金枪鱼延绳钓捕捞作业状态的数值模拟

一种基于有限元原理的非线性混合法被用于预测捕捞作业中的金枪鱼延绳钓的形状与张力,为渔具设计提供理论方法,并以期在设计阶段能替代传统的水槽模型试验,为实际渔业生产作业调整提供有益的技术参数。构成延绳钓渔具的绳索可以被一系列绝对柔软的被称为绳索要素的单元所模拟,因此,整个延绳钓渔具可以被看作为一系列绳索要素在其两端点通过无摩擦铰接连接而成的集合体。根据最小位能原理,可以导出描述系统平衡状态的非线性基本平衡方程式。利用Newton-Raphson方法,通过一系列的负荷-形状迭代法求解基本平衡方程式,可以获得海流作用下延绳钓渔具作业时的形状和张力分布的数值解。简化模型的回流水槽试验验证表明,本方法具有较好的计算精度和解的收束性与稳定性。     

基于龙格库塔法的漂流延绳钓沉降过程数值模拟

掌握延绳钓渔具的沉降过程对于提高目标鱼种的渔获率、减少其他物种的兼捕具有重要意义.本研究基于有限元理论,采用集中质量法建立延绳钓三维动力学沉降模型,把2016年3月至2016年7月海上实测的12个站点的风速和风向、不同深度的三维海流数据、渔具参数以及作业参数输入模型,应用七级六阶龙格库塔法求解模型,得出与12个实测站点...     

金枪鱼延绳钓力学性能研究进展

延绳钓的力学性能直接影响渔获效率与能源消耗。文章总结了国内外金枪鱼延绳钓力学性能由最初的海上实测到动水槽模型试验再到数值模拟研究的相关研究方法与成果。结果显示:1)延绳钓的力学分析已从静态分析发展为动态分析;2)进行小尺度延绳钓模型试验,目的是验证特定情况下数值模拟分析的准确性;3)根据数值模拟和实测结果确定了延绳钓干线垂直阻力系数(CN90)为1.12和惯性力系数(Cm)为3。建议今后对延绳钓力学性能研究为:1)研究渔具材料刚度、阻尼对数值模拟精度的影响;2)结合金枪鱼的行为特征研究其上钩后的水动力,并将其考虑到模型之中,使模型与实际作业状态更加接近;3)对于渔具与海流、渔船、绞机和渔获物之间的相互作用机理进行深入的数值模拟研究。     

基于有限元分析的金枪鱼延绳钓钓钩力学性能研究

掌握金枪鱼延绳钓钓钩的应力、变形等力学性能有利于改进钓钩设计和正确选用材料。实验针对生产实际中常用的2种钓钩(环形钩和圆形钩)进行三维实体建模,利用ANSYS软件对其进行有限元分析,获得钓钩的等效应力、变形的分布模式和可能的破坏条件及形式;由同尺寸和同结构钓钩的拉伸实验结果验证了数值分析得到的最大应力和变形结果,并根据数值分析的结果对钓钩进行了结构优化分析。结果显示:(1)同规格环形钩的抗拉强度优于圆形钩15.80%~29.40%,环形钩X、Y轴最大变形率比圆形钩分别小3.00%和0.21%;(2)钓钩的主要受力区域在后弯处(承受83.00%~86.00%的应力),轴头孔下端存在应力集中;(3)对后弯、前弯表面进行压扁处理(压下率为15.00%),适当增加钓钩后弯的圆弧曲率(曲率半径由14 mm增至16 mm)、钩轴采用圆弧过渡等措施,可提升钓钩强度4.60%~10.80%。研究表明,圆形钩是良好的生态保护型钓钩,强度满足使用要求,可在延绳钓渔业中使用。     

网渔具计算机数值模拟的研究进展

对近年来网渔具的计算机数值模拟中使用的几何拓扑分解方法、数学建模思想和模型算法等进行了归纳和系统整理,并探讨了各种算法的稳定性和收敛性。分析认为:刚体有限元法数学建模的优点是模型简化,能基本反映网具粗糙形状,缺点是忽略网线张力,无法精确反映网具的受力和网具的运动状态;基于质量弹簧体系和牛顿力学的柔性有限元法是主流,数值模拟结果更符合网具的实际状况,网形更细腻逼真,计算结果与网具实测拟合较好;显式算法对时间步长较敏感,稳定性和精度不如隐式算法好。NEWTON-RAPHSON和NEWMARK-β算法具有无条件稳定性和收敛性,大部分研究采用了此算法。     

