浑水中兆赫频率的声衰减实验研究

文章报道了浑水中的声衰减的实验研究结果，超声波的频率分别为1、2、3、4、5MHz。实验表明：在同一个含沙量M的浑水中，声衰减系数β大致随频率f的增加而线性增加；对同一个频率f，声衰减系数β大致随含沙量M的增加而线性增加；在同一个频率，和相同含沙量M的情况下，声衰减系数β随泥沙粒径的增加而增加。     

微波网络衰减及衰减测量方法

衰减测量是微波测量的重要组成部分。微波传输器件,要考虑功率在传输中的损耗问题,需要进行衰减测量。多数的微波传输器件可用微波网络代表。     

梯度高分子溶液的声衰减

聚合物在溶解过程中形成聚合物膜、溶胀层、高浓度溶解层及低浓度溶解层,从而形成梯度高分子溶液,此种梯度高分子溶液对声信号有很好的衰减效果．文中详细研究了梯度高分子溶液在不同频率下,聚合物厚度及梯度结构的变化对反射声衰减效果的影响．结果表明,梯度高分子溶液浓度梯度的形成是声衰减效果好坏的关键。溶液浓度梯度很大或很小时,声衰减效果均不好,只有当浓度梯度适当时,其声衰减效果才最佳。     

水溶性高分子溶解过程中的声衰减

详细研究了不同频率下水溶性高分子溶解过程中可溶盐(KC l、N aC l、N aB r)及EDTA对其声衰减效果的影响。试验结果表明,在低频条件下可溶盐对水溶性高分子溶解过程中的声衰减有明显的影响,若在其中加入EDTA可以基本消除这种“盐效应”的影响。     

海底沉积物声衰减与含水量关系的实验研究

海底沉积物从海底采样之后,要经过保存和运输之后才进行室内的声学物理参数测量,在这个过程中,样品不可避免的受到各种干扰。在实验室里制作了沉积物人工样品,模拟样品受到的干扰,通过测量受扰动的含水量的变化及其与声衰减系数的关系,经过频谱分析,得出随机扰动不易辨别,容易造成错误测试结果。对可能的扰动进行物理分析,并提出沉积物声衰减实验测量的若干建议。     

海底沉积物样品声衰减与温度关系的实验研究

不同海区海水温度不同,导致不同海区沉积物温度不同;实验室环境温度变化造成沉积物温度的变化。模拟沉积物的温度变化来研究沉积物声衰减的变化,分别从声衰减系数和本文提出的温变衰减系数描述声衰减。以原状样品和人工样品为例说明了在一定厚度的海底沉积物中,声波的传播能力受到沉积物本身分布的均匀度的影响,会出现不同的衰减趋势;通过定义温变衰减系数得到了海底沉积物对能量的传播能力随温度的升高而降低。     

基于光声差分衰减频谱的骨质评估仿真研究

光声层析成像术(Photoacoustic Tomography,PAT)在骨组织微结构的量化评估方面具有潜力,但在传统PAT工作模式下,松质骨的固液两相多孔结构导致骨小梁等分布式光吸收成分激发的光声信号混叠,增加了定量分析骨微结构特性的难度和复杂度。针对这一问题,文章将PAT系统改进为偏心激励-差分检测模式,获取差分衰减频谱(Differential Attenuation Spectrum,DAS);并通过数值仿真计算和验证了松质骨孔隙率与光声差分衰减频谱特征参数的相关性。研究结果表明：提取的光声差分衰减频谱特征参数与骨头孔隙率呈强线性相关,基于光声差分衰减频谱的分析方法可有效实现骨质定量评估和诊断。     

基于小波包分析的声发射信号界面的衰减研究

在声发射的应用场所中,采集的声发射信号很多都经过界面传输.主要研究构成不连续界面的两个构件尺寸对信号传输的影响,利用小波包技术分析信号在不同频率范围内的衰减特性.研究表明,不连续界面对信号存在衰减,构成界面的构件相对尺寸的大小对衰减影响较大,构件尺寸相差较大时,由于波在小构件上的多次反射作用,使得采集信号能量反向增强,信号畸变程度增大.建议在经过界面采集信号时,尽量选择在构件相对尺寸相当且结构较简单的部位进行.     

声发射检测中背景噪声对线定位精度影响研究

为了定量分析背景噪声对声发射源线定位的影响,分别在半消声室、一般实验室和建筑工地三种环境下,进行了声发射模拟源直线定位的测试,并且通过改变门槛值分析测量定位值同实际定位值之间的误差.实验结果表明,背景噪声对声发射传感器附近声源的影响大于定位区间中部的声源.     

新型气固两相流亚微米级粉体浓度及浓度分布测量方法

提出了一种新型的基于激光散射原理的气固两相流亚微米级粉体浓度及浓度分布测量方法, 适合流场的物质组成及其浓度分布等气固两相流特性分析。以烟气烟尘浓度检测为例, 介绍了基于上述测量原理的烟尘浓度监测装置的设计及其工程实现方法, 可望推广到石油、医药等其它化学工业的气固两相流浓度分析。     

基于气固两相流的反循环潜孔钻头柱齿拓扑优化设计

 为了解决现有反循环潜孔钻头排岩屑效率低的问题,利用几何拓扑方法设计了一种新型钻头.该新型钻头在传统钻头基础上优化了钻头齿间距、齿的数量等,并提出了一种对数螺旋线式齿排列方式.然后,利用大型流体商用软件仿真分析了几何优化前后钻头的气流情况,并利用试验验证了仿真模型的有效性.研究发现,优化前、后钻头附近的气流速度从约16.5 m/s提升到约19.25 m/s,并且气流速度变得更均匀,即优化后钻头的排岩屑能力更强、更平稳.设计的优化钻头可以更好地满足工程实际需求.     

