吊杆式拱架结构静力特性研究

以汤峪河渡槽为例,对新型吊杆式拱架结构的内力特性进行了全面分析,结果表明,该结构与下承式桁架拱比较,具有内力分布均匀且控制性内力显著减小,无需采用预应力措施,更便于采用分块吊装拼接工艺施工,是密实砂卵石基或岩基上修建大跨度渡槽的一种经济实用的新型模式。     

汤峪河渡槽吊杆式拱架支承结构抗震性能分析

汤峪河渡槽采用的吊杆式拱架支承结构是国内外水工渡槽及道路工程中首创的一种工程支承结构。以汤峪河渡槽为工程实例 ,运用当今普遍采用的振型分解反应谱法和 P11D平面静力计算程序 ,分析了这种结构形式的地震反应特性。结果表明 :(1)下弦杆分缝的处理方法有效地释放了地震力所引起的结构超静定内力 ;(2 )在头道梁的拱脚附近的截面上 ,地震内力与常规荷载内力叠加后产生了巨大的偏心 ,这给结构的配筋及混凝土抗裂性要求增加了一定难度 ,设计时应重视该处截面尺寸的拟定 ,可在该处加设梗胁结构 ,加强构造配筋。     

石拱桥拱脚开裂过程中的内力分析

采用空间梁单元对实际的石拱桥拱脚开裂现象进行了有限元模拟分析。随着开裂深度的变化，主拱圈中的内力进行重新分配，得出了不同开裂深度时主拱圈中的内力分布规律，对实际的各种受力状态和开裂过程中的内力进行了较精确的数值描述。当拱脚裂纹扩展时，拱脚截面上的弯矩明显减小，轴力明显增大，而其它截面上的弯矩增大，轴力也增大，截面上的内力值与开裂深度成非线性关系。     

某水库灌溉渡槽结构应力分析与配筋计算

根据某水库灌溉渡槽的结构特点,划分为纵向、横向平面结构进行计算,采用经典的结构力学方法细致详尽的分析了灌溉渡槽的内力情况,为灌溉渡槽的结构安全性评价提供了精确可靠的内力值和配筋计算,并为后续修复加固设计、施工等相关技术活动提供必要的基础数据。     

连续墙梁的应力分布规律

本文通过有限元分析 ,研究了多跨连续墙梁在竖向均布荷载作用下墙梁各点的应力分布规律 ,总结出多跨连续墙梁拉杆拱的受力模型 ,为连续墙梁内力计算和承载力计算打下良好的基础 ,而进一步制定规范建立可靠的理论依据。     

谈渠系建筑物——渡槽的修建技术

1常采用的的渡槽基本结构型式1.1型式Ⅰ：渡槽槽身既是输水结构,又是纵向的梁式（或拉杆）承重结构,属于这种型式的有简支式、双悬臂式、连续梁式、下承式桁架拱式。1.2型式Ⅱ：渡槽槽身置于拱式支承结构（包括实腹拱和     

考虑二阶弯矩效应的自由扭转圆曲梁静力分析

针对拱形温室结构在轴向风荷载作用下的受力变形及屋面荷载作用下平面外稳定问题,根据考虑曲梁的大位移特征及二阶弯矩效应,建立圆曲梁的弯矩平衡方程,结合其他平衡方程、几何方程、物理方程,获得非线性圆曲梁挠度和扭转角的控制方程,得到含系数的圆曲梁几何非线性位移、变形和内力模型,给出圆曲梁几何非线性位移及内力的计算方案。鉴于圆曲梁的受力变形与圆拱平面外失稳特征变形的相似性,在此研究的基础上,分析圆拱平面外失稳问题,给出圆拱平面外分岔失稳临界荷载的计算方法。分析结果表明:本研究得到的圆曲梁几何非线性静力分析模型,可用于拱形温室屋面结构的非线性受力分析及平面外分岔及极值点失稳计算。     

有无拉杆矩形渡槽槽身受力差异分析

渡槽是一种重要的水工结构,对农业灌溉和生产具有重要作用。准确分析其承受荷栽对内力分析乃至对后期配置钢筋和抗剪、抗裂验算具有重要作用。基于此,对有横拉杆和无横拉杆矩形渡槽槽身结构进行对比分析,分别对2种渡槽槽身人行道、侧墙、底板和横拉杆进行荷载分析和内力计算,以反映出有无拉杆矩形渡槽槽身受力差异,旨在为后期配置钢筋和抗剪、抗裂验算奠定基础,对工程设计具有参考价值。     

连拱活载内力的计算方法

一般多孔拱桥,应按连拱内力影响线布置荷载,计算拱中最大活载内力.本文提出任意多孔连拱内力影响线的计算公式和最大活载内力的计算方法.     

