Hydraulic radius and mesh size of gels

For materials with high porosity, the hydraulic radius (r _h ) is not proportional to the characteristic dimension of the pore space. Techniques (e.g., NMR) that measure r _h will give much larger pore sizes than techniques (e.g., thermoporometry) that measure pore entry radii. In this note, estimates of the relation between hydraulic radius and pore size of gel networks are obtained from cell models. The constant in the Kozeny equation, which relates permeability to r _h , is strongly density-dependent at low densities. For gels it is suggested that the permeability is more directly related to the mesh size of the network than to the hydraulic radius. The mesh size is also critical for immobilization of dyes or enzymes in a gel, and r _h is a misleading measure of the ability of a network to entrap a large molecule.     

轴流式水力机械转轮中局限空化流动的面元奇点解法

轴流式水力机械转轮中局限空化流动的面元奇点解法刘四清，常近时（北京农业工程大学水利与建筑工程系北京１０００８３）关键词：空化，水力机械，转轮。ＳＯＬＵＴＩＯＮＴＯＰＡＲＴＩＡＬＣＡＶＩＴＡＴＩＯＮＦＬＯＷＩＮＩＭＰＥＬＬＥＲＯＦＡＸＩＡＬ－ＦＬＯＷＨ...     

Numerical simulation of minimum B‐jumps at abrupt drops

A numerical simulation of minimum B‐jumps in horizontal rectangular channels having an abrupt drop is given. Gradually varied, steady, supercritical flow is assumed as the initial condition. An unsteady flow is created by increasing the downstream depth. One‐dimensional, unsteady Saint‐Venant equations are solved by using the MacCormack and the dissipative two–four explicit finite difference schemes. The steady flow solution is obtained by treating the time variable as an iteration parameter and letting the solution converge to the steady state. The abrupt drop is treated as an interior boundary and solved by the method of characteristics. The results are compared with experimental and analytical studies. Copyright © 2007 John Wiley & Sons, Ltd.     

Central schemes for open‐channel flow

The resolution of the Saint‐Venant equations for modelling shock phenomena in open‐channel flow by using the second‐order central schemes of Nessyahu and Tadmor (NT) and Kurganov and Tadmor (KT) is presented. The performances of the two schemes that we have extended to the non‐homogeneous case and that of the classical first‐order Lax–Friedrichs (LF) scheme in predicting dam‐break and hydraulic jumps in rectangular open channels are investigated on the basis of different numerical and physical conditions. The efficiency and robustness of the schemes are tested by comparing model results with analytical or experimental solutions. Copyright © 2003 John Wiley & Sons, Ltd.     

转子系统振动的CSFDB主动控制实验研究

采用可控挤压油膜阻尼器作为主控元件,进行转子系统振动主动控制研究,设计开发了锥形可控挤压油膜阻尼器（Controllable Squeeze Film Damping Bearing,CSFDB).CSFDB的外环轴向位置通过专门设计的电液伺服系统来调节其平淡同的轴向位置对应不同的油膜间隙,使转子系统、CSFDB、电液伺 服系统形成一个闭环控制系统,即主动控制转子系统的振动,本文的实验研究工作内容有,CSFDB-转子系统振动特性实验研究;CSFDB-转子系统加、减速振动特性试验研究;转子系统振动的CSFDB主动控制实验研究。转子模型为一单盘悬臂转子,研究结果表明,CSFDB控制效果明显,所研制的控制仪工作可靠,能满足实时必研究;CSFDB外环位置调节系统设计思路可行,性能可靠避孕药推广应用前景。     

用于剥裂球形坚果的碾磨盘间距优化

将坚果与碾盘的相互作用简化为带有固定端约束的圆环（半径为R）,采用方法建立了可能危险截面上的弯矩与磨盘间距的关系。数值计算表明优化磨盘间距为3．317R。     

发展中的集成霍尔传感器及在高科技领域中的应用

简述集成霍尔传感器的分类、特性及其在物理实验中的应用。并着重介绍其在工业、交通、家电等领域的广泛应用。     

基于知识的模糊神经网络的旋转机械故障诊断

提出了一种基于知识的模糊神经网络并用于故障诊断．首先基于粗糙集对样本数据进行初步规则获取,并计算规则的依赖度和条件覆盖度,然后根据规则数目进行模糊神经网络结构部分设计,规则的依赖度和条件覆盖度用于设定网络初始权重,而用遗产算法对神经网络输出参数进行优化．这样的模糊神经网络称为基于知识的模糊神经网络．使用该网络对旋转机械常见故障进行诊断,结果表明,和一般模糊神经网络相比,该网络具有训练时间短而诊断率高的特点．     

几何耦合对直升机桨叶液压减摆器等效线性阻尼的影响研究

建立了直升机前飞时,计入变距/挥舞/摆振几何耦合和力-速度非线性关系的液压减摆器分析模型;用4阶龙格-库塔法在时域内计算减摆器的轴向速度;根据减摆器轴向速度的瞬态响应成分,利用基于富里叶级数的移动矩形窗方法计算了减摆器等效线性阻尼。结果表明,存在变距/挥舞/摆振几何耦合的液压减摆器,在直升机前飞时其等效线性阻尼将大幅度下降。