结构裂缝损伤识别的连续小波分析方法

应变模态是对结构局部特征变化比较敏感的参数,以应变模态作为响应信号,利用小波变换在时域和频域都具有的强局部化性质、易提取信号奇异部分的特点,采用连续小波进行裂缝损伤定位及定量化研究,建立了模极大值与裂缝位置、李氏指数与损伤程度之间的关系,解决了仅从应变模态数值的变化不能完全反映结构损伤程度的问题.数值模拟表明,连续小波分析的损伤识别方法不仅实现精确损伤定位,而且小波变换的李氏指数能较好的表征损伤程度,无论单处裂缝损伤还是多处裂缝损伤李氏指数均随着裂缝深度的增大而减小.     

预裂缝减震作用下爆破地震波的频谱特征分析

研究在微风化花岗岩石场地深孔爆破地震波通过一条长26 m,深7 m的预裂缝振动传播规律.试验数据分析表明,预裂缝的减震效果与测点与预裂缝的减震效果有关.通过对试验中5个测点处不同测点间的振动强度与比例距离的数据回归分析,预裂缝的减震效果具有一个有效作用范围,在比例距离范围为0.031～0.051kg1/3/m时,减震效果为15%～30%.试验中预裂缝对爆破地震波的透射率为19%～31%.频谱分析表明,预裂缝对爆破地震波的振动频率具有选择吸收的作用,相当于一个滤波器.经预裂缝作用下的爆破地震波在近测点处具有2个明显主振频带;随着传播距离的增加,地震波的两主振频带信号开始混叠,频带逐渐接近并表现为一个主振动频带.     

减震沟对爆破地震波能量特性影响试验研究

在减震沟两侧相邻区域内布设五个测点,对爆破震动试验展开监测。采用小波包能量谱分析法对采集的爆破振动信号进行分析,得到地震波经过减震沟的能量变化情况及各个测点的能量分布。试验与分析结果表明,减震沟对爆破地震波能量具有有效的衰减作用,但在沟后一定距离上存在能量放大现象;减震沟对初始能量主要分布在中高频的信号具有降频作用,对初始能量主要分布在低频的信号具有升频作用。     

预裂缝对爆破振动频谱分布特征的影响

预裂孔首先起爆形成贯通预裂缝对随后主爆孔爆破的振动频谱特征和能量分布产生重大影响。依托金沙江白鹤滩水电站左岸坝肩边坡开挖爆破试验,通过对预裂孔爆破和主爆破(主爆孔+缓冲孔)的振动信号进行小波包分析,获得预裂孔爆破和主爆破的功率谱和能量谱。通过对比发现:爆破振动的能量主要集中于40 Hz以内且分布极不均匀,存在多个主振频带。而在同一次爆破试验中,不同测点预裂孔爆破的主振频带比主爆破的主振频带分布更广,主爆破的主振频带集中于低频段,并且主爆破的能量和功率向低频的主振频带集中,反映出预裂孔爆破形成的预裂缝能很好地阻挡主爆破能量的传播,并存在高频滤波效应,频率较高、波长较短的振动应力波被预裂缝过滤,而频率较低、波长较长的应力波能更好地穿透预裂缝。试验结论对揭示预裂缝和对爆破振动传播及其频谱特征变化的影响具有参考价值。     

基于小波包变换的爆破地震波时频特征提取及分析

为了研究爆破地震波振动分量的传播规律，在微风化花岗岩石场地进行了孔径为76ram，孔深为5mm的单孔和单段多孔爆破试验，获得该场地爆破地震波加速度衰减规律，加速度衰减系数为k=3698，a=2．046，并研究出该场地基频范围为48Hz～74Hz。采用小波包技术对爆破地震波测试信号进行时频特征量提取，分析试验所测得爆破地震波不同频带下小波包系数的衰减规律。在此基础上通过研究场地介质对爆破振动分量的动态响应衰减作用，分析形成爆破地震波多频带特征的机理。     

小波变换轮廓术中小波尺度的一种快速确定方法

从传统的小波变换理论出发,给出了小波变换轮廓术的基本原理和实现算法,对连续小波变换轮廓术中小波尺度选择进行深入分析,探讨了条纹信号相位和条纹信号的连续小波变换模极大值之间的内在联系,为小波变换轮廓术中小波尺度选择提供一种快速确定方法.利用该方法进行实验验证,试验结果证实了该方法的可行性.     

移动荷载作用下梁裂缝识别的小波方法研究

利用小波分析对简支梁的裂缝进行识别。通过对带裂缝简支梁在移动荷载作用下的跨中响应用Mexicanhat小波进行连续小波变换，从小波系数的模极大值点有效地得到荷载经过裂缝的时间，从而识别裂缝位置，从模极大值处的Lipschitz指数判断裂缝深度，Lipschitz指数随裂缝深度的增加而减小。同时讨论了荷载移动速度和裂缝位置对Lipschitz指数的影响。通过分析和仿真计算获得满意结果，在梁结构损伤诊断中具有较高的应用价值。     

爆破震动信号的特征提取及识别技术研究

本文采用传统的频谱分析方法和小波多分辨分析技术，对几种典型的爆破震动信号进行了分析，并将爆破震动信号与其它振动信号在j=l-6尺度上进行了小波分解后的对比研究。通过本文有针对性的分析，发现距爆源较远的振动信号在j=6尺度下的小波变换分量具有初始振动向上的特征，同时信号能量也主要集中在这一尺度下的小波分解分量上，而距爆源较近的震动信号能量主要集中在j=4尺度上。     