拉索预应力折线型立体桁架拱布索方案研究

针对折线型立体桁架拱结构，提出了4种拱平面内的布索方案，研究了4种方案下预应力拱结构的静力及稳定性能，分别从结构位移的减小、索初始预拉力值的高低、水平支反力的降幅、杆件内力分布的均匀性及结构稳定性的提高5个方面与未布索立体桁架拱作了综合对比.结果表明，按照桁架拱在极限荷载作用下的屈曲形态布置撑杆拉索能够最有效地改善拱的静力性能，提高其稳定极限承载力.另外，由对预应力桁架拱的失稳模态分析发现，拉索通过撑杆对结构施加预应力能更有效地约束结构的整体变形.     

小流域测流建筑物设计的初探

本文以河北省平山县树石小流域为例,详细介绍了小流域测流建筑物的设计方法和计算步骤。其中包括设计流量的计算,测流建筑物型式的选择和测流建筑物的设计计算,并且给出了确定流量的计算公式及水位-流量关系曲线。     

喷雾机喷杆拉力测量试验

针对某水旱两用喷杆喷雾机喷杆连接件断裂问题,开展喷雾机喷杆田间拉力测量试验.针对喷杆组件结构和受力特点,开发设计了喷杆拉力测量系统并进行静态标定.在田间设置喷雾机试验跑道,分别进行1.93、1.42、0.90 m/s 3种速度的喷杆拉力数据采集.结果表明,最大拉力随喷雾机速度的增大而增大.基于耿贝尔极值理论,对3种速度下的最大静态拉力进行推理,3种速度条件下最大拉力分别为1 000、700、500 N.对采集数据进行频谱分析,发现喷杆拉力信号主要是0～13 Hz以内的低频信号.     

无喉堰流量计算公式的理论推导

无喉堰量水槽因其量水精度高、结构简单、过水能力大、上游壅水低等诸多优点而成为最适合于农业灌区应用的量水建筑物。目前,利用无喉堰测量流量已经在部分农业灌区得到应用。但在调查中发现,利用无喉堰量水尚没有应用规范的计算公式,而且各种情况下出流对流量计量的影响尚未明确。为此,笔者对无喉堰自由出流和淹没出流2种状态的流量计算公式进行了理论推导给出了修正的经验公式。     

Estimating off-rate pesticide application errors resulting from agricultural sprayer turning movements

Pesticide application is an essential practice on many U.S. crop farms. Off-rate pesticide application errors may result from velocity differential across the spray boom while turning, pressure fluctuations across the spray boom, or changes in boom-to-canopy height due to undulating terrain. The sprayer path co-ordinates and the status (on or off) of each boom control section were recorded using the sprayer control console which provided map-based automatic boom section control. These data were collected for ten fields of varying shapes and sizes located in central Kentucky. In order to estimate potential errors resulting from sprayer turning movements, a method was developed to compare the differences in application areas between spray boom control sections. The area covered by the center boom control section was considered the “target rate area” and the difference in these areas and the areas covered by remaining control sections were compared to estimate application rate errors. The results of this analysis conducted with sprayer application files collected from ten fields, many containing impassable grassed waterways, indicated that a substantial portion of the fields (6.5–23.8%) could have received application in error by more than ±10% of the target rate. Off-rate application errors exceeding ±10% of the target rate for the study fields tended to increase as the average turning angles increased. The implication of this is that producers may be unintentionally applying at off-label rates in fields of varying shapes and sizes where turning movements are required.     

Three-dimensional numerical simulation of flow in trapezoidal cutthroat flumes based on FLOW-3D

To solve the common problem of flumes flow-measurement accuracy without sacrificing water head, a new type of trapezoidal cutthroat flume to measure the discharge in terminal trapezoidal channels is presented. Using the computational fluid dynamic method, three-dimensional flow fields in trapezoidal cutthroat flumes were simulated using the RNG k-ε three-dimensional turbulence model along with the TruVOF technique. Simulations were performed for 12 working conditions, with discharges up to 0.075 m³·s⁻¹ to determine hydraulic performance. Experimental data for the trapezoidal cutthroat flume in terminal trapezoidal channel were also obtained to validate the simulation results. Velocity distribution of the flume obtained from simulation analyses were compared with observed results based on time-averaged flow field and comparison yielded a solid agreement between results from the two methods, with relative error below 10%. The results indicated that the Froude number and the longitudinal average velocity increased along the convergence section and decreased in the divergent section. In the upper throat, the Froude number was less than 0.5, which meets the water measurement requirement, and the critical flow appeared near the throat section. The maximum water head loss of the trapezoidal cutthroat flume was less than 9% of the total head, compared to the rectangular cutthroat flume, and head loss of trapezoidal cutthroat flume was significantly less. Regression models developed for upstream depth versus discharge under different working conditions were satisfactory, with a relative error of less than 2.06%, which meets the common requirements of flow measurement in irrigation areas. It was concluded that trapezoidal cutthroat flumes can improve flow-measurement accuracy without sacrificing water head.     

