改进相关系数法在介质损耗角测量中的应用研究

针对相关系数法计算介质损耗角时,谐波和直流分量对所测量值的计算结果影响较大的问题,提出了先对信号进行陷波处理,再用相关系数法计算介质损耗角的方法。仿真结果表明,该方法计算介质损耗角时的误差,较单独使用相关系数法时减少18%以上,克服了谐波及直流分量的影响,提高了相关系数法测量介质损耗角的精度。该改进方法测量介质损耗角更加准确,为绝缘在线监测系统测量电容型设备介质损耗角提供了科学准确的测量方法。     

发动机尾气射流特性研究

利用高速摄影仪实时拍摄发动机尾气的射流运动过程,通过Im age-Pro6.3专业图像处理软件,选择气体射流顶点为研究对象,根据自由射流理论,得到发动机尾气贯穿距离、射流锥角、射流速度随射流时间变化的规律。结果表明:尾气射流分为两个阶段,射流起始段和射流主体段。当发动机转速一定时,在整个射流过程中,射流贯穿距离随射流时间的增加而增加,射流锥角基本保持不变,射流速度随射流时间的增加而减小;当发动机转速提高时,射流贯穿距离、射流速度均有所减小,而射流锥角增大。在此基础上,确定了射流贯穿距离与射流速度之间的数学模型。     

滴灌条件下积盐范围内混种耐盐草及盐分变化趋势的研究

以pH=7.9的水作为灌溉水源,土壤含水率、土壤密度及滴头流量不同的条件下,对土壤湿润体的变化过程进行试验,确定湿润峰及积盐范围,在积盐范围内混种盐角草和猪毛菜。测定土壤酸碱度及易溶盐离子总量的减少量,并积盐范围内混种的盐角草和猪毛菜与普通土壤中栽培的盐角草和猪毛菜的盐含量进行对比。结果表明,盐角草吸走部分Na＋、Cl...     

DETERMINATION OF T1 RELAXATION TIME OF NORMAL EQUINE TENDONS USING MAGIC ANGLE MAGNETIC RESONANCE IMAGING

Seven isolated equine front limbs were used to establish the normal T1 relaxation time of equine superficial digital flexor tendon (SDFT), deep digital flexor tendon (DDFT), and suspensory ligament (SL) using magic angle magnetic resonance (MR) imaging. MR imaging of the metacarpi was performed with the limbs positioned at 55° (the magic angle) relative to the main magnetic field. Transverse spin‐echo proton density and inversion recovery images were acquired. T1 relaxation time was calculated based on ratios of signal intensity determined from the different pulse sequences. T1 relaxation times for SDFT, DDFT, and SL were 288 (±17), 244 (±14), and 349 (±16) ms, respectively. The difference in T1 values between SDFT, DDFT, and SL was statistically significant. T1 values of equine tendons can be determined with magic angle imaging on a clinical MR system using <10 min total scan time. The knowledge of the normal range of T1 values may be useful to identify horses with chronic tendinopathy, where based on the human literature, an increased T1 value may be expected.     

利用OWRK法预测桃叶表面润湿性能的研究

对桃叶表面润湿性能的预测方法进行了研究。应用OWRK法对不同生长期桃叶的近轴面、远轴面的表面自由能及其分量进行了测定。无论近轴叶面还是远轴叶面,随着桃叶生长期的增长,均表现出表面自由能减小,润湿性能变差,极性分量所占比例下降,色散分量所占比例上升等特性。这些变化与前人对于桃叶表皮蜡的蜡质含量、组份含量变化的研究成果相一致。说明用OWRK法测定桃叶表面自由能及其分量所得结果可靠,可以较好地描述桃叶表面的润湿性能和能量特征。     

泥石流入汇主河淤积规律的水槽试验研究

以试验为基础,研究了泥石流入汇主河后淤积规律,主要探讨了淤积量及淤积分布问题。通过试验分析认为,泥石流入汇主河后的淤积量基本随流量比的增大而增大,就其淤积速率而言,有先增大后减小的变化规律。淤积量在流量比大约为0.5时出现峰值,在流量比为0.65时出现谷值,淤积量与流量比关系变化曲线以倾斜向上的直线为对称轴,呈倾斜向上的正弦波形。各工况下淤积范围基本不变,但试验中反映出,淤积范围有随交汇角增大而增大的趋势。     

