引水式水电站变顶高尾水洞水力特性和体型优化

考虑引水式水电站常用的有压尾水洞和变顶高尾水洞两类布置型式,采用基于特征线法的有压管道瞬变流分析模型和适用于明满流过渡过程分析的改进狭缝法模型,分别分析系统的过渡过程特性和尾水洞体型参数的敏感性,研究不同的尾水洞型式下尾水系统的水力特性,进一步揭示了变顶高尾水洞的底宽、洞高和顶坡对尾水管进口最小内水压力的影响规律。结果表明,与增大面积的有压尾水洞比较,变顶高尾水洞是一种可行的布置型式,可有效提高尾水管进口的最小内水压力且水锤过程衰减较快;合理增大变顶高尾水洞底宽、洞高或顶坡均可不同程度地改善尾水管进口最小内水压力,其中顶坡的影响相对明显,为体型优化设计提供了参考依据。     

Direct Numerical Simulation of Particle Dispersion in the Flow Around a Circular Cylinder

The major objective of the paper is to use direct numerical simulation method to get the dispersion patterns of different Stokes number particles in cylinder wake at low Reynolds numbers. The gas fluid structure is simulated by a spectral-element method with third-order accuracy. Non-reflecting boundary condition is specified for the outlet downstream boundary. Lagrangian approach is used to trace particle trajectory. The simulation results show factors to be considered to characterize the particle dispersion and find different particle dispersion pattern in a circular cylinder wake and in a plane wake.     

Experimental study of Ni/CeO2 catalytic properties and performance for hydrogen production in sulfur–iodine cycle

The Ni/CeO₂ catalysts with different calcination temperatures have been tested for hydrogen production in sulfur–iodine (SI or IS) cycle. TG-FTIR, BET, XRD, HRTEM and TPR were performed for catalyst characterization. It was found that the Ni²⁺ ions could be inserted into the ceria lattice. This brought about the strong interaction between Ni and CeO₂ and the generation of oxygen vacancies. Perfect crystallites were formed in the catalysts. It was evident that there was a change in particle size and morphology as the calcination temperature increased from 300 to 900 °C. The Ni/CeO₂ catalysts with different calcination temperatures showed better catalytic activity by comparison with blank yield, especially Ni/Ce700. A hypothetic mechanism of HI catalytic decomposition on Ni/CeO₂ has been constructed. The two important reactive sites were assumed for HI catalytic decomposition.     

A novel flame energy grading conversion system: Preliminary experiment and thermodynamic parametric analysis

The focus of this study is to improve the efficiency of the thermal power cycle from the perspective of photo energy and thermal energy grading conversion. A new concept of combined radiation and heat engine model was proposed to establish a novel flame energy grading conversion system based on photovoltaic conversion and the Rankine cycle. From the perspective of energy utilization, the spectral radiative energy characteristics in oxy-coal combustion were experimentally investigated, and a preliminary thermodynamic model of the new system was established based on the experimental results. Finally, energy and exergy analyses were conducted to determine the general characteristics of the proposed system and assess the improvements to the Rankine cycle. The results indicated that temperature was the main factor affecting the short-waveband energy ratio. Compared with the Rankine cycle, the new flame energy grading conversion system improved the system efficiency by about 3.5%. The exergy analysis indicated that the proposed system reduced the exergy loss factor in the heat transfer of the boiler by about 3% to 6%. This study provides references for improving the thermal power cycle efficiency.     

Experimental investigations and constitutive modeling of cyclic interface shearing between HDPE geomembrane and sandy gravel

This paper presents the results of experimental investigations and constitutive modeling of cyclic interface shearing between HDPE geomembrane and cohesionless sandy gravel. A series of cyclic interface shear tests was performed using a large-scale cyclic shear apparatus with servo controlled system. Particular attention was paid to the influences of the amount of shear-displacement amplitude, number of cycles, shear rate and the normal pressure on the mechanical response. The experimental results show that the path of the shear stress against the cyclic shear displacement is strongly non-linear and forms a closed hysteresis loop, which is pressure dependent, but almost independent of the shear rate. For small shear-displacement amplitudes, the obtained damping ratio is significantly greater than zero, which is different to the behavior usually observed for cyclic soil to soil shearing. In order to describe the pressure dependency of the hysteresis loop using a single set of constitutive parameters, new approximation functions are put forward and embedded into the concept of the Masing rule. Further, a new empirical function is proposed for the damping ratios to capture the experimental data for both small and large cyclic shear-displacement amplitudes. The included model parameters are easy to calibrate and the new functions may also be useful in developing enhanced constitutive models for the simulation of the cyclic interface shear behavior between other geosynthetics and soils.     

国外大屏幕和平板显示的一些发展

电视技术的发展和人们视觉特性的要求,尤其是HDTV的出现,使图象显示正在向高清晰度、高亮度、大屏幕、平板化方向发展。各种各样的新型显示技术和产品正在加紧研制开发和推出,图象世界正在进入百花争妍的时代。本文拟就大屏幕和平板显示的一些国外发展情况作一介绍。     

菊粉生物学作用及机制研究进展

菊粉是一种水溶的膳食纤维,近年来,菊粉作为保健食品或食品添加剂得到广泛应用。该文对菊粉多种有益的生物学功能、特定条件下可能存在的风险以及菊粉发挥生物学功能的作用机制进行总结,以期为菊粉作为保健食品、食品添加剂和医用辅料的安全性和有效性提供依据。     

基于BP神经网络的液滴图像识别方法

通过CCD监测白酒和掺入50％水的白酒两种不同液体液滴的生长过程,针对最大的液滴提取特征参数,利用主成分分析技术对特征参数进行优化,确定了5项有效的特征参数。最后采用BP神经网络识别不同的液滴。结果表明：不同液体液滴的轮廓特征参数是有区别的。因此,结合模式识别的图像液滴分析技术可以应用于分析和鉴别液体。     

无升程限制器舌簧阀在微型无油压缩机上的应用

介绍了一种无升程限制器舌簧阀,可在不同大气压工况下安全运行,环境适应性强。通过对气阀动力学模型的简化,并根据气阀全开时弹簧力与气体推力的关系,推导出了气阀计算的工程近似法,可求出在无升程限制器状态下气阀理论升程,然后再结合气阀结构参数来校核阀隙马赫数。