The wind-field structure in a stably stratified atmospheric boundary layer over a rough surface

Both wind turning with height and ageostrophic flow in a stably stratified atmospheric boundary layer are analyzed using a three-parameter turbulence model. For a quasi-steady state of the boundary layer, the cross-isobaric flow is determined only by turbulent stress at the surface in the direction of geostrophic wind. The “operative” prediction models, in which the first-order turbulence closure schemes are used, tend to overestimate the boundary-layer depth and underestimate the angle between the surface and geostrophic winds when compared to “research” models (schemes of high-level turbulence closure). The true value of the angle between the surface and geostrophic winds is significant for the presentation of a large-scale flow. A nocturnal low-level jet is a mesoscale phenomenon reflected in data obtained from measurements in a stably stratified atmospheric boundary layer. It is found that such jets are of great importance in transporting humidity, momentum, and air pollution. In this study, the difference between jet flows over a homogeneous underlying surface and over a spatially localized large-scale aerodynamic roughness is shown.     

Modeling a neutrally stratified turbulent air flow over a horizontal rough surface

The neutrally stratified boundary layer over a smooth rough surface is consider. The turbulent flow is simulated using a finite-difference eddy-resolving model of the atmospheric boundary layer (ABL). The model includes different turbulence closure schemes and numerical approximations for advection components of the momentum balance equation. We investigate the quality of reproduction of spectral characteristics of the turbulent flow and the model’s capabilities to reproduce the observed profile of mean wind velocity near the rough surface. It is shown that the best result is obtained by coupling a numerical scheme of higher order of accuracy with a mixed closure scheme based on an adaptive estimation of the mixing length for subgrid-scale fluctuations. Here, we are able to reproduce the asymptotics of the fluctuation spectrum of the longitudinal component of wind velocity near the surface and within the boundary layer as well as the logarithmic profile of mean velocity near the surface.     

Acoustic plane-wave scattering from a rough surface over a random fluid medium

Acoustic plane-wave scattering from a rough surface overlying a fluid half-space with a sound-speed distribution subject to a small random variation is considered. Under the assumption that the surface roughness and medium randomness are statistically independent, the scattered field may be derived by first solving for the mean field in the medium, and then incorporating with boundary-perturbation method to obtain the total mean field and the power spectral density of the scattered field. The employed algorithm is compatible to the analysis available in the existing literature so that the formulations are conveniently integrated. The results for the power spectral density have shown that the effects of medium inhomogeneities on the rough surface scattering are limited in a spectral regime where the scattered components have shallow grazing angles. The distribution of the power spectral density over the space is primarily governed by the power spectrum and correlation lengths of the rough surface.     

Acoustic plane-wave reflection from a rough surface over a random fluid half-space

Plane-wave reflection from a rough surface overlying a fluid half-space, with a sound speed distribution subject to a small and random perturbation, is considered. A theory based upon a boundary perturbation method in conjunction with a formulation derived from Green's function for the coherent field in the random medium have been applied to a typical oceanic environment to study their effects on the plane-wave reflection. By considering the coherent field itself, the plane-wave reflection may be obtained straightforwardly through a procedure consistent with the formalisms currently employed in rough surface scattering. The results show that both the rough surface and medium inhomogenieties may reduce the plane-wave reflection, however, the characteristics of the curves representing their effects are different, enabling us to identify the dominant scattering mechanism. The results for the coherent reflection due to the individual scattering mechanism are compatible with those found in the existing literature.     

The partition wavenumber in acoustic backscattering from atwo-scale rough surface described by a power-law spectrum

Scattering from the ocean bottom is often assumed to be controlled by two spatial scales: the larger scale associated with reflections from plane facets, and the smaller one associated with diffuse scattering from height variations. Choosing the wavenumber for this partitioning has proven to be important but troublesome. For this work, scattering data are simulated using Helmholtz-Kirchhoff or physical optics theory and selected input geomorphology. These data are inverted to provide rms slope of facets and rms heights of small-scale roughness using a simple two-scale roughness model introduced previously (J. W. Caruthers and J. C. Novarini, IEEE J. Oceanic Eng., vol. 18, pp. 100-106, 1993). Bottom relief is described by power spectra of the power law form, and the bottom is assumed to be impenetrable. The work introduces a new criterion for effecting this partition based on setting a roughness parameter equal to unity. The criterion is shown to be valid for the cases analyzed based on the ability of the inversion model to recover the input geomorphology     

