Modelling droplet motion and interfacial tension in filters collecting liquid aerosols

Extensive experimental investigations have shown some of the differences between the behaviours of the barrel and the clamshell shapes of droplets on filter fibres in flow fields. Realistic flow velocities (such as those used in many industrial filter systems) were utilised. The forces acting are air drag, interfacial tension and gravity. The properties of the interfacial restoring force are modelled, and show agreement with the experimental results, at least in the linear extension region before the onset of oscillatory behaviour of the droplets (induced by instability of the flow field). The model for the oscillatory behaviour is explored, and the natural frequencies of oscillation in the radial and transverse directions are shown to be the same, for the barrel shape. The clamshell shape also has the same natural frequencies, but they are different to those of the barrel shape. The coupling of the radial and transverse oscillation modes is explored for both the barrel and clamshell shape. Some contact angle results are given, both without airflow acting on the droplet and with increasing airflow.     

On the determination of the steady film profile for a non-Newtonian thin droplet

A shooting method is used to determine a solution to a third-order ODE modeling the steady profile of a non-Newtonian thin droplet. We compare a direct approach to an iterative approach using a secant method. We obtain a nonlinear relationship between the contact angle ? and the position of the contact line r. From this nonlinear relationship we use curve fitting to obtain an empirical law of the form tan?∝r^f(k) where k is the power law coefficient and f is a nonlinear function of k.     

求解最小闭包球问题改进的SMO-型算法

研究n维空间中m个点的最小闭包球(MEB)问题。通过结合确定并删除内部点的技术到序列最小最优化(SMO)方法中,提出一种近似求解MEB问题的改进的SMO-型算法。证明了该算法具有线性收敛性。数值结果表明对于一些mn的大规模数据集,改进的算法与原算法相比速度可以提高10倍以上。尤其,当n等于100且m等于100000时,改进的SMO-型算法仅需执行8s。此外,对于n等于10000且m等于1000的大规模数据集,改进的算法也仅需执行150s。     

Sensitivity analysis of important parameters affecting contact pressure between a respirator and a headform

Respirator comfort and fit are two important parameters for respirator design, usage, and standard development. The contact pressure (as measured between a respirator and the wearer) plays an important role in comfort and fit. This work attempts to investigate the contact mechanism and factors that affect the contact pressure. This paper focuses on mechanical factors such as strap tension, strap orientation, strap location, friction, and seal material. A finite element (FE) model-based method was developed to assess the contact pressure. The FE models for both the headform and the respirator have multiple layers. The headform is a medium size headform developed by the National Institute for Occupational Safety and Health (NIOSH) and the respirator is an MSA Affinity Ultra respirator. The results show that the positive Z directional force of strap tension that forces the respirator to move towards the headform is the most important parameter for measuring pressure distribution. Other factors such as strap orientation, friction, strap location, and softness of the seal material were found to affect the contact pressure distribution in this study. Strap orientation and friction coefficient have no significant effect on maximum pressure and maximum shear stress. The dispersive strap location increased the contact pressure on the nose-bridge area of the wearer, while concentrated location had no considerable effect on contact pressure. A softer seal material causes larger deformations and transfers the location of the maximum pressure from the nose-bridge to the tip of the nose.

Relevance to industry

This study investigates the effect of important parameters on contact pressure between a respirator and a headform. The sensitivity analysis can provide insights of the interaction between a respirator and a headform. The findings are critical to respirator designers, users, and standard developers to ensure maximal respirator fit and comfort.     

SB70变频器、自整角机与角位移变送器在矿用提升机上的应用

本文介绍了传统的绕线式电动机转子串电阻调速方式提升机。结合该矿井提升机的实际条件,采用变频器、自整角机和角位变送器,对其进行改造以实现变频无级调速。在改造时保留原来的工频系统作为备用,并保持原有的操作装置和操作习惯。     

测定外延层电阻率的面接触方法研究

评论了美国科学家C.C. Allen等于1966年发表的“测定外延层电阻率的点接触方法”之论文的局限性,从而提出了本方法。本方法从理论上解一维Poisson方程并与C.C。Allen法的公式相比较,获得某些公式。文中导出了面接触方法雪崩击穿电压V_(Ba)~∞(V)及点接触方法雪崩击穿电压V_(Bp)~∞(V)的比值为V_(Ba)~∞=0.456;同时还导出了点接触方法外延层耗尽层宽度为t_(min p)(μm)和面接触方法外延层耗尽层宽度t_(mina(μm)的比值为t_(minp)/t_(mina)=2.565。在实践上,为证实两种模型的功能,利用两种探针进行了对比测试。一种是通常被采用的点接触锇尖探针:另一种是利用φ0.8±0.1mm的银针,在银针顶上吸上φ0.4±0.1mm的汞球,以实现面接触。理论和实验吻合良好。     

Effects of cricket ball colour and illuminance levels on catching behaviour in professional cricketers

In recent years there have been many alterations to equipment and technology in professional cricket, including the introduction of white balls during day — night matches. In the present study simulated slip-catching performance and movement initiation time were examined in professional cricketers when ball colour and illuminance levels differed. Five male professional cricketers (mean age: 27.3 ± 1.4 years) volunteered to catch a total of 60 cricket balls, 20 (10 red and 10 white) under each of three illuminance levels (571, 1143 and 1714 lux). Balls were projected from a ball machine at 20 m s^?1 (45 mph) over a distance of 8.4 m, to the subject's dominant side. Catching performance was measured using an established catching scale. Movement initiation times for each hand were also calculated for each trial using a motion-analysis system. Data were submitted to separate two-way (ball colour [2] × illuminance level [3]) repeated measures analysis of variance. No significant effects were obtained for ball colour or illuminance levels for either catching performance or movement initiation time. Neither ball colour nor light level (within the range tested) affected slip-catching performance and movement initiation times in professional cricketers. Therefore it was concluded that the changes made to ball colour and light conditions in professional cricket were not detrimental to catching performance.     

Influence of particle elasticity in shear testers

Two dimensional simulations of non-cohesive granular matter in a biaxial shear tester are discussed. The effect of particle elasticity on the mechanical behavior is investigated using two complementary distinct element methods (DEM): Soft particle molecular dynamics simulations (Particle Flow Code, PFC) for elastic particles and contact dynamics simulations (CD) for the limit of perfectly rigid particles. As soon as the system dilates to form shear bands, it relaxes the elastic strains so that one finds the same stresses for rigid respectively elastic particles in steady state flow. The principal stresses in steady state flow are determined. They are proportional to each other, giving rise to an effective macroscopic friction coefficient which is about 10% smaller than the microscopic friction coefficient between the grains.     

基于接触的水下夹桩器压块齿非线性有限元分析

水下夹桩器是一种广泛应用于海洋石油平台建设的液压夹具。基于扩展的拉格朗日算法,使用ANSYS软件对钢桩和夹桩器压块齿的接触问题进行了数值模拟受力分析,获得压块齿实际工况下的接触压力及其挤压变形等结果。并将该结果与理论计算结果进行了比较,计算结果满足工程要求。分析结果显示,将有限元接触分析技术应用于水下夹桩器压块齿的设计是一种有效的方法,为水下夹桩器压块齿结构进一步改进,提供了理论依据。