排序方式: 共有52条查询结果,搜索用时 15 毫秒
21.
小型单拖网渔船V 型网板水动力性能研究 总被引:1,自引:0,他引:1
网板是拖网的重要属具之一, 广泛应用于近岸小型单拖渔船的生产作业中, 其水动力性能的优劣直接关系到拖网的生产效果和经济效益。作者以网板面积1 m2、展弦比0.55的 V 型网板为例进行小型单拖渔船的水动力性能研究。 基于田内相似准则, 相似比为2制作网板模型, 进行循环水槽模型试验, 实验冲角在10~60°范围内, 来流速度在0.2~0.7 m/s, 得出网板升阻力系数等流体动力特性曲线、临界冲角、最大升阻比。结果表明, 该型网板的最大升阻比约为1.86, 达到最大升阻比的临界冲角在15~25°附近, 该结果可为渔业生产操作中网板冲角的设置提供依据。实验结果同时显示, 该型网板的水动力效率略低于其他类型网板, 说明其板型仍有较大的改进空间。 相似文献
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The estimation of gear selectivity is a critical issue in fishery stock assessment and management. Several methods have been
developed for estimating gillnet selectivity, but they all have their limitations, such as inappropriate objective function
in data fitting, lack of unique estimates due to the difficulty in finding global minima in minimization, biased estimates
due to outliers, and estimations of selectivity being influenced by the predetermined selectivity functions. In this study,
we develop a new algorithm that can overcome the above-mentioned problems in estimating the gillnet selectivity. The proposed
algorithms include minimizing the sum of squared vertical distances between two adjacent points and minimizing the weighted
sum of squared vertical distances between two adjacent points in the presence of outliers. According to the estimated gillnet
selectivity curve, the selectivity function can also be determined. This study suggests that the proposed algorithm is not
sensitive to outliers in selectivity data and improves on the previous methods in estimating gillnet selectivity and relative
population density of fish when a gillnet is used as a sampling tool. We suggest the proposed approach be used in estimating
gillnet selectivity. 相似文献
23.
附着基粗糙度及表面沉积物对6种海藻孢子附着和幼苗数量的影响 总被引:1,自引:0,他引:1
本项研究试验了人工放散的蜈蚣藻(Grateloupia asiatica)与多管藻(Polysi phonia urceolata)孢子及其幼苗在不同粗糙度的附着基上的附着数量、三叉仙菜(Ceramium kondoi)、假根羽藻(Bryopsis corticulans)、酸藻(Desmarestia viridis)和尾孢藻(Urospora penicilli formis)在海水中自然附着幼苗在不同粗糙度的附着基上的附着数量;还试验了不同粗糙度附着基上不同类型的沉积物对自然附着酸藻和尾孢藻的幼苗数量的影响。试验方法是以市售塑料扎带模拟表面粗糙度不同的人工藻礁,使人工刺激后释放的海藻孢子附着在其表面后,吊挂于海中使孢子萌发;空白附着基吊挂于海水中使海藻繁殖体(孢子、合子或受精卵)附着并萌发生长。以普通海泥、高温灭活海泥、底栖硅藻3种不同沉积物覆盖于人工附着基表面,统计各种沉积物在各种粗糙度的附着基上海藻幼苗数量。结果表明,对于无鞭毛的繁殖细胞(蜈蚣藻、多管藻和三叉仙菜的孢子,假根羽藻的合子、酸藻的受精卵)萌发成的幼苗数量受附着基粗糙度影响显著;在一定范围内,两者呈正相关。而萌发自游动孢子的尾孢藻,附着基的粗糙度影响不显著。3种沉积物中,高温灭活的海泥更有利于尾孢藻和酸藻的附着。 相似文献
24.
Flume experiments and numerical simulation were conducted to characterize the hydrodynamics of a trapezoid artificial reef. Measurements in particle image velocimetry were conducted to observe the formation of upwelling and vortices; and forces for the reef model were measured by load cell. The results of flume experiments agree well with the numerical data. In addition, the flow structure around a reef combining trapezoidal and cubic blocks was simulated numerically under two deployment schemes, showing a more complicated flow structure than that of a stand-alone reef. Relationship between drag coefficient and Reynolds number suggest that the degree of turbulence can be assessed from the value of drag coefficient downstream from the reef. The role of the reef in water flow is to reduce flow velocity and generate turbulence. 相似文献
25.
