Numerical investigation of cavitating flow behind the cone of a poppet valve in water hydraulic system

Computational Fluid Dynamics (CFD) simulations of cavitating flow through water hydraulic poppet valves were performed using advanced RNGk-epsilon turbulence model. The flow was turbulent, incompressible and unsteady, for Reynolds numbers greater than 43000. The working fluid was water, and the structure of the valve was simplified as a two dimensional axisymmetric geometrical model. Flow field visualization was numerically achieved. The effects of inlet velocity, outlet pressure, opening size as well as poppet angle on cavitation intensity in the poppet valve were numerically investigated. Experimental flow visualization was conducted to capture cavitation images near the orifice in the poppet valve with 30° poppet angle using high speed video camera. The binary cavitating flow field distribution obtained from digital processing of the original cavitation image showed a good agreement with the numerical result. Project supported by the National Natural Science Foundation of China (No. 59835160) and Scientific Research Foundation for Returned Overseas Chinese Scholars, State Education Ministry of China (No. 50175097)     

Modeling water and carbon fluxes above summer maize field in North China Plain with back-propagation neural networks

INTRODUCTION Dynamics of carbon and water vapor fluxesexchange between the atmosphere and the ecosystembiosphere, depend on complex and non-liner interplayamong physiological, ecological, biochemical andedaphic factors and meteorological conditions (Jarvis,1995; Leuning et al., 1995). There are many studiesquantifying the fluxes across different time and spacescales as well as assessing the environment con-straints on them by some kinds of biophysical orempirical models whose resul…     

美国高校校园安全管理现状及启示

安全事件的频发已成为高校管理中的一大棘手问题。本文从政府、社会、高校三个方面探讨了美国高校校园安全管理的现状及运行机制,试图为我国高校校园安全管理提供一些经验和启示。     

法院调解制度的价值

通过质疑诉讼和解论的可行性，分析处于现代化和社会转型背景下的中国社会纠纷解决的现实，阐明法院调解制度在法制化进程中的特殊价值，以对当前法院调解制度改革有所裨益。     

逻辑教学中频率副词的逻辑语义刻画

频率副词是一种与时间相关的量化语义,刻画频率副词的逻辑涵义就需要时态逻辑这个理论工具.在介绍时态逻辑思想的基础上,通过对汉语频率副词的分类,分析什么叫副词的量化意义,重点刻画不同频率的副词量化意义的区别.运用时态逻辑工具刻画频率副词的量化语义,进而刻画包含量化副词的汉语量化表达式的逻辑语义,揭示部分汉语量化表达式的语义特征.     

构建和谐"信息生态"突围教育信息化困境

当前教育信息化的发展面临不可回避的深层次结构性问题,根本出路在于采用系统观和生态观来指导教育信息化的实践.本文介绍了教育信息生态的概念,构建了一个典型的校园信息生态模型,并以促进教师和学生的全面发展,强调人、技术、教学实践之间的和谐互动的教育信息生态核心价值观为基本出发点,对当前教育信息化的深层次发展提出了建议.     

Filtration of micro-particles within multi-fiber arrays by adhesive DEM-CFD simulation

A 3D multi-time scale discrete element method-computational fluid dynamic (DEM-CFD) coupling approach was applied to investigate the filtration of micron-sized particles by different types of fiber arrays. Both the pressure drop and the filtration efficiency were examined to indicate the filtration performance of the fiber arrays. Fibers that were uniformly arrayed in a parallel or staggered manner were compared. Results showed that the staggered array showed a better performance than the parallel array in terms of both pressure drop and filtration efficiency. Further, we compared the performance of different staggered arrays, i.e. a regular case, one densified in the front layers and another densified in the back layers. The front densified array was found to enter the clogging and cake filtration stage in the shortest time, leading to the highest filtration efficiency, but the highest pressure drop. The back densified array still achieved a much higher filtration efficiency, despite a much lower pressure drop comparable to that of the regular array. The results suggest that the two kinds of densified arrays may be suited for different purposes, e.g. baghouse filters or breathing masks.     

A novel multi-objective optimization method for the pressurized reservoir in hydraulic robotics

The pressurized reservoir is a closed hydraulic tank which plays a significant role in enhancing the capabilities of hydraulic driven robotics. The spring pressurized reservoir adopted in this paper requires comprehensive performance, such as weight, size, fluid volume, and pressure, which is hard to balance. A novel interactive multi-objective optimization approach, the feasible space tightening method, is proposed, which is efficient in solving complicated engineering design problems where multiple objectives are determined by multiple design variables. This method provides sufficient information to the designer by visualizing the performance trends within the feasible space as well as its relationship with the design variables. A step towards the final solution could be made by raising the threshold on performance indicators interactively, so that the feasible space is reduced and the remaining solutions are more preferred by the designer. With the help of this new method, the preferred solution of a spring pressurized reservoir is found. Practicability and efficiency are demonstrated in the optimal design process, where the solution is determined within four rounds of interaction between the designer and the optimization program. Tests on the designed prototype show good results.     

图式理论与阅读教学

借助图式理论,分析了语言图式、内容图式和形式图式在阅读理解中的作用。为了提高学生的阅读能力,在阅读教学中,教师要注重这三方面的教学。