基于转轮进口水流角的贯流水轮机最优工况应用

贯流式水轮机是农村小水电电网中的重要组成部分,其低水头、大流量的特点,易导致电站机组效率低下、出力降低。而贯流式水轮机运行中的最优运行问题很少引起学者关注,目前最优工况的研究仅仅局限于某点或线。该文从转轮水力损失的角度,理论上分析了影响贯流式水轮机效率的翼型阻力损失、端部损失与撞击损失,依据现场实际导叶与桨叶翼型,在定水头、定桨叶方式下,通过改变转轮进口水流角,对转轮进、出口速度三角形进行计算,从能量角度,进行工况优化,得到转轮10°工况下导叶在53.9°~58.8°的最优特性区域,效率可提高约3%~8%。利用数值仿真技术,对其工况做相应的数值仿真,并进行流场分析,在此基础上,进行真机试验,结果与理论分析相符,与数值仿真计算的误差小于2%,采用此方法对电站机组的全工况进行了计算,全工况范围内进行区域工况优化,得到转轮在7°~42°,导叶在0~78°的最优特性曲线,通过一段时间运行,数据显示机组的能量特性与稳定性效果比较理想。     

Effects of rake angle of chisel plough on soil cutting factors and power requirements: A computer simulation

A computer simulation was conducted to predict the effects of rake angle of a chisel plough and soil bulk density on angle of soil failure plane, rupture distance, width of side crescent, frictional, overburden, cohesion and adhesion soil cutting factors, draft forces and drawbar power requirements. The experimental work was carried out in two locations. Soil of the first location was sandy clay with the soil bulk densities of 1.75 and 1.70 g/cm³ for firm and loose soil conditions, respectively, with an angle of internal friction of 30° and a surface friction angle of 20°, cohesion of 2.5 kN/m² and adhesion of 1.2 kN/m². Soil of the second location was clay loam with the soil bulk densities of 1.65 and 1.50 g/cm³ for firm and loose soil conditions, respectively, with an angle of internal friction of 34° and a surface friction angle of 23°, cohesion of 2.4 kN/m² and adhesion of 1.14 kN/m². The prediction showed that the angle of failure plane found to decrease with the rake angle. The rupture distance decreased with the rake angle from 15° to 55° and then increased as the rake angle increased over 55°. The width of the side crescent increased as the rake angle increased and the maximum value and the minimum value were recorded at 75° and at 15°. Values of frictional and overburden factors decreased as rake angle increased. The maximum and minimum values were recorded at 15° and 75°, respectively. The values of cohesion factor increased as rake angle increased. The maximum value was recorded at rake angle of 75° and the minimum value was recorded at rake angle of 15°. Adhesion factor was found to change inversely with the rake angle from 15° to 55° and then to change directly with the rake angle over 55°. The draft force decreased with the rake angle and reached its minimum value at 45° rake angle. Over 45°, the draft force increased and reached its maximum value at 75° rake angle. The draft increased with soil bulk density. The power required for moving the plough recorded the maximum value at rake angle of 15°, while the minimum value was recorded at 55° rake angle. The values of power increased with decrease of soil bulk density. The predicted values demonstrated some deviations from the experimental values of the draft force and the drawbar power.     

Effect of soil drying on mucilage exudation and its water repellency: a new method to collect mucilage

Despite the importance of mucilage for soil–plant relations, little is known about the effect of soil drying on mucilage exudation. We introduce a method to collect mucilage from maize growing in wet and dry soils. Mucilage was collected from brace roots. The amount of mucilage exuded did not change with soil water content and transpiration rate. Mucilage exuded in dry soils had a higher degree of hydrophobicity, suggesting that the wetting properties of mucilage change in response to soil drying.     

除草用四足机器人稳定性的判定与分析

针对除草用四足机器人在不规则农田地面行走稳定性难以评定的问题,在力–角稳定性度量法的基础上,提出了三棱锥法,根据对其角点倾翻角和轴线倾翻角的推导,得到用最小稳定角作稳定性的评判标准。引入倾翻性能系数综合评价四足机器人的静态和动态稳定性,并通过数值模拟,讨论在不规则农田里的地面倾角、外载荷及外力矩对机器人稳定性的影响。使用由舵机驱动的8自由度,尺寸为170 mm×130 mm×140 mm的机器人物理样机在0°~45°的不规则玉米地上进行试验,测量最小稳定角。结果表明:合外力与地面倾角对机器人稳定性影响显著,地面倾角对其影响接近线性单调,试验所测最小稳定角度值与预测结果相比,平均相对误差为9.46%,相关系数为0.979 6。