Invariants of Spectral Moments and their Degeneracy for a Gaussian Surface

The transformation and symmetry properties of surface derivatives and spectral moments under rotation of the coordinate axes are examined. It is shown that the moments as well as the derivatives are generally represented in terms of their rotational invariants. For a Gaussian surface, which is characterized by additional symmetry of correlation matrices, the even moments higher than the second order are degenerate; i.e., only three of them are independent, and only two invariants are nonzero. Specific properties of spectrum symmetry and the joint statistical distribution of the mean and differential curvatures are found in this case. As an application of these results to observation of the sea surface, a simple optical method is suggested for simultaneous remote-sensing measurement of the second- and fourth-order moments. This method is based on the count of reversely reflected light impulses, arising from sea-surface scanning by the continuous laser radiation.     

Recent increase in surface fCO<Subscript>2</Subscript> in the western subtropical North Pacific

We observed unusually high levels (> 440 μatm) of carbon dioxide fugacity (fCO₂) in surface seawater in the western subtropical North Pacific, the area where Subtropical Mode Water is formed, during summer 2015. The NOAA Kuroshio Extension Observatory moored buoy located in this region also measured high CO₂ values, up to 500 μatm during this period. These high sea surface fCO₂ (fCO_2SW) values are explained by much higher normalized total dissolved inorganic carbon and slightly higher normalized total alkalinity concentrations in this region compared to the equatorial Pacific. Moreover, these values are much higher than the climatological CO₂ values, even considering increasing atmospheric CO₂, indicating a recent large increase in sea surface CO₂ concentrations. A large seasonal change in sea surface temperature contributed to higher surface fCO_2SW in the summer of 2015.     

榴辉岩套的类型及其地质意义

根据全球榴辉岩的分布、相关岩石组合、成岩物理化学条件和区域构造特征,将榴辉岩套分为两种类型:1)高温榴辉岩套(H型),形成于陆—陆碰撞造山带下部的高温超高压环境,是陆壳俯冲—推覆构造作用的标志;2)低温榴辉岩套(L型),形成于洋—陆碰撞带下部的低温高压环境,是洋壳俯冲—推覆构造作用的标志。     

Scarifying and fingering surfaces of plunging jets

The local surface deformation resulting from the oblique impact of a columnar water jet has been computed, using a three-dimensional large eddy simulation, as a model of the overturning jet of a breaking wave. The emergence of the secondary jet from the front face of the initial jet has been examined and the organisation of the vortices within the jet characterised. As the secondary jet emerges, the vorticity field becomes unstable under the action of the strong shear beneath the jet surface and pairs of longitudinal counter-rotating vortices stretched along the direction of the jet projection are formed. The presence of these longitudinal vortex pairs creates convergent surface flows, resulting in the formation of longitudinal scars on the rear face of the projecting jet. Following significant growth of the scars on both its upper and lower surfaces, the jet decouples into fingers. The lateral widths of the longitudinal vortices provide a minimum measure of the finger size. A horizontal Froude number Fr_h, representing a measure of strength of horizontal shear in a gravity-dominated impacting flow is defined, which characterises the organisation of the longitudinal vortices occurring in the shear flow, and the resultant formation of scars and fingers. For higher Fr_h, stronger longitudinal vortices and deeper scars are formed at longer lateral intervals, enhancing the fingering process during the splashing event. Fundamental features of material transport in the vicinity of the surface of jets (e.g. gas transfer across a sea surface) are related to the entrainment of surface fluid by the longitudinal vortices, and is thus also characterised by Fr_h.     

The symmetry and stability of unstructured mesh C-grid shallow water models under the influence of Coriolis

The symmetry and stability properties of two unstructured C-grid discretisations of the shallow water equations are discussed. We establish that a scheme in which the circumcentres of the mesh triangles are used as the surface elevation points has advantageous symmetry properties and derive a Coriolis discretisation which preserves these properties. It is shown that the resulting scheme is conservative in a discretised energy norm. We then establish that schemes in which the water surface elevations are stored at the mesh triangle centroids do not share these advantageous symmetry properties. Finally we show examples which demonstrate that the centroid based scheme is subject to unstable growing modes, particularly in long timescale, Coriolis dominated problems; while the energy conservative circumcentre based scheme suffers from no such limitation. We conclude that unstructured C-grid methods using the triangle circumcentres and the conservative Coriolis scheme derived here therefore have advantages for this sort of problem over those schemes based on centroids.     

