呼吸性裂纹转子的瞬态振动特性分析

旋转机械转子轴萌生裂纹后,瞬态加速过程中转涡差角时变使裂纹周期性开合,系统发生不同于稳态情况的振动。本文基于中性轴法确定裂纹开合,数值计算了呼吸裂纹引起刚度时变的转子过临界转速的瞬态振动,分析了裂纹大小、方向角和重力对线性加速转子瞬态振动的影响,以及定功率加速瞬态过程中系统振动响应及稳定性。结果发现,瞬态条件下带呼吸裂纹转子系统亚谐波共振并不明显;裂纹越大,过临界转速时瞬态振幅越大;在临界转速附近裂纹瞬时张开会激起很大的振动;定功率加速过程下,若功率不足够提供转子顺利穿过临界转速,则会出现外界扭矩与瞬态振动的能量耦合,大裂纹还可能造成瞬态振动发展成混沌。     

对中缺陷对拉杆组合转子的动力学影响

基于静动联合分析方法,研究了三维拉杆转子中对中缺陷所造成的影响。通过使用三维有限元法和牛顿迭代法,说明了含缺陷拉杆转子的静动力学特性。对中缺陷导致了复杂的不平衡现象,包括质心偏移和随速度而改变的转子弯曲,而转子弯曲则明显降低了转子的稳定性,加大了其振幅。无论是否施加了动平衡,拉杆转子的弯曲特性决定了其振幅在超过临界转速后将会再次上升,在精度设计中应特别注意这一特点。同轴度公差是根据其稳定性特征所获得的,解释了为什么在拉杆转子中对径向定位表面的加工精度有着高度要求。此外,当对中缺陷存在时,采用不均匀的预紧也可减少对动态特性的不利影响。     

不平衡转子扭转振动特征的测试

采用ＤＫ－Ⅱ型扭振测量系统，进行了不同转速下不平衡转子的弯曲，扭转振动的联合测量，得到了存在不平衡的故障转子的扭振特征和变化规律，即当转动频率小于一阶扭振固有频率时，扭振幅值随转速的升高而增大；当转动频率大于一阶扭振固有频率时，扭振幅值随转速的高而减小；当通过扭振界转速时，扭振相位翻转１８０°。     

单支撑1000MW超超临界汽轮机轴系不平衡响应分析

建立单支撑1 000 MW超超临界汽轮机不平衡响应分析有限元模型,计算升速过程中轴系不平衡响应特性,比较单、双支撑机组不平衡响应差别。研究结果表明,不平衡响应分析时可将转子两侧单支撑轴承视为该转子的双支撑,由此两轴承振动分析不平衡面及不平衡型式。单支撑汽轮机转子之间振动耦联性较强,突显于相邻转子两临界转速附近。工作转速远离临界转速时相互间影响并不大。虽转子二阶临界转速远高于工作转速,但采用单支撑模式机组转子不平衡力偶与振动间相位滞后角大多在120°以上。通过对1 000 MW汽轮机组进行低压转子现场高速动平衡试验,不平衡响应分析结果获得试验验证。     

基于特征值分析的摩擦转子热稳定性研究

针对摩擦转子系统动力特性问题,建立一种热弯曲/振动耦合分析模型。耦合方程中既包含了热弯曲对转子振动的影响,也包括了振动对热弯曲的影响。在频域内应用特征值分析法,研究了摩擦转子的热稳定性。分析了某发电机转子升速过程中热特征值随转速的变化趋势,研究了碰摩刚度对热特征值和热弯曲旋转周期的影响。研究表明,临界转速之前,摩擦引起的热弯曲出现发散状态,碰摩热特征值实部随碰摩刚度升高而升高。临界转速之后,轻微摩擦引起的热弯曲是稳定的,但是当摩擦恶化到一定程度后,由此引起的热弯曲也是不稳定的。随着刚度的增加,热弯曲波动周期减小。     

