共查询到20条相似文献，搜索用时 93 毫秒
1.
据田内相似准则设计了一模型网箱，通过试验测量其不同装配、不同流速、不同配重下，网箱表征容积（网箱横截面的投影面积）的变化。结果表明。流速增加使网箱有效容积受到很大损失；增加配重对于改善网箱的变形是有限度的，在网箱底部加装底框可在一定程度上改善网箱的耐流性能，而作者开发的网箱耐流锚泊技术，可以在较大的流速情况下很好地改善网箱的变形，减少网箱的容积损失，提高网箱抗流性能。 相似文献
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一种适用于网箱耐流特性有限元分析的网目群化方法 总被引：3，自引：0，他引：3
养殖网箱耐流特性是网箱工程设计中的重要问题之一,探求对这一问题的数值解法在近几年得到了空前的重视。但是,由于深水抗风浪网箱箱体规模大,如果在有限元分析中单纯以网衣网目脚为单元进行数值计算,其计算量相当庞大。文中介绍1种可供网箱箱体有限元分析的网目群化方法,根据保持群化前后网衣水中重量和投影面积相等以保证网箱网衣总体水动力相同的原则,将若干个真实网目群化为1个虚拟的计算网目,以达到有效减少计算单元、提高运算效率和节省运算时间的目的。通过不同群化条件下数值例的计算结果与实验值的比较,验证网目群化方法的可行性。在一般条件下,8×8群化或6×6群化能够有效实现计算精度与计算效率的兼顾。 相似文献
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针对单点系泊(SPM)网箱系泊力大于传统网箱,离岸环境承受风浪时风险更高的问题,研究设计了一种相较传统圆形网箱拥有更小系泊力的船型网箱,运用正交原理制定了三因素三水平的试验方案,对网箱浮架进行了计算机数值模拟,分析网箱在波流共同作用下的水动力特性变化。研究表明,在兼顾经济成本与网箱安全性的条件下,长24 m,宽9 m,头部角度为60°的网箱浮架具有较优良的水动力性能和相对较低的养殖成本。该网箱系统能随着潮流改变方向而在锚点周围移动,从而极大减小网箱底部的养殖残渣堆积并降低锚固安装成本,可为我国深水网箱的发展提供一定的理论参考依据。 相似文献
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鲆鲽网箱结构在海中受到水流的冲击作用会发生运动与变形,针对鲆鲽鱼特有的栖底习性,为确保网底结构的稳定有必要对其进行动力分析。为此利用有限元方法建立了流场中网箱受力和变形的数学计算模型,运用该数学模型对底框中加有支撑管结构并装配方形网目网衣的鲆鲽网箱整体位移进行了数值模拟。数值模拟结果表明,网箱的网衣部分在水流作用下形态变化比较大,网底的水平位移与垂直位移随流速的增加而增大,而网箱的底框架在不同流速条件下均能保持在水平位置,且未发生明显的倾斜。由此可见,此类鲆鲽网箱具有较好的耐流性能。 相似文献
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对安装在海上风电钢管桩基础上的升降式网箱结构的波浪场特性进行研究，掌握升降式网箱结构内部及结构后方水体的运动特征及速度场变化情况。基于OpenFOAM软件包开发了波、流与孔隙介质结构相互作用的数值计算模型，将网箱结构按等效阻力简化为多孔介质结构，开展升降式网箱结构的波浪场特性研究。研究结果表明：网箱结构对流体具有一定的阻流作用，网箱结构内部速度场得到一定程度的减小，网箱结构背浪侧也有一定的速度衰减区域；对比网箱结构顶部不同潜深条件下的网箱结构内部流场特征，网箱结构顶部潜深在1/4D~1/2D（D为水深）范围内网箱结构内部流场速度最小、流场最为稳定、速度分布均匀，网箱结构向浪侧前方和背浪侧后方流场波动较小。所得结论表明在钢管桩基础上安装升降式网箱结构时需要关注的网箱结构对流场特性的影响，充分考虑网箱结构阻力对流速的作用，掌握极端工况下升降式网箱结构保持优良养殖环境需要下潜的高度范围，以保障升降式网箱的安全。 相似文献
6.
