Hierarchal structure of the simplified Navier-Stokes equations (SNSE) and its mechanical connotation and application

The hierarchial structure and mathematical property of the simplified Navier-Stokesequations (SNSE) are studied for viscous flow over a sphere and a jet of compressible flu-id. All kinds of the hierarchial SNSE can be divided into three types according to theirmathematical property and also into five groups according to their physical content. Amultilayers structure model for viscous shear flow with a main stream direction is pre-sented. For the example of viscous incompressible flow over a flat plate there existthree layers for both the separated flow and the attached flow; the character of thetransition from the three layers of attached flow to those of separated flow is elucidated.A concept of transition layer being situated between the viscous layer and inviscidlayer is introduced. The transition layer features the interaction between viscous flow andinviscid flow. The inner-outer-layers-matched SNSE proposed by the present author inthe past is developed into the layers matched (LsM)-SNSE.

冲压模具激光表面强化的搭接工艺研究

针对激光相变强化搭接带存在的回火软化等问题,对激光强化的球墨铸铁材料QT700-2搭接区的显微硬度、表面粗糙度、物相变化等进行了测试,并分析了强化机理。结果表明:选用合理的搭接率等工艺参数,球墨铸铁激光搭接强化后的硬度可达到50HRC以上,调节搭接宽度可以避免搭接区的回火软化问题。多道搭接强化后表层的马氏体组织呈区域性交错分布,材料表面形成非均匀、多尺度强化结构,强化后的表面具有良好的耐磨性和耐疲劳性。通过上述结果,对材料激光搭接强化的工艺参数进行了合理的优化。

湍流空气射流引射特性的模拟研究

本文采用数值模拟方法,研究了湍流空气射流对环境空气的引射特性,包括等温射流和非等温射流情形.结果表明,由于射流不停地引射环境空气,射流"势核"区下游的温度与轴向速度迅速降低;射流引射量的模拟结果与文献中报道的、采用多孔壁技术进行实验所建立的关联式良好符合.

民航客机防爆箱的研制

本文简介研制民航客舱防爆箱遇到的困难,指出这是爆炸火球区内抗爆容器的设计问题。在实验和理论分析基础上,就爆炸火球区内抗爆措施提出了建议并得到验证。

An Improved CE/SE Scheme for Numerical Simulation of Gaseous and Two-Phase Detonations

A new structure of solution elements and conservation elements based on rectangular mesh was pro- posed and an improved space-time conservation element and solution element (CE/SE) scheme with sec- ond-order accuracy was constructed. Furthermore, the application of improved CE/SE scheme was extended to detonation simulation. Three models were used for chemical reaction in gaseous detonation. And a two-fluid model was used for two-phase (gas–droplet) detonation. Shock reflections were simu- lated by the improved CE/SE scheme and the numerical results were compared with those obtained by other different numerical schemes. Gaseous and gas–droplet planar detonations were simulated and the numerical results were carefully compared with the experimental data and theoretical results based on C–J theory. Mach reflection of a cellular detonation was also simulated, and the numerical cellular pat- terns were compared with experimental ones. Comparisons show that the improved CE/SE scheme is clear in physical concept, easy to be implemented and high accurate for above-mentioned problems.

Broadband high-gain optical parametric chirped-pulse amplification near 780 nm with LBO-I near-degenerate near-collinear phase match

Near-degenerative near-collinear phase-match geometry for broadband optical parametric chirped-pulse amplification (OPCPA) at approximate to 780 nm is calculated in comparison with nondegenerate noncollinear phase-match geometry. In an experiment on LBO-I near-degenerate near-collinear OPCPA, high gain with broad gain bandwidth (approximate to 71 nm, FWHM) at approximate to 780 nm is achieved by using an approximate to 390-nm pumping pulse. The stretched broadband chirped signal pulse near 780 nm is amplified to approximate to 412 mu J with a pumping energy of approximate to 15 mJ, and the total gain is > 3.7 X 10(6), which agrees well with the calculation. For a broadband (covering approximate to 100 nm) chirped signal pulse, the theoretical gain bandwidth has been attained experimentally for the first time. (c) 2005 Society of Photo-Optical Instrumentation Engineers.

