并流喷雾干燥塔的计算机辅助设计研究

喷雾干燥广泛应用于众多工业品的生产。图解积分法是目前求喷雾干燥塔塔径和塔高常用的方法，但是图解积分法计算过程繁琐，误差大且无法编程计算。因此将喷雾干燥塔中雾滴运动的阻力系数与雷诺数之间的关系用误差极小的多项式取代图解积分法中使用的误差较大的Allen公式，并给出了喷雾干燥塔塔径和塔高的积分式，利用四阶复化高斯～勒让德数值积分法计算喷雾干燥塔塔径和塔高，有效地提高了设计精度，利用可视化语言Visual Basic6．0开发计算机辅助设计软件。算例表明：计算机辅助设计方便、结果精确，为进一步实现并流喷雾干燥塔的优化设计提供了一个有效的设计方法与手段。同时建立以年总费用为目标函数的并流喷雾干燥塔经济评价模型，对并流喷雾干燥塔的设计参数如空气进出口温度、空气进口湿度等参数进行经济评价与分析，探讨其对并流喷雾干燥塔运行费用与年总投资的影响，对实现并流喷雾干燥塔的优化设计，降低能耗，节省投资具有一定的参考价值。     

A fast integral approach for drag force calculation due to oscillatory slip stokes flows

In this paper, we describe an efficient numerical method for modelling oscillatory incompressible slip Stokes flows in three dimensions. The efficiency is achieved by employing an integral approach combined with an accelerated boundary‐element‐method (BEM) solver. First the integral representations for slip flows with two different slip models are formulated. The resulting integral equations are then solved using the BEM combined with the precorrected‐FFT accelerated technique. 3D numerical codes have been developed based on the method described above. These codes are then used to calculate the drag forces on oscillating objects immersed in an unbounded slip flow. Three objects are considered, namely a sphere, a pair of plates and a comb structure. The simulated drag forces on these objects obtained from the two slip models are compared. In the sphere case, the simulated results are also compared with the analytical solutions for both the steady‐state case and the no‐slip oscillatory case and are found to be in good agreement. In addition, qualitative comparison of the simulation results with the experimental results in the plate problem is also presented in this paper. Copyright © 2004 John Wiley & Sons, Ltd.     

沟槽面在湍流减阻中的应用

对近些年来的沟槽面湍流减阻技术的工业应用方向 ,沟槽的几何形状和尺度、流场压力梯度、沟槽面放置方式对于沟槽减阻效能的影响 ,沟槽面对于湍流边界层流动特性的影响 ,沟槽面的湍流减阻机理几方面研究进展进行了综述。从湍流拟序结构理论出发提出 :具有减阻效应的沟槽面不但能通过控制低速制条带间距来降低湍流“猝发”频率 ,而且在“猝发”后的高速“下扫”过程中因其几何结构使藏在槽内的安静流体避免或部分避免因高速“下扫”而“诱导”出较大速度剪切层 ,从而实现减阻。同时指出需要利用先进的实验技术如PIV等图像处理手段并结合直接数值模拟对湍流边界层的瞬时流场进行研究 ,以其找出湍流边界层的流动结构及其运动规律。     

气体-颗粒两相流动力学及其在气溶胶采样中的应用

大气颗粒物切割器的工作原理主要是重力沉降、离心分离和冲击分离,是气体-颗粒物两相流的动力学分离过程.气固两相流动力学方程可以较方便地用来分析大气颗粒物在切割器中的运动轨迹,具体计算过程中阻力系数CD和边界条件应根据具体情况分析选定.本文给出了两个利用数值计算模拟切割器工作的例子,对采样仪的采样效率、切割粒径及切割器结构尺寸等设计参数对切割粒径的影响进行计算,表明两相流动力学是对采样切割器中颗粒物的运动进行数值模拟的有效工具,能对采样仪、切割器的设计、制造提供有力的帮助.     

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.     

Physico-chemical concept of drag reduction nature in dilute polymer solutions (the Toms effect)

The physicochemical concept of turbulent drag reduction (the Toms effect) integrates physicochemical characteristics of polymer solutions with hydrodynamic and rheological flow parameters into a generalized equation, where the increment in volumetric flow rate Q_P is a function of the external shear stress τ_w, temperature, volume of macromolecular coils with immobilized solvent V_c and a function of their volume fraction Ψ = C · [η]/(1 + C · [η]). The Q_P depends on the coil intrinsic elasticity [G] = kT/V_c as well. This model allows one: (1) to describe the Toms effect in terms of useful elastic work spent by macromolecular coils with immobilized solvent to overcome the frictional forces (i.e. the forces of intermolecular interactions), (2) to forecast the initial conditions of the Toms effect (τ_* ≈ (RT)/(M · [η])) and (3) to explain the unusual temperature dependence of the polymer solutions flow.     

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.     

Blade sections for wind turbine and tidal current turbine applications–current status and future challenges

The designers of horizontal axis wind turbines and tidal current turbines are increasingly focusing their attention on the design of blade sections appropriate for specific applications. In modern large wind turbines, the blade tip is designed using a thin airfoil for high lift : drag ratio, and the root region is designed using a thick version of the same airfoil for structural support. A high lift to drag ratio is a generally accepted requirement; however, although a reduction in the drag coefficient directly contributes to a higher aerodynamic efficiency, an increase in the lift coefficient does not have a significant contribution to the torque, as it is only a small component of lift that increases the tangential force while the larger component increases the thrust, necessitating an optimization. An airfoil with a curvature close to the leading edge that contributes more to the rotation will be a good choice; however, it is still a challenge to design such an airfoil. The design of special purpose airfoils started with LS and SERI airfoils, which are followed by many series of airfoils, including the new CAS airfoils. After nearly two decades of extensive research, a number of airfoils are available; however, majority of them are thick airfoils as the strength is still a major concern. Many of these still show deterioration in performance with leading edge contamination. Similarly, a change in the freestream turbulence level affects the performance of the blade. A number of active and passive flow control devices have been proposed and tested to improve the performance of blades/turbines. The structural requirements for tidal current turbines tend to lead to thicker sections, particularly near the root, which will cause a higher drag coefficient. A bigger challenge in the design of blades for these turbines is to avoid cavitation (which also leads to thicker sections) and still obtain an acceptably high lift coefficient. Another challenge for the designers is to design blades that give consistent output at varying flow conditions with a simple control system. The performance of a rotating blade may be significantly different from a non‐rotating blade, which requires that the design process should continue till the blade is tested under different operating conditions. Copyright © 2012 John Wiley & Sons, Ltd.     

Water transport according to temperature and current in PEM water electrolyzer

Recently, various studies have been conducted on hydrogen energy as a means of replacing conventional fuels. Polymer electrolyte membrane water electrolyzers (PEMWEs) are being studied as a means of producing hydrogen for renewable energy. The PEMWE can be operated over a wider range than other types of water electrolyzers and can be connected to a renewable energy source, such as solar or wind. However, further studies are required because the water accompanying the hydrogen in the cathode presents a problem regarding hydrogen purity and storage. The phenomenon of water transport which is occurred on the PEMWE is analyzed by electro-osmotic drag and diffusion in the membrane. Electro-osmotic drag coefficients which are calculated by mass flow rate of discharged water with hydrogen are compared to the results of previous studies. The results of Electro-osmotic drag coefficient are different from previous studies at each operating condition. This difference is considered to be caused by the capacity of PEMWE such as active area and the number of cell.