水流作用下重力式网箱浮架结构的动力响应研究

近年来深水网箱养殖设施得到了广泛的应用,浮架作为网箱结构的重要组成部分,其安全性对网箱的设计至关重要。基于有限单元法采用SHELL单元建立了浮架结构的荷载-变形数值模型,对水流作用下浮架的应力和变形进行了数值模拟,并开展物理模型试验对该数值模型进行验证。结果表明,该数值模型可以准确模拟浮架的变形,采用该数值模型,分析了不同流速条件下浮架的变形和应力,数值模拟结果显示:随着流速的增加,浮架的变形和应力逐渐增加。相同流速条件下,注水下潜后,浮架的应力和变形能够显著减小;因此,在强流条件下,可以采用浮架注水的方式,使浮架处于下潜状态,以改善浮架结构的变形和应力分布。     

桑沟湾水动力特征及其对养殖容量影响的研究——观测与模型

主要介绍了从动力学研究桑沟湾养殖容量的主要思路、方法及结果。研究以精细过程观测为基础,以数值模型为手段,从物理海洋学角度考察养殖海区水动力特征,研究水动力对物质循环的影响、对颗粒态/溶解态营养物质的补充和对养殖生物量的影响,探寻不同养殖模式效果的技术路线;介绍了两个航次设计方案与目的。通过观测发现养殖对水动力垂直结构有很大影响,底层流速最大并滞后表层,发现弱动力条件下海底颗粒物和营养盐无法进入水体上层的事实。据此提出双边界层动力模型,建立一维数值模型进行机制探讨,将养殖阻力三维化建立水动力数值模型,定量给出养殖对水动力和水交换的阻碍;以此驱动三维养殖生态模型,充分考虑养殖对水动力的影响、水动力对生源要素的输运。建立了一个真正的物理-生物过程耦合模型。利用该模型进行的数值模拟和实验表明,贝藻兼养多元养殖是健康、高效养殖的有利措施;桑沟湾在现有养殖模式下,目前已基本达到了它的养殖容量,养殖品种分布不变,减少养殖密度至目前的0.9倍会略微提高产量,降低成本;减少湾口海带养殖密度,会大幅度提高贝藻兼养区的营养盐总量和养殖生物产量,从海带与贝类经济价值对比会有更高的效益。人为提高水动力混合或许是解决湾内营养盐缺乏的途径。     

大规模养殖活动对罗源湾潮动力的影响

基于罗源湾2013年4至5月潮位、潮流实测数据,结合数值模拟,对比分析历史资料和模拟结果,研究了大规模高密度养殖区内潮动力结构的特征及其对养殖活动的响应。潮流在罗源湾养殖区,基本呈两层结构,近表层以落潮流为主,中底层以涨潮流为主,潮流主要从中下层流入,表层流出。高密度的养殖设施和生物的存在,阻碍了海湾水体的流动,致使水平流速垂向上出现"双边界层"结构,表层和底层的流速较小,最大值出现在中下部,平均流速整体减小,潮汐不对称效应减弱,潮波变形程度降低。     

海底涌泉——上升流

<正> 汹涌澎湃的海洋,无时无刻不在运动。潮汐、波浪、海流是人们所熟知的海水运动形式,它们都是水平运动。然而,还有一种不被人们所注意的运动形式,那就是海水的垂直流动。尽管这种流动速度很小,仅为每秒0.00001厘米至0.01厘米,但它的作用却不小,由它引起下层海水与上层海水的交换,对海洋生物资源产生非常明显的影响。其中垂直向上的流动好比海底涌泉,被人们称为“上升流”。来自深海的上升流把海底丰富的硝酸盐、磷酸盐等营养盐类带到表层有光带,使这里的浮游植物得到大量     

