立式曲面V型网板在拖网系统中的力学配合计算研究

为获知网板对拖网系统力学配合计算的影响,本文运用网板平衡方程结合钢索张力方程,建立拖网系统力学配合计算模型,并选取一款广泛使用的立式曲面V型网板及其相应的中层拖网,将网板水动力性能水槽实验数据,结合“龙腾”号的拖网及拖船实测数据带入力学模型,从翼端处的张力起始,逐步计算及分析手纲、网板、曳纲的受力情况,得到网板工作冲角、曳纲长度及张力、拖网翼端深度等拖网系统参数值。对网板各参数对拖网系统的影响进行了分析讨论,分析证明:冲角、曳纲长度和翼端深度随拖曳速度增加而减小;翼端深度及曳纲张力随曳纲连接点Z坐标的增加呈指数增长,随手纲连接点Z坐标增加呈线性减小;通过调节曳纲连接点Z坐标在0.1m-0.6m范围内,可控制工作冲角在17.77°-18.55°之间,翼端深度在124.3m-192.3m之间,曳纲张力在40210N-42219N之间变化;通过调节手纲连接点Z坐标在-0.4m--0.05m范围内,可控制工作冲角在16.54°-19.85°之间,翼端深度在75.9m-679.5m之间,曳纲张力在39533.5N-57933N之间变化;减少网板在水中质量,可减小拖船功率负荷,更适合在浅层作业;减小网板面积,可降低网板工作冲角,同时减小拖船功率负荷,更适合在稍深的水层作业。本文总结了网板参数的配合计算规律并建立了估算公式,为网板的合理使用和进一步开发提供参考依据。     

网袖长度对底层大网目拖网性能的影响的研究

为掌握拖网网袖对大网目底拖网网具性能的影响, 本研究针对东海区典型的大网目底拖网(72 目×18 m), 设计试验6种纵向拉直长度不同的网袖, 分析比较了不同袖长比L_w/L(L_w–网袖纵向拉直长度, L–网具纵向拉直长度)对网具阻力、网口高度和水动力性能的影响。结果表明, (1) 随着L_w/L的增大, 网具阻力增加, 但增加到36.45%之后, 阻力几乎不再变化; (2) L_w/L对阻力的影响与拖速有关, 速度越大, 阻力随L_w/L的变化越大; (3) 网口高度随L_w/L的增大而提高, 在L_w/L为36.45%~38.69%时达到最佳, 随后降低; (4) L_w/L对网口高度的影响与拖速有一定关系, 低速下网口高度变化小, 高速下网口高度随L_w/L有明显的变化; (5) L_w/L在大于36.45%之后水动力性能相对较高, 增大L_w/L, 水动力性能会有小幅度降低, 反之会有较大幅度的下降; (6) 此规格拖网网袖长度不宜过短, L_w/L以36.45%为宜, 根据作业条件, 在设计网具时可适当增加网袖长度。试验结果可对大网目底拖网网袖部位的设计和改进提供技术参考。

     

渔船拖网绞车张力自动控制系统设计及试验

为了补偿拖网渔船作业过程中绞车纲绳张力波动或渔船转向造成的负载不对称性,保持网具良好的开口形状,基于电液控制技术设计了拖网张力自动控制系统。对拖网曳纲张力采集方法进行了研究,采用油压力传感器间接测量拖网左右曳纲张力数据作为输入信号,传输到控制器进行逻辑运算,控制先导溢流阀调整马达溢流压力,改变绞车输出扭矩,从而驱动拖网绞车收、放来控制左右曳纲张力,达到系统动态平衡。并基于实验室虚拟仪器工程平台(laboratory virtual instrument engineering workbench,Lab VIEW)对系统软件进行了设计,实现绞车张力控制系统的参数设置与控制管理。为了验证系统的张力控制特性和实用性,对系统进行了海上应用试验,在张力自动控制模式下,拖网绞车根据渔船航速和水流自动调节收放网速度,减少作业过程中曳纲张力波动。拖曳过程中拖网曳纲长度范围为350~490 m,绞车曳纲张力范围为118~148 k N,对应系统压力为2.3~2.7 MPa,渔船平均拖速为5.6节。试验结果表明,左右曳纲张力差在合理范围内,系统能很好调节曳纲张力大小,为渔船安全生产提供了保障;启用张力控制系统后网口面积比未使用张力控制系统前增大了9.5%,有效调整了网口扩张,提高了捕捞效率。     

拖速和曳纲长度对南极磷虾中层拖网网位的影响

利用2015年2—7月随青岛远洋捕捞有限公司南极磷虾(Euphausia superba)大型中层拖网渔船"明开轮"赴南极南舍得兰群岛水域执行农业部南极海洋生物开发利用项目期间收集的网位(D)、网口高度(H)、曳纲投放长度(L)和拖速(V)等数据,分析了拖速和曳纲长度对拖网网位和网口高度的影响。本研究中,网口高度定义为网口上下纲深度之差;网位定义为网口中心位置水深。根据渔船作业习惯和虾群群体特点,曳纲投放长度范围138~258 m,每档间隔20 m。拖速1~3 kn,间隔0.5 kn。结果表明:(1)网口高度变化范围为13.6~24.1 m,网位水深变化范围为50~70 m;(2)作业过程中,南极磷虾拖网网位变化主要由曳纲长度决定,曳纲从138 m开始投放时,每增加20 m,网位平均下降深度约1.9 m,网口高度平均减小1.1 m,曳纲长度对网位和网口高度均产生极为显著的影响(P0.01);(3)拖速由1.0 kn变化至3.0 kn时,网位平均上升速率约2.9 m/kn,网口高度平均减小速率为2 m/kn,平均降低19.8%,拖速对网位和网口高度的影响显著(P0.05);(4)不同曳纲长度时的各拖速区间内的平均网位变化速率呈先减小后逐渐增大的规律。本研究结果不仅可为南极磷虾渔船船长根据虾群的群体大小、水层变化及其与网具的位置关系,适时调整曳纲长度和拖速,使网位到达预设水层,实现瞄准捕捞提供参考,还可为研究南极磷虾拖网网具性能的优化以及南极磷虾拖网网具设计的改进提供基础资料。     

