MacCormack算法在长输管道瞬变流动仿真中的应用

为了提高长输管道仿真精度和速率,基于MacCormack格式基本原理和流动方程建立了长输液体管道水力瞬变流动仿真模型。以某管道为例,分别采用该仿真算法和特征线法模拟了阀门关闭和流量增加引起的瞬变流动,并探讨了MacCormack格式中不同边界条件处理方法及Courant常数值对模拟结果的影响。结果表明:MacCormack格式可用于精确仿真长输管道瞬变流动过程,采用特征线法求解预估层边界参数后,其振荡幅度、收敛速度均优于特征线仿真方法;同时,采用特征线法处理MacCormack格式边界条件较线性外插法更易收敛。研究成果可为长输管道瞬变流动仿真提供参考。     

蕹菜芽苗菜对LED 光强和光质的生长响应

以阔叶空心菜为试材，研究蕹菜芽苗菜对LED 光强和光质的生长响应。结果表明：绿化阶段结束时处理L₇₀₀₀RBW4∶1∶1（光强7 000 lx，红光∶蓝光∶白光为4∶1∶1）的脱壳率显著高于其他处理；光强为7 000 lx 时，3 种光质处理的蕹菜芽苗菜可食部分干质量均显著高于白光对照；光照强度过高显著影响叶绿素的累积，高光强（L₁₁₀₀₀）下的叶绿素a、叶绿素b 含量及叶绿素总量随红光比例的增加而降低，同时子叶白化现象越发明显；不同光强条件下，3 种光质处理的抗坏 血酸含量均随着红光比例的增加而降低，而可溶性糖含量处理间差异不显著；主成分分析结果表明，L₇₀₀₀RBW4∶1∶1 在本试验条件下表现最佳，是较适宜蕹菜芽苗菜工厂化生产的LED 光源配方。     

Influences of sand cover on erosion processes of loess slopes based on rainfall simulation experiments

Aeolian-fluvial interplay erosion regions are subject to intense soil erosion and are of particular concern in loess areas of northwestern China.Understanding the composition,distribution,and transport processes of eroded sediments in these regions is of considerable scientific significance for controlling soil erosion.In this study,based on laboratory rainfall simulation experiments,we analyzed rainfall-induced erosion processes on sand-covered loess slopes(SS)with different sand cover patterns(including length and thickness)and uncovered loess slopes(LS)to investigate the influences of sand cover on erosion processes of loess slopes in case regions of aeolian-fluvial erosion.The grain-size curves of eroded sediments were fitted using the Weibull function.Compositions of eroded sediments under different sand cover patterns and rainfall intensities were analyzed to explore sediment transport modes of SS.The influences of sand cover amount and pattern on erosion processes of loess slopes were also discussed.The results show that sand cover on loess slopes influences the proportion of loess erosion and that the compositions of eroded sediments vary between SS and LS.Sand cover on loess slopes transforms silt erosion into sand erosion by reducing splash erosion and changing the rainfall-induced erosion processes.The percentage of eroded sand from SS in the early stage of runoff and sediment generation is always higher than that in the late stage.Sand cover on loess slopes aggravates loess erosion,not only by adding sand as additional eroded sediments but also by increasing the amount of eroded loess,compared with the loess slopes without sand cover.The influence of sand cover pattern on runoff yield and the amount of eroded sediments is larger than that of sand cover amount.Furthermore,given the same sand cover pattern,a thicker sand cover could increase sand erosion while a thinner sand cover could aggravate loess erosion.This difference explains the existence of intense erosion on slopes that are thinly covered with sand in regions where aeolian erosion and fluvial erosion interact.     

考虑水文变异的水库生态流量研究

为探讨水文变异对生态流量影响,确定最佳水库生态流量推求方法,针对尼尔基水库生态问题,采用Mann-kendall突变检测法、滑动T检验法和有序聚类法,结合序号总和理论和Spearman相关系数计算对水文时间序列作综合识别,确定水库发生水文变异年份为1963年和1999年。利用NGPRP法和逐月频率年内展布计算法分别计算天然状态、次天然状态、现状和不考虑水文变异条件下最小生态流量和适宜生态流量。参考Tennant法评价结果表明水库生态系统退化主要受人类扰动影响,观察次天然状态和不考虑变异状态下生态径流过程,最小生态流量占多年平均流量百分数相差9.21%和1.70%,适宜生态流量相差3.04%和1.47%。研究应更多考虑次天然生态径流过程,其最小生态流量仅可作为生态流量下限。     

