Numerical Analysis of the Electromagnetic Fields Induced by Wave Motions in the North Part of the Aegean Sea

The results of investigations of internal waves carried out in three test ranges located in the north part of the Aegean Sea and characterized by different dynamics of wave motions and water masses are used to study the electromagnetic waves induced by wave motions. We analyze their dependence on the period of waves and wavelength, reveal specific features of the behavior of the electric and magnetic fields and their phases as functions of depth, and compare the intensities of electromagnetic fields obtained under different hydrological conditions.     

Investigation of the electromagnetic fields induced by sea wave motion

This paper discusses a theoretical model of the electromagnetic field induced by internal waves of baric origin. Comparison of thein situ data on the differences between the horizontal electrical field potentials conditioned by internal waves in some Black Sea and tropical Atlantic areas and of the results of calculations of the model electrical field's intensity in those areas shows their good agreement. The dependences of the electromagnetic field component amplitudes on the internal waves parameters and sea-bed rock conductivity are considered. Translated by Vladimir A. Puchkin.     

Wave boundary layers near the surface and bottom in a stratified fluid

The paper examines so-called wave boundary layers arising in a bounded stratified fluid for large times. Each the layer is a narrow domain in the vicinity of the fluid surface and/or bottom characterized by sharp, growing with increasing time, vertical gradients of the buoyancy and horizontal velocity. The layers arise as a result of free linear wave evolution of the initial fields if the initial buoyancy at the boundaries depends on the horizontal coordinates. An asymptotic solution for the boundary layer for large times is presented, and it is shown that this solution describes exact fields fairly well even for moderate times.     

海浪感应磁场矢量的模型研究

海水作为一种电的良导体,其在地磁场中的运动将激发感应磁场.应用电磁场的基本理论,结合海浪运动学模型,推导了海浪感应磁场的三分量模型.该模型给出了三分量的海浪感应磁场与地磁场、海水特性参数、空间位置等要素之间的关系.分析了三分量的海浪感应磁场信号的时域、频域和空间分布特征,对海浪感应磁场相关领域的研究,具有参考意义.     

Two-Layer Non-Hydrostatic Model for Generation and Propagation of Interfacial Waves

When pycnocline thickness of ocean density is relatively small, density stratification can be well represented as a two-layer system. In this article, a depth integrated model of the two-layer fluid with constant density is considered,and a variant of the edge-based non-hydrostatic numerical scheme is formulated. The resulting scheme is very efficient since it resolves the vertical fluid depth only in two layers. Despite using just two layers, the numerical dispersion is shown to agree with the analytical dispersion curves over a wide range of kd, where k is the wave number and d the water depth. The scheme was tested by simulating an interfacial solitary wave propagating over a flat bottom, as well as over a bottom step. On a laboratory scale, the formation of an interfacial wave is simulated,which also shows the interaction of wave with a triangular bathymetry. Then, a case study using the Lombok Strait topography is discussed, and the results show the development of an interfacial wave due to a strong current passing through a sill.     

Modelling of high amplitude internal waves integrating the primitive (Navier–Stokes) equations

In this paper we use an industrial Navier–Stokes (NS) solver to model high amplitude internal waves. The model simulates a fluid with a shallow upper layer with linear stratification and a deep lower layer with constant density, relevant to conditions in the ocean at several locations. Waves are generated by trapping a volume of light water behind a gate in one end of the numerical wave tank. The velocity and vorticity fields predicted by the model agree well with experiment. The high amplitude waves produced by the NS solver experience an upper bound on the velocity and a broadening in agreement with experiment. These effects have not previously been captured by theoretical models.     

Hybrid Surface Waves from a Harmonic Perturbation Source

The problem of constructing uniform asymptotics of surface perturbations of far fields from a localized harmonic source in the flow of a heavy homogeneous fluid of infinite depth is considered. It is shown that the wave pattern of generated far fields at specific parameters is a system of hybrid wave disturbances that simultaneously possesses the properties of waves of two types: annular (transverse) and wedgeshaped (longitudinal) waves. The properties of the phase structure and wave fronts of the generated fields are studied. Uniform asymptotics of the solutions describing hybrid surface wave disturbances far from a harmonic source are constructed.     

