基于粒子图像测速的坡面流水动力学特性

粒子图像测速(Particle Image Velocimetry, PIV)技术具有多点同时测量、对水流无干扰的优点,该研究利用高分辨率PIV(分辨率为64 pixels/mm),测量了7组坡面流(水深范围为0.5～1.1 cm,雷诺数范围为1 000～3 000),并测量1组深水明渠紊流作为对照,研究了流速轮廓线和修正系数、紊动强度和雷诺应力、偏态系数和峰度系数的变化规律。结果表明:1)PIV能够有效观测坡面流床面至水面的流速分布。当坡面流流态为过渡流时,流速修正系数随着雷诺数的增加呈对数增加,均值为0.77;2)对比深水明渠紊流的紊动强度,坡面流的流向紊动强度较大,而垂向紊动强度较小,且随着水深及雷诺数的增加,坡面流紊动强度逐渐与深水明渠紊流的特征吻合。深水明渠紊流中受雷诺应力影响的流体占比约80%,而坡面流中受雷诺应力影响的流体占比小于80%,随着雷诺数的增加坡面流中受雷诺应力影响的流体占比变大;3)对比深水明渠紊流的峰度系数,坡面流的峰度系数大部分大于3,表明坡面流较深水明渠紊流出现极端流速事件的概率小。PIV技术有利于实验室研究坡面水力侵蚀的力学机理机制问题。     

泥炭块制作机应用前景展望

介绍了泥炭块育苗技术的优点，分析了泥炭块制作机制作泥炭块的工艺流程及其关键技术，展望了泥炭块制作机的应用前景。     

How to characterize ‘good’ and ‘greening’ in the EU Common Agricultural Policy (CAP): the case of clay soils in the Netherlands

The change in the Common Agricultural Policy (CAP) of the European Union from product to producer support, including requirements for ‘good agricultural and environmental conditions’ and ‘greening’, is excellent. However, these requirements are now defined in rather general terms. Questions can be raised about suitable indicators, and there is a recognized need for effective management recommendations to support farmers in achieving the required ‘good’ conditions. These recommendations are bound to be quite different for different soils in different countries. A study of Dutch clay soils was based on a storyline describing current problems and management options for improvement, which were quantified using a soil–water–crop simulation model. Indicators were defined for agricultural conditions and suggestions made for the use of the model in a predictive mode to help farmers improve their soil management. Environmental conditions were judged by current environmental guidelines for water and air. When modelling, implicit assumptions that soils are homogeneous were shown to be unrealistic for these clay soils, requiring development of innovative methods and procedures, presenting a challenge for soil research.     

坎儿井衰减与地下水补排系统响应关系

为了探究坎儿井衰减与地下水补排系统响应关系,利用地下水位观测资料和坎儿井流量监测资料,结合鄯善县历次地下水资源调查评价资料和坎儿井统计数据,分析了地下水补给量、排泄量对坎儿井衰减的影响,并建立了最小二乘回归模型,在执行最严格水资源管理制度下对2020年、2030年坎儿井出水量进行了预测。结果表明,坎儿井流量动态与地下水位动态基本同步;北盆地的坎儿井出水量主要受地下水补给量的影响,南盆地主要受地下水开采量的影响。地下水开采量是影响鄯善县坎儿井衰减的关键因素,在最严格水资源管理制度下鄯善县坎儿井出水量将会在2020年恢复至0.83亿m~3,2030年恢复至0.87亿m~3。     

两种血清抗性检测方法的比较分析

采用流式细胞术法对大肠杆菌的血清抗性进行检测,并与传统涂板法相比较,探讨流式细胞术在血清抗性检测方法中的应用。结果表明,两者呈正相关关系(P=0.0340.05),流式细胞术法可以代替涂板法对大肠杆菌的血清抗性进行检测。该方法可以减少由于涂板不均匀、人工计数等造成的误差,且易操作、计算少、耗时少,数据更准确。     

Assessing appetite of the swimming fish based on spontaneous collective behaviors in a recirculating aquaculture system

In order to realize the real-time appetite-based feeding in aquaculture, a novel and practical method, based on the quantification of the spontaneous collective behaviors, was proposed in this study to assess the real-time appetite of the swimming fish in a recirculating aquaculture system. First, foreground feature points of fish school were extracted using an improved complex network. Then, covariance, a modified social force model and a kinetic energy model were used to analyze the collective behaviors of the school from perspectives of dispersion degree, interaction force and the changing magnitude of the water flow field, respectively. Finally, the quantified behavioral characteristics were integrated and used to assess the appetite of fish school. The presented method shows its good performance in the expression of the collective behaviors representing five typical appetites (0.01, 0.52, 1.28, 2.26 and 2.92), and the assessing accuracy of the appetite of the school is also maintained at a low non-match rate ((2.19 ± 0.81)% best) in the context of ten different sampling durations.     

