电磁振动排种器机电磁联合仿真研究

采用机电磁联合仿真的方法,建立电磁振动排种器机电磁联合仿真模型,研究了电磁铁电感对线圈电流、激振力波形和排种器工作性能的影响,且对模型进行了验证。结果表明:建立的机电磁联合仿真模型精度较高,电磁铁电感对线圈电流、电磁激振力波形和电磁振动排种器的工作性能有较大的影响,且激振力为方波时,排种器工作性能较好;控制电路使电磁铁线圈电流和激振力波形接近方波有利于提高排种器的工作性能。     

车辆电磁悬挂系统技术综述

对电磁悬挂相关技术进行了分类,并从整体上论述了悬挂系统的应用现状。以电磁执行机构为核心,分别对电磁作动器和磁流变阻尼器研究现状进行了论述,并分析了其特点与不足。对已有电磁悬挂技术中存在的问题进行了分析,指出了电磁悬挂未来的发展趋势,并得出将电磁作动器与磁流变阻尼器相集成的电磁悬挂技术将会有良好的应用前景。     

电磁喷油器的检修

喷油器是发动机燃料供给系统的重要功能零件,文章分析了电磁喷油的结构、原理,研究了电磁喷油器的检修方法与步骤.     

风力发电机的电磁设计

文章主要讲述三相异步发电机的电磁设计方法,重点阐明三相感应式发电机和三相感应式电动机的电磁设计的异同点,三相感应式发电机电磁设计的整套设计方案。     

电磁调速电机控制系统优化与维修分析

电磁调速电机是由电磁转差离合器和交流异步电动机构成的,它在现代工业生产中得到了广泛的应用.文章从电磁调速电机的工作原理方面入手,分析了电磁调速电机控制系统存在的主要问题,并针对这些问题提出了优化与维修应用建议,以供借鉴和参考.     

混合电磁悬架作动器设计与试验

为了解决车用线性电磁作动器(直线电机)可靠性差的问题,设计了一种将直线电机与液压阻尼器集成的混合电磁作动器。采用改进天棚控制策略进行性能匹配,对混合电磁作动器的性能参数进行优化,得到天棚阻尼系数、被动阻尼系数以及直线电机需要提供的峰值电磁推力,并以优化得到的峰值电磁推力为优化目标,优化混合电磁作动器的结构参数。根据优化得到的结构参数试制实体样机,对其进行台架试验,包括混合电磁作动器的外特性试验,以及包含混合电磁作动器的混合电磁悬架主动控制试验。试验结果表明,设计的混合电磁作动器用于悬架系统时,能够较好地改善车辆动力学性能,与被动悬架相比,混合电磁悬架车身加速度和悬架动挠度分别降低了23. 35%和14. 97%,虽然轮胎动载荷增加了13. 20%,但根据"3σ"原则,在可接受范围之内,验证了混合电磁作动器样机的有效性。     

起动机电磁开关故障检修

一辆黄河JN150型货车,起动时突然出现起动机电磁开关工作不正常,时有时无的现象,按起动按钮时,电流表指针向放电方向摆动,电磁开关不工作,用起子搭接电磁开关上的电源接柱与按钮接柱,有火花出现,随之电磁开关恢复正常工作。拆检发现:原来是电磁开关的吸拉线圈与起动机接柱的连接线脱焊松动,接触不良所致。     

电磁振动给料器数字控制及应用研究

针对大量粉粒状物料对自动定量给料要求 ,在分析传统电磁振动给料器给料性能基础上 ,研制了一种电磁振动给料器数字控制系统 ,实现给料器给料量自动调节控制。论述了应用电磁振动给料器数字控制实现混合式自动定量方法 ,并对给料器定量给料进行实验研究。实验表明 ,电磁振动给料器数字控制提高了定量给料稳定性、准确性和可控性 ,能适应不同工作环境 ,满足了大量粉粒状物料自动定量给料速度和准确度要求     

电磁驱动泵设计原理

揭示了一种通过电磁线圈对柱塞产生电磁感应并使之作往复运动的电磁泵的原理。作往复运动的柱塞使得电磁线圈形成了一个封闭的电磁回路。     

农用车电磁制动系统自校正模糊神经网络控制

对农用机动车电磁制动机构的组成及其工作原理进行了详细的阐述,并建立电磁制动机构的模型,进而建立了农用机动车整车电磁制动系统的整体模型.采用模糊神经网络控制完成了农用机动车电磁制动系统控制算法的设计,并采用遗传算法实现了对模糊规则的优化,增大了制动力矩且使滑移率被控制在较小的范围内.     