乳山湾养殖区甲烷释放速率及其分布特征

选择乳山湾养殖滩涂为研究对象,测定了不同养殖密度区底质中CH4浓度、有机质含量和硫化物含量以及相关环境因子;探讨了不同沉积物剖面甲烷浓度与有机质、硫化物的关系。结果表明,乳山湾养殖滩涂区域海水中溶存甲烷的平均浓度为59.9&#177;7.75nmol/L,不同养殖密度区海水中的甲烷含量无明显差异。底泥释放甲烷速率的实验显示,不同养殖密度区中沉积物的甲烷释放速率：非养殖（老化）区（高密度区（中密度区（低密度区。沉积物间隙水中甲烷的浓度随深度的增加而降低,剖面上高浓度中心位于0～5cm,在不同密度区同一深度的底质中甲烷含量均表现为：非养殖（老化）区≥中密度区（低密度区（高密度区。不同剖面沉积物间隙水中甲烷浓度与有机质的垂直分布呈显著正相关,与硫化物的垂直分布呈显著负相关关系。     

平面网衣在水流作用下的受力和变形特性数值模拟研究

基于集中质量点法和牛顿第二定律,建立了网衣在水流作用下的受力和运动响应数学模型.采用计算机数值模拟方法,研究了水流作用下网衣的动态变形情况以及网衣受力平衡后的空间分布形状.在2种配重(GW1=4.12 N、GW2=16.38 N)和6种流速(U=0.17、0.22、0.28、0.33、0.39和0.44 m · s-1)条件下对网衣稳定后沿水流方向的总水流力、网衣底端的水平及垂直位移进行了数值计算.计算结果表明,配重及流速大小对网衣受力和变形特性具有较大的影响.随着水流速度的增大,网衣在水流作用下的运动变形加剧,且当配重增大时,网衣变形减小,网衣受力随流速的变化增幅明显加快.为了验证模型的正确性和有效性,文章还将数值模拟结果与前人的试验结果进行了比较,效果良好.     

圆形网衣在水流作用下的运动变形特性

研究网衣在水流作用下的运动变形是深入了解网箱耐流特性的关键。本研究基于集中质量点法,建立了圆形网衣在水流作用下的数值计算模型,并利用前人的试验结果对数值模型进行了验证。验证结果表明,无论是网衣的变形还是受力情况,模拟结果都与试验结果吻合良好。在此基础上,针对实际应用中的圆形网衣,在不同配重(GW1=400kg、GW2=800kg)和流速(U=0.3～0.9m/s)条件下,对网衣变形、网衣底端前后点位移、网衣底端倾角进行了数值模拟,探讨了流速、配重大小对网衣运动变形特性的影响。结果表明,水流速度的增大会加剧网衣的变形,在配重GW1、流速U=0.75m/s时,网衣容积损失率达到50%以上。网衣底端前点的水平位移大于后点的水平位移,前点的垂直位移则小于后点的垂直位移,随着流速的增大,网衣底端前后点的位移差异将更为明显。当配重增加时,网衣底端位移、倾角以及网衣容积损失率可相应减小,网衣变形得到一定改善。数值模拟证明,本研究所建立的数值计算模式具有较好的稳定性和解的收敛性,可为下一步波浪、流联合作用下的整体网箱模拟奠定良好的理论基础。     

重力式网箱浮架结构的动力响应特性研究

利用离岸网箱进行水产养殖近年来受到了越来越多的重视,离岸区域海况条件恶劣,浮架结构的安全性对于网箱的设计具有极其重要的意义。为研究网箱浮架结构在动态波浪荷载作用下的动力响应,采用有限元法利用PIPE单元建立了浮架的数值模型,并根据物理模型试验结果对该数值模型进行验证,发现有限元模型的计算结果与模型试验结果吻合较好。基于该模型,重点分析了网箱的连接构件数量和个别锚绳发生断裂对浮架动力响应的影响,得到了浮架结构连接处的应力值、变形值以及浮架的变形模式图。结果显示,数值模型能较好地模拟网箱浮架的受力和运动响应;连接构件数量增加时,浮架的应力和变形将会减少;当下游同侧两根锚绳同时断裂时浮架应力和锚绳力最小。研究表明,动力特性是结构优化分析的重要依据,24套连接构件的浮架应优先使用。     

