Numerical Study on the Hydrodynamic Characteristics of Biofouled Full-Scale Net Cage

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.     

Numerical Study on the Hydrodynamic Characteristics of Biofouled Full-Scale Net Cage

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.     

秋刀鱼舷提网渔具性能模型试验与海上实测结果的比较评估

舷提网是秋刀鱼（Cololabis saira）作业的主要方式之一，由于渔获率较高得到迅速推广。模型试验和海上实测是研究网具性能最为普遍的两种方式，两者试验结果的对比评估对于更好地测定网具作业性能具有十分重要的意义。根据2014年11-12月进行的秋刀鱼舷提网静水槽模型试验以及2015年7-10月和2016年6-10月在"鲁蓬远渔019"号船上进行的秋刀鱼舷提网网具性能测试试验测定的网具数据，采用多元线性回归方法，对网具的沉降深度和提升速度进行了标准化，并利用Bootstrap法分析了舷提网模型试验和海上实测试验结果。结果表明:（1）通过Bootstrap法得出标准化后的实测网最大沉降深度的均值分布范围为20.37~29.54 m，95%置信区间为21.76~28.13 m；模型网网具最大沉降深度均值的范围为26.42~37.58 m，95%置信区间为27.70~36.20 m。实测网网具中部最大沉降深度均值大约是模型网网具中部最大沉降深度均值的0.731~0.783倍。（2）通过Bootstrap法得出标准化后的实测网提升速度的均值分布范围为0.107~0.193 m/s，95%置信区间为0.111~0.191 m/s；模型网网具提升速度均值的范围为0.204~0.316 m/s，95%置信区间为0.207~0.312 m/s。实测网网具中部提升速度均值大约是模型网网具中部提升速度均值的0.591~0.611倍。（3）当假设海流速度为0时，求得实测网网具的平均沉降深度为29.14~41.21 m，约为模型网网衣中部最大沉降深度均值的0.751~0.807倍。（4）30 m和60 m水深的海流速度均对实物网网具中部的沉降深度有所影响，60 m水深的流速影响更加显著（P<0.05）。     

A New model to forecast fishing ground of Scomber japonicus in the Yellow Sea and East China Sea

The pelagic species is closely related to the marine environmental factors, and establishment of forecasting model of fishing ground with high accuracy is an important content for pelagic fishery. The chub mackerel(Scomber japonicus) in the Yellow Sea and East China Sea is an important fishing target for Chinese lighting purse seine fishery. Based on the fishery data from China's mainland large-type lighting purse seine fishery for chub mackerel during the period of 2003 to 2010 and the environmental data including sea surface temperature(SST), gradient of the sea surface temperature(GSST), sea surface height(SSH) and geostrophic velocity(GV), we attempt to establish one new forecasting model of fishing ground based on boosted regression trees. In this study, the fishing areas with fishing effort is considered as one fishing ground, and the areas with no fishing ground are randomly selected from a background field, in which the fishing areas have no records in the logbooks. The performance of the forecasting model of fishing ground is evaluated with the testing data from the actual fishing data in 2011. The results show that the forecasting model of fishing ground has a high prediction performance, and the area under receiver operating curve(AUC) attains 0.897. The predicted fishing grounds are coincided with the actual fishing locations in 2011, and the movement route is also the same as the shift of fishing vessels, which indicates that this forecasting model based on the boosted regression trees can be used to effectively forecast the fishing ground of chub mackerel in the Yellow Sea and East China Sea.     

基于空间自回归和空间聚类的渔情预报模型

作者针对远洋渔场渔情预报精度偏低的问题,提出一种基于空间自回归和空间聚类的渔情预报模型。该模型利用空间自回归对收集到的渔业历史数据进行预处理,然后通过空间聚类将所有数据样本根据地理位置分划成若干个区域,最后研究每个区域中环境数据与渔获数据之间的数学关系,各自建立栖息地适宜性指数模型(Habitat Suitability Index,HSI),并以印度洋大眼金枪鱼(Thunnus obesus)为例进行验证。结果表明,本模型的均方差为0.1742,与传统线性回归方法的均方差0.2363相比,能更好地表达海洋环境数据与渔获量之间的关系,预测精度显著提高。     

