用CFD方法模拟日光温室温度环境初探

日光温室温度环境为一动态变化过程，该文建立了求解晴天室内温度环境的计算模型。将室外的水平面太阳辐照度、天空辐射温度、室外空气相对湿度、空气温度、风速及室内1.0m深土壤温度作为边界条件，采用计算流体动力学技术（CFD）中的非稳态方法求解控制方程，模拟了晴天室内温度随外界气候条件的变化，结果显示模拟得到的室内空气温度及土壤温度变化规律与实测值变化规律相同，盖帘后室内空气温度及土壤0.2 m深土层的温度模拟值与实测值相差约在1℃以内；探讨了边界条件中冷风渗透、土壤表面太阳能转换显热份额及1.0 m深土壤温度的取值变化对室内温度的影响。日光温室内温度动态变化模拟模型的建立对优化温室设计参数和预测不同天气情况下室内的温度环境变化具有参考意义。     

迷宫滴头水力特性的计算流体动力学模拟

建立了迷宫滴头的CFD(Computational Fluid Dynamics)数值模型,并对滴头的压力流量关系、流道内部的压力和流速分布进行了数值模拟计算。利用原型滴头和滴头放大模型实测值对模型和模拟计算结果进行了实验验证。结果表明,滴头流量压力关系模拟计算值与实测值之间的平均偏差小于5%;滴头放大模型内部压力分布的模拟值与实验值间的平均偏差小于3%。结果还表明,迷宫式滴头流道内压力沿流道长度呈线性变化,在滴头齿尖附近的主流区流速达1.6～2.8 m/s,而滴头齿根附近的旋流区的流速为0.1～0.4 m/s,在其它尺寸保持不变时,滴头齿距对滴头流态指数的影响不大。CFD数值模拟可以为滴头水力性能的进一步研究提供有效的研究手段。     

墙体材料对日光温室温度环境影响的CFD模拟

日光温室墙体材料影响温室的蓄热保温性能。该研究以室外气象因子为模拟输入条件,分别对复合墙、全砖墙及全苯板墙的12 m跨度日光温室的温度环境进行了模拟,复合墙、全砖墙内的温度分布变化与以往的测试结果一致。以2004年2月18日实测的气候条件为输入条件,模拟得到复合墙温室温度超过全砖墙温室温度最大值为0.8℃,复合墙温室夜间室温超过全苯板墙温室温度最大值为1℃。早晨揭帘前,复合墙中隔热层以内的砖墙及部分隔热层成为放热体,砖墙中靠近室内近1/3的墙体温度高于室内空气温度,而全苯板墙只有内表面附近略高于室内空气温度。白天复合墙、全砖墙及全苯板墙温度均低于室内空气温度,均为吸热体。采用日光温室温度环境动态模拟模型,可以预测不同温室墙体可能形成的室内温度状况,并且根据不同墙体内温度分布,可优选温室墙体结构。     

离心泵叶轮内的网格生成与计算流体力学分析

根据离心泵叶轮通道的几何和流场特点，探讨了离心泵叶轮通道结构化多块网格划分中的一些处理方法。同时应用标准k-ε紊流模型加壁面函数法对离心水泵叶轮内部的三维紊流流动进行了雷诺平均N-S方程的数值计算与分析。分析了离心泵叶轮叶型对流速分布、压力分布和泵性能的影响，研究了离心泵叶轮通道内流动规律，并以计算流体力学(CFD)分析结果为依据，对离心泵叶轮进行了叶型优化设计。结果表明进行离心泵叶轮内三维紊流数值计算可为离心泵叶轮叶型优化提供详细的数据，应用CFD分析技术可提高离心泵叶轮的设计水平。     

基于CFD的养殖污水净化内循环流化床反应器结构优化

针对水产养殖污水净化对内循环流化床反应器的相关要求及流化状态下反应器结构、操作参数与相流体力学行为的密切关系,该文利用构建的描述不同结构、操作参数反应器气液两相流动的计算流体力学数学模型,分析了不同结构、操作参数下反应器液体流场、液体循环流量、气含率的变化规律,得到了对于内径200 mm、底部采用均孔布气盘的反应器,在表观气速为0.5~2.5 cm/s时,导流筒与反应器的内径比0.5,导流筒高度与反应器内径比6,导流筒下端到反应器底部距离50 mm,导流筒上端到液面距离100 mm为最优值;针对液体循环流量,使用相关数学模型求解理论值并与试验值进行比对,通过偏差分析探究了数学模型应用的局限性;使用MATLAB最小二乘法拟合了反应器在最优结构参数下表观气速与液体循环流量、气含率的关系,验证了拟合公式的精确性。该研究为内循环流化床反应器在水产养殖污水处理中的设计应用提供理论和技术参考。     

