Event enhancement of reflections from subsurface layered media

The problem of obtaining amplitude and delay parameters associated with the response of subsurface layered sedimentation to impulse-type acoustic excitations is considered. We use a linear lossless model which characterizes the subsurface in terms of layerwise homogeneous segments. The parameters of the model are the time delays associated with the wave propagation in the various layers and amplitude parameters which are functions of the reflection coefficients at the interfaces. With knowledge of the travel time in a sediment of rock layer, its thickness can be estimated if the medium velocity is known. This paper extends theory developed by the authors. In particular, a procedure to enhance the detection of reflection events is presented. The procedure utilizes a balance property shown by the derivative of the input waveform signal to obtain an improved display of reflection-event portions of the received signals. Computational results are given in the paper to illustrate the effectivess of the procedure.     

Maximum likelihood estimation of the parameters of a tone using real discrete data

The exact form of the maximum likelihood (ML) estimates for the amplitude, phase, and frequency of a tone is obtained for the real discrete data case, and is applicable tO arbitrary data record lengths.     

On the use of discrete seasonal and directional models for the estimation of extreme wave conditions

Extreme value theory is commonly used in offshore engineering to estimate extreme significant wave height. To justify the use of extreme value models it is of critical importance either to verify that the assumptions made by the models are satisfied by the data or to examine the effect violating model assumptions. An important assumption made in the derivation of extreme value models is that the data come from a stationary distribution. The distribution of significant wave height varies with both the direction of origin of a storm and the season it occurs in, violating the assumption of a stationary distribution. Extreme value models can be applied to analyse the data in discrete seasons or directional sectors over which the distribution can be considered approximately stationary. Previous studies have suggested that models which ignore seasonality or directionality are less accurate and will underestimate extremes. This study shows that in fact the opposite is true. Using realistic case studies, it is shown that estimates of extremes from non-seasonal models have a lower bias and variance than estimates from discrete seasonal models and that estimates from discrete seasonal models tend to be biased high. The results are also applicable to discrete directional models.     

On the estimation of Morison force coefficients and their predictive accuracy for very rough circular cylinders

This paper makes an assessment of the various method that may be used to analyse experiment data on the force experienced by a circular cylinder in waves and combined wave and current flows to estimate drag and inertia coefficients for use in Morison's equation. Most of the widely used techniques are considered together with a weighted least squares approach for time domain analysis. A set of data obtained from experiments on heavily roughened circular cylinders of diameters 0.513 and 0.216 m in the Delta wave flume at De Voorst in Holland in waves and simulated current has been analysed in turn by all these techniques. The experiment data was split into two halves. The first was used for the analyses and the second was used to assess the predictive accuracy of Morison's equation. Using the force coefficients obtained from the different analysis techniques corresponding predicted force time series were constructed using the particle kinematics measured in the second parts of the data sets. These predicted time series were then compared with the corresponding measured force time histories. The root mean square error and the bias in the estimation of maximum force in each wave cycle are used as measures of predictive accuracy and as a basis for comparing the efficiency of the different analysis techniques. It was found that the weighted least square method generally gave the best predictive accuracy, but only by a small margin.     

Penetration response of spudcans in layered sands

The behaviour of spudcan foundations during the installation and preloading in two-layer sand sediments was investigated through large deformation finite element (LDFE) analyses. The LDFE analyses were carried out using the coupled Eulerian-Lagrangian approach, modifying Mohr-Coulomb soil model to capture hardening and subsequent softening effects of sand. Parametric analyses were undertaken varying the top layer thickness, relative density of sand and spudcan diameter. Both loose to medium dense-over-dense and dense-over-loose to medium dense sand deposits were explored. The results showed that, for the investigated relatively thin top layer thickness of ≤ 5 m, spudcan behaviour was dictated by the bottom sand layer with a minimal influence of the top layer. For assessing the penetration resistance profile in two-layer sands, the performance of the ISO, SNAME, InSafeJIP, and other existing theoretical design methods were evaluated.     

