无囊围网缩结系数研究

通过对缩结系数与网衣用量、下纲沉降速度的关系之分析，结合我国围网生产实际，提出了围网主网衣上、下边缘水平缩结系数的合理参考范围及其选取方法；通过对我国围网缩结系数统计资料的综合分析，提出了上缘网衣、下缘网衣、网头网衣或侧缘网衣的水平缩结系数等的选取参考范围。     

The effect of netting solidity ratio and inclined angle on the hydrodynamic characteristics of knotless polyethylene netting

Knotless polyethylene(PE) netting has been widely used in aquaculture cages and fishing gears, especially in Japan. In this study, the hydrodynamic coefficient of six knotless PE netting panels with different solidity ratios were assessed in a flume tank under various attack angles of netting from 0?(parallel to flow) to 90?(perpendicular to flow) and current speeds from 40 cm s~(-1) to 130 cm s~(-1). It was found that the drag coefficient was related to Reynolds number, solidity ratio and attack angle of netting. The solidity ratio was positively related with drag coefficient for netting panel perpendicular to flow, whereas when setting the netting panel parallel to the flow the opposite result was obtained. For netting panels placed at an angle to the flow, the lift coefficient reached the maximum at an attack angle of 50? and then decreased as the attack angle further increased. The solidity ratio had a dual influence on drag coefficient of inclined netting panels. Compared to result in the literature, the normal drag coefficient of knotless PE netting measured in this study is larger than that of nylon netting or Dyneema netting.     

Numerical Simulation of Mechanical Characteristics of a Metal Net for Deep-Sea Aquaculture

The investigation on hydrodynamic characteristics of a cage is important for its application in the deep-sea aquaculture in our country. With finite element method, the beam element is used to simulate a three-dimensional metal chain net, and the connector element is introduced as the interaction between metal net lines. A mechanical model for the metal net is constructed to simulate the hydrodynamic characteristics of a metal net subjected to fluid current forces. The static simulation results show that the relative errors of the displacements are 2.13%, 4.19%, 6.64%, and 11.35% compared with static concentrated load tests under concentrated forces of 20, 40, 60, and 80 N, respectively. Both the transient hydrodynamic deformations and drag forces of the netting structures under different current velocities are obtained by solving the hydrodynamic equation of the netting structure. The average relative error of the current forces obtained by numerical simulations shows an 8.13% deviation from the drag tests of the metal nets in the tank under five current velocities. The effectiveness and precision of the simulation approach are verified by static and dynamic tests. The proposed simulation approach will provide a good foundation for the further investigation of the hydrodynamic characteristics of deep-sea aquaculture metal cages and the parameter design for the safety of such cage systems.     

Deposition pattern of stony and muddy debris flow at the confluence area

Debris flow fan affects the river profile and landscape evolution.The propagation of multiple debris flows along a river can cause inundation and breaching risk,which can be exemplified by the Min River after the Wenchuan earthquake,Sichuan province,China.In this work,large flume tests were conducted to examine the interactions between debris flows and water current with the fan geometry,momentum,runout distance,deposited width,the relative water level upstream and dominated stress.The results reveal that stony flow commonly travels at a high speed and forms a long rectangle shape fan,while the muddy flow generally travels at a low speed and forms a fan-shaped depositional area.The stony flow can block a river even when the momentum is close to the water current;the muddy flow can block a river when the momentum is lower than that of water current.In case of complete river damming,the relative water level upstream indicates that the inundation risk from the muddy flow damming river would be higher than the inundation risk of stony flow.The diversion ratio of muddy flow decreases as damming ratio.Comparison of dimensionless numbers reveals that stony flow is dominated by grain collision stress combined with turbulent mixing stress,while the muddy flow is dominated by viscous shear stress over friction stress.The fan geometry,damming ratio,diversion ratio,and the dominated stress all together indicate that stony flow strongly interacts with water current while the muddy flow does not.The results can be helpful for understanding the physical interactions between water current and various debris flows,and debris flow dynamics at the channel confluence area.     