基于北斗卫星船位监控系统数据的南海双拖渔船作业特征研究

船位监控系统（vessel monitoring system,VMS）数据在渔船作业特征挖掘分析方面已有较多应用。本文以粤渔10000/10011双拖渔船2017年8月16日—9月16日的VMS数据为例,详细分析了该双拖渔船的作业状态,研究了航次和网次提取方法,并对捕捞强度的空间分布进行了分析。研究结果表明,粤渔10000/10011有4个航速区间,分别为<1.0 m/s、1.0~1.8 m/s、1.8~2.9 m/s和>2.9 m/s,对应渔船的抛锚和慢速、夜间拖网航速、白天拖网航速和巡航状态;2017年8月16日—9月16日期间,粤渔10000/10011共进行了5个航次19个网次的拖网作业,其捕捞强度空间分布呈现近岸海域高离岸海域低的特征,且夜间拖网主要在离岸海域,白天拖网会转移到水深相对浅的近岸海域。     

Numerical simulation of the hydrodynamic behaviour of submerged plane nets in current

The aim of this paper is to investigate the shape and tension distribution of fishing nets in current. A numerical model is developed, based on lumped mass method to simplify the net. The motion equation is set up for each lumped mass. The Runge–Kutta–Verner fifth-order and sixth-order method is used to solve these simultaneous equations, and then the displacement and tension of each lumped mass are obtained. In order to verify the validity of the numerical method, model tests have been carried out. The results by the numerical simulation agree well with the experimental data.     

基于北斗船位数据的渔业信息解译与应用研究——以中国毛虾限额捕捞管理为例

2020年6月15日—7月15日,我国首次中国毛虾(Acetes chinensis)限额捕捞试点于江苏连云港实施。本研究提取62艘毛虾网船在限额捕捞期间的421700条北斗船位数据经纬度、航速、航向等信息,运用缓冲区叠加分析法、DBSCAN密度聚类算法、平均中心算法、核密度估计以及数据库查询对捕捞努力量等管控要素进行分析研究。结果显示,所有毛虾网船累计作业239个航次、1942个网次,捕捞过程分为航行、抛锚布网、等待渔获、收渔获、停航等5个状态,中国毛虾捕捞状态船位点呈直线分布,总捕捞时长为4413.73h,82.4%的单网次捕捞时长为1.5—3.5h,各网次捕捞产量呈现多核心空间分布模式,总捕捞努力量为108106343 m~2·h,计算62艘的捕捞总产量值约为2328 t,比上报产量高12.6%;本文通过北斗船位数据解译和提取捕捞努力量以计算中国毛虾捕捞产量及资源空间分布情况,有效应用于中国毛虾限额捕捞,为解决我国单品种限额捕捞难点积累了宝贵经验。     

Experimental Investigation and Numerical Analysis to Develop Low-Energy Large-Midwater Trawls

Fuel consumption in fisheries is a primary concern because of its effects on the environment and the costs incurred by fishermen. Many studies have been conducted to reduce the fuel consumption in fishing operations. Fuel consumption due to fishing gear during a fishing operation is generally related to the hydrodynamic resistance on the gear. This means that fuel consumption is proportional to the drag created by the towing speed. Based on numerical methods, this study suggests a new approach to reduce fuel consumption in fisheries. The results of the simulation are in good agreement with those of model experiments. The total as well as partial resistance forces on the gear are calculated by simulation. The simulation results suggest improved materials and gear structure for reducing the hydrodynamic forces on the gear while maintaining gear performance. The method for assessing the gear performance involves measuring the height and width of the net mouth. Furthermore, this study investigates the efficiency of a low-energy trawl from an economic point of view. The findings of this study will be useful in reducing greenhouse gas (GHG) emissions in fishing operations, and thereby contribute toward lowering fishing costs by saving fuel.     