The estimation of acid dissociation constants in sea-water media from potentiometric titrations with strong base. II. The dissociation of phosphoric acid

The three dissociation constants of phosphoric acid have been determined in seawater media over the temperature and ionic strength ranges 5–30°C and 0.3-0.9 m. The results obtained fitted the equations (concentrations in mol per kg of solution):

$\text{pK}{}_{\mathrm{1P}}\text{=}\text{-75}\text{T}\text{+2.16-0.35I}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{(}\text{rmsdeviation 0.034}\text{)}$

$\text{pK}{}_{\mathrm{2P}}\text{=}\text{737.6}\text{T}\text{++4.176-0.851I}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{(}\text{rmsdeviation 0.015}\text{)}$

$\text{pK}{}_{\mathrm{3P}}\text{=}\text{2404}\text{T}\text{+1.31-0.87I}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{(}\text{rmsdeviation 0.17}\text{)}$

The results are only in moderate agreement with those of Kester and Pytkowicz (1967). The reason for this lies partly in differences between the pH scales adopted and partly in the poor precision inherent in their method.     

On motions in steady,layered, geostrophic models

The interior motions in steady, layered, geostrophic models of large scale wind-driven phenomena are severely constrained if there is no stress transfer across the interfaces. In particular, there will be no motion in the subsurface layers except in regions where the layers rise to the surface and are exposed to the wind-stress or unless the layers are in contact with lateral boundary layers with which they exchange fluid. These results follow directly from quite general considerations that are outlined in this paper.     

海上风电吸力基础在分层土中的沉贯特性研究综述

吸力基础与海洋工程大直径钢桩相比,具有成本低、安装周期短、对环境影响小、不受海况影响及可回收再利用等优点,近年来在海上风电工程中得到推广应用。吸力基础沉贯至海床预定位置,是其发挥承载力和确保服役稳定性的前提。海床地基土体常以分层土形式分布,且各层土体强度、压缩性和渗透性等存在显著差别,导致吸力基础吸力沉贯机理非常复杂。明确吸力基础在分层土中沉贯特性,有助于指导吸力基础在海上风电工程中的推广应用。对目前吸力基础在分层土中沉贯特性研究进行综述和总结,归纳了其沉贯机理研究进展,并对影响吸力基础在分层土中沉贯因素进行了分析;提出了分层土中吸力基础沉贯的研究方向和改进的沉贯方法。     

The estimation of acid dissociation constants in seawater media from potentionmetric titrations with strong base. I. The ionic product of water — Kw

The various assumptions implicit in the calculation of acid dissociation constants (based on ionic medium standard states) from potentiometric titrations using a cell with liquid junction (i.e. a pH measuring cell) have been examined. It was concluded that results can be obtained having an accuracy commensurate with the experimental precision. It has been shown that although the precise composition of the medium is a function of the hydrogen ion concentration (because of the protolytic nature of some of the ions in the media, e.g., sulphate and fluoride), the effect of such variations in the medium composition can be compensated for when defining the activity of hydrogen ion on an ionic medium standard state by defining the concentration of hydrogen ion as:

where β_HSO4 and β_HF are the relevant association constants and S_T and F_T are the total concentrations of sulphate and fluoride, respectively.This approach was used to obtain values for the ionic product of water (K_W) in artificial seawater media at various temperatures and ionic strengths. These were fitted to give the equation (molal concentration units):

$\text{pK}{}_{\mathrm{w}}\text{=}\text{3441.0}\text{T}\text{+2.256-0.7091}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{(}\text{rms deviation 0.01}\text{)}$

where I is the formal ionic strength of the artificial seawater medium and T is the absolute temperature. The values obtained are in reasonable agreement with those found by previous workers.     

On the decay of layered structures in a stratified shear flow

The effect of a vertical velocity shear on the decay of small-scale perturbations in an unbounded thermally-stratified fluid is considered. The behaviour of perturbations at the final stage is shown to be controlled by the combined effects of viscosity, thermal conductivity, collapse, and material line stretching due to velocity shear. The behaviour of density and velocity perturbations has been analysed for the case of dominating viscosity forces and a velocity shear.UDK 532.529+532.517.4Translated by Vladimir A. Puchkin.     

Acoustic wave propagation in horizontally variable media

An overview of the multipath expansion method of solving the Helmholtz wave equation to describe the underwater sound field for a fixed point source in a plane multilayered medium is presented. The approach is then extended to account for horizontal variations in bottom depth, bottom type, and sound speed in the stationary phase approximation. Comparisons of model results to a limited number of measured data sets and standard propagation codes are presented.     

