共查询到19条相似文献，搜索用时 243 毫秒
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基于悬垂平板偏转角的明渠流量估算模型及验证 总被引：2，自引：0，他引：2
针对平板量水设施缺乏适用性广泛的流量计算模型,该文从2个角度提出流量估算模型,首先分析绕轴自由旋转薄平板在水中的受力,根据升力简化为竖直方向静水压力设想,提出压力体计算假设,根据动量定理与力矩平衡公式得到了流量、角度、水深三者的理论关系式,通过U型和矩形渠道进行试验,验证假设合理性;根据闸孔出流流量公式针对矩形渠道建立闸孔出流半径验计算模型,拟合得出半径验流量公式。对于第1种模型,对于U型渠道,2种压力体假设均适用于流量计算,除流量小于10 L/s时,相对误差超过10%,其他均小于10%,流量大于17 L/s时误差均在5%左右;对于矩形渠道,仅假设1适用流量计算,假设2不成立,应用假设1计算压力体时,当流量较小(10 L/s左右)时的个别工况误差会偏大,大部分工况下计算误差均小于10%;对于闸孔出流计算模型,计算流量与实测流量之间最大误差不超过18%,大部分工况下计算误差在10%以下。当悬垂薄平板与明渠横断面等大时,来流量与偏转角度存在单值对应关系,角度随着来流量的增大而增大;同一流量下,板前后水深比、板前与下游水深比分别与偏转角度呈现出单独的函数关系,板前后水深比、板前与下游水深比随着平板偏转角度的增大而减小,但减小幅度变缓。对于不同流量,板前后水深比、板前与下游水深比随着角度增大而增大,但增大幅度变缓。研究可为灌区量水设施设计及应用提供新思路。 相似文献
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黄世伟 《广西农业生物科学》1990,(3)
本文利用可靠性理论对拖拉机零件磨损量数据进行统计分析,以及如何评价拖拉机磨损件的可靠性。论述了磨损量分布计算方法,便于在任意工作时间测定磨损量。在此基础上。又按容许磨损量从理论上来确定拖拉机零件在规定工作时间时的可靠度,以及在给定可靠度条件下的耐磨寿命,后者可用来作为拖拉机零件中进行维修或更新的依据。 相似文献
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农具质量对拖拉机悬挂农具系统振动特性的影响 总被引：10，自引：8，他引：2
为研究不同悬挂农具质量对拖拉机+悬挂农具系统振动特性的影响,该文以常发CF700型拖拉机(常发集团)为研究对象,用仿真和试验相结合的方法,建立了拖拉机+悬挂农具系统振动微分方程和仿真模型,仿真研究了拖拉机悬挂不同质量农具时拖拉机+悬挂农具系统振动特性,得到悬挂农具质量对拖拉机+悬挂农具系统垂向振动固有频率,俯仰振动固有频率,座椅安装处垂向振动加速度,俯仰振动角加速度,前、后轮动载系数的影响规律。研究结果表明,当悬挂农具质量从0增大到1 000 kg时,拖拉机+悬挂农具系统垂向振动固有频率从3.42逐渐减小到2.74 Hz,俯仰振动固有频率从3.07逐渐减小到1.78 Hz;当行驶速度相同时,座椅安装处垂向振动加速度和俯仰振动角加速度随悬挂农具质量的增大而减小,垂向振动加速度从2.73减小到1.02 m/s2,俯仰振动角加速度从2.56减小到0.82 rad/s2;前轮动载系数从0.09增大到0.33,随悬挂农具质量的增大而增大;速度较低时,后轮动载系数从0.06减小到0.03,随农具质量的增大略有减小,速度较高时,后轮动载系数随农具质量的增大逐渐增大,从0.06增大到0.17。该研究为拖拉机减振系统的设计提供了重要参考。 相似文献
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提高燃油经济性的拖拉机变速控制策略 总被引：4，自引：4，他引：0
为实现对液压机械无级变速拖拉机的最佳燃油经济性控制,分析发动机及液压机械无级变速器(hydro-mechanical continuously variable transmission, HMCVT)对拖拉机燃油经济性的影响,研究拖拉机最佳燃油经济性无级变速控制策略,该文针对发动机和HMCVT二元调节无级变速拖拉机,分析了发动机燃油消耗率和变速器的效率变化特性,提出了以发动机有效燃油消耗率g_e与HMCVT传动效率η_b的比值g_e/η_b为指标的最佳燃油经济性无级变速控制策略及拖拉机负载反馈控制原理。采用参数循环算法,求算出拖拉机在负载特性场内任意工作点下的最佳发动机转速、转矩、HMCVT的最佳变速比,保证了二元协同调节下拖拉机最佳燃油经济性变速控制策略的工程实现。计算结果显示:最佳变速比的分布呈现梯田状,平台部分的最佳变速比对应HMCVT纯机械传动时的工作状态,此时HMCVT处于传动效率最高点,并且在变速器传动效率高于0.92的工作区,最佳变速比的分布比例高达72.84%。相比较一元调节下分别以g_e、g_e/η_b为指标、二元调节下以g_e为指标的3种变速控制策略,明显降低了拖拉机燃油消耗率。牵引功率范围内,当拖拉机在某一目标车速下稳定工作时,在基于g_e/η_b最小化的二元调节变速控制策略调控下,拖拉机更可能在较低油耗状态下工作。表明以g_e/η_b为指标的二元调节拖拉机最佳燃油经济性变速控制策略能够提高拖拉机在任意工况下的燃油经济性。 相似文献
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该文旨在优化太阳能膜蒸馏淡化水系统运行过程。采用试验手段确定了该系统的最佳运行工况,测试了最佳工况下该系统的运行效果,说明了系统运行过程的电力平衡情况。测试结果表明:呼和浩特地区该系统光热部分最佳循环流量为150 L/h;光伏光热系统以连续跟踪方式运行;热工质加热过程控制方法为,当辐照度低于500 W/m~2时仅开启光伏发电系统加热热工质,当辐照度介于500~700 W/m~2时采用光伏光热互补方式加热热工质,当辐照度大于700 W/m~2时仅开启光热系统加热热工质;该系统于最佳工况运行时平均膜通量为14.92 kg/(m~2·h),且系统可维持电力平衡;该系统于优化工况下运行时7组膜组件串联即可满足1个4口之家的饮水需求。系统于优化工况下运行,单位产水量所需的膜面积为0.067 m~2。该研究可为膜蒸馏淡化水系统应用研究提供一定参考。 相似文献
