Early flame propagation of hydrogen enriched methane-air mixtures at quasi laminar conditions in a rapid compression expansion machine

The temporal evolution of the kinematic properties of hydrogen enriched, lean premixed methane-air flames was studied experimentally in a rapid compression expansion machine (RCEM) during transient operation. Schlieren imaging was used to capture the flame front propagation, while the temporally evolving flow field was simultaneously acquired by particle image velocimetry (PIV). A statistical analysis based on probability density functions (PDFs) of non-dimensional formulations of the flame curvature, stretch rate and displacement speed was performed to study the effect of the onset of flame instabilities on the aerodynamic characteristics of the propagating flame kernel. It was found that initial perturbations stemming from the presence of the spark plug electrodes and from the gas expansion led to the formation of large scale cusps related to the hydrodynamic instability, which is manifested by a notable negative skewness of the curvature PDF, validating recent numerical findings. Under the influence of thermal-diffusive effects, small scale cellular structures develop along the flame front beyond a certain radius, with their appearance shifting to earlier times with increasing hydrogen content or for leaner mixtures. The increasing width of the normalized curvature and stretch rate PDFs is proposed as an indicator for the onset of this type of instability. The adopted methodology allows to track the self-acceleration of the propagating flame front effecting from hydrogen enrichment of methane. The findings of this study provide valuable physical insight and aid in the development of more accurate models, capable of capturing these complex phenomena.     

球囊扩张式血管支架介入对弯曲血管的生物力学损伤研究

构建了球囊扩张式血管支架介入系统的非线性有限元模型,考虑了血管斑块类型对其本构模型的影响,分析了A型与B型血管支架在血管狭窄率-24%、40%、50%,曲率半径-6 mm、10 mm、20 mm,狭窄血管的壁面应力分布规律,研究了血管支架构型、狭窄血管几何参数和血管生物力学损伤的关系。数值分析结果表明,血管壁面应力随着狭窄率的增加而显著升高,随着血管曲率半径的增加而下降相对平缓;但是,扩张加载阶段的血管壁面应力显著高于卸载阶段,易于引起血管斑块的脆性断裂引起血管生物力学损伤。由于A型血管支架相对于B型血管支架具有纵向柔顺性更优的联接筋构型,导致A型血管支架引起的血管壁面应力低于B型支架,因而降低了A型血管支架对于血管的生物力学损伤。     

青年男性肩点横截面曲线及其体型细分

为建立基于横截面曲线形态指标细分青年男性肩部体型的方法,选取了年龄在18~26周岁的213名在校青年男性,用三维人体扫描仪测量获得其肩部数据,借助IMAGEWARE 12.0与Mat Lab R2012b软件,利用冒泡排序算法实现了肩点的自动准确提取,且肩高相对误差控制在(0,0.011)之间;通过分析肩点横截面形态特征,提取了曲线曲率半径及矢额径比作为分类指标,对比曲率半径均值,确定了5个特征点角度为-50°、-35°、0°、50°与90°;应用K-Means聚类方法及方差分析,将肩部体型划分为4类,建立了依据特征点曲率半径与矢额径比细分肩部体型的方法,通过对比肩点截面曲线形态,进一步定性描述了4类肩部截面的曲线变化特征。     

Orthogonal nonnegative matrix factorization based local hidden Markov model for multimode process monitoring

Traditional data driven fault detection methods assume that the process operates in a single mode so that they cannot perform well in processes with multiple operating modes. To monitor multimode processes effectively, this paper proposes a novel process monitoring scheme based on orthogonal nonnegative matrix factorization (ONMF) and hidden Markov model (HMM). The new clustering technique ONMF is employed to separate data fromdifferent processmodes. ThemultipleHMMs for various operating modes lead to highermodeling accuracy. The proposed approach does not presume the distribution of data in each mode because the process uncertainty and dynamics can bewell interpreted through the hidden Markov estimation. The HMM-based monitoring indication named negative log likelihood probability is utilized for fault detection. In order to assess the proposed monitoring strategy, a numerical example and the Tennessee Eastman process are used. The results demonstrate that this method provides efficient fault detection performance.     

Effect of Space Charge on the Propagation Path of Air Gap Discharge

The existence of space charge may be addressed as one of the reasons that could cause shielding failure of transmission lines. In order to study the effect of s...     

引入蛇模型的曲率驱动扩散图像修复方法

数字图像修复方法可以自动地修复数字图像中用户定义的污损区域。T.F.Chan等人提出的非纹理的曲率驱动扩散算法是基于偏微分方程的图像修复的代表算法之一。通过在该算法中应用蛇模型的图像增强项,提出了引入蛇模型的曲率驱动扩散图像修复方法,在热扩散过程中,拉动曲线向目标边界演化,达到修复污损图像中的断裂边缘的目的,从而较好保持图像的视觉连通性。实验结果表明,在迭代次数相同的条件下,可以比原始的曲率驱动扩散图像修复算法获得更好的修复效果。     

基于四阶非线性扩散方程的新型图像去噪方法

提出了一种基于新型扩散系数函数的图像去噪方法,这种扩散系数函数是利用图像特征的一些特殊性质构造出来的。该函数较常用的P-M启发性扩散系数函数,在图像去噪的过程中,不仅能更好地抑制、平滑噪声,较完整保留了图像的细节,使图像更平滑清晰,而且还大大降低了参数的选取难度以及参数对实验效果的影响程度。并通过基于该方法的四阶非线性扩散的图像去噪实验,结果表明了该方法的有效性。     

辊式板带矫直机压下量的计算和设定

在研究矫直辊间板带弯曲挠度的基础上,给出了压下调整量的计算方法,建立了基于反向弯曲挠度和弹复曲率计算弯曲力矩的方法,更便于考虑材料的强化和矫直机的型式及调整方案,对矫直机的设计和生产具有实际应用价值。     

江西城门山矿区ZKJ4-10孔螺杆定向纠斜技术

江西省九江县城门山矿区补充勘查项目设计钻孔多为超斜孔,钻孔弯曲度要求高,施工难度大。该矿区多个钻孔都面临着纠斜的难题。本文结合矿区深孔ZKJ4-10孔定向纠斜实例,详细介绍了螺杆钻定向纠斜技术的工作原理、配套设备、操作方法及注意事项。通过矿区钻孔纠斜效果,总结了该技术的优点及不足,为今后地质深孔定向纠斜施工提供了借鉴。     

TiN薄膜的残余应力调控及力学性能研究

残余应力是制约物理气相沉积（Physical vapor deposition,PVD）硬质薄膜厚度的关键因素。采用多弧离子镀技术在高速钢基体上制备了厚度从3.7 m到15.5 m的TiN薄膜,结合曲率法和有限元法研究残余应力及结合性能随膜厚的变化规律。结果表明,随着膜厚的增加,基片弯曲程度加剧,而薄膜平均残余应力降低;膜层内残余应力的整体水平决定了界面切应力大小,薄膜结合性能随界面切应力的增加而降低。增加基体偏压、降低工作气压均导致薄膜内部残余应力的升高。当残余压应力较高时,TiN薄膜具有细小、致密的柱状晶结构,并呈现（111）择优取向,薄膜硬度及断裂韧度较高,耐磨性能良好。研究结果提示我们,通过残余应力的调控可提高硬质薄膜的力学特性。