Spectral evolution of surface waves in a deep sea due to the effect of wave-wave interactions

The wave-wave kinetic equation for surface gravity waves in a deep sea is solved numerically, using the Runge-Kutta technique. Spectral evolution of waves resulted only from their being non-linear, with no wave generation and decaying taking place. To perform computations the JONSWAP-type frequency spectra and a variety of angular wave spectra were used. The angular spectrum of waves turned out to be stable. The frequency spectrum differed from the JONSWAP spectrum in that it had a high-frequency part, which was not similar to the Phillips spectrum. The form of the high-frequency spectral slope was determined as a result of spectral evolution and proved to have the form of the ‘−6’ law. Translated by Vladimir A. Puchkin.     

Phase velocities of surface waves in a sea of finite depth

Dispersion relations and phase velocities of surface gravity waves, with their non-linearity being considered, have been derived numerically from an equation for a nonvortical incompressible fluid of finite depth. For all the depths being considered, the dispersion relations are readily realized for the wavenumbers smaller than the wavenumber of the basic harmonic. Then the acquired relations tend to increasingly deviate from the linear dispersion relations. This is the case for all the depths and wave steepnesses under discussion. When the depth of the sea diminishes, the deviations dramatically increase in both cases, when waves grow steeper and when the form of the wave spectrum changes from wide to narrow. This also holds for the phase velocity of waves. Numerical results are matched up with the experimentally derived data. For calculations, JONSWAP spectra of various width have been used. Translated by Vladimir A. Puchkin.     

The surge motion of a circular cylinder containing a concentric cylindrical hole in finite depth

This paper deals with hydrodynamic forces of a single semisubmerged circular cylinder containing a concentric cylindrical hole constrained to move in a water domain of finite depth. The fluid domain is divided into inner and outer regions. The Laplace equations governing velocity potentials for the three regions are solved by separation of variables and expressed in terms of eigenfunctions of the resulting equations which satisfy appropriate boundary conditions. Continuity of pressure and velocity at the interface of the regions provides the necessary equations from which the velocity potentials, pressures and forces are obtained. Numerical results are plotted for added mass and damping coefficients for different draft-to-depth and radius-to-depth values and for various wave amplitudes.     

Joint statistical distribution of two-point sea surface elevations in finite water depth

Based on the second-order random wave solutions of water wave equations in finite water depth, a joint statistical distribution of two-point sea surface elevations is derived by using the characteristic function expansion method. It is found that the joint distribution depends on five parameters. These five parameters can all be determined by the water depth, the relative position of two points and the wave-number spectrum of ocean waves. As an illustrative example, for fully developed wind-generated sea, the parameters that appeared in the joint distribution are calculated for various wind speeds, water depths and relative positions of two points by using the Donelan and Pierson spectrum and the nonlinear effects of sea waves on the joint distribution are studied.     

Simulation of surge phenomena in a bounded sea basin

By using the method of mathematical simulation, we study surge oscillations caused by the action of tangential wind stresses in a bounded basin whose geometric parameters correspond to Lake Donuzlav. The dependences of the amplitudes of surges on the magnitude and direction of the wind velocity are analyzed at several points of the coast. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 6, pp. 3–12, November–December, 2006.     

A1B气候情景下海平面变化对东中国海风暴潮的影响

用三维水动力模型Ecomsed,在第四次IPCC评估报告SRES A1B气候情景下,分析21世纪海平面变化对东中国海风暴潮及沿岸脆弱性的影响。在A1B气候情景海平面变化影响下,对17个台风个例进行模拟。结果表明:受海平面变化影响风暴潮增减水出现大概10 cm的变化,风暴潮增水提前,风暴潮增水时段延长;台风强度越大,海平面变化对风暴潮增水强度的影响越明显。海平面变化对海岸带脆弱性具有很大影响,苏北浅滩及环渤海海岸带脆弱性将增强,校核水位在东中国海将会增大。     