底拖网网目长度和网线粗度的确定

提出了“网衣理论总强度”、“网衣相对强度”两个概念。解决了底拖网设计中根据母型例或设计参考网初步确定设计网网口网线粗度的问题。并根据“网衣理论总强度”和“网衣相对强度”概念统计出我国沿海各种渔船主机功率的底拖网各部位网衣理论总强度和网衣相对强度数字范围,为我国底拖网设计网目长度与网线粗度之间关系的处理提供了理论依据。     

A numerical study on water diversion ratio of the Changjiang (Yangtze) estuary in dry season

We studied the flood, ebb and tidal averaged along (net) water diversion ratio (WDR) during dry season in the Changjiang (Yangtze) estuary, China, along with the effects of northerly wind, river discharge, tide and their interactions on WDR using the improved version of three-dimensional numerical model ECOM. Using data for annual mean wind speed and river discharge during January, we determined that the flood, ebb, net WDR values in the North Branch of the estuary were 3.48%, 1.68%, −4.06% during spring tide, and 4.82%, 2.34%, −2.79% during neap tide, respectively. Negative net WDR values denote the transport of water from the North Branch into the South Branch. Using the same data, the corresponding ratios were 50.09%, 50.92%, 54.97%, and 52.33%, 50.15%, 43.86% in the North Channel and 38.56%, 44.78%, 103.96%, and 36.92%, 43.17%, 60.97% in the North Passage, respectively. When northerly wind speed increased, landward Ekman transport was enhanced in the North Branch, increasing the flood WDR, while the ebb WDR declined and the net WDR exhibited a significant decrease. Similarly, in the North Channel, the flood WDR is increased, the ebb WDR reduced, and the net WDR showed a marked decrease. In the North Passage, the flood WDR also increased while the ebb and net WDR declined. As the river discharge increased, the flood and ebb WDR of the North Branch increased slightly and the net WDR increased markedly. In the North Channel the flood and ebb WDR changed very slightly, while the net WDR declined during spring tides and increased during neap tides. The WDR in the North Passage changed slightly during flood and ebb tides while the net WDR showed a marked increase. The WDR values of different bifurcations and the responses to northerly wind, river discharge, and tide are discussed in comparison with variations in river topography, horizontal wind-induced circulation, and tidal-induced residual current.     

Flow variability along a vegetated natural stream under various sediment transport rates

The influence of vegetation and sediment on flow characteristics in open channels cannot be neglected. To study the flow variability under the effects of the instream natural vegetation and sediment supply, experiments were conducted with varied water and sediment supply in a movable bed of a river prototype. The instantaneous three-dimensional velocities near two types of vegetation patches (the shrub and the weed) and along the centerline of the main channel with vegetation belts were measured using a 3-D side-looking acoustic Doppler velocimetry. The experimental results show that both the instream vegetation and sediment supply strongly affect the flow and turbulence characteristics. In the case of vegetation patches, both the shrub and weed have a considerable influence on the distribution of the streamwise velocity and turbulence intensity of their surrounding water. The streamwise velocity distribution followed as J-shape and linear shape around the weed and shrub under different experimental conditions. The turbulence intensity was large at the top of the weed and shrub; the shrub had its greatest influence on the downstream water flow. In the case of vegetation belts, the streamwise velocity along the centerline of the main channel exhibited an S-shape, J-shape and linear shape at different locations under varied water, vegetation structures and riverbed configurations. The turbulence intensity along the centerline of the main channel ranged from 0.0 to 0.1. The upstream turbulence intensity was affected considerably by a sediment supply, while the downstream turbulence intensity changed with the varied vegetation characteristics and riverbed topography. The second flow coefficient M-value increased longitudinally and was almost positive along the centerline of the main channel, implying that the rotational direction of the secondary current cell was clockwise.     

