基于FBM模型的多媒体通信流特性分析

提出分形布朗运动(FBM)模型,将其应用于多媒体通信流特性分析。通过NS仿真实验得到有线网络和动态无线网络下的多媒体通信流,研究2种通信流的自相关系数、概率特性和突发性,结果证明典型的FBM模型无法全面刻画多媒体通信流。     

快速计算一维分层粗糙面之间金属目标复合散射的互耦迭代算法

为研究一维分层介质粗糙面之间金属目标的复合电磁散射特性,该文提出了一种结合前后向迭代算法(FBM)和双共轭梯度法(Bi-CG)的快速互耦迭代算法(CCIA)。推导了分层粗糙面与金属目标的耦合边界积分方程组,采用FBM和Bi-CG分别求解分层粗糙面与目标的边界积分方程,目标和分层粗糙面的相互作用通过更新两方程的激励项来实现。计算了双层介质高斯粗糙面及无限长金属圆柱的复合电磁散射特性,当目标尺寸趋于零时与只有分层粗糙面的散射系数相吻合,验证了该算法的正确性;分析了不同粗糙面情况下该算法的收敛性;讨论了目标尺寸与位置变化对复合散射系数的影响。结果表明,金属目标的存在明显影响了分层粗糙面的散射特性。     

基于FBM分形特征的快速小波地形模拟算法

该文基于FBM分形原理,采用Haar小波对自然地形数据进行模拟构建。在分析自然地形分形系数与小波系数之间关系的基础上,建立基于Haar小波的地形构建模型;通过对真实地形数据不同阶层小波系数统计计算得到分形特征参数;以构建模型为基础,结合分形特征参数,模拟生成自然地形。该算法相对真实地形数据具有小的交叉熵,且计算复杂度较小,仿真数据验证了算法的有效性。     

A model for drop size prediction during cross-flow emulsification

The formation of drops is a topic of great interest in a wide variety of engineering applications, such as membrane emulsification. In order to develop an improved force balance model that is capable of predicting the final size of the detached drop, the formation of drops into a cross-flowing continuous phase has been studied with computational fluid dynamics (CFD). The force balance model developed takes into account the drop deformation that occurs as the drop approaches detachment. The results given by the model have been compared with CFD simulations, and the drop diameters agree within 10%, except at low wall shear stresses. The model has also been compared with experimental results on drop formation using various membranes, cross-flow velocities and surfactants. The difference between the model and experimental results is mainly due to the adsorption of surfactants onto the drop interface and the shape of the membrane pores.     

基于理想导体界面的三维激光漫反射特性

针对激光点对点通信方式的不足,提出了利用海面作为激光漫反射媒介进行组网通信的设想,并对激光入射理想导体表面后产生的散射场进行了的研究。首先利用三维锥形波对三维入射激光束进行了模拟;然后对散射场在各个方向上的分量之间的耦合关系进行了研究,并列出矩阵方程;最后通过结合格林函数谱积分加速算法的前后向迭代法求解矩阵方程,得出三维散射系数,准确的表示了基于理想导体界面的三维激光漫反射特性,为进一步研究三维激光海面漫反射特性奠定了基础。     

实测海杂波频域分形特性分析

该文主要研究海杂波在频域中的分形特性以及不同参数对频域分形特性的影响。首先,该文以分数布朗运动(FBM)为例,较为系统地阐述了在时域FBM具有分形特性的前提下,FBM频谱也具有分形特性。然后,采用X波段与S波段实测海杂波数据验证频域中海杂波的分形特性,并分析了不同参数对频域海杂波分形特性的影响。结果表明,实测海杂波频谱在统计意义下满足自相似条件,具有分形特性,且频域分形特征对海杂波与目标回波表现出一定的可分性,具有在海杂波微弱目标检测中应用的潜力。     

Combinatorial fractal Brownian motion model

To solve the problem of how to determine the non-scaled interval when processing radar clutter using fractal Brownian motion (FBM) model, a concept of combinatorial FBM model is presented. Since the earth (or sea) surface varies diversely with space, a radar clutter contains several fractal structures, which coexist on all scales. Taking the combination of two FBMs into account, via theoretical derivation we establish a combinatorial FBM model and present a method to estimate its fractal parameters. The correctness of the model and the method is proved by simulation experiments and computation of practial data. Furthermore, we obtain the relationship between fractal parameters when processing combinatorial model with a single FBM model. Meanwhile, by theoretical analysis it is concluded that when combinatorial model is observed on different scales, one of the fractal structures is more obvious.     

基于分形的土壤水分输运机制与模型研究

通过对土壤中水分输运的物理机制的分析,利用分数布朗运动（FBM）解释了土壤内水分输运的物理机制,得出土壤内水分输运的定量数理解析模型,模型的解析解是具有分形特征的列维（Lévy）分布。用实例验证了土壤内水分的反常输运特征,揭示了土壤水分运动的内在机制,研究结果具有实际可应用性。     

Practical Time-Scale Fitting of Self-Similar Traffic with Markov-Modulated Poisson Process

Recent measurements of packet/cell streams in multimedia communication networks have revealed that they have the self-similar property and are of different characteristics from traditional traffic streams. In this paper, we first give some definitions of self-similarity. Then, we propose a fitting method for the self-similar traffic in terms of Markov-modulated Poisson process (MMPP). We construct an MMPP as the superposition of two-state MMPPs and fit it so as to match the variance function over several time-scales. Numerical examples show that the variance function of the self-similar process can be well represented by that of resulting MMPPs. We also examine the queueing behavior of the resulting MMPP/D/1 queueing systems. We compare the analytical results of MMPP/D/1 with the simulation ones of the queueing system with self-similar input.     

表征真实骨料形态的三维数值骨料建模

利用图像处理技术将骨料截面轮廓处理为二值图像,识别出各独立轮廓的形态特征后获取Hurst指数值的统计学规律,并使用改进的分形布朗运动(FBM)生成随机的数值骨料截面轮廓.使用该轮廓作为垂直于构建轴线的三维骨料上下两部分的连接面,基于改进的随机中点位移法,分别建立三维骨料的上曲面和下曲面并组装成完整的三维骨料模型.按相同纵长比生成的数值骨料与真实骨料具有相近的轮廓、扁平比和球度,且随机生成的数值骨料样本库与实测的真实骨料样本库具有类似的体积分布规律.按级配生成数值骨料并投放生成圆柱形沥青混凝土数值试件,相同工况下的仿真结果与单轴压缩蠕变试验数据的趋势吻合.