Biological interactions between microorganisms in the sea

Marine ecosystems, like terrestrial biological communities, are generally considered to depend, regarding their structure and functioning, upon the trophic and sexual relationships between organisms, either “horizontally”, between individuals at the same level, or “vertically”, all the way down the various levels of the food chains. Nevertheless, the functioning of biosystems is mostly governed by their structure, i.e., the qualitative and quantitative distribution of individuals within biocenoses, as well as the relationships with one another and with the environment. Therefore, it is vital to get to know how these connections work in order to outline the main causes of microbiological equilibrium in the sea. Actually, the major problem remains that of communication between individuals in biocenoses. This is a general problem as far as life is concerned, but it proves especially acute when it comes to microbial life because of its importance in the oceanic cycles.Data available in the literature, together with the results of our own studies in this field, led us to the assumption that some of the dissolved organic substances present in seawater might well be responsible for the control of the relationships between species. These substances would be active at various degrees of concentration, after they have been released into the medium by certain species. This theory, already adumbrated by Lucas (1938, 1947, 1955), Nigrelli (1958) and Fontaine (1970) concerning direct relationships between marine species or groups of organisms, was resumed and generalized by M. Aubert (1971) who called these substances “telemediators”.Such chemical communication plays a major role in a variety of fields including sexual behaviour, nutrition and predation, as well as defense mechanisms, mobility and migration.Remote connection of two organisms through a chemical mediation involves a sequence of actions and reactions which raises a number of problems of biochemical microecology. The organism that produces the telemediator must synthesize it — either spontaneously or in an induced way — and release it into the medium, during its active growth or after cell lysis. Next, the mediator is conveyed to the remote receiving organism, which it should reach without being degraded or chemically modified (or after such a modification. Its concentration must remain equal to or higher than its activity threshold. The receptor detects it, with or without absorption, and reacts by modifying its own metabolism or behaviour. This may go as far as causing the receptor the receptor to die. In even more complex situations, another mediator will be synthesized and released into the medium.Theoretical as it may be, such a pattern is a useful guide to explain the microbial interactions in a marine environment. It involves a number of complex microecological phenomena, some phases of which begin to be known. One specific problem is chemoreception in microorganisms, hence chemotaxis. Telemediator activity threshold and turnover in the natural environment must also be investigated.One should also take account of the physical context in which the phenomena take place. For instance, it is a known fact that an important fraction of the bacterial flora in the sea is adsorbed on solid or particulate substrates. Thus, the relationships with which they are concerned are much more probable in a sphere of a few fractions of a millimeter: this emphasizes the significance of the biochemical processes which cause the microorganisms to colonize substrates and to compete with one another in so doing. Another point of interest is how they modify the substrate until they are replaced by higher organisms.In the microbial field, communication between species has been described at various levels. Horizontally, it can take place between different bacteria or between various species of algae. Vertically, it may involve bacteria and planktonic algae, bacteria and protozoa, or algae and zooplanktonic organisms.Besides, the communication may be “positive”, if the mediator enhances the growth of the receiving organism — then, it is used as a source of carbon or nitrogen, or as a growth factor — or “negative” whenever the mediator is toxic (antibiotic, antiseptic or toxin) or induces a lethal metabolic modification in the receiver.In fact, there are various telemediation mechanisms, which correspond to increasing degrees of complexity in the biological systems: a primary mechanism, in which the mediator is synthetized by a species and controls (or modifies) the metabolism of another species in one step, and a secondary mechanism, where the mediator is synthetized by a species, and modifies the metabolism of another species; the latter, in turn, releases a primary mediator which controls the functions of a third species. This might be a longer sequence, involving a higher number of species.If the mechanism becomes cyclic, feedback may occur: as far as we know, such feedback may be either positive or negative ecologically, depending on whether it speeds up or slows down a biological process.A conception of a marine universe whose equilibrium would be controlled by the interaction of organisms within a more or less dense biotic network, with meshes made up of the relationship functions as a whole, is highly suggestive of an homology with cybernetic structures. Then, each marine organism can be considered as a separate functional unit characterized by some particular properties, its functions, which govern its activity. These units are involved in the functioning of complex and varying systems in which they intervene locally to channel up the flow of energy and matter to a given extent and in a given direction.The analogy is still more pronounced as there are feedbacks, which can control various sectors of the system. In a series of studies based on biological systems regulated by various chemical mediators, authors were able to demonstrate that the introduction of varied chemical pollutants into the marine environment entails modifications in the structure of the biological components of seawater and results in either the modification or the destruction of the mediating metabolites or “signals”. The result could be a more or less pronounced ecological drift, that varies according to the activity of the pollutant.     