上川岛公湾海域环境对其网箱养殖容量限制的研究 总被引：1，自引：0，他引：1
通过计算单个网箱产生氮（N）和磷（P）的负荷量，并以水体富营养化的限制因子N和P的最高限制值作为控制值，利用数学模型模拟公湾海域环境对其网箱养殖容量的限制情况。研究结果表明：公湾海域环境所能承受的网箱养殖容量规模约为65000个网箱。 相似文献
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网箱浮架是我国深水养殖的重要设施装备，其水动力特性直接关系其工作稳定性。文章针对3层桁架式海洋网箱浮架建立有限元模型，采用流固耦合方法对17级台风正面来流条件下的网箱浮架水动力特性展开模拟计算，并对比分析有无网衣时网箱浮架水动力特性的变化规律。结果表明：在台风正面来流的情况下，网箱浮架的饵料舱侧向支撑点、上层步道板连接管迎浪侧和中层承力结构交叉点是应力集中的主要区域；当浮架悬挂网衣结构时，其垂荡距离减小，但纵摇程度加剧，即网衣结构有利于浮架结构在垂直方向上的稳定，但增加其纵摇运动强度；当悬挂网衣结构时，由于浮架在垂直方向上更为稳定，其饵料舱侧向支撑点、上层步道板连接管迎浪侧的最大应力分别降低5.1%和3.2%，中层承力结构交叉点的最大应力变化不明显，而迎浪侧中下层连接管的最大应力降低8.7%。 相似文献
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上川岛公湾海域环境对其网箱养殖容量限制的研究 总被引：17，自引：0，他引：17
通过计算单个网箱产生氮（Ｎ）和磷（Ｐ）的负荷量，并以水体富营养化的限制因子Ｎ和Ｐ的最高限制值作为控制值，利用数学模型模拟公湾海域环境对其网箱养殖容量的限制情况，研究结果表明，公湾海域环境所能承受的网箱养殖容量规模约为６５０００个网箱。 相似文献
10.
网箱养殖生态学研究进展 总被引：3，自引：0，他引：3
网箱养殖生态学是水产养殖生态学的重要分支,是研究网箱养殖生物及养殖活动与养殖水体环境相护作用关系、依据当地环境状况为养殖设施建设及养殖活动管理提供理论指导的科学。本文简述了网箱养殖活动的历史沿革,重点介绍了网箱养殖生态学在养殖水环境管理、养殖容量评估和深远海养殖领域的研究进展。在此基础上,对网箱养殖生态学的未来研究方向进行了展望,以期为水产养殖活动的相关研究提供参考。 相似文献
11.
HDPE深水网箱抗风浪流性能的海区验证试验 总被引：5，自引：0，他引：5
对HDPE深水网箱2000～2004年间的抗风浪流性能进行了海区验证试验.通过对HDPE深水网箱扶栏、框架、网具以及固泊系统受损率的统计,根据扶栏、框架、网具以及固泊系统在整个深水网系统中的重要程度,分别给予一定的权重统计出深水网箱的整体受损率,能比较客观地反映深水网箱的抗风浪流性能.海区验证试验结果表明,HDPE深水网箱抗风力达35 m/s、抗浪高6 m、抗流速1.0 m/s,与其设计参数基本相同.同时,为了增加HDPE深水网箱的抗风浪流性能,建议扶手管从110 mm改为125 mm、主浮管从250 mm改为300 mm、扶栏高度从1 m降低为0.8 m或0.6 m.风力主要影响扶栏系统,流速主要影响网具系统,而波浪对HDPE圆形浮式深水网箱的框架、网具、固泊系统以及网箱整体结构均有明显影响. 相似文献
12.
