Solid-state green-light-emitting upconversion coherent random laser in macroporous LiNbO_3:Er

A solid-state green-light-emitting upconversion coherent random laser was realized by pumping macroporous erbium-doped lithium niobate with a 980 nm laser. The lasing threshold was determined to be about 40 k W∕cm~2.Above the threshold, the emission intensity increased sharply with the increasing pump intensity. Moreover, a narrow multi-peaks structure was observed in the green-light-emission band, and the positions of lasing lines were various at different angles. The results were the direct evidences of coherent random lasing emission from macroporous erbium-doped lithium niobate. These phenomena were attributed to the coexistence of upconversion emission and a multiple scattering feedback mechanism.     

螺旋线螺纹模型的有限元分析

针对精细化模型与Abaqus摩擦模型所存在问题, 提出一种基于螺纹几何特征的螺旋线螺纹模型, 采用脚本语言实现了螺旋线螺纹模型生成自动化, 并应用到某发动机机体主轴承盖螺栓螺孔的强度分析. 分析结果表明, 仿真计算得到的螺栓及机体螺孔处的应力很好地表征了螺栓连接结构螺纹处的实际应力分布, 与螺纹精细模型相近, 比Abaqus摩擦模型精度更高, 且计算方便、实用、高效, 验证了本文方法的准确、可行.     

基于直角网格法的单个和阵列布置下柔性水翼绕流数值模拟

研究柔性水翼在不可压缩流体中的水动力特性,对于船舵和减摇鳍等海洋结构物的设计和性能优化具有重要意义.本文将自主开发的径向基函数虚拟网格法求解器扩展到模拟绕单个或多个柔性水翼的不可压缩流动问题.数值模型基于虚拟网格有限差分法考虑浸入边界对流场的影响,引入紧支径向基函数(compact supported radial basis function,CSRBF)以物面Lagrangian质点追踪复杂的柔性动边界.基于该方法,首先模拟了均匀流中主动拍动的柔性水翼,升阻力系数良好的网格收敛性结果验证了本文方法的精度和可靠性.并研究了柔性水翼在不同振荡频率下的水动力特性,阐述了柔性水翼的推力生成机制.然后模拟了绕阵列布置柔性水翼的流动现象,研究了不同间距和不同振荡频率下水翼表面的升阻力系数变化规律和尾涡特性,观察到紧密布置的柔性水翼在高频振荡下推力系数存在显著的放大效应,同时推力为零时的临界频率提前.     

抽油烟机新风系统对住宅厨房空气品质的影响

采用仿真与测试相结合的方法定量分析了室内抽油烟机某新风系统对厨房空气品质的影响, 总结建立了以空气龄、换气效率为依据的厨房空气品质评价方法. 结果表明, 在开启该新风系统的厨房环境中, 室内平均空气龄为94.7s, 换气效率为82.4%, 平均空气龄比新风系统关闭时低79.8%, 空气质量由新风系统关闭时的中度污染改善至清新. 此仿真分析流程可为深入研究厨房室内空气品质、定量评估新风系统提供指导.     

基于CFD技术的风幕式抽油烟机厨房环境分析

为了研究某新型风幕式抽油烟机工作下的厨房环境,建立了基于零方程湍流模型的标准试验厨房CFD数值模型,并利用6?标准化处理后的油烟浓度测试数据对计算模型和分析流程进行标定分析,建立了实测油烟浓度与水蒸气仿真油烟浓度之间的近似关系式,利用标定后的模型对厨房内的气流组织状态进行了详细的模拟分析研究,最后利用该模型有效地模拟了不同风幕状态下的厨房环境,为评估及改善厨房环境奠定了基础.     

Light transmission in porous silicon dioxide filled with liquids of different refractive indices

Optical transmission at 532 nm from nonabsorbing disordered porous silicon dioxide has been studied experimentally. The transmission behaviors can be adjusted by filling the pores with liquids of different refractive indics, which are analyzed based on the theory of diffusion in a weak scattering regime. In our experiment, the transmission coefficient changes from a value less than 1% to one that is greater than 75%, that is, the opaque sample becomes transparent, which means that the transport mean free path of light within the material has been effectively adjusted. In addition, this method is a useful nondestructive method to derive the refractive index of an unknown bulk porous material.