The present study theoretically as well as experimentally investigates the interaction between waves and an array of porous circular cylinders with or without an inner porous plate based on the linear wave theory.To design more effective floating breakwaters,the transmission rate of waves propagating through the array is evaluated.Each cylinder in the array is partly made of porous materials.Specifically,it possesses a porous sidewall and an impermeable bottom.In addition,an inner porous plate is horizontally fixed inside the cylinders.It dissipates the wave more effectively and eliminates the sloshing phenomenon.The approach suggested by Kagemoto and Yue(1986) is adopted to solve the multiple-scatter problem,while a hierarchical interaction theory is adopted to deal with hydrodynamic interactions among a great number of bodies,which efficiently saves computation time.Meanwhile,a series of model tests with an array of porous cylinders is performed in a wave basin to validate the theoretical work and the calculated results.The draft of the cylinders,the location of the inner porous plate,and the spacing between adjacent cylinders are also adjusted to investigate their effects on wave dissipation. 相似文献
26.
Seasonal variation in community structure and body length of dominant copepods around artificial reefs in Xiaoshi Island, China 总被引:2,自引:0,他引:2
This study aims to investigate the seasonal variations in copepod community structure and prosome length of dominant species from March 2009 to January 2010 around artificial reefs in Xiaoshi Island,Yellow Sea,Weihai,China.Samples were collected using two types of plankton net(Model I and Model II) for different-sized copepods.The number of taxon was calculated from the data of both the net types,while the copepod abundance was done using the samples from Model II only.Sixteen species of planktonic copepods,including 5 dominant species,were recorded.Results reveal that Oithona similis was the first dominant species from March to June,and was replaced by Paracalanus parvus in September;both dominated the copepod community in January.Acartia hongi was the second dominant species from March to September.Centropages abdominalis was the third dominant species from March to June,and was replaced by O.similis in September and Corycaeus affinis in January.C.affinis was the fourth dominant species in September.Population density of the dominant copepods was compared with that of other similar regions.We found that the dominant species were mostly small copepods(<1 mm) except for adult Centrapages abdominalis.Seasonal variation in prosome length of O.similis,C.abdominalis,and C.affinis,and their copepodites were studied for the first time in China.For P.parvus and A.hongi,seasonal trends in prosome length variation were similar with those in Jiaozhou Bay,Yellow Sea,Qingdao,China,in a similar temperate domain.The results are helpful for future calculation of copepod biomass and production,and for investigation of the relationship between copepods and fish resources. 相似文献
27.
根据目前我国深海抗风浪网箱电力设备的配置情况 ,通过对 LA361 K51 S型太阳能电池性能的测试 ,确定了太阳电池的电流、电压、太阳强度及气温等随时间变化的规律以及天气变化情况对太阳电池的功率、转化效率的影响。在计算深海抗风浪网箱日用电量的基础上 ,对所需太阳电池的功率、蓄电池的容量进行了计算 ,并依此确定了深海抗风浪网箱配置太阳电池和蓄电池的规格及型号 相似文献
28.
印度洋金枪鱼渔业现状 总被引:6,自引:0,他引:6
报道了印度洋海域金枪鱼渔业近十年的生产概况,结果显示,印度洋金枪鱼渔业从业国家和地区已达40个,从业国家(地区)中以欧共体、印度尼西亚、印度、伊朗、斯里兰卡、中国台湾、马尔代夫等所占份额较高,以2000年计占当年印度洋金枪鱼渔业总产量的68.17%。产量140万吨,以金枪鱼类所占份额最高.主要金枪鱼渔获种类依次为鲣、黄鳍金枪鱼和大眼金枪鱼,主要渔业方式为金枪鱼围网、刺网及延绳钓。中国在印度洋海域金枪鱼渔业中年占份额较小,捕捞产量从1995年的444吨逐渐上升到2000年的6408吨。 相似文献
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