拖拉机自动转向系统设计研究

在对自动转向系统研究方案进行详细论证的基础上,提出步进电机输出轴固定有摩擦装置,驱动拖拉机转向盘转向控制系统。该转向系统由上位机(笔记本电脑)、下位机(转向控制器)、步进电机、步进电机驱动器、角位移传感器、摩擦轮等装置组成。系统工作时,上位机调出预存的期望路径与定位传感器接收的当前位置信号进行比较,得到期望路径相对于当前位置的偏差信号,将偏差信号发送到下位机(转向控制器),通过控制算法计算得到步进电机转向和转速的控制信号从而执行转向,缩小偏差。     

植保机械用容积式泵工作性能测试系统方案设计

植保机械用容积式泵主要用于经济林木和大田作物的药物喷洒,也可用于日常清洗及卫生消毒等领域。基于行业发展和检测能力提升的要求,研制具备较高自动化和智能化水平的工作性能测试系统已成为必然。容积式泵工作性能指标包括容积效率和总效率,是设计测试系统的依据和目的。测试系统主要设计内容包括具备空间多自由度的通用安装平台、高精度的质量法流量计量装置及采用传感器和计算机技术的控制系统,并给出测试系统中工作性能和拟合曲线数学模型。     

Temperature Effect Analysis for structural state Estimation of PC Cable stayed Bridge

The temperature effect was of crucial importance to estimate structural state of existing PC cable stayed bridges. Taking Yonghe Bridge in Tianjin as a case, the influence of temperature effect, including temperature change of whole bridge, difference in temperature of cable and main girder, temperature Gradient in the transverse section of main girder, and temperature gradient in the transverse section of tower, was analyzed on geometry of bridge deck, inclined displacement at the top of tower and cable force. Based on observation data of Yonghe Bridge during the First and Second maintenance, effectiveness of temperature effect analysis based on the present bride code in China was verified. And then a modifying method of temperature effect in structural state estimation was proposed. It was shown that the temperature change of whole bridge and the difference in temperature of cable and main girder were the main factors to inclined displacement at the top of tower, and the difference in temperature of cable and main girder was the main factor to the deflection of main girder. Although a small error between measured and theoretical results caused by the rigidity deterioration of old bridge, the temperature effect analysis based on the present bride code in China could be feasible in structural state estimation of existing PC cable stayed bridges and provided reference for maintenance and construction control.     

覆盖层厚度对闸室结构影响分析

在进行水闸设计时,覆盖层厚度的不同对闸室结构应力的计算结果有着很大影响。目前针对含有一定厚度覆盖层的地基,运用得较成熟的分析方法是弹性地基梁法,而在使用该方法时,又可由覆盖层厚度情况分为两种假定：“文克尔”型地基和“半无限大弹性体”型地基。对于这一应用范围的假定,其合理性目前还没有较系统的研究,本文结合ANSYS大型有限元分析软件,以福堂水电站2 #泄洪闸为基本计算结构,通过改变覆盖层厚度,建立多个有限元计算模型,根据计算结果分析覆盖层厚度变化后对闸室结构位移和应力的影响,从中找出规律,探讨弹性地基梁法对于应用范围假设的合理性,有限元分析所得的覆盖层主要影响范围较之传统的弹性地基梁法认为的范围要小,即传统的弹性地基梁法考虑得偏于保守。     

甘蔗收获机双向变量柱塞泵动态响应特性仿真

采用功率键合图法建立了甘蔗收获机双向变量柱塞泵的数学模型,对其中一些影响较小的非线性因素采用近线性化或忽略的方式进行处理,针对伊顿公司生产的1系列64变量泵,在Matlab/Simulink中通过改变变量泵的斜盘倾角来分析系统的流量、压力响应特性和换向特性,结果表明该双向变量泵系统具有良好的动态特性,能够满足4GZ-56型甘蔗收获机液压行走系统的动力性要求.     

