油麦兼用型气送式集排器匀种涡轮设计与试验   总被引：1，自引：0，他引：1  

王磊  席日晶  廖宜涛  张青松  林翩  廖庆喜 《农业机械学报》2021,52(8):62-72，97

针对油麦兼用型气送式免耕播种机宽幅播种时各行排量一致性受地表坡度变化影响的问题,设计了一种利用输送气流驱动转动、安装于分配装置的匀种涡轮,分析了匀种涡轮进口工作角和出口工作角对输送气流速度的影响,确定了影响3种匀种涡轮工作特性的关键参数。应用CFD仿真中的6自由度动网格模型及台架试验,对比分析3种匀种涡轮对输送气流分布及匀种涡轮转速的影响,结果表明：进口工作角和出口工作角均为锐角的匀种涡轮可提高种子的输送及搅拌性能。选择叶片数量为4、6、8、10的匀种涡轮进行了分配装置内流场分布仿真试验,结果表明,增加匀种涡轮叶片数量可提高匀种涡轮出口处输送气流分布的稳定及均匀性。利用智能种植机械测试平台模拟田间作业不同地表坡度时,安装不同数量叶片的匀种涡轮对各行排量一致性的影响,结果表明：转速为20～50 r/min,沿播种机作业方向的前后与侧向单向组合摆动、前后与侧向往复组合摆动角相对平整地表在-5°～5°变化,叶片数量为8时,油菜及小麦各行排量一致性变异系数最小,分别为4.99%～5.82%和3.85%～4.92%;前后与侧向单向组合摆动角绝对值为5°时,叶片数量为8的匀种涡轮比无匀种涡轮排种油菜和小麦时各行排量一致性变异系数分别降低7.53、11.98个百分点,满足地表坡度变化时油菜及小麦的排种要求。  相似文献   

施加生物炭对黑土区坡耕地改土培肥效应的持续影响   总被引：8，自引：0，他引：8  

魏永霞  肖敬萍  王鹤  石蕴  刘慧 《农业机械学报》2021,52(3):305-314

为探明施加生物炭对黑土坡耕地的持续影响,以东北黑土区1.5°、3°、5°的坡耕地田间径流小区为研究对象,对土壤结构及其养分进行为期4年的观测。于2016年试验开始前,按75 t/hm2一次性施加玉米秸秆生物炭,各坡度均设置不施加生物炭的对照组,共计6个小区,后续年份不再施加生物炭。结果表明,单次施加生物炭能够提高土壤气相、液相比例,提高通气性和持水能力,改善土壤三相比例,较对照组土壤孔隙度提高2.83%～5.56%,土壤容重降低1.89%～3.62%。施炭后土壤中有机质、铵态氮、速效钾含量显著提高,分别提高9.54%～18.21%、21.35%～28.02%、11.99%～22.71%。各项指标均随着时间的推移有所降低。采用随机森林回归模型评估得出综合肥力等级指数,并拟合回归方程预测2020—2022年等级指数,比较肥力变化情况得出单次施用生物炭对培肥土壤作用的有效年限为6～7年。  相似文献   

基于V3V的泵站进水池内附底涡动力特性研究     

宋希杰  刘超 《农业机械学报》2021,52(6):177-185

采用体三维速度场测试系统V3V测量漩涡工况下立式轴流泵喇叭管下方的流场,分析了附底涡演变过程中漩涡区速度梯度分布、漩涡强度及漩涡涡动能的变化。结果表明：附底涡的发生过程是一个伴随着附底涡区速度梯度、漩涡强度及漩涡涡动能不断变化的过程。随着时间的推移,附底涡区速度梯度、漩涡强度及漩涡涡动能先增大,达到最大后保持0.4s, 然后迅速减小,附底涡形成发展的时间大于漩涡溃退消失的时间。在漩涡发展初期,随着距离进水池底部高度的增大,漩涡强度逐渐减小;在漩涡进入保持阶段后,附底涡满足漩涡强度守恒定理;受喇叭管内复杂环境的影响,附底涡强度从喇叭管内最先溃退消失,从上向下逐渐减小。本研究可为进水池优化设计提供理论指导。  相似文献   

库区红层泥岩水化特性及干湿循环作用下的渐进损伤研究     

陈纪昌 《中国农村水利水电》2021,(3)

库岸边坡长期受到大气循环、水位调节等水流往复运动而带来的渗透侵蚀影响。特别是在我国西南红层区的水利工程中,水的长期浸入和干湿循环作用导致红层泥岩特性出现严重的劣化。以川西南红层区某水库为工程依托,通过室内试验和理论分析深入研究了红层区泥岩的水化特性及干湿循环作用下的渐进损伤破坏。结果表明:红层泥岩发生水岩作用后微观结构更加疏松,颗粒间黏结变弱。浸水初期变形显著,并且干湿循环进一步加剧了岩体膨胀变形。红层泥岩抗压强度和黏聚力分别同干湿循环次数呈线性降低和凹二次函数下降关系,内摩擦角在多次循环后有小幅上升。围压和干湿循环耦合效应对红层泥岩的渐进损伤积累产生严重不利影响,当循环超过3次时,多数工况下试样损伤变量值已超过60%,岩体强度大幅衰减。  相似文献   

