Micro-failure process and failure mechanism of brittle rock under uniaxial compression using continuous real-time wave velocity measurement

In this study,the micro-failure process and failure mechanism of a typical brittle rock under uniaxial compression are investigated via continuous real-time measurement of wave velocities.The experimental results indicate that the evolutions of wave velocities became progressively anisotropic under uniaxial loading due to the direction-dependent development of micro-damage.A wave velocity model considering the inner anisotropic crack evolution is proposed to accurately describe the variations of wave velocities during uniaxial compression testing.Based on which,the effective elastic parameters are inferred by a transverse isotropic constitutive model,and the evolutions of the crack density are inversed using a self-consistent damage model.It is found that the propagation of axial cracks dominates the failure process of brittle rock under uniaxial loading and oblique shear cracks develop with the appearance of macrocrack.

Reaction Crystallization of Struvite in a Continuous FB MSZ Type Crystallizer with Jet Pump Driven by Compressed Air

The results of struvite reaction crystallization from diluted water solutions of phosphates （V） （0.20 mass% of PO43-） by means of magnesium and ammonium ions are presented. Continuous FB MSZ crystallizer with jet pump driven by compressed air was used. Influence of pH and mean residence time of suspension on the crystal product quality was determined. Increase in pH from 9 to 11 resulted that mean crystal size decreased nearly two-time： from 27.1 to 15.1μm for mean residence time of suspension 900 s. Elongation of this time from 900 to 3,600 s influenced struvite crystal size advantageously-it increased from 27.1 to 41.2 μm at pH 9. From the population density distributions nucleation and growth rates of struvite were calculated based on the simplest SIG model of mass crystallization kinetics in MSMPR crystallizer. Linear growth rate ofstruvite crystals decreased nearly two-time with the increase in environment pH from 9 to 11, and more than 2.5-time with the elongation of mean residence time of crystal suspension in a crystallizer from 900 to 3,600 s from 1.34× 10-8 m/s （pH 9, τ= 900 s） to 2.60×10-9 m/s （pH 11, τ= 3,600 s）.

基于连续小波变换和模型无关元学习的压燃式活塞发动机气门故障诊断研究

针对压燃式活塞发动机缸盖表面振动信号样本少及传统故障诊断方法特征提取和选择困难的问题,提出了一种基于连续小波变换(continuous wavelet transform,CWT)和模型无关元学习(model agnostic meta learning,MAML)的压燃式活塞发动机气门间隙异常故障诊断方法。通过将CWT的特征提取能力和MAML的快速学习能力相结合搭建故障诊断模型。试验结果表明该方法能有效识别气门间隙故障,并且其准确率高于传统基于CWT和卷积神经网络(convolutional neural network,CNN)的故障诊断方法。通过跨域故障对比试验,研究了不同气门故障类型对模型诊断能力的影响,验证了该方法在解决小样本和跨域故障问题时具有更高的准确率和泛化能力。

基于弹性权重巩固的视频单曝光压缩成像算法研究

【目的】为视频单曝光压缩成像(Snapshot Compressive Imaging,SCI)设计一种对原始压缩比例、调制掩模和测量分辨率等超参数具有较高鲁棒性的统一模型。【方法】本文基于弹性权重巩固(EWC)对所提出的模型进行训练,该模型具有结合了Transformer和卷积神经网络两种网络结构的特殊设计,在此基础上本文在初始化阶段引入广义交替投影进一步增加了模型对于不同掩码的鲁棒性。【结果】广泛的实验结果表明,本文提出的统一模型可以很好地适应不同的压缩比、调制掩膜和测量分辨率,同时实现了最先进的结果。实验结果在PSNR、SSIM方面表现优于之前的SOTA算法,其中平均PSNR涨幅超过5 dB。【局限】尽管本文提出的模型在适应性和平均PSNR指标上优于之前的SOTA算法,但引入了EWC的模型在特定单一任务上的结果可能不会优于针对该特定任务训练的模型。【结论】通过引入广义交替投影和EWC以及对于网络结构的特殊设计,本文提出的具有高度适应性的模型为解决其他复杂场景下的压缩感知重建任务提供了新的思路和方法。

