变分理论在一维非均匀介质中波传播的应用

基于变分理论研究一维情况下非均匀各向同性介质中的波的特性。变分方程利用有限元方法,通过数值解法求解,并对含有空心砖的墙体给出数值结果。推导出的变分公式能够处理介电常数和磁导率变化的各种分布,同时也能够处理水平和垂直极化的问题。     

非均匀介质中弹性波的传播

对弹性波在非均匀介质传播时的波幅进行了研究,用解析方法探讨了非均匀区域性质变化时对弹性波波幅的影响,将非均匀区域离散成薄层,建立了波动方程和波幅传递矩阵,通过数值计算结果与解析解的比较,为弹性波在工程中的应用提供了计算分析的依据.     

非均匀介质中Maxwell方程的积分解

在无散射的非均匀介质自由空间中,将Maxwell方程进行三维空间的Fourier变换,并把它记为三阶矩阵和幺矩阵形式,利用它得到E的积分解;研究了电磁波在非均匀介质中的传播,并进行具体计算。     

一种新的非均匀介质表面漫反射光成分提取方法

在非均匀介质表面,强光是漫反射光成分和镜面反射光成分的线性组合．结合非均匀介质表面反射特点和漫反射光成分之间的线性组合关系,文中提出一种新的基于测定光度的线性化方法,它可以计算出不同光照条件下图像之间的线性组合系数,并在此基础上提取非均匀介质表面漫反射光成分．实验结果表明,该方法可以有效地提取真实瓷器表面的漫反射光成分．     

一种非均匀介质中光线方程的解

对一种折射率非均匀分布介质中的光线方程进行了求解，在傍轴近似及εｘ《１的条件下，求得了光线在该介质中的传播的轨迹，并对其结果进行了分析与讨论。该结果应用于弯曲光纤中光线的传播，可以求出一系列的重要的参数。从而对弯曲光纤的很多物理现象作出符合实际的理论解释。     

基于非均匀光照下文本图像二值化改进算法

针对传统局部阈值算法分割非均匀光照图像效果不佳,且计算时间较长的问题,提出了一种基于局部均值的图像二值化改进算法。该算法首先使用积分图像的快速算法计算出局部均值,再将计算出的局部均值代入改进的阈值模型算法中,最终完成分割,从而进一步改善了在非均匀光照下的图像分割效果。对比实验结果表明,改进的二值化算法大大提高了运算效率,增强了图像分割效果,在视觉效果和处理时间2个方面都优于Niblack算法、Sauvola算法、Bernsen算法以及基于局部对比度和均值的算法。     

非均匀介质激发极化二次电流场欧姆定律微分形式及异常特征

在一般条件下,非均匀介质中,二次极化电场的异常电流密度和异常电场强度的关系,不能用通常简单的欧姆定律微分形式表达。二次异常电流密度不仅与二次极化异常电场强度有关,而且还与一次场有关,两者的方向一般不同,甚至相反。     

单轴加载下煤样失稳破坏的多参量前兆特征

建立了多参量监测系统,包括声发射、介电常数、应变场和表面温度场等监测手段,来研究在单轴压缩条件下,变形局部化演化过程中煤样失稳破坏的多参量前兆特征.研究发现:在煤样劈裂破坏过程中,变形局部化带的演化经历了3个阶段:在第Ⅰ阶段中,变形局部化相对滑动分量占据主导;第Ⅱ阶段中,相对拉伸分量快速增加;第Ⅲ阶段中,相对拉伸分量和相对滑动分量均急剧增大.样品表面温度场前兆特征发生在第Ⅱ阶段,介电常数前兆特征发生在第Ⅲ阶段,声发射前兆特征发生在第Ⅰ和第Ⅱ阶段.     

存在复杂非均匀层的一维大地电磁正演

二、三维大地电磁（ＭＴ）正反演常采用一维反演结果作为初始迭代模型或利用一维模型响应定义边界条件,为进一步研究复杂地层条件下的ＭＴ响应,本文推导了非均匀层电导率随深度按线性－指数函数变化和指数－线性函数变化的一维ＭＴ正演的解析解形式,在此基础上对不同的地层组合情况进行讨论,分析了非均匀层埋深、厚度对ＭＴ响应的影响,并与地下介质均匀以及非均匀层电导率随深度按单一函数变化的ＭＴ响应进行对比。结果表明,既存在线性变化又存在指数变化的介质模型ＭＴ响应远比单一变化介质模型复杂,随着过渡层厚度增大、埋深变浅,其视电阻率和相位幅值与均匀介质模型响应幅值差异变大。     

