轴流泵多工况压力脉动特性试验

为了掌握不同流量工况下的轴流泵压力脉动特性,在轴流泵叶轮段和导叶段外壁面布置了6个压力脉动监测点,对多个流量工况的压力脉动进行了动态测量,揭示了轴流泵内部不同位置处压力脉动规律。试验结果表明,叶轮进口监测点P1的波形为规则的正弦波形,叶轮内部中间测点P2的压力脉动峰峰值最大,叶轮进口监测点P1压力脉动次之。叶轮进口、叶轮中间和叶轮出口监测点由于受到叶轮内压力梯度的交替变化影响,时域脉动周期与叶片旋转周期一致,在小流量工况下叶轮内部涡流诱导了明显的二次谐波。基于快速傅里叶变换,获得了不同监测点压力脉动频域分布结果,并发现叶轮区域3个压力脉动测点在不同工况的主频均为叶片通过频率(BPF),谐频为叶频的倍数,其幅值呈指数形式衰减。但在导叶进口、导叶中间和导叶出口监测点的压力脉动频域中出现了撞击和回流诱导的低频信号,同时也存在叶轮的主频及其谐频。     

离心泵小流量工况不稳定空化特性研究

为了研究离心泵小流量工况不稳定空化特性,通过数值模拟和试验,研究了离心泵小流量工况不同空化程度泵的内流特性及泵进出口压力脉动特性。结果表明:小流量工况下,蜗壳隔舌与叶轮间的动静干涉对离心泵内部不稳定流动具有重要影响,叶轮流道内受空化影响所产生的漩涡与受蜗壳隔舌影响所产生的漩涡的流动方向相反。随着空化的发展,离心泵进口压力脉动的主频由2倍轴频逐渐向低频段迁移,且存在一定的波动;泵进口压力脉动存在于2倍叶频处的峰值,随着空化发展到一定程度而消失;受叶轮与隔舌动静干涉的影响,泵出口压力脉动的主频为叶频,在2倍轴频处存在波动较大的峰值;泵进出口压力脉动的宽频脉动随着空化余量的降低存在明显变化。     

余热排出泵内部压力脉动特性分析

为了研究余热排出泵内部压力脉动特性,基于ANSYS CFX软件,采用SST湍流模型,对模型泵进行三维非定常数值模拟,得到了余热排出泵的水力性能,并与试验结果进行对比,计算了泵内不同位置的压力脉动情况,对计算结果进行了时域和频域分析.研究结果表明:叶轮与导叶内的压力脉动均呈现周期性变化,叶轮内周期为7,压力脉动与导叶叶片数密切相关,导叶内周期为5,压力脉动与叶轮叶片数密切相关;叶轮进口、中间流道、叶轮出口的压力脉动系数幅值分别为0.018 23,0.106 76,0.177 51,压力脉动信号逐渐增强,导叶进口、中间流道、导叶出口的压力脉动系数幅值分别为0.095 56,0.076 02,0.012 44,压力脉动信号逐渐减弱;叶轮内监测点的主频均为7f_p,压力脉动主要由转频决定,从叶轮进口至出口导叶的影响程度逐渐增强,导叶进口主频为15f_p,中间流道和出口主频为5f_p,导叶内压力脉动主要由叶频决定,沿流道至出口叶轮的影响逐渐削弱;蜗壳监测点主频为35f_p,压力脉动主要由叶频决定,且与导叶叶片数相关.     

不同空化工况下的轴流泵装置压力脉动试验

为研究不同空化工况下轴流泵装置内部压力脉动特性,采用动态压力传感器对派河口泵站轴流泵装置模型叶轮进口、叶轮出口、导叶出口3个压力监测点在2.5、3.5、4.5、5.4m扬程分别在未发生空化、临界空化(泵装置效率下降1%)、深度空化(泵装置效率下降3%)12种工况下进行了压力脉动试验。试验结果表明:叶轮进口处的压力脉动曲线为平滑的近似正弦曲线,叶轮出口处压力脉动曲线幅值最大且只有在高扬程未发生空化工况下在一个旋转周期内表现出明显有规律的二次谐波特性;导叶出口的压力脉动时域特性与叶轮进口相似;快速傅立叶变换(FFT)结果表明:各监测点在各工况下的主频为叶片通过频率的整数倍频,在同一扬程工况下,随着空化程度的加深,各监测点的主频附近的谐频逐渐向低频段移动;导叶出口与叶轮进口受叶频影响较小且表现出相似的频率特性。1     