Time domain simulation of side-by-side floating bodies using a 3D numerical wave tank approach

The coupled system of two side-by-side fixed and/or floating bodies interacting with a large amplitude nonlinear wave is studied using a direct time domain solution method. The numerical model is based on a three-dimensional mixed Eulerian–Lagrangian (MEL) method under certain simplifying approximations permitting Rankine panel scheme to be implemented over a time-invariant boundary surface to solve the boundary value problem for the unknown velocity potentials. A 4th order Adams–Bashforth–Moulton scheme is used for time marching of rigid-body motion histories of the individual bodies and evolution of the free-surface including the gap region in which large resonant fluid motions occur. A systematic study has been carried out to evaluate the performance of the developed time domain method in simulating the forces and motions as well as the fluid motion in the gap region for the two body system under various arrangements and in different wave-headings. At first, the computed numerical results have been validated and verified with computational and experimental results available in literature for standard geometries such as vertical truncated cylinders and rectangular boxes. Secondly, effectiveness of the damping lid model which is introduced to suppress wave resonance in the gap region is investigated including its influence on maximum sway forces on fixed and floating rectangular barges in side-by-side configurations. Thirdly, comparative studies on absolute and relative motion response for two cases (two rectangular barges, and a FLNG-FPSO + shuttle tanker) in side-by-side arrangement are detailed to bring out the importance of nonlinearities arising due to steep nonlinear incident waves. Finally, coupled motions of the two-body system of an FPSO and a shuttle tanker floating in side-by-side configuration in a steep nonlinear wave field are studied in which the two bodies are connected through hawsers, and also the FPSO is moored to the ground. Additionally there is a fender between the two bodies.     

Effects of presence of a circumpolar region on buoyancy-driven circulation

Effects of the presence of a circumpolar region on buoyancy-driven circulation are investigated by using an idealized numerical ocean model. Comparison of circulation and meridional density (heat) transport is made between a closed ocean and an ocean with a cyclic gap near its southern boundary. The presence of the circumpolar region leads to disconnection of the meridional overturning across the circumpolar region. And the circumpolar eastward flow reaches the bottom of the ocean. It is essential for this that the pycnocline is deeper than the bottom of the gap. Since the amount of the mass transported northward must return southward at the levels deeper than the bottom of the cyclic gap, the weak stratification, hence weak vertical geostrophic shear, at the deeper levels leads to inactive communication across the circumpolar region. Meridional heat transport across the circumpolar region is made mainly by horizontal diffusion for the ocean with the cyclic gap, while the contribution of the advection is dominant for the closed ocean. Sensitivity of meridional heat transport to change in horizontal diffusivity is studied. The meridional heat transport for the ocean with the cyclic gap is more sensitive than for the closed ocean. The change in heat transport occurs not only in the circumpolar region but also in the rest of the ocean. It is suggested that subgrid scale phenomena, especially mesoscale eddies, in the circumpolar region controls the whole ocean to a great extent.     

仿生胸鳍的三维尾涡结构与参数影响分析

为研究仿胸鳍推进的机理和流体动力特性及缩小机器鱼与生物原型之间的性能差距,利用浸入边界法数值模拟了做耦合旋转运动胸鳍的非定常绕流问题。详细探讨胸鳍非定常运动的三维尾涡结构演化和推进机理,并开展胸鳍推进性能与尾涡结构的参数影响分析。结果表明:迎流面在背、腹侧边缘及鳍梢部显著涡旋结构的作用下所出现的低压力区,加之鳍表面和上游来流之间好的垂直度共同造成了在动力划水阶段的高推力;在恢复划水阶段的高升力与背侧边缘涡强度的持续增加,以及因鳍表面倾斜而引起的水动力被分解到竖直方向的比重提升有关;胸鳍尾流场被一个三维双环涡结构所支配;当前的模拟为仿胸鳍推进建立了一个最优的斯特劳哈尔数St范围(在0.55附近),在此之后平均推力仍随St的增大而增加,而推进效率则表现出一个缓慢降低的趋势;当前后拍动与纵倾运动之间的相位差为90度时,胸鳍同时取得最佳的推力和效率。     