渭河干流浅层地下水与地表水中重金属Cd污染特征及风险评价

为了解渭河流域水体重金属污染现状及健康危害风险,沿渭河干流采集浅层地下水和地表水水样,采用单因子指数法和美国环境保护署(USEPA)健康风险评价模型揭示了水体中重金属Cd污染现状和健康风险。结果表明:2018年渭河干流地下水和地表水中Cd浓度分别为426.40~1104.27 ng·L^-1和224.70~1154.12 ng·L^-1;参照《地下水质量标准》(GB/T 14848-2017)和《地表水环境质量标准》(GB 3838-2002)得知,地下水和地表水中Cd浓度均在GB/T 14848—2017和GB 3838-2002Ⅰ~Ⅲ类标准限值内;水体中Cd浓度表现出明显的空间分异性,沿河流流向均表现为逐渐增加的趋势;地下水与地表水中Cd浓度高值区相一致,即集中分布于陕西省兴平市和渭南市临渭区;由水体中Cd浓度单因子指数评价结果可知,渭河干流水体中Cd污染属于清洁水平;沿河流流向,渭河中游和下游水体中Cd浓度单因子污染指数远高于上游;水体中重金属Cd对成人和儿童产生的致癌风险分别为(1.48~2.05)×10^-4和(1.84~2.55)×10^-4,说明水体中Cd对人体可能会产生一定的健康风险。     

Numerical simulation of the transport and diffusion of dissolved pollutants in the changjiang (Yangtze) river estuary

Based on a coupled hydrodynamic-ecological model for regional and shelf seas (COHERENS), a three-dimensional baroclinic model for the Changjiang (Yangtze) River estuary and the adjacent sea area was established using the sigma-coordinate in the vertical direction and spherical coordinate in the horizontal direction. In the study, changing-grid technology and the “dry-wet” method were designed to deal with the moving boundary. The minimum water depth limit condition was introduced for numerical simulation stability and to avoid producing negative depths in the shallow water areas. Using the Eulerian transport approaches included in COHERENS for the advection and dispersion of dissolved pollutants, numerical simulation of dissolved pollutant transport and diffusion in the Changjiang River estuary were carried out. The mass centre track of dissolved pollutants released from outlets in the south branch of the Changjiang River estuary water course has the characteristic of reverse current motion in the inner water course and clockwise motion offshore. In the transition area, water transport is a combination of the two types of motion. In a sewage-discharge numerical experiment, it is found that there are mainly two kinds of pollution distribution forms: one is a single nuclear structure and the other is a double nuclear (dinuclear) structure in the turbid zone of the Changjiang River estuary. The rate of expansion of the dissolved pollutant distribution decreased gradually. The results of the numerical experiment indicate that the maximum turbid zone of the Changjiang River estuary is also the zone enriched with pollutants. Backward pollutant flow occurs in the north branch of the estuary, which is similar to the backward salt water flow, and the backward flow of pollutants released upstream is more obvious.     

Evaluation of FAD-associated purse seine fishery reduction strategies for bigeye tuna (Thunnus obesus) in the Indian Ocean

In the Indian Ocean, bigeye tuna supports one of the most important fisheries in the world. This fishery mainly consists of two components: longline and purse seine fisheries. Evidence of overfishing and stock depletion of bigeye tuna calls for an evaluation of alternative management strategies. Using an age-structured operating model, parameterized with the results derived in a recent stock assessment, we evaluated the effectiveness of applying constant fishing mortality (CF) and quasi-constant fishing mortality (QCF) strategies to reduce fishing effort of purse seining with fish aggregating devices (FADs) at different rates. Three different levels of productivity accounted for the uncertainty in our understanding of stock productivity. The study shows that the results of CF and QCF are similar. Average SSB and catch during simulation years would be higher if fishing mortality of FAD-associated purse seining was reduced rapidly. The banning or rapid reduction of purse seining with FAD resulted in a mean catch, and catch in the last simulation year, higher than that of the base case in which no change was made to the purse seine fishery. This could be caused by growth overfishing by purse seine fisheries with FADs according to the per-recruit analysis. These differences would be more obvious when stock productivity was low. Transferring efforts of FAD-associated purse seining to longline fisheries is also not feasible. Our study suggests that changes are necessary to improve the performance of the current management strategy.     

