波浪在缓变海底上传播的一个简单数学模型

基于Liu和Shi(2008)的波浪势函数零阶、一阶近似解,采用四阶龙格-库塔法,对缓变海底上一维波浪传播理论模型进行了数值求解,并对波浪在定常坡度的斜坡地形、双曲正切地形为例的传播、变形进行了研究。为了更逼真地描述流体质点的波动特性,将在Euler坐标系下得到的解转换至Lagrange坐标下的解,并绘制Lagrange坐标下坡度为0.2的海滩上的一个波周期内临近破碎前的波形的详细变化过程。此外,计算得到了变水深区域波浪速度势以及自由面的分布,并与Athanassoulis and Belibassakis[34]的结果进行了对比,表明本文模型比保留了六个瞬息项的后者更有效。     

An empirical microwave emissivity model for a foam-covered sea

A model for computing microwave emissivity of a wind-driven foam-covered sea is presented. The effect of roughness and foam is modeled by combining early measurement results and theoretical analysis. Recent Seasat-SMMR measurements are used to fine tune the model and derive an "effective" fractional foam coverage expression in terms of frequency and wind speed. The model incorporates polarization characterization and view angle dependence of the foam-cover emissivity. For48.8degincidence angle and wind speed less than 15 m/s, the emissivity values calculated from this model differs by <8 percent from those calculated from Wilheit's model. At nadir and at 25 m/s wind speed, the emissivity calculated from the two models differ bysim15percent.     

Pipeline breakout from sea floor under wave action

The vertical stability of a submarine pipeline laid half-buried on the sea floor under wave action is studied. As the wave-induced lifting force acts to detach the pipe from the sea floor, mud suction resistance will be developing at pipe-soil interface, acting to hold the pipe in place. This couples the pipe equilibrium with the seabed response which is modelled as a poroelastic media, following the formulation of Biot. Conditions for pipe detachment or breakout from the sea floor are investigated for typical seawave, pipe, and seabed parameters. A general power law will describe the slow quasistatic breakout of the pipe. In the case when the forcing wave period is much shorter than the quasistatic breakout time, the response function of the coupled pipe-seabed system will involve weak nonlinear terms of higher harmonics. The possibilities for resonating the system in such case are examined by including the inertia of the pipe in the analysis.     

Gas-related sea floor craters in the Barents Sea

A cluster of craterlike depressions in the central Barents Sea are several hundred meters across, have steep walls, and are cut into underlying Triassic rocks. Their formation is explained in relation to the glacial history of the region, and a possible model suggests that gas from a deeper, thermogenic source allowed a hydrate layer of considerable thickness to form during the Late Weichselian, when grounded ice covered the area and increased the hydrostatic pressure. After a rapid retreat of the marinebased ice sheet, the hydrates decomposed and the layer thinned rapidly until pressurized free gas, trapped below the hydrates, erupted and formed the sea-floor depressions.     

Direct estimation of motion from sea floor images for automaticstation-keeping of submersible platforms

Maintaining a fixed position near the sea floor is a critical capability during the deployment of remotely operated or intelligent (autonomous) undersea vehicles in a variety of missions, including inspection and repair of undersea structures, data collection, and surveillance. We present an automatic optical station-keeping system for application to submersible vehicles in deep waters by exploiting the information in sea floor images. Readily measurable spatio-temporal image gradients are used to detect and compute the vehicle's translational and yaw motions using a direct motion vision technique. The vision system has been implemented on a Windows-NT Pentium platform, and the estimated positions and yaw angles are communicated via a serial link to the control system, running on a PC-386. Accurate station-keeping is demonstrated in experiments with a three-thruster floating vehicle in a 6-ft×12-ft×6-ft water tank     

A physical radar cross-section model for a wind-driven sea with swell

A new spectrum model for the ocean surface is proposed. We determine the two unknown parameters in this spectrum by fitting it to radar observations. We find that this spectrum combined with two-scale scattering theory can predict much of the observed dependence of the radar cross section on radar frequency, polarization, angle of incidence, and wind velocity at incidence angles in the0deg-70degrange. The spectrum model is combined with a model for swell to examine the effect of swell on the radar cross section. We find that the effect of swell is significant for low radar frequencies (Lband) and near normal incidence but can be nearly eliminated by using higher frequencies (K_{u}band) and large angles of incidence (approx 50deg).     