Investigation of near-collinear degenerated quasi-phase matching optical parametric amplification using PPKTP crystal

The gain properties of near-collinear degenerated phase-matched optical parametric amplification (OPA) using PPKTP crystal are investigated theoretically. The results indicate that the type-0 phase matching of PPKTP has larger accepted angle and better gain spectrum by tuning crystal temperature or rotating crystal angle.

Tunable transverse superresolution with phase-only pupil filters

A new set of pure phase filters for realizing transverse superresolution is presented in this paper. The filters, whose significant features are their ability to tune and their simplicity, consist of one half-wave plate between two quarter-wave plates; the half-wave plate is made of two zones that can rotate with respect to each other. By rotating any zone of the half-wave plate, the central lobe width of the irradiance point spread function (PSF) in the transverse direction can be tunably reduced. At the same time, the axial intensity distribution is analysed in detail.

A novel three-dimensional imaging array recording and computational method by means of coded cameras reconstruction

In this paper, we propose a novel three-dimensional imaging method by which the object is captured by a coded cameras array (CCA) and computationally reconstructed as a series of longitudinal layered surface images of the object. The distribution of cameras in array, named code pattern, is crucial for reconstructed images fidelity when the correlation decoding is used. We use DIRECT global optimization algorithm to design the code patterns that possess proper imaging property. We have conducted primary experiments to verify and test the performance of the proposed method with a simple discontinuous object and a small-scale CCA including nine cameras. After certain procedures such as capturing, photograph integrating, computational reconstructing and filtering, etc., we obtain reconstructed longitudinal layered surface images of the object with higher signal-to-noise ratio. The results of experiments show that the proposed method is feasible. It is a promising method to be used in fields such as remote sensing, machine vision, etc. (c) 2006 Elsevier GmbH. All rights reserved.

碱性氧化物对铋掺杂硅酸盐玻璃超宽带红外发光的影响

通过冷却熔融法制备出铋掺杂的硅酸盐玻璃，这些玻璃具有覆盖1000—1600nm波段的超宽带红外发光，荧光的半高宽（FWHM）超过200nm；荧光寿命超过400μs；荧光强度随着玻璃碱性的增加而减弱。荧光峰随碱性氧化物的种类不同而移动。除了红外发光，还观察到了发光峰在640m左右的可见发光。640m的可见发光和红外发光有可能来源于同一种发光离子。认为红外发光源于低价态铋离子。铋掺杂的硅酸盐玻璃由于它们的超宽带特性，有可能成为超宽带光纤放大器的增益介质。

Growth and spectral properties of Er:Gd2SiO5 crystal

Er3+ -doped Gd2SiO5 (Er:GSO) single crystal with dimensions of circle divide 35 x 40 mm(3) has been grown by the Czochralski method. The absorption and fluorescence spectra of the Er:GSO crystal were measured at room temperature. The spectral parameters were calculated based on Judd-Ofelt theory, and the intensity parameters Omega(2), Omega(4) and Omega 6 are obtained to be 6.168 x 10(-20), 1.878 x 10(-20), and 1.255 x 10(-20) cm(2), respectively. The emission cross-section has been calculated by Fuechtbauer-Ladenbury formula. (c) 2007 Elsevier B.V. All rights reserved.

Bulk crystal growth and efficient diode-pumped laser performance of Yb 3+:Sc2SiO5

A bulk crystal of Yb:Sc2SiO5 (Yb:SSO) with favorable thermal properties was successfully obtained by the Czochralski method. The energy level diagrams for Yb:SSO crystal were determined by optical spectroscopic analysis and semi-empirical crystal-field calculations using the simple overlap model. The full width at half maximum of the absorption band centering at 976 nm was calculated to be 24 nm with a peak absorption cross-section of 9.2x10(-21) cm(2). The largest ground-state splitting of Yb3+ ions is up to 1027 cm(-1) in a SSO crystal host. Efficient diode-pumped laser performance of Yb:SSO was primarily demonstrated with a slope efficiency of 45% and output power of 3.55 W.