钛合金室温受压蠕变损伤本构模型

为了解决工程上在评估深潜器耐压壳体安全可靠性时不考虑拉压蠕变破坏机理产生的差异,会导致较大计算误差问题,本文提出了适用于室温蠕变的蠕变损伤本构模型。通过分析钛合金材料蠕变特性,考虑了室温环境下位错堆积造成的蠕变阻力,并且位错堆积的现象与时间有关。基于微分自洽法提出了适用于室温环境下的钛合金蠕变本构模型,得到受压情况下TC4ELI的相关材料参数,并将该模型用USDFLD和CREEP子程序进行定义。研究表明:对于受压结构而言,使用通过拉伸蠕变实验得到的本构模型的计算结果会过于保守,对于含V型缺口平板受压时等效蠕变应变的相对误差为168.20%。本文所提出的模型适用于环肋耐压壳结构的蠕变损伤分析。

吴茱萸热敷腹部对ICU机械通气及连续性血液透析治疗并发胃肠功能障碍病人的干预效果

目的:探讨吴茱萸热敷腹部对重症监护室(ICU)机械通气及连续性血液透析治疗并发胃肠功能障碍病人的影响效果。方法:选取广西中医药大学附属瑞康医院重症医学科二区2021年5月—2022年9月收治的行机械通气及连续血液透析治疗并发胃肠功能障碍病人80例作为研究对象,采用随机数字表法分为对照组和干预组,各40例。对照组给予西医常规护理,干预组在对照组基础上给予吴茱萸热敷腹部。比较两组病人首次排便时间、首次排气时间、住院天数、胃肠功能障碍评分、急性生理学和慢性健康状况评价系统Ⅱ(APACHEⅡ)评分、序贯器官衰竭(SOFA)评分。结果:干预组首次排便时间、首次排气时间均早于对照组,干预组住院天数少于对照组,差异均有统计学意义(P<0.05);干预组胃肠功能障碍评分、APACHEⅡ评分、SOFA评分均低于对照组,差异均有统计学意义(P<0.05)。结论:吴茱萸热敷腹部可有效改善ICU机械通气及连续性血液透析治疗病人并发的胃肠功能障碍。

无需信源数先验的快速稀疏增强DOA估计方法

文章提出了一种无需信源数先验的超分辨波达方向(Direction of Arrival,DOA)估计方法,该方法利用稀疏增强的原子范数形式重新表征信号稀疏度,利用对数-行列式函数建立原子范数与l0原子范数的平滑关系,并通过泰勒展开形式简化其优化过程,以求解一个新的迭代加权优化问题为目标,使优化结果更加稀疏和精确;基于增强稀疏结果的信号重构Capon空间谱,从而在不需要信源先验的情况下,也可以准确估计目标的DOA。文章还针对这一特殊的迭代加权优化问题,给出了一种基于原对偶内点法的快速优化流程,问题中特殊的Toeplitz矩阵结构可以通过快速傅里叶变换技术提高计算效率。理论推导证明了该算法相较于CVX等凸优化工具,具有更快的计算效率,并且能够在信号数目未知的情况下,利用较少的快拍数实现高精度的DOA估计,具有很好的鲁棒性。实验仿真验证了该算法的有效性。

