ANSYS 7.0分析实例与工程应用

冲压发动机喷气催化复合效应研究

在高超声速飞行条件下，流入冲压发动机燃烧室并降至低速的空气的温度随飞行马赫数增加而愈来愈高。燃料与高温空气混合燃烧释放的化学能中的一部分将转化为解离能。这些解离能在长度受限的尾喷管中难以充分复合形成推力，使冲压发动机推力在高超声速范围内随飞行马赫数增大而下降，难以满足高超声速飞行器的推进要求。 与亚燃冲压发动机相比，流入超燃冲压发动机燃烧室的空气的温度在同样飞行马赫数条件下将明显降低，上述困难可大大缓解。然而目前超燃冲压发动机还存在关键性难点有待克服。若保持现有亚燃冲压发动机的吸气与燃烧方式，通过催化促进燃气解离组分在尾喷管膨胀过程中复合，可以增大冲压发动机的推力，满足高超声速飞行器的推进要求，为高超声速飞行器推进提供新的选择。 本论文主要研究内容如下： （1） 研究了亚燃冲压发动机燃烧室内燃气解离能与飞行马赫数的关系。通过对冻结流、平衡流和有限化学反应速率的流动的数值计算，确定了回收解离能增大推力的潜力。 （2） 以双爆轰技术为基础，建立起一套地面燃气产生装置。所产生的燃气的组分、温度和压力均与冲压发动机在高空飞行时燃气完全相同。调试出总温3200K、总压20Bar（对应来流马赫数6）和试验时间17.5ms以及总温4000K、总压5Bar（对应来流马赫数8）和试验时间12.5ms两种状态参数的试验用燃气。 （3） 建立了基于动量守恒原理的通过皮托管测压力换算推力的测量方法。对催化复合增大推力的实验而言，一般要进行特定流动条件下喷水与未喷水两种情况下推力大小的比较，其精度可以达到2%甚至更高。 （4） 完成了尾喷管喉道下游管壁喷水试验，成功释放出高温燃气中的解离能，有效增大了推力，证实了催化增推的想法是可行的。在来流马赫数6的条件下获得了11.0%的推力增量；在来流马赫数8.0的条件下也获得了11.7%的推力增加。

Effect of phases on the dynamic evolution of a Lambda system with spontaneously generated coherence

The dynamic evolution of a A system coupled by two strong coherent fields is investigated by taking spontaneously generated coherence (SGC) into account. By numericaly simulation, it is shown that the relative phase of the two coherent fields affects significantly the time scale to the coherent population trapping state. In addition, an analytical expression to the evolution rate which is consistent with the numerical results is given. (c) 2005 Elsevier B.V. All rights reserved.

Generation of sub-5 fs pulses through cascade of filamentation and hollow fiber compression

A pulse-compression scheme based on cascade of filamentation and hollow fiber has been demonstrated, Pulses with duration of sub-5 fs and energy of 0.2 mJ near 800 nm have been generated by compressing the similar to 40 fs pulses from a commercial laser system. This method is promising to generate near monocycle high energy pulses. [GRAPHICS] Measured autocorrelation curve of the final compressed pulses with duration of sub-5 fs (black solid) and the simulated autocorrelation curve of 4.6 fs pulse near 800 rim (red dash) (C) 2008 by Astro Ltd. Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA

消色差相位匹配在光参量啁啾脉冲放大中的应用

Optical parametric chirped-pulse amplification (OPCPA) supplies broadband gain for ultrashort pulses. A new theoretic explanation of OPCPA has been obtained by introducing the concept of tilted pulse front in this paper, and the distribution of broadband amplification has been twice expanded by introducing the technology of achromatic phase matching (APM). The prospect of APM in OPCPA has been discussed in detail. Finally, a design for the amplification of chirped pulses at 1600 nm has been firstly proposed and numerically simulated. (C) 2004 Elsevier B.V. All rights reserved.