基于数值模拟的丁字湾海洋环境恢复研究

2011年,山东半岛蓝色经济区上升为国家战略后,丁字湾被定位为海洋旅游文化产业聚集区.然而,目前丁字湾沿岸由于近几十年来养殖和盐田业过度围垦造成海湾面积急剧萎缩,湾内水流不畅,淤积严重,湾内大部分海域水质已不能满足要求,海洋生态环境严重衰退.本文应用数值模型模拟了拆除养殖和盐田堤坝后丁字湾水动力、水交换率和纳潮量的变化.计算结果显示拆除堤坝后湾内水动力条件得到了显著增强,半交换时间明显缩短,纳潮量增加近一倍多,对改善丁字湾海洋环境质量、缓解泥沙淤积、增强污染物稀释能力和增加海洋环境容量具有重要的现实意义.此外,本研究还基于数值模拟结果,探讨了丁字湾海洋环境修复的有关建议.     

水流作用下筏式养殖设施动力响应的数值模拟

利用有限单元法建立了水流作用下筏式养殖设施动力响应的数学计算模型,通过数值求解对浮标和吊笼结构的最大位移以及锚绳受力进行分析。计算机模拟结果表明,筏绳在水流作用下产生明显的变形,其形态变化与实际基本相符。当流向一定时,浮标和吊笼的最大位移值以及左右两侧的锚绳受力均随流速的增加而增大。其中,浮标最大位移值7.6m,吊笼最大位移值9.6m。当流速一定时,浮标和吊笼的最大位移值与右侧锚绳受力随着来流角度的增加而增大。左侧锚绳力受来流方向变化影响不明显,其最大值为3 780N。     

YDJ35／80延绳钓起钓机的研制与试验

本装置由起钓机，液压组件，油箱管路三部分组成。起钓装置采用(2．45～5．88MPa)液压传动起钓作业中，柴油机推动子船低速前进，并驱动油泵工作。压力油通过软管进入起钓机上的油马达，从而推动起钓机工作。回油经调速阀回油箱。控制阀操纵开、行机器。     

基于ANSYS Workbench力学仿真的金枪鱼延绳钓钓钩深度

钓钩深度对金枪鱼延绳钓渔获性能有重要影响,本研究基于田内准则对延绳钓渔具进行缩小,采用ANSYS Workbench 19.2数值仿真软件对金枪鱼延绳钓进行双向流固耦合仿真,并选取2016年波利尼西亚群岛附近海域(4°S～15°S,140°W～160°W)金枪鱼延绳钓作业实测的6个作业站点42枚钓钩深度数据与ANSYS...     

基于FUNWAVE-TVD模型的离岸养殖围网内外波浪场数值模拟研究

本研究利用完全非线性Boussinesq数值模型FUNWAVE-TVD耦合多孔介质模型,建立了模拟围网波浪场的数值模型。将计算结果和实验数据进行对比分析,验证了该模型计算规则波在穿过网箱后传播过程的准确性。进一步研究了波高和周期等因素对围网内外波浪场特性的影响,探讨了围网波浪场特性与这些水动力因素的内在联系。结果显示,离岸养殖围网的存在使波浪场背浪侧出现衰减,波高衰减率受波浪周期影响较大,最大波高衰减达到93.3%。同时,较低频规则波的波高衰减区域呈辐射状趋势扩散,并随着波浪进一步传播,最大波高衰减位置开始向两侧扩散,围网背浪侧的波高衰减程度减小,波高有恢复趋势,而高频波浪的波高衰减区域则较为集中。本研究可为实际海域桩网围护的位置和构造提供分析依据。     

Effects of circle versus J-style hooks on target and non-target species in a pelagic longline fishery

