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河口盐淡水混合的几个认识和概念问题 总被引：3，自引：0，他引：3
本文讨论了河口的定义,范围以及盐淡水混合的类型、程度和强度等问题,认为盐淡水混合状态 淡水混合作用是两个不同的概念,不能混为一谈。 相似文献
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海水入侵机制及因素分析 总被引：3，自引：0，他引：3
通过山东沿海地下咸淡水突变界面位置与地下淡水位动态的相关分析发现,一旦地下淡水位发生变化,成淡水突变界面就会发生相应位移,即地下淡水位升高时,成淡水突变界面向海侧移动,反之则海水向陆地地下入侵,与Ghyben-Herzberg成淡水界面模型基本相符。分析了自然因素中引起海水入侵的基本条件,但最终导致海水入侵发生发展的是人为因素——过度超采地下淡水、采补失调及其他人为活动影响。 相似文献
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文章利用观测和模式数据, 并基于混合层盐度收支方法, 研究了热带东太平洋淡水池的季节变化。研究发现: 热带东太平洋淡水池具有显著的季节变化, 由海表强迫(蒸发与降水)、水平平流和次表层过程共同控制。淡水池的季节变化主要分为扩张与收缩两个阶段。4月至11月为扩张阶段, 淡水池向西扩张, 最大体积和面积比最小时扩大将近一倍, 分别达到2.83×10 5km 3和8.94×10 6km 2。热带辐合带向北移动带来的强降水是淡水池扩张的主要原因, 海表强迫决定了混合层盐度降低。12月至3月为淡水池收缩阶段, 海表淡水通量的减弱、水平平流和次表层过程的增强导致混合层盐度升高, 淡水池向东收缩。 相似文献
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水资源特别是淡水资源是人类生存的根本。生命的衍续、人类生活时时刻刻离不开淡水。随着世界上人口的增加和工农业生产的发展,人类对于淡水资源的需求日趋增加,为了生存和发展,人类被迫去寻求途径解决淡水短缺问题。从长远来看,向海洋要淡水已成为世界淡水开发的趋势。 相似文献
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水资源特别是淡水资源是人类生存的根本。生命的衍续、人类生活时时刻刻离不开淡水。随着世界上人口的增加和工农业生产的发展,人类对于淡水资源的需求日趋增加,为了生存和发展,人类被迫去寻求途径解决淡水短缺问题。从长远来看,向海洋要淡水已成为世界淡水开发的趋势。 相似文献
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10个凡纳滨对虾全同胞家系淡水耐受性比较 总被引：1，自引：0，他引：1
目前,生长性状和抗逆抗病性状是对虾遗传选育的主要指标。本文报道了同一批次的10个凡纳滨对虾全同胞家系淡水耐受力和生长性状的比较结果,耐受性试验从P13开始直至4月龄大小,经过连续4次的淡水耐受力试验和生长性状测量比较,结果表明:在同一时期不同家系之间的淡水耐受力存在显著差异,其中P13仔虾中家系C15、C17、C19在淡水中的平均存活时间分别为:78、55和96min。随着日龄的增长耐受力也逐渐增强,2月龄、3月龄、和4月龄的试验中家系C17和C19在淡水中48h的平均存活率最高,分别为25%、65%、40%和60%、55%、48%;综合生长和淡水耐受性分析得出家系C17和C19可以作为耐淡水优良家系选育的候选材料,为进一步选育凡纳滨对虾淡水耐受新品系提供了基础。 相似文献
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夏季珠江冲淡水扩散路径分析 总被引：9，自引：0，他引：9
利用1978~1988年国家海洋局南海分局南海北部断面调查获得的盐度资料,分析了珠江口附近海域盐度的时空分布特征,描述了夏季珠江冲淡水的扩散路径。通过统计分析相应时间段的风场、平均海平面高度、珠江径流以及陆地降水等资料,讨论了影响珠江冲淡水扩散的主要因子。我们发现:夏季珠江冲淡水扩散方向与南风强度(频率和平均风速)、近岸海面月平均高度以及径流强度的关系极为密切,如果西南季风强盛,珠江冲淡水向东扩散就多;如果近岸海面高度显著增高,珠江冲淡水向西流动就特别强。 相似文献
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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。 相似文献
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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. 相似文献
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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. 相似文献
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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. 相似文献
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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. 相似文献
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The generation and propagation mechanisms of a Kyucho and a bottom intrusion in the Bungo Channel, Japan, have been studied
numerically using the hydrostatic primitive equations by assuming density stratification during summer. The experiments are
designed to generate a Kuroshio small meander in Hyuga-Nada, which acts as a trigger for these disturbances. After the current
speed of the Kuroshio is changed, a small meander is generated. At the head of the small meander, warm Kuroshio water is engulfed,
and encounters the southwest coast of Shikoku. However, convergence of heat flux on the bump off Cape Ashizuri suppresses
the generation of a warm disturbance, if the current speed is large. As the cold eddy associated with the small meander approaches
Cape Ashizuri, the heat flux diverges on the bump. This heat source forces a warm disturbance, which intrudes along the east
coast of the Bungo Channel as a baroclinic Kelvin wave (a Kyucho). After the cold eddy passes off Cape Ashizuri, the Kuroshio
