金枪鱼围网网具水动力特性及沉降性能研究

发布时间：2018-04-28 15:43

  本文选题：网具水动力 + 占空率　； 参考：《上海海洋大学》2017年博士论文

【摘要】：金枪鱼围网是围捕类渔具中最为先进的一种作业方式,其作业原理是利用中上层鱼类的表层集群行为,采用圈捕的方式,通过收绞底纲完成包围鱼群,达到捕鱼目的。这种围捕的基本技术最初应用于鲐鱼、沙丁鱼和溊鱼等小型鱼种,后来扩展到表层金枪鱼渔业中。目前,金枪鱼围网的目标鱼种包括鲣鱼Katsuwonus pelamis、黄鳍金枪鱼Thunnus albacares等。由于以前的捕捞技术是建立在渔业资源相对比较丰富、能源成本较低以及捕捞对环境影响较小的基础上,但随着渔业资源不断被开发利用,现在的渔具渔法更关注于生态环境的保护,以及能源成本的节约,从而引发了渔具设计理念的转变。围网网具发展步入到了网具性能优化的阶段,这主要是渔业管理的驱动,使人们不仅仅只关注高效的围网网具,更多地去关注生态保护及节能的优化网具。围网研究的主要内容有网具沉降特性、水动力特性及网具形态三方面,为了实现网具性能的优化适应现如今的捕捞策略,本研究立足于围网沉降特性和水动力特性研究,对网具本身属性和捕捞参数进行优化,以期提高网具的作业性能。网具优化的参数可包括:网具结构、网具本身属性、捕捞操作参数、放网模式等。但在网具性能优化过程中,1)围网网具的主要作业指标及影响因素有哪些?2)不同材料的网片水动力特性的变化规律?3)对于围网和拖网渔具,在水中运动均与水流呈小冲角运动,网具的水动力特性如何表现?4)优化参数对网具特性的影响效果评估?5)如何评价优化网具的渔具性能?这些问题是造成我国金枪鱼围网网具性能优化的方向不明确的一些主要原因。为此,本研究通过海上实测调查的结果,得到了网具的作业性能的影响因素,在实测的基础上开展新兴材料的网具水动力特性研究,了解不同材料和不同结节类型的网片水动力特性,量化分析下纲配重、放网速度对网具性能的影响,以及不同材料的网具沉降特性的差异,最终提出我国金枪鱼围网的优化方案,并通过动水槽试验评估优化后网具性能效果。主要研究结果如下:(1)渔船的放网速度及网具的沉降速度为决定捕捞成功与否的关键因素;鱼群的运动速度越快,捕捞的可能范围将急剧下降。当鱼群移动速度(下潜速度)超过1.5 m/s时,除非极具表层洄游性鱼类之外,稍具有一定深度的鱼群,则无捕获的可能;投网位置的选择不能忽视,投网位置与鱼群中心的距离越近,易导致鱼群的反应,从而增加逃逸概率;网具规模较大时,必须配合操作条件及鱼群的动态性能的判断作业,从而增加捕获成功率。(2)海洋环境和捕捞参数对围网沉降特性影响:应用广义可加模型(GAMs)对88网次的海上实测自由鱼群捕捞数据进行分析得到:120 m水层的海流速度是环境因素当中对围网沉降深度影响最大的因素;长高比较小的围网具有较好的沉降性能;长高比、放网时间和括纲长度对沉降深度影响显著;而长高比、放网时间、60 m水层流速、括纲长度和跑纲长度对沉降速度影响显著;建立的沉降深度和沉降速度最佳模型可用于预测在不同渔法操作和环境条件下的网具沉降性能,这对于成功捕捞自由鱼群是十分必要的。(3)动水槽试验结果显示,无结节聚乙烯(PE)网片的水动力系数与网目占空率有关;当网片平行于来流方向时,占空率与阻力系数存在负相关关系,而当网片垂直于来流时两者关系为正相关;网片倾斜于水流放置时,阻力系数随着冲角的增加而增大,升力系数在冲角为50°(临界冲角)时达到最大;当冲角小于该临界冲角时和大于临界冲角时,阻力系数和占空率的关系正好相反,即在小冲角下升、阻力系数与占空率均呈负相关关系,而在大冲角时呈现完全相反的结果。通过非线性拟合得到了聚乙烯网片的水动力系数公式:C_(D90)=5.568α~(0.292)Re~(-0.125)(500 Re 5300)C_(D0)=0.127α~(-0.534)Re~(-0.040)(500 Re 5300)C_(Dθ)=C_(D90)sinθ+（C_(D0)-1.775αsinθ）cos~2θC_(Lθ)=0.251α~(-0.481)C_(D90)sinθcosθ(4)对尼龙(PA)网片,雷诺数和占空率对其水动力系数的影响较为显著,随着雷诺数的增大,阻力系数减小并逐渐趋于平稳;占空率与平行阻力系数存在负相关关系,而与法向阻力系数呈正相关关系;网片倾斜于水流时,升力系数在冲角为50°(临界冲角)时达到最大;当冲角小于该临界冲角时和大于临界冲角时,阻力系数和占空率的关系正好相反,即当冲角趋于0°时占空率越小阻力系数越大,而当冲角趋于90°占空率越大阻力系数越大;在相同条件下,有结网片的阻力系数是无结网片阻力系数的1.23~1.35倍;当雷诺数低于2200,PE网片的阻力系数较PA网片大;但当雷诺数大于2200,PA网片阻力系数反而小于PE网片。根据试验结果拟合了尼龙网片的水动力系数经验公式:C_(D90)=1.691α~(0.114)Re~(-0.011)(400 Re 3600)；C_(D90)=19.371R_h~(-0.643)+1.139C_(D0)=0.172α~(-0.407)Re~(-0.031)(500 Re 5500)C_(Dθ)=C_(D90)sinθ+（C_(D0)-0.889αsinθ）cos~2θC_(Lθ)=0.38α~(-0.162)C_(D90)sinθcosθ(5)小冲角是围网和拖网渔具在水中作业时较普遍的情况,通过自主设计的试验装置,进行了网片水动力的小冲角试验。发现试验框架在0-20°范围内表现稳定,即框架阻力低于总阻力的20%,满足试验的基本要求;小冲角条件下,网片阻力系数与雷诺数、占空率和冲角有关;阻力系数随着冲角的增大而增大,但与占空率和冲角呈负相关关系;相同占空率的无结节尼龙网片的阻力系数约占有结节网片的77.9%。根据试验结果推导出了小冲角条件下的网片阻力系数公式:C_D=0.172α~(-0.407)Re~(-0.031)（1+sinθ~(0.905)~(1.822)上式可应用在渔具(围网、拖网等)与水流呈小冲角作业时,网具理论计算及数值模拟方面,同时也可利于此公式对围网模型准则进行修正。(6)聚乙烯、尼龙和涤纶3种网片的沉降性能动水槽试验结果表明:网片的沉降深度随着沉降时间的增加而增加,直至达到最大沉降深度;下纲配重的增加使网片的沉降特性有着显著性的提高,其中聚乙烯网片的提升幅度最大,其次是尼龙和涤纶网片;占空率与网片的平均沉降速度呈负相关关系;不同材料的网片沉降特性存在显著性差异,涤纶网片的沉降特性最佳,依次是尼龙网片和聚乙烯网片;试验结果证明结节网片的沉降特性劣于无结网片。(7)下纲配重和放网速度对沉降特性影响:利用天然水域中的金枪鱼围网模型网试验结果与海上实测结果进行了对比。结果发现,下纲重量的增加和放网速度的增大,有利于模型网的沉降性能提升;下纲配重是影响网具沉降性能最重要的因素;对比网具中部和取鱼部的沉降速度,围网翼端位置的沉降速度最大;模型网的沉降速度达到实物网的97.2%左右,可近似认为模型网的沉降速度能够客观反应实物网的沉降速度。这表明了我们的模型试验可作为一种重要的补充方法去评估原型网的实测性能。(8)在基础试验的结果上,利用小冲角阻力系数公式对围网模型网准则进行修正,然后制作模型网和设计模型网动水槽试验。本研究采用两种优化的模型网进行动水槽试验:模型网主网衣部位的网目由原来的25 mm更换为30 mm;模型网主网衣1/3部位(靠近下缘网附近)网衣由30 mm更换为45 mm。通过试验结果发现:1)侧流放网是较为理想的放网模式,相比于其它放网模式可使优化网具在沉降特性、包围面积方面有着显著的提高;2)从括纲张力角度来说,顺流放网为较佳放网模型,因其产生较小的括纲张力。取鱼部的张力较网翼部的张力大,两个部位的张力均在绞纲完成时达到最大;3)网目增大使网具沉降性能提升和括纲绞收时间减小。对下缘网附近的网目进一步增大,使网具阻力减小9.26%;4)顺流放网时,网船移动距离和漂移距离均最小,网目增大网具阻力减小使网船的漂流距离减小。可认为上述网具优化方案是切实可行的,在网具节能、网具形态和沉降特性方面均有显著性作用,可作为我国大型围网网具性能优化的主要方向。
