固定边界发汗冷却系统的最优控制问题

对固定边界发汗冷却控制系统的最优控制问题进行了讨论;利用测度理论,将最优控 制问题转化为在一定的正测度空间上求解带线性约束条件的线性优化问题.从而给出了控制律 及冷却剂携带量最优值的计算方法,数据试验显示此方法是有效的.     

粉末冶金多孔材料性能研究

为了研究多孔结构的渗透特性和机械性能,采用粉末冶金模压烧结技术制备微孔尺寸约5μm不锈钢、高温合金和铜合金非等厚回转体多孔发汗结构,研究了其微孔分布均匀性、气体渗透性能和力学性能与孔隙率的关系,渗透率随孔隙率增大而增大,强度随孔隙率增大而降低,除铜合金外,延伸率随孔隙率增大而降低。金属粉末冶金多孔材料可用于热防护结构的发汗冷却。     

Global models for the biomechanics of green plants. Part 1

The paper considers the biomechanics of green plants for low Reynolds number flow in the stem. In particular, it is assumed that the stem is cylindrical and the flow is fully-developed. Then if the aspect ratio is defined as the ratio of the stem radius to its length, for a small aspect ratio, analytical solutions have been developed for the concentration, temperature and axial velocity. The processes of translocation and transpiration are discussed quantitatively.     

一维发汗控制问题的线方法

对发汗控制问题进行了数值分析，对固定边界和活动边界情形，分别进行空间离散化，得到两组常微分方程组。采用显式和隐式Ｅｕｌｅｒ方法对上述发汗控制系统进行了全数字仿真，得到了数值结果可以为研究发汗系统的控制问题提供有效的依据。     

水发汗温度场控制

在文献[1,2]研究氦气发汗的基础上,本文探讨了水发汗剂.水在沸点会汽化,热层内存 在热漏,对此采用"假想节点"思想,导出了差分公式,建立了三对角方程组,并进行了数字仿 真.当给定控制参数mL的函数形式为级数时,闭合回路控制数字仿真结果表明,该级数能够 有效地控制热层温度.     

Simulating Root Water Uptake from a Heterogeneous Vegetative Cover

A small body of knowledge exists on the root water uptake (RWU) and evapotranspiration in humid environments having a mixture of natural vegetative cover. In this paper, we assess the impacts of atmospheric conditions and land cover on RWU from a natural vegetative cover. An intensive field investigation was carried out to monitor water table fluctuations along two flow transects comprising an upland grass area and a lowland riparian zone. Calibration and validation of the soil hydraulic parameters using the two-dimensional variably saturated ground water flow model, HYDRUS-2D, confirms the reliability of the model to simulate satisfactorily the large-scale daily fluctuation of RWU. Simulation results revealed that the actual RWU during the wet season is about 40% higher than RWU in the dry season due to high water table levels and temperatures prevailing throughout the wet season. Simulation results using HYDRUS-2D, which was modified to accommodate variable surface boundary conditions and heterogeneous root distribution, showed that the RWU from the riparian zone was 38 and 56% higher than RWU from the pasture land during the dry and wet seasons, respectively.     

Contribution of Evapotranspiration Reduction during Sprinkler Irrigation to Application Efficiency

The effect of reduced corn evapotranspiration (ET) during solid-set sprinkler irrigation on application efficiency was analyzed on two subplots. During each irrigation event, one subplot was irrigated (moist treatment) while the other was not (dry treatment). ET (weighing lysimeter) and transpiration (heat balance method) rates were determined at each subplot before, during, and after the irrigations. During daytime irrigations, there was a significant decrease in ET (32–55%) and transpiration (58%) for the moist treatment. After the irrigations (1–2?h), ET significantly increased (34%) and transpiration decreased (20%). Gross wind drift and evaporation losses (WDELg) were found to be 19.3% of the applied water. Taking into account the ET changes during and after the irrigations, net sprinkler evaporation losses (SELn) were 14.4–17.5% of the applied water. During nighttime irrigations, changes in ET and transpiration were almost negligible, and SELn were slightly greater than WDELg (9.5 and 8.1%, respectively, of applied water). SELn was mainly a function of wind speed. Reduced ET and transpiration during daytime irrigations moderately increased solid-set sprinkler application efficiency.     

二维动边界发汗控制数学仿真研究

本文给出二维加热且具有表面烧蚀的发汗控制数学模型。采用时间跨半步的交替方法,将二维活动边界分布参数控制方程差分化,得到三对角方程组。对电磁炮弹飞行进行数学仿真后表明:控制参数对温度场和活动边界的控制是有效的;该数学模型符合实际物理过程。从数值角度提供了数学理论问题解析性质的依据,给出了二维温度场特点并讨论了同步烧蚀问题。     

硼对烤烟生理生化及产质量的影响

本试验对烤烟的Ｂ＾３＋肥效应进行了研究。结果表明,施用适量的Ｂ＾３＋,可促进烤烟生长发育,改善其植物学性状,增加色素含量,提高光合强度和蒸腾速率,使烟叶增产、增质、增收。同时还发现Ｂ＾３＋能使烟株提前２～３ｄ现蕾开花,中下部烟叶提前落黄采收。这一特性,对烤烟生产具有重要的作用。     

Effect of transpiration on combined heat and mass transfer in mixed convection along a vertical plate

The effect of transpiration velocity on the heat and mass transfer characteristics of mixed convection flow along a permeable vertical flat plate under the combined effects of thermal and mass diffusion is analysed. The diffusion-thermo and thermo-diffusion effects as well as the interfacial velocities due to mass diffusion are negligibly small. The plate is maintained at a uniform temperature and species concentration. Numerical results for the local skin-friction, the local Nusselt number and the local Sherwood number, as well as for the velocity, the temperature and the concentration profiles, are presented for diffusion of common species into air only. In general, it has been found for thermally assisted flow that the local surface shear-, heat-, and mass-transfer rates decrease owing to suction of fluid. This trend reversed for blowing of fluid. In addition this trend is higher for species of larger Schmidt number as well as for increasing buoyancy force.