中国热带6种海参骨片的种类和形态研究

利用扫描电子显微镜对我国6种热带海参(蛇目白尼参、玉足海参、花刺参、梅花参、子安辐肛参和巨梅花参)背脊部骨片的组成和结构进行了观察。结果表明,蛇目白尼参骨片有3种类型的花纹样体和1种杆状体;玉足海参骨片有2种类型的桌形体和1种扣形体;花刺参骨片有2种类型的桌形体、1种C形体和1种花纹样体;梅花参骨片有4种类型的杆状体;子安辐肛参骨片有1种花纹样体;巨梅花参骨片有1种杆状体、1种拟桌形体和1种颗粒体。结果显示,与之前学者光镜下观察的结果存在差异,玉足海参桌形体底盘中央是单孔而非4孔;花刺参桌形体立柱之间没有横梁连接。并发现了新的骨片类型:蛇目白尼参Ⅲ型花纹样体和杆状体;玉足海参顶部周缘小孔桌形体;花刺参顶部5簇小齿桌形体;梅花参Ⅱ型、Ⅲ型、Ⅳ型杆状体。     

与岸线协调的水深自动选取方法

针对当前水深自动选取中水深点与岸线的协调匹配问题,提出了一种与岸线协调的水深自动选取方法。通过分析资料水深点与岸线的平面位置关系,提取出与岸线协调的待选水深点;从航海安全角度考虑,优先选取浅水深点;在此基础上,分别定义水深点与岸线弯曲处、平直处的协调度,并建立协调度评估模型;通过定量计算协调度,选取出与岸线协调匹配的水深点。实验结果表明,所提方法能在岸线弯曲处优先选取出协调的水深点,同时能保证在岸线平直处附近所选取的水深点分布合理;所提方法能够较好地考虑水深点与岸线的图上位置关系,避免水深注记中断岸线、水深注记"上陆"的情况出现。     

EPSONDE: an instrument to measure turbulence in the deep ocean

EPSONDE is a tethered free-fall profiling system used to obtain temperature microstructure and velocity turbulence data to a depth of at least 1500 m. EPSONDE, which carries a variety of slow and fast sensors, is deployed on a loose kevlar multiconductor cable by a specialized wire-handling system. Data are transmitted from this underwater unit (1792 samples per second) to a shipboard system which includes a dedicated microcomputer for data logging and online data processing. The performance of this system is demonstrated by discussing a study of turbulent mixing processes in a lens of Mediterranean water (a MEDDY) found at a depth of 1000 m in the Canary basin. These studies indicate that turbulent kinetic energy dissipation may be an important mechanism in determining the decay and lifetime of a MEDDY     

Damping of gravity–capillary waves on water surface covered with a visco-elastic film of finite thickness

Results of laboratory studies of the damping of gravity–capillary waves on a water surface covered with a film of petroleum product (diesel fuel) in a wide range of change in a film thickness are presented. A nonmonotonic dependence (with a local maximum) of a damping coefficient on film thickness is discovered. Numerical calculations of the dispersion equation for gravity–capillary waves in the presence of a viscoelastic film of arbitrary thickness, which confirmed the existence of the maximum of the damping coefficient as a function of film thickness, are performed. Based on a comparison of the calculation results and the data of laboratory measurements of wave characteristics, the values of parameters in the diesel fuel films are estimated in a wide range of a change in their thickness.     

Experimental study of turbulent-wake expansion from a surface ship

We studied the time dynamics of a turbulent region excited by a moving surface vessel in a field experiment. The time dependences of the geometrical sizes of the turbulent region are obtained, and it is shown that the time dependence of the width of the turbulent wake at the initial stage is close to the power-law function with an exponent of 0.4 for different experiments (the depth of the wake remaining practically constant). In the semiempirical turbulence theory, we suggested a qualitative model describing the process of the initial expansion of a ship wake as a diffusion of a one-dimensional layer of turbulized liquid due to a pulsed source.     

The optimum dimensions for a long-range, autonomous, deep-diving, underwater vehicle for oceanographic research

From the results of a parameter optimization process based on a “minimum feasible volume” criterion, it is shown that the optimum shape for a transatlantic, deep-diving, autonomous submersible is a “low drag” hull shape with a displaced volume of 4.4 m³, a length of 5.97 m and a maximum diameter of 1.33 m. Calculations show that a vehicle of these dimensions, travelling in a minimum drag “cruise” configuration at a depth of 3000 m, say, and at a velocity of 2.5 m/sec could have a maximum range of 7000 km provided the “hotel” power consumption is kept low.     

