Flamelet-Modeling of Inverse Rich Diffusion Flames

An experimental and numerical investigation of a confined laminar inverse diffusion flame (IDF) with pure oxygen as oxidizer and carbon dioxide diluted methane as fuel with a global stoichiometry of partial oxidation processes (equivalence ratio of 2.5) is presented. The present burner setup allows studying both the flame and the post-flame zone in a simplified geometry considering typical operating conditions as found in large-scale gasifiers. This partial oxidation flame setup is characterized by very high temperatures close to the stoichiometric oxidation zone due to oxy-fuel combustion, whereas lower temperatures and slow endothermic post-flame conversion reactions with long residence times are found in the fuel rich post-flame region. The scope of this paper is to investigate different modeling approaches suitable for both regimes by comparing the simulation results to detailed experimental data. Planar OH laser-induced fluorescence (OH-LIF) was performed for measuring the hydroxyl radical in the reaction zone and the results are compared to CFD calculations. Based on this comparison, the necessary level of detail of diffusion flux modeling, which includes Soret and Dufour effects, is analyzed and established. Finally, steady and unsteady non-premixed flamelet approaches based on a single mixture fraction are used in order to study their applicability for both the oxidation and post-flame zone. Significantly different time scales are obtained using different flamelet paths. Their influence on the results is investigated in the steady flamelet and the Lagrangian flamelet approach.     

粘弹性介质中逆散射问题的求解方法

本文讨论了一维粘弹性介质中的逆散问题,给出了两种反演粘弹性介质松弛模量的方法。这两种方法只利用了介质层一侧波的反射数据,其中一种方法只需已知一个走时来回时间内的反射数据就可以确定介质的松弛模量在任意时刻的值。文中最后给出了数值算例,可以看出,数值反演的结果与初始给定的松驰模量吻合得很好。     

Two-Dimensional Elastic Herglotz Functions and Their Applications in Inverse Scattering

In this work solutions of the spectral Navier equation that satisfy the Herglotz boundedness condition in two-dimensional linear elasticity are presented. Navier eigenvectors in polar coordinates are introduced and it is established that they form a linearly independent and complete set in the L ²-sense on every smooth curve. It is also proved that the classical solutions of the spectral Navier equation are expressed via Navier eigenvectors, and this expansion converges uniformly over compact subsets of R ². Two far-field patterns, the longitudinal and the transverse one corresponding to the displacement field are introduced, and the Herglotz norm is expressed as the sum of the L ²-norms of these patterns over the unit circle. It is also established that the space of elastic Herglotz functions is dense in the space of the classical solutions of the spectral Navier equation. Finally, connection to inverse elasticity scattering is established and reconstructions of rigid bodies are presented. This revised version was published online in June 2006 with corrections to the Cover Date.     

基于Mie散射理论的磷化镓粒子散射特性

基于Mie散射理论,对磷化镓微球粒子从紫外光区到红外光区的光散射特性进行了数值计算与理论分析,得到了散射强度与散射角、粒子尺寸参数、偏振度与散射角以及光学截面与粒子尺寸参数的关系。结果表明,入射波长越长,粒子半径越小,散射越弱;并且在红外波段光散射很弱,在散射角90°方向上能观测到线偏振光,这为磷化镓材料的制备与应用提供了理论参考。     

制备特定尺寸的纳米金颗粒方法及性能表征

通过化学还原法制备出不同粒径的纳米金颗粒。利用紫外可见分光光度计和透射电子显微镜对纳米金颗粒的形貌及尺寸进行表征。讨论了还原剂种类、还原剂用量、试剂加入顺序、反应温度等因素对纳米金颗粒稳定性、粒径、形貌和分散性的影响。结果表明：Na3C6H5O7为还原剂制得纳米金颗粒粒径在15-20 nm之间,NaBH4为还原剂制得的纳米金颗粒粒径在3-10nm之间,柠檬酸钠与氯金酸的摩尔比为1.5：1时最佳,Na3C6H5O7为还原剂时,采用HAuCl4溶液加入到加热的Na3C6H5O7与聚乙烯吡咯烷酮（PVP）混合溶液比Na3C6H5O7溶液加入到加热的HAuCl4与PVP混合溶液制得的纳米金溶胶的颗粒分散性好,粒径小且更均一。     

柔性机械臂的两种逆动力学方法

本文提出了柔性机械臂运动控制和振动抑制的两种有效的开环控制方法——两点边值逆动力学方法和轨迹规划逆动力学方法。两种逆动力学方法所设计的开环输入不仅可以实现柔性机械臂的点位运动或跟踪优化轨迹，而且同时显著降低或消除了结构柔性对其精确定位的影响。数值模拟和实验证实了理论分析结果     

