非预混燃烧大涡模拟的代数二阶矩模型

一种改进的代数二阶矩燃烧模型被应用在Flame-D的大涡模拟中。代数二阶矩模型能够将化学反应速率的脉动项进行模拟,更准确地计算化学反应速率。在实际燃烧过程中,化学反应速率不仅与当地的温度以及组分浓度等相关,更与反应物的混合速率有密切的关系。研究考虑了亚网格尺度内混合速率对化学反应速率的影响,提出了改进的代数二阶矩模型。通过与相同模拟条件下的涡耗散概念模型的模拟结果以及实验结果进行对比,改进的代数二阶矩模型的准确性得到了验证,同时亚网格化学反应速率的模拟对总化学反应速率的影响也得到了研究。     

氢-空气绕流无限长斜劈斜爆震波数值模拟

采用二维多组分有化学反应的Euler方程,考虑单步化学反应,采用有限反应速率模型,对斜爆震波进行计算,通过将数值模拟结果与实验结果对比,验证了数值模拟方法的有效性。在此基础上,对氢空气绕流无限长斜劈的斜爆震过程进行了数值模拟,分析了斜劈角度对斜爆震波特性的影响。结果表明:当斜劈角度增大时,爆震波中的化学反应速率随之增大,相应的斜爆震波的角度也增加,波后的温度更高,同时波后法向马赫数减小。     

轴对称钝体后湍流扩散燃烧的PDF模拟

在无结构网格中，对轴对称钝体驻定的湍流扩散火焰进行数值模拟．采用有限容积(FV)／Monte Carlo(MC)混合算法求解湍流燃烧问题的混合算法．Monte Carlo法求解脉动速度一标量．频率的联合概率密度函数方程，有限容积法求解平均质量、动量和能量方程．求解的两组方程是相容的，合理的耦合方式可以减少统计偏差，计算精度和效率显著优于单独的颗粒方法．文中对化学反应采用层流火焰面模型，并将数值计算结果与实验结果作了比较和分析．     

再入飞行器驻点流光辐射特性的理论建模

本文用直接模拟蒙特卡罗法，对再入体驻点区域的流场、光辐射特性进行了研究．针对头部锥体驻点区（包括激波层），建立了流场中的化学反应模型，中性粒子和等离子体的热运动、粒子间碰撞的理论模型，碰撞激发辐射和化学发光辐射的物理模型．给出了样本粒子运动方向和速率、粒子碰撞对的选择等蒙特卡罗法概率模型和计算方法．     

基于有限反应速率的扩散燃烧大涡模拟

本文发展了一种基于有限反应速率的湍流燃烧大涡模拟方法。基于此方法,对常压下,甲烷/空气平板射流扩散燃烧进行了大涡模拟.甲烷/氧气反应采用包含七种组分的四步反应简化反应机理,考虑了基于Arrienius定律的有限化学反应速率,瞬态结果和时均结果与DNS结果都符合很好。为了解决考虑有限反应速率后计算量急剧增加的问题,本文引入等效化学反应速率模型,在压力泊松方程的求解中采用了求解效率较高的快速傅里叶变换方法,并对整个程序进行基于区域分解的MPI并行编程处理。     

非平衡化学反应流场NS方程计算研究

介绍一种新的与化学问题相耦合的NS方程数值方法,用来计算有限速率化学反应再入流场.采用迎风TVD差分格式的激波捕捉法,求解控制方程。本项研究针对轴对称流动。然而,可以直接推广到三维流动和其它的化学反应系统。所采用的整个泰氟隆-空气化学反应模型是由23个化学组元和35个化学反应所组成。对钝头球锥体全流场(包括前体和近尾迹)进行了数值模拟,获得了充分收敛的数值解。对清洁空气流场计算的峰值电子数密度与实验结果符合很好。     

NO_x生成的有限反应速率二阶矩封闭模型

本文用有限反应速率二阶矩封闭模型对大速差射流燃烧室内煤粉燃烧过程中NO的生成进行了数值模拟，并将该模型的计算结果与Arrhenius模型的计算结果进行了比较，模拟结果表明，燃烧室中NO的生成是由燃料NO的生成机理来控制，Arrhenius模型计算得到的NO的浓度值高于有限反应速率二阶矩封闭模型的计算结果．     