舟山沿岸四种藤壶类壳板的亚显微结构

本文研究了舟山沿岸四种藤壶（三角藤壶Ｂａｌａｎｕｓｔｒｉｇｏｎｕｓ，纹藤壶Ｂ．ａｍｐｈｉｔｒｉｔｅａｍｇｈｉｔｒｉｔｅ，白脊藤壶Ｂ．ａｌｂｉｃｏｓｔａｔｕｓ及日本笠藤壶Ｔｅｔｒａｃｌｉｔａｊａｐｏｎｉｃａ）壳板的亚显微结构。结果表明，壳板表面的亚显微结构主要有生长脊（包括毛脊、大脊、微脊）和放射脊。其中，大脊和放射脊系本文首次报道。大脊于蔡壶蜕皮后毛脊（刚毛）形成的同时或其后形成，与蜕度周期有关。放射脊的形成可增加壳板的坚固度。各种生长脊的数量及强弱变化反映了藤壶的生理代谢状况及环境对藤壶成长的影响。本文比较了四种藤壶之间壳板表面的亚显微结构，发现它们有很大的差异。通过比较四种藤壶成体和幼体之间壳板表面的亚显微结构，发现藤壶壳板表面结构与年龄有密切关系，尤以生活于潮间带中上区的白脊藤壶和日本笠藤壶为显著。环境，尤其是潮区，对藤壶壳板的生长有很大影响。日本笠藤壶、白脊藤壶、纹藤壶壳板结构明显受其生活的潮区影响。     

基于神经网络的卫星高度计海面风速反演算法

通过对TOPEX/Poseidon高度计资料与NDBC浮标实测数据进行时空匹配处理,得到同步数据集,利用人工神经网络方法试验得到海面风速反演算法,并与业务运行的M CW算法进行分析比较,指出考虑波浪状态影响因素的神经网络算法在均方根误差和对称性方面的优越性。研究表明利用神经网络方法反演海面风速是可行的。     

Peculiarities of Polluted Water Spreading from a Submarine Source in Stratified Coastal Environment

We study the spreading of wastewaters from an underwater source in a stratified coastal environment using the results of satellite monitoring and mathematical modeling. The problem is considered as applied to deepwater discharge in the region of Golubaya Bay of the Black Sea near Sebastopol. The main factors preventing upwelling of pollution to the sea surface are analyzed on the basis of a numerical model. It is shown that peculiarities of wastewater spreading depend on the character of stratification and velocity of the background current. The main factor influencing the uplift of these waters to the surface is the existence of water layers with high vertical gradients of water density. We reveal the structure of the wastewater field consisting of a plume and a jet extended in the direction of the background current, which is located in the density interface. If stratification is weak, the plume may reach the sea surface and form a local region of water pollution, which is recorded in multispectral satellite images. It is found that the mass of polluted waters is characterized by negative anomalies of temperature and salinity.     

Generation of internal waves in the sea by local perturbations of wind and density flows on the surface

On the basis of a nonlinear model taking into account viscosity, density diffusion, and currents, we perform the numerical analysis of propagation of perturbations formed in the abyssal part of the Black Sea as a result of the action of tangential wind stresses or density flows in the form of a strip on the sea surface. It is shown that, in the course of time, in the region of the bottom slope, these perturbations generate a train of waves in the sea, which causes oscillations of the fields of density and currents. There are some differences between the generation of internal waves by the flows of density and the wind. Unlike the wind action, in the presence of flows of density in the upper layer in the region of the strip, the initial period of generation is characterized by the formation of intense perturbations without train structure. Translated by Peter V. Malyshev and Dmitry V. Malyshev     

