Fatigue life assessment of a low pressure steam turbine blade during transient resonant conditions using a probabilistic approach

This paper presents a sequential approach used in fatigue life prediction of a low pressure steam turbine blade during resonance conditions encountered during a turbine start-up by incorporating probabilistic principles. Material fatigue properties are determined through experimental testing of used blade material X22CrMoV12-1 along with statistical modelling using regression analysis to interpret the stress-life diagram. A finite element model of a free-standing LP blade is developed using the principle of sub-structuring which enables the vibration characteristics and transient stress response of the blade to be determined for variations in blade damping. Random curve fitting routines are performed on the fatigue and FEM stress data to ensure that the selection of the random variables used in fatigue life calculations is stochastic in nature. The random vectors are selected from a multivariate normal distribution. The use of confidence intervals in the probabilistic fatigue life model works effectively in being able to account for uncertainty in the material fatigue strength parameters and varying stress in the blade root. The predicted fatigue life of the blade is shown to be in good agreement with discrete life modelling results.     

Numerical simulation analysis and experimental validation on wear/fracture mechanisms of polycrystalline cubic boron nitride superabrasives in high-speed grinding

In this study, a two-dimensional finite element model is proposed to investigate the wear/fracture mechanisms of polycrystalline cubic boron nitride (PCBN) superabrasives in high-speed grinding process. The special geometric microstructures of PCBN grains are constructed by using the classic Voronoi tessellation technique, and cohesive elements are embedded into the geometric model of PCBN grains as the potential crack propagation paths for simulating the wear/fracture behaviours of PCBN grains under grinding loads. The effects of uncut chip thickness per grain (a_gmax) on the stress distribution characteristics and wear/fracture behaviours of PCBN grains during grinding are discussed in detail. Results show that the wear behaviour of PCBN grains during grinding mainly occurs around the grain vertex region; however, the fracture behaviour, leading to the quick failure of PCBN grains, is prone to appear around the grain–filler bonding interface, which is usually on the opposite side of the in-feed direction. Moreover, to separate the PCBN grains from the macro-fracture during grinding, the uncut chip thickness per grain should be kept smaller than 1.0?µm to prevent the unfavourable fracture behaviour from appearing around the grain–filler bonding interface. Furthermore, the corresponding single-grain grinding trials are performed to validate the numerical simulation results by evaluating the wear/fracture morphologies of the PCBN superabrasives in the actual grinding operation.     

Electrical and optical characteristics of atmospheric helium jet array plasma

In this paper, a honeycomb structure jet array with seven jet units was adopted to generate plasmas. Both the average discharge power and the emission intensity of the main excited species increase with increasing applied voltage. There are three stages of discharge evolution at different applied voltages: initial discharge, uniform discharge and strong coupling discharge.The spatial distribution of the emission intensity of the excited species can be divided into three categories: growth class, weakening class and variation class. The gas temperature along the whole plasma plume at different applied voltages is maintained at around 320K and can be widely used in heat-labile applications.     

Visual perception of Fourier rainbow holographic display

The rainbow hologram provides views of reconstruction with rainbow color within a large viewing zone. In our recent paper, a Fourier rainbow holographic display using diffraction grating and a white‐light LED source was introduced. In this technique, the rainbow effect is realized by the dispersion of white‐light source on diffraction grating, while the slit is implemented numerically by reducing the demands of the space‐bandwidth product of the display. This paper presents a novel analysis on the visual perception of the Fourier rainbow holographic display using Wigner distribution. The view‐dependent appearance of the image, including multispectral field of view and viewing zone, is investigated considering the observer and the display parameters. The resolution of the holographic view is also investigated. For this, a new quantitative assessment for image blur is introduced using Wigner distribution analysis. The analysis is supported with numerical simulations and experimentally captured optical reconstructions for the holograms of the computer model and real object generated with different slit size, reconstruction distance, and different observation conditions.     

Ab Initio Molecular-Dynamics Simulation Liquid and Amorphous Al_94-xNi₆La_x (x=3-9) Alloys

Ab initio molecular-dynamics simulations have been used to investigate the liquid and amorphous Al94-xNi6Lax (x=3-9) alloys. Through calculating the pair distribution functions and partial coordination numbers, the structure and properties of these alloys are researched, which will help the design bulk metallic glass. The concentration of La atoms can affect the short-range order of Al94-xNi6Lax alloys, which is also studied in this calculation result.     

基于经验分布和KL散度的协同过滤推荐质量评价研究

提出了一种基于经验分布和KL散度的协同过滤推荐质量评价方法RQE-EDKL（recommendation quality evaluation based on empirical distribution and KL divergence）。RQE-EDKL首先利用历史用户—商品数据生成不同商品数量下的商品历史使用概率分布；然后，利用该分布与各个协同过滤推荐方法得到的用户商品使用概率进行比较，计算其KL散度；最后，将KL散度最小的推荐结果视为最佳推荐结果并推送给用户。在TalkingData数据集上的实验结果表明，RQE-EDKL评价方法能够有效地在不同的推荐结果中选择更为切合用户真实需求的推荐结果，从而提高了协同过滤推荐的质量。     

基于神经网络算法的井下裂缝诊断与堵漏技术

在钻井过程中，常常钻遇不同宽度的井下地层裂缝。钻遇裂缝时容易发生钻井液漏失现象，甚至发生钻井液失返现象，严重影响了安全、高效钻井。目前裂缝封堵的方法常存在封堵成功率不高、堵漏承压能力低的问题，其中一个重要的原因是对井下地层的裂缝宽度等特征认识不清。基于地层裂缝产生的岩石力学机理，确定影响裂缝宽度关键的6个力学和工程因素，并利用神经网络计算的非线性、大数据特点建立了井下地层裂缝宽度的分析模型，模型包含输入层、输出层和3个隐藏层。通过该模型诊断井下裂缝宽度，提高了计算精度，平均误差仅为2.09%，最大误差为5.88%，解决钻井现场仅凭经验判断裂缝误差较大和依靠成像测井成本较高的问题。同时根据神经网络模型诊断得到的裂缝宽度优化堵漏材料的粒径配比，提高了裂缝内的架桥封堵强度和架桥的稳定性，封堵层的承压能力达到12.8 MPa，反向承压能力达到4.5 MPa。现场堵漏试验最高憋压10 MPa，经过封堵作业后大排量循环不漏，达到了裂缝性地层高效堵漏的目的，堵漏一次成功。      

考虑时变效应的致密气井产能评价——以延安气田为例

在致密气井的生产过程中，压裂裂缝导流能力、储层流体分布和气水相渗都会不断发生变化，具有时变效应，而传统的产能评价往往忽略了这种效应。针对这一问题，通过建立考虑裂缝导流能力时变效应和储层气水相渗时变效应的渗流数学模型，评价了时变效应对气井产能的影响。研究结果显示：压裂裂缝导流能力的时变效应增加了流体流动阻力，缩短了气井的稳产期；气井生产过程中，除了流体和岩石本身的膨胀能外，气水相渗的时变效应能够减小束缚水饱和度，使得部分束缚水转化为可动水，增大了水相渗透率，减小了气相渗透率，加快气井见水并增大气井产水量，促使气井递减提早出现。延安气田的实际气井生产表明，不考虑时变效应预测的稳产期偏长，预测的产水量远低于实际气井的产水量，时变效应对气井生产的影响不可忽略，结合延安气田开发实际还需进一步研究在立体井网开发模式下考虑时变效应的气井产能模型。