桑沟湾多元养殖生态模型研究：Ⅰ养殖生态模型的建立和参数敏感性分析

建立了一个与考虑养殖阻力的水动力模型耦合的、以浮游植物生物量、无机氮浓度、悬浮有机颗粒物浓度、海带生物量为变量的桑沟湾三维多元养殖生态模型。模型考虑了养殖生物海带对海水流动的阻碍作用随其生长的动态变化,以及养殖生物和浮游植物之间对无机氮营养盐的竞争。最后,分别以浮游植物生物量和海带产量为目标变量,对参数的敏感性进行了分析。     

方形箱网结构减流效果试验

根据降低流速对深水网箱养殖的影响这一需要,依据目前深水网箱的尺寸和渔具模型试验方法,设计并制作一个浮式箱网结构模型,同时进行水槽实验。实验在箱网的尾部设定一系列的断面和测量点,通过三维流速仪测量各点在不同实验流速下的流速,通过分析相关数据,探讨了该箱网减流结构尾部的流速分布和减流效果。实验流速采用了32.23 cm/s、50.19 cm/s、67.79 cm/s,分别相当于实际流速45.58 cm/s、70.79 cm/s、95.67 cm/s。实验测量了减流装置尾部减流区域50 cm到125 cm处的流速分布,相当于实际海域中距离减流装置尾部15 m到37.5 m处的流速分布。实验结果显示,箱网尾部的流速减小区域是在网箱网袋与来流垂直的投影面上,减流百分比在20%～45%左右,而箱网两侧的流速略有增加。从实验结果来看,这一结构能有效减小流速,通过合理的设计和在海域中布设,能够满足深水网箱养殖的减流需要。     

以CFD-DEM为基础的养殖槽排污性能及底坡优化

由于能提高资源利用率，减少环境污染，低碳高效池塘循环流水养殖(IPA)作为一项新型养殖技术被大力推广。为了提高养殖过程中的集污排污效率，本研究拟采用构造负坡底面的方法对养殖槽结构进行优化。通过建立二维养殖槽简化模型，结合计算流体力学—离散单元法(CFD-DEM)模拟计算与核偏最小二乘(KPLS)建模方法，建立槽内垂向流速分布与底面坡度和粗糙度的关系模型。在此基础上结合泥沙运动理论，获得了槽内颗粒起动流速与单宽输沙率模型，在构建颗粒起动和输运两方面的性能指标后，利用基于偏好的多目标粒子群算法(DP-MOPSO)寻求最优底面坡度。寻优结果显示，随着底面粗糙度的增加，最优坡度略有减小，范围为0.013~0.015；仿真实验结果显示，构造最优底坡可有效提高颗粒的起动概率和槽体的颗粒运输能力，且对于表面较为粗糙槽体，坡型底面在颗粒起动方面的优越性更为显著，说明通过构建底坡来改变水流结构，从而实现养殖槽排污性能的优化是合理的。     

One-dimensional biophysical modelling of fish egg vertical distributions in shelf seas

Modelling the vertical distribution of fish eggs is important when assessing fish stocks with egg production methods and for monitoring the reproductive potential of fish populations. Fish eggs are passive particles and their vertical distribution is determined by a few parameters such as egg density, egg diameter, wind‐ and tide‐induced turbulence, and vertical hydrographic structure. A one‐dimensional vertical biophysical, numerical model was developed which was adapted to the hydrography of shelf seas under the influence of tidal currents, wind‐induced circulation, and river discharges. The biological part of the model parameterized the ascent velocity of the egg as a function of egg properties (diameter, density) and water properties (density, viscosity, turbulence). The model contains a turbulence closure which makes the model dynamic. The model parameters were surface wind, tidal currents, T‐S profile, and egg diameter and density, which were kept constant in time. The model has the capacity to generate sub‐surface egg maxima in different hydrographic conditions, e.g. in areas under the influence of river plumes, and can also homogenize the egg distribution under wind and tide forcing. Sensitivity tests were carried out to study the response of the model to variations in the model parameters for a variety of hydrographic conditions. The modelled egg vertical distributions were validated by comparison of the model results with egg distributions sampled in the field. The analysis highlighted variability in fish egg density of anchovy, sardine, and sprat across years and areas, with a potential link between egg density and surface sea water density. The validated model is a tool for the analysis of shelf seas fish egg vertical distributions.     