Temporal variations and trends of CFC11 and CFC12 surface-water saturations in Antarctic marginal seas: Results of a regional ocean circulation model

The knowledge of chlorofluorocarbon (CFC11, CFC12) concentrations in ocean surface waters is a prerequisite for deriving formation rates of, and water mass ages in, deep and bottom waters on the basis of CFC data. In the Antarctic coastal region, surface-layer data are sparse in time and space, primarily due to the limited accessibility of the region. To help filling this gap, we carried out CFC simulations using a regional ocean general circulation model (OGCM) for the Southern Ocean, which includes the ocean–ice shelf interaction. The simulated surface layer saturations, i.e. the actual surface concentrations relative to solubility-equilibrium values, are verified against available observations. The CFC surface saturations driven by concentration gradients between atmosphere and ocean are controlled mainly by the sea ice cover, sea surface temperature, and salinity. However, no uniform explanation exists for the controlling mechanisms. Here, we present simulated long-term trends and seasonal variations of surface-layer saturation at Southern Ocean deep and bottom water formation sites and other key regions, and we discuss differences between these regions. The amplitudes of the seasonal saturation cycle vary from 22% to 66% and their long-term trends range from 0.1%/year to 0.9%/year. The seasonal surface saturation maximum lags the ice cover minimum by two months. By utilizing observed bottle data the full seasonal CFC saturation cycle can be determined offering the possibility to predict long-term trends in the future. We show that ignoring the trends and using instead the saturations actually observed can lead to systematic errors in deduced inventory-based formation rates by up to 10% and suggest an erroneous decline with time.     

Numerical Analyses of Bearing Capacity of Deep-Embedded Large-Diameter Cylindrical Structure on Soft Ground Against Lateral Loads

1 .IntroductionThe large-diameter cylindrical structure for coastal and offshore engineering has been widely usedin China .Thistype of structureis composed of a steel or reinforced concrete cylindrical thin-wall shellplaced partlyintothe ground by a speci…     

Evidence on target factors used for port state control inspections

Target factors aim at setting criteria to select foreign vessels that should be inspected by port state control authorities. Although a relative consensus exists on the main factors to consider in selecting vessels, the weight to be given to these factors is still unclear. Using data on 26 515 PSC inspections that took place within the Indian Ocean MoU region from 2002 to 2006, we investigate the determinants of the number of deficiencies and of the probability of detention. Our results show that the main contributors to detention are the age of the vessel at inspection (40%), the recognised organization (31%) and the place where the inspection occurs (17%). Also, differences in detention rates amongst various inspecting authorities are essentially explained by differences in the characteristics of vessels calling in a specific country rather than by differences in the way inspections are done.     

Dynamic models for Icelandic meteorological data sets

Dynamic models are derived from pairs of time series of daily surface and 500 hPa height observations in the Icelandic region in order to interpret these data. The models describe the motion of data points in the phase plane spanned by a pair of variables. For each pair, a regression model of first order (R-model) is derived, which assumes linear motion in the phase plane. The coefficients of the corresponding Fokker–Planck equation (FP) are also derived from the data. This equation describes changes of the probability density distribution of the data pair and takes nonlinear aspects into account. The data are interpreted in the light of both models. The R-model yields a mean rotation and convergence which characterize the basic type of motion inherent in a data set. It is found in all cases that the timescale of contraction is shorter than the "dynamic" timescale linked to the rotation. The FP equation yields a mean motion which resembles quite often that in the R-model as well as a diffusive part. The R-model is not satisfactory in some cases which involve the meridional surface winds. For example, southerlies (northerlies) and temperature rotate clockwise (anticlockwise). Meridional and zonal surface winds rotate anticlockwise in a southerly flow, but clockwise in a northerly one. Therefore, new aspects of the Icelandic meteorology can be extracted form the data by use of the FP equation.     