The U.S. Atlantic coastal pelagic longline fishery that targets tunas and swordfish also interacts with a wide range of non-target species including billfishes and sea turtles. Preliminary studies indicate that a change in terminal gear from J-style hooks to circle hooks may reduce bycatch mortality, but the effects of this change on catch rates of target species are unclear. To evaluate this, we monitored catch composition, catch rates, hooking location, and number of fish alive at haulback during 85 sets in the fall and spring seasonal fisheries from a commercial vessel operating in the western North Atlantic. Circle (size 16/0, 0° offset) and J-style (size 9/0, 10° offset) hooks were deployed in an alternating fashion. Hook–time recorders were used to assess time at hooking and temperature–depth recorders to measure gear behavior. Catch rates for most species categories were not significantly different between hook types (P < 0.05), although circle hooks generally had higher tuna catch rates in the fall and lower swordfish catch rates in the spring. In the fall, both total catches and catches of pelagic rays were significantly higher on J-style hooks. Yellowfin tuna in the fall and dolphinfish in the spring caught on circle hooks were significantly larger than those caught on J-style hooks. In both seasonal fisheries, circle hooks caught fishes in the mouth more frequently than J-style hooks, which hooked more often in the throat or gut, although these differences between hook types were not statistically significant. Yellowfin tuna in the fall fishery were over four times more likely to be hooked in the mouth with circle hooks than with J-style hooks. Several target and bycatch species showed higher rates of survival at haulback with circle hooks, although only for dolphinfish in the fall fishery was this difference statistically significant. Our results suggest that the use of 0° offset circle hooks in the coastal pelagic longline fishery will increase the survival of bycatch species at haulback with minimal effects on the catches of target species.     

Dynamic simulation of tuna longline gear using numerical methods

ABSTRACT:   The underwater shape and hook depth of tuna longline gear are important factors determining fishing performance. In this study, how the shape of tuna longline gear changes in response to sea conditions and gear rigging is explained. Physical models of underwater gear shape were made to simulate fishing gear and analyzed according to the direction and velocity of currents. Then experiments with small-scale models were conducted in a flume tank to confirm the accuracy of the simulation analysis. Finally, the simulation was examined relative to actual longline fishing gear. This approach provided an improvement over previous analytical methods that did not consider fishing gear shape in response to different sea conditions. A useful result is an improved understanding of the relationship between ocean currents and the configuration of longline gear (the shortening ratio, and number of hooks per basket). These factors affect hook depth which, in turn, affects selectivity. Application of these results could lead to more effective and efficient fishing under different sea conditions.     

金枪鱼延绳钓钓钩和起重机吊钩材料及力学性能研究进展

了解金枪鱼廷绳钓钓钩作业时的受力和应力应变情况,有利于改进钓钩设计和材料选择.本文对有关金枪鱼延绳钓钓钩种类、材料和力学性能,起重机吊钩应力、位移变化、优化设计和检测等国内外相关文献进行整理分析,目前的研究虽取得了一定的成果,但关于钓钩的仿真模拟、钓钩受力分析和优化设计的研究较少.本文建议:(1)参考起重机吊钩材料及力学性能研究的方法,采用有限元软件ANSYS对金枪鱼钓钧建立不同的3D模型,对比得出更好的建模方法;(2)对不同材料钓钩受力产生的拉伸、弯曲、扭转、断裂等变形情况进行模拟分析和实验;(3)分析各种钓钩所能承受的最大拉伸、弯曲、扭转负荷及钓钩最大应力、应变的分布情况;(4)对金枪鱼钓钩的结构进行设计和优化.     

Standardized catch and survival rates,and effect of a ban on shark retention,Palau pelagic longline fishery

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A review of reported effects of pelagic longline fishing gear configurations on target,bycatch and vulnerable species

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Effects of fishing practice changes on pelagic shark longline captures in the Gulf of Gabes,Tunisia