Spectral radiometric measurements of the temperature and radiation capacity of a rough sea surface

The results of radiometric remote simultaneous field measurements of the temperature and radiation capacity of the upper layer of the sea-surface temperature film 0.2 mm thick are presented. The measurements were conducted in the presence of wind waves and were characterized by an increased accuracy, which was achieved owing to the use of measurements of the intensity of radio radiation from the surface illuminated by radiation of a specified varying power. In our experiment, this illumination was provided by the radio radiation of the atmosphere, whose radiance temperature varies significantly, depending on the frequency at the slope of the absorption band of molecular oxygen (52.5–56 GHz). As a result, the radiation capacity and temperature of the skin layer were determined from the correlation dependence between the radiance temperatures of the surface and atmosphere measured by a radiometer-spectrometer in a number of channels separated in frequency. The radiance temperatures of the sea and atmosphere were measured at four frequencies of the 5-mm spectral range (53–55 GHz) on a vertical polarization. For absolute measurements, a calibration method was developed on the basis of a blackbody disk and two reflecting mirrors with the same solid angles. The measured values of the radiation capacity are variable and substantially smaller than the theoretical values determined by the models accepted for the permittivity of water and sea roughness. A possible cause of this can be the change of the permittivity of water in a thin surface layer of the temperature film (0.2 mm) due to the concentration of gases dissolved in water and surface-active substances within this layer.     

Countergradient heat transfer in the atmospheric boundary layer over a rough surface

The nonlocality of the mechanism of turbulent heat transfer in the atmospheric boundary layer over a rough surface manifests itself in the form of bounded areas of countergradient heat transfer, which are diagnosed from analysis of balance items in the transport equation for the variance of temperature fluctuations and from calculation of the coefficients of turbulent momentum and heat transfer invoking the model of “gradient diffusion.” It is shown that countergradient heat transfer in local regions is caused by turbulent diffusion or by the term of the divergence of triple correlation in the balance equation for the temperature variance.     

Features of turbulent momentum and heat transfer in a stably stratified boundary layer over a rough surface

The features of the structure of a stable boundary layer over an urbanized surface are studied using a nonlocal model for the turbulent momentum and heat fluxes, which physically adequately takes into account the effect of buoyancy on turbulent transfer. The transformation of the structure of the boundary layer during transition from a state of convective mixing to a stable state is described by unified expressions for the turbulent momentum and heat fluxes. In some known schemes, different models are used for unstable and stable states. The model reproduces a stable dependence of the Prandtl number on the Richardson number and countergradient heat transfer in a strongly stable boundary layer. The results of numerical simulation are compared to the data of a laboratory experiment and the data obtained using the large-eddy simulation (LES) method.     

Experimental study of the fine structure of the wind field near a rough surface

The air-flow velocity field near the water surface is studied in the zone of wind-wave intensification. Caused by a periodic separation of eddies, a nonzero time-averaged value of the wind velocity in the near-water streamline is detected at the leading slope of the wave. The distribution of pressure along the wave with allowance for the vertical velocity shear and disturbances produced by eddies and a periodic deceleration of the viscous layer was calculated with the aid of the Cauchy-Lagrange integral. This procedure made it possible to calculate the growth rate of the wave amplitude, whose value was found to be close to its experimental value at the initial stage of acceleration.     

Lidar sensing of topographic inhomogeneities on the rough sea surface

The results of lidar sensing of the sea surface carried out from an oceanographic platform in the Black Sea under different hydrometeorological conditions are considered. It is found that the frequency, time, and intensity of the mirror-reflected lidar specks of light vary essentially when the wind wave structure anomalies appear, which arise owing to some physical processes evolving in the air-sea boundary layers. The effects conditioned by an unsteady and non-uniform wind, the hydrological front, the slicks related to internal waves and Langmuir circulation, industrial pollution of the sea surface by surface-active substances, and rainfall are estimated quantitatively. A conclusion about the prospects of application of the lidar specks indication method for ecological monitoring and control of the sea surface state and internal basins is drawn.Translated by Mikhail M. Trufanov.     

