齿形尾缘小型轴流风扇的气动性能研究

小型轴流风扇是计算机散热的主要部件,其通风量和噪声等会直接影响计算机的正常运行和寿命,散热风扇的高性能和低噪声已成为计算机配置的关键问题之一.为此,设计了一种尾缘齿形化小型轴流风扇,该风扇齿形从叶根到叶顶由密到疏分布.并用流体力学软件对尾缘齿形化小型轴流风扇进行静态特性和声学性能模拟,对其进行流场和气动声学分析.结果表明:尾缘齿形化后对小型轴流风扇的静态特性基本没有影响,但在大流量下,效率比原型风扇低;对叶顶间隙和出口区某点的噪声监测发现叶顶间隙处的噪声基本没有变化,而出口区的噪声降低很多;尾缘齿形化后的转子表面的声功率级比原型风扇低,且低声功率级的区域比原型风扇大.     

两种传递路径不同振动信号的特征分析

针对齿轮故障诊断中使用的齿轮箱箱体振动加速度信号的传递环节多,信号存在非线性交叉耦合的情况,研究了使用从传动轴端测取的扭转振动信号进行诊断的方法.对比了这两种传递路径不同振动信号的双谱特征,箱体振动加速度信号的传递路径复杂,导致其频率成分复杂;而扭转振动信号的传递环节少,获取信号的路径直接,干扰因素减少,信号频率成分比较单纯,利用通常使用的谱分析,故障特征就可以清晰地提取出来,利于齿轮故障的准确判断.     

声电联合技术检测GIS局部放电的试验

利用超声波法和特高频法对GIS中的典型局部放电进行试验研究,包括GIS内部尖端放电、金属颗粒、高电位接触不良．建立GIS局部放电模拟检测平台,包括局部放电模拟系统、声电联合检测系统．在此基础上,得到不同类型局部放电超声波和特高频信号的发生发展规律,并给出信号的统计谱图．试验结果表明,声电联合检测技术检测局部放电信号的灵敏度高,信号统计谱图可以显示出典型故障模型的不同特征,GIS设备的局部放电检测可为GIS的状态检修提供可靠的数据．     

一种新型射流式液动锤的应用

液动脉冲旋转钻井技术是解决硬岩钻进难题最有效的方法之一,近年来再次成为各国钻井专家广泛关注的热点。液动冲击器应用于石油钻井具有大幅度提高地层钻井效率,降低钻井成本;减少井眼偏斜,提高钻井质量;减弱钻柱振动,避免钻柱的蹩跳现象等优点。从YD-1型新型射流式液动锤结构及工作原理、内部活塞冲锤运动、现场试验等方面进行分析研究,进一步说明该新型射流式液动冲击器在提高钻井速度、降低钻井成本、延长钻头使用寿命等方面具有重要作用。     

遗传算法工具箱在半主动-TMD参数优化中的应用

提出一种新型的结构振动控制变频TMD半主动控制系统,采用遗传算法工具箱分析了结构的动力放大系数,证实了其对结构振动控制的可行性和有效性。结果表明,单个变频-TMD作为一种半主动驱动器能有效降低结构反应,与传统TMD相比,具有更大的减振频带宽度,而且效果显著。     

非线性体系动力可靠性分析的等效Duffing体系法

等效线性化法是非线性结构体系的随机反应分析最常用的方法,但使用等效线性化法给出的反应结果进行结构动力可靠性分析会带来很大的误差.将一般非线性体系通过均方最小误差原则等效为Duffing非线性体系来进行结构动力可靠性分析.Duffing非线性体系可以通过FPK方程求得其稳态精确解析解,所以使用该等效非线性法进行结构动力可靠性分析不仅计算上方便可行而且精度较高.算例分析表明了等效非线性法分析结果可靠,且比等效线性化法的计算精度有明显提高.     

The vibration discomfort of standing people: evaluation of multi-axis vibration

Few studies have investigated discomfort caused by multi-axis vibration and none has explored methods of predicting the discomfort of standing people from simultaneous fore-and-aft, lateral and vertical vibration of a floor. Using the method of magnitude estimation, 16 subjects estimated their discomfort caused by dual-axis and tri-axial motions (octave-bands centred on either 1 or 4 Hz with various magnitudes in the fore-and-aft, lateral and vertical directions) and the discomfort caused by single-axis motions. The method of predicting discomfort assumed in current standards (square-root of the sums of squares of the three components weighted according to their individual contributions to discomfort) provided reasonable predictions of the discomfort caused by multi-axis vibration. Improved predictions can be obtained for specific stimuli, but no single simple method will provide accurate predictions for all stimuli because the rate of growth of discomfort with increasing magnitude of vibration depends on the frequency and direction of vibration.     

An optimal sampling approach to modelling whole-body vibration exposure in all-terrain vehicle driving

Abstract

Exposure to whole-body vibration (WBV) presents an occupational health risk and several safety standards obligate to measure WBV. The high cost of direct measurements in large epidemiological studies raises the question of the optimal sampling for estimating WBV exposures given by a large variation in exposure levels in real worksites. This paper presents a new approach to addressing this problem. A daily exposure to WBV was recorded for 9–24 days among 48 all-terrain vehicle drivers. Four data-sets based on root mean squared recordings were obtained from the measurement. The data were modelled using semi-variogram with spectrum analysis and the optimal sampling scheme was derived. The optimum sampling period was 140 min apart. The result was verified and validated in terms of its accuracy and statistical power. Recordings of two to three hours are probably needed to get a sufficiently unbiased daily WBV exposure estimate in real worksites. The developed model is general enough that is applicable to other cumulative exposures or biosignals.

Practitioner Summary: Exposure to whole-body vibration (WBV) presents an occupational health risk and safety standards obligate to measure WBV. However, direct measurements can be expensive. This paper presents a new approach to addressing this problem. The developed model is general enough that is applicable to other cumulative exposures or biosignals.     

Sextic spline solution of variable coefficient fourth-order parabolic equations

We report new three-level implicit methods of O(k ²+h ⁴) and O(k ⁴+h ⁴) for the numerical solution of fourth-order non-homogeneous parabolic partial differential equation with variable coefficients. We use sextic spline in space and finite difference in time directions. Sextic spline function relations are derived by using off-step points. The linear stability of the presented method is investigated. We solve test problems numerically to validate the derived methods. Numerical comparison with other existence methods shows the superiority of our presented scheme.     

五味子木脂素超声循环提取工艺条件的优化

采用超声循环提取的方法从五味子中提取五味子醇甲等木脂素类有效成分,考察溶剂、超声时间、超声功率、液固比和温度对提取工艺的影响．结果表明采用85％的乙醇作为提取溶剂,在单因素实验的基础上通过正交实验得出最佳工艺条件：超声功率500W,超声时间10min,温度30℃,液固比20,五味子木脂素提取率达到80．84％．