1. In order to increase their catches, longliners targeting sharks in the Gulf of Gabes, Tunisia, have increased the number of hooks per basket and have included new bait types instead of mackerel (Scomber scombrus). This paper reports the effects of these changes on catch composition, catch rates, size distribution, life‐stage captures, and mortality at haulback.
2. Data from 48 and 96 longline sets, carried out during the shark fishing seasons of 2007 and 2008, with two hooks per basket, and 2016 and 2017, with five hooks per basket, respectively, were examined to assess the effect of gear change. Moreover, the effects of bait types were inspected based on 33 fishing sets using whole mackerel, 19 using salema (Sarpa salpa) halves, and 27 using pieces of stingray (Dasyatis spp.), sampled during 2016 and 2017.
3. The species composition indicated that longliners expand the vertical distribution of their hooks to operate from the surface to the bottom. The catches with both longline designs were dominated by sandbar shark (Carcharhinus plumbeus). Despite gear changes, the catch rate of C. plumbeus decreased by 42.21%, suggesting population decline. The size composition indicated a shift towards larger specimens, mainly adult females, which could jeopardize the shark population. Moreover, the mortality of the main species at haulback seems to be affected by the design of the longline.
4. The bait used, mainly pieces of stingray, significantly increased the catch rate of sandbar shark, which suggests a greater attractiveness of the new bait; however, fish size and mortality rates at haulback were unchanged in response to bait variation.
5. The fishery operates in shark nursery grounds, which exposes these fish (principally C. plumbeus) to considerable exploitation pressure. The new fishing practices intensified the pressure and thus the risk of a rapid depletion of populations. To preserve the shark species in the area, the use of new gear and attractive bait should be banned.

     

Study on the potential of suspended longline mariculture of the scallop Chlamys farreri in offshore areas

The growth and survival of the scallop Chlamys farreri exposed to different initial densities were evaluated in culture systems from inshore and offshore areas of Sungo Bay, China, from May 2007 to March 2008. Water quality data (e.g. temperature, salinity, current speed, chlorophyll a and total particulate material) were measured concurrently. The C. farreri reached the market size after 10 months of cultivation. Average survival rates for the same initial densities were lower in the inshore area than those in the offshore area. Survival rates also were inversely proportional to the initial densities. Scallops in offshore area with initial densities of 20 and 30 individuals per disc resulted in significantly greater shell heights, soft tissue weights and muscle weight compared with the other experimental groups. Tissue weight increased rapidly from May to September. However, scallops in offshore area had a second growth peak during October to November. Scallops in the offshore area had higher growth and survival rates, which may be attributed to high water current speed resulting in increased food supplies. Results indicate that the scallop C. farreri has an aquaculture potential in offshore cultivation systems.     

Effect of type of bait on pelagic longline fishery–loggerhead turtle interactions in the Gulf of Gabes (Tunisia)

• 1. Sea turtles may migrate vast distances from their feeding areas to home rookeries where they nest. During these migrations sea turtles are subject to many threats, among which are interactions with pelagic longlines.
• 2. This gear is used frequently in the summer period in the Gulf of Gabes targeting mainly the sandbar shark (Carcharhinus plumbeus). Hooks are baited with mackerel (Scomber scombrus) or pieces of stingray (Dasyatis pastinaca).
• 3. Twenty‐one fishing trips (48 sets with a total of 35 950 hooks deployed) were conducted using onboard observers in the south of the Gulf of Gabes during the months of July, August and September in 2007 and 2008. Stingray and mackerel bait were used in 19 and 29 sets, respectively.
• 4. In total, 29 loggerhead sea turtles (Caretta caretta) were captured; the majority of them were juvenile and active. Turtles were caught at a statistically greater frequency on sets with hooks baited with mackerel than on sets with hooks baited with pieces of stingray.
• 5. The type of bait also affected the catch of the target species by increasing the efficiency when pieces of stingrays were used.
• 6. These results encourage further research into new baits to mitigate turtle catch by longline fisheries without affecting the catch of target species. Copyright © 2010 John Wiley & Sons, Ltd.

     

基于渔船捕捞行为特征的远洋延绳钓渔场捕捞强度计算

渔场捕捞强度信息可以为渔业资源评估和管理提供帮助。本研究结合2017年10—11月船舶自动监控系统(AutomaticIdentificationSystem,AIS)信息和同期中国中西太平洋延绳钓渔船捕捞日志数据,通过挖掘延绳钓渔船作业航速和航向特征,建立渔场作业状态识别模型,提取渔场捕捞强度信息。以3～9节为航速阈值和0°～10°及300°～360°为航向阈值,渔船作业状态识别准确率为68.29%。阈值识别和日志记录的捕捞强度信息在空间上相关性很高(0.96),基于AIS信息挖掘的渔船捕捞强度空间分布特征和实际非常相似。阈值识别和日志记录的捕捞强度信息在空间上与单位捕捞努力量渔获量(catch per unite of effort, CPUE)、渔获尾数、渔获重量和投钩数的空间相关系数均大于0.62,基于AIS信息挖掘的渔船空间捕捞强度也可替代用于渔业资源分析。