Wall and fluid inlet temperature effect on heat transfer in incompressible laminar oscillating flows

This paper deals with the problem of oscillating flows occurring in devices such as Stirling or thermoacoustic engines and refrigerators. Since the global governing equations cannot be solved, the authors propose to introduce a few simplifications; the most simplifying reduction is that the fluid is assumed to be incompressible. However, specific attention is paid to describing the flow characteristics that's why the Lagrangian formalism which allows the individual study of each fluid particle is adopted. Thereby each particle contribution to global thermal effects can be evaluated and the gas temperature profiles along the exchanger can be computed. Various situations are presented including the case of a non-uniform temperature at the wall and a phase lag between pressure and temperature at the fluid entrance. The efficiency of the wall to fluid thermal exchange is analyzed. The authors show that this exchange depends upon two important parameters: the geometric ratio between the exchanger length and the particle oscillating displacement, and a thermal parameter “β”, governing the temperature profiles and related to the Prandtl number, the operating frequency and the phase lag between the instantaneous heat flux and the wall to fluid temperature difference.     

Application of perfectly matched layer to soil-foundation interaction analysis

Despite of the limitation in modeling infinite space, the finite element method (FEM) is one of the most used tools to numerically study the geotechnical problems regarding the capacity of simulating different geometries, conditions and material behaviors. A kind of absorbing layer named perfectly matched layer (PML) has been applied to modeling the radiation damping using FEM, which makes the dynamic analysis of soil-structure interaction more accurate. The PML is capable of absorbing incident waves under any angle and frequency, ensuring them to pass through the model boundaries without reflection. In this context, a new FEM program has been written and the PML formula has been implemented by rewriting the dynamic equation of motion and deriving new properties for the quadrilateral elements. The analysis of soil-foundation interaction by applying the PML is validated by the evaluation of impedance/compliance functions for different ground conditions. The results obtained from the PML model match the extended mesh results, even though the domain is small enough that other types of absorbing boundaries can reflect waves back to the foundation. The mechanism of the wave propagation in the region shows that the forced vibrations can be fully absorbed and damped by the boundaries surrounded by PMLs which is the role of radiation damping in FEM modeling.     

U-E连轧失张对钢轨“高点”的影响分析

为了解决现场万能轧机与轧边机连轧60kg/m钢轨过程中距尾部3.6m处出现局部"高点"的问题,经试验与分析,对可能导致"高点"产生的第3道次轧制过程利用有限元仿真软件进行了仿真模拟,分析得出连轧失张产生的收缩力是导致局部"高点"产生的主要原因,最后从纵波和能量的角度提出了措施,解决了该问题。     

利用信号拼接提高调频连续波激光测距系统的分辨力

提出了一种对等频率间隔的采样信号进行拼接来提高调频连续波激光测距系统的测距分辨力的方法。研究了调频连续波激光测距的原理,设计搭建了基于一种双干涉系统的光纤调频连续波激光测距系统。利用辅助干涉系统产生的时钟信号对测量干涉系统的信号进行等光频间隔的采样,然后对采样信号进行拼接。使用LabVIEW设计了信号错误检测处理、采样和拼接的信号处理系统。利用该测距系统进行了实验验证,结果显示,将等光频间隔的采样信号进行拼接的方法可以突破激光器扫描范围的限制,减少光源非线性的影响,从而提高系统的测距分辨力。得到结果表明,在测量距离为8.7m时,该系统的测距分辨力可达70μm,30组测量结果的重复性标准差为35μm。     

爆破地震波在地层介质中产生的能量集中效应

论述了爆破地震在地层介质中传播的规律，分析了地质地层条件造成爆破能量集中对建(构)筑物产生的危害，探讨不同岩石性质的爆破震动效应，可为矿区建(构)筑物的位置选择及防震提供参考。     

材料生热效应基础研究和作用机理的探讨

根据各种需要,要求材料在各种特定的环境温度下发生变化,产生热效应。根据材料的发热机理和生热条件的不同,经常利用的生热条件是吸收微波生热和在交变磁场作用下的磁致生热。本文综述了两种生热条件下材料热效应的研究现状和发展情况。     

横波声场中倾斜平面反射特征的研究

与入射波束成一定角度的面状缺陷的声场反射特征和垂直入射时的反射特征不同。通过对横波声场中一系列不同宽度的 ４５°模拟裂纹的反射回波特征进行研究,得出了主波束入射、扩散波束入射时端角反射、面反射、端部反射的声压、声程落点的规律。     

交-直-交变频装置产生的谐波对电力系统的影响

结合引黄工程的实际情况,分析了引黄工程中拟采用的交直交电流型负载换相同步电动机变频调速装置整流侧产生的高次谐波电流。计算了供电网各级母线谐波电压畸变水平和谐波电流分布,说明变频装置必须装设相应滤波器,才能达到国家对电能质量谐波标准的要求。     

碟片填料旋转床气阻与气液传质实验研究

实验测量了超重力旋转床气液传质反应器在采用同心环波纹碟片填料的时的气相压降和气液传质特性,对不同转速,气流量,液流量条件下的气相阻力与气液传质性能进行了实验研究和分析,结果表明干床的气相压降是相同状态下采用金属丝网填料的气相压降的６０％左右。     

超声波传感器在长桩测试中的应用

在当今桩基础建设工程中,桩尤其是长桩,因深埋在地下,给质量检测带来不便,本文探讨利用超声波传感器测试长桩质量,分析了多路超声波及遥控装置的设计,检测长桩质量原理及评定方法。