基于D-H法的果园作业平台工作空间分析与试验

针对蒙特卡洛方法分析果园作业平台工作空间存在边界不清、点浪费等问题,该研究采用D-H法建立了作业平台运动学模型,利用U形反正弦分布函数改进了蒙特卡洛方法,得到其工作空间点云图。考虑农机农艺融合和工作人员舒适度,分析了平台理想工作空间;采用网格化算法对改进前后生成的工作空间进行分析,改进后最底层与最顶层边界层面积分别增大180.70 %和102.69 %,表明边界清晰度明显提高;改进后在X、Y、Z三个方向的空间差异系数较改进前分别降低了6.92 %、8.99 %、2.64 %。利用高速摄像机对平台参考点跟踪测试,平台参考点的实测值与计算值最大差值仅为6.2 mm;实际果园试验结果表明,平台参考点实际工作空间与可达工作空间在X、Y、Z方向最大值、最小值均值的差异系数分别为0.27 %、0.76 %和0.01 %,改进方法有效。该研究为果园作业平台结构参数优化、智能控制和同类农业机械工作空间分析提供理论参考。     

棚架果园自主导航机器人快速上线方法与试验

棚架果园是一种适用于葡萄、梨和猕猴桃等水果的枝蔓布于架上的果树种植方式,棚架果园环境对卫星信号遮挡严重,现有研究多通过分析果园局部环境特征实现农机的自主导航作业.自主导航的行头上线性能影响生产作业的质量和效率.为了实现棚架果园环境下基于相对定位导航方式机器人的快速上线,该研究提出了一种基于电子罗盘与激光雷达航向信息融合...     

基于CFD的循环生物絮团系统养殖池固相分布均匀性评价

为探索循环生物絮团系统相对原位生物絮团系统在生物絮团分布均匀性方面的改善,以欧拉-欧拉多相湍流模型为理论框架,运用计算流体力学(computational fluid dynamics)技术,对两种系统养殖池固液气三相三维流动进行了数值模拟,分析了两种养殖池的液相速度云图、液相流线图以及固相分布特性。模拟结果表明:在水力停留时间为0.90 h时,循环养殖池流场相对复杂,流向变化较乱且分布于整个空间,紊流相对剧烈,流场速度大小分布更均匀,死区相对较少,固相主要分布在中心大范围区域,便于循环,在底部未出现沉积现象,能够避免生产中由于生物絮团在桶底角处的沉积造成厌氧病菌的滋生。另外,循环养殖池生物絮团固相体积分数约为0.1,比较适宜罗非鱼等养殖对象的生长。通过与实测数据对比,模型的模拟值误差均在20%之内,模拟结果可信,该研究说明循环生物絮团系统能够解决原位生物絮团系统中生物絮团分布不均匀以及流场死角多的问题。     

Assessment of soil compaction using soil shrinkage modelling: Experimental data and perspectives

Soil compaction assessment is an important and difficult issue. In particular, it is difficult to quantify separately the compaction of macro-pores and micro-pores in the soil, and to account for spatial variability in soil properties at field scale. According to recent publications, the measurement and modelling of soil shrinkage curves (ShC) could help to overcome these difficulties. This is discussed in this paper on the basis of a field study. Control and compacted undisturbed samples originating from the surface layer of a cropped field are compared. The methods for measurement and modelling of the ShC are presented. Calculations of the micro-porosity, identified to be the soil plasma-porosity, and of the macro-porosity in the soil samples, at any water content, are described, and the accuracy of the results is discussed. A good agreement between field observation and ShC modelling is observed. The method allows for quantifying the compaction, with distinction between plasma-porosity and macro-porosity compaction. The forming of occluded macro-pores is also detected and quantified. The presented method offers numerous advantages in soil compaction assessment. It is precise, simple and easy to operate. It can be realized on clods of unspecified shape and containing a coarse fraction, and can be calculated for the fine earth fraction without the coarse fraction. The pore systems are quantified at any water content, and the determination covers the full range of pore sizes with quantitative distinction between the plasma-porosity and the macro-porosity compaction. According to previous results, it is possible to remove a certain amount of spatial variability in soil clay content by scaling the shrinkage parameters with clay content. The measurement and modelling of soil ShC is, therefore, a promising tool for soil compaction assessment.     

Flumioxazin soil persistence and mineralization in laboratory experiments

Flumioxazin is an herbicide registered for use in soybean and peanut. However, few published papers concerning the soil persistence of flumioxazin are available. Therefore, laboratory studies were initiated to determine the half-life (t(1/2)) of flumioxazin in Greenville sandy clay loam and Tifton loamy sand soils when incubated at 15 and 25 degrees C. Results indicated that temperature had little effect on flumioxazin persistence. The t(1/2) for the Greenville soil was 17.9 and 16.0 days while the Tifton soil was 13.6 and 12.9 days, at 15 and 25 degrees C, respectively. These data correspond to the greater clay content of the Greenville soil (32%) as compared to the Tifton soil (2%). Therefore, the Greenville soil had greater soil adsorption and less flumioxazin was generally available to be degraded by soil microorganisms. In soils that were heat treated to reduce microbe populations, 99% of initial flumioxazin was accounted for after 16 days. Mineralization of flumioxazin, measured as 14CO2 evolution, was also greater in the Tifton soil (2.2% after 64 days) than in the Greenville soil (2.0% after 64 days). From these data, it was concluded that microbes were the most influential factor concerning the degradation of flumioxazin.     

