准线性光传输系统的非线性噪声研究

采用一阶摄动理论分析了准线性光传输系统的非线性相位噪声,在此基础上得出中置光学相位共轭器的准线性光传输系统的非线性相位噪声的方差的理论表达式,并围绕理论推导得出的非线性相位噪声的性能参数进行数值计算。计算结果表明在光放大器和传输系统的终点到光学相位共轭器等距的情况下,采用光学相位共轭器的色散补偿光传输系统可以完全消除非线性相位噪声对非线性系数的一阶影响。     

不同煤块的强度变形特性及强度准则的回归方法

与沉积岩的局部缺陷不同，煤层具有分布的裂隙和弱面，不仅影响强度，也会影响变形。煤样单轴压缩的强度和杨氏模量离散性很大，但两者具有明显的相关性。在围压下压缩时，闭合裂隙可以通过摩擦承载，使煤样强度和杨氏模量的离散性减小。不同煤块加工的试样强度不同，但围压对三轴强度的影响系数R相同，即内摩擦系数是一个材料参数，因而可以对不同煤块的试验结果进行联合回归。这不仅可以消除煤块的差异对内摩擦系数的影响，而且可以评价煤块强度的离散程度。     

Influence of geometrical and operational parameters on the axial dispersion in an aerated channel reactor

Residence time distribution experiments have been performed on an activated sludge 3000 m³ channel reactor aerated by gas diffusion (for different liquid flowrates under constant aeration rate and constant water depth) and on a bench-scale channel reactor aerated from the bottom (for different liquid and gas flowrates and water depths) in order to characterize their hydrodynamics. Both units can be modeled as plug flow reactors with axial dispersion. A general correlation has been obtained to predict the axial dispersion coefficient as a function of the gas and liquid velocities and the geometrical parameters of the full-scale and bench-scale reactors. Finally, to facilitate the simulation of biological reactions in transient state, an equivalent model based on tanks-in-series with variable back-mixing flowrate is proposed.     

Dispersion in a street canyon for a wind direction parallel to the street axis

We investigate pollutant dispersion in a street canyon for an external wind direction parallel to the street axis, a case which has been poorly documented in the literature. The study is performed numerically and analytically by means of a model based on a series of simplifying assumptions. The range of validity of these assumptions is discussed by comparing analytical and numerical results for two different street aspect ratios. Our results show that, for a critical length of the street, ground level concentration can be higher than those observed in a street canyon whose axis is perpendicular to the external wind direction. We show that this critical length depends on the street aspect ratio.     

油氢合建站氢气泄漏扩散模拟及影响因素分析

利用 FLACS 软件建立某油氢合建站三维物理模型,对高压储氢瓶及加注机泄漏事故进行模拟,并分析不同罩棚形状、环境风速、风向对氢气泄漏事故的影响规律。研究表明：加氢机处发生泄漏时,现有加油站罩棚会造成氢气大量聚集,带斜角顶棚能显著降低可燃氢气云团量,油氢合建站改造过程中需将罩棚一并改造。高压储氢瓶泄漏扩散后形成的气云区域随着环境风速 的增加在水平方向逐渐增大,垂直方向逐渐减小,气云偏向地面聚集,点燃风险增加;环境风对泄漏氢气具有吹散和稀释作用,但在不利风向条件下,氢气进入高阻塞度障碍区域,可燃气云量反而增大,需考虑当地主导风速风向,对加氢站进行合理布局。     

An analytical model for solute mixing in surcharged manholes

A mathematical model has been developed to describe solute mixing in surcharged manholes using the submerged jet theory. The model has been applied for straight-through flow manholes and for manholes with a difference in the level of the inlet and outlet pipes. The model is applicable to dissolved substances, i.e. the model has not been validated for high sediment concentrations (above 1 g/l) and care should be taken in such cases. Simulation results from the new model are compared with laboratory measurements and are further compared to conventional modelling techniques currently available in commercial software specially developed for modelling the water quality in sewers. The results prove that the new model produces considerably better results compared to the traditional assumption of full mixing in a manhole. The new model compares well to the laboratory measurements and hence improves the accuracy of modelling soluble pollutant transport in sewers. The applicability of the new modelling approach is discussed and further studies are recommended.     

单相流体在多孔介质中的流动和换热研究

本介绍了单相流体在多孔介质内部的传热和流动过程及其研究方法,给出单相流体大多孔介质内部传热的数理模型,对模型的有效性进行了验证。同时分析了流速、孔晾率、固体颗粒的直径大小及固体骨架和流体的导热系数之比等因素对多孔介质内部传热和流动的影响,提出了增加传热而不使流动阻力过多增加的方法．     

LED路灯的散热设计及可靠性研究

大功率LED（Light Emitting Diode）作为新一代光源,它的光转换效率高,具有耗电小,绿色环保,寿命长等优点正被广泛应用于室内照明和外部照明。在整个照明耗电量中道路照明约占20％-30％,因此将LED应用于道路照明具有巨大的经济价值和市场前景。大功率自光LED是半导体照明的关键器件,在不断提高光效、降低成本的同时,对其可靠性也提出了更高要求。这里从提高散热和可靠性方面提出了一些看法。     

电能变换领域中随机脉宽调制技术研究概况及展望

相较于传统的脉宽调制技术,随机脉宽调制具备有效的谐波频谱分散能力,从而实现机电负载噪声的削弱。随机脉宽调制技术包括起步的随机开关调制、后续的随机脉冲位置与随机开关频率等3个基本方法。随着电力电子技术的整体发展,随机脉宽调制已从传统的载波调制逐渐拓展到空间矢量调制之中,应用范围日趋广泛,谐波频谱分散与功率谱峰值抑制的效果不断提升。同时,新的优化方案不断被提出,对谐波频谱及功率谱的分散效果亦在不断提高。梳理了随机脉宽调制的研究历程,总结了数种典型的随机脉宽调制的基本原理,并对未来随机脉宽调制的研究方向作出展望,为随机脉宽调制技术的深入研究提供参考。     

Use of electromagnetic two-layer wave-guided propagation in the GPR frequency range to characterize water transfer in concrete

The objective of this paper is to adapt a recent innovative technique for extracting and exploiting the Electromagnetic (EM) waveguide dispersion of civil engineering materials by means of GPR, and allowing to monitor the water ingress front during the absorption process for various concrete mixes. This technique is based on an inversion procedure that applies the Electromagnetic Waveguide Model (WGM) to invert phase velocity dispersion curves in their modal form. A Parallel homogenization model, derived from the Lichtenecker-Rother equation, has been employed to extend the waveguide model from a one-layer to a two-layer medium. The WGM outputs are then used to estimate the geometric parameters of the propagation medium and offer a primary application to water transfer monitoring in concrete through capillarity effects. The initial WGM validation is carried out on FDTD-simulated propagation signals, while the second validation relies on GPR data acquired from homogeneous materials. Then, a broad-based experimental study is conducted for the purpose of correlating electromagnetic waveguide dispersion parameters with both the geometric and hydric characteristics of various concrete mixes. Results obtained using the two-layer WGM serve to monitor the water ingress front during an absorption process. These results are then compared to the moisture gradients generated on cores using gammadensimetry, which is set as the reference. This procedure yields a number of trends, which in turn provide key information on the conditioning state of the studied concretes.