麻山药种植田沙壤土流动性离散元模型颗粒放尺效应

为简化麻山药-沙壤土复合体离散元模型，提高离散单元法在农业领域中的计算效率，以沙壤土为研究对象，在EDEM离散元软件中构建非球形颗粒，进行双目标参数标定试验，采用放大颗粒粒径方法，利用转鼓、坍塌与FT4流变仿真试验，从颗粒群动态堆积角、流动质量、流动速率以及能量等方面探究了颗粒放尺效应对颗粒群物理特性的影响。试验结果表明：干燥处理后的2 mm粒径沙壤土基质静态堆积角和动态堆积角平均值分别为32.16°和35.02°；与独立标定试验相比，双目标标定试验获得的仿真参数更具准确性与唯一性；在动态堆积角试验中，真实沙壤土颗粒在转鼓中所形成的动态堆积角随粒径和旋转速度的增大而减小，而在仿真试验中，转鼓转速相同情况下，非球形颗粒群在增大粒径的情况下所产生的动态休止角差异较小；坍塌试验中，不同粒径颗粒群在流动过程中的流动质量与平均流速变化趋势基本一致，但误差随粒径增大而增大；颗粒质量相同时，将粒径分别放大2倍及4倍，颗粒数量同比减少87.24%、98.92%，仿真时间明显缩短，计算效率显著提高；FT4流变试验表明，当放尺因子S为2时，阻力FV及其力矩T随时间变化的拟合曲线值约为原尺时的2倍，而当放尺因子S为4时，与原尺相比，拟合曲线斜率差异显著，相关性明显降低。研究结果可为构建沙壤土离散元放尺模型提供理论依据，同时也可为农业工程离散元放尺仿真计算提供一定参考。     

中隔墩长度对斜式轴伸泵装置出水流道水力特性的影响

为研究大型低扬程泵站斜式出水流道水力特性,采用数值模拟方法对某斜20°轴伸泵装置三维湍流流场进行了数值计算,发现斜式出水流道内存在严重的偏流问题,基于4种计算方案的数值模拟结果分析了偏流的成因,在研究了中隔墩长度对斜式出水流道流态和水头损失影响的基础上提出了解决偏流的措施,并得到模型试验的验证。研究结果表明:顺水流方向看,中隔墩长度为14 m时的斜式出水流道内的主流明显偏于左侧,在流道右侧下部存在较大范围的旋涡区;导叶体出口具有较大周向速度分量的水流呈螺旋状进入"S"形弯曲的斜式出水流道,两者相互作用导致斜式出水流道产生偏流;随着中隔墩长度的增加,斜式出水流道左右孔的偏流系数逐渐减小、流道水头损失呈先减小再增大趋势,当中隔墩加长至23.35m时出水流道左右两侧的出流流量达到基本相等;采用长中隔墩斜式出水流道的泵装置模型试验最优工况点效率达到80.56%,泵装置模型试验结果与数值模拟结果一致,取得了预期的纠偏效果,得到有关工程设计院的认可,并应用于工程实际。     

基于广义回归神经网络的灌溉系统首部多用户配水快速PID控制

针对多用户配水状态下灌区流量、压力需求变化范围大,传统流量、压力控制响应速度慢等问题,建立适用于多用户灌区配水的灌溉系统首部控制技术。该研究通过分析供水系统流量、压力调节方式,提出了流量、压力PID(Proportion Integration Differentiation)耦合调节方法,建立以电动阀开度为流量控制量、变频器频率为压力控制量对流量和压力进行调控的灌溉首部控制系统。为了减少系统的调节时间,提高系统的运行效率,采用广义回归神经网络(Generalized Regression Neural Network,GRNN)建立流量、压力和电动阀控制模拟量、变频器控制模拟量间的预测模型,形成神经网络PID控制模型(GRNN_PID),并进行模型精度和控制精度验证。GRNN训练结果显示,变频器控制模拟量的相对误差为0.11%～3.86%,电动阀控制模拟量相对误差为0.09%～5.74%,模型精度较高。使用3个调节过程模拟3个用户的需水行为对模型进行验证,结果表明,GRNN_PID模型3个过程的调节时间分别为11.6、10.7和7.2 s,PID模型3个过程的调节时间分别为31.7、29.6和16.9 s,GRNN_PID模型大幅减少了系统的调节时间,提高了系统的运行效率;分别计算了2种模型的控制精度,GRNN_PID调节方法和传统PID调节方法的稳态流量和压力误差都在1%以内,最大超调量为8%,控制精度较高但相差不大,表明GRNN是从策略上加速系统调节速度,其本身并没有对PID的参数进行调整,因此对系统的控制精度影响不大。研究可为灌溉系统流量压力快速控制提供参考。     

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.     

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。     

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。