浅埋煤层群采场周期来压顶板结构及支架载荷

现场勘查发现,神府矿区浅埋煤层群间隔岩层厚度大多在15～45 m时,间隔岩层易存在单一关键层结构。文章通过现场实测得出了浅埋煤层群开采周期来压的基本特征:来压步距减小、强度增大、煤壁片帮严重,动载现象、台阶下沉现象和大、小周期来压现象明显。物理相似模拟实验揭示了间隔岩层关键层与上煤层已扰动关键层同步与非同步破断的大、小周期来压机理,发现了间隔岩层关键层与已扰动关键层共同形成的"梁-拱-壳"结构形态,给出了上煤层已扰动关键层结构形态的判别方法,得出了浅埋煤层群开采顶板周期破断可形成"台阶-台阶"、"砌体-台阶"、"砌体-砌体"的基本结构。综合建立了浅埋煤层群开采间隔岩层周期破断结构与力学模型,给出了支架受动静载荷作用的工作阻力计算方法,并得到了现场验证。     

Asynchronous control for two‐dimensional hidden Markovian jump systems with partly known mode observation conditional probabilities

This study focuses on the asynchronous control problem for two‐dimensional discrete‐time hidden Markovian jump systems where the mode observation conditional probability matrix is partly known. Considering the original system modes are invisible, the observed modes emitted from an observer serve as an alternative for stability analysis and controller design where a mode observation conditional probability matrix is constructed to characterize the emission between system modes and observed modes. Specially, only partly known information of the mode observation conditional probability matrix is accessible. With the introduction of the free‐connection weighting matrices, the asymptotic mean square stability criterion is firstly derived based on Lyapunov method. This introduction provides a further degree of relaxation and less conservatism is therefore achieved. Secondly, we present synthesis conditions for asynchronous state feedback controller design given in terms of a set of interconnected linear matrix inequalities. Moreover, cluster concept based on the partitions of observed modes is adopted which helps to decrease the number of controllers and simplify the design complexity. A numerical example, regarding the cases with and without clustering of the observed modes, is presented to illustrate the effectiveness of the proposed method.     

Reference governors and maximal output admissible sets for linear periodic systems

ABSTRACT

In this paper, we consider the problem of constraint management in Linear Periodic (LP) systems using Reference Governors (RG). First, we introduce the periodic-invariant maximal output admissible sets for LP systems. We extend the earlier results in the literature to Lyapunov stable LP systems with output constraints, which arise in RG applications. We show that, while the invariant sets for these systems may not be finitely determined, a finitely-determined inner approximation, which is periodically invariant, can be obtained by constraint tightening. We then analyze the geometric and algebraic relationship between these sets and show that these sets are related via simple transformations, implying that it suffices to compute only one of them for real-time applications. This greatly reduces the memory burden of RG (or other similar constraint management strategies), at the expense of an increase in processing requirements. We present a thorough analysis of this trade-off. In the second part of this paper, we present two RG formulations, and discuss their properties and algorithms for their computation. Numerical simulations demonstrate the efficacy of the approach.     

The periodic system and the idea of a chemical element: From Mendeleev to superheavy elements

Like other scientific concepts, the idea of a chemical element has changed considerably over time, since it was first established in the Enlightenment era. In Dmitri Mendeleev's construction of the periodic system, he distinguished between simple substances and elements as defined by their atomic weights. The foundation of the periodic system on the latter concept led to several challenges. For example, the system seemed unable to accommodate the radioactive substances eventually recognised as isotopes. Around 1920, elements were consequently redefined in terms of their atomic numbers, a nuclear property that could be determined by X‐ray spectroscopy. Although this understanding of an element has stood the test of time, new questions turned up relating to the concept of an element following the syntheses of transuranic elements since the early 1940s. These syntheses of very heavy elements have additionally led chemists and physicists to reconsider the criteria for the discovery of a new element. Recently, elements have been officially recognised on the sole ground that a small number of very heavy atomic nuclei were identified. The paper discusses how the notion of an element was modified during different periods of time, the reasons for the modifications, and the values ascribed to them in the communities of chemists and physicists.     