Age and origin of carlsbad cavern and related caves from 40Ar/39Ar of alunite

40Ar/39Ar dating of fine-grained alunite that formed during cave genesis provides ages of formation for the Big Room level of Carlsbad Cavern [4.0 to 3.9 million years ago (Ma)], the upper level of Lechuguilla Cave (6.0 to 5.7 Ma), and three other hypogene caves (11.3 to 6.0 Ma) in the Guadalupe Mountains of New Mexico. Alunite ages increase and are strongly correlative with cave elevations, which indicates an 1100-meter decline in the water table, apparently related to tectonic uplift and tilting, from 11.3 Ma to the present. 40Ar/39Ar dating studies of the hypogene caves have the potential to help resolve late Cenozoic climatic, speleologic, and tectonic questions.     

河渠种树水流特性试验研究

河渠或沟道植树是利用生物措施来治理泥沙的一种有效方法，河渠或沟道植树又称为植物“柔性坝”。本研究通过室内水槽模型试验，探讨了植物“柔性坝”的布置方式、种植密度对河渠水流的影响。由实验得出，植物“柔性坝”可以起到阻缓水流、拦截泥沙的作用，并且植物“柔性坝”的种植密度和坝长不同，阻水作用亦不同。试验表明，坝长的阻水作用较坝的密度要大得多。     

Quantification of self-propelled sprayers turn compensation feature utilization and advantages during on-farm applications

Agricultural sprayers are utilized in applying pesticides to control pests and diseases in crops. The increase in machine size and a better control system have been associated with increased productivity, improved efficiency and minimized the impact of the chemical on the environment. However, wider booms may contribute to application error due to the difference in speed between the inner and outer boom section when applying in curvilinear passes. Field tests were conducted in three irregular shaped fields with varying terrain using a 36.6-m self-propelled sprayer with a turn compensation technology. The results showed that turning occurred near the grassed waterways, boundaries and end of headlands. The product was applied during turning to 19.0% of Field 1, 17.8% of Field 2 and 22.5% of Field 3. These could have been the percentage of field areas that may receive more or less product if the sprayer was not equipped with turn compensation technology. As expected, the speed difference between the inner and outer boom increases as the radius of turn decreases. The speed difference could translate to an under-application on the outer boom section where the speed is much faster and over-application on the inner boom section where the speed is slower. The application errors from such speed differential could vary from ??48.2 to +?1058.0%, depending on the turning radius. However, the pulse width modulation system implemented duty cycles based on turning speeds, which resulted to a 90.0% application rate uniformity across the field regardless of the travel path during operation.

     

不同植保机械施药对水稻病虫防治效果的研究

对自走式喷杆喷雾机、多旋翼植保飞行器、背负式机动弥雾机3种不同植保机械施药的作业效果及水稻病虫防治效果进行比较。结果表明,自走式喷杆喷雾机与植保飞行器工效远高于背负式机动弥雾机,是背负式机动弥雾机的6.7~10.0倍。且自走式喷杆喷雾机用工成本较低,每公顷24元,植保飞行器用工成本每公顷36元,是背负式机动弥雾机的1/5~1/3。多旋翼植保机飞行器喷药速度比自走式喷杆喷雾机快,但电池充电耗时较长。自走式喷杆喷雾机喷幅宽,喷雾均匀、用水量足,与多旋翼植保飞行器均适用于大面积推广,值得应用。多旋翼植保飞行器对水稻病害的防治效果较差,其用水量与病害控制效果有一定的关系,建议加大用水量或添加沉降剂使用。     

U型薄壳渡槽短壳槽身应力的三维模型光弹性试验研究

通过三维模型光弹性试验,研究了短壳槽身的应力状态。得到了分别在自重、半槽水、设计水、满槽水荷载及在自重与上述几种荷载共同作用下槽壳、端肋、横杆上的表面应力以及在设计水荷载下端肋的主拉应力轨迹线和在设计水与自重共同作用下槽壳表面的主拉应力等值线图详细结果。