大跨连续刚构桥桥墩计算长度系数的取值研究

桥墩计算长度系数是影响桥梁结构安全与经济性指标的一个控制性因素,国内外规范关于受压杆件计算长度系数的取值相近,且都仅是针对理想边界条件的情况,在实际应用中有必要根据具体的结构形式作适当调整。为得到更接近结构实际情况的数值,该文从结构整体稳定分析入手,分析不同因素对连续刚构桥成桥及最大双悬臂阶段计算长度系数的影响规律,主要包括不同桥墩类型、墩身高度、桩基柔度、邻跨边界、单墩失稳或者整体失稳等。结果表明:不同桥墩类型顺、横向的计算长度系数不能简单地采用某一固定值,随墩高的变化也不是简单的线性关系;考虑桩基柔度影响后的结果会增大20%左右,且横桥向比顺桥向的影响更加显著;考虑交接墩影响后计算长度系数的取值更大;需要考虑各墩同时受轴向荷载作用下的整体屈曲反应;连续刚构施工阶段最大双悬臂工况下顺桥向计算长度系数分布范围为1.20~1.35。

试样厚度对室内测定黄土压缩变形的影响

为研究试样厚度对室内测定黄土压缩变形的影响及水、力相互作用下的压缩变形特性,基于改造后的WG-2型固结仪,针对厚度分别为20 mm和40 mm的原状黄土,开展了不同初始上覆荷载条件下连续增湿压缩试验。结果表明,在同一上覆荷载条件下,试样压缩变形随着增湿含水率的增大而逐渐增大;同一增湿条件下,上覆荷载较小时,不同厚度试样的沉降变形相差不大;不同厚度试样的压缩变形量随着上覆荷载的增大而呈现增大的趋势。初始上覆荷载越小,含水率越低,试样厚度对压缩变形量的影响越大,随着增湿含水率和上覆荷载增大,可以忽略试验厚度对于压缩变形的影响。

基于压缩感知的中频感应加热设备边缘用电数据缺失重构方法

为解决因用电数据缺失造成的电量失衡问题,确保重构后的中频感应加热设备能够保持相对稳定的运行状态,设计基于压缩感知的中频感应加热设备边缘用电数据缺失重构方法。对用电数据样本进行两次转化处理,得到电信号稀疏变换结果,通过构建压缩矩阵的方式,描述中频感应加热设备边缘用电数据的失稳现象,求解基于压缩感知的中频感应加热设备边缘用电数据脆弱性函数。设置电网网格结构,按照缺失数据的自编码形式,计算连续重构阈值指标的取值范围,完成压缩感知下中频感应加热设备边缘用电数据缺失重构方法的设计。实验结果表明,数据缺失区域内的最大电压数值只能达到30.0 V,电网主机可以根据实时电压的不同,确定缺失数据所处区间,对于解决电量失衡问题、增强重构后电网的运行稳定性可以起到促进性影响作用。

An Optimal Feed Interpolator Based on G^2 Continuous Bézier Curves for High-Speed Machining of Linear Tool Path

A numerical control (NC) tool path of digital CAD model is widely generated as a set of short line segments in machining. However, there are three shortcomings in the linear tool path, such as discontinuities of tangency and curvature, huge number of line segments, and short lengths of line segments. These disadvantages hinder the development of high speed machining. To smooth the linear tool path and improve machining efficiency of short line segments, this paper presents an optimal feed interpolator based on G^2 continuous Bézier curves for the linear tool path. First, the areas suitable for fitting are screened out based on the geometric characteristics of continuous short segments (CSSs). CSSs in every area are compressed and fitted into a G^2 Continuous Bézier curve by using the least square method. Then a series of cubic Bézier curves are generated. However, the junction between adjacent Bézier curves is only G^0 continuous. By adjusting the control points and inserting Bézier transition curves between adjacent Bézier curves, the G^2 continuous tool path is constructed. The fitting error is estimated by the second-order Taylor formula. Without iteration, the fitting algorithm can be implemented in real-time environment. Second, the optimal feed interpolator considering the comprehensive constraints (such as the chord error constraint, the maximum normal acceleration, servo capacity of each axis, etc.) is proposed. Simulation and experiment are conducted. The results shows that the proposed method can generate smooth path, decrease the amount of segments and reduce machining time for machining of linear tool path. The proposed research provides an effective method for high-speed machining of complex 2-D/3-D profiles described by short line segments.

