声场中空化气泡的耦合振动及形状不稳定性的研究

计算了两个具有非球形扰动的气泡所组成系统的能量,并基于Lagrange方程得到了有声相互作用的非球形气泡的动力学方程和形状稳定性方程,研究了声场中非球形气泡间相互作用力对非球形气泡的形状不稳定性和气泡形状模态振幅的影响.研究结果表明声场中具有非球形扰动的气泡之间的耦合方式有两种:形状耦合模式和径向耦合模式,气泡之间的耦合方式取决于气泡形状扰动模态.由形状耦合及径向耦合产生的气泡之间的相互作用力能够改变单个气泡的形状不稳定及形状模态振幅,具体影响因素取决于声场驱动条件、气泡形状模态、相邻气泡的初始半径.     

混凝土材料的动态空腔膨胀理论

采用三段式线性状态方程和考虑拉伸破坏的带剪切饱和的Mohr-Coulomb屈服准则描述混凝土材料的本构关系,运用相似变换方法推导出了空腔膨胀动态响应的理论表达式,并运用Runge-Kutta-Felhberg数值方法给出了球形空腔动态响应的数值解。结果表明:空腔膨胀压力随空腔膨胀速度和剪切饱和强度的增加而增加,在空腔膨胀速度较高时,考虑剪切饱和时的空腔膨胀压力明显小于不考虑剪切饱和时的空腔膨胀压力。     

Preparation of spherical Y2SiO5 powders for thermal-spray coating

Yttrium silicate, for its high oxidation resistance, is an important candidate for protective coating for carbon-fiber-reinforced composites at temperatures above 1600 ℃. A novel method, consisting of coprecipitation, spray-drying, heat-treatment and plasma-densification, is developed to prepare Y2SiO5 powders for thermal-spraying. The composition, morphology and flowability of the synthesized Y2SiO5 powders are investigated by XRD, SEM and Hall Flowmeter, respectively. The results show that the synthesized Y2SiO5 powders are nearly spherical with high purity. The apparent density and flowability of the Y2SiO5 powders are 1.87 g/cm^3 and 37 s/50 g, respectively, which lead to a high deposition efficiency of up to 80700 for atmospheric plasma spraying.     

Influence of liquid layers on energy absorption during particle impact

The influence of the thickness of a covering liquid layer and its viscosity as well as the impact velocity on energy loss during the normal impact on a flat steel wall of spherical granules with a liquid layer was studied. Free-fall experiments were performed to obtain the restitution coefficient of elastic-plastic γ- Al2O3 granules by impact on the liquid layer, using aqueous solutions of hydroxypropyl methylcellulose with different concentrations for variation of viscosity （1-300 mPa s）, In the presence of a liquid layer, increase of liquid viscosity decreases the restitution coefficient and the minimum thickness of the liquid layer at which the granule sticks to the wall. The measured restitution coefficients were compared with experiments performed without liquid layer. In contrast to the dry restitution coefficient, due to viscous losses at lower impact velocity, higher energy dissipation was obtained, A rational explanation for the effects obtained was given by results of numerically solved force and energy balances for a granule impact on a liquid layer on the wall. The model takes into account forces acting on the granule including viscous, surface tension, capillary, contact, drag, buoyancy and gravitational forces. Good agreement between simulations and experiments has been achieved.     

一种ZF与SP结合的BLAST译码算法

多输入多输出虽能显著增加信道容量,但译码复杂度与精度一直是亟待解决的核心问题之一。将现有的贝尔实验室分层空时码检测迫零算法与球形译码算法充分结合,重点考察无线多输入多输出信道基本特征即信道条件数与信噪比,提出了一种自适应的贝尔实验室分层空时码解码算法,在保证误比特率性能的条件下,降低了系统的译码复杂度;为无线通信的长期演进研究奠定了良好基础。     

基于时域多分辨率的非球形气溶胶散射并行计算模型设计及验证EI北大核心CSCD

为解决串行时域多分辨率(MRTD)散射模型运行时间长和内存消耗大的问题,基于消息传递接口(MPI)技术设计了一种非球形气溶胶散射并行计算模型。介绍了MRTD散射模型的基本框架和2种并行数据通信方案,并基于MPI重复非阻塞通信技术实现了MRTD散射模型的并行化设计;搭建了网络并行计算平台,实现了模型的并行化计算。将MRTD散射模型与Mie散射模型、T矩阵法进行了对比,验证了并行MRTD散射模型的计算准确性。结果表明,MRTD模型可较准确地模拟非球形粒子散射特性,并行计算技术可显著提高计算效率;电磁场分量同时交换的并行设计方案的计算效率略高于仅交换磁场分量的方案;通过增加中央处理器核数,程序的并行加速比随之增大,但单核运行效率却略有降低。随着粒子尺度参数的增大,单核计算效率随之增加,复折射率的改变并不会显著影响并行计算效率。     

白磷钙石的水热合成

在180 ℃含CaO、Mg(NO3)2和H3PO4的水热系统中,反应2~4 h,成功沉淀出白磷钙石晶体.对产物进行了SEM、XRD和FTIR分析.初步的研究表明:样品主要由5~15 μm的单晶体和球形聚集体组成,XRD、FTIR图谱与合成白磷钙石(Ca19Mg2H2[PO4]14)相吻合.     

莫来石轻质球形料结构与性能

对以铝矾土为主要原料制备获得的莫来石轻质球形料进行了系统的结构与性能研究,研究结果表明:轻质莫来石球形料的主要化学成分为Al2O3和SiO2,物相为莫来石相,球形颗粒表面莫来石柱状结晶交织排布,内部含有大量气孔,堆积密度为1.60 g/cm3,颗粒体积密度为1.75 g/cm3,显气孔率为38;,耐火度大于1790℃,800℃下导热系数为0.245 W/(m· K),热震5次后球形保持率大于95;.     

基于Kriging模型的非概率可靠度计算

Kriging模型可以适应各种极限状态函数,HL-RF修正算法可以有效地计算非线性问题。对于难以获得极限状态函数的结构,提出了用Kriging模型进行回归拟合极限状态方程,同时使用HL-RF修正算法计算结构的非概率可靠度指标的计算方法。数值算例以及球形压力容器可靠性分析表明,本文提出的计算方法具有求解精度好、适应能力强的特点。     

球形透镜表面特性数值分析

球形透镜表面在一些高精度的光学系统变得越来越重要,它们和其他透镜表面一样必须满足一样的质量标准。本文采用数值计算方法分析了球形透镜的表面特性,并以Snell定律为基础,建立了用于计算球形表面特性的公式。通过与已有的球面特性公式进行比较,采用该方法计算球形透镜表面特性的拟合误差小于1μm。