Experimental and numerical study of a horizontal-vertical gas-solid two-phase system with self-excited oscillatory flow

To better explore the energy-saving mechanism and flow characteristics of the self-excited oscillatory flow, the experiment is performed by a new self-excited oscillatory flow generator that the 45° oblique sheet is mounted through the pipe axis in a horizontal-vertical closed pneumatic conveying system. The experimental study focuses on the optimum air-velocity and power consumption, and results shows the maximum reduction of the optimum air-velocity and the coefficient of power consumption are approximately 8.2% and 16.4%, respectively. In addition, the CFD-DEM coupled approach is first developed to investigate the interaction of gas-solid flow in terms of the gas turbulent kinetic energy and spatial particle flow characteristics. Compared with the conventional pneumatic conveying, it is found that the optimum air-velocity and power consumption are reduced by the new self-excited oscillatory flow at lower air-velocities. The numerical results show that the approximately symmetric distribution of axial velocity and the intensive tangential velocity is emerged in the self-excited oscillatory flow at upstream. Particles is efficiently dispersed and suspended by the self-exited oscillatory flow reflecting in the smaller particle variation coefficient and the lager particle suspension coefficient. And since the airflow kinetic energy is utilized more fully to promote particles flowing, the spatial particle axial velocity is accelerated and reached early steady state. As a result, the developed numerical model is further explained the mechanism of energy saving with the self-excited oscillatory flow.     

穿孔管阻性消声器消声性能计算及分析

一维解析法和三维子结构边界元法被用于计算和分析穿孔管阻性消声器的消声性能，以及考查消声器内非平面波对消声特性的影响。直通穿孔管阻性消声器传递损失的预测结果与实验测量结果比较表明：一维解析法只适合于消声器的低频声学性能计算，对于高频声学性能的精确预测需使用三维计算方法。边界元法进而被用于研究吸声材料的填充密度（流阻率）和几何参数对穿孔管阻性消声器消声性能的影响。增加吸声材料的填充密度、穿孔管的穿孔率和穿孔长度、以及吸声材料的厚度，均能有效地改善阻性消声器的中高频声学性能，而对消声器的低频消声效果影响较小。     

A deflagration analysis of porous energetic materials with two-phase flow and a multiphase sequential reaction mechanism

A theoretical analysis for the unconfined deflagration of a porous energetic material is developed for a two-step global reaction mechanism that consists of the condensed-phase combustion of the reactive material to produce gas-phase intermediates, followed by a gas-phase reaction that produces final gas-phase products. An asymptotic approach is employed, leading to explicit formulas for the deflagration velocity in specific parameter regimes. The results clearly indicate the influences of two-phase flow and the multiphase, multi-step chemistry on the burning rate, and serve to further characterize the combustion behavior of a significant class of degraded nitramine-type propellants for which the present analysis is applicable.     

Development of neutron radiography facility for boiling two-phase flow experiment in Kyoto University Research Reactor

To visualize boiling two-phase flow at high heat flux by using neutron radiography, a new neutron radiography facility was developed in the B-4 beam hole of KUR. The B-4 beam hole is equipped with a supermirror neutron guide tube with a characteristic wavelength of 1.2 Å, whose geometrical parameters of the guide tube are: 11.7 m total length and 10 mm wide ×74 mm high beam cross-section. The total neutron flux obtained from the KUR supermirror guide tube is about 5×10⁷ n/cm² s with a nominal thermal output of 5 MW of KUR, which is about 100 times what is obtainable with the conventional KUR neutron radiography facility (E-2 beam hole). In this study a new imaging device, an electric power supply (1200 A, 20 V), and a thermal hydraulic loop were installed. The neutron source, the beam tube, and the radiography rooms are described in detail and the preliminary images obtained at the developed facility are shown.     

Experimental and simulation study of the effect of gravity on the solid-liquid two-phase flow and erosion of ball valve

The ball valve is an important control component in the pipeline hydraulic transmission system. Its internal solid-liquid two-phase flow and erosion characteristics have an important effect on the safety and stability of the entire pipeline system. Therefore, the erosion characteristics and positions of the ball valve body, the spool flow channel, and the pipeline surface behind the valve should be accurately predicted to ensure the safety of the pipeline. In this study, the experimental setup of the ball valve was designed. The experimental study on the erosion caused by the solid-liquid two-phase flow on the inner surface of the ball valve was conducted. And the numerical calculation research based on the CFD-DEM simulation method was performed. Results show that the placement of the ball valve has a great effect on the two-phase flow and erosion distribution inside the valve; the surface of the erosion plate will form a corrugated texture under the impact of particles at small openings; the placement method changes from vertical to horizontal due to the change in the direction of gravity. As a result, the particle distribution easily gathers near some wall surfaces to form a protective layer, which reduces the erosion rate.