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以能值理论方法为手段,从资源的投入和输出结构角度,对广东省惠州市惠阳区典型水稻种植户的耕牛和小型拖拉机这两种典型的农业驱动力产出系统的转化与生产效率,环境负载和可持续性进行比较分析与评价。研究表明：耕牛系统在单位面积水稻田上消耗的不可更新资源量是拖拉机系统的4.57倍;人力能值消耗是拖拉机系统的6.14倍。相对于拖拉机动力,耕牛产出动力处于较低的能量等级,其环境负载率(ELR)仅是拖拉机系统的24%,可持续能值指标(ESI)是拖拉机系统的4.25倍,但有巨大的优化空间和可能。而广东小型拖拉机系统产出驱动力的使用效率则稍高于典型65 kW拖拉机系统。从提高能值效率角度分析,减少耕牛系统生产过程中过多的人力投入,着力提高耕牛系统产出驱动力的利用效率比发展小型拖拉机系统更有潜力。生产过程中的人力投入和使用过程中的维护投入是农机驱动力产出系统不可忽视的能值投入项。 相似文献
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为了实现对拖拉机多段液压机械无级变速传动(hydro-mechanical continuously variable transmission,HMCVT)在任意稳定行驶速度和许可牵引负载下经济性最佳的控制,该文对拖拉机经济性最佳的无级变速规律进行了研究。根据拖拉机能量传递的特点,考虑HMCVT在不同传动比下存在效率差异的特征,把研究拖拉机的经济性最佳转化为对整车效率最大的研究。在分析整机传动系统效率特性的基础上,针对效率最大的目标函数和约束条件,求解了整车效率数值,结果表明在任意目标车速和牵引负载下,优化后拖拉机整车效率在35%~40%之间,并得出了效率最大时HMCVT最佳传动比、发动机转速和转矩,确定了基于整车效率最大的拖拉机HMCVT传动变速原理。研究表明:基于整车效率最大化原则能够实现拖拉机在任意车速和牵引负载下的整车经济性最佳,根据整车效率最大化确定的拖拉机多段HMCVT经济性最佳无级变速规律,为下一步制定装备多段HMCVT的拖拉机的经济性最佳控制策略提供参考。 相似文献
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The results presented are from field studies in which soil compaction was measured under tractors working with different wheel loads and levels of wheel-slip. Wheelslip proved to be more important in causing compaction than additional wheel loading, and this effect was more pronounced for more powerful tractors. In most agricultural circumstances the aim is to secure the best compromise between weight and slip as alternative means of achieving greater work output from tractors. The results indicate that in situations where there is a need to avoid compaction, particular attention should be given to providing sufficient wheel loading and the possibility of moving faster to take up more power at lower slip. For the range of soil moistures encountered sinkage was the most convenient and satisfactory method of assessing total reduction in porosity, and differentiated between treatments better than any of the other methods (see below) apart from water-entry rates. Measurement of soil density at three levels to 15 cm depth accounted for less than 50 per cent of the loss of porosity estimated from sinkage and the method did not detect differences due to treatment. Shear strength measured at one depth (3.5 cm) differentiated between treatments, but penetration resistance at 7.5 cm did not. Water-entry rates sensitively detected treatment differences but the method was too time-consuming for comparison of all treatments. The efficiency of traction of four- and two-wheel-drive tractors was measured at intervals during the winter on a clay loam and the results related to surface moisture contents. After a steep reduction in efficiency, when the soil returned to field capacity, subsequent changes in efficiency were small. 相似文献