桑沟湾增养殖水文环境研究

对桑沟湾大规模开展增养殖前后的水文环境作了研究。由于大面积高密度养殖，桑沟湾的水动力状况和１０年前相比发生了明显变化，潮流速度减缓了５０％，水交换率降低了１．７％，海湾海水半交换周期延长了１１个潮周期。营养物质输送和海水自净能力受到严重影响。部分养殖品种产量下降，表明养殖容纳量已达饱和状态。和其他海湾相比，桑沟湾的水交换条件还是比较好的，只要科学合理地设置养殖品种和养殖密度，仍不失为一个重要的增养     

Numerical model of an aquaculture structure under oscillatory flow

Marine aquaculture is widely distributed in coastal areas. The aquaculture farms generate drag resistance to fluid motion and alter ambient hydrodynamics. Meanwhile, aquacultural structures are subjected to complex flow conditions including waves and currents. With the expansion to more open areas with severe flow field conditions, marine aquacultural structures face greater challenges and risks of damage. Culture unit is an important component of aquacultural structures and shows flexibility in both field observations and laboratory measurements. Underestimating or overestimating the drag resistance of culture units under the action of fluid flow can lead to damage risks or overdesign of the structure. A dynamic model is developed to estimate the deflection of flexible culture units and is incorporated into an aquacultural structure numerical model in this paper. Critical factors for safety as well as routine operation of aquacultural structures are considered including structural responses and mooring line forces. A suspended mussel long line system is taken as an example, and the results show that the calculated value (9.2 kN) of the maximum tension of the north mooring line is in good agreement with the measured data (9.8 kN) under the action of tide flow. The influence of different flow field parameters on structural dynamic responses is investigated. The numerical results indicate that decreasing wave height can reduce maximum mooring line tension and longitudinal and vertical motion amplitude of the main line. The maximum tension of the mooring line generally decreases with the increase of the angle between the main line and the inflow direction under the action of waves and tide flows. In structural design, the arrangement angle of structures can be determined according to the force calculation of mooring lines based on the numerical model. The spacing of culture units and the distance between adjacent long lines can be determined by referring to the motion calculation of structures to avoid damage due to intertwinement of structural components.     

规模化透水性人工鱼礁阻流效应的数值模拟

为在大尺度海洋模型中合理体现透水性人工鱼礁组合，基于海洋数值模式FVCOM（finite volume community ocean model）模拟了大陈岛拟建人工鱼礁区的水动力情况，比较了阻滞力法、实心礁法和附加底摩擦法在投礁前后的垂向流速、礁顶平面流速、水体向上输运通量和背涡流体积的差异，并根据投礁前后的流速差异，应用经验公式预测了投礁一年后底床泥沙冲淤情况。数值模拟结果表明，礁体组合迎流面产生上升流，礁体背流面流速减小，涨急时刻所形成缓流区长度在礁体组合长度20倍以上，年底床淤积厚度约0.05 m。阻滞力法以减少来流的动态功率密度来模拟礁体对水流的阻滞作用，可有效合理地实现对透水性人工鱼礁流场效应的模拟，避免了实心礁法在透水性鱼礁模拟中过高估计流场效应的问题，也没有附加底摩擦法只适用于低矮礁体的缺陷。阻滞力法可根据透水性礁体的造型、迎流面积、组合个数、布放方式和所处水层而设置各向和各水层的阻流参数，不仅适用于置底型透水性鱼礁，也适用于浮鱼礁。阻滞力法的建立、完善和应用对于今后的人工鱼礁水动力学和生态动力学研究具有重要意义。     

Use of non-linear regression to evaluate drag force and volume coefficient of structure of square cage