Timeliness of irrigation

Despite considerable discussion of the importance of timeliness as a key dimension of irrigation performance, few studies have assessed how well irrigation systems deliver timely water supplies, nor the magnitude of the effect on agricultural production. This paper lays out indicators of timeliness of irrigation supply which distinguish between deliveries which meet crop needs, and surplus water supplies which cannot be used by crops. These indicators are then applied to empirical data from the Sone Irrigation System of Bihar, India. Using these indicators in an analysis of the contribution of irrigation to rice production shows that incorporating measures of timeliness explains much more of the variability in agricultural production than do simple measures of total water applications over a season. Results of production functions show that if water deliveries cannot be matched with crop requirements, they have a negative, rather than a positive, impact on yields. Water scarcity has the greatest adverse impact in production in the middle of the season, while surpluses are most damaging at the beginning and end of the season. Temporal redistribution from surplus periods to times of water scarcity therefore offers considerable scope to increase productivity without increasing water use.An earlier version of portions of this paper was presented at the IFPRI/ICAR Workshop on Agricultural Growth in India: A Review of Research Findings, 1–6 May 1994 in New Delhi.     

带分流叶片水泵水轮机转子强度及模态分析

以带分流叶片的水泵水轮机为研究对象,基于CFD与FSI方法分析其泵工况下转子的振动特性,对3种开度即小开度9.8°、最优开度17.5°和大开度24.8°下的流场进行数值模拟,将额定工况下的流场结果导入转子结构实现单向流固耦合,对带预应力的转子模型进行形变与等效应力分析.此外,还计算了转轮的干湿模态,对比分析了不同条件下转轮的振动特性.结果表明:不同开度对应的预应力下转轮形变与等效应力分布规律相似,转轮形变主要发生在上冠低压侧.按ND(节径数)在转轮圆周方向划分振动扇区描述振型规律时发现,各扇区内转轮上冠、下环低压侧的振幅较大.湿模态下水介质对转轮振型影响不大,但会明显降低转轮的振幅.预应力对转轮固有频率影响较小,可忽略不计,但在湿模态下,转轮固有频率会显著下降,这表明分析结构振动特性时应充分考虑水介质作用.     

Effects of construction defects on hydraulic performance of Kalpani distributary, NWFP, Pakistan

The hydraulic performance of canals designed to deliver water by proportional allocation is highly dependent on the accuracy of construction of water division structures. If construction is inaccurate then inequity of water delivery is built into the system from the onset. A survey of hydraulic performance of Kalpnai distributary in NWFP Pakistan immediately after construction showed that the canal could only deliver 90% of designed discharge due to deficiencies in construction of two siphons, and that the tail end of the canal only received 70% of designed discharge. When operated at 70% of design discharge tail end reaches received 50% of designed discharge. Measurements of outlet structures showed that 57% of structures were built as intended and had not been damaged. All orifice outlets delivered more than 115% of design discharge and on average delivered 40% more than intended. Only 20% of open flumes were within 10% of design width, while 58% were more than 30% wider. As a result of these construction defects many watercourses were able to obtain much higher discharges than intended. The lack of control gates means there is no managerial remedy to redress the existing inequity. The only solution is to reconstruct a high proportion of outlet structures. Potential causes of poor construction are many, including lack of involvement of the agency responsible for subsequent operation, lack of dialogue with water users, and lack of accountability built into the project framework.     