[Abstract]:Tuna is one of the most advanced mode of operation in hunting fishing gear, its working principle is the use of the surface cluster behavior of pelagic fish, the captured the way through to twist the bottom line complete surrounded by fish, fishing to reach. The basic technologies should be initially used for the hunting fish Xia chub mackerel, sardines and small fish, later Extended to the surface tuna fisheries. Currently, the target species of the tuna Seine include the bonito Katsuwonus pelamis, the yellow fin tuna Thunnus albacares and so on. The fishing technology is based on relatively rich fishery resources, low energy costs and less impact on the environment, but with the continuous fishing resources With the exploitation and utilization, the fishing gear and fishing method now pays more attention to the protection of the ecological environment and the saving of the energy cost, which leads to the change of the design concept of fishing gear. The development of the Seine net has stepped into the stage of the optimization of the performance of the net gear, which is mainly driven by the fishery management, which makes people not only pay attention to the efficient Seine net, and go more to the customs. The main content of the study on the ecological protection and energy saving. The main contents of the study are the settlement characteristics of the nets, the hydrodynamic characteristics and the shape of the net gear in three aspects. In order to optimize the performance of the nets to adapt to the current fishing strategy, this study is based on the study of the settlement characteristics and hydrodynamic characteristics of the Seine, and the properties of the nets and the fishing parameters are optimized. In order to improve the performance of the net, the parameters of the optimization can include the structure of the net, the property of the net, the fishing operation parameters, the mode of the net, and so on. But in the process of optimizing the performance of the net, 1) what are the main operating indexes and the influencing factors of the Seine net? 2) the change law of the hydrodynamic characteristics of the mesh of the material? 3) for the Seine net And trawl fishing gear, moving in water with small punching angle in water, how to perform the hydrodynamic characteristics of the nets? 4) optimizing the effect of parameters on the property of the net gear? 5) how to evaluate the performance of the fishing gear for the optimization of the net gear? These problems are the main reasons for the uncertain direction of the performance optimization of the tuna Seine nets in China. In this study, the influence factors of the performance of the net gear are obtained by the results of the survey on the sea. On the basis of the measurement, the hydrodynamic characteristics of the new materials are studied. The hydrodynamic characteristics of the mesh of different materials and different types of nodules are understood, the weight of the next class is quantified, the effect of the net speed on the performance of the net is different, and the difference of the net speed is different. In the end, the optimization of tuna Seine in China is put forward, and the performance effect of the optimized net is evaluated through the flume test. The main results are as follows: (1) the speed of the fishing boat and the speed of the net gear settlement are the key factors to determine whether the fishing is successful or not; the faster the speed of the fish is, the fishing The possible range will decline sharply. When the fish group moves faster than 1.5 m/s, the fish group with a certain depth is not possible except for the highly migratory fish. The selection of the net position can not be ignored and the location of the net is closer to the distance from the center of the fish, which can lead to the response of the fish, thus increasing the escape probability. When the size of the net is large, it is necessary to match the operating conditions and the dynamic performance of the fish group to increase the capture success rate. (2) the influence of the marine environment and the fishing parameters on the settlement characteristics of the Seine net: using the generalized additive model (GAMs) to analyze the fishing data of the measured free fish group at sea at the 88 net times: the current velocity of the 120 m water layer It is the most important factor affecting the settlement depth of the enclosing