考虑气流激振效应的离心式压缩机叶轮强度分析＊

以往离心式压缩机的叶轮强度设计主要基于静力分析结果,忽略了非定常气动力引起的脉动应力。工程实际表明,许多叶轮的破坏并非静强度不足,而是材料的高周疲劳破坏。考虑离心式压缩机叶轮的非定常气流激振效应,给出了动应力计算和结果后处理过程中应注意的几个问题。气流激振下的动应力分析可以确定叶轮在气动荷载和机械荷载联合作用下的交变应力,为疲劳分析和可靠性设计打下基础。     

离心压缩机叶轮尾流激振载荷特性对动应力的影响

阐述叶轮尾流激振机理及尾流激振引起的振动应力的计算方法。通过对非定常CFD计算结果处理得到叶轮气动载荷特性,并详细分析了叶轮通过频率载荷幅值与相位分布。利用完全载荷模型进行叶轮动应力计算。将完全载荷模型得到的动应力结果与简化相位分布的载荷模型、简化幅值与相位分布的载荷模型得到的动应力结果进行比较,分析简化模型的不足。可为叶轮设计中动应力的准确预估和叶轮疲劳破坏机理的研究提供参考。     

基于ABAQUS的离心叶轮力学性能研究

介绍了离心叶轮疲劳破坏的原因,利用有限元方法,通过对离心叶轮模态与尾流激振响应分析,研究了离心叶轮是否发生轮盘叶片耦合振动及单只叶片振动,得到危险工况点,计算出离心力、稳态气流力及非稳态交变应力,运用Goodman的方法修正载荷谱,并计算出疲劳寿命。     

流固耦合下轴流压气机叶片振动特性数值研究

气流扰动触发的叶片振动是导致叶片疲劳失效的主要原因,针对此问题,首先,建立叶片流固耦合时域计算模型,研究叶片振动特性,并进行叶片失效分析;其次,建立压气机叶片振动分析模型,结合叶片振动试验来验证模型的有效性;然后,考虑气体与叶片的耦合作用,通过数值仿真模拟得到典型工况下的叶片表面气动载荷,并将其引入旋转叶片有限元振动分析模型进行叶片振动响应计算;最后,引入坎贝尔图确定叶片危险工况,得到危险工况下的叶片动应力分布,并进行叶片疲劳失效分析。结果表明:临界工况下叶片振动应力分布与发生共振的模态振型密切相关;临界转速下叶片发生的1阶共振是造成叶片失效的主因。     

气流激振力作用下离心叶轮的瞬态响应分析

为研究流场中离心叶轮受气流激振的瞬态响应问题,利用叶盘结构的循环对称性编制计算程序,实现了使用单扇区模型计算非循环对称力作用下离心叶轮的受迫振动。应用时间倾斜方法计算非等栅距情况下导叶/叶轮干涉的非定常流场,将叶片表面的气动力数据由流体网格插值到结构网格。使用FEAST求解器计算基本扇区各节径下的振型数据,并将其由基本扇区展开至所有扇区,根据各扇区所受周期激励的时间差建立载荷矢量,结构动力方程的时域积分使用Newmark方法完成。以一半开式径向叶轮为例,进行了两种转速下叶盘结构的瞬态响应分析。单扇区模型与整体模型计算的位移响应结果符合较好,两个潜在共振点附近激振频率的振动响应均呈现出近于发散变化的趋势,表明了算法的正确性和预测气流激励导致共振的有效性。     

时序效应对离心压缩机叶片非定常气动负荷影响

针对国内某大型企业不同机组离心压缩机叶轮叶片进行非定常流动数值分析,通过求解三维瞬态N-S方程组,得到流场分布和叶片表面的静压载荷信息。利用数值实验方法获得离心压缩机不同时序位置叶轮叶片表面动载荷的变化,并通过傅里叶变换得到叶轮叶片表面动载荷的分布特性,进而分析不同时序位置叶轮叶片表面气动负荷的差异。数值计算表明,时序效应对离心压缩机流道内流动以及叶轮叶片的非定常气动负荷存在不可忽略的影响,且合适的时序位置具有改进压缩机级性能的潜能。动载荷是压缩机叶轮叶片结构发生疲劳破坏的诱因,且不同机组离心压缩机中的时序效应对气动载荷的影响具有一致性。     

基于ANSYS的压气机叶轮振动特性有限元仿真分析

车用涡轮增压器的压气机叶轮常常因为振动而导致破坏,对压气机叶轮进行模态分析是避免叶轮与激振频率发生共振的常用手段,能有效避免因发生共振而导致的叶轮破坏问题。利用AN-SYS软件,采用子结构分析方法对压气机叶轮的中低阶固有频率进行了数值仿真计算,获得了不同转速和不同节径时的频率,并根据计算结果绘制了Campbell图,找出了与压气机叶轮固有频率产生共振的转速,为压气机叶轮的优化设计提供了依据,同时说明采用子结构分析的方法可以较精确地获得整体模型的低阶固有频率解。     

轴流通风机叶片模态仿真及其对气动噪声的影响

利用有限元模型对叶轮模态进行了计算，判断分析了各阶模态振型对气动噪声的影响程度，求解中利用了ANSYS的模态循环对称功能，同时分析了旋转软化、应力强化对叶轮真实运转状况下模态频率的影响。     