基于小波模极大值模糊熵的遥测振动信号异常检测

针对遥测振动信号频域成份复杂、非平稳非线性和强噪声特性,提出一种基于小波模极大值模糊熵的遥测振动信号异常检测方法。首先对采集到的遥测振动信号进行零漂修正和趋势项消除;然后对经预处理后的振动信号进行一维连续小波变换,计算所有尺度空间中的小波模极大值序列;最后将原信号及其小波模极大值序列的模糊熵构成的特征向量输入到SVM分类器,根据模糊熵的变化情况对遥测振动信号进行异常检测。实测数据验证了该方法的有效性。     

基于小波变换模极大值恢复的信号消噪方法

大多数的信号常具有某种奇异性，并携带有随机噪声，首先回顾了信号奇异性与小波变换模极大值之间的关系，然后利用信号与噪声的Lipschitz指数的符号不同，在S.Mallat等人工作的基础上，给出了从信号中去除噪声的具体算法。     

Insertion of triangulated surfaces into a meccano tetrahedral discretization by means of mesh refinement and optimization procedures

In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method.     

From Industry 4.0 to Research 4.0. Development of High Performance Fibers in the Light of Digitization

We associate a variety of innovations with the term ＂Industry 4.0＂. The pioneer of many 4.0 modifications forms the basisfor the trend towards the integrated di...     

Roman iron and steel: A review

ABSTRACT

The production of ferrous metal increased during the Roman Late Republican period, Principate and Empire. The direct bloomery process was used to extract the metal from its ores using slag-tapping and slag-pit furnaces. The fuel was charcoal and an air blast was introduced by bellows-operated tuyères. Iron formed as a bloom, often as a spongy mass of metal, which contained impurities from the smelting process, including unreacted ore, fuel, slag and fragments from the furnace walls, while the metal was often inhomogeneous with varied carbon contents. Blooms were either smithed directly into bars or ingots or they were broken up, which also allowed the removal of gross impurities and a selection of pieces with similar properties to be made. These could then be forge-welded together and formed into characteristically shaped ingots. Making steel in the furnace seems to have been achieved: it depended on the ore and the furnace and conditions within it. Surface carburization was also carried out. Iron and steel were used extensively in construction and for tools and weapons. Fire welding was often used to add pieces of steel to make the edges of tools and weapons, which could be heat-treated by quenching to harden them.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

The Research of Anti-Wear Properties of Organomolybdenum Compounds in the Engine Oils

A four-ball tester was used to evaluate the anti-wear performance of three kinds of organomolybdemun compounds in the engine oils, i. e., molybdenum dialkyldithiophosphate (MoDDP), molybdenum dialkyldithiocarbamate ( MoDTC), and sulphur and phosphorus freeorganomolybdeum (Molybdate). The results indicate that a low concentration of MoDDP doesn' t improve the anti-wear properties of the commercial engine oils, but a high concentration of MoDDP can obviously improve the anti-wear properties and the load-carrying capacity of the engine oils. MoDTC doesn' t improve the antiwear properties of the engine oils, but worsens the anti-wear properties of the oils. Signifi can timprove ment of frictional and wear characteristics is obtained with Molybdate added in the commercial engine oils and the formulated oils.     

Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.     

Synthesis of Alumina-Zirconia Nanocomposites by Solgel Process

Al₂O₃-ZrO₂ nanocomposites were developed starting with the solgel process. Composite alumina-zirconia nanopowders were synthesized from metallorganic precursors (Aluminium secondary butoxide and zirconium Iso propoxide) using the solgel process. The parameters affecting the synthesis—solvent, concentration of precursor, R/H ratio (i.e., dilution of water in solvent)—were varied as also the temperature and pH. BET and TEM were used to measure nanosize. Diffuse reflectance spectroscopy and also qualitative optical absorption led to identical particle size estimate. The variation of process parameters was used to study the effect and interdependence of process parameters. Artificial Neural Networks was used to rigorously analyze the process. Although this led to confirmation of interdependence of parameters, the presence of a single overwhelming solvent variable was also established. Then the optimal process was used to synthesize more nanopowder. To produce bulk nanocomposite the nanopowders were sintered by varying the temperature and time period. The sintered lithoids were probed with a vickers hardness tester to measure elastic modulus, hardness, and fracture toughness. The results showed high elastic modulus, modest hardness, and very high fracture toughness.     

Refrigerators Enter a New Era of Health Preservation Frestech initiates the establishment of China's first standard for household sterilization refrigerators

On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……     

Friction Stir Processing Strategies for Uniform Distribution of Reinforcement in a Surface Composite

Friction stir processing (FSP) is an important technique for preparing surface composites. Fabricating defect-free surface composites with uniform particle distribution by FSP is a challenging task. In this study, silicon carbide particles reinforced AA5083 alloy surface composites was fabricated using different FSP strategies including variation in process parameters, dual-tool processing and tool offset overlapping. Material flow of the processed material with reinforcement particles demonstrated that the distribution of particles was influenced by the stirring action of the probe as well as the extrusion of the plasticized material due to the movement of the tool. Process parameters, particularly rotational speed, showed a dominant influence on the distribution of silicon carbide particles.