Transient soil response in a porous seabed with variable permeability

The soil permeability of many natural marine sediments decreases with depth because of consolidation under overburden pressure. This is accompanied by a decrease in porosity and void ratio that also affect the permeability. Conventional theories for wave-induced soil response have assumed a homogeneous porous seabed. This paper presents a new approach for the wave-induced response in a soil matrix, with variable permeability as a function of burial depth. The soil matrix considered is unsaturated and anisotropic, and is subject to a three-dimensional wave system. The pore pressure and effective stresses induced by such a system are obtained from a set of equations incorporating a variable permeability. Verification is available through reduction to the simple case of uniform permeability. The results indicate that the effect of variable soil permeability on pore pressure and vertical effective stress may be significant, especially in a gravelled seabed and for unsaturated sandy soils.     

Estimation of the Roll Hydrodynamic Moment Model of a Ship by Using the System Identification Method and the Free Running Model Test

When a fast container ship or a naval vessel turns, accompanying roll motions occur. This roll effect must be considered in the horizontal equations of the motion of the ship to predict the maneuverability of the ship properly. In this paper, a new method for determining a model structure of the hydrodynamic roll moment acting on a ship and for estimating the hydrodynamic coefficients is proposed. The method utilizes a system identification technique with the data from sea trial tests or from free running model (FRM) tests. To obtain motion data that is applied to the proposed algorithm, an FRM of a large container ship was developed. Using this model ship, standard maneuvering tests were carried out on a small body of water out of doors. A hydrodynamic roll moment model was constructed utilizing the data from turning circle tests and a 20-20 zig-zag test. This was then confirmed through a 10-10 zig-zag test. It was concluded that a model structure of the hydrodynamic roll moment model could be established without difficulty through a system identification method and FRM tests.     

The use of artificial neural networks for the intelligent optimalcontrol of surface ships

Many conventional ship autopilots use proportional integral and derivative (PID) control algorithms to guide a ship on a fixed heading (course-keeping) or a new heading (course-changing). Such systems usually have a gyrocompass as a single sensory input. Modern sea going vessels have a range of navigation aids most of which may be interconnected to form integrated systems. It is possible to employ the navigational data to provide best estimates of state vectors (Kalman filter) and optimal guidance strategies. Such techniques require powerful computing facilities, particularly if the dynamic characteristics of the vessel are changing, as may be the case in a maneuvering situation or changes in forward speed. This paper investigates the possibility of training a neural network to behave in the same manner as an optimal ship guidance system, the objective being to provide a system that can adapt its parameters so that it provides optimal performance over a range of conditions, without incurring a large computational penalty. A series of simulation studies have been undertaken to compare the performance of a trained neural network with that of the original optimal guidance system over a range of forward speeds. It is demonstrated that a single network has comparable performance to a set of optimal guidance control laws, each computed for different forward speeds     

A brief catalogue of failures: Framing evaluation and learning in fisheries resource management

We propose a framework for enabling a systematic evaluation of a fisheries resource management system, which we define as a feed-back mechanism coupled to a fishery. The resource management system includes four basic functions: diagnostics, intervention, goal setting, and decision making. This model allows for the development of an evaluation framework for fisheries resource management by facilitating a typology of failures. We suggest that the potential for systemic and interdisciplinary learning will be significantly enhanced through the process of developing such a framework.     

A Lagrangian particle random walk model for simulating a deep-sea hydrothermal plume with both buoyant and non-buoyant features

This paper presents a computational model of simulating a deep-sea hydrothermal plume based on a Lagrangian particle random walk algorithm. This model achieves the efficient process to calculate a numerical plume developed in a fluid-advected environment with the characteristics such as significant filament intermittency and significant plume meander due to flow variation with both time and location. Especially, this model addresses both non-buoyant and buoyant features of a deep-sea hydrothermal plume in three dimensions, which significantly challenge a strategy for tracing the deep-sea hydrothermal plume and localizing its source. This paper also systematically discusses stochastic initial and boundary conditions that are critical to generate a proper numerical plume. The developed model is a powerful tool to evaluate and optimize strategies for the tracking of a deep-sea hydrothermal plume via an autonomous underwater vehicle (AUV).     