硅单粒子位移损伤多尺度模拟研究

本文结合分子动力学方法和动力学蒙特卡罗方法, 研究了单个粒子入射硅引起的位移损伤缺陷的产生和演化过程; 基于Shockley-Read-Hall理论计算了单个粒子入射引起的位移损伤缺陷导致的泄漏电流增加及其演化过程, 比较了缺陷退火因子与泄漏电流退火因子之间的差异, 并将计算结果与实验值进行了对比. 结果表明, 计算泄漏电流时, 仅考虑一种缺陷的情况下缺陷退火因子与泄漏电流退火因子相同, 考虑两种缺陷类型情况下二者在数值上有所区别, 但缺陷退火因子仍能在一定程度上反映泄漏电流的退火行为. 分子动力学模拟中采用Stillinger-Weber势函数和Tersoff势函数时缺陷退火因子和泄漏电流退火因子与实验结果一致, 基于Stillinger-Weber势函数的计算结果与实验值更为接近.     

含内热源碳纳米管的热导率研究

采用分子动力学方法研究了含内热源单壁碳纳米管（5，5）的热导率，并与恒温差法结果进行了比较。研究发现，尽管两种模拟方法所得热导率均随管长增加而增加，但内热源法计算的热导率比恒温差法计算的热导率小，最大差别可达一倍左右。本文结合声子动力学理论建立了简单一维导热模型，较好地解释了这一现象。     

虚时间分裂算符方法研究溶剂电子转移动力学

在Sumi-Marcus理论中，采用虚时间分裂算符方法研究电子转移动力学．此方法具体应用于计算嗪-1和N,N-二甲基苯胺分子之间的电子转移速率常数．通过计算得到的两种反应物态的平均速率常数和一个长时间的速率常数，揭示了不同的sink函数时的电子转移动力学．在数值模拟过程中还发现了一些新的电子转移特性．     

介观化学反应体系中非平衡相变最可几路径的熵产生

针对一个双稳的介观化学反应体系计算了在非平衡相变时最可几路径的熵产生. 利用概率产生函数和程函近似,将化学主方程转化为经典的哈密顿-雅可比方程并通过相空间的零能轨线找到双稳态之间转变的最可几路径. 通过计算前向和逆向最可几路径的熵产生,发现在共存点系统熵变和介质熵变都为零,而在非共存点系统熵变和介质熵变皆不为零.     

开链烷烃13C化学位移统计分析

将开链烷烃的¹³C化学位移与分子中¹³C核邻近原子上的电子集居数及¹³C原子的局部空间能相关联,对14个典型烷烃分子中的72个碳原子的数据用逐步回归方法进行处理,所得结果表明:¹³C化学位移与上述诸因子间存在明显的线性关系.72个碳原子的¹³C化学位移预报值的均方根偏差为0.835ppm,最大偏差为2.232ppm.     

脉冲泵浦的掺镱光纤放大器中放大自发辐射动态变化模拟

在低重复率、高能量脉冲的应用场合,光纤放大器中采用脉冲泵浦的方式具有重要意义.本文模拟了脉冲泵浦方式下掺镱双包层增益光纤中放大自发辐射功率的动态变化,为优化脉冲泵浦方式提供了参考.通过有限元分析方法求解光纤中镱离子的速率方程和各光场的功率传输方程,模拟了正向泵浦条件下,泵浦脉冲开始后0~740 μs时间内光纤内部正向、反向放大自发辐射功率分布情况的动态变化以及光纤两端放大自发辐射输出功率随泵浦时间的变化.模拟结果发现了光纤两端正向、反向放大自发辐射功率增长速度的差异之处,以及光纤内部两种放大自发辐射功率分布动态演变的一些特征.     

The importance of chemical mechanisms in sonochemical modelling

A state-of-the-art chemical mechanism is introduced to properly describe chemical processes inside a harmonically excited spherical bubble placed in water and saturated with oxygen. The model uses up-to-date Arrhenius-constants, collision efficiency factors and takes into account the pressure-dependency of the reactions. Duplicated reactions are also applied, and the backward reactions rates are calculated via suitable thermodynamic equilibrium conditions. Our proposed reaction mechanism is compared to three other chemical models that are widely applied in sonochemistry and lack most of the aforementioned modelling issues. In the governing equations, only the reaction mechanisms are compared, all other parts of the models are identical. The chemical yields obtained by the different modelling techniques are taken at the maximum expansion of the bubble. A brief parameter study is made with different pressure amplitudes and driving frequencies at two equilibrium bubble sizes. The results show that due to the deficiencies of the former reaction mechanisms employed in the sonochemical literature, several orders of magnitude differences of the chemical yields can be observed. In addition, the trends along a control parameter can also have dissimilar characteristics that might lead to false optimal operating conditions. Consequently, an up-to-date and accurate chemical model is crucial to make qualitatively and quantitatively correct conclusions in sonochemistry.     