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Many used tractors that are imported from Japan are adding to the current national inventory in the U.S. and Canada of farm tractors that lack a rollover protective structure (ROPS). Gray-market tractors are built for use by the manufacturer for a certain country but are imported against the manufacture's wishes to a second country for use there, usually as a used tractor. Gray-market tractors may lack ROPS and seatbelts, depending on the date of manufacturer. The objective of this investigation is to describe the gray market for tractors imported from Japan into the U.S. and the policy implications regarding the hazards associated with these imports. Operator manuals and warning labels are typically not written in English. Foreign manufacturers that market tractors in the U.S. have established a variety of disincentives for the importation of gray-market tractors, including issuing warnings, not servicing or providing parts for these tractors, and banning their importation through actions by the U.S. International Trade Commission. Nonetheless, a U.S. market has developed that imports and provides services and parts for gray-market tractors, and some companies provide certified ROPS on the tractors that they sell. A product safety perspective and related policies are presented as an approach to ensuring that these imports are equipped with ROPS and seatbelts. 相似文献
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在拖拉机上使用电控机械式自动变速器(AMT)很有必要。该文首先分析了拖拉机的换档特性，根据需求特性场与供应特性场的关系，确定出拖拉机AMT的换档方法；然后根据驱动轮滑转率数学模型和发动机的能量方程，以及拖拉机理论计算基本公式，推导出与发动机不同油门位置相应的拖拉机驱动力Fq与车速Va的关系，从而建立了动力性换档的数学模型。将不同油门下相邻两档Fq与Va曲线的交点连接，得到对应的升档曲线；最后由试验数据，采用计算机编程计算，对东方红-1302R履带拖拉机的换档规律进行了实例分析。这些为拖拉机AMT的设计与研究提供了理论依据，为提高我国拖拉机的技术含量和国际竞争力作出了有益的探索。 相似文献
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为深入了解拖拉机实际作业的能效情况,该研究提出基于实际作业工况的拖拉机能效评价方法,对拖拉机整体能效进行全面度量。基于距离最短分区原理,通过K-means聚类与成对比较矩阵方法进行拖拉机发动机常用工况点提取;通过对186台162 kW的拖拉机能效分析,提出拖拉机能效等级划分标准,确定能效限值和各级能效比限值,并对不同作业环节的平均能效进行分析。研究结果显示:拖拉机发动机实际8工况点和ISO稳态8工况点区别较大;不同拖拉机能效差异较大,50%的拖拉机能效值分布在3.20～3.65 (kW·h)/kg区间;162 kW拖拉机实际能效合格限值为3.07 (kW·h)/kg;拖拉机不同作业环节的平均能效值差异大,旋耕作业的平均能效值最高,行走模式最低。研究结果可为发动机节能减排技术升级提供数据基础,也可为农机节能考核、与绿色化作业水平挂钩的应用补贴方法研究等提供参考。 相似文献
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Sanderson WT Madsen MD Rautiainen R Kelly KM Zwerling C Taylor CD Reynolds SJ Stromquist AM Burmeister LF Merchant JA 《Journal of agricultural safety and health》2006,12(1):71-81
Agriculture remains one of the most hazardous industries in the U.S., with tractor overturns producing the greatest number of agricultural machinery-related fatalities. Rollover protective structures (ROPS) and seatbelts effectively reduce tractor overturn deaths. However, a large proportion of tractors in use in American agriculture are older tractors without ROPS and seatbelts. This article describes the tractor-related responses from participants in a population-based study conducted in Keokuk County, Iowa. This study was designed to measure rural and agricultural adverse health and injury outcomes and their respective risk factors. Questionnaires were partially developed from