Dynamic recrystallization of AZ91 magnesium alloy during compression deformation at elevated temperature

High temperature compressive tests of AZ91 Mg alloy were carried out at 573723 K and strain rates of 0.0011 s-1. The microstructures of as-compressed samples were observed by optical microscopy and transmission electron microscopy （TEM）, and the microhardness was also tested. It is shown that with the increase of temperature or the decrease of strain rate, the flow stress decreases, at the same time the dynamic recrystallization （DRX） of the alloy is more noticeable. The microstructures reveal that continuous dynamic recrystallization, which develops through conversion of low-angle grain boundaries into high-angle boundaries, occurs preferentially at the grain boundary.

Study on strip buckling in continuous annealing lines/hot galvanizing

In continuous annealing lines/hot galvanizing,strips are guided by upper and lower rolls in an alternate up and down vertical motion.This kind of process consisting of heating,soaking,and cooling furnaces(or zones) has several advantages in terms of productivity and product quality.Main problems encountered in continuous annealing lines are misguiding and formation of buckling.The strip buckling causes the strip to be rejected and,in the worst case,the strip breaks and the continuous annealing lines are compelled to stop.In this paper the elastic-plastic model of the strip traveling and the corresponding boundary condition were constructed dependant on the theory of mechanic.Simulations are performed in two steps.First,a homogeneous longitudinal tensile stress is applied at one end of the strip,the other end of the strip and the roll are restricted.In the second step,the applied tension remains constant.A uniform displacement is applied to the other end of the strip and a rotation to the roll. The transverse compressive stress,the buckling formation during strip traveling process,the location for the buckling taking place and the buckling criterion were investigated systematically.The result shows that the transverse compressive stress increases with the increase of the tensile stress and the crown of the tapered roll. Because the contact area between the tapered roll and the strip increase with the decrease of the crown,the tensile stress distribution is more homogeneous in the transverse direction of the strip.An additional transverse compressive stress is created and a buckling is also observed due to the friction during the strip motion in the second step.Once the buckling is appearance,it is very hard to be removed only through decreasing the applied longitudinal tension,because the strip wrinkle still keeps high level due to the effect of the buckled strip,the wrinkle would evolve into buckling eventually.The buckling formation process predicted by the finite element model is very similar to those observed in industrial processing lines.It takes place on the cylindrical part of the tapped roll and the buckling is moving to the middle part of the tapped roll with the increase of the crown,its width is about 2-4 mm.The criterion for the buckle occurrence is also discussed,in the prescribed situation,the transverse shell curvature increases with the strip displacement,if the transverse shell curvature reaches 0.1 mm^(-1), the buckling would take place.

Continuous Piecewise Linear Approximation of BV Function

Nonlinear approximation is widely used in signal processing. Real-life signals can be modeled as functions of bounded variation. Thus the variable knot of approximating function could be self- adaptively chosen by balancing the total variation of the target function. In this paper, we adopt continuous piecewise linear approximation instead of the existing piecewise constants approximation. The results of experiments show that this new method is superior to the old one.

Protective effect of compressing arc extinguishing lightning protection device on superimposed lightning strikes

Traditional lightning protection measures can not solve the problem of superimposed lightning strikes.This paper presents a compressing arc extinguishing lightning protection device,which can solve the problem of superimposed lightning strikes.This device can extinguish the power frequency continuous current arc quickly in 1-2 ms.It is far less than the response time of relay protection,which can avoid lightning trips and improve the reliability of power supply.The computer simulation and engineering practice show that the compressing arc extinguishing device has good protection effect on superimposed lightning strikes.

The Linearity of the Euler Equation as a Result of the Compressibility of a Fluid

It is shown that when the compressibility of a fluid is taken into account, the nonlinear term disappears in the Euler equation. The validity of this approach is proved by the example of capillary waves.