GPR、XGBoost和CatBoost模拟江西地区参考作物蒸散量的适应性研究     

《灌溉排水学报》2021,(1)

【目的】提高机器学习模型模拟参考作物蒸散量在江西省适应性和精度。【方法】基于江西南昌等15个气象站2001—2015年日值气象数据(最高气温、最低气温、地表辐射、大气顶层辐射、相对湿度和2 m高风速),以FAO-56Penman-Monteith(P-M)公式的计算结果作为对照,建立了计算ET0的高斯过程回归(GPR)、极限梯度提升(XGBoost)和梯度提升决策树(CatBoost)模型,并分别与经验模型进行比较。【结果】各气象参数对机器学习模型模拟ET0的精度影响由大到小依次为:Rs、Tmax和Tmin、RH、U2,且采用Tmax、Tmin、Rs和RH气象参数组合的机器学习模型(RMSE0.2mm/d)模拟ET0精度高。此外,3种机器学习模型在有限的气象数据时具有较好的适用性,且优于传统经验模型,其中GPR和CatBoost模型的预测精度高,但GPR模型稳定性最好。【结论】考虑到所研究模型调参的复杂性、预测精度和稳定性,GPR模型可作为江西地区参考作物蒸散量模拟的推荐方法。  相似文献   

底坡对U形渠道量水平板测流影响分析     

《灌溉排水学报》2021,(1)

【目的】量水平板具有构造简单、不易淤积等优点,虽已建立流量与平板偏转角、上下游水深及板型等因素的关系式,但底坡对量水平板水力特性的影响还缺乏系统研究,有必要深入分析,以提高量水平板测流公式的适用范围。【方法】以北方灌区常见U形渠道为试验水槽,选择断面最佳收缩比0.439的U形渠道量水平板为试验对象。通过设置3种水槽底坡(0.000 2～0.001)和4～7种流量(10～44 L/s)共18种试验工况,分析了各工况下水面线和平板偏转角的变化规律,研究了底坡对水面线、相对水头损失、能量转化系数、平板偏转角度和综合流量系数的影响。基于闸孔淹没出流公式,拟合出含底坡变量i的半经验流量公式。【结果】在相同流量情况下,板后水跃长度、能量转化系数以及综合流量系数随底坡增大而增大;水面线、相对水头损失和平板偏转角度均随底坡增大而减小;在试验流量范围内,拟合流量公式的平均相对误差为2.6%,最大相对误差为6.5%,满足灌区量水要求。【结论】底坡对U形渠道量水平板测流影响显著,建立了包含渠道底坡的U形量水平板测流公式,提高了其适用性。  相似文献   

Variability in timing and magnitude of spring bloom in the Oyashio region, the western subarctic Pacific off Hokkaido, Japan   总被引：6，自引：0，他引：6  

HIROMI KASAI  HIROAKI SAITO  AKIRA YOSHIMORI  & SATORU TAGUCHI 《Fisheries Oceanography》1997,6(2):118-129

The spring bloom of phytoplankton is a well-established, regular, seasonal event in the western subarctic Pacific and is considered one of the most important conditions of massive production of pelagic fishes. A series of 12 cruises was conducted from 1990 to 1992 to examine the timing and magnitude of the spring phytoplankton bloom in the Oyashio region, the western subarctic Pacific off Hokkaido, Japan. An interannual variability in the bloom events was also analysed. On the basis of hydrographical characteristics, the study area was divided into three water masses: the Oyashio Water Mass, the Mixed Water Mass, and the Coastal Water Mass. Spring blooms were observed first in April in the Oyashio and the Coastal Water Masses, and continued to May in 1991 and 1992. However, no bloom was recorded in the Mixed Water Mass. High nutrient supply into the surface mixed layer during winter is likely to be one of the factors supporting an intense spring bloom in the Oyashio Water Mass. A significant positive relationship between log-transformed surface chlorophyll a concentration and maximum density gradient (MDG) within the euphotic layer was obtained in April, indicating the importance of vertical stability of the water column in the initiation of spring blooms in the Oyashio and the Coastal Water Masses. The spring blooms in 1991 were much more extensive and lasted longer than in 1990. It is suggested that meteorological conditions and abundance of grazers were responsible for this interannual difference.  相似文献   

Springtime ichthyoplankton of the slope region off the north-eastern United States of America: larval assemblages, relation to hydrography and implications for larval transport   总被引：2，自引：1，他引：2  