轴流泵马鞍区水力性能与压力脉动测试与分析

为了分析轴流泵在马鞍区工况的运行特性,对一轴流泵不同工况下的外特性和压力脉动进行了测试,重点分析了轴流泵马鞍区水力特性和压力脉动特性.试验结果表明:模型泵H-Q曲线在0.50Q_d~0.60Q_d内表现出明显的马鞍形,且扬程在马鞍区内0.55Q_d工况时达到最小值,较0.60Q_d工况扬程降低0.33 m,为设计工况下扬程的5.5%;叶轮进口和泵出口处压力脉动具有较为明显的周期性,单个周期内压力脉动表现出明显的4波峰4波谷特征;0.55Q_d工况时,叶轮进口处压力脉动峰峰值为设计工况的2.3倍;各工况下导叶中间和出口处压力脉动规律较为复杂;叶轮进口压力脉动主频为叶片通过频率,0.55Q_d工况叶频处的幅值最大,高于设计工况27.6%.小流量工况下,导叶中间、导叶出口处压力脉动在频域内出现较多低频信号,压力脉动频率成分较复杂.泵出口压力脉动主频在1.00Q_d工况下明显表现为叶频.研究成果可为轴流泵不稳定运行特性的优化提供参考.     

立式管道离心泵多工况压力脉动试验

为研究不同工况下立式管道离心泵内部压力脉动特性,文中采用动态压力传感器在模型泵进口弯管处、蜗壳隔舌附近、蜗壳扩散管处分别设置压力监测点,对0.6Q_d,1.0Q_d和1.4Q_d这3种流量下的压力脉动进行了测试,得到了压力脉动时域图、频域图和时频域图.试验结果表明:蜗壳隔舌附近的压力脉动信号波动最大.随着流量的增加,各监测点的压力脉动幅值先减小后增加.小流量和设计流量下,进口弯管处的压力脉动主频为2倍轴频,大流量下主频为轴频,幅值表现出强烈的波动特性.蜗壳隔舌附近的压力脉动主频均为叶频,幅值随流量增加而增大,在小流量和设计流量下高频处表现出较宽频段的波动性.蜗壳扩散管处的压力脉动在小流量和设计流量下主频为叶频,大流量下主频为轴频,轴频的幅值随流量增大而减小.     

叶轮参数对泵出口压力脉动的影响

为了研究串并联泵出口处的振动特性,采用快速傅里叶变换和多相干分析方法,首先进行了两参数三水平的正交试验,评价了叶片数和叶片出口安放角对叶轮出口处压力脉动的影响,然后对叶轮出口压力信号进行拟合,首、次级叶轮出口压力信号拟合度分别为0.809 6和0.818 0,泵出口压力信号拟合度为0.719 4.运用多相干分析方法给出了首级叶轮和次级叶轮对泵出口处压力脉动的主次影响,研究结果表明:在频域上,叶轮出口处压力峰值均出现在倍叶频处,符合转频规律;首级叶轮叶片数对泵出口压力脉动影响最大;泵出口处压力脉动频域主峰幅值随着叶片数的增加而减小.研究结果对串并联泵的设计和应用提供了理论依据和参考.     

不同空化工况下轴流泵装置压力脉动试验

为研究不同空化工况下轴流泵装置内部压力脉动特性,采用动态压力传感器对派河口泵站轴流泵装置模型的叶轮进口、叶轮出口、导叶出口3个压力监测点,分别在2.5、3.5、4.5、5.4m扬程和未发生空化、临界空化（泵装置效率下降1%）、深度空化（泵装置效率下降3%）等12种工况下进行了压力脉动试验。试验结果表明：叶轮进口处的压力脉动曲线为平滑的近似正弦曲线;叶轮出口处压力脉动曲线幅值最大,且只在高扬程、未发生空化工况下的一个旋转周期内表现出明显有规律的二次谐波特性;导叶出口的压力脉动时域特性与叶轮进口相似。快速傅里叶变换(FFT)结果表明：各监测点在各工况下的主频为叶片通过频率的整数倍频,同一扬程工况下,随着空化程度的加深,各监测点主频附近的谐频逐渐向低频段移动;导叶出口与叶轮进口受叶频影响较小,且表现出相似的频率特性。     

