角钢热连轧过程的温度场有限元分析

采用有限元软件MSC．Superform对角钢热连轧过程进行有限元模拟。介绍了模拟过程中的模型建立、材料参数、边界条件以及载荷的定义,分析了轧制过程中轧件温度场的分布和变化过程,分析结果对制定角钢热连轧过程的温度制度提供了有效参考。     

炉卷轧线轧辊磨床数控系统改造

轧辊数控磨床是炉卷轧机生产线的关键设备,在使用过程中出现了一些影响生产的问题,通过对不稳定因素进行分析研究,提出并实施了一系列改造方案,通过技术改造,解决了长期以来严重影响生产的几个问题。     

功勋轧机牌坊下横梁修复技术分析

文章对舞钢4200mm轧机牌坊下横梁磨损修复技术进行了分析,根据轧机使用要求和牌坊磨损具体情况,进行详细的技术分析,制定合理的加工工艺,恢复轧机牌坊的使用精度,使得项目得以保质保量完成。     

Evaluation of aerodynamic and rolling resistances in mountain-bike field conditions

Abstract

Aerodynamic and rolling resistances are the two major resistances that affect road cyclists on level ground. Because of reduced speeds and markedly different tyre-ground interactions, rolling resistance could be more influential in mountain biking than road cycling. The aims of this study were to quantify 1) aerodynamic resistance of mountain-bike cyclists in the seated position and 2) rolling resistances of two types of mountain-bike tyre (smooth and knobby) in three field surfaces (road, sand and grass) with two pressure inflations (200 and 400 kPa). Mountain-bike cyclists have an effective frontal area (product of projected frontal area and drag coefficient) of 0.357 ± 0.023 m², with the mean aerodynamic resistance representing 8–35% of the total resistance to cyclists' motion depending on the magnitude of the rolling resistance. The smooth tyre had 21 ± 15% less rolling resistance than the knobby tyre. Field surface and inflation pressure also affected rolling resistance. These results indicate that aerodynamic resistance influences mountain-biking performance, even with lower speeds than road cycling. Rolling resistance is increased in mountain biking by factors such as tyre type, surface condition and inflation pressure that may also alter performance.     

热轧机轧制时序控制方法的设计与实现

无论板带热轧机生产厚板还是薄板,其常规设计的轧制控制时序都直接影响生产线的作业率和产能的发挥,乃至影响企业的经济效益。本文介绍了一种可以实现快速出钢的板带热轧机轧制时序控制方法,使用该方法可以大幅提高板带热轧机的生产作业率,提高产能。     

重载铁路货车轴承突发性损伤类故障检测

重载的铁路货车滚动轴承极易出现损伤类故障,因故障的突发性使得振动信号具有非线性、非平稳的特性,且振动信号极易受非检测部位振动的干扰,而使得有效信号不易被提取,传统的基于傅里叶变换的检测方法无法有效将非平稳的振动信号中的干扰去除,造成最终的检测准确率不高的问题。为了提高检测准确率,提出基于小波包的检测方法,首先针对振动信号的非平稳特性采用小波滤波有效去除其中的干扰,然后通过最小二乘支持向量机提取出非平稳振动信号中的故障特征信号并完成故障检测。实验表明,这种方法能够有效去除振动信号中的干扰,并准确检测重载铁路货车上的滚动轴承损伤故障。     

板材热轧过程速度场与温度场的耦合数值解法

板材在国民经济各部门都有着广泛的用途.板材轧制是一个非常复杂的金属变形过程,主要体现在轧件变形区域的速度场与温度场之间的相互作用.为达到模拟轧制变形区真实速度场与温度场的目的,文章探讨了板材轧制过程速度场与温度场的二维耦合数值求解.做了如下工作:(1)分列咬入单元,实现耦合,并编程计算;(2)分析轧制变形区的温度场;(3)分析轧制力.     

基于时间序列的参数模型和Fisher判别分析的滚动轴承故障诊断方法

提出了基于时间序列参数模型和Fisher判别分析的滚动轴承故障诊断方法。该方法通过对轴承振动信号建立自回归模型,将自回归模型的特征参数作为特征向量,然后采用Fisher判别分析方法对轴承状态进行分类与识别,实验结果验证了所用方法的有效性。     

Dynamics of basketball-rim interactions

A dynamic model for motion of a basketball on the rim is derived. The model is used to investigate shot success sensitivity to initial conditions and to search for initial conditions that lead to long rim contact times. Nonlinear ordinary differential equations describe three components of ball angular velocity and contact point position on the toroidal rim. The model includes radial ball compliance and dissipation and contains three sub-models describing slipping contact, nonslipping contact and purely gravitational flight. Switching between the three sub-models depends on contact point velocity and friction forces. Equivalent radial stiffness and damping constants are estimated using experimental ball force-deflection hysteresis data. General initial conditions almost always involve slip of the ball on the rim. Bouncing on the rim can also occur. After contact it is possible for the ball to enter the rim with its centre passing significantly below the rim plane before rising and ultimately escaping. Exotic quasi-equilibrium periodic circular trajectories exist inside but below the rim plane, relying for their existence on a combination of centripetal force, friction and gyroscopic precession of radial spin about the contact point. Trajectories, and consequent ball capture or escape, are extremely sensitive to initial conditions, especially rim contact position and backspin angular velocity. Backspin aids capture on longrolling trajectories.     

玉米螟成虫羽化早期飞行能力研究

利用昆虫飞行磨测试玉米螟Ostrinia furnacalis成虫羽化早期1~4日龄在室温条件下的飞行能力,最终获得22头个体的飞行数据,其中最大累计飞行距离为5 952.06 m,最长累计飞行时间为7 279.55 s,平均飞行速度最大为1.23 m/s,最大飞行速度1.55 m/s,最久单次起飞飞行时间最大值为4 902.21 s,最远单次起飞平均速度最大值为1.28 m/s,最远单次起飞飞行距离最大值为2 895.92 m.统计分析结果表明：玉米螟羽化早期的雌雄虫在飞行距离、飞行时间、平均飞行速度、最大飞行速度、最久单次起飞所飞行的时间、最远单次起飞平均速度、最久单次起飞所飞行的距离等方面差异均不显著（P〉0.05）.