基于提升回归树的东、黄海鲐鱼渔场预报

为提高东、黄海鲐鱼渔场预报准确率、降低渔业生产成本,研究提出了一种基于提升回归树的渔场预报模型。研究采用2003—2010年我国大型灯光围网渔捞日志数据,以有网次记录的小渔区为渔场,以渔捞日志未记录的区域作为背景场随机选择假定非渔场数据,以海表水温等环境因子作为预测变量构建东、黄海鲐鱼渔场预报模型并以2011年的实际作业记录对预报模型进行精度验证。验证计算得到预报模型的AUC(area under receiver operating curve)值为0.897,表明模型的预报精度较高。模型的空间预测结果表明,预报渔场与实际作业位置基本吻合,其位置移动也与实际情况相符。这表明基于提升回归树的渔场预报模型可以用来进行东、黄海鲐鱼渔场的预报。     

厦门海域渔业资源评估

以初级生产力和渔业统计资料为材 ,分别应用Tait沿岸海域生态系能流分析法、营养动态法和Cushing等 3种模式 ,估算厦门沿岸海域的渔业资源自然生产量。同时 ,分别应用Schaefer和Fox两种剩余产量模式估算最大持续产量和最大持续捕捞力量。前 3种模式估算该海域的资源生产量分别为 2 0 1 0 5t,1 8463t和 1 7489t,平均 1 8686t。后两种模式估算最大持续产量平均值分别为 9639t和 91 0 4t。估算的最大持续捕捞力量 :5种作业综合总功率为 1 5976kW ;以厦门机定置渔船单位功率渔捞效率为标准估算的总功率为 2 7351kW ;以厦门机刺网渔船单位功率渔捞效率为标准估算的总功率为 432 1 3kW。 1 997年实际渔获量和捕捞力量均超过了估算的最大持续产量和最大持续捕捞力量。文中还讨论了捕捞力量的调整问题。     

Numerical simulation of the influences of sinker weight on the deformation and load of net of gravity sea cage in uniform flow

1IntroductionThe fish farming and aquaculture industry areexpanding and the demand for suitable locations forfish farms is increasing.In the future,more of thefish farms will be located offshore,as the number ofsuitable nearshore locations is limited.Futu…     

Numerical Investigation on Severe Slugging in A Catenary Riser

A mathematical model is presented to study the main characteristics of severe slugging in a downward inclined pipeline followed by a catenary riser. In this model, both simplified transient model and phase distribution model are included so that the flow characteristics of each stage for severe slugging can be accurately reproduced, especially for blowout stage. The results show that the flow features of severe slugging can be simulated by the proposed mathematical model. A good agreement between the experimental data and the numerical results is observed. The model can predict the transient fluctuation of many respects, such as the superficial gas velocity at the bottom of the riser and the average velocity at the outlet of the riser.     

基于深度学习和时空特征融合的海洋渔船密度预测方法

为了从海量渔船轨迹数据中挖掘隐含的信息和知识,进而为渔业行政主管部门的决策提供科学依据,本研究以AIS渔船轨迹数据为研究对象,提出了一种基于深度学习和面向时空特征融合的海洋渔船密度预测方法：首先,利用渔船轨迹数据集对渔船行驶区域进行网格划分;其次,筛选出渔船高密度区域进行研究,避免数据稀疏性问题;再次,根据渔船轨迹数据的时空分析,构建三维时空融合矩阵;最后,通过卷积循环神经网络模型捕获渔船分布的时间和空间特征,并利用卷积神经网络的堆叠加强对空间特征的学习。实验通过东海海域渔船真实轨迹数据进行具体测试,结果表明渔船密度预测值与真实值非常接近,平均绝对误差为4×10-4,模型较好地拟合了渔船密度分布特征,有效地提高了渔船捕捞热点预测的准确性和鲁棒性。     

Research on the short-term fishery forecasting of Spanish mackerel (Scomberomerus niphonius)

-This paper presents the use of the hydrographic factors in short-term fishery forecasting of the spawning migration stock of the Spanish mackerel and salinity describes more concretely the correlativity of water temperature, salinity and air temperature with the fishing season in spring. The data have been collected from the hydrographic environmental investigation at the fixed position on the sea and the telegraph recordings of the drift net operation in the spring fishing season during the period of April and May from 1972 to 1980. The correlation coefficients of various factors with the data of the fishing season have been calculated by using the monadic regression method.The main reference targets of the forecasting are: (1) By using the upper-layer water temperature as the forecasting factor at the beginning of the fishing season, the accuracy is high; (2) the distribution and location of the isotherm of the upper-layer water at 10°C at the beginning of April are used as an important factor for d     