空化对超低比转数离心泵内压力脉动的影响研究

为研究空化对超低比转数离心泵内压力脉动的影响,采用实验和数值模拟相结合的方法,研究了IB 50-32-250型超低比转数离心泵在不同有效汽蚀余量下不同位置处的压力脉动,并对其频域和幅值特性进行了分析。结果表明:空化会诱导产生低频及宽频脉动。无空化时,叶轮流道内压力脉动主频为转频及其倍频,蜗壳内压力脉动受叶轮和隔舌间的相互作用激励,主频为叶频及其倍频,且与隔舌越近脉动越强。随着有效汽蚀余量的减小,叶轮通道中大部分测点的压力脉动幅值减小,但空化区边缘的脉动幅值增大;临界空化时,叶轮进口附近的压力脉动主频由转频变为1/6倍转频。此外,蜗壳内流场的不均匀变化导致蜗壳内压力脉动幅值增大;临界空化时,蜗壳及泵出口处的主频仍为叶频,但1/6倍转频成为幅值较大的次频。     

混流泵内流场压力脉动特性研究

基于RANS方程和SST湍流模型,应用SIMPLEC算法,对混流泵内流场进行非定常数值模拟,分析了不同流量工况和不同转速工况时混流泵内4个代表性监测面上压力脉动的时域和频域特性.取非定常计算的功率平均值与试验值对比,证明该数值模型可较准确描述泵内流场特征.结果表明:混流泵内最大压力脉动在叶轮进口,从轮毂到轮缘脉动幅值递增;在叶轮进口和叶轮出口压力脉动频率主要为叶轮叶频,而导叶中间和导叶出口压力脉动频率与流量工况相关;偏离最优工况越远脉动越大,偏小流量对叶轮进口压力脉动影响明显;不同转速时最优工况压力脉动频率成分相似,脉动幅值随转速增加而增加.     

Overland water and salt flows in a set of rice paddies

Cultivation of paddy rice in semiarid areas of the world faces problems related to water scarcity. This paper aims at characterizing water use in a set of paddies located in the central Ebro basin of Spain using experimentation and computer simulation. A commercial field with six interconnected paddies, with a total area of 5.31 ha, was instrumented to measure discharge and water quality at the inflow and at the runoff outlet. The soil was classified as a Typic Calcixerept, and was characterized by a mild salinity (2.5 dS m⁻¹) and an infiltration rate of 5.8 mm day⁻¹. The evolution of flow depth at all paddies was recorded. Data from the 2002 rice-growing season was elaborated using a mass balance approach to estimate the infiltration rate and the evolution of discharge between paddies. Seasonal crop evapotranspiration, estimated with the surface renewal method, was 731 mm (5.1 mm day⁻¹), very similar to that of other summer cereals grown in the area, like corn. The irrigation input was 1874 mm, deep percolation was 830 mm and surface runoff was 372 mm. Irrigation efficiency was estimated as 41%. The quality of surface runoff water was slightly degraded due to evapoconcentration and to the contact with the soil. During the period 2001–2003, the electrical conductivity of surface runoff water was 54% higher than that of irrigation water. However, the runoff water was suitable for irrigation. A mechanistic mass balance model of inter-paddy water flow permitted to conclude that improvements in irrigation efficiency cannot be easily obtained in the experimental conditions. Since deep percolation losses more than double surface runoff losses, a reduction in irrigation discharge would not have much room for efficiency improvement. Simulations also showed that rice irrigation performance was not negatively affected by the fluctuating inflow hydrograph. These hydrographs are typical of turnouts located at the tail end of tertiary irrigation ditches. In fact, these are the sites where rice has been historically cultivated in the study area, since local soils are often saline-sodic and can only grow paddy rice taking advantage of the low salinity of the irrigation water. The low infiltration rate characteristic of these saline-sodic soils (an experimental value of 3.2 mm day⁻¹ was obtained) combined with a reduced irrigation discharge resulted in a simulated irrigation efficiency of 60%. Paddy rice irrigation efficiency can attain reasonable values in the local saline-sodic soils, where the infiltration rate is clearly smaller than the average daily rice evapotranspiration.     