network among the environmental factors; the relatively small long height of the fence has better settlement performance; the length and height ratio, the length of the length of the 60 m water layer, the length of the outline and the length of the running program have significant influence on the settlement velocity, and the depth of the settlement. The optimum model of degree and settlement velocity can be used to predict the settling property of the nets under different fishing operation and environmental conditions, which is necessary for the successful fishing of free fish. (3) the results of the flume test show that the hydrodynamic coefficient of the nodular polyethylene (PE) mesh is related to the net occupancy rate; when the net is parallel to the direction of the flow, it occupies the direction of the net. There is a negative correlation between the void fraction and the drag coefficient, while the relationship between the mesh and the flow is positive. The drag coefficient increases with the increase of the angle of impact when the net is inclined to the flow, and the lift coefficient reaches the maximum when the punching angle is 50 degrees (critical angle); when the punching angle is smaller than the critical angle and the critical angle is larger than the critical angle, the drag coefficient is the resistance system. The relationship between the number and the occupancy rate is the opposite, that is, the drag coefficient is negatively correlated with the occupying ratio at the small punching angle, and the result is completely opposite at the big punching angle. The hydrodynamic coefficient formula of the polyethylene mesh is obtained by nonlinear fitting. C_ (D90) =5.568 alpha ~ (0.292) Re~ (-0.125) (500 Re 5300) C_ (D0) =0.127 a (-0.534) Re~ (-0.0) 40) (500 Re 5300) C_ (D theta) =C_ (D90) sin theta + (C_ (D0) -1.775 alpha sin theta) cos~2 theta (theta) C_ (theta), theta theta (4), the Reynolds number and the occupying ratio have a significant influence on the hydrodynamic coefficients. With the increase of Reynolds number, the drag coefficient decreases and tends to be stable, and the occupying ratio and the parallel drag coefficient are negative. There is a positive correlation between the coefficient of resistance and the coefficient of resistance. When the net is inclined to the flow, the lift coefficient reaches the maximum when the impact angle is 50 degrees (critical angle). When the impact angle is less than the critical angle and the critical angle of impact, the relation between the drag coefficient and the duty ratio is exactly opposite, that is, the smaller the space ratio is, the smaller the drag coefficient is, the more the drag coefficient is. In the same condition, the resistance coefficient is 1.23~1.35 times of the resistance coefficient of no net plate, and when the Reynolds number is lower than 2200, the resistance coefficient of the PE mesh is larger than that of the PA mesh, but when the Reynolds number is greater than 2200, the resistance coefficient of the PA mesh is smaller than that of the PE mesh. According to the experimental results, the results are in accordance with the test results. C_ (D90) =1.691 alpha ~ (0.114) Re~ (-0.011) (400 Re 3600); C_ (D90) =19.371R_h~ (-0.643) +1.139C_ (D0). The small punching angle test of the net sheet hydrodynamic force is carried out by the self designed test device. It is found that the test frame is stable in the range of 0-20 degrees, that is, the frame resistance is lower than 20% of the total resistance, which satisfies the basic requirements of the test; the resistance coefficient of the mesh and the Reynolds number, the occupying ratio and the impact under the small punching angle condition. The resistance coefficient increases with the increase of the punching angle, but has a negative correlation with the occupying ratio and the punching angle; the resistance coefficient of the nodular nylon mesh with the same occupancy rate is about 77.9%. of the nodular mesh. The formula of the resistance coefficient of the mesh under the condition of small punching angle is derived: C_D=0.172 alpha ~ (-0.407) Re~ (-0.031) (1+sin theta ~ (0.)) 