Jonathan A. Hare  Michael P. Fahay  & Robert K. Cowen † 《Fisheries Oceanography》2001,10(2):164-192

Larval transport in the slope region off north‐eastern North America influences recruitment to juvenile habitats for a variety of fishes that inhabit the continental shelf. In this study, collections of larval fishes were made during springtime over the continental slope to provide insights into larval distributions and transport. Ichthyoplankton composition and distribution mirrored the physical complexity of the region. Three larval fish assemblages were defined, each with different water mass distributions. A Gulf Stream assemblage was found predominantly in the Gulf Stream and associated with filaments of discharged Gulf Stream water in the Slope Sea. Larvae of this assemblage originated from oceanic and shelf regions south of Cape Hatteras. Several members of this assemblage utilize habitats in the Middle Atlantic Bight (MAB) as juveniles (Pomatomus saltatrix, Peprilus triacanthus) and other members of the assemblage may share this life cycle (Mugil curema, Sphyraena borealis, Urophycis regia). A Slope Sea assemblage was found in all water masses, and was composed of epi‐ and mesopelagic fish larvae, as well as larvae of benthic shelf/slope residents. Larvae of one member of this assemblage (U. tenuis) are spawned in the Slope Sea but cross the shelf‐slope front and use nearshore habitats for juvenile nurseries. A MAB shelf assemblage was found in MAB shelf water and was composed of larvae that were spawned on the shelf. Some of these species may cross into the Slope Sea before returning to MAB shelf habitats (e.g. Enchelyopus cimbrius, Glyptocephalus cynoglossus). Previous studies have examined the effect of warm‐core rings on larval distributions, but this study identifies the importance of smaller‐scale features of the MAB shelf/slope front and of filaments associated with Gulf Stream meanders. In combination with these advective processes, the dynamic nature of larval distributions in the Slope Sea appears to be influenced, to varying degrees, by both vertical and horizontal behaviour of larvae and pelagic juveniles themselves.  相似文献   

Quantifying spatio-temporal dispersion of bark beetle infestations in epidemic and non-epidemic conditions     

Markus Kautz  Kai DworschakAxel Gruppe  Reinhard Schopf 《Forest Ecology and Management》2011,262(4):598-608

Spatio-temporal dispersal of pest species such as bark beetles plays a key role in their population ecology and outbreak dynamics. Understanding the underlying patterns is crucial for applying appropriate management strategies.In contrast to most existing studies which focus on dispersing beetles, we analysed patches of killed trees resulting from bark beetle infestation. The study was based on a 22-year time series of annually captured colour-infrared (CIR) images of the Bavarian Forest National Park (Germany), where Ips typographus L. (Coleoptera, Curculionidae, Scolytinae) propagates undisturbed by human activity. Newly infested patches comprising at least 5 spruce trees were identified in every time step. This investigation of spatio-temporal spread of infestations primarily focused on (i) parameterizing the size and shape of infestation patches, (ii) modelling an infestation gradient and (iii) evaluating the risk of subsequent infestations on landscape scale. We developed a GIS-based distance ring approach to quantify the distance relation of subsequent infestations, including the distribution of potential hosts.Infestation spread was revealed to be strongly distance dependent, following an inverse power law function: on average 65% of new infestations occurred within a 100 m radius of the previous year’s infestations, and 95% within 500 m. ‘Distance’ proved to be a major determinant of I. typographus dispersal on the landscape scale in each time step of the 22-year series we investigated. Infestation distance thus describes the outcome of beetle dispersal very accurately. The time series showed two alternating periods of epidemic and non-epidemic infestation. These gradation stages did not affect the size and shape of infested patches, but epidemics correlated significantly with a higher percentage of infestations within short distances. Additionally, the resulting infestation risk is highly sensitive to the gradation stage, particularly within the first 100 m around source spots where it increases up to 30%.Our study therefore contributes to a better understanding of the outbreak dynamics of I. typographus and suggests concentrating efficient bark beetle management on areas in the close vicinity of previous years’ infestations.  相似文献   

丘陵地桉树无性系人工林生长调查     

陈健波  刘建 《林业科技开发》2011,25(4):67-70

采用标准地法,对广西南宁市南部丘陵地2.25～2.67年生的桉树无性系人工林进行了调查研究。结果表明:林木平均保存率为89.3%,平均年蓄积生长量达30.0 m3/(hm2.a),林木径阶以10 cm居多,其次是12 cm径阶,二者合计占80%。林分生长量与无性系种类、林地坡位有一定关系,无性系的生长排序为DH33-29>DH33-26>DH33-28,坡位排序为下坡位>中坡位>上坡位,但差异均较小。林地土壤有效N含量对桉树生长影响显著,含量少的林地桉树生长量显著低于含量多的林地。林地土壤有效N、P、K含量普遍不足,林地施肥应充分考虑N、P、K养分,以满足桉树生长对各种元素养分的需要。  相似文献