变孔径多孔集水管的水力设计

由于管壁的摩擦阻力和管内流体速度沿轴向增大 ,多孔集水管内的压力沿轴向减小 .基于水力学原理推导出多孔集水管内各种变量间的无量纲关系式 ,并给出了变孔径多孔集水管水力设计的一种简易方法 .     

小参数高阶项对射孔段套管屈曲摄动解的影响

采用摄动法求解射孔套管的屈曲临界压力时,一般仅取小参数ε的一次项,忽略其高阶项必然对计算结果产生一定的影响。针对此问题,建立了考虑小参数二阶项影响的射孔段套管弹性屈曲近似控制方程,给出了含有ε2项影响的射孔段套管屈曲问题摄动解的一般形式;分析了小参数变化时,ε2项对射孔段套管抗挤能力系数的影响。数值计算结果表明,计算孔眼的轴向最大尺寸、布孔格式和孔密度发生变化对小参数及射孔段套管抗挤能力都有直接的影响。当计算孔眼的轴向最大尺寸小于30mm、孔密度小于40孔/m时,仅考虑ε一次项可以给出满意的结果,而不必考虑小参数高阶项的影响。     

储粮害虫声检测隔声室的设计

基于双层墙隔声和多孔吸收原理，结合储粮害虫活动声的特征，设计了一种体积为6m^3的隔声室．该隔声室利用胶合板作为双层墙壁材料，两墙壁间距离为0．08cm，外墙壁均匀穿孔，孔径为1mm，间距为1．5cm，并在支撑物上加垫较硬吸声材料组成准双重穿孔隔声结构．实验表明，在125～2000Hz的频带范围内，隔声室能均匀隔离环境噪声，平均隔声量为22dB，可满足储粮害虫活动声的频率范围和声压级要求．     

抗性消声器中穿孔板结构的声传递特性

本文利用声波在管中粘滞阻尼方面的理论,研究了存在气流时穿孔板结构的声传递特性。研究表明:穿孔板的声阻与孔板厚度、孔径、穿孔数目、声波频率和气流速度等因素有关。     

Relationship between action potential, contraction-relaxation pattern, and intracellular Ca2+ transient in cardiomyocytes of dogs with chronic heart failure

Abnormalities of contractile function have been identified in cardiomyocytes isolated from failed human hearts and from hearts of animals with experimentally induced heart failure (HF). The mechanism(s) responsible for these functional abnormalities are not fully understood. In the present study, we examined the relationship between action potential duration, pattern of contraction and relaxation, and associated intracellular Ca²⁺ transients in single cardiomyocytes isolated from the left ventricle (LV) of dogs (n = 7) with HF produced by multiple sequential intracoronary microembolizations. Comparisons were made with LV cardiomyocytes isolated from normal dogs. Action potentials were measured in isolated LV cardiomyocytes by perforated patch clamp, Ca²⁺ transients by fluo 3 probe fluorescence, and cardiomyocyte contraction and relaxation by edge movement detector. HF cardiomyocytes exhibited an abnormal pattern of contraction and relaxation characterized by an attenuated initial twitch (spike) followed by a sustained contracture ('dome') of 1 to 8 s in duration and subsequent delayed relaxation. This pattern was more prominent at low stimulation rates (58% at 0.2 Hz, n = 211, 21% at 0.5 Hz, n = 185). Measurements of Ca²⁺ transients in HF cardiomyocytes at 0.2 Hz manifested a similar spike and dome configuration. The dome phase of both the contraction/relaxation pattern and Ca²⁺ transients seen in HF cardiomyocytes coincided with a sustained plateau of the action potential. Shortening of the action potential duration by administration of saxitoxin (100 nM) or lidocaine (30 μM) reduced the duration of the dome phase of both the contraction/relaxation profile as well as that of the Ca²⁺ transient profile. An increase of stimulation rate up to 1 Hz caused shortening of the action potential and disappearance of the spike-dome profile in the majority of HF cardiomyocytes. In HF cardiomyocytes, the action potential and Ca²⁺ transient duration were not significantly different from those measured in normal cells. However, the contraction-relaxation cycle was significantly longer in HF cells (314 ± 67 ms, n = 21, vs. 221 ± 38 ms, n = 46, mean ± SD), indicating impaired excitation-contraction uncou pling in HF cardiomyocytes. The results show that, in cardiomyocytes isolated from dogs with HF, contractile abnormalities and abnormalities of intracellular Ca²⁺ transients at low stimulation rates are characterized by a spike-dome configuration. This abnormal pattern appears to result from prolongation of the action potential. Received 22 January 1998; received after revision 16 March 1998; accepted 27 March 1998     

稀释水应用于匀浆辊流浆箱的数值模拟

为了确定匀浆辊流浆箱能否采用稀释水来调节纸页横幅定量偏差,文中采用计算流体动力学软件Fluent对匀浆辊流浆箱内的流场进行数值模拟,利用Multiphase-Mixture模型分析了两种流体在匀浆辊流浆箱中的混合情况,利用旋转坐标系统(RRF)模型考察流场内旋转域对流场的影响,计算在不同进浆流速和匀浆辊转速的情况下,稀释水的调节效果.模拟结果表明:稀释水的调节效果与匀浆辊转速符合一次函数关系.实验证明,采用稀释水调节后,横幅定量偏差降低了3个百分点以上,该结果与数值模拟结果相符,说明稀释水调节单元可用于匀浆辊式流浆箱.     

基于模型参考自适应控制的穿孔轧机控制系统设计

对穿孔轧机速度控制系统进行模型的建立和简化,并针对轧制控制过程中参数变化等不确定性因素的影响,设计了基于波波夫超稳定理论的模型参考自适应控制方法,通过MATLAB仿真技术验证了该控制系统具有较好的动态控制性能和跟踪精度。     

射孔水平井的产量预测及影响因素分析

国内外大量研究表明水平井筒内的压降对水平井内的生产动态有较大影响,本文将给出考虑水平井压降时射孔水平井产量的耦合方程并用Visual Basic软件编制计算产量的可视化窗口;通过实例计算对影响产量的敏感性因素进行分析,并对无限导流情况下的水平井的产量和考虑水平井压降时水平井的产量进行对比。     

自由水面式半圆体开孔海洋结构物水动力性能实验研究

提出了自由水面式半圆体开孔这一海洋结构物的新型式,并对该型式结构物进行了不同水深、不同模型浸水深度,以及不同波高和周期下系统的规则波及不规则波的模型实验研究.对结构物的透射系数Ct、反射系数Cr以及能量耗散系数Cl进行了系统总结.通过研究发现自由水面式半圆体开孔海洋结构物的消波性能随着模型相对水深以及相对板宽的增加而增强;并且该结构具有较小的波浪反射率以及较好的能量耗散效果,适合在海岸基础设施中推广建造.     

Optimization of the Arrangement of Mixing Sheets in VK Tube

The flow mechanism of Nylon-6 melt over perforatedbaffles with conical shape in the VK tube is explained bycomputerized analysis based on a rational assumption ofStokes’flow.The governing equations for a two-dimen-sional flow are solved by finite difference method to gen-erate the stream function profile,velocity field and resi-dence time distribution.Optimization of the geometriesof the baffle structure brings about a uniform residencetime distribution of the melt,so as to ensure a homoge-neous extent of reaction for the final product.Furthertheoretical investigation shows that dead zones areformed and that a rule of thumb has to be practiced fortheir elimination.