Calculation of the far field finite depth green's function

This note presents a numerical method for calculating the far field part of the Green's function for a source in steady translation below the surface of fluid of finite depth. The principal steps of the numerical scheme are outlined, with emphasis on those aspects which are needed for a computer implementation of the scheme. Numerical results are given to show the behavior of the function in various parts of the computation domain, the computer requirements of the method, and its expected accuracy.     

粤东沿海台风风暴潮特征及数值模拟

粤东地区是我国沿海经济较为发达的地区之一,也是遭受风暴潮灾害较为严重的地区,本文重点分析了自1969年以来40年间影响粤东沿海的典型风暴潮过程,并建立起了一个适用于粤东沿海地区的高分辨率的风暴潮数值预报模式.此模式采用变网格技术,在可以保证使计算区域足够大的基础上,又能实现对重点区域的河口、海湾等地形加密处理,精细地刻...     

Random wave-current interactions in water of varying depth

Refraction of incoherent random gravity waves with currents and bottom topography results in spatial variations in the spectral characteristics of the free surface. Prediction of such variations based on the radiation transfer equation is in a simple analytic form for the case of one dimensional inhomogeneities in currents and topography. This analytic form is examined in terms of two-dimensional wave number- and polar frequency-direction spectra along the associated dynamic and kinematic constraints relevant to wave breaking and reflection. Results are specialized to the simplest case of horizontal shear currents in deep and shallow water with explicit examples to illustrate the relative and combined effects of currents and topography on free surface spectra.     

浅水环境下波浪能能流密度计算方法研究

本文列举了3种波浪能能流密度计算方法,通过实测资料和数值模拟的实验,分析了3种方法在浅水环境中的适用性。分析得知,定义方法对浅水环境中的海浪特征考虑最为周全,计算结果最准确,但强烈依赖海浪谱的存在,适用面较窄;经验方法仅依赖常规海浪参数,对各种基础资料几乎都适用,但对波能能流密度的估计往往偏低,且不能明显反应出地形抬升对波能能流密度的汇聚效应;修正方法考虑了浅水的影响,通过适当的选取参数,可以给出较准确的结果,但对于大的波能能流密度值存在过高估计的问题。3种计算方法各有优劣,可以根据实际需要适当选择。     

Determination of the sea depth using the light pulse location technique

Through analysis of the regularities in the signal-to-noise ratio variation we have determined the maximum depths of bottom location using the method of laser sounding, depending on the bottom albedo, the optical properties of the sea-water layer, the characteristics of the radiation source and detector, the magnitude of all types of noise, dark-current noise, Schottky noise, the noise of a light pulse propagation channel, and background noise. Simple formulae have been derived for technological calculations, optimization, and assessment of the efficiency of specific sounding systems.Translated by Vladimir A. Puchkin.     

Ship motions and sea loads in restricted water depth

The influence of the sea bottom on ship motions and sea loads is examined. It is described how to calculate the vertical motions and loads for a ship with non-zero forward speed in regular waves by use of sttip theory and fluid finite element method. Results of such calculations are shown. The effects of shallow water are significant as is seen from several figures.     

Risk analysis and assessment of overtopping concerning sea dikes in the case of storm surge

Risk analysis and assessment relating coastal structures has been one of the hot topics in the area of coastal protection recently. In this paper, from three aspects of joint return period of multiple loads, dike failure rate and dike continuous risk prevention respectively, three new risk analysis methods concerning overtopping of sea dikes are developed. It is worth noting that the factors of storm surge which leads to overtopping are also considered in the three methods. In order to verify and estimate the effectiveness and reliability of the newly developed methods, quantified mutual information is adopted. By means of case testing, it can be found that different prior variables might be selected dividedly, according to the requirement of special engineering application or the dominance of loads. Based on the selection of prior variables, the correlating risk analysis method can be successfully applied to practical engineering.     