A suspended-particle rosette multi-sampler for discrete biogeochemical sampling in low-particle-density waters

To enable detailed investigations of early stage hydrothermal plume formation and abiotic and biotic plume processes we developed a new oceanographic tool. The Suspended Particulate Rosette sampling system has been designed to collect geochemical and microbial samples from the rising portion of deep-sea hydrothermal plumes. It can be deployed on a remotely operated vehicle for sampling rising plumes, on a wire-deployed water rosette for spatially discrete sampling of non-buoyant hydrothermal plumes, or on a fixed mooring in a hydrothermal vent field for time series sampling. It has performed successfully during both its first mooring deployment at the East Pacific Rise and its first remotely-operated vehicle deployments along the Mid-Atlantic Ridge. It is currently capable of rapidly filtering 24 discrete large-water-volume samples (30–100 L per sample) for suspended particles during a single deployment (e.g. >90 L per sample at 4–7 L per minute through 1 μm pore diameter polycarbonate filters). The Suspended Particulate Rosette sampler has been designed with a long-term goal of seafloor observatory deployments, where it can be used to collect samples in response to tectonic or other events. It is compatible with in situ optical sensors, such as laser Raman or visible reflectance spectroscopy systems, enabling in situ particle analysis immediately after sample collection and before the particles alter or degrade.     

LS-SVM曲面在多波束测深数据质量评估中的应用

在利用曲面滤波方法对深度不符值进行自动筛选的过程中,针对多项式曲面函数无法有效削弱噪声影响的问题,提出了利用LS-SVM曲面求解深度不符值的方法。在对深度不符值计算方法分析的基础上,构建LS-SVM海底趋势面,该趋势面从整体上反映了海底地形的实际变化情况,并且保留了海底地形的细节信息,可有效削弱噪声的影响。实测算例表明,LS-SVM曲面筛选得到的重合点水深不符值不存在较大偏差,计算得到的水深测量结果,能准确地反映测量数据的成果质量。     

Geostrophic adjustment and frontogenesis in stratified two-component media

A nonlinear problem of geostrophic adjustment in an ideal rotating two-component fluid in the field of gravity is studied analytically. The stratification of the fluid’s density is composed of its temperature stratification and stratification of the concentration of an admixture (in particular, these are salt seawater and moist air). Stationary states, which are reached after the adjustment process is terminated, are found with the use of Lagrange conservation laws. If the amplitudes of smooth initial disturbances are sufficiently large, discontinuity surfaces can appear in the course of evolution. Allowance for a two-component character of the medium makes qualitative properties of such surfaces especially varied. For example, a jump may be strongly marked in the field of one substance alone. It is shown that, if the initial ageostrophic property is related to temperature and/or admixture-concentration disturbances, the evolution of the fields of these substances can differ qualitatively from classical solutions to adjustment problems. For example, in the course of adjustment, the initial heat pulse can lead to the formation of a stationary temperature disturbance with a larger amplitude and/or the opposite sign. During the evolution of a smoothed temperature “step,” nonmonotonic distributions of temperature whose amplitudes are much greater than the amplitude of the initial step may appear. Some of such effects can manifest themselves even in a linear approximation.     

非均匀激发介质中螺旋波的演化

采用简单的离散可激发介质模型研究了不同性质和形状的小异质性颗粒对螺旋波演化的影响,在小异质性颗粒均匀分布的情况下,螺旋波的失稳与小异质性颗粒的形状、分布密度和性质有关.数值研究结果表明:在适当的条件下,可以观察到稳定螺旋波发生漫游和螺旋波漂移出系统边界现象,首次观察到螺旋波破碎成空间无序的周期变化斑图和破碎成时空有序的迷宫斑图现象,简要讨论了产生这些现象的物理机理.     

Clay migration and entrapment in synthetic porous media

Water-sensitivity in sandstones is commonly ascribed to mobilization, transport and recapture of clays in downstream pore throats. This is based mainly on knowledge of the clay mineral content and its electrochemistry. This paper describes a method for directly observing water-sensitivity mechanisms under the microscope using pore networks etched in glass, with clays introduced into the networks. This allows direct identification of colloidal and transport factors, which is not possible in sandstone cores. The migration behaviour has been investigated with variations in flow rate, acceleration forces and salinity. Migration was observed to occur in two distinct modes: (1) as flocs, especially in concentrated brines and at high flow rates, (2) as deflocculated individual particles, especially in distilled water. Recapture of clays occurs by the formation of ‘particle briges’. The upstream pressure indicates that particle recapture is related to decreasing permeability.     

