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381.
382.
Effects of drag coefficient of netting for dynamic similarity on model testing of trawl nets 总被引:1,自引:0,他引:1
SUMMARY: For design or improvement of fishing nets, a model test based on Tauti's law or Froude's law is well executed. However, because these modeling rules are based on the proportion of the drag of the net to the square of water velocity, the converted drag of the net from the result of model testing is considerably large compared with the observed value. In this study, Tauti's law and Froude's law were corrected considering the drag coefficient of the net to the Reynolds number based on the twine diameter used experimentally. Three different scale models: 1/12, 1/20 and 1/50 of a midwater trawl net of 61 m in total length were made according to the modified Tauti's law and Froude's law, and the full-scale and model experiment were carried out. Consequently, the difference between the converted drags of full-scale by three scale models and measured values was within 10%. Each of these modified modeling rules is effective for the model test of trawl nets. 相似文献
383.
养虾池底播魁蚶技术研究 总被引:3,自引:0,他引:3
对养虾池混养魁蚶的底质选择、播苗密度、苗种规格、池水调近和魁蚶在虾池中越冬等进行了试验研究,270亩混养试验池,平均亩产对虾106.3kg,魁蚶124.1kg,混养比单养平均亩增效益1438.4元,总增效益38.84万元。技术鉴定认为:本研究成果属国内领先水平。 相似文献
384.
底拖网资源调查的昼夜误差分析 总被引:3,自引:0,他引:3
利用1985和1986年秋季底拖网资源调查数据,分析了昼夜平均渔获量的差异,采用Bray-Curtis系数测量其不相似性。结果表明,除底层鱼类外,总平均和中上层鱼类平均渔获得昼液差显著,白天平均渔获量远高于晚上,特别是中上层鱼类相差10余倍,主要种类的差异亦较大。 相似文献
385.
The relationship between fishing line height (FLH), shrimp catch and bycatch in a semi-pelagic ocean shrimp (Pandalus jordani) trawl was investigated using a newly developed recording inclinometer. The inclinometer was effective at measuring FLH and indicating trawl performance deficits. FLH was determined to be stable during a haul and also between hauls within a given footrope and groundline configuration. FLH was readily adjusted with simple modifications to the footrope “dropper” chains. Inclinometer data showed that FLH can be unequal between double-rigged nets of identical configuration. Shrimp catch and the bycatch of flatfish and juvenile rockfish varied inversely with FLH, suggesting FLH can be adjusted to equalize the catch of shrimp, flatfish and juvenile rockfish between two double-rigged shrimp nets. 相似文献
386.
387.
Sensitivity of forest-floor mosses in boreal forests to nitrogen and sulphur deposition 总被引:1,自引:0,他引:1
R. Mäkipää 《Water, air, and soil pollution》1995,85(3):1239-1244
The response of forest-floor mosses to deposition of nitrogen (N) and sulphur (S) was examined in field conditions in a 60-year-old Norway spruce (Picea abies Karst.) stand in southern Finland. The experimental plots received nitrogen (25 kg N ha–1) and sulphur (30 kg S ha–1) as ammonium sulphate once a year for 4 years.The dominant moss species on the site were Pleurozium schreberi (Mitt.) and Dicranum polysetum (Sw.). The biomass of the dominant moss species was decreased significantly by N and S deposition during the study period. Due to the addition of N and S, the biomass of Pleurozium schreberi was decreased by 60% and the biomass of Dicranum polysetum by 78%. 相似文献
388.
针对现有底挑消能共轭水深计算公式未考虑坎底离心力影响,根据水力学理论推导了考虑离心力影响的坎底收缩水深非线性方程,该方程形式复杂,通常采用试算法或牛顿迭代法求解;通过无量纲原理及高精度数值拟合,巧妙地将复杂非线性方程转换为可公式求解的一元三次方程,进而给出收缩水深解析计算式,并认为考虑离心力影响后坎底收缩水深比规范一般算法成果稍大;并通过工程实例计算比较,该解析计算式方便简捷、精度可靠。 相似文献
389.
采用大田试验研究基肥不同施肥方式和基追肥比例对烤烟产质量及减氮效应的影响。结果表明,在多雨条件下,采用挖大穴、施用穴肥(60%基肥条施+40%基肥穴施)的方式能够促进烟株前期吸收更多养分,促进烟株早生快发,提高中部叶质量。当施氮量为127.5 kg·hm~(-2),追肥比例由50%提高到65%时,烤烟上部叶开片度、叶面积、单叶重均有所提高,上部烟叶营养得到改善。在总施氮量比CK(150 kg·hm~(-2))减少15%条件下,通过调整基肥施肥方式和基追肥比例,烟叶产值和烟叶质量均得到提升,既节约了成本,又提高了烟农效益。 相似文献
390.
Asad Sarwar W.G.M. Bastiaanssen Th.M. Boers J.C. van Dam 《Irrigation and Drainage Systems》2000,14(4):257-280
A transient drainage simulation model,SWAP, was used to evaluate the performanceof drainage systems in (semi-) arid zones.Before application, the model wascalibrated by using 14-months datacollected from two sample fields of theFourth Drainage Project (FDP), Punjab,Pakistan. During the calibration process,emphasis was given to the accuratedetermination of soil hydraulic parameters,reference evapotranspiration, drainage fromsample fields and bottom boundarycondition. Laboratory determined soilhydraulic parameters were foundnon-representative of the field conditions.Difference between laboratory and fielddetermined soil water retention curves werefound significant. The pressure heads andsoil water contents measured in depthincrements of 15 cm were in good agreementwith the simulated values after applying afield measured retention curve. A closeproximity was also found between measuredand simulated average root zone salinity at0–1.0 m depth. The referenceevapotranspiration calculated by thePriestly-Taylor (PT-ET
o) methodwas found physically more realistic thanthe Penman-Monteith (PM-ET
o)method due to ignorance of the feed backmechanism of vapor pressure deficit onstomatal closure. The simulated cumulativedrainage from two sample fields wascomparable with the calculated values. Theanalysis of piezometer data shows thatthere is a negligible water exchangebetween the deep aquifer and theunsaturated zone. Therefore for scenarioanalysis, no flow conditions at the bottomof the soil profile can be applied as abottom boundary. 相似文献