198kW渔船绳拖网试验报告

１９８ｋＷ渔船绳拖网试验报告ＥＸＰＥＲＩＭＥＮＴＡＬＲＥＰＯＲＴＯＮＴＨＥＲＯＰＥＴＲＡＷＬＵＳＥＤＩＮ１９８ＫＷＦＩＳＨＩＮＧＢＯＡＴ孙泰昌崔国平邹惠君李烟芬（山东省海洋水产研究所,烟台２６４０００）陈家乐刘全成刘来军山东省海洋水产研究所,烟台２６...     

How “The Blob” affected groundfish distributions in the Gulf of Alaska

We investigated the distributional shifts of groundfish in response to anomalous ocean conditions, particularly the recent anomalously warm period (2014–2016; “The Blob”), based on data from ten Gulf of Alaska bottom trawl surveys conducted by the Alaska Fisheries Science Center during 1996–2015. Six groundfish species were considered: Pacific cod (Gadus macrocephalus), arrowtooth flounder (Atheresthes stomias), walleye pollock (Gadus chalcogrammus), Pacific ocean perch (Sebastes alutus), northern rock sole (Lepidopsetta polyxystra), and southern rock sole (Lepidopsetta bilineata). Ontogenetic differences were examined by dividing data for each fish species into size classes. Our study demonstrated that after accounting for size‐specific depth preferences, the spatial responses of groundfish to anomalous ocean conditions differed by species and foraging guild in the central Gulf of Alaska. Pacific cod and arrowtooth flounder showed similar responses to ocean warming, but different responses to cooling. In general, Pacific cod moved to deeper depths in warmer years and moved to shallower depths in colder years. Arrowtooth flounder also moved deeper in warmer years. However, in colder years, large arrowtooth flounder (>40 cm) shifted toward shallower depths while smaller‐sized fish shifted toward deeper depths. In warmer years, large pollock (>30 cm) moved to deeper waters while smaller pollock (10–20 cm) moved to shallower waters. Pacific ocean perch exhibited an opposite response to thermal changes in habitat compared with Pacific cod and arrowtooth flounder. They moved deeper in colder years, but there was no clear change in depth as a function of size in response to warmer habitat.     

Effect of population structure, sampling strategy and sample size on the estimates of selection parameters for shrimp (Crangon crangon) trawls

In selectivity experiments with shrimp trawls, very high numbers of animals in the catches of single hauls are a common feature and therefore, sub-sampling is inevitable. In order to find an acceptable balance between work-load and accuracy in the estimation of the selection parameters, it is important to have a sensible idea on the minimum numbers of shrimps to be measured in each catch fraction (cover, discards and landings). The present theoretical study tries to answer this question by means of computer simulations of different sampling strategies and sample sizes applied to catches with known size compositions.

The results of the simulations are discussed in relation to population structure, shape of the cod-end selection curve, sampling strategy (as the relative amounts measured from the different catch fractions) and sample size, and the method used to calculate the selection parameters.

Samples of 750 animals provide an acceptable compromise between work-load and reliability of the estimated selection parameters, provided that sufficient numbers of length classes are available. Population structure, selection curve and sample size (in that order) largely determine the reliability of the estimates, whereas the sampling strategy, on the other hand, only has a minor effect.     

基于栖息地指数模型的毛里塔尼亚头足类底拖网渔场研究

毛里塔尼亚专属经济区是我国西非过洋性渔业底拖网渔船的主要作业海域之一。本研究根据2010—2015年上海某远洋渔业公司的底拖网渔船生产数据,结合卫星遥感获得的表温和海面高度等数据,利用栖息地指数方法,采用几何平均模型和算术平均模型对毛里塔尼亚底拖网渔场进行了比较研究。结果显示,毛里塔尼亚海域底拖网作业的时间为1—4月和7—12月。各月基于表温、海面高度距平值和海底水深的适应性指数表明渔场的适宜海洋环境范围有差异。AMM模型中,HSI大于0.6的作业网次比例为76.10%,作业产量比例为78.66%,平均网次产量随着HSI的增加逐渐增大,从HSI为0~0.2时的29.37 kg/网次,增加到HSI为0.8~1.0时的47.20 kg/网次;GMM模型中,作业网次所占比例只有66.71%,作业产量比例为71.18%,平均网次产量随HIS的增加没有呈现合理的规律。本研究认为AMM模型更加适合于毛里塔尼亚底拖网渔场的预报。     

舟山市单拖资源利用现状分析

根据2008-2010年的单拖渔业监测资料及2001-2006年舟山市渔业调查数据,从单拖渔业的发展状况、经济效益、渔获组成及资源密度变化等几方面进行研究.并针对舟山市单拖作业存在问题,提出了几点建议供管理部门参考.