numerical results revealed that the ship advance, transfer, and tactical diameter mainly increased with the decrease in the ratio of water depth to draft, closely associated with the complicated interactions between the hull wake, boundary layer, propeller, vortex, and sea floor. [ABSTRACT FROM AUTHOR]

This study experimentally investigates the effect of shallow water depth on the mixing of 30° and 45° inclined dense jets. Three different mixing regimes were identified, namely, the full submergence, plume contact, and centerline impingement regimes. The mixing characteristics in these three regimes, including the jet trajectory and minimum dilution at the water surface () as well as at the return point near the seabed (), were quantified with respect to the densimetric Froude number () and cover water depth (). The nondimensional cover water depth, , was found to be a suitable normalization parameter for shallow water scenarios. The transitional among the regimes, the asymptotic limits of the minimum surface dilution at large , and the various linear coefficients were also determined. Overall, it was found that the surface constraint in the plume contact and centerline impingement regimes, lengthens the jet-spreading distances and reduces the surface dilution, while the bottom dilution remains relatively constant. The results enable the assessment of the mixing characteristics of the inclined dense jet in shallow coastal waters with possible surface contact for environmental impact assessment. [ABSTRACT FROM AUTHOR]

Current practices for modeling the ocean floor in underwater explosion simulations call for application of an inviscid fluid with soil properties. A method for modeling the ocean floor as a Lagrangian solid, vice an Eulerian fluid, was developed in order to determine its effects on underwater explosions in shallow water using the DYSMAS solver. The Lagrangian solid bottom model utilized transmitting boundary segments, exterior nodal forces acting as constraints, and the application of prestress to minimize any distortions into the fluid domain. For simplicity, elastic materials were used in this current effort, though multiple constitutive soil models can be applied to improve the overall accuracy of the model. Even though this method is unable to account for soil cratering effects, it does however provide the distinct advantage of modeling contoured ocean floors such as dredged channels and sloped bottoms absent in Eulerian formulations. The study conducted here showed significant differences among the initial bottom reflections for the different solid bottom contours that were modeled. The most important bottom contour effect was the distortion to the gas bubble and its associated first pulse timing. In addition to its utility in bottom modeling, implementation of the non-reflecting boundary along with realistic material models can be used to drastically reduce the size of current fluid domains. [ABSTRACT FROM AUTHOR]

Reduction of distance between the ship floor and the seabed when a ship is moving forward is called squat. Squat causes grounding of the ship that may result in severe damage to the ship and in extreme cases may lead to complete loss of port or channel capabilities. If a ship moves in the shallow waters then the velocity of the fluid flow at the bottom of the ship increases and the pressure decreases which in turn leads to the decrease of buoyancy force and the increase of the ship draught. The purpose of the presented research was to determine the squat for vessels with the Series-60 hull forms in various depths by experimental methods. For this reason, a set of facilities for testing the ship movement in shallow waters were prepared and then the measurement tools were calibrated. A series of models of the vessel were manufactured and many tests were carried out. Disregarding the non-acceptable data, the test results were analyzed in various depths and draughts. To generalize the test results, some new non-dimensional squat parameters were introduced. The examination of the test data through regression analysis resulted in an empirical equation for ship squat as a function of ship parameters as well as depth of the water. [ABSTRACT FROM AUTHOR]

Complex structure distribution and wide-spread Meso-Paleozoic carbonate strata have limited the use of the seismic investigation in the South Yellow Sea, China. To figure out the carbonate strata distribution, we conducted magnetotelluric data acquisition in the Central Uplift of the South Yellow Sea Basin at a water depth of ~20 m. Novel Ocean Bottom Electromagnetic (OBEM) receivers with a smaller size and a lower center of mass were used to reduce the instability caused by the shallow water motions. Magnetic fields associated with the ocean motions, mainly tides and gravity waves, were identified and segmentation multi-station processing was applied to the data. We conducted 1-D and 2-D inversions to derive the resistivity models. Significantly elevated resistivity zone is obtained at depths between 3 and 8 km. Combining the seismic data, drilling well and local geology, we concluded that the marine carbonate strata at the Central Uplift hold a thickness of over 7 km, which starts from the Indo-Chinese unconformity interface at a depth of ~650 m and extends to the metamorphic basement at a depth of ~8 km. • Magnetotelluric measurement was conducted in the South Yellow Sea Basin to explore the marine carbonate strata. • Electromagnetic fields associated with the shallow water motions are strong noises in the magnetotelluric experiment • The new-developed receiver sis less affected by the water motions compared with the receivers previously used in deep water • The thickness of the marine carbonate strata is inferred to be over 7 km by the resistivity model. [ABSTRACT FROM AUTHOR]