某矿井下粉尘浓度与矽肺发病关系调查及其容许浓度探讨

为考核某锡矿的防尘效果,我们对该矿井下1958～1979年的粉尘浓度与矽肺发病情况作了回顾性调查,在此基础上采用田凤调、符绍昌氏提出的研究制定粉尘容许浓度标准的直线回归分析法,对该矿井下22年来的粉尘资料及矽肺发病资料进行统计分析,为国家修改现行粉尘卫生标准提供参考数据。材料与方法     

Sliding mode robust fault-tolerant control for uncertain systems with time delay

Considering the modeling uncertainties and external disturbance, a kind of sliding mode robust H∞fault-tolerant control method for time delay system with actuator fault is proposed. The upper-bound of the uncertainties is considered as a known constant, while the upper-bound of the actuator fault is unknown. A sufficient condition for the existence of an integral sliding mode dynamics is given in terms of linear matrix inequality(LMI). A novel adaptive law is given to estimate the unknown upper-bound of faults. On this basis, a type of sliding mode robust H∞fault-tolerant control law is designed to guarantee the asymptotic stability and the H_∞ performance index of the system. Finally, the simulation on quad-rotor semi-physical platform demonstrates the reliability and validity of the method.     

基于Fluent的超声波流量计水流特性研究

超声波流量测量技术是一种先进的流体流量测量方法.文中对超声波流量计测量原理进行了分析,并推导出流量计算公式;采用Fluent软件对水流特性进行了数值模拟,分析了管内流体的流场分布、压力分布规律.模拟结果显示超声波接收端与发射端液流存在漩涡,入口段中心线与水平管道中心线的夹角对测量精度影响显著.模拟结果与实际相符,对流量计结构的优化设计具有一定的借鉴意义.