Serum Amyloid A and Haptoglobin Concentrations and Liver Fat Percentage in Lactating Dairy Cows with Abomasal Displacement

Background: There has been increased interest in measuring the serum concentration of acute phase reactants such as serum amyloid A [SAA] and haptoglobin [haptoglobin] in periparturient cattle in order to provide a method for detecting the presence of inflammation or bacterial infection.
Objectives: To determine whether [SAA] and [haptoglobin] are increased in cows with displaced abomasum as compared with healthy dairy cows.
Animals: Fifty-four adult dairy cows in early lactation that had left displaced abomasum (LDA, n = 34), right displaced abomasum or abomasal volvulus (RDA/AV, n = 11), or were healthy on physical examination (control, n = 9).
Materials and Methods: Inflammatory diseases or bacterial infections such as mastitis, metritis, or pneumonia were not clinically apparent in any animal. Jugular venous blood was obtained from all cows and analyzed. Liver samples were obtained by biopsy in cattle with abomasal displacement.
Results: [SAA] and [haptoglobin] concentrations were increased in cows with LDA or RDA/AV as compared with healthy controls. Cows with displaced abomasum had mild to moderate hepatic lipidosis, based on liver fat percentages of 9.3 ± 5.3% (mean ± SD, LDA) and 10.8 ± 7.7% (RDA/AV). [SAA] and [haptoglobin] were most strongly associated with liver fat percentage, r _s=+0.55 ( P < .0001) and r _s=+0.42 ( P = .0041), respectively.
Conclusions and Clinical Importance: An increase in [SAA] or [haptoglobin] in postparturient dairy cows with LDA or RDA/AV is not specific for inflammation or bacterial infection. An increase in [SAA] or [haptoglobin] may indicate the presence of hepatic lipidosis in cattle with abomasal displacement.     

抗滑桩施工中边坡稳定系数分析

采用连续介质快速拉格朗日差分分析方法,结合强度折减技术,设定解不收敛的破坏标准,来探讨抗滑桩施工过程中桩孔开挖对边坡安全系数的影响这一三维问题.结合工程实例,模拟几种开挖顺序,结果表明,合理的施工方案对边坡扰动甚微;而随意开挖桩孔可能使边坡失稳,且失稳时的位移不大,破坏征兆不明显,破坏更加突然,应特别注意.分析施工等因素对边坡稳定系数的影响,特别是处在极限状态下的边坡,十分必要.     

用体积置换法测量木材渗透系数的计算与修正

从体积置换法测量木材气体渗透系数的基本原理出发,针对水柱上升和水柱下降两种体积置换法的测量装置,分析了体积置换法测量过程中气体渗透压强的变化,以及非稳态条件对体积置换法测量结果的影响．并详细推导了测量中的有关计算式和对非稳态测量补偿的修正因子．此外,运用动力学分析方法,论证了气体渗透压强在测量中的线性变化．其中关于测量的计算及其修正的关键设定的合理性,进一步从理论上阐明了体积置换法测量木材气体渗透系数的精确性．     

用像面全息散斑干涉法测裂纹尖端三维位移场

提出了显微像面全息和散斑干涉分离术测试三维位移的新方法，并应用该技术对裂纹尖端附近的位移及应变场进行了测试和计算。此外，还提出了一种再现像面全息的简单而有效的方法。     

西宁盆地黄土区荷载条件下植被护坡力学效应

为探讨西宁盆地黄土区边坡在荷载条件下植物根系对边坡稳定性的影响,该项研究以西宁盆地西山长岭沟流域为试验区,在自建边坡上种植草本植物垂穗披碱草(Elymus nutans)和灌木植物柠条锦鸡儿(Caragana korshinskii),通过在边坡坡顶施加载荷,边坡坡面布设位移计与土压力盒的方式,监测荷载条件下边坡坡面土体位移与土压力变化;在此基础上,对边坡植被根-土复合体开展剪切试验,分析荷载条件下边坡坡面不同位置处根-土复合体抗剪强度及其变化特征。试验结果表明:在坡顶荷载条件下,在边坡相同位置处的根-土复合体粘聚力c值均大于施加载荷前;3种植物边坡的根-土复合体粘聚力c值均大于相同条件的未种植素土边坡;在荷载条件下,组合植被边坡的坡面土体位移量显著小于单一植被边坡和素土边坡,组合植被边坡在竖直和水平方向的位移量与草本植被边坡相比减小1.60~1.77 mm,与灌木植被边坡相比减小3.78和4.11 mm,与素土边坡相比减小7.39和6.29 mm。研究结果对防治高寒半干旱地区坡面水土流失、浅层滑坡等地质灾害,具有参考价值和指导意义。