考虑不平衡电磁拉力的偏心转子非线性振动分析

水轮发电机组转子相对偏心引起的不平衡磁拉力对转子振动有较大影响。从水轮发电机转子的气隙磁场能表达式出发,推导发电机转子的电磁刚度矩阵。利用拉格郎日方程,建立了刚性和短轴承弹性两种支承方式下考虑电磁刚度的转子振动模型。利用李雅普诺夫非线性振动稳定性理论,研究了电磁刚度和轴承弹性支承对转子的临界转速和偏心力作用下的横振幅值的影响,并分析了电磁、机械、轴承等参数对临界转速的影响程度。为进一步深入研究水轮发电机组轴系统在电磁,水力和机械结构参数共同作用下的动力特性打下基础。     

具有初始弯曲的不平衡转子碰摩条件的研究

建立了一个具有初始弯曲的不平衡转子模型,通过d'Alembert原理推导了振动方程。通过解析方法,分析了此类转子转静件间发生碰摩的条件。引入并求解了判断碰摩发生的碰摩因子和碰摩起始转速,分析了质量偏心量、初始弯曲长度、转子阻尼系数,和质量偏心与初始弯曲之间相位角对碰摩因子和碰摩转速的影响。该研究对于防止或预测此类转子碰摩的发生和降低碰摩带来的损失具有重要的意义。     

应用变参数挤压油膜阻尼器的柔性转子振动控制

本文以具有变参数挤压油膜阻尼器(Variable Parameter Squeeze Film Damper,缩写为VPSFD)鼠笼式弹性支承的单盘转子为试验模型,研究了VPSFD参数变化对振动共振幅值的抑制作用.在稳态试验的基础上,对转子过前两阶临界转速的振动抑制进行了研究,并实施开环瞬态振动控制.研究结果表明,适时调节VPSFD的参数,可使转子系统前两阶共振幅值大为降低,使转子能平稳通过前两阶临界转速.     

高速转子分布式不平衡量无试重识别方法

为有效抑制分布式不平衡量所导致的转子故障振动,提出一种高速转子分布式不平衡量识别方法,该求解方法无需试重,且振动测试过程可在低于临界转速下进行。通过扩展影响系数动平衡方法与转子动力学模型的比较分析,得出了动力学传递函数与影响系数之间的关联关系。基于有限元动力学模型结点,实现了分布式不平衡具体描述,通过增加振动测试转速的方式,实现了动力学传递函数矩阵的满秩,进而给出了分布式不平衡量的求解公式,并在转子动平衡实验平台上进行了实例验证。结果表明,按该方法识别的不平衡量进行配重校正后,转子临界转速前后残余振动比动平衡前降幅非常明显,验证了该方法所识别不平衡量的准确性。     

双盘柔性转子系统整机平衡原理和测试方法

双盘柔性转子的动挠度曲线是一条随转速变化的空间曲线,而且转子在任意转速下转动时,其振动曲线是转子各阶主振型分量的叠加,故按振型分理的原理和方法进行平衡,能消除由不平衡离心惯性力的各阶振型分量产生的振动,从而能达到良好的平衡效果。整机平衡的方法和步骤如下:在两只轴承上分别装上传感器,并输入测振仪和相位仪,分别测得两端轴承处的振幅和相位。利用计算的方法,求得一阶和二阶振型曲线,然后按振型分理平衡的原理,确定低速(在一阶临界转速附近)和高速(工作转速)下,两只转子的平衡校正面上的加重比例,再由实测方法确定低速和高速下     

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...     

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.     

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.……     

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.     

Certification Becomes Important for the I Quality; and Safety Supervision of the Chinese Liquor Sector

The end of 2007, over 200 unit products of more than 80 Chinese firms have passed the quality grade certification for liquor products. These products involve distilled spirits, beer, wine, yellow wine, fruit syrup wine and others, and cover over 80% of the national top-branded liquor products.……     

Deposition and Coating Properties on CVD Tungsten

Surface characterization and microstructure studies are performed on chemical vapor deposited (CVD) tungsten coating. There is about 2 μm thickness diffusion layer of tungsten in the molybdenum substrate. The thermal shock test shows tungsten coating has good adhesion with molybdenum substrate, but the elements of oxygen and carbon in the tungsten coating have the bad affection to the adhesion. The result of high-temperature diffusion experiment is the diffusion rate from molybdenum substrate to tungsten coating is faster.     

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.