用双光源相位共轭型非相干光时间延迟简并四波混频测量超快速过程

本文提出用双光源相位共轭型非相干光时间延迟简并四波混频测量失相时间和布居弛豫时间的理论,并对其应用进行了讨论.     

Ultrasonic absorption in aqueous solutions of amino acids at neutral pH

Ultrasonic absorption coefficients in aqueous solutions of glycine, L-alanine, imidazole, L-phenylalanine, L-histidine and L-tryptophan at neutral pH were measured in the range from 0.8 to 220 MHz at 25 degrees C. A characteristic ultrasonic relaxation phenomenon was observed only in the solution of L-histidine with a relaxation frequency at around 2 MHz at neutral pH. It was proposed from the concentration independent relaxation frequency and the linear concentration dependence of the maximum absorption per wavelength that the relaxation mechanism was associated with a perturbation of the rotational isomeric equilibrium of the L-histidine molecule. The existence of two rotational isomeric forms of L-histidine in water was examined by semiempirical quantum chemical methods, in order to determine the free energy difference between the two states. The forward and backward rate constants were determined from the relaxation frequency and the energy change. Also, the standard volume change of the reaction was estimated from the concentration dependence of the maximum absorption per wavelength. It was speculated that L-histidine fulfills a specific function among amino acids because of the rotational motion in the molecule, in addition to its well-established acid-base properties.     

Determination of the spectral values of the real part of the relative refractive index of human blood erythrocytes from the measured directional scattering coefficients

An easily automated method for determining the real part of the refractive index of human blood erythrocytes in the range 0.3–1.2 μm is proposed. The method is operationally and metrologically reliable and is based on the measurement of the coefficients of light scattering from forward and backward hemisphere by two pairs of angles and on the use of multiple regression equations. An engineering solution for constructing a measurement system according to this method is proposed, which makes it possible to maximally reduce the calibration errors and effects of destabilizing factors.     

Backward Monte Carlo simulation for apparent directional emissivity of non-isothermal semitransparent slab

A backward Monte Carlo method based on radiation distribution factor is extended to compute the apparent directional emissivity of one-dimensional absorbing-emitting-scattering semitransparent slab with specular semitransparent surface and opaque diffuse substrate. A non-isothermal semitransparent slab is taken as an example to examine the efficiency of backward Monte Carlo method. The apparent directional emissivity of the semitransparent slab is determined by backward Monte Carlo simulation and compared with that determined by forward Monte Carlo simulation. The results show that the backward Monte Carlo method is very efficient in solving the apparent directional emissivity of the semitransparent slab. The backward Monte Carlo method converges more quickly than the forward Monte Carlo method.     

Comparative study of the forward and backward methods for calculating jet properties in pp collisions at s~(1/2)=7 TeV

We propose a forward method based on PYTHIA6.4 to study the jet properties in ultra-relativistic pp collisions.In the forward method,the partonic initial states are first generated with PYTHIA6.4 and then hadronized in the Lund string fragmentation model,and finally the hadronic jets are constructed from the created hadrons.Jet properties calculated with the forward method for pp collisions at √s=7 TeV are comparable to those calculated with the usual anti-kt algorithm(backward method)in PYTHIA6.4.The comparison between the backward and forward methods may contribute to the understanding of the partonic origin of jets in the backward method.     

Cyclic voltammetry characterization of a La0.8Sr0.2Co0.2Fe0.8O3 − δ electrode interfaced to CGO/YSZ

The electrochemical characteristics of a La_0.8Sr_0.2Co_0.2Fe_0.8O_3 − δ cathode electrode interfaced to the CGO layer of a double layer CGO/YSZ electrolyte were studied using cyclic voltammetry, at temperatures of 600 to 850 °C and under oxygen partial pressures ranging from 0.07 to 21 kPa. The aim was to identify the electrochemical processes taking place under cathodic polarization on the basis of differences in the features of the cyclic voltammograms with changing conditions. Depending on temperature, sweep rate and oxygen partial pressure, current peaks appeared both in the forward and backward scans. Furthermore, reversed hysteresis was observed, i.e. higher currents in the backward scan than in the forward scan, with increasing oxygen partial pressure and decreasing temperature. The observed behavior was related to the electrochemical redox of B-sites and concomitant stoichiometry change as well as to the competing reaction of electrochemical oxygen redox, taking also into account the competitive action of chemical reactions occurring in the presence of gaseous oxygen.