well-documented national surveys. Questions about agricultural machinery use, presence of safety equipment on the machinery, work practices, and attitudes about farm safety were included. Study participants on farms who owned tractors had an average of 3.1 tractors with an average age of 27 years. Only 39% of the 665 tractors had ROPS. Tractor age was associated with the presence of ROPS; 84% of tractors manufactured after 1984 were ROPS-equipped, whereas only 3% of tractors manufactured before 1960 were ROPS-equipped. ROPS-equipped tractors were significantly more common on larger farms and households with higher income. Only 4% of the farmers reported that their tractors had seatbelts and they wore them when operating their tractors. The results of this study support the findings of other studies, which indicate that many older tractors without ROPS and seatbelts remain in use in American agriculture. Until a dramatic reduction in the number of tractors in the U.S. operated without ROPS and seatbelts is achieved, the annual incidence of 120 to 130 deaths associated with tractor overturns will persist. 相似文献
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Spielholz P Sjostrom T Clark RE Adams DA 《Journal of agricultural safety and health》2006,12(4):325-333
A survey of farms in Washington State was conducted to determine tractor characteristics and the presence of rollover protective structures (ROPS) in a state with more inclusive rules on tractor retrofitting than federal regulations. A total of 544 valid surveys were completed from a proportional random sample across different types of farms. Responders indicated that 58% of tractors overall were equipped with ROPS, and 42% of the tractors without ROPS were exempt from the state rules. Seatbelts on tractors equipped with ROPS were reportedly used "sometimes" or more 30% of the time, and 17% of these tractors had no seatbelt installed. Tractors used for row crop farming were significantly more likely to be equipped with ROPS than those used for tree, vine, or hops farming. Older tractors were used for fewer hours, were less likely to be ROPS-equipped, and were less likely to be operated while wearing a seatbelt. The results were consistent with a positive effect of the Washington State ROPS requirements, demonstrated by the increased percentage of ROPS-equipped pre-1976 tractors, as compared to other states, and by the difference between ROPS-equipped tractors in exempt and non-exempt types of farming. The results point to the need for prevention activities to increase seatbelt use on ROPS-equipped tractors, and for further development of practical protection for tractors operating under overhead obstacles. 相似文献
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柴油机作为农用运输车、汽车及拖拉机配套动力时,其使用工况有区别,因而对柴油机一些特性点—负荷率、标定功率点、转矩适应性系数、工作稳定性、稳定调速率等的选取有所不同,分析指出应在研究中予以注意。 相似文献