某高铁隧道小口径井抽水试验探讨

指出了在某高铁隧道勘察中采用小口径抽水试验方法,具有操作简单便捷,成本低的优势。通过小口径井抽水试验查明场地的水文地质条件,得出了水文地质原始数据资料,根据单孔稳定流承压水非完整井的水文地质实际情况,选取合适的公式分别计算出了隧道岩层渗透系数及影响半径,为高铁隧道的勘察设计及顺利施工提供参考。     

Unravelling the relationship between a seasonal environment and the dynamics of forage growth in grazed swards

It is well reported in the scientific literature that pastures can have similar net forage accumulation when managed with contrasting structures. However, we hypothesized that the dynamics of forage accumulation in grazed swards is linked to seasonal-environmental conditions. Marandu palisadegrass (Brachiaria brizantha [Hochst. ex A. Rich.] was used as the forage species model. The experimental treatments were four grazing heights (10, 20, 30 and 40 cm) allocated to experimental units according to a randomized complete block design with four replicates and evaluated throughout four contrasting environmental seasons (summer, autumn, winter–early spring and late spring). Under rainy and warm periods, greater net forage accumulation was observed in pastures maintained taller; on the contrary, during the mild and dry periods, net forage accumulation rate reduced as grazing height increased. Such patterns of responses were related to compensations between tiller population density and tissues flows during summer and late spring and the reduced capacity of taller canopies to compensate lower population with greater growth rates during autumn and winter–early spring. Grazed swards changed their patterns of forage growth as they transitioned from favourable to more abiotic stressful conditions, suggesting that seasonal adjustments in grazing intensities are necessary in order to maximize forage production.     

立式双曲面网板水动力性能及流场可视化研究

网板是拖网作业系统中重要的属具之一,其水动力性能的优劣直接关系到拖网网口的扩张,并影响其生产效果和经济效益。采用单因素试验法,利用水槽模型试验和数值模拟(computational fluid dynamics, CFD)研究立式双曲面模型网板在不同展弦比λ(2.5、3.0、3.5、4.0)、弯曲度f/C(10%、15%、20%)、后退角Λ(0°、10°、15°)下的水动力性能,分析不同结构参数的网板水动力性能,对比两种方法的结果,并实现网板周围流场可视化。结果显示:①2号网板(λ=3.0、f/C=15%、Λ=10°)升力系数最大,冲角25°时,模型试验值为1.70,数值模拟值为1.88,阻力系数随冲角增大一直增大,且后部流速的模拟值和测定值平均偏差为4.40%,两种方法获得的结果吻合度高。②2号网板在流场分布中边界层分离点随冲角增大逐渐向翼端前沿移动,中心面后部涡旋随冲角增大一直增大,左翼板侧低压区随冲角增大呈先增大后减小趋势,网板尾部随冲角增大形成明显的翼端涡,产生涡升力对网板提供附加升力,使得立式双曲面网板比其他类型网板有较高升力。     

不同生育期成龄灰枣树茎流速率与气象因子的关系

【目的】在微喷灌的灌溉方式下,研究不同天气和不同气象因子条件下成龄灰枣树的茎流速率,精准测定出成龄枣树的耗水量,为优化枣树的土壤水分管理提供生产指导。【方法】采用针式茎流计,连续监测灰枣树茎流速率,分析枣树的茎流速率受不同天气和气象因子的影响程度。【结果】晴天和阴天茎流速率的波动变化过程呈倒“U”型的单峰曲线,而多云天气下呈“M”型的双峰曲线。1 d中枣树的茎流累积趋势呈“S”变化,各生育期耗水量大小排序为果实膨大期>成熟期>花期>萌芽展叶期。只有成熟期枣树的茎流速率与空气温度相关程度最高,其余都是太阳辐射。各生育期太阳辐射与枣树茎流速率的相关系数R_D1=0.964^**、R_D2=0.969^**、R_D3=0.957^**和R_D4=0.886^**。利用多元线性回归在枣树的各生育期内对茎流速率和气象因子进行输入回归,建立不同天气条件下,各生育期枣树茎流速率和气象因子的多元线性回归模型,经过回归系数和相关系数检验,各生育期的多元线性回归方程均达到了显著水平。【结论】各生育期内,典型天气的茎流速率排序为晴天>多云>阴天,整个生育期中的需水关键期是果实膨大期,对枣树的茎流速率产生最大影响的气象因子是太阳辐射和空气温度。