Investigation of noncollinear QPM optical parametric amplification based on periodically poled KTP

The properties of noncollinear optical parametric amplification based on quasi-phase matching of periodically poled KTP are investigated theoretically. Our numerical simulation focuses on the gain spectrum of dependence upon noncollinear angle, crystal temperature and crystal angle. At the optimal noncollinear angle and grating period with fixed temperature, there exists a broadest gain bandwidth about 130 nm at signal wavelength of 800 nm. The deviation from optimal noncollinear angle can be compensated by accurately tuning the crystal angle or temperature with a fixed grating period for phase matching. (c) 2004 Elsevier B.V. All rights reserved.

Optimal feedback control of two-photon fluorescence in Coumarin 515 based on genetic algorithm

An optimal feedback control of two-photon fluorescence in the Coumarin 515 ethanol solution excited by shaping femtosecond laser pulses based on genetic algorithm is demonstrated experimentally. The two-photon fluorescence intensity can be enhanced by similar to 20%. Second harmonic generation frequency-resolved optical gating traces indicate that the optimal laser pulses are positive chirp, which are in favor of the effective population transfer of two-photon transitions. The dependence of the two-photon fluorescence signal on the laser pulse chirp is investigated to validate the theoretical model for the effective population transfer of two-photon transitions. The experimental results appear the potential applications in nonlinear spectroscopy and molecular physics. (c) 2005 Elsevier B.V. All rights reserved.

The effect of the group delay ripple of chirped fiber grating on composite second-order in optical fiber CATV system

The effect of group delay ripple of chirped fiber gratings on composite second-order (CSO) performance in optical fiber CATV system is investigated. We analyze the system CSO performances for different ripple amplitudes, periods and residual dispersion amounts in detail. It is found that the large ripple amplitude and small ripple period will deteriorate the system CSO performance seriously. Additionally, the residual dispersion amount has considerable effect on CSO performance in the case of small ripple amplitude and large ripple period. (c) 2004 Elsevier B.V. All rights reserved.

Comparison between complex amplitude envelope representation and complex analytic signal representation in studying pulsed Gaussian beam

Analytic propagation expressions of pulsed Gaussian beam are deduced by using complex amplitude envelope representation and complex analytic signal representation. Numerical calculations are given to illustrate the differences between them. The results show that the major difference between them is that there exists singularity in the beam obtained by using complex amplitude envelope representation. It is also found that singularity presents near propagation axis in the case of broadband and locates far from propagation axis in the case of narrowband. The critical condition to determine what representation should be adopted in studying pulsed Gaussian beam is also given. (C) 2004 Elsevier B.V. All rights reserved.

Enhancement of three-photon absorption cross-sections in a novel class of symmetrical charge transfer fluorene-based molecules

The three-photon absorption effect (3PA) of two novel symmetrical charge transfer fluorene-based molecules (abbreviated as BASF and BMOSF) has been determined by using a Q-switched Nd:YAG laser pumped with 38 ps pulses at 1064 nm in DMF. The measured 3PA cross-sections are 84 x 10(-78) and 114 x 10(-78) cm(6) s(2), respectively. The geometries and electronic excitations of these two molecules are systematically studied by PM3 and ZINDO/S methods. The relationships between 3PA cross-sections and intramolecular charge transfer are discussed micromechanically. The experimental and theoretical results have shown that the larger intramolecular charge transfer, which was characterized by the charge density difference between the ground state (SO) and the first excited state (S-I), the greater enhancement of the 3PA cross-sections. (c) 2005 Elsevier B.V. All rights reserved.

Large three-photon absorption cross-section in a novel class of bis-(N-carbazolyl) fluorene derivatives

Two novel symmetrical charge transfer fluorene derivatives (abbreviated as BCZF and BVCZF) with carbazole end-group as the donor moieties have been synthesized. Three-photon absorption cross-sections of these two compounds have been determined by using a Q-switched Nd:YAG laser pumped with 38 ps pulses at 1064 nm in DMF. The measured 3PA cross-sections are 140 x 10(-78) and 400 x 10(-78) cm(6) s(2) for BCZF and BVCZF, respectively. The geometries, electronic structures and electronic spectra of these two compounds are systematically studied by AM1 and ZINDO/S methods. On the basis of correct UV-vis spectra, the influence of different molecular structure on three-photon absorption cross-sections is discussed micromechanically. (C) 2005 Elsevier B.V. All rights reserved.