The computational fluid dynamics study is performed to analyze the impact of the cultured fish on the flow field through net cage and the deformation of net cage. The shear stress turbulent k-omega model is applied to simulate the flow field through the net cage, and the large deformation nonlinear structure model is adopted to conduct the structural analysis of the flexible net cage. To validate the net-fluid interaction model of the net cage in current, a series of physical model tests are conducted, which indicate that the numerical model can accurately simulate the flow field around the net cage and the deformation of the net cage. A fish model is used to simulate the effect of fish behavior on the flow pattern around the net cage and the deformation of the net cage. In addition, the flow fields around the net cage in current are investigated considering different fish group structures, fish swimming speeds, fish distributions and fish stocking densities. The results indicate that the circular movement of fish in the still water leads to a low pressure zone at the center of net cage, which causes a strong vertical flow along the center line of the net cage. The drag force on the net cage is significantly decreased with the increasing fish stocking density, but the most severe deformation of net cage occurred in the case of medium fish stocking density. 相似文献
13.
Model experiments of a floating fish cage subjected to waves and current have been performed. The objective was to study the dynamic behaviour of the fish cage model in waves and current. The fish cage model was composed of a model net, a flexible floating collar of the circular plastic type and a weight system. It was found that there are many wave periods in which cancellation of the wave-induced forces on the model occur. These cancellation wave periods are within the range of dimensioning wave periods commonly used for testing of fish farm structures and hence are important to be aware of. Large deformations of the net under realistic wave and current conditions were observed, where contact between the net and other parts of the structure were identified. This may cause damages to the net due to abrasion. 相似文献
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Mixing downstream of a submerged fish cage: a numerical study 总被引：2，自引：0，他引：2
As part of the overall Hawaii Open Ocean Research Project (HOARP) a fish cage of biconical shape (OceanSpar SeaStation 3000) has been placed in the waters of the coast of Ewa, HI, to enable research on the effect of cage culture of fish in tropical waters. One of the goals of HOARP is to examine the nature of the waste product stream of the fully submerged fish cage. HOARP activities began as a research effort but now are conducted in conjunction with a commercial operator that has three cages installed. For our analysis of the impact of the farm, an estimate of the mixing downstream of an individual cage is needed to assess the potential water quality impact of the farm operation to nearby waters. Federal regulations (40 CFR 122.24) require aquaculture systems to obtain a NPDES permit if they annually produce more than 45 454 kg harvest weight (about 100 000 lbs.) of warm water fish (CWA sections 318 and 402). The current farm off Ewa meets this criterion, thus a "mixing zone" needs to be established. A CFD simulation was made to evaluate the mixing downstream of the fish cage. This mixing consists of two parts, the turbulence generated by water passing through the cage, and the vortical flow generated by the general obstruction to water flow that is caused by the cage. The small scale turbulence increases the effective diffusion, and thus increases dilution of the pollutant, within the mixing zone. Parametric studies have been made to examine the effect of current speed on the initial mixing thereby enabling an estimation of the total mixing downstream of the cage. This estimate of the effective diffusion is essential for the establishment of the boundaries of the mixing zone. 相似文献
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《中国海洋工程》2015,(3)
The effect of biofouling on the hydrodynamic characteristics of the net cage is of particular interest as biofouled nettings can significantly reduce flow of well-oxygenated water reaching the stocked fish. For computational efficiency, the porous-media fluid model is proposed to simulate flow through the biofouled plane net and full-scale net cage. The porous coefficients of the porous-media fluid model can be determined from the quadratic-function relationship between the hydrodynamic forces on a plane net and the flow velocity using the least squares method. In this study, drag forces on and flow fields around five plane nets with different levels of biofouling are calculated by use of the proposed model. The numerical results are compared with the experimental data of Swift et al.(2006) and the effectiveness of the numerical model is presented. On that basis, flow through full-scale net cages with the same level of biofouling as the tested plane nets are modeled. The flow fields inside and around biofouled net cages are analyzed and the drag force acting on a net cage is estimated by a control volume analysis method. According to the numerical results, empirical formulas of reduction in flow velocity and load on a net cage are derived as function of drag coefficient of the corresponding biofouled netting. 相似文献
18.