Inverse Estimation of the Effective Diffusion of the Filter in the In Situ Diffusion and Retention (DR) Experiment

Porous filters are often used in laboratory and in situ diffusion and retention experiments. The proper interpretation of these experiments requires knowing the effective diffusion, D _e, of the filter which is commonly determined from laboratory diffusion experiments or estimated from the filter porosity. The D _e of the filter in the in situ experiment may differ from the D _e of the filter measured in the laboratory due to pore clogging. Here, we present an inverse method to estimate the D _e of the filter of in situ diffusion experiments. The method has been tested for several sampling schemes, numbers of synthetic data, N, and standard deviations of the noise, ??. It has been applied to the following tracers used in the in situ diffusion and retention (DR) experiment performed in the Opalinus clay at Mont Terri underground research laboratory: HTO/HDO, Br^?,I^?, ²² Na⁺,¹³³ Ba²⁺,⁸⁵ Sr²⁺, Cs⁺/¹³⁷Cs⁺, and ⁶⁰Co²⁺. The estimation error increases with the standard deviation of the noise of the data and decreases with the number of data. It is smallest for sorbing tracers. The D _e of the filter can be properly estimated from 12 data collected within the first 3?days for conservative tracers as long as ????? 0.02 and for sorbing tracers as long as ??????0.05. The estimate of D _e for conservative tracers is poor when data are collected from a 10-day experiment with daily sampling. The convergence of the estimation algorithm for conservative tracers improves by starting with a value of the D _e smaller than the true value. The choice of the initial value of D _e does not affect the convergence of the estimation algorithm for sorbing tracers. Filter clogging and vertical flow though the filter can influence the tracer transport through the filter. The use of the D _e of the filter obtained from a laboratory test for the in situ experiment may result in large errors for strongly sorbing tracers. Such errors can be overcome by estimating the equivalent D _e of the filter with the proposed inverse method which will be useful for the design of in situ diffusion experiments.     

Elastic Wave Scattering and Dynamic Stress Concentrations in Stretching Thick Plates with Two Cutouts by Using the Refined Dynamic Theory

Based on the refined dynamic equation of stretching plates, the elastic tensioncompression wave scattering and dynamic stress concentrations in the thick plate with two cutouts are studied. In view of the problem that the shear stress is automatically satisfied under the free boundary condition, the generalized stress of the first-order vanishing moment of shear stress is considered. The numerical results indicate that, as the cutout is thick, the maximum value of the dynamic stress factor obtained using the refined dynamic theory is 19% higher than that from the solution of plane stress problems of elastic dynamics.     

SH波对内含裂纹衬砌结构的散射及动应力集中

当衬砌结构内含裂纹时 ,采用Green函数的方法 ,研究了SH波对裂纹的散射及其动应力集中 ,构造了在含有半圆形衬砌的弹性半空间上 ,在水平面上任一点承受时间谐和出平面线源载荷作用时的位移函数作为Green函数 ;推导了SH波对衬砌内有裂纹的散射定解积分方程组 ,进而求得裂纹尖端的动应力因子 ,重点讨论了衬砌及周围介质对裂纹尖端动应力因子的影响 ,给出了介质参数变化对裂纹尖端动应力因子的影响曲线 ,为工程设计提供了依据。     

简单柔性机械臂的构造性逆动力学方法

本文提出了适于简单柔性机械臂的一种基于谱分析的构造性逆动力学方法。数值模拟和实验结果表明，这种方法提供的开环输入力矩，不仅可以实现机械臂特定的刚体转动，而且可以有效地减弱柔性对机械臂精确定位的影响。     

Scattering of ultrasound by minority phases in polycrystalline metals

The scattering of ultrasound by minority phases in polycrystalline metals is discussed. For discrete inclusions, the scattering theory of Ying and Truell describes well the attenuation of longitudinal waves. To treat the scattering by a second phase formed by segregation at a grain boundary, the scattering by a spherical shell with density and elastic constants different from those of the surrounding medium is developed. Reflection of ultrasound at this boundary is found to enhance the attenuation at low frequencies in agreement with experiments of Kamigaki. Application is made to the scattering by manganese sulphide in free-machining steel.     

