Aeroacoustic Simulations Using Compressible Lattice Boltzmann Method

This paper presents a lattice Boltzmann (LB) method based study aimed at numerical simulation of aeroacoustic phenomenon in flows around a symmetric obstacle. To simulate the compressible flow accurately, a potential energy double-distribution-function (DDF) lattice Boltzmann method is used over the entire computational domain from the near to far fields. The buffer zone and absorbing boundary condition is employed to eliminate the non-physical reflecting. Through the direct numerical simulation, the flow around a circular cylinder at $Re$=150, $M$=0.2 and the flow around a NACA0012 airfoil at $Re$=10000, $M$=0.8, $α$=$0^◦$ are investigated. The generation and propagation of the sound produced by the vortex shedding are reappeared clearly. The obtained results increase our understanding of the characteristic features of the aeroacoustic sound.     

Tail wavelets in merger of binary compact objects

We present a model for tail wavelets, a phenomenon known as "echo" in the literature. The tail wavelet may appear in signal reconnaissances in the merger of binary compact objects, including black holes and neutron stars. We show that the dark matter surrounding the compact objects lead to a speculated tail wavelet following the main gravitational wave(GW). We demonstrate that the radiation pressure of the main wave is fully capable of pushing away the surrounding matter to some altitude, and splashing down of the matter excites the tail wavelet after ringing down of the main wave. We illustrate this concept in a simplified model, where numerical estimations are conducted on the specific distribution of dark matter outside the black hole horizon and the threshold values in accordance with observations. We study the full back reaction of the surrounding dark matter to the metric and find that the effect on to the tail wavelets is insignificant. We reveal the fine difference between the tail wavelets of a dressed and a bare black hole. We demonstrate that the tail wavelet can appear as a natural phenomenon in the frame of general relativity, without invoking modified gravities or quantum effects.     

Adsorption of CO, NH3 and O2 on Fe site of La0.875Sr0.125FeO3 (0 1 0) surface by density function theory calculation

The adsorption of CO, NH₃ and O₂ gas molecules on Fe site of La_0.875Sr_0.125FeO₃ (0 1 0) surface has been investigated based on the density functional theory (DFT) with the spin polarized generalized gradient approximation (GGA). The optimal adsorption orientations as well as the adsorption energies for these molecules adsorption on Fe site of La_0.875Sr_0.125FeO₃ (0 1 0) surface are derived. Results show that adsorption configurations with C-down for CO, N-down for NH₃ are stable. For the O₂ molecule adsorption, the mode with an angle about 120° between the oxygen molecule and La_0.875Sr_0.125FeO₃ (0 1 0) surface is stable.     

Multilayer thin-film inspection through measurements of reflection coefficients

A vibration-insensitive interferometer is described to measure the thickness, refraction index and surface profile of thin-film stack at normal incidence. By satisfying the continuous boundary conditions of electric and magnetic fields at interfaces in a multilayer film stack, the reflection coefficient phase of the thin-film stack can be distinguished from the phase of spatial path difference, thus thickness and refraction index can be extracted. The experiment results showed that the measurement precision is significantly increased after the phase analysis was added into the reflectance analysis.     

端部周期加热下管内气温奇异分布的实验研究

设计搭建了端部周期加热时管内气体热声对流的实验平台,对端部周期加热引起的气体热声对流作用下管内气体的温度分布进行了实验研究。该实验以氩气为工质,利用三极管控制加热电路实现周期性加热;测量了不同加热频率下管内的气体温度,并与常热流加热时的温度分布进行对比,结果表明端部周期加热时管内气体的温度分布与同功率下常热流加热时存在明显的差异,并且在某些测点出现了温度的奇异分布。本实验验证了超温现象的存在,为管内气体热声对流现象的进一步研究奠定了基础。     

Temperature or strain induced adjustable-chirp characteristics of uniform fibre grating with tapered metal coating

Temperature and strain characteristics of uniform fibre grating with tapered metal coatings have been analysed theoretically, by which adjustable chirp characteristics of such gratings are shown. Electroplating is adopted to fabricate such gratings, and the tapered metal coating is obtained by gradually drawing the fibre grating out of the solution during the process of electroplating. The gradually changing cross-sectional area of the metal coating is calculated by a newly suggested numerical method. By combining the theoretical and numerical simulation analyses, the gratings' characteristics are given at various temperatures and strains. The results obtained using such a method are also testified by experiments.     

相变过程的格子Boltzmann方法模拟

应用Shan提出的伪势多相模型替代R-K着色模型,建立一种新的描述气液相变过程的格子Boltzmann理论模型,模拟蒸发(高密度转化为低密度)过程.改进了计算效率,且得到较好的计算结果.同时应用该模型从孔隙尺度模拟了多孔介质中的相变现象,验证了该模型模拟复杂相变问题的可行性.     

Trap States in Al2O3 InAlN/GaN Metal-Oxide-Semiconductor Structures by Frequency-Dependent Conductance Analysis

We present a detailed analysis of the trap states in atomic layer deposition Al2O3/InAlN/GaN high electron mobility transistors grown by pulsed metal organic chemical vapor deposition. Trap densities, trap energies and time constants are determined by frequency-dependent conductance measurements. A high trap density of up to 1.6×1014 cm？2eV？1 is observed, which may be due to the lack of the cap layer causing the vulnerability to the subsequent high temperature annealing process.     

热处理对CH薄膜表面粗糙度及力学性能的影响

利用低压等离子体化学气相沉积法制备厚度约为7 m的辉光放电聚合物薄膜,将制备的薄膜样品放入通有氩气保护的热处理炉中加热至300 ℃,分别进行6,10,24 h的保温热处理。通过白光干涉仪观察分析了不同保温时间下辉光放电聚合物薄膜的表面粗糙度; 利用傅里叶变换红外吸收光谱分析了300 ℃条件下不同保温时间对薄膜结构的影响; 采用纳米压痕仪表征了不同保温时间热处理后,薄膜硬度及模量的变化。结果表明:随着保温时间的增加,薄膜的表面均方根粗糙度由12 nm降至4.43 nm。薄膜结构中甲基的相对含量减少,双键的相对含量增加,碳链变长,同时薄膜网络结构的交联化程度增强。硬度和模量随着保温时间的增加先减小后增大。     

增程式电动汽车动力总成参数匹配设计

增程式电动汽车作为一种新型节能环保型汽车,是传统内燃机汽车向纯电动汽车过渡的一种车型;根据动力传动系统的设计原则和设计目标,基于铃木奥拓燃油汽车改装设计了增程式电动汽车的动力传动系统的参数匹配方法,根据电动汽车基本参数及其控制目标,对动力总成系统的关键零部件进行了匹配设计;匹配结果表明:电动机的额度电压为60 V,最高转速为4 000 r/min,额定功率为8 kW,额定转矩为40.43 N·m,峰值功率为11 kW,最大扭矩为80.86 N·m;增程器采用马勒增程器和两缸直列四冲程发动机;动力电池组采用磷酸铁锂子电池,单组额定容量为80 Ah、总电压为96 V;对于指导增程式电动汽车的开发、提高汽车性能和安全性,以及对于电动汽车底盘集成控制系统的开发都具有重要的工程应用意义。