基于分段线性模型的卡尔曼滤波非均匀校正算法

为了降低探测器响应的漂移以及非线性对非均匀性校正的影响,提出了一种基于分段线性模型的卡尔曼滤波红外焦平面阵列非均匀性校正算法。该算法引入探测器响应曲线的分段线性模型,对基于卡尔曼滤波器的红外焦平面非均匀性校正算法进行了扩展和改进,不仅能减小探测器的偏置和增益随时间漂移对校正的影响,而且还能消除探测器响应非线性对非均匀性校正性能的影响。一组利用真实红外图像序列进行的实验验证了该算法可获得较好的校正性能。     

Catastrophe model and its experimental verification of static loading rock system under impact load

According to the catastrophe model for impact buckling of static loading structures, a new catastrophe model for impact loading failure of a static loading rock system was established, and one dimension （1D） catastrophe model was analyzed. The analysis results indicate that the furcation collection where catastrophe may take place is not only decided by mechanical system itself but also relates to exterior loading, which is different from the results obtained under mono-static loading where the bifurcation collection is only determined by mechanics of the system itself and has nothing to do with exterior loading. In addition, the corresponding 1D coupled static-dynamic loading experiment is designed to verify the analysis results of catastrophe model. The test is done with Instron 1342 electroservo controlled testing system, in which medium strain rate is caused by monotony rising dynamic load. The parameters are obtained combining theoretical model with experiment. The experimental and theoretical curves of critical dynamic load vs static load are rather coincided, thus the new model is proved to be correct.     

弹体材料不同偏移量脆性带的破碎过程模拟

为了优选弹体材料脆性带加工方案,增强弹丸杀伤威力,提高材料利用率,运用有限元软件ANSYS的显示动力学部分,分别对不含脆性带、含有对称分布以及有偏移量的十字形脆性带合金钢试件断裂过程进行了模拟.通过网格和应力波变化图以及冲击过程中锤头所受阻力加速度和能量转化的对比分析,结果表明:含脆性带的试件比不含脆性带的试件冲击时更易断裂;含脆性带试件断裂先产生应力的位置是脆性带附近,断裂沿脆性带发生;将对称分布和有偏移量的脆性带试件断裂过程对比,能量转化值与锤头所受阻力加速度值相近,说明脆性带的偏移量对试件断裂影响不显著.     

俯斜开采超高水材料袋式充填体失稳机理及防治

针对俯斜开采条件下采空区超高水材料袋式充填体容易失稳的情况,进行了袋式充填体失稳机理及防治方法的研究.提出了采空区袋式充填体有垮塌失稳、滑移失稳和倾倒失稳3种失稳形式,建立了充填体力学模型,分析并计算了各种失稳形式下的充填体失稳条件,给出了防治方法.研究表明:减小工作面俯斜角对充填体的各种失稳形式均能起到有效的防治作用;减小充填体高度、提高充填体的早期强度、延长对充填体的临时支护时间有助于防止充填体发生垮塌失稳;增大充填体宽度、减小充填体高度有助于防止充填体发生倾倒失稳.另外,适当增大工作面的控顶距,待充填体与顶板接触后再移除其前方的支护设备,也可有效防止充填体发生滑移失稳和倾倒失稳.     

Mechanical behavior and failure analysis of brittle sandstone specimens containing combined flaws under uniaxial compression

Based on the axial stress-axial strain curves, the effect of fissure angle on the strength and deformation behavior of sandstone specimens containing combined flaws is analyzed. The mechanical parameters of sandstone specimens containing Combined flaws are all lower than that of intact specimen, but the reduction extent is distinctly related to the fissure angle. The results of sandstone specimens containing combined flaws are obtained by the acoustic emission, which can be used to monitor the crack initiation and propagation. The ultimate failure mode and crack coalescence behavior are evaluated for brittle sandstone specimens containing combined flaws. Nine different crack types are identified on the basis of their geometry and crack coalescence mechanism （tensile crack, hole collapse, far-field crack and surface spalling） for combined flaws. The photographic monitoring was also adopted for uniaxial compression test in order to confirm the sequence of crack coalescence in brittle sandstone specimens containing combined flaws, which recorded the real-time crack coalescence process during entire deformation. According to the monitored results, the effect of crack coalescence process on the strength and deformation behavior is investigated based on a detailed analysis for brittle sandstone specimens containing combined flaws by using digital photogrammetry.     