饱和不可压正交各向异性多孔弹性板的动力弯曲分析

基于多孔介质理论,在Kirchhoff直法线假定以及小变形和线性本构关系前提下,建立了饱和不可压正交各向异性多孔弹性板的线性动力分析模型.针对流体的面内扩散问题,在忽略面内惯性项的影响下,进一步简化了分析模型,给出了相应的基本控制方程以及初始和边界条件的一般描述.根据所建立的模型,采用Fourier级数展开法研究了四边简支透水正交各向异性矩形多孔弹性板在冲击载荷作用下的拟静态和动力弯曲响应,数值分析了不同参数下孔隙流体压力等效弯矩、固相有效应力等效弯矩以及挠度的变化规律和动力特征.研究表明在外载荷作用初始阶段,孔隙流体对板弯曲变形的影响不可忽视.     

Scattering of directed radiation by a cylinder

Summary A new asymptotic method of Karp and Zitron is employed to study the effect of the directivity of a source on the scattering pattern when the radiation emanating from the source is incident upon a circular cylinder. Numerical results are obtained and presented graphically when the source is a slotted cylinder for the case of H-polarization.     

Scattering of SH waves by embedded cavities

Scattering of plane SH waves by sub-surface circular cavities and thin slits in a semi-infinite elastic medium is analyzed in this paper. Two methods of solution are used to obtain the displacements on the free-surface. One of these is a method of matched asymptotic expansion that is very effective when the wavelength is long compared to the dimensions of the cavity (or the crack). The other is a combined finite element and analytical technique, which is useful in the long to intermediate wavelength range. The results obtained by these two techniques are shown to agree quite well for long wave-lengths. Numerical results for the surface displacements for various incident wave angles are seen to depend significantly on the depth and size of the cavity and the crack. In the latter case the orientation of the crack has a significant influence on the scattered field.     

Scattering of elastic waves by non-planar cracks

A modification of the null field approach is used to study the scattering of elastic waves by non-planar cracks. A fictitious surface is added to the crack so that a convenient closed surface is obtained and the surface fields on this closed surface are expanded in vector spherical harmonics. The edge conditions are introduced into these expansions and this is shown to be essential for the numerical convergence. Total cross sections and backscattering amplitudes as functions of frequency are computed numerically for rotationally symmetric cracks which are part of spherical or spheroidal surfaces. By integration in frequency backscattered pulses are also computed. Some cases with two cracks are also considered.     

SH波绕界面孔的散射

用波函数展开方法研究了SH波绕界面孔的散射问题。由入射、反射和透射波组成的自由波场与孔的散射场叠加成总波场。按照一定方式将两个半平面散射波场延拓于全平面，通过Hankel-Fourier展开方法求得了任意形状孔散射场的级数解。以椭圆形孔为例计算了孔边缘的动应力集中系数。     

双相介质半空间内椭圆夹杂对透射SH波的散射

为探究双相介质弹性半空间内椭圆弹性夹杂对透射SH波的散射问题,主要采用Green函数法、复变函数法、保角映射法和极坐标移动技术。首先,引入复变量并在复平面上运用保角映射的方法将椭圆边界映射为单位圆边界;然后,将双相介质沿垂直边界剖开分成两个四分之一空间,在剖分面上作用附加力系使SH波在垂直边界上满足位移和应力连续的条件,并构造四分之一空间内点源荷载作用下的Green函数位移场;进而,利用"契合"的思想在垂直边界上建立定解积分方程组,并利用SH波衰减的性质进行有限项截断来求解未知附加力系。最后,通过具体算例得出在不同参数情况下椭圆夹杂周边动应力集中因子分布情况。结果得知,SH波的入射角度和频率以及介质的性质对夹杂周边动应力集中分布有一定影响。     

Scattering of guided waves by circumferential cracks in composite cylinders

A somewhat generalized numerical procedure is used in this paper to study the problem of wave scattering by circumferential cracks in composite pipes. The study is motivated by the need to develop a model for the quantitative, ultrasonic non-destructive evaluation of cracks in pipes. For this purpose, a stiffness-based Rayleigh–Ritz type approach is employed first to obtain the approximate wave numbers and wave modes. Using the wave function expansions of the incident and scattered fields in the axial direction and decomposing the problem into separate symmetric and anti-symmetric problems, a three-dimensional wave scattering problem is reduced to two, independent two-dimensional problems over the circular cross-section. Both these problems can be reduced further to quasi-one-dimensions by discretizing the cross-section into finite elements and using a transfer matrix approach in the circumferential direction. This simplification greatly reduces the computational time. A comparison of the results for an isotropic pipe demonstrates the reliability and accuracy of the modified numerical procedure. Numerical results for the reflection and transmission coefficients of different incident wave modes are also presented for a 2-ply composite pipe with a crack. The crack may have an arbitrary circumferential length and radial depth. Simple extrapolations from one wave to another wave, separately incident on a crack, are demonstrated to be impossible due to different mode conversions by the crack.