Geostrophic adjustment of linear disturbances in two-component media

The linear problem of geostrophic adjustment in a rotating stratified medium is generalized to the case of binary mixtures stratified with respect to both the temperature and admixture concentration (such as, for example, saline seawater and humid air). It is shown that, if the initial ageostrophicity is related to the temperature and/or admixture concentration disturbances, the evolution of the fields of these substances may qualitatively differ from the classical solutions of the adjustment problems. For example, in the course of adjustment, jumps in the temperature and salinity may be retained and enhanced, in contrast to those in the velocity, pressure, and buoyancy. The latter are smoothed by the adjustment process and are distributed over relatively spacious areas with horizontal sizes of the order of the Rossby scale. The initial thermal pulse may lead to the development of a temperature disturbance with a significantly greater amplitude and/or opposite sign and to an intensive disturbance in the admixture concentration.     

Inverse modeling of discrete interaction approximations for nonlinear interactions in wind waves

In the last two decades, the Discrete Interaction Approximation (DIA) has been the only economically feasible parameterization for nonlinear wave–wave interactions in operational wind wave models. Its major drawback is its limited accuracy. Several improvements to the DIA have been suggested recently. The present study summarizes these improvements and suggests some new modifications to the DIA. Using inverse modeling techniques, where the potential of various DIAs is assessed by optimal fitting to exact solutions, a comprehensive comparison of the potential of several such improvements is made. An in depth analysis of the behavior of DIAs in full wave models will be the subject of a second study, to be reported elsewhere. The major findings of this study are that: (i) An expanded definition of the representative quadruplet with additional degrees of freedom is necessary for an accurate representation of the exact interactions; (ii) Slowly varying the free parameters in such a DIA as a function of the spectral frequency f results in a (mostly qualitative) improvement; (iii) A DIA with expanded quadruplet definition and with four representative quadruplets is found to reproduce the exact source term accurately; (iv) Adding additional tunable constants to the equation for the strength of the interactions has little impact on the quality of the DIA.     

SMOS卫星盐度数据在中国近岸海域的准确度评估

盐度是描述海洋的关键变量,对海表面盐度进行观测可以推进对全球水循环的理解。本文的主要目的是在中国近海海域对SMOS卫星盐度数据进行准确度评估。主要方法是将SMOS卫星L2海洋盐度数据产品(V317)与实测ARGO数据和走航数据进行匹配,并采用统计学的方法对SMOS卫星数据准确度进行评估。结果表明:匹配数据的线性关系不显著,SMOS卫星盐度数据(V317)在南海和东海的均方根误差分别约为1.2和0.7,应用海表面粗糙度修正模型得到的3组海表盐度数据准确度都相对较低,尤其在近岸强风场区域,海表盐度卫星数据相对于实测数据偏高,这可能是由于海表粗糙度和陆地射频干扰(RFI)作用影响的结果;SMOS卫星数据在东海的均方根误差比南海高0.5左右,这可能是由于东海海域为相对开阔海域,受陆地RFI影响相对南海较小;在中国近岸海域,应用SSS1和SSS3模型得到的盐度数据准确度相对较高,可以对模型进行地球物理参数修正,进行局地化改进,预计可以提高近岸海域盐度反演的准确度。     

Longitudinal dynamic impedance of a static drill rooted nodular pile embedded in layered soil

The static drill rooted nodular (SDRN) pile is a new type of precast pipe pile with equally spaced nodes distributed along the shaft and wrapped by the surrounding cemented soil. In this paper, the longitudinal dynamic response of the SDRN pile embedded in layered soil is investigated with respect to the complexity of the pile body structure and the pile–soil contact condition. First, the shear complex stiffness transfer model is used to simulate the radial inhomogeneity of the surrounding soil. Then, the governing Equations of the pile–soil system subjected to longitudinal dynamic loading are established. The analytical solution for the dynamic response at the pile head is obtained by the shear complex stiffness transfer method and the impedance function transfer method. The degenerate case of the present solution is compared with the published solution to verify its reliability, and the complex impedance of the SDRN pile is compared with that of the precast pipe pile and the bored pile. Finally, a parametric study is conducted to investigate the influence of pile–soil parameters on the complex impedance at the pile head within the low frequency range concerned in the design of the dynamic foundation.