905) ~ (1.822) can be applied to the theoretical calculation and numerical simulation of the net gear when the fishing gear (Seine, trawl, etc.) and the water present a small punching angle. At the same time, this formula can also help to correct the mesh model criterion. (6) the settlement dynamic flume test results of 3 kinds of net sheet of polyethylene, nylon and polyester show that the subsidence depth of the mesh is with the sink. The increase of the drop time increases until the maximum settlement depth is reached. The increase of the lower class weight makes the settlement characteristics of the mesh significantly improved, among which the polyethylene mesh is the largest, followed by nylon and polyester mesh; the occupying ratio has a negative correlation with the average settlement velocity of the mesh; the net sheet settlement characteristics of different materials exist. In the significant difference, the settlement characteristics of the polyester mesh were the best, followed by nylon mesh and polyethylene mesh. The experimental results proved that the settlement characteristics of the nodular mesh were inferior to that of the non net plates. (7) the influence of the lower class weight and the net speed on the settlement characteristics: the results of the tuna Seine model net test in the natural waters were carried out with the measured results from the sea. The result shows that the increase of the weight of the lower class and the increase of the speed of the net, which is beneficial to the settlement performance of the model net, is the most important factor affecting the settlement performance of the net, and the settlement velocity of the wing end of the fence is the largest, and the settlement speed of the model net reaches 97.2% of the physical network. The settlement velocity of the model net can objectively reflect the settlement velocity of the physical network. It shows that our model test can be used as an important supplementary method to evaluate the measured performance of the prototype network. (8) in the result of the basic test, the formula of the small punching angle resistance system is used to correct the net model net criterion. This study uses two optimized model net moving flume tests: the mesh mesh of the main mesh of the model net is replaced by the original 25 mm to 30 mm; the network coat 1/3 part of the model net (near the lower edge net) is replaced by 30 mm to 45 mm. and is found by the test results: 1) the side flow network is compared. Compared with the other mode, the optimal net mode can improve the settlement characteristics and the area of the surrounding area. 2) from the point of view of the outline tension, the smooth discharge network is a better net model, because it produces smaller outline tension. The tension of the fish section is larger than the net wing, and the tension of the two parts is all hanging. When the program is completed, it reaches the maximum; 3) the net mesh device subsidence performance enhancement and the outline hoisting time decrease. To further increase the net mesh near the lower edge network, the net gear resistance is reduced by 9.26%; 4) the net ship moving distance and drift distance are the least, the net mesh resistance decreases and the drift distance of the net ship decreases. The optimization scheme of the net gear is practicable. It has a significant effect on the energy saving of the net, the shape of the net and the characteristics of the settlement. It can be used as the main direction of the performance optimization of the large Seine nets in our country.

【学位授予单位】：上海海洋大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：S972.21
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本文编号：1815898