Sparse three-dimensional imaging for forward-looking array SAR using spatial continuity

For forward-looking array synthetic aperture radar(FASAR),the scattering intensity of ground scatterers fluctuates greatly since there are kinds of vegetations and topography on the surface of the ground,and thus the signal-to-noise ratio(SNR)of its echo signals corresponding to different vegetations and topography also varies obviously.Owing to the reason known to all,the performance of the sparse reconstruction of compressed sensing(CS)becomes worse in the case of lower SNR,and the quality of the sparse three-dimensional imaging for FASAR would be affected significantly in the practical application.In this paper,the spatial continuity of the ground scatterers is introduced to the sparse recovery algorithm of CS in the threedimensional imaging for FASAR,in which the weighted least square method of the cubic interpolation is used to filter out the bad and isolated scatterer.The simulation results show that the proposed method can realize the sparse three-dimensional imaging of FASAR more effectively in the case of low SNR.

高速铁路中低压缩性土路基沉降计算与分析

高速铁路路基沉降计算与分析是路基设计及评估的重要环节。为准确计算高速铁路中低压缩性土路基沉降,从中低压缩性土的工程特性出发,基于考虑时间效应的压缩层厚度计算方法和分层连续加载下地基沉降计算理论,建立更适应于高铁路基荷载特征的高铁中低压缩性土路基沉降计算方法。利用吉珲铁路珲春试验工点得到的地基土物理和力学指标,计算路堤分级堆载条件下,不同埋深处上层硬塑粉质黏土和下层全风化泥质粉砂岩地基的时效变形规律。结果表明,在路基填筑过程中,基底附加应力计算方法获取的基底附加应力与实测值较为吻合。进一步对比理论与现场实测结果发现,截至第700天,地基总沉降的计算误差约2mm;地基分层沉降的理论值与计算值误差在±5%以内,验证了计算方法的可靠性和准确性;针对考虑时间效应的压缩层厚度计算确定的地基压缩层厚度,其随路基填筑高度呈线性正相关。上述方法不仅为合理选择并优化高速铁路中低压缩性土的地基加固措施及方案提供了关键的技术支撑,也为精确计算和预测工后沉降提供了保障。

连续燃烧分缸工作型发动机理论热力循环分析

连续燃烧分缸工作型发动机因其热效率及功率密度高,振动及噪声小,未来将在小型无人机及鱼雷上具有很好的应用前景。该型发动机将压缩、燃烧和膨胀过程分缸进行,同时使用进气掺水、不等缸径、回热器和连续外燃技术,被认为具有极高的热功转换潜力,但目前缺乏对其热力循环的研究,导致在发动机设计过程中缺乏理论指导。将发动机各工作阶段等效为定温压缩、定容加热、定熵膨胀、排气放热与回热共5个工作过程,构建出新型理论热力循环并推导出指示热效率公式。研究结果表明:指示热效率主要由工质热物性、压缩比、膨胀比和回热率决定,增大压缩比或降低膨胀比均可提升指示热效率;应用定温压缩后可扩大回热温差,提升指示热效率,同时还可保持较低的缸内温度和压力;该型发动机热效率及可靠性较传统汽油机、柴油机具有显著优势,发动机指示热效率可达65%以上。

连续多步置氢处理步数对TC21合金显微组织和室温压缩性能的影响

采用OM、XRD和TEM方法研究连续多步置氢处理步数对TC21合金显微组织的影响。通过室温压缩实验研究连续多步置氢TC21合金在不同压缩速度下的压缩性能。结果表明:随着连续多步置氢处理步数的增加,α相的含量减少,β相和δ氢化物的含量增多,仅置氢1步时TC21合金中出现α'马氏体。连续多步置氢TC21合金的极限变形率在不同压缩速度下的变化规律相同,即随着连续多步置氢处理步数的增加,极限变形率先减小再增大最后又减小。连续多步置氢处理后,TC21合金的极限变形率比原始TC21合金最大增幅达到93.96%。分析了连续多步置氢TC21合金压缩性能变化的原因。