Acoustic estimations of porosity and thickness for thin soft surface layer of sea floor

Abstract

In some areas, the sea floor contains a surface layer with high porosity and a thickness of 10–30 cm. The characters of an explosive pulse reflected at such a sea floor are discussed. The thickness and porosity estimations for the surface layer by acoustic method are studied, and the estimated and measured results are listed.     

Vertical spatial coherence model for a transient signalforward-scattered from the sea surface

The treatment of acoustic energy forward scattered from the sea surface, which is modeled as a random communications scatter channel, is the basis for developing an expression for the time-dependent coherence function across a vertical receiving array. The derivation of this model uses linear filter theory applied to the Fresnel-corrected Kirchhoff approximation in obtaining an equation for the covariance function for the forward-scattered problem. The resulting formulation is used to study the dependence of the covariance on experimental and environmental factors. The modeled coherence functions are then formed for various geometrical and environmental parameters and compared to experimental data     

The past, present and future of the East/Japan sea in change: a simple moving-boundary box model approach

The East/Japan Sea is a mid-latitude marginal sea that has undergone dramatic changes during the last 50–60 years. One of the most prominent characteristics of these changes is a rapid decrease in the amount of dissolved oxygen in deep waters. As a consequence of these changes, some investigators have even argued that the East/Japan Sea might become an anoxic sea in the next 200 years. While the causes of these changes are still under investigation, it has been shown that they are mainly due to modifications in the mode of the deep water ventilation system in the East/Japan Sea: a slowdown and complete cessation of bottom water formation accompanied by an enhancement of upper water formation instead. A simple moving-boundary box model (MBBM) was developed in order to analyze and quantify the processes involved in such changes over the last 50–60 years. Using a MBBM, we estimated the levels of several conservative chemical tracers (CFCs, Tritium, SF₆, ¹³⁷Cs) and bioactive tracers (oxygen and phosphate) in the deep water masses of the East/Japan Sea, comparing these with the historical data available, and making predictions for the near future. The model predicts that the East/Japan Sea should remain well-oxygenated, despite recent rapid oxygen decreases in its deep waters, accompanied by such structural changes as a shrinking of its oxygen-depleted deeper waters and an expansion of its oxygen-rich upper waters over the next few decades.     

A simple analytical model for surface water waves on a depth-varying current

A perturbation analysis is presented in which a series of small amplitude regular waves co-exist with an arbitrarily sheared current, U(z). Assuming that the current velocity is weak, i.e. U(z)/c=O(ε), the solution is extended to O(ε²), where c is the phase velocity and ε=ak the wave steepness. This provides a first approximation to the non-linear wave-current interaction, and allows simple explicit solutions for both the modified dispersion relation and the water-particle kinematics to be derived. These solutions differ from the existing irrotational models commonly used in design and, in particular, highlight the importance of the near-surface vorticity distribution. These results are shown to be in good agreement with laboratory data provided by Swan et. al. [J. Fluid Mech (2001, in press)]. Perhaps more surprisingly, good agreement is also achieved in a number of strongly non-linear wave-current combinations, where the results of the present analytical solution are compared with a fully non-linear numerical wave-current model.     