R-T instability model of magnetic fluid and its numerical simulations

The Rayleigh-Taylor(R-T) instability of ferrofluid has been the subject of recent research,because of its implications on the stability of stellar.By neglecting the viscosity and rotation of magnetic fluid,and assuming that the magnetic particles are irrotational and temperature insensitive,we obtain a simplified R-T instability model of magnetic fluid.For the interface tracing,we use five-order weighted essentially non-oscillatory(WENO) scheme to spatial direction and three-order TVD R-K method to time direction on the uniform mesh,respectively.If the direction of the external magnetic field is the same as that of gravity,the velocities of the interface will be increased.But if the direction of the external magnetic field is in opposition to the direction of gravity,the velocities of the interface will be decreased.When the direction of the external magnetic field is perpendicular to the direction of gravity,the symmetry of the interface will be destroyed.Because of the action which is produced by perpendicular external magnetic field,there are other bubbles at the boudaries which parallel the direction of gravity.When we increase the magnetic susceptibility of the magnetic fluids,the effects of external magnetic fields will be more distinct for the interface tracing.     

Analysis of progressive failure of pillar and instability criterion based on gradient-dependent plasticity

A mechanical model for strain softening pillar is proposed considering the characteristics of progressive shear failure and strain localization. The pillar undergoes elastic, strain softening and slabbing stages. In the elastic stage, vertical compressive stress and deformation at upper end of pillar are uniform, while in the strain softening stage there appears nonuniform due to occurrence of shear bands, leading to the decrease of load-carrying capacity.In addition, the size of failure zone increases in the strain softening stage and reaches its maximum value when slabbing begins. In the latter two stages, the size of elastic core always decreases. In the slabbing stage, the size of failure zone remains a constant and the pillar becomes thinner. Total deformation of the pillar is derived by linearly elastic Hooke‘s law and gradient-dependent plasticity where thickness of localization band is determined according to the characteristic length. Post-peak stiffness is proposed according to analytical solution of averaged compressive stressaverage deformation curve. Instability criterion of the pillar and roof strata system is proposed analytically using instability condition given by Salamon. It is found that the constitutive parameters of material of pillar, the geometrical size of pillar and the number of shear bands influence the stability of the system; stress gradient controls the starting time of slabbing, however it has no influence on the post-peak stiffness of the pillar.     

双主体动态异质性报酬组合激励机制的建模与应用

基于激励源的多维和多层次特征,研究委托-代理关系中的异质性报酬组合激励问题,讨论报酬组合激励机制的构建途径,给出双主体异质性报酬组合激励模型.分析指出激励效果不但取决于企业管理者的能力,而且也取决于企业所有者的激励模式;长期内,企业管理者的潜力是有效激励的关键.基于企业生命周期理论和人生心理发展周期理论,以企业成长为主线,讨论企业管理者不同阶段的双主体异质性报酬组合激励模式,体现激励的动态性.     

静载下连杆裂解裂尖塑性区及其对裂解质量的影响

对静载条件下连杆裂解过程进行了数值分析,将连杆裂尖附近塑性区形状与理想状态进行了对比,定性给出了连杆断裂前裂纹区应力应变状态,并据此分析了不同位置的断裂状态。结果表明,连杆厚度方向不同的层面处于不同的平面应变与平面应力状态,裂尖塑性区大小也不同,启裂首先发生在塑性区较早达到变形极限的平面应变区。裂尖塑性区的差异造成启裂点散布、裂纹扩展不同步,扩展路径不同,极易造成裂纹分叉、交汇异常等问题,并引起撕裂、崩角、断裂面台阶、夹屑、外缘爆口等裂解缺陷,从而影响连杆裂解加工质量。     

热电材料碲化铅PbTe的晶体生长及物理性质研究

研究了用于热电变换器件的半导体材料碲化铅晶体气相生长和区熔生长的生长特性,测试了碲化铅的热电性质,结果表明,不掺杂的碲化铅室温下为Ｐ型,温差电动势率随温度的升高先缓慢增大然后快速减小,最后转变为Ｎ型。     

混凝土拉伸荷载条件下细观破损过程的CT试验研究

对静力、动力拉伸荷载条件下混凝土的细观破损过程进行了CT试验研究,获得了试样内部裂纹萌生、扩展、贯通的全过程CT图像。通过对CT图像及图像兴趣区中整体统计区域、局部统计区域CT数均值的分析,研究了混凝土拉伸荷载条件下细观破损过程。结果表明:静力拉伸荷载条件下,裂纹在界面的薄弱区域形成后逐渐往相邻的薄弱部位扩展,两个统计区域CT数均值呈降低趋势,试样破坏时伴有少量骨料被拉断的现象;动力拉伸荷载条件下,裂纹从界面薄弱区域形成后追随最快的路径扩展,局部统计区域CT数均值呈下降趋势,而整体统计区域CT数均值变化幅度较小,破坏后骨料沿界面脱离砂浆粘结,且试样破裂面更为平整;由于加载速率的提高,骨料被拉断的现象非常显著。