辐照土豆片热风干燥工艺的试验研究

将土豆经^60Coγ射线辐照预处理后进行热风干燥，与未辐照的对比结果表明：辐照预处理后切片土豆的失水过程仅为降速过程，干燥速率增加，辐照剂量增加，干燥速率提高，以辐照剂量、热风温度及土豆切片厚度为试验因素对干燥速率、VC含量，干制品外观质量和复水比等指标进行了二次正交旋转回归的较优的干燥工艺研究，同此获得二次回归的方法和较优的干燥工艺。     

木薯机械化种收装备研究现状与展望

木薯生产机械化程度低是制约我国木薯产业发展的瓶颈之一。种植机械和收获机械是木薯生产机械化发展中需要解决的两大技术难题。鉴于木薯生产机械化实现的迫切需要,重点阐述了木薯种植和收获现有的机械装备及其关键部件的研究进展,并对木薯种植机与收获机的进一步研究做出展望,以期为木薯产业发展提供参考。      

基于模型与CFD辅助的射流式混药器设计

射流式混药器结构简单,是实现药水分离的最简单有效的关键部件之一。针对混药器内部流体流动过程的复杂性,目前没有通用的理论模型来指导设计计算,没有直观的试验方法观察内部流动的问题。从非弹性介质的动量定理出发,推导出射流式混药器的特性方程,建立面积比、喷嘴与混合室距离的理论计算模型。采用多相流Mixture模型中的Zwart-Gerber-Belamri空化模型法,模拟分析混药器内部的相变过程。研究结果显示理论模型法、仿真法与试验方法的拟合优度大于0.98,证明研究方法的有效性。射流式混药器在低压力比下会发生空化现象,空化产生的气体使引射流量保持稳定,该特性能够满足稳定的混药比要求。设计面积比为1.31的混药器,混药比为0.049 8,混药比变异系数为1.23%。引射流体与工作流体在距离喷嘴出口40 mm处,其速度场已趋于一致,即混药器的混药均匀性可以满足实际需求。该研究为射流式混药器研究与应用提供技术支撑。     

土壤理化性质对吸附重金属镉的影响

以我国4种较典型的土壤为对象,采用批量平衡法针对土壤pH、有机质、粘粒质量分数等土壤理化性质对重金属镉吸附的影响进行了研究。研究结果表明,土壤中镉的吸附为快反应,24h内吸附均达到平衡。土壤对镉的吸附随土壤pH及有机质质量分数的增大而增大,决定镉吸附能力的不是粘粒的数量而是其粘粒矿物的组成。因此,针对我国不同地区土壤理化性质的特点可以通过改良其土壤理化性质使镉的吸附增大,减小其在土壤环境中的活性。     

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.     

The impact of design approximations on the operational performance of an irrigation scheme

A method is presented to analyse the impact of the selection of irrigation gates on operational performance of the Sungai Muda Irrigation Scheme in Malayisa. The method examines the discharge capacity of the water control gates at all levels in order to compare the specific water supply (the ratio of supply to command area) with the specific water demand which is the required hydromodule. The term hydromodule is the reciprocal of water duty and thus has units of litres/second/hectare. The greater the deviation between the two, the greater the potential loss of control during the operation of the scheme. The method is relatively simple but is more complex in this particular example as two hydromodules are used for the irrigation of basin rice; one for the presaturation period and one for the normal supply period. The most common cause of loss of water control is found to be provision of oversized turnout gates at the head of secondary and tertiary canals. Such design approximations enable more water to be used in those command areas thus leading to waste and to shortage of water in other areas. It is suggested that during design and rehabilitation of irrigation schemes, the operational implications of design approximations should be examined more carefully.     

时段划分对棉花作物水模型的影响与改进

为了改善时段划分对作物水模型模拟精度的影响，依据山西水利职业技术学院试验基地2006和2008年棉花田间试验资料，将棉花全生育期等间隔地划分为不同时段，用非线性优化方法求得了不同时段数条件下的作物水模型参数，分析研究了模型参数与时段数的关系，据此在作物水模型的水分敏感指数累积函数中引入了时段数，并与现有的作物水模型进行了比较。结果表明，引入时段数的作物水模型模拟产量的相对误差随时段数的增加而减小，当时段数大于11时，相对误差平均值和最大值分别减小到7%和15%以下，与现有的作物水模型比较，模拟精度有所提高，但参数个数未增加。该模型更多地反映了水分胁迫时间对作物产量影响的信息。