加速国际海底区域资源开发产业化的战略思考

21世纪是海洋世纪,《联合国海洋法公约》生效后各沿海国纷纷推行缓陆重海的发展战略,中国经济的复兴必须实现海洋事业的振兴。国际海底区域(以下简称“区域”)利益前景巨大,开发活动高技术密集,法律地位特殊,是未来国际社会经济、科学甚至政治、军事竞争的重要场所。国际海底区域开发产业化研究是我国争取海洋权益、发展高新技术、振兴海洋     

A hybrid coordinate ocean model for shelf sea simulation

The general circulation in the North Sea and Skagerrak is simulated using the hybrid coordinate ocean model (HYCOM). Although HYCOM was originally developed for simulations of the open ocean, it has a design which should make it applicable also for coastal and shallow shelf seas. Thus, the objective of this study has been to examine the skills of the present version of HYCOM in a coastal shelf application, and to identify the areas where HYCOM needs to be further developed. To demonstrate the capability of the vertical coordinate in HYCOM, three experiments with different configurations of the vertical coordinate were carried out. In general, the results from these experiments compares quite well with in situ and satellite data, and the water masses and the general circulation in the North Sea and Skagerrak is reproduced in the simulations. Differences between the three experiments are small compared to other errors, which are related to a combined effect of model setup and properties of the vertical mixing scheme. Hence, it is difficult to quantify which vertical coordinate configuration works best for the coastal region. It is concluded that HYCOM can be used for simulations of coastal and shelf seas, and further suggestions for improving the model results are given. Since HYCOM also works well in open ocean and basin scale simulations, it may allow for a realistic modelling of the transition region between the open ocean and coastal shelf seas.     

GLORIA imagery of sea floor structures in the northern North Fiji Basin

GLORIA side-scan imagery from the northern North Fiji Basin reveals modern and relict sea-floor fabric. The South Pandora Ridge is marked by steep escarpments and small rift basins, but no recent volcanism. The northern and eastern limbs of the 16°58S, 173°55E triple junction are marked by rift grabens flanked by steep escarpments, but little recent volcanism is apparent there. At present, there is no well-organized spreading system in the northern North Fiji Basin; extension and shearing are occurring within narrowly confined areas. It is uncertain how these areas relate to one another and fit into the regional tectonic framework.     

Time-evolution of high-resolution topographic measurements of the sea floor using a 3-D laser line scan mapping system

A laser line scan system was used to characterize the high-resolution spatial variability and temporal evolution of the sea floor as a function of environmental conditions for a small section of the sea floor in the Gulf of Mexico during a period of nine days. High-resolution bathymetric profiles (<1 mm) covering about two sand ripple periods on the sea floor were acquired over a one-dimensional transect 1.35 m in length. The system was also used to measure reflectance and to produce three-dimensional bottom maps of the test area. Over the nine-day period, the sand ripple peak-to-trough height was observed to decrease slowly from about 2.5 cm to about 2.0 cm. Similar gradual changes we also observed in the time-evolution of bottom profile correlations and of the bottom roughness spectra. However, when smaller sections were examined individually, the time-evolution of the profile correlation was observed to vary acutely and in a transitory manner in some regions but not in others, and without preference for crests or troughs. In general, bottom roughness for spatial frequencies greater than 0.044 cycles/cm completely decorrelated within 20-30 h. However, this gradual trend was also marked by acute and transitory changes in bottom topography believed to be primarily from fish feeding on epibenthic prey.     

Dynamic-stochastic model for assimilation of remotely-sensed sea surface temperature data

We consider the possibility of assimilating sea surface temperature data by a combined ocean dynamics model incorporating a three-dimensional hydrodynamic model for synoptic variability for the considered ocean area and an integral model block describing the upper mixed layer. Model numerical simulations and experiments involving satellite-derived data are analysed.Translated by V. Puchkin.     

Mass movement of fine-grained sediment to the basin floor,bering sea,Alaska

Large volumes of fine-grained sediment have been transported to the deepbasin floor in the Bering Sea, especially during glacial low stands of sea level. Turbidity currents and several types of mass movement have been the chief transporting agents.