A diagnostic modelling framework to construct indices of biotic integrity: A case study of fish in the Zeeschelde estuary (Belgium)

We propose a coherent regression model building framework to construct fish-based indices. More specifically, we concentrate on the selection of an optimal set of metrics which remains a difficult problem. The paper departs from the observation that an index of biotic integrity (IBI) is analogous to a diagnostic model in medicine assessing the health condition of a patient from a series of biomarkers. In the same vein, an IBI is a diagnostic model predicting the ecosystem condition of a site from a set of (scored) metrics. Metrics are community attributes sensitive to anthropogenic pressure and their scores express the “distance to target” to a reference condition. In a medical context, Receiver Operating Characteristic (ROC) curves are commonly used to assess the diagnostic accuracy of laboratory tests. An ROC curve plots the sensitivity of a test (Se; the capacity to detect a disease or degradation) as a function of its false positive fraction (FPF) which is the complement of the specificity (Sp = 1 - FPF; the capacity to recognise a healthy person or a reference condition). The ROC curve represents the strength of the index to discriminate between degraded and reference sites. Higher curves correspond to stronger tests as then a higher sensitivity can be combined with a lower false positive fraction. Hence, it is intuitively clear to use summary statistics of the ROC curve as criteria to optimise medical tests or biotic indices. In this paper, we illustrate the value of this modelling framework with a case study in the Zeeschelde estuary in Belgium. In essence, a “traditional” IBI is an average of metrics scoring relevant properties of the ecosystem. We demonstrate this average score model (AVG) is a special member of the more flexible predictive logistic model (PLM) family. The selection of a set of metrics becomes equivalent to variable selection in statistical model building. We apply model building techniques as best subsets regression to facilitate the search for an optimal suite of metrics from a candidate set and use cross-validation to avoid overfitting. The results show that a few metrics suffice to discriminate between most-impacted and least-impacted sites.     

Experiments on Surface Waves Interacting with Flexible Aquatic Vegetation

Surface wave interaction with aquatic vegetation appears to play a key role in coastal hydro-morpho-dynamics. As an example, the presence of a dense meadow at intermediate water depth is usually associated with a stable and resilient shore. Wave-meadow interactions are investigated here by means of physical modelling, with a focus on wave height distribution and hydrodynamics. The central part of a wave flume is covered by flexible artificial seagrass, composed of polyethylene leaves. This vegetation is tested in both near emergent and submerged conditions. The wave height reduction is evaluated by means of a drag coefficient defined from linear wave theory, which contains all the unknowns of the adopted methodology. The behaviour of such a coefficient is investigated as a function of a wave related Reynolds number. The influence of the flexibility of the leaves is also considered, together with a wave frequency parameter. The results show a complex behaviour with three different trends for near rigid, intermediate or highly flexible leaves. Amplitudes of the orbital velocities are investigated and show a fairly good match with the linear wave theory. On the contrary, the mean velocity along the water column appears to be modified by the seagrass for submerged leaves.     

The motion of a 9.1 m yacht hull buoy moored in open sea

A 9.1 m yacht hull was instrumented to measure its three-dimensional motion when moored in the open sea. The hull was deployed on three occasions for a total period of about 2 months and encountered a wide range of wind-wave conditions including a strong gale. The data have been analysed to give the response for each component of motion in terms of amplitude and relative phases. The hull motion is compared spectrally to the waves observed by a nearby Waverider. The hull was found to behave as a surface-keyed buoy, with a well defined response for a wide range of conditions. The presence of a resonance in pitch and roll is evident in the data with typical rms values being 5° and 10°, respectively, for significant wave height of 5 m. From data on the mooring dynamics it is concluded that the peaks observed in the tension are a result of the viscous drag opposing the change in the catenary of the mooring and the slow drift oscillations of the buoy. This type of hull is a versatile and economical candidate as a platform for meteorological and oceanographic instrumentation.     

Probability assessment for deep-draft navigation channel design

This paper describes a method for assessing the probability of a ship accident in an entrance channel for different recurrence intervals using model data. This new method includes a rational criteria for evaluating various channel configurations and depths for a range of realistic environmental (i.e., wind, wave, and current) conditions and annual number of ship calls. This four-component climatology-interactive model includes a Poisson probability law for number of ship arrivals, a Bernoulli probability law for grounding in a single random ship arrival, an estimation of the probability parameter in the Bernoulli law from model tests, and a determination of recurrence intervals or return periods. A remote-controlled model of a C9 containership was used to evaluate the navigability of existing and proposed harbor and entrance-channel configurations for a range of environmental conditions in a three-dimensional physical model of Barbers Point Harbor, Oahu, HI.     