Investigation of electric fields inside and outside a magnetised cold plasma sphere

Based on the scales transformation of electromagnetic theory, the analytical expressions of electric fields inside and outside a magnetised cold plasma sphere are presented by reforming the spherical electromagnetic parameter. The obtained results are in good agreement with that in the literature. The angle between the direction of inside field and that of outside field is derived. In S wave band, calculations for the effects induced by parameters of the inner field are established. Simulations show that the angle between incident field and the outside magnetic field influences the inner field remarkably. The inner field will increase as the electron density increases. The inner field varies with frequency nonlinearly. There is an angle between the inner field and the incident field, it changes nonlinearly with the frequency.     

On the use of a two-layer fluid stratification model in studies of topographically-generated baroclinic tides

Internal waves generated by a baroclinic internal wave impinging on an oceanic ridge are studied. Two stratification models are considered: a two-layer ocean model (with a density jump) and a continuously stratified ocean model (model pycnocline). The results yielded by different stratification models are compared analytically. The analysis makes possible the application of a piecewise-constant approximation of the fluid stratification to study topographically-generated baroclinic tides. Translated by V. Puchkin.     

起伏海面的雷电电磁场传播特征及其对闪电定位精度的影响

为了研究起伏海面对雷电电磁传播的影响,本文利用Barrick表面阻抗理论和Wait近似算法,采用改进二维分形海面模型模拟起伏海面,利用数值模式,分析起伏海面的雷电电磁传播特征,并进一步讨论了起伏海面对时差法闪电定位系统定位精度的影响。结果表明:起伏海面对垂直电场和磁场的峰值的影响不显著,但会引起波形的上升期时间的延长,浪高越大,影响越明显;随着观测距离的增加,雷电垂直电场波形的上升时间逐渐变长;风速的变化与雷电垂直电场波形的上升时间成正比;由于海面起伏引起雷电电磁场波形在传播中的变化会影响基于时差法闪电定位系统的定位精度,定位误差可达几至十几公里。     

Surface manifestations of internal waves investigated by a subsurface buoyant jet: Part 2. Internal wave field

In a large test reservoir with artificial temperature stratification at the Institute of Applied Physics, Russian Academy of Sciences, a major simulation of internal wave actuation by buoyant turbulent jets generated by wastewater flows from underwater collector diffusers in conditions of temperature stratification with deep and shallow thermocline has been performed. Using a modification of the particle tracing velocimetry (PTV) method in the stratification mode with shallow thermocline, the velocities of currents generated by internal waves at the surface of the water area are measured. A theoretical model is developed describing the fields of internal waves in the presence of jet stream. Dispersion relations and structures of lower (first and second) modes of internal waves in the stratified basin for different rates of liquid outflow from the collector model are obtained. The experimentally measured field of isothermal shifts with respect to the system of characteristic modes of internal waves is decomposed. A mixed regime of internal wave actuation with the simultaneous existence of the first and second modes is observed. The characteristics of perturbations in the liquid column and on its surface are compared. This analysis allows us to prove that the velocity fields on the surface are indeed surface manifestations of internal waves.     

Trapped bottom topographic waves over the inclined bottom

In the Boussinesq approximation, we study baroclinic topographic waves trapped by the flat meridional slope. The existence of these waves is explained by stratification, inclined bottom, and Earth's rotation. We deduce the evolutionary equation for the square of the envelope of a narrow-band wave packet of trapped waves. In the second order of smallness relative to the wave amplitude, we find the mean fields of velocity and density induced by the packet. It is shown that, in the limiting case of weakly nonlinear plane waves, the induced current is zonal. In the Northern hemisphere, depending on the slope of the bottom γ₁, the sign of the phase velocity σ/k (k is the zonal wave number) is either always positive (for γ₁>γ_1cr) or always negative (for γ₁<γ_1cr). If we neglect the vertical component of the Coriolis acceleration, then γ_1cr=0. Translated by Peter V. Malyshev and Dmitry V. Malyshev     

海浪对水下电磁场幅值影响的分析

讨论了海浪波动基本规律,分析了海浪波动对水下接收点电磁场幅值的影响。理论计算表明,这种影响取决于海浪的有效波高和电波穿透深度的比值。在近似正态分布的海浪作用下,水下场强幅值呈现出对数正态分布的规律。海浪波动会造成场强均值增加和场强幅值波动。海浪对场强幅值的影响随着电磁场频率的下降显著地降低。     

Ekman Convective Layer Flow of a Viscous Incompressible Fluid

Analytical solutions for generalizing the Ekman stationary flow of a viscous incompressible fluid in an infinite layer are obtained. The solution of an overdetermined system of the Oberbeck–Boussinesq equations is considered. It is suggested to use a class of exact solutions for this problem. It is shown that the structure of the solutions allows one to preserve the advective derivative in the heat-conductivity equation; this makes it possible to model the stratification of the temperature and pressure fields and describe the oceanic countercurrents.     