approaches the bump again. Strong convergence of heat flux then occurs on the bump, which forces a cold disturbance. This
disturbance propagates as a topographic Rossby wave along the shelf break at the mouth of the channel. After the topographic
wave reaches the west end of the shelf break, it intrudes along the bottom layer of the channel as a density current (a bottom
intrusion). These results suggest that a Kyucho and a bottom intrusion are successive events associated with the propagation
of the small meander. 相似文献
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Hyeon Kyu Yoon Nam Sun Son Gyeong Joong Lee 《Oceanic Engineering, IEEE Journal of》2007,32(4):798-806
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. 相似文献
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Spatial and temporal variability and size fractionation of chlorophyll a in the tropical and subtropical Pacific Ocean 总被引：1，自引：0，他引：1
ZHANG Dongsheng WANG Chunsheng LIU Zhensheng XU Xuewei WANG Xiaogu ZHOU Yadong 《海洋学报(英文版)》2012,31(3):120-131
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. 相似文献
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Two new types of mechanism for the generation of tidal residual flow are revealed with the use of a hydraulic model experiment. A remarkable anticlockwise tidal residual circulation is formed in a model bay due to the presence of a tidal current, the Coriolis force and a horizontal boundary. A similar circulation is also formed due to the presence of a bottom slope, a horizontal boundary and a tidal current which flows normal to the inclination of the bottom slope. The residual circulation in the Sea of Iyo in the Seto Inland Sea is considered to be due to a combination of the effects of the Coriolis force, a bottom slope, a horizontal boundary and the tidal current. We classified some of the generation mechanisms of tidal residual flow which have been described to date into seven types on the basis of vorticity considerations. 相似文献
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The underwater tapping machine is composed of a center bit,a tapping cutter,a sesl box,a main drive box,aboring bar assembly,a envelop,a gear case,a counter and so on.The drive system in underwater tapping machine consists of a worm drive,a gear drive system and a screw drive.The worm drive is in the main drive box.The worm is connected with a hydraulic motor and driven by the hydraulic motor.The gear drive system is a combined gear train which is the combinations of the fixed axes and differential gear train in the gear case.On the one hand,by means of the fixed axes gear trains the turn and power of transmission shaft are transferred to the boring bar and the screw rod,causing differential tam between the boring bar and the screw rod.On the other hand,the turns of the boring bar and the screw rod are transferred to the differential gear train.The differential gear train is used to drive a special counter to count axial travel of the boring bar.The screw drive is composed of a feed screw and a nut on the boring bar.There is the differential turn between the boring bar and the feed screw.By means of the nut,the boring bar can feed automatically.With the movement of the sliding gear 7 in the gear case,the designed drive system can also be provided with the ability of fast forward and fast backward movement of the boring bar in its idle motion,restdting in the increase of the tapping efficiency. 相似文献