Double-celled circulation in coastal upwelling

Simple numerical experiments on two-dimensional coastal upwelling are made with emphasis on the role of non-geostrophic solenoidal field of density in the formation of double-celled circulation and multi-celled density front. Geometry of shelf and slope is not taken into account. Existence of poleward undercurrent presumably caused by the longshore variation of the large scale pressure field is also suppressed for the sake of simplicity.The results are, (1) double-celled circulation revealed in the present experiment is closely related with the internal frictional layer, where the horizontal density gradient balances with the vertical gradient of the longshore velocity and the vertical diffusion of the vorticity. (2) density front formed by the emergence of the pycnocline to the sea surface is successively advected offshoreward by the Ekman transport. (3) the pycnocline intersecting the sea surface forms the density front which is nearly vertical on account of the small scale convection. The surface currents converge at the front and construct an anti-clockwise circulation (viewed from the lee side). (4) small coefficient of eddy viscosity and strong wind stress lead the Ekman transport unstable and form a multi-celled structure in the frontal region.     

Alternating zonal flows in a two-layer wind-driven ocean

Alternating zonal flows in an idealized wind-driven double-gyre ocean circulation have been investigated using a two-layer shallow-water eddy-permitting numerical model. While the alternating zonal flows are found almost everywhere in the time-mean zonal velocity field, their meridional scales differ from region to region. In the subpolar western boundary region, where the energetic eddy activity induces quasi two-dimensional turbulence, the alternating zonal flows are generated by the inverse energy cascade and its arrest by Rossby waves, and the meridional scale of the flows corresponds well to the Rhines scale. In the eastern part of the basin, where barotropic basin modes are dominant, the zonal structure is formed through the nonlinear effect of the basin modes and is wider than the Rhines scale. Both effects are likely to form zonal structure between the two regions. These results show that Rossby basin modes become an important factor in the formation of alternating zonal flows in a closed basin in addition to the arrest of the inverse energy cascade by Rossby waves. The wind-driven general circulation associated with eddy activities plays an essential role in determining which mechanism of the alternating zonal flows is possible in each region.     

Wave run-up on a coaxial perforated circular cylinder

This paper describes a plane regular wave interaction with a combined cylinder which consists of a solid inner column and a coaxial perforated outer cylinder.The outer perforated surface is a thin porous cylinder with an annular gap between it and the inner cylinder.The non-linear boundary condition at the perforated wall is a prime focus in the study;energy dissipation at the perforated wall occurs through the resistance to the fluid across the perforated wall.Explicit analytical formulae are presented to calculate the wave run-up on the outer and inner surfaces of the perforated cylinder and the surface of the inner column.The theoretical results of the wave run-up are compared with previous experimental data.Numerical results have also been obtained:when the ratio of the annular gap between the two cylinders to incident wavelength(b-a)/L≤0.1,the wave run-up on the inner surface of the perforated cylinder and the surface of inner column can partially or completely exceed the incident wave height.     

Correlation between the low-frequency variability of surface temperature and the heat flux through the surface in the North Atlantic

Using the data of UWM/COADS (University of Wisconsin-Milwaukee/Comprehensive Ocean—Atmosphere Data Set), we have performed cluster and spectral analyses of the average monthly anomalies of temperature and heat balance of the surface of the Atlantic Ocean in three frequency ranges (intraannual, interannual, and decadal). It is shown that these anomalies are closely related on intraannual scales, where the anomalies of the surface temperature of the ocean can be regarded as a result of the direct local generation by heat balance anomalies. The generation mechanism is explained within the known Hasselman model [1, 2]. On interannual scales, this mechanism is not valid, and nonlocal effects related to heat advection become important. On decadal scales, the local generation of anomalies of the surface temperature of the ocean is insignificant, local correlation between fluctuations of heat balance and the surface temperature of the ocean is completely broken, and the spatial structure of anomalies of the surface temperature of the ocean is governed by the global system of currents, which redistributes heat flux from the ocean to the atmosphere. Violations of the local correlation between anomalies of heat balance and the surface temperature of the ocean are observed on intraannual scales in regions with powerful jet currents and in the equatorial region. In some parts of the World's ocean with weak advection, the correlation between heat balance and the surface temperature of the ocean persists up to a decadal period. Translated by Peter V. Malyshey and Dmitry V. Malyshey