Numerical and Experimental Investigation of Interactions Between Free-Surface Waves and A Floating Breakwater with Cylindrical-Dual/Rectangular-Single Pontoon

This paper investigates the hydrodynamic performance of a cylindrical-dual or rectangular-single pontoon floating breakwater using the numerical method and experimental study. The numerical simulation work is based on the multi-physics computational fluid dynamics (CFD) code and an innovative full-structured dynamic grid method applied to update the three-degree-of-freedom (3-DOF) rigid structure motions. As a time-marching scheme, the trapezoid analogue integral method is used to update the time integration combined with remeshing at each time step. The application of full-structured mesh elements can prevent grids distortion or deformation caused by large-scale movement and improve the stability of calculation. In movable regions, each moving zone is specified with particular motion modes (sway, heave and roll). A series of experimental studies are carried out to validate the performance of the floating body and verify the accuracy of the proposed numerical model. The results are systematically assessed in terms of wave coefficients, mooring line forces, velocity streamlines and the 3-DOF motions of the floating breakwater. When compared with the wave coefficient solutions, excellent agreements are achieved between the computed and experimental data, except in the vicinity of resonant frequency. The velocity streamlines and wave profile movement in the fluid field can also be reproduced using this numerical model.     

平面无结节网衣水阻力系数的试验研究

通过物理模型试验,统计分析得到了无结节网衣的水阻力系数在不同状态下随雷诺数、倾角和布置状态的变化规律,并通过网衣沉子的组合试验验证了所得经验公式的正确性和适用性,为深水网箱等渔具的水动力计算提供了依据.     

南海北部金线鱼最大可持续产量和总可捕量的研究

限额捕捞试点工作逐步展开,预示着我国海洋渔业管理进入全面有序的管理时代。文章根据2008—2017年南海北部渔港渔业生产抽样调查数据,统计出南海北部金线鱼的产量主要来自刺网,占累计总产量的72.90%。剩余产量模型分析认为南海北部金线鱼的最大可持续产量在168 632.99~31 0518.85 t,平均为251 765.59 t。2017年实施最严格的休渔制度后,当年的捕捞努力量投入和渔业产量均未超过最适值,当前总可捕量可设为158 515 t。文章研究结果可为该鱼种限额捕捞政策实施提供参考。     

A timely opportunity to protect North Atlantic right whales in Canada

The survival of federally protected North Atlantic right whales (Eubalaena glacialis) requires an immediate reduction in the risk of entanglement in commercial fishing gear. This paper argues that at least a 30% reduction in risk is needed to meaningfully contribute to the conservation of right whales. The argument follows from risk estimates calculated using time and space intersections of right whales and fishing gear in Canadian waters. Almost all the risk occurs during July, August and September (12%, 50%, 37% respectively) and the groundfish fishery contributed the greatest proportion (86%) of annual risk. Given that efforts in the USA to reduce entanglement risk through modified fishing gear have been unsuccessful to date, we address the alternative option of restricting certain fishing gear at times and locations where entanglement risk is elevated. There are many options that Canada could employ to achieve the above risk reduction and our results clearly point to the most effective and efficient action being seasonally restricted fishing in two relatively small regions; the Grand Manan Basin and the Roseway Basin. Fully a third (34%±4%) of the annual risk is associated with these two basins, though fishery catch estimates in the basins are relatively small and declining.     

一种基于有限状态机模型的局部转向避碰路径规划算法

针对多礁石、渔船等障碍物的近海复杂环境下的一些应用,提出了一种基于有限状态机(finite-state machine,FSM)模型的无人船(unmanned surface vehicle,USV)局部转向避碰路径规划算法。首先,基于速度障碍法和障碍物区域分层方法,获取无人船固定航速条件下的航向角约束解析结果。然后,基于该约束条件及障碍物探测情况设计FSM的有限状态及执行动作和状态迁移条件,其中,通过转向控制实现向目标位点或缓冲位点进行导航的状态为FSM的2个重要状态。最终通过FSM的执行实现局部转向避碰路径规划。仿真结果表明提出的多障碍物避碰算法具有可行性和实用性。该方法易于改进和扩展,且容易与当前主流的无人船控制系统结合,有利于无人船避碰系统快速工程化的实现。