基于熵加权K-means全局信息聚类的高光谱图像分类

目的 高光谱图像波段数目巨大，导致在解译及分类过程中出现“维数灾难”的现象。针对该问题，在K-means聚类算法基础上，考虑各个波段对不同聚类的重要程度，同时顾及类间信息，提出一种基于熵加权K-means全局信息聚类的高光谱图像分类算法。方法 首先，引入波段权重，用来刻画各个波段对不同聚类的重要程度，并定义熵信息测度表达该权重。其次，为避免局部最优聚类，引入类间距离测度实现全局最优聚类。最后，将上述两类测度引入K-means聚类目标函数，通过最小化目标函数得到最优分类结果。结果 为了验证提出的高光谱图像分类方法的有效性，对Salinas高光谱图像和Pavia University高光谱图像标准图中的地物类别根据其光谱反射率差异程度进行合并，将合并后的标准图作为新的标准分类图。分别采用本文算法和传统K-means算法对Salinas高光谱图像和Pavia University高光谱图像进行实验，并定性、定量地评价和分析了实验结果。对于图像中合并后的地物类别，光谱反射率差异程度大，从视觉上看，本文算法较传统K-means算法有更好的分类结果；从分类精度看，本文算法的总精度分别为92.20%和82.96%， K-means算法的总精度分别为83.39%和67.06%，较K-means算法增长8.81%和15.9%。结论 提出一种基于熵加权K-means全局信息聚类的高光谱图像分类算法，实验结果表明，本文算法对高光谱图像中具有不同光谱反射率差异程度的各类地物目标均能取得很好的分类结果。     

基于FLAC3D的综放面矿压显现规律研究

为了确保矿井的安全开采，揭示某矿矿压显现规律，采用FLAC^3D数值模拟软件对工作面走向、倾向力学和位移特征以及工作面初步来压步距、周期来压步距进行了模拟分析。研究得出:在沿走向方向，工作面顶板面形成拱形分布的应力释放区，随着工作面的推进，顶板的覆岩高度和应力拱结构逐渐向上发展；在沿倾向方向，工作面顶底板的位移分布呈现非对称的特征，顶板应力轮廓向工作面倾斜上方偏移；工作面的初次来压步距为40 m，周期来压平均步距为11.8 m，为工作面的支护选择和支护方式提供理论依据，为顶板围岩控制提供了重要参数。     

基于加权法的砾类土含水率检测

砾类土在工程建设中有着广泛的应用,其含水率是一项非常重要的指标,但现有测试方法耗时较长。以砂砾石料的砾类土为试验对象,基于加权法思想,将饱和面干含水率替代法和虚拟比重法进行结合,开展砾类土含水率快速检测方法的研究,并对现有的饱和面干含水率测定操作进行一定的改进和优化。采用多种数学方法(绝对误差、均方偏差平方和,相关曲线的相关系数和F显著性检验分析法)对加权法和烘干法的结果进行对比分析。通过试验统计数据分析,证实加权法与烘干法的测定结果基本一致。该分析结果为现场土料含水率快速测定提供了一种新的思路和手段。     

富水覆岩长壁综放开采矿压显现规律研究

为了进一步研究富水覆岩长壁综放工作面推进过程中的矿压显现机理，以大佛寺煤矿40301工作面为工程背景，采用相似模拟的方法，研究工作面推进过程中的矿压显现规律，并掌握上覆岩层在工作面推进过程中变形破断和裂隙发展规律。研究表明，综放工作面上覆岩层矿压显现明显，基本顶初次来压和周期来压步距分别为63~72 m和27~33 m，在工作面的推进过程中，上覆岩层的裂隙发展会波及洛河组砂岩，可能会对采空区和工作面产生一定程度的危害。研究结果可为大佛寺煤矿综放开采提供理论依据，对同类地质条件下的综放开采有一定的借鉴意义。     

常村煤矿聚能预裂爆破弱化顶板技术研究

为缩短常村煤矿S2采区S206综放面的初次来压步距,以邻近的S208综放面为工程背景,根据聚能爆破机理分析,研究出一种聚能装药结构,利用聚能爆破的特性来提高顶板预裂效果。再通过ANSYS/LS-DYNA数值模拟,从应力云图、裂隙半径及压力-时间历程分析直接装药和聚能装药两种方式爆破的预裂效果,得出聚能装药爆破具有聚能效应,预裂效果更佳,更能弱化顶板,保障初采期安全。最终得出S208综放面初次来压步距为15.2m,与S206综放面相比,缩短了2.4m,提高了初采采出率,具有良好的经济价值和应用价值。