Simulation of Kelvin wakes in optical images of rough sea surface

Kelvin wake is one of the common wakes generated by moving ships and contains rich information about ships. In this paper, free wave elevations of Kelvin wake are calculated based on the Michell thin ship theory combined with a point source perturbation model. The probability density function of sea surface slopes is introduced to calculate the specular reflection of sunlight and skylight and the refraction of scattered light underwater. Satellite-detected Kelvin wakes are then simulated by adding surface specular reflectance and water-leaving reflectance. Simulation results agree well with satellite measurements. The specular reflection of sunlight is the decisive factor affecting the features of Kelvin wakes according to the simulation results. The main factors that influence the specular reflection of sunlight, such as the incident direction and observation direction, ship parameters, and background environment, are discussed. This study is helpful for wake detection and provides a preliminary theoretical method for the retrieval of ship information.     

The pressure impulse in a fluid saturated crack in a sea wall

When a wave breaks against a sea wall containing a crack, such as might exist within the blockwork, pressure pulses can travel through the fluid and propagate into the crack. This can cause high stresses to act on the sides and roof of the crack and may even cause the constituent blocks to move. The Pressure Impulse, P, is used to model the effect of wave impact against a wall in which there is a fluid filled crack. A two-dimensional field equation is derived for P that is applicable in plane cracks of non-uniform, narrow width. This is solved for several geometries relating to cracks between constituent blocks of sea walls, in order to compare the impulsive forces with the gravitational force on a block. It is shown that a large block can be lifted due to the impulse exerted by the fluid in a crack beneath it.     

The 0-1 test algorithm for chaos and its applications

To determine whether a given deterministic nonlinear dynamic system is chaotic or periodic, a novel test approach named zero-one (0-1) test has been proposed recently. In this approach, the regular and chaotic motions can be decided by calculating the parameter K approaching asymptotically to zero or one. In this study, we focus on the 0-1 test algorithm and illustrate the selection of parameters of this algorithm by numerical experiments. To validate the reliability and the universality of this algorithm, it is applied to typical nonlinear dynamic systems, including fractional-order dynamic system.     

Characteristics of turbulent boundary layers over a rough bed under saw-tooth waves and its application to sediment transport

A large number of studies have been done dealing with sinusoidal wave boundary layers in the past. However, ocean waves often have a strong asymmetric shape especially in shallow water, and net of sediment movement occurs. It is envisaged that bottom shear stress and sediment transport behaviors influenced by the effect of asymmetry are different from those in sinusoidal waves. Characteristics of the turbulent boundary layer under breaking waves (saw-tooth) are investigated and described through both laboratory and numerical experiments. A new calculation method for bottom shear stress based on velocity and acceleration terms, theoretical phase difference, φ and the acceleration coefficient, a_c expressing the wave skew-ness effect for saw-tooth waves is proposed. The acceleration coefficient was determined empirically from both experimental and baseline k–ω model results. The new calculation has shown better agreement with the experimental data along a wave cycle for all saw-tooth wave cases compared by other existing methods. It was further applied into sediment transport rate calculation induced by skew waves. Sediment transport rate was formulated by using the existing sheet flow sediment transport rate data under skew waves by Watanabe and Sato [Watanabe, A. and Sato, S., 2004. A sheet-flow transport rate formula for asymmetric, forward-leaning waves and currents. Proc. of 29th ICCE, ASCE, pp. 1703–1714.]. Moreover, the characteristics of the net sediment transport were also examined and a good agreement between the proposed method and experimental data has been found.     

Traveling wavefront ray tracing and its applications

The current discussion of whether marine geodesy is something entirely new or part of oceanography or geodesy can be clarified by re‐examining our notions about the basic business of geodesy. This paper contends that the same basic geodetic services, which were needed for millenia to chart and control new territory, are being adapted now to the marine environment to suit modern accuracy standards. In a brief historical review it is shown that conceptually, the oceanic regions were always an integral part of geodetic concern. The oceans were certainly part of the world for the ancient map makers and for Pythagoras’ spherical earth model. Notions connected with the marine geoid were implied in ancient speculations. Distances and directions at sea, even depths, were determined to meet the requirements of the times. With the modern sophistication in geodetic theory and measuring techniques, these ideas became more refined and demanding in turn, but they were there all the time. For obvious reasons, land geodesy developed faster; marine geodesy will catch up now, because only now there is the technical capability and also an urgent economic motivation.     