Sediment transport in the nearshore area of Phoenix Island

Based on the measured data, suspended sediment concentration, surface sediment grain size, current and waves, the sediment transport mechanisms and pathways in the Phoenix Island area were analyzed using methods of flux decomposition and Grain Size Trend Analysis (GSTA). The results show that net suspended sediment is mainly transported by average current, Stokes drift, and gravitational circulation. The transport direction of suspended sediment is varying and basically following the direction of residual tidal currents. Surface sediment transport pathways are primarily parallel to the coastline along with two convergent centers. Waves and longshore currents have a significant influence on sediment transport, but the influence is limited due to a steep and deep underwater bank. Tidal current is the main controlling factor for sediment transport, especially in the deep water area. Neither suspended nor surface sediment is transported towards the southwest. The South Shandong Coastal Current (SSCC) has little effect on sediment transport processes in the nearshore area of Phoenix Island.     

贵州一次降雹过程的数值催化试验

针对贵州威宁2000年6月4日的一次降雹过程，利用三维冰雹云催化数值模式，采用立体催化数值试验，模拟催化剂量、催化高度、催化时间对高炮消雹效率和消雹区域的影响；通过比较催化雹云和未催化雹云的总含水量，分析催化消雹机制，从而揭示贵州37高炮防雹作业的有效性和最佳催化方案。     

Responses of Yellow Sea Cold Water Mass to Typhoon Bolaven

A two-month seabed-mounted observation(YSG1 area) was carried out in the western Yellow Sea Cold Water Mass(YSCWM) using an RDI-300 K acoustic Doppler current profiler(ADCP) placed at a water depth of 38 m in late summer, 2012. On August 2012, Typhoon Bolaven passed east of YSG1 with a maximum wind speed of 20 m s-1. The water depth, bottom temperature, and profile current velocities(including u, v and w components) were measured, and the results showed that the typhoon could induce horizontal current with speed greater than 70 cm s-1 in the water column, which is especially rare at below 20 meters above bottom(mab). The deepening velocity shear layer had an intense shear velocity of around 10 cm s-1 m-1, which indicated the deepening of the upper mixed layer. In the upper water column(above 20 mab), westward de-tide current with velocity greater than 30 cm s-1 was generated with the typhoon's onshore surge, and the direction of current movement shifted to become southward. In the lower water column, a possible pattern of eastward compensation current and delayed typhoon-driven current was demonstrated. During the typhoon, bottom temperature variation was changed into diurnal pattern because of the combined influence of typhoon and tidal current. The passage of Bolaven greatly intensified local sediment resuspension in the bottom layer. In addition, low-density particles constituted the suspended particulate matter(SPM) around 10 mab, which may be transported from the central South Yellow Sea by the typhoon. Overall, the intensive external force of the Typhoon Bolaven did not completely destroy the local thermocline, and most re-suspended sediments during the typhoon were restricted within the YSCWM.     

渭北翘起带镶嵌构造格局及其控水作用

本文划分了渭北翘起带的镶嵌构造格局,分析了构造控水作用,揭示了渭北地下水的网状流及其“偏流效应”规律,指出了“贫水带”与“富水带”相互依存的辩证关系,为深入研究该区地下水开辟了一条新的途径。     

西北内陆盆地浅层地下水温度场及动态类型:以酒泉东盆地为例

温度是地下水的固有属性,地下水温度场和动态特征是地下水流系统的外在表现。为揭示地下水开采等人类活动影响下西北内陆盆地浅层地下水温度场特征与地下水流系统的关系,基于多点位、长序列、高精度的地下水温度监测数据,在酒泉东盆地开展了地下水温度场及动态特征研究。结果表明：酒泉东盆地浅层地下水温度9.33～20.77℃不等,平均水温为13.54℃,自地下水补给区至排泄区,沿地下水径流方向,浅层地下水温度逐渐升高;循环深度相近的不同地下水流系统对比表明,浅层地下水温度与地下水动力条件呈负相关,地表水入渗补给大、水动力条件强的水流系统地下水平均温度低,入渗补给小、水动力条件弱的地下水平均温度高;浅层地下水温度动态受自然地下水循环和地下水开采等人类活动共同影响,从山前地下水补给区到中游绿洲区再到下游排泄区,浅部地下水温度动态可划分为4种基本类型,依次分别为河流补给型、水温稳定型、开采相关型、正弦波动型。     