Bifurcation of barotropic flow and homogenization of potential vorticity in a rotating laboratory model

Laboratory experiments with a rotating tank confirm the bifurcation character of a barotropic flow driven by an inflow and an outflow described by Sakai (1986). The model, a circular basin with a topographic β-effect, simulates a mid-latitude oceanic feature. At a low Rossby number, stationary Rossby waves are observed which are symmetrical with a line connecting the inlet and the outlet. As the Rossby number increases, a bifurcation occurs and two kinds of vortex flows are observed. In the vortex, potential vorticity is almost uniform. In addition to the two vortex flows, a jet-like inertial flow can also be observed. In general, thre results of these experiments agree well with those of a low-order model and a numerical model.     

Wave dispersion equation in a porous seabed

The wave dispersion equation has played a very important role in the development of ocean surface wave theories. The evaluation of the length of a water wave is an essential example of solving the dispersion relation. Conventional ocean wave theories have been based on an assumption of a rigid impermeable seabed. Thus, the conventional wave dispersion equation can only be used in the case of a wave propagating over a rigid impermeable seabed. For waves propagating over a porous seabed (such as a sandy bed), the conventional dispersion relation is no longer valid because of the absence of the characteristics of the porous seabed. The objective of this study is to establish a new wave dispersion equation for waves propagating over a porous seabed. Based on the new relation, the effects of a porous seabed on wave characteristics (such as the wavelength and wave profile) are discussed in detail.     

Spatial and temporal variability and size fractionation of chlorophyll a in the tropical and subtropical Pacific Ocean

The spatial and temporal variability and size fractionation of chlorophyll a(Chl a) were investigated in the tropical and subtropical Pacific Ocean during four survey cruises from 2005 to 2009.The surface Chl a(S-Chl a) concentration ranged from 0.002 to 0.497 mg/m 3 and was obviously higher in the eastern Pacific than in the western and central Pacific.The vertical distribution of Chl a displayed a single peak pattern,and the maximum Chl a layer(MCL) was observed at a shallower depth in the eastern Pacific than in the western Pacific.All three size fractions of Chl a measurements in the surface water showed a similar distribution to total Chl a and were found in higher concentrations in the eastern Pacific than in the western and central Pacific.Picoplankton dominated the phytoplankton in the surveyed tropical and subtropical Pacific Ocean.Furthermore,pico-Chl a(0.2-2 μm) accounted for a larger percentage of the total Chl a in the central Pacific than it did in the western Pacific and eastern Pacific.In the western Pacific,there seemed to be a latitudinal variability in the phytoplankton community composition where small-sized phytoplankton(<2 μm) were more dominant in the tropical than in the subtropical western Pacific.The spatial and temporal variability and size fractionation of Chl a were controlled by hydrological and chemical characteristics and climate events,such as El Nin o and La Nin a.     

高阶非线性完全频散性波浪数值模型及应用

为更精确地模拟强非线性完全频散性波浪的传播,采用长波上非线性重力表面波传播高阶数学模型,综合参考此模式已有的研究成果,建立了一个高达五阶的完全频散性非线性数值模型。应用该五阶模式对斜坡地形、潜堤地形及正弦沙链地形进行模拟计算,并与已有的实验资料进行对比,结果显示五阶模式较低阶模式模拟结果的精度上有了明显提高,模拟波形与实验结果吻合度良好,证明高阶模式更适用于高频散高非线性波浪传播的数值模拟。     

Morphological and statistical approaches to improve detection in the presence of reverberation

The detection of a target echo in a sonar image is usually a difficult task since the reverberation, consisting of a large number of spurious echoes, generates a lot of false alarms. In this paper, we propose two new detectors derived from image processing algorithms. These detectors are respectively based on a morphological and a statistical contrast. Each detector only requires setting a few parameters. This setting is done using some prior knowledge about the data (shape of the emitted signal and the used antenna, characteristics of the reverberation). Nevertheless, an extensive statistical study of the detection performances proves that the proposed methods are robust and that even an imprecise setting of the parameters leads to satisfactory results. Applied to the real data, these detectors and their sequential combination lead to a significant improvement on the performances: The false alarm rate is drastically reduced while the detection probability is preserved. Based on different contrasts, these detectors have complementary behaviors. Therefore, a further improvement is achieved by a fusion of the different results to classify the remaining echoes as whether spurious or true detection.