Effect of a submerged plate on the near-bed dynamics underincoming waves in deep water conditions

It is well known that wave induced bottom oscillations become more and more negligible when the water depth exceeds half the wavelength of the surface gravity wave. However, it was experimentally demonstrated for regular waves that the bottom pressure oscillations at both first and second wave harmonic frequencies could be significant even for incoming waves propagating in deep water condition in the presence of a submerged plate [16]. For a water depth h of about the wavelength of the wave, measurements under the plate (depth immersion of top of plate h/6, length h/2) have shown bottom pressure variations at the wave frequency, up to thirty times larger than the pressure expected in the absence of the plate. In this paper, not only regular but also irregular wave are studied together with wave following current conditions. This behavior is numerically verified by use of a classical linear theory of waves. The wave bottom effect is explained through the role of evanescent modes and horizontally oscillating water column under the plate which still exist whatever the water depth. Such a model, which allows the calculation of the velocity fields, has shown that not only the bottom pressure but also the near bed fluid velocity are enhanced. Two maxima are observed on both sides of the location of the plate, at a distance of the plate increasing with the water depth. The possible impact of such near bed dynamics is then discussed for field conditions thanks to a scaling based on a Froude similarity. It is demonstrated that these structures may have a significant impact at the sea bed even in very deep water conditions, possibly enhanced in the presence of current.     

Rocking buoy wave energy converter

A device for converting ocean wave energy into electricity utilizing a rocking buoy and a hydrogen pressure cell is described. The moored buoy contains a pneumatic tube filled with a dense liquid which rocks back and forth as a result of the ocean wave activity. Hydrogen gas, maintained above the dense fluid is alternatively compressed and expanded by the moving fluid. The hydrogen gas communicates with a hydrogen pressure cell and the resulting pressure difference across the cell leads to an electrical voltage and under load, to electrical power.     

The generation of baroclinic tides over steep non-uniform bottom topography

The internal waves generated by semi-diurnal barotropic tides over steep non-uniform bottom topography are considered within the framework of the general linear theory. For the distribution of a fairly general form of the Bruth-Väsälä frequency, a method is suggested for computing the wave fields over critical and post-critical topographic non-uniformities which takes into account wave motion in shadow areas. A specific analysis has been carried out for the fluid stratification, modelling pycnocline, and the bottom profile given by a simple trigonometric relation.Translated by V. Puchkin.     

Thermal conductivity and permeability assessment by electrical resistivity measurements in marine sediments

Abstract

The problem of radioactive waste containment, the modeling of hydrocarbon formation processes, and the proposed laying of fiber‐optic communication cables on the seafloor have recently focused attention on the thermal and fluid flow properties of porous media. Both properties are difficult to determine accurately for large volumes of material, particularly where disturbance is inevitable either on sampling or penetration of the measuring device. Both properties, however, have been tentatively identified as bearing some form of analogy with electrical flow, and evaluation of these relationships with electrical measurements may provide practical means of obtaining rapid coverage of the sediment from a semi‐remote position. Using a variety of laboratory cells, an attempt has been made to evaluate useful relationships between electrical formation factor and thermal conductivity and/or permeability for both sands and clays. Formation factor exhibits a close relationship with permeability, and the capability of predicting permeability to within an order of magnitude is shown providing the grade of sediment is identified (e.g., sand or clay). Formation factor is related to porosity and while any one sample is best represented by Archie's (sands) or Winsauer's (clays) empirical law, the overall trend is a third‐degree polynomial; particle shape appears to dominate both porosity and permeability relationships with electrical formation factor. Thermal conductivity shows a clear dependence on the porosity of a saturated sediment. The successful prediction of thermal conductivity using a geometrical model requiring volume and thermal conductivity values for the components has been demonstrated for a variety of particle shapes and sizes. Thermal conductivity may be related to formation factor through the porosity of the sample for both sands and clays.     

Variation of the polarization characteristics of electromagnetic waves in a horizontally-inhomogeneous environment

The paper considers the propagation of the electromagnetic fields having a range of tens of cycles per second in a horizontally-inhomogeneous ocean. The TM-wave characteristics in the presence of a horizotal conductivity jump are estimated. The amplitudinal and phase values of the electric intensity's vertical component are provided for various conductivities of a two-segment sea of constant depth. A conclusion is made that marine environment inhomogeneities can he studied through electromagnetic techniques.Translated by V. Puchkin.