瓦房店市水果生产标准化发展研究

瓦房店市是我国重要的水果生产基地,在国内水果生产领域占有重要地位。随着水果市场化的不断深入,如何满足和适应国内外市场需求成为瓦房店市水果生产的关键问题。从瓦房店市水果生产实际出发,阐述了实施水果生产标准化的必要性,提出了发展水果生产标准化的具体措施。     

金谷子耐旱TG118引种试种及推广应用

对引进的谷子新品种金谷子耐旱TG118进行品种比较试验和多点试种。结果表明：该品种抗旱、耐瘠、适应性强,稳产、高产、抗病抗风抗倒伏强,品质优良,粮草兼用,种植简单,省工易管;一般产量在6000kg/hm2以上,比当地主栽品种增产20%以上。最高产量达9450kg/hm2,适于在辽西北地区推广应用。     

对《种子法》存在问题的探讨

《种子法》是我国种植业第一部法律。自实施以来,为依法加强种子管理提供了有力的法律支撑,促进我国种子产业发生翻天覆地的变化。但随着依法管理工作的深入和种子产业的快速发展,《种子法》及配套规章的一些问题逐步显现出来。对《种子法》及配套规章存在的问题进行深入分析,对需要进一步补充的章节以及需要调整的内容进行深入探讨,以求更加完善和明确。     

Review of the Egyptian experience in implementing land drainage projects

About 30 years have passed since the Government of Egypt embarked on implementing a series of large scale drainage projects. At present, about 3.8 million acres have been provided with drainage systems on the basis of systematic pre-drainage investigations and designs. The target is to provide drains in approximately 6.4 million acres in the Nile Valley and Delta.The implementation of the subsurface drainage system is carried out by the public sector and private contractors under direct supervision of governmental regional departments. The implementation process depends on many factors related to the drainage material, machinery, manpower, site requirements, farmers and organizations involved. Problems and constraints are sometimes challenging, however, the annual rate of implementation has gradually increased to 170,000 acre/year.This paper discusses the different aspects involved in the implementation process of drainage systems. The development in materials, machinery and construction technologies will be reviewed. Institutional and management factors are going to be also considered.     

和谐社会理论建设的几点哲学思考

在新世纪,面对机遇和挑战,党的十六大把“社会更加和谐”作为全面建设更高水平的小康社会的一个重要目标。中国人素有社会和谐的理想;西方人自古也向往社会和谐;借鉴东西方两种和谐社会思想的经验、教训,构建社会主义和谐社会理论。     

A European irrigation map for spatially distributed agricultural modelling

We present a pan-European irrigation map based on regional European statistics, a European land use map and a global irrigation map. The map provides spatial information on the distribution of irrigated areas per crop type which allows determining irrigated areas at the level of spatial modelling units. The map is a requirement for a European scale assessment of the impacts of irrigated agriculture on water resources based on spatially distributed modelling of crop growth and water balance. The irrigation map was compiled in a two step procedure. First, irrigated areas were distributed to potentially irrigated crops at a regional level (European statistical regions NUTS3), combining Farm Structure Survey (FSS) data on irrigated area, crop-specific irrigated area for crops whenever available, and total crop area. Second, crop-specific irrigated area was distributed within each statistical region based on the crop distribution given in our land use map. A global map of irrigated areas with a 5′ resolution was used to further constrain the distribution within each NUTS3 based on the density of irrigated areas. The constrained distribution of irrigated areas as taken from statistics to a high resolution dataset enables us to estimate irrigated areas for various spatial entities, including administrative, natural and artificial units, providing a reasonable input scenario for large-scale distributed modelling applications. The dataset bridges a gap between global datasets and detailed regional data on the distribution of irrigated areas and provides information for various assessments and modelling applications.     

粉质仪和拉伸仪在面粉生产中的应用

在介绍粉质仪和拉伸仪结构和原理的基础上,探讨了粉质曲线中吸水率、形成时间、稳定时间、弱化度和评价值等指标与面粉品质的关系,以及如何根据拉伸曲线中面团最大拉伸阻力、延伸度和拉伸曲线面积等指标来评价面团品质,并结合生产实际,概述了粉质仪和拉伸仪在面粉生产中的作用。     

农村信息化服务的现状及建设措施

分析当前我国农村信息化服务的现状,提出加强农村信息化服务的新举措。     

车辆ABS控制算法的研究及探讨

对现代汽车的ABS控制算法作了一些简单的介绍,同时指出了它们的一些缺陷,相应地提出了几种对ABS的其它控制方法并加以探讨,其中着重论述了ABS门限值控制算法中参考车速的确定方法和基于附着系数的控制算法。