离心泵快速变工况瞬态过程特性模拟

为研究离心泵在不同工况点快速切换过程中的瞬态特性,该文以一台低比转速离心泵为研究对象,对其工况流量突然减小的瞬态过程,分别采用理论分析和数值计算的方式进行了外特性预测和内流场仿真研究。首先基于叶轮机械广义欧拉方程式,对离心泵模型在流量突然减小瞬态过程中的附加理论扬程进行了定量计算与分析。结果表明,同等条件下,变工况过程结束后的稳定流量越小,附加理论扬程越大,瞬态效应愈发明显;同时该瞬态过程后期的瞬态效应比前期更为明显。动静干涉效应对泵出口流动参数产生显著影响,而对泵进口流动参数的影响并不明显;动静干涉效应对小流量工况时各个流动参数的影响将尤为显著。叶片与隔舌相对位置最近时,计算扬程最小;当隔舌位于叶轮流道中间位置稍后时,计算扬程最大。同一个转动周期(T)内,选取叶片转过隔舌后的0.225 T和0.825 T位置进行单次定常计算可取得较高精度的数值预测结果。动静过流部件和粘性效应使得叶轮和蜗壳内的轴向速度分布规律完全相反。瞬态过程中流体加速效应使得瞬态流场演化整体上滞后于准稳态流场。     

高速电磁阀电磁力近似模型的构建与分析

为提高高速电磁阀动态响应速度,采用近似模型方法,以建立电磁阀多物理场零维近似耦合模型,实现其性能高效预测及优化。首先创建了柴油机电控单体泵高速电磁阀电磁力有限元计算模型,并通过与试验对比验证了模型的精度。结合面中心复合设计、嵌套中心复合设计、最优拉丁超立方设计与二次多项式响应面模型、Kriging模型、径向基函数模型,构建了18组电磁力近似模型。分析了不同样本点集大小、试验设计方法及近似方法对近似模型精度的影响。得出近似模型的精度随着样本点集的增大并非呈现单调递增的关系;而最优拉丁超立方试验设计与Kriging模型、径向基函数模型具有良好的适应性。构建高速电磁阀工作气隙、驱动电流、线圈匝数、副磁极半径、衔铁厚度、衔铁半径等关键参数的电磁力近似模型最佳方案是最优拉丁方试验设计与Kriging模型的组合,样本点集大小为二次多项式响应面模型所需最少样本点数的1.5倍,模型复相关系数、平均绝对误差、均方根误差值分别为0.97、0.06、0.09。该研究为高速电磁阀多物理场零维近似耦合模型的建立及其优化提供了参考。     

Effect of long-term application of fertilizers on soil quality and rice yield in a salt-affected coastal region of India

The studied soils were collected from a 24-year long-term fertilizer experiment with rice (Oryza sativa L.) grown on tropical Typic Endoaquepts during monsoon season only. The organic carbon (OC) and total nitrogen (TN) status of the soils improved with the N₁₀₀P₂₂K₄₂ treatment than the initial values at the start of the experiment. The available P status of the soils depleted in the N₁₀₀P₁₁K₂₂ and N₀P₀K₀ treatments than the initial value. Soil microbial biomass carbon (MBC) and basal soil respiration (BSR), activities of urease, acid and alkaline phosphatases as well as fluorescein diacetate hydrolyzing activity (FDHA) were the highest in the N₁₀₀P₂₂K₄₂ treatment. The highest percentage of MBC in OC in the N₁₀₀P₂₂K₄₂ treatment revealed the accumulation of organic matter with an overall improvement in nutrient status of soil, since MBC is a labile pool of plant nutrients. Long-term application of fertilizers (N₁₀₀P₂₂K₄₂) had no deleterious effect on microbial and biochemical soil quality parameters. Rice grain yields were inconsistent with N₁₀₀P₀K₀ and N₀P₀K₀ while that of N₁₀₀P₂₂K₄₂, N₁₀₀P₁₁K₂₂ and N₁₀₀P₂₂K₀ increased gradually during the course of the experiment for each block period of six years. The grain yield of rice showed high significant correlation with the microbial and biochemical soil parameters.     

进水池表面吸气涡数值模拟与试验

为了有效地消除表面吸气涡,对进水池内流场进行了数值计算,模拟了表面涡吸气的动态过程;建立了试验模型,验证CFD方法的可靠性;并提出了圆形盖板消涡装置,探求其有效性;采用了螺旋度密度分析法,揭示了表面涡的吸气及其抑制机理。结果显示:采用的CFD方法可以较好地预测表面吸气涡的动态过程;吸气准备阶段,自由水面出现凹陷,喇叭管进口附近形成螺旋度密度管;随着气体从自由水面进入水体,自由水面下方形成另一螺旋度密度管;当连续气柱形成时,两个螺旋度密度管相互连通,形成气体通道;通过在自由水面和喇叭管进口之间放置一定尺寸的圆形盖板装置,可以消除表面吸气涡。     