Video cathodoluminescence microscopy of diagenetic cements and its applications

Diagenetic studies of sedimentary rocks using cold cathodoluminescence (CL) microscopy have been severely limited because of the very low intensity of visible luminescent emissions, which required long photographic exposure times, and because of the difficulty in obtaining quantitative data from CL observations. The solution to this problem is to fit the microscope with a high-sensitivity digital colour video camera linked to a computer with image enhancement and image analysis software. The new technique described in this paper:

• produces digital CL images of consistent high quality, both quickly and cheaply;

• controls the capture and editing of CL images, to reveal detailed textural information even from minerals exhibiting low level luminescence such as quartz;

• acquires quantitative information on pore systems and the abundance of cement zones from CL images.

Examples are presented to demonstrate the high quality of images produced in this way and the range of uses to which the new technique can be applied. The ability to image exactly the same field of view in both plane polarised light and CL is a particular advantage. Image analysis techniques have been developed to give a statistical characterisation of both pore systems and cement phases that infill them. The abundance of contrasting cement zones seen in CL can be measured and the abundance of cement phases can be mapped across a reservoir. The history of porosity occlusion can be reconstructed quantitatively and integrated with burial history and hydrocarbon migration. Porosity can be measured accurately and, since the technique obtains data on pore geometry as well as abundance, the pore system can be characterised by pore size distributions and pseudo-capillary pressure curves. This also opens the possibility of estimating permeability from thin sections.     

Experimental studies of thermal radiation intensity dependence on near-water wind speed for rough sea surface

The results of in situ measurements of the characteristics of intrinsic microwave radiation from the sea surface are presented. The studies were carried out on the oceanographic platform of the Experimental Department of Marine Hydrophysical Institute during the summer–fall periods for 3 years, which made it possible to accumulate a significant amount of information on the change in the radiation intensity of under different meteorological conditions. Attention is primarily focused on the construction of wind-radiation dependences and their steepness analysis based on the measurement data obtained by a radiometer-polarimeter with a central frequency of received radiation equal to 37.7 GHz. The results are compared with the previous experimental studies and the model estimates of this effect.     

Primary yielding locus of cement-stabilized marine clay and its applications

ABSTRACT

Strength and stiffness properties of materials are widely studied and used in civil engineering practice. However, most studies are based on unconfined conditions, which are different from real status of soil. This study investigated the primary yielding and yield locus for cement-stabilized marine clay. In this study, two types of cement-stabilized soils were studied through isotropic compression, triaxial drained shearing, unconfined compression, and bender element testing. Specimens with 20–50% of cement content and 7–90 days of curing period were used for the tests. Stress–strain behavior and primary yielding were evaluated, followed by construction of the primary yield locus. The characteristics of the primary yield locus and its development with curing time then were studied. The results showed that the properties of the primary yield locus were dependent on the type of stabilized soil, but were independent of the cement content and curing period. Thus, the approach provides a way to estimate the primary yield stress and drained stress path before primary yielding for cement-stabilized soil under confined condition. An empirical function was used to fit the primary yield locus. The primary isotropic yield stress was correlated to unconfined compressive strength or maximum shear modulus. Three indirect methods were proposed to predict the primary yield stress for cement-stabilized marine clay. The results showed that the primary yield stress can be estimated with reasonable accuracy.     

黄河口粉质土矿物成分特征及对水动力条件响应的研究

黄河三角洲潮坪上构筑的道路使得道路两侧水动力条件出现差异。在道路两侧各选典型区域,取样进行X-ray衍射物相分析,概略分析潮坪沉积物的矿物成分及含量对水动力条件响应的变化,发现了强水动力环境使沉积物中碎屑矿物含量增大,黏土矿物含量减小,非均匀性增大的规律,此规律在表层沉积物中更为明显。     

韵律模式及其在热带气旋预报中的应用

本文从单站气压,气温和湿度时间变化曲线图上分析归纳得到的６个月韵律模式,在入侵厦门同安区的热带气液长期预报服务实践中收到了良好的效果。本韵律模式预报简便,预报准确度高出气候概率４倍以上。