地下厂房围岩变形的分形特性研究

依据地下厂房围岩各点位移在时域上的变化特征,剖析了围岩各点变形的分形特性,探讨了分形维数的变化规律与趋势。研究发现,仪器各测点的位移时域曲线分形维数的极大值均出现在被裂缝穿越的厂(横)0+115.60断面上,究其原因,是该断面相对其他部位存在更多引发围岩变形的因素,导致所测位移时间曲线的不规则程度增大,使其存在更多精细结构,因而量测出的维数将更大。位移时间曲线维数达到极大值极有可能是仪器埋设处围岩开裂的迹象与先兆,这可作为围岩开裂与否的判据。     

分形维数与铣削参数的模型关联及验证

基于工程粗糙表面的微观形貌具有统计自相似分形特征,将分形几何学运用于金属材料表面形貌研究。粗糙表面的分形参数与加工条件密切相关。铣削加工过程中,切削参数会影响表面分形维数和表面粗糙度,考察了分形维数和传统表面粗糙度参数之间的关系,分别建立铣削参数与表面分形维数和表面粗糙度之间关系模型,并采用实验进行验证。实验结果表明,铣削加工表面具有分形特征;铣削表面分形维数D基本不随切削速度增加而变化,但表面粗糙度Ra会随切削速度的增加而减小;表面粗糙度与加工进给量成正相关,分形维数先增大后减小,并存在临界点;分形维数D与表面粗糙度Ra呈幂指数关系;所建立模型合理。相关研究结果可以为提高工程表面的使用性能及降低成本提供参考。     

分形分析在齿轮箱缺陷检测中的应用

具有多尺度(分辨)分析和时-频局部化特性的分形分析技术,特别适用于边缘信号和峰值突变信号的处理和特征提取,因此在齿轮箱缺陷检测中和诊断将会有很大的发展前途.用分形变换的方法对齿轮传动过程中进行初步缺陷检测和诊断,结果表明分形分析在齿轮箱缺陷检测中和诊断有很好的应用前景.     

高阶煤的孔隙结构特征及其对煤层气解吸的影响

以沁水盆地高阶煤3^#煤层为研究对象,借助高压压汞实验对高阶煤的孔隙参数进行测试,研究了高阶煤的孔隙结构特征,采用解吸速率实验对高阶煤的解吸速率和解吸量进行分析,并探讨了孔隙结构对煤层气解吸产出的控制规律。结果表明:3^#煤层的孔隙半径较小,煤层孔隙结构复杂;煤层主要以气体吸附孔和气体扩散孔为主,气体渗流孔占比很少,煤层的吸附气体体积大、吸附性能强、气体的扩散、渗流条件差。3^#煤层孔隙结构分形特征曲线呈"两段型",孔径大于940.7 nm时,不具有分形特征;孔径小于940.7 nm时,分形维数介于2.67~2.76之间,具有很好的分形特征。高阶煤的煤层气解吸特征具有快速解吸和慢速解吸2个阶段,快速解吸时间短,解吸量占比低;慢速解吸时间长,解吸量占比高,煤层气解吸困难。煤层的孔隙结构对煤层气的解吸具有重要影响,高阶煤较差的孔隙结构控制着煤层气解吸速率慢、解吸量低、产出程度低,煤层气井生产实践中表现为开始阶段产气量增长快,产气高峰时间短,稳产气量低、生产时间长,煤层气开发难度大。研究结果为高阶煤的煤层气抽采效果评价提供参考依据。     

一种基于分形图像编码的数字水印新技术

以不降低图像质量而提高水印鲁棒性为目的,提出了一种利用图像中存在的局部自相似性嵌入水印的数字水印新技术.对数字图像进行传统的分形编码后,选取一定数量的值域子块作为"水印块",根据水印信号对"水印块"进行分形编码参数修正,从而实现水印嵌入.计算机仿真实验和数据分析表明,与传统方法相比,方法对图像质量几乎没有影响,而且在抗剪切处理、抗噪声干扰、抗低通滤波和抗JPEG压缩方面有更好的鲁棒性.仿真结果证明了自相似性分形图像编码理论在数字水印技术中的成功应用.     

基于支持向量机的复杂地质分形特征自动提取

为了提升勘探工作效率,准确提取复杂地质分形特征,提出一种支持向量机的复杂地质分形特征自动提取方法.在两种线性可分情况下,将最佳的分类面简化为最佳分类直线,获得最佳分类平面;考虑噪声及其它干扰因素造成线性不可分的状况,得到广义的最佳分类面;基于两点可以得出支持向量机内积;通过抽取异常重磁分维数的频率域角度获得分维值,反映...     

Microstructure–function relationships of heat-induced gels of porcine haemoglobin

The purpose of this work was to use image analysis to study the microstructural properties of haemoglobin gels, with structural changes induced by pH conditions, and their correlations with physical properties such as texture and water holding capacity (WHC). Two types of networks showing great differences in the dimensions of the gel structure were obtained as influenced by pH. At pH < 5.5 there was a shift from an aggregated to a fine-stranded gel type. Fractal dimension values revealed that more complex structures corresponded to softest and non-exudative gels. Lacunarity and pore size, which were used to study the pore distribution within the network, confirmed that softest gels with high WHC showed large number of small cavities. Finally, correlations between textural attributes, i.e. springiness and adhesiveness, and spatial variability, referred quantitatively to the degree of compactness, were also established.     

On the fractal characteristics of low Damköhler number flames

Knowledge of the fractal properties of premixed flame surfaces can potentially be used to help develop turbulent combustion models. Here, direct numerical simulations of low Damköhler number flames are used to analyse the fractal nature of the flames. Two sets of data are considered: (i) thermochemical hydrogen–air turbulent premixed plane-jet flames with detailed chemistry and (ii) thermonuclear flames in type Ia supernovae. A three-dimensional box counting method is used to investigate fractal dimension of the flame surface, characterising the self similarity of flame fronts. In the premixed flames, the fractal dimension is found to vary in time between 2.1 and 2.7. The supernovae flames in distributed combustion regimes yield fractal dimension about 2.7. The results for the maximum fractal dimensions are higher than previously reported. They are explained theoretically by a Reynolds number similarity argument which posits that the high Reynolds number, low Damköhler number limiting value of the fractal dimension is 8/3. Also tested is Mandelbrot’s fractal additive law which relates the fractal dimension determined in two dimensions, which is typical of experimental measurements, to that in three dimensions. The comparison of the fractal dimension in both two-dimensional and three-dimensional spaces supports the additive law, even though the flames considered do not formally satisfy isotropy. Finally, the inner-cut off is extracted from the hydrogen flames and found to be consistent in order of magnitude with Kolmogorov scaling.     

Fractal finite element method based shape sensitivity analysis of multiple crack system

This paper presents fractal finite element based continuum shape sensitivity analysis for a multiple crack system in a homogeneous, isotropic, and two dimensional linear-elastic body subjected to mixed-mode (modes I and II) loading conditions. The salient feature of this method is that the stress intensity factors and their derivatives for the multiple crack system can be obtained efficiently since it only requires an evaluation of the same set of fractal finite element matrix equations with a different fictitious load. Three numerical examples are presented to calculate the first-order derivative of the stress intensity factors or energy release rates.