Research on flow field in a modified ring spinning system with the air nozzle

Twisting is one of the most important steps in the yarn spinning, which influences the geometry of spinning triangle and determines the properties of spun yarns. Airflow is one of the most important measures on improving yarn spinning. In this paper, a kind of air nozzle with vortex guiding channel was designed and used on the modification of ring spinning system, and the spun yarn qualities was studied by analyzing the airflow field in the nozzle. Firstly, the three-dimensional physical model of nozzle was given using CAD software according to the geometrical size of the practical nozzle model. Then, the numerical simulations of the three-dimensional flow field in the nozzle were given using Fluent software. Finally, two different kinds of yarns 10Ne and 20Ne were spun in the modified ring spinning system with the nozzle installed. The airflow pressure 0.01 Mpa and two different swirling directions, anticlockwise and clockwise, were chosen. The qualities of spun yarns, hairiness, strength, evenness, and number of snarling were measured and analyzed. It is shown that the high vortex airflow can be produced in the nozzle, and then corresponding twist can be produced. For the Z(S) twisting spun yarn, under the effects of the clockwise (anticlockwise) vortex airflow, the pre-twisting would be produced and the yarn twist can be strengthened, while under the effects of the anticlockwise (clockwise) vortex airflow, the untwisting effect would be produced, and the yarn twist can be decreased.     

基于fluent的气体止推轴承出口性能仿真与分析

采用基于有限体积法的流体动力学软件fluent,仿真气体轴承气膜出口处的压力分布,并对层流模型和湍流模型仿真的结果进行对比。在用湍流模型仿真时,对比理想光滑壁面和粗糙壁面的仿真结果,分析了壁面粗糙度对气体轴承性能的影响,同时fluent仿真的结果也有效地验证了传统数值仿真时为简化模型所做的一系列假设都是合理的。     

多级水封进口流速的fluent数值计算

多级水封管通常应用在电厂轴封加热器、汽泵等设备内的凝结疏水或密封水输送到凝汽器的管上,水封管是靠疏水两端的压差来进行疏水的,多级水封在运行过程中的进口流速不能过大否则容易造成水封运行的不稳定,利用fluent对水封密封水进口流速进行数值计算,分析得出多级水封的运行稳定性与密封水进口流量成反比,造成这种现象的主要原因是密封水在流入水封管之后会有两次从高处往低处以自由落体、淋浴、附壁流等方式排挤水封原来建立的空气柱,考虑到轴加、给水泵等的密封水出口流量值和水封的运行稳定性,应该将进水速度控制到0.1m/s~0.5m/s,这样既能保持较高的疏水量又能维持水封的运行稳定性。     

基于Fluent的阀门开启过程阀芯气动力仿真研究

利用Fluent动网格和UDF技术对适当简化的阀门2D模型进行数值模拟,得到开启过程中作用在阀芯上的轴向气动力变化规律。     

某型发动机高温转速不足分析

文章分析了某型发动机在外场点火试车试验中,发动机到达一定的转速后,发动机转速增加缓慢,伺服阀可能产生的原因.重点从系统油压波动、油液温度、液流流态等方面对伺服阀进行了分析.     

基于流演算理论的动态访问控制模型研究

访问控制模型为系统的信息安全提供了一个理论框架,其目的是保护系统资源不被非法用户盗用,防止合法用户对受保护信息进行非法使用。然而,现有的访问控制模型大部分属于静态授权模型,不能方便地描述大规模、异构的分布式网络系统中授权过程的动态变化。为了解决上述不足,在充分研究流演算理论的基础上,提出了一个基于流演算理论的访问控制模型(FCDAC)。FCDAC将动态世界中的所有授权过程都看作是动作的结果,通过动作来实现状态的变化,并且在系统中只需描述动作的前提条件公理和状态更新公理就可容易地实现权限的变化。最后,通过一个教务管理实例验证上述理论,结果表明FCDAC是可行的。     

循环流化床炉膛扩口角的优化设计及数值模拟研究

以130t／hCFB锅炉炉膛为参考,对其扩口角设计进行优化．采用0．618法对参数进行挑选,利用大型流体计算软件FLUENT进行数值模拟研究．结果表明：通过对扩口角的设计可以改进炉膛内的流动特性,得出扩口角在67°-68°之间有较好的流动特性．     

基于CFD的电液伺服阀衔铁组件啸叫研究

该文利用Gambit和Fluent对伺服阀衔铁组件的啸叫问题进行了CFD分析,模拟计算了产品内部油路结构的流固耦合,发现在伺服阀衔铁组件啸叫的时候,流体在产品内部的产生了一明显的狭长负压区,改变产品内部结构再次进行CFD的模拟计算,负压区消失,对该结构的产品进行实际的通压通液测试,伺服阀啸叫的问题得到解决。     

Working memory, short-term memory, and speech rate as predictors of children's reading performance at different ages.

This study explored the contribution of 2 working memory (WM) systems (the phonological loop and the central executive) to reading performance in younger (9-year-old) and older (14-year-old) children. The results showed that (a) significant age-related differences in verbal and visual-spatial WM performance were maintained when articulation speed and short-term memory (the phonological system) were partialed from the analysis and (b) WM predicted age-related differences in word recognition and comprehension performance independent of the contribution of a short-term memory and articulatory rate. The results were interpreted as support for the notion that both the phonological and the executive systems are important predictors of age-related changes in reading but that these processes operate independent of each other in predicting fluent reading. Several implications of the results are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Numerical Analysis of Thermal and Dynamic Behavior of a Roof Solar Collector

In some regions with a specific climate, summer comfort in the rooms located below the roof becomes critical if the roof system is not well designed. In order to analyze the efficiency of this system a numerical model was developed. This model is based on the study of the natural convection coupled with radiative heat transfer in an inclined air channel. The configuration studied is an inclined channel formed by two parallel plates. The upper and lower plates were maintained at fixed temperatures. The air flow in the channel which is due to the buoyancy forces is fully turbulent and the turbulence was modeled by using the k‐ε model. Some numerical results obtained were validated using the experimental works of Khedari and colleagues and those of Nouanégué and colleagues. The effect of physical and geometrical parameters and the radiative heat transfer on the channel behavior is shown. Correlations for Nusselt numbers and air flow rate were obtained as functions of the geometric parameters and the Rayleigh number. These correlations can be used in other models that represent this system.