地下工程建设对岩溶水流场的影响及其修复

工程建设改变地下水流场危及建筑物的安全。以济南经十路沿线大型地下综合体为例,通过数值模拟计算工程建设对地下水渗流场的影响,并建立了地下水流场修复模型。结果表明：地下空间结构会阻挡地下水运移,地下水水位壅高造成地基承载力降低;将地下工程设置导流措施后,其迎水面水位随时间呈现衰减趋势,且越接近天然状态水位衰减速率越慢;因地层结构差异,壅高水位基本回落的时间存在较大差异;不同地质条件下流场修复所需导流井数量与导流几何体结构参数呈负相关关系,所需导流井数量的预测方程反映了地质条件的复杂性和多变性。除导流几何体自身结构外,围岩水力梯度与渗透系数对导水能力产生影响,其中渗透系数大小制约导水速率的快慢,水力梯度则控制导水行为的发生。导流措施的实施可减小工程建设对地下水环境的影响,确保地下工程建设对水环境影响可控。     

陕西关中盆地地热资源及壳幔温度结构的地球物理分析

陕西关中盆地地下热水资源丰富,是中国典型的隐伏型中、低温地热资源分布区.为研究关中盆地中、低温地热系统形成机理,认识深部热源条件,利用地球物理方法分析了该区壳幔温度结构.结果表明:计算得到的居里面平均深度为25.0 km,莫霍面平均深度为36.6 km,地壳平均地温梯度为22.60℃·km-1,咸礼断阶、西安凹陷、固市...     

Influence of light availability on the specific density,size and sinking loss of Anabaena flos-aquae and Scenedesmus obliquus

Harmful algal blooms in eutrophic waters pose a serious threat to freshwater ecosystems and human health. In-situ light availability control is one of the most commonly used technologies to suppress algae in lakes and reservoirs. To develop a better understanding of the effects of light on algal growth, specific density, colony size and sinking loss, Anabaena flos-aquae(cyanobacteria) and Scenedesmus obliquus(green algae) were evaluated in varying light scenarios. The results showed that the specific density and colony size of these two species varied during growth, and there were obvious differences among the light scenarios. At the end of exponential phase, S. obliquus incubated under light-limited condition maintained a higher specific density and formed larger aggregates, whereas A. flos-aquae formed a longer filament length. Both species exhibited higher sinking loss rates with lower light availability. These results implied that the sinking loss rate was not always constant but should be considered as a variable response to the change of light availability, and in-situ light availability control might result in a significant increase of the sinking loss of algae due to the change of size and specific density, thereby further affecting the algal biomass in the water column.     

Failure mechanism and stability analysis of the Zhenggang landslide in Yunnan Province of China using 3D particle flow code simulation

Based on the principle of 3D particle flow code, a numerical landslide run-out model is presented to simulate the failure process of the Zhenggang landslide (in southwestern China) under the effect of water after a rainfall. The relationship between the micro-mechanical parameters and the macro-shear strength of the grain material is determined through numerical calibrations. Then the rainfall effect is considered in numerical simulations and rain-induced sliding processes are performed, which help us to discuss the mechanism of deformation and failure of this landslide together with field observations. It shows the Zhenggang landslide would most likely be activated in Zone I and would gain momentum in Zone II. In order to prevent the potential disaster, a tailing dam is advised to be designed about 175 m downstream from the current landslide boundary of Zone II. Verified by field observations, the presented landslide model can reflect the failure mechanism after rainfall. It can also provide a method to predict the potential disaster and draft disaster prevention measures.     

MOLAR RATIOS OF C, N, P OF PARTICULATE MATTER AND THEIR VERTICAL FLUXES IN THE YELLOW SEA

The vertical fluxes and molar ratios of carbon, nitrogen and phosphorus of suspended particulate matter in the Yellow Sea were studied based on the analysis of suspended particulate matter,sediments and sinking particles obtained by use of moored sediment traps. The POC ： PON ratios indicate that most of the particulate organic matter in the Yellow Sea water column comes from marine life rather than the continent. The vertical fluxes of SPM, POC, PON and POP in the Yellow Sea are much higher than those in other seas over the world, and present a typical pattern in shallow epicontinental seas. The estimated residence time of the bioactive elements showed that the speed of the biogeochemical process of materials in the Yellow Sea is much shorter than that in the open ocean as there was high primary productivity in this region.