ABSTRACT:   Cage aquaculture is increasing in importance in fisheries. However, in past studies the relationship between drag force and volume coefficient of the cage bag, and four key factors affecting its efficiency, i.e. flow velocity, ratio of depth to width of the cage, twine diameter to bar length of netting ( d/l ), and weight of the cage has been limited to partial regression and qualitative discussion. This paper establishes two non-linear regressions of the drag force and volume coefficient of a cage bag with seven flow velocities, five ratios of depth to width of the cage, four d/l , and five weights of the cage. The experimental data are processed using the forward selection method in the stepwise regression selection procedure in order to prioritize each factor, and then establish non-linear regressions of the drag force and volume coefficient using multiregression analysis. The results show that factors affecting the drag force are, in order of importance, flow velocity, ratio of depth to width of the cage, d/l and weight. With respect to the volume coefficient, factors in order of importance are flow velocity, weight, ratio of depth to width of the cage, and d/L. The two regressions can predict drag force and volume coefficient more comprehensively than those in previous studies. Finally, the regressions are applied to the full-scale structure of the cage by Tauti's modeling rules.     

网口部分网衣结构对帆式张网性能的影响

通过对帆式我模型水池试验，研究了帆式张网网中部分网衣结构对网具性能的影响。试验表明：（１）背腹网网口网农弧形剪后，背腹网网衣受力均匀程度明显改善，网具阻力平均下降３．５％，网口垂直扩张平均增加４．７％，水平扩张平均增加７．２％。（２）背腹、侧网网口网衣剪成弧形后，网具阻力平均下降２４．２％。水平扩张低速时有所下降，但高速时开始增加，平均增幅为３．５％，侧网网口网衣弧形剪对网口垂直扩张影响不大。     

Assessment of the production and dispersal of faecal waste from the sea‐cage aquaculture of spiny lobsters

Despite the rapid expansion of spiny lobster aquaculture, very little is known about its potential environmental impacts. In an effort to understand the potential impacts of sea‐cage culture of spiny lobsters, the faecal output and settling velocity of faeces of spiny lobster were quantified. These data were then used in hydrodynamic modelling to assess the dispersal pattern of faecal material from two sizes of hypothetical spiny lobster farms, so that inferences about likely benthic impacts could be made by modelling different scenarios of farm stocking density and food conversion efficiency. The overall mean settling velocity of lobster faecal strands was 0.9 ± 0.05 cm s^?1. There was a positive correlation between both the weight and density of faecal strands and their settling velocity. Conversely, neither the length nor the surface area of faecal strands was correlated with the settling velocity. Hydrodynamic modelling showed that faecal material deposition mainly occurred directly beneath the sea‐cages. The density of faecal material deposition increased proportionately with higher stocking density and FCR values. Overall, the results indicate that the deposition of faecal waste from sea‐cage lobster aquaculture is unlikely to cause widespread benthic impacts when operating to the current highest commercial stocking and feeding levels.     

Experimental study of the drag on fine-mesh netting

The hydrodynamic forces on netting have been investigated by many researchers. They proposed equations to estimate the drag and lift coefficients of the netting, taking the effects of the Reynolds number and solidity ratio into account. However, there are few studies on the hydrodynamic forces on netting with a fine mesh, which is sometimes used in Japan for farming small fish, such as young sardines. The size of the fine mesh is a few millimeters, whereas the solidity ratio of the netting is similar to that of standard netting. The drag on fine-mesh netting may increase because of the effects of blocking. In the present study, the drag on fine-mesh netting was examined by means of a towing experiment in a water tank. The experiment included an investigation of the drag on a planar net, a half-circular net, a circular net, and a circular net with a bottom, to understand the effect of the attack angle of the water current and wake. As a result, the drag coefficient of the plane net was in the range of those proposed in the previous studies. The effect of the attack angle of the water current was approximately reproduced by the cosine function. The reduction factors for the water current velocity through the circular net also agreed with those proposed in the previous studies, whereas it was approximately at the maximum among the previous estimations. Consequently, the drag on fine-mesh netting could be well explained by the estimates from the previous studies. However, the drag at the bottom of the net, parallel to the water current, was overestimated if hydrodynamic forces act on each transverse twine normal to the flow direction. The effects of the interactions among the twines, which are aligned parallel to the flow direction, should be specifically examined as a future study.