Challenges in modelling dissolved organic matter dynamics in agricultural soil using DAISY

Because dissolved organic matter (DOM) plays an important role is terrestrial C-, N- and P-balances and transport of these three components to aquatic environments, there is a need to include it in models. This paper presents the concept of the newly developed DOM modules implemented in the DAISY model with focus on the quantification of DOM sorption/desorption and microbial-driven DOM turnover. The kinetics of DOM sorption/desorption is described by the deviation of the actual DOM concentration in solution from the equilibrium concentration, C_eq. The C_eq is soil specific and estimated from pedotransfer functions taking into account the soil content of organic matter, Al and Fe oxides. The turnover of several organic matter pools including one DOM pool are described by first-order kinetics.The DOM module was tested at field scale for three soil treatments applied after cultivating grass–clover swards. Suction cups were installed at depths 30, 60 and 90 cm and soil solution was sampled for quantification of dissolved organic C (DOC) and dissolved organic N (DON). In the topsoil, the observed fluctuations in DOC were successfully simulated when the sorption/desorption rate coefficient k was low. In the subsoil, the observed concentrations of DOC were steadier and the best simulations were obtained using a high k. The model shows that DOC and DON concentrations are levelled out in the subsoils due to soil buffering. The steady concentration levels were based on the C_eq for each horizon and the kinetic concept for sorption/desorption of DOC appeared a viable approach. If C_eq was successfully estimated by the pedotransfer function it was possible to simulate the DOC concentration in the subsoil. In spite of difficulties in describing the DOC dynamics of the topsoil, the DOM module simulates the subsoil concentration level of DOC well, and also—but with more uncertainty—the DON concentration level.     

果园货运链索风致振动非线性动力学分析

为解析风荷载持续激励对果园货运系统工作稳定性的影响,研究了行进链索在不同风荷载条件下的风致振动响应。基于Hamilton原理推导了风荷载作用下行进链索横向振动的动力学微分方程,采用Crank-Nicolson半显示数值离散方法对方程进行离散求解,仿真分析了行进链索在不同平均风速作用下的横向振动特性。设计了链索货运系统的风荷载试验平台,采用Lab Windows/CVI对采集视频分帧后的图像进行处理,试验对比研究了不同平均风速风荷载激励的链索横向振动。研究结果表明,平均风速在0~10 m/s范围内变化的低速风荷载起到了一定的气动阻尼作用,行进链索的横向振动幅值减小并呈收敛趋势。该文为风荷载作用下轴向行进链索横向振动控制研究提供了理论参考。     

Cation binding in a mor layer: batch experiments and modelling

The understanding of cation binding in the mor layer is important to correctly assess the biogeochemical cycling of metals and other cations in forested ecosystems. In a series of batch experiments, the binding of cations was examined in two mor layers from central Sweden. We examined the effect of Ca and Al on the binding of Zn, and also the binding of added Pb, Cu and Cd. Two models, WinHumicV and the Stockholm Humic Model (SHM), were tested for their ability to describe the data obtained. We found that for Zn, the pH at 50% sorption was increased from 2.8 to 4.2 after the addition of 3 m M Al. The proton titration data were well described by both WinHumicV and SHM after optimization of the concentrations of 'active' Al and humic substances. Applying generic parameters for cation binding produced deviations between the model simulations and the observations, particularly for the dissolved Pb and Cu concentrations, which were underestimated. A revised set of cation complexation constants was presented that improved the fit, particularly for SHM. For WinHumicV, there were still poor overall fits. The difference in model performance may be due to the greater number of adjustable parameters in the SHM, but probably also to other model-specific differences. According to the SHM simulations, the binding of Ca, Mg and Mn was mainly non-specific, whereas Pb, Cu and Al were bound as mono- or bidentate complexes. For Zn and Cd, binding occurred through both counter-ion accumulation and monodentate complexation.     

果园防霜机模糊控制系统设计及防霜效果试验

为预防果树霜冻害,提高果园管理水平,该文设计了一台基于模糊控制策略的果园防霜机。利用STM32微控制器和触摸屏开发了防霜自动化控制系统,通过无线射频网络进行环境信息采集,设计了回转平台的摆头速度变频控制系统,实现不同摆头速度的360°往复运动。防霜机有效工作半径为5～48m,最大保护面积约7150m2。试验结果表明,防霜机摆头速度和防霜机的距离对温度和风速有交互作用,在模糊控制条件下,平均温度和风速的下降量小于常规控制条件的下降量。在试验期间,应用模糊控制和常规控制的平均温升均分别是3.1和2.8℃,模糊控制和常规控制下的苹果树芽孢受冻率分别是5.6%和11.6%,模糊控制的防霜机运行时间节省21.1%。结果说明该防霜机可以实现防霜智能控制,运行模糊控制策略后,防霜效果好于常规控制,并且运行时间相对较短。