磁悬浮转子真空计的研究历程

磁悬浮转子真空计被广泛应用于各个领域,在10^-4-1 Pa下具有相当高的精确度,以其优越的性能在其中占有重要地位,被广泛用于传递标准。然而,残余阻尼的存在严重影响了磁悬浮转子真空计的下限扩展,其中以涡流效应的影响最为显著,相对于涡流效应,测量产生的弛豫效应和科里奥利效应可以忽略不计。本文简要介绍了磁悬浮转子真空计的结构和原理,概述了其研究历程,重点阐述了残余阻尼和切向动量传递系数的相关研究,并分析并总结了一些重要因素对它们的影响。残余阻尼的相关研究主要从涡流效应、温度效应、弛豫效应、科里奥利效应和振动这几个方面进行了介绍;在切向动量传递系数方面上,主要说明了气体种类和压力对它的影响。最后提出了一些改进猜想及后续工作的研究方向。     

Design of high performance badminton shuttlecocks: virtual and rapid prototyping approach

In this paper, a framework utilising virtual and rapid prototyping to aid design of a shuttlecock skirt was proposed and implemented. A standard template for flow simulation on ANSYS® CFX was developed to predict the aerodynamic performance of the virtual prototypes, with focus on reduced simulation time and complexity. This forms the basis of the computer aided design model – computational fluid dynamics – performance evaluation loop in the proposed framework. Steady state flow simulation was conducted for three simple computer aided design models of shuttlecocks, with different gap dimensions on the skirt. Wind tunnel drag study of the models reproduced through rapid prototyping validated the simulation result. The proposed methodology can also be applied to the existing design process for integration of virtual and rapid prototyping to reduce the burden of design iteration.     

Electromyography applied to sport ergonomics

Abstract

The improvement of electromyographic (EMG) devices for the detection of electric potentials produced in voluntary complex movements and the evolution of methodological approaches to data acquisition and computerized analysis of patterns, are responsible for the increased applications of EMG in bioengineering, rehabilitation, sport and occupational biomechanics, physiology and zoology and to a lesser extent in ergonomics. This paper describes three different EMG applications related to a sport environment using three different EMG registration and data acquisition approaches.

The first study examined the relation between the swimming action in water and its simulation using training equipment on land. It was found that with respect to the mechanical aspects of dry-land equipment and to the biomechanical differences in the execution of the front crawl action on dry land and in water, based on EMG activity of the propulsion muscles, the best results were found when using devices with accommodating resistance. Recovery muscles were best imitated using isokinetics, but despite the greater effort on land, lower EMG activity was recorded than in water. It was generally observed that whenever the swimmer acted against a mechanical resistance an important pattern deviation was noted.

Second, a study to determine the influence of ski materials on the EMG muscle activity of skiers showed systematic differences between the use of racing, soft and compact skis. The results supported the idea that the soft ski should be more highly recommended than the compact or racing ski for both general and competive use.

Finally, in a third study we found that there was a very high degree of similarity in the pattern and intensity of muscle activity in both free swimming and swimming against a mechanical resistance (MAD swimming), even though the kinesiological aspects of the movement trajectory were proved different beforehand.     

轧机开卷卷取直流电机工作电流分析

对直流驱动开卷卷取机工作过程进行分析,按照励磁磁通饱和,和励磁弱磁两种工况分别考虑,计算出张力转矩和动态补偿转矩与料卷卷径的关系,从而求出在一道次轧制过程中的电机最大电流     

Shear Plugging and Frictional Behaviour of Composites and Fabrics Under Quasi‐static Loading

Experimental studies are presented on the shear plugging and frictional behaviour of composites and fabrics under quasi‐static loading. The primary focus is on the effect of specimen thickness on quasi‐static shear plugging behaviour. In the present study, quasi‐static shear plugging and through‐the‐thickness frictional tests are carried out on three types of materials. The materials investigated are 2D plain weave E‐glass/epoxy, 2D plain weave T300 carbon/epoxy and 2D plain weave E‐glass fabric. Typical results on shear plugging strength and frictional behaviour are presented. Effect of specimen thickness on quasi‐static shear plugging behaviour is also investigated.     

On the simulation of laminar strained flames in stagnation flows: 1D and 2D approaches versus experiments

The present work is essentially devoted to the simulation of a laminar strained flame using two approaches: 2D realistic and 1D simplified. The studied case corresponds to a laminar burner that creates an upward-oriented round jet of stoichiometric methane–air mixture impacting on a horizontal metal disk. 2D numerical simulations have been performed using the Fluent® 6.3 software in the axisymmetric configuration. Detailed thermochemical and transport models are applied. Results of the 2D and 1D simulations are analyzed and compared with experimental data on flow velocity obtained by particle image velocimetry (PIV). Limitations of the classical 1D approach are identified and further commented on. Measurement errors due to the particle slip are evaluated by simulating the particle motion with inclusion of the gravity, Stokes drag, and thermophoretic forces.     

永磁-感应子式混合励磁电机转子油摩损耗

以充油运行永磁-感应子式混合励磁电机为对象,对电机转子油摩损耗进行了研究。根据电机结构特点,将电机中光滑转子与齿槽转子分开考虑,采用不同方法分别计算两部分的油摩损耗。基于流体力学理论,采用流体场数值计算方法,重点分析齿槽转子油摩损耗的影响因素,得到了油摩损耗与电机转速和定子内径的数值关系,揭示了温度对转子油摩损耗的影响规律。样机实验结果与计算结果基本一致,验证了计算方法的有效性。     

Frictional contact analysis of functionally graded materials with Lagrange finite block method

Based on the one‐dimensional differential matrix derived from the Lagrange series expansion, the finite block method was recently developed to solve both the elasticity and transient heat conduction problems of anisotropic and functionally graded materials. In this paper, the formulation of the Lagrange finite block method with boundary type in the strong form is presented and applied to non‐conforming contact problems for the functionally graded materials subjected to either static or dynamic loads. The first order partial differential matrices are only needed both in the governing equations and in the Neumann boundary condition. By introducing the mapping technique, a block of quadratic type is transformed from the Cartesian coordinate of global system to the normalized coordinate with eight seeds. Time dependent partial differential equations are analyzed in the Laplace transformed domain and the Durbin's inversion method is applied to determine all the physical values in the time domain. Conforming and non‐conforming contacts are investigated by using the iterative algorithm with full load technique. Illustrative numerical examples are given and comparisons have been made with analytical solutions. Copyright © 2015 John Wiley & Sons, Ltd.     

An enriched FEM technique for modeling hydraulically driven cohesive fracture propagation in impermeable media with frictional natural faults: Numerical and experimental investigations

In this paper, an enriched finite element technique is presented to simulate the mechanism of interaction between the hydraulic fracturing and frictional natural fault in impermeable media. The technique allows modeling the discontinuities independent of the finite element mesh by introducing additional DOFs. The coupled equilibrium and flow continuity equations are solved using a staggered Newton solution strategy, and an algorithm is proposed on the basis of fixed‐point iteration concept to impose the flow condition at the hydro‐fracture mouth. The cohesive crack model is employed to introduce the nonlinear fracturing process occurring ahead of the hydro‐fracture tip. Frictional contact is modeled along the natural fault using the penalty method within the framework of plasticity theory of friction. Moreover, an experimental investigation is carried out to perform the hydraulic fracturing experimental test in fractured media under plane strain condition. The results of several numerical and experimental simulations are presented to verify the accuracy and robustness of the proposed computational algorithm as well as to investigate the mechanisms of interaction between the hydraulically driven fracture and frictional natural fault. Copyright © 2015 John Wiley & Sons, Ltd.