大田土壤间歇入渗试验方法及其精度提高措施

间歇灌,又称波涌灌,这种新的地面节水灌水技术的出现,使土壤入渗规律的研究分为土壤连续入渗规律和间歇入渗规律两方面的研究。间歇入渗条件下,土壤入渗规律除受连续入渗的影响因素制约外,还受构成其特殊灌水过程的灌水技术参数的影响。影响因素的增加,加之野外土壤条件的时、空变异性,决定了间歇入渗试验工作量大,且具有更大的复杂性。为提高成果精度和工作效率,笔者根据1991年冬季和1992年春季在陕西关中宝鸡峡灌区灌溉试验站进行的141组一维土壤连续和间歇单点入渗试验实践,介绍了用双套环入渗仪进行单点间歇入渗试验的方法,提出了提高土壤间歇入渗试验精度的可行措施,可供参考。     

Computation of Three-Dimensional Temperature Distribution and Thermal Analysis to Integrated Circuit Substrates

The exact three di me nsional temperatu re distribution and thermal analysiS to inte-grated circuit substrates have been presen ted by means of numerical method of a fin ite difference.Thismethed.which will overcome the di fficuItv of mathematical deduction mav be consltieredas an analytical way aided by com puters for thermal design of electron ic compon ents.     

基于超高压水切割法的木制工艺品加工参数优选与分析

在我国木材加工领域,数控超高压水射流技术的应用尚处于起步阶段,多用于珍贵木材的切割。为优化水切割在木材加工领域中的应用,笔者将中密度纤维板和意杨实木作为试验材料,采用正交试验法,以调砂速度、气干密度、水切割压力、进给速度、靶距工艺参数作为对其加工表面粗糙度的影响因素。利用数控工作系统设计CAD图案后进行的水切割试验,并通过对试件表面粗糙度的测量和相关计算,得到各工艺参数影响显著度程度及其最优方案。该研究对花式木地板及其木刻、木结构室内装饰板、红木家具等木制工艺品的加工领域提供工艺参数优选,具有较高的应用价值和现实意义。     

延安地区降雨引发黄土泥流的试验研究

在野外模拟降雨条件下,研究了黄土粒度分布和微结构在降雨前后的变化及其对泥流启动的影响.结果表明,采自径流沉积物的降雨后土样中的细黏粒、粗黏粒体积含量分别相对增加了22％和18％,而粗粉粒、微砂体积含量分别相对减少了7.6％和3.3％.坡面残余土的粒度“粗化”,降雨后土骨架连接松散,这些由降雨引起的黄土的粒度和微结构变化说明降雨后黄土的抗剪强度和抗压能力将降低,导致泥流启动的可能性增加.随着降雨入渗,当沿坡面的黄土重力分力与抗剪强度间的平衡被打破,黄土开始滑移并发展成泥流.有效防止坡面土粒度“粗化”是遏制水土流失的关键.     

用遗传算法确定考虑温度历程的混凝土水化放热模型参数及试验验证

目前,考虑温度历程绝热温升模型存在参数较难确定和尚未有现场非绝热温升试验验证其精度2个问题。为了解决这2个问题,该文提供了一种合适的遗传算法实现方法,设计了2个温度历程不同的混凝土非绝热温升试验,并将一个混凝土块的试验数据及该方法反演获得的参数应用到模拟另一个混凝土块温度场中。试验结果表明,即使温度历程差异较大,遗传算法也能获取准确的参数。应用遗传算法解决考虑温度历程混凝土水化放热模型具有可行性;且较未考虑温度历程模型,考虑温度历程的混凝土水化放热模型精度有明显提高。未考虑温度历程模型的平均误差为1.1℃而考虑温度历程模型平均误差仅为0.4℃。     

Effect of supplying P to a portion of the soybean root system on root growth and P uptake kinetics 1

Abstract

Knowledge of the effect of supplying P to portions of the soybean (Glycine max L. Merr) root system on P influx kinetics and root growth is important in developing P fertilizer placement practices for efficient fertilizer use. The objective of this research was to determine the effect of restricting P supply to portions of the root system on plant P status, root growth, and P influx kinetics. Two solution experiments were conducted in a controlled climate chamber. Phosphorus influx kinetics were determined on 25‐day‐old soybean plants that had been grown with 100, 75, 50, 25, and 12.5% of their roots initially exposed to P. Phosphorus influx kinetics were also measured on 25‐day‐old plants that had been P‐starved for the last 1, 2, 4, and 6 days prior to the determining P influx kinetics in order to relate plant P status to P influx kinetics.

Reducing the portion of the roots supplied with P reduced P uptake. This resulted in a reduction in plant P concentration and was related to a 3.41‐fold increase in maximum P influx measured on 25‐day‐old plants. Restricting the proportion of roots supplied with P had no significant effects on the Michaelis‐Menten constant or on the concentration in solution where net influx was zero. Root growth rate of the roots in the P containing solution was not significantly different from those in the ‐P solution.

Phosphorus uptake was correlated with final root surface area exposed to P (r² = 0.88??). Starving the plants for P reduced P concentration in the shoot and root and this resulted in as much as a 1.68‐fold increase in maximum influx.