The effect of biofouling on the hydrodynamic characteristics of the net cage is of particular interest as biofouled nettings can significantly reduce flow of well-oxygenated water reaching the stocked fish. For computational efficiency, the porous-media fluid model is proposed to simulate flow through the biofouled plane net and full-scale net cage. The porous coefficients of the porous-media fluid model can be determined from the quadratic-function relationship between the hydrodynamic forces on a plane net and the flow velocity using the least squares method. In this study, drag forces on and flow fields around five plane nets with different levels of biofouling are calculated by use of the proposed model. The numerical results are compared with the experimental data of Swift et al. (2006) and the effectiveness of the numerical model is presented. On that basis, flow through full-scale net cages with the same level of biofouling as the tested plane nets are modeled. The flow fields inside and around biofouled net cages are analyzed and the drag force acting on a net cage is estimated by a control volume analysis method. According to the numerical results, empirical formulas of reduction in flow velocity and load on a net cage are derived as function of drag coefficient of the corresponding biofouled netting. 相似文献
19.
《中国海洋工程》2021,(3)
The fish cage design requires accurate predictions of long-term extreme loads and responses. Compared with the time-consuming full long-term analysis method integrating all the probability distribution of the short-term extremes,the environmental contour method gains much attention in predicting the long-term extreme values due to the less computational effort. This paper investigates the long-term extreme response of a fish cage using the environmental contour method. The fish cage is numerically simulated based on the lumped-mass method and the curved beam theory. Based on the one-dimensional(1D) and two-dimensional(2D) environmental contour, the extreme responses,including the surge and heave motions, mooring force, and vertical bending of the floater, are predicted for different return periods and compared with the full long-term analysis results. Results indicate that the 1D method greatly underestimates the extreme values. The 2D environmental contour method with a higher percentile level, namely90%, provides reasonable estimations and seems to be suitable for the long-term value analysis. Sensitivity studies show that the mooring arrangement and the bending stiffness have great effects on the bending moment and the mooring force and the mooring line pre-tension has minor effects on the fish cage response. 相似文献
20.
Environmental consequence analyses of fish farm emissions related to different scales and exemplified by data from the Baltic--a review 总被引：3，自引：0，他引：3
The aim of this work is to review studies to evaluate how emissions from fish cage farms cause eutrophication effects in marine environments. The focus is on four different scales: (i) the conditions at the site of the farm, (ii) the local scale related to the coastal area where the farm is situated, (iii) the regional scale encompassing many coastal areas and (iv) the international scale including several regional coastal areas. The aim is to evaluate the role of nutrient emissions from fish farms in a general way, but all selected examples come from the Baltic Sea. An important part of this evaluation concerns the method to define the boundaries of a given coastal area. If this is done arbitrarily, one would obtain arbitrary results in the environmental consequence analysis. In this work, the boundary lines between the coast and the sea are drawn using GIS methods (geographical information systems) according to the topographical bottleneck method, which opens a way to determine many fundamental characteristics in the context of mass balance calculations. In mass balance modelling, the fluxes from the fish farm should be compared to other fluxes to, within and from coastal areas. Results collected in this study show that: (1) at the smallest scale (<1 ha), the "footprint" expressing the impact areas of fish cage farm often corresponds to the size of a "football field" (50-100 m) if the annual fish production is about 50 ton, (2) at the local scale (1 ha to 100 km2), there exists a simple load diagram (effect-load-sensitivity) to relate the environmental response and effects from a specific load from a fish cage farm. This makes it possible to obtain a first estimate of the maximum allowable fish production in a specific coastal area, (3) at the regional scale (100-10,000 km2), it is possible to create negative nutrient fluxes, i.e., use fish farming as a method to reduce the nutrient loading to the sea. The breaking point is to use more than about 1.1 g wet weight regionally caught wild fish per gram feed for the cultivated fish, and (4) at the international scale (>10,000 km2) related to the Baltic Proper, the contribution from fish farms to the overall nutrient fluxes are very small. We have also given two case-studies at the local scale where the impact of the fish farm emissions are greatest and the idea is to identify coastal areas unsuitable and suitable for fish cage farms and the reasons why. It should also be stressed that the results presented here are exemplified using emissions from fish farms, but that the underlying principles to evaluate the ecosystem effects of nutrient discharges from point source emissions are valid in a wider and more general perspective. 相似文献