杰氏风暴潮预报方法在珠海及粤西海域的应用

珠海及粤西海域是风暴潮灾害的多发区,本文通过杰氏风暴潮预报方法对历史上给珠海和粤西海域造成较大影响的台风增水事件进行后报试验并通过统计分析方法对原有的预报公式进行订正,总结出适合珠海及粤西海域的风暴潮预报公式。并利用5年的时间对珠海及粤西海域的台风增水进行试报,结果表明预报准确率分别达95.0%和87.6%,这说明订正后的公式能对珠海及粤西海域的风暴潮预报起到较好的预报效果。     

Consistent expressions for the free-surface Green function in finite water depth

Fast and accurate computation of the free-surface Green function is of key importance for the numerical solution of linear and second-order wave-structure interaction problems in three dimensions. Integral and series expressions for the Green function are derived for which the limiting values for zero and infinite frequency are consistent with the zero and infinite frequency Green function defined in terms of infinite series of Rankine image sources. The integral expressions presented here have the advantage that they are slowly varying with the non-dimensional wave frequency, making them more efficient to approximate compared with previous expressions.     

Hydrodynamic coefficients of a submerged pulsating sphere in finite depth

By extending the work of Linton (Linton, C.M., 1991. Radiation and diffraction of waver waves by a submerged sphere in finite depth. Ocean Engineering 18 (1/2), 61–74), the problem of radiation of water waves by a submerged pulsating sphere in finite depth is formulated using the multipole method. As in Linton (1991), this leads to an infinite system of linear equations, which are easily solved numerically. Simple expressions are derived for the hydrodynamic characteristics of such a body. Results showing the effect of varying both the immersion depth and the water depth on the hydrodynamic coefficients of the pulsating sphere are given. The paper resumes the work presented in Lopes (Lopes, D.B.S., 1999. On the study of the Archimedes wave swing device for wave energy utilization (in Portuguese). MSc on the Management and Modelling of the Marine Environment, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa.).     

Evolution of the thickness distribution of ice in the sea of Japan

Simple mathematical models of the thermodynamics of the ice-cover thickness and the thermodynamics of the area of an individual ice floe are proposed. The equations of the models allow for an explicit consideration of the spatial boundedness of the seawater region containing ice covers. A kinetic model of the evolution of the distributions of ice area and ice thickness is formulated on the basis of the gas-dynamic theory. Integration of the equations of this model over the surface areas of individual floes gives the thickness distribution of ice areas. Several special cases are studied analytically. The adequacy of the models is assessed. The results of simulations are presented.     

海平面上升对河北黄骅台风风暴潮漫滩影响的数值研究

基于河北省黄骅地区的风暴潮漫滩灾害风险评估模型,利用成熟的业务化台风风暴潮数值预报模式、100m分辨率的风暴潮漫滩数值模式,以及该地区的海平面上升和地面沉降结果数据,对台风登陆地点、路径、方向进行科学组合,利用各种组合参数条件进行数值计算,得到了995、985、975、965hPa四种台风强度下,海平面上升对风暴潮漫滩的影响。在相对海平面上升50cm和100cm情况下,四种台风强度的风暴潮平均最大漫滩面积分别增加了约35%和86%;台风强度中等,即985或975hPa时,风暴潮最大漫滩面积的增加更为显著。研究表明,海平面上升对该地区的漫滩影响非常明显,有效防范风暴潮灾害的同时,在气候变化的大背景下,应进一步研究和提出应对海平面上升的长效防治措施。     

On the nonlinear interactions in triads of edge waves on the sea shelf

We study nonlinear three-wave interactions between edge waves propagating in the same direction over the shelf step. The conditions of synchronism are determined and the coefficient of interaction is computed for the cases where the waves of the five lowest modes participate in the interaction. The space-time dynamics is studied by analyzing, as an example, a single triad of edge waves. The possibility of interaction of edge waves in the regions with actual topography is demonstrated. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 3, pp. 3–19, May–June, 2008.