预应力模态下对旋风机叶片流致振动特性

为了研究预应力模态下对旋风机叶片流致振动特性,采用基于预应力模态的强迫振动响应方法进行仿真分析,以非定常流场压力脉动为激励载荷,对叶片实现强迫振动响应计算。分析了流场非定常激振力的特征频率,对比了无预应力模态和预应力模态下监测点的强迫振动响应特性。研究结果表明,对旋风机流场激振力特征频率为一级、二级叶轮的通过频率及其倍频;由于一级叶轮的3倍叶频与一级叶片2阶固有频率接近,二级叶轮4倍叶频与二级叶片3阶固有频率接近,从而叶片结构发生小幅共振,分别产生相应监控点的振动加速度最大峰值;无预应力模态由于忽略了预应力下的刚化效应,其监控点振动加速度曲线峰值高于预应力模态,两种模态计算出的监控点总振动加速度级差值最大约1.5 dB。     

离心式压缩机叶轮非定常流动特性及动力响应研究进展

评述了近年来关于离心式压缩机叶轮在非定常气流激振状态下的流动特性及动力响应的研究进展。在流体动力学方面,总结了叶轮内部流场在非定常工况下的脉动和不稳定特性研究;在固体动力学方面,总结了在瞬态流场激振下的叶轮动力响应分析方法。指出应在气动载荷特性分析的基础上,深入研究流-固耦合激振机理、振动响应随流动特性的变化规律,开发高效、可靠的叶轮随机振动响应分析方法,为大型压缩机叶轮的疲劳设计、损伤评定和寿命预估打下基础。     

Minimal Realization of Linear Graph Models for Multi-physics Systems

An engineering system may consist of several different types of components,belonging to such physical"domains"as mechanical,electrical,fluid,and thermal.It is t...     

INTEGRAL EQUATION METHOD＇S APPLICATION IN HOLE-EDGE STRESS OF COMPOSITE MATERIAL PLATE WITH DIFFERENT SHAPED HOLES

The strength of composite plate with different hole-shapes is always one of the most important but complicated issues in the application of the composite material. The holes will lead to mutations and discontinuity to the structure. So the hole-edge stress concentration is always a serious phenomenon. And the phenomenon makes the structure strength decrease very quickly to form dangerous weak points. Most partial damage begins from these weak points. According to the complex variable functions theory, the accurate boundary condition of composite plate with different hole-shapes is founded by conformal mapping method to settle the boundary condition problem of complex hole-shapes. Composite plate with commonly hole-shapes in engineering is studied by several complex variable stress fimction. The boundary integral equations are founded based on exact boundary conditions. Then the exact hole-edge stress analytic solution of composite plate with rectangle holes and wing manholes is resolved. Both of offset axis loadings and its influences on the stress concentration coefficient of the hole-edge are discussed. And comparisons of different loads along various offset axis on the hole-edge stress distribution of orthotropic plate with rectangle hole or wing manhole are made. It can be concluded that hole-edge with continuous variable curvatures might help to decrease the stress concentration coefficient; and smaller angle of outer load and fiber can decrease the stress peak value.     

Non-monotonic material contrast in scanning ion and scanning electron images

30 keV Ga⁺ focused ion beam induced secondary electron (iSE) imaging was used to determine the relative contrast between several materials. The iSE signal compared from C, Si, Al, Ti, Cr, Ni, Cu, Mo, Ag, and W metal layers does not decrease with an increase in target atomic number Z₂, and shows a non-monotonic relationship between contrast and Z₂. The non-monotonic relationship is attributed to periodic fluctuations of the stopping power and sputter yield inherent to the ion–solid interactions. In addition, material contrast from electron-induced secondary electron (eSE) and backscattered electron (BSE) images using scanning electron microscopy (SEM) also shows non-monotonic contrast as a function of Z₂, following the periodic behavior of the stopping power for electron–solid interactions. A comparison of the iSE and eSE results shows similar relative contrast between the metal layers, and not complementary contrast as conventionally understood. These similarities in the contrast behavior can be attributed to similarities in the periodic and non-monotonic function defined by incident particle–solid interaction theory.     

Application of Feature Extraction through Convolution Neural Networks and SVM Classifier for Robust Grading of Apples

This paper proposes a novel grading method of apples,in an automated grading device that uses convolutional neural networks to extract the size,color,texture,an...     

分布动态载荷识别的抗噪处理

针对正交多项式频域法在用多种响应对矩形薄板进行载荷识别中抗噪性较差的问题,综合运用平均法、矩阵预处理和奇异值截断法等方法对之进行改善,并引入空间映射的思想,将该方法的应用范围拓展为复杂的模型.利用仿真算例,证实了该方法具有较好的抗噪性.     

基于MELTAC-N平台的核电厂安全级DCS环网研究与测试

针对工程实践中环网通讯相关问题的处理缺乏理论基础及国产化安全级DCS平台的开发缺乏成熟经验借鉴问题,对基于MELTAC-N平台核电厂安全级DCS环网的软硬件实现进行了研究。提出了安全级DCS环网双环网冗余设计、光切换开关设计等硬件设计方法,以及以RPR协议为基础,采用全数据收发策略的软件设计方法。在CPR1000安全级DCS平台上对安全级DCS环网的可靠性及实时性进行了评价,并进行了容错能力、响应时间及响应时间稳定性测试验证实验。结果表明,基于MELTAC-N平台安全级DCS环网软硬件设计具有较好的容错能力及响应时间稳定性。     

Short-Term Relay Quality Prediction Algorithm Based on Long and Short-Term Memory

The fraction defective of semi-finished products is predicted to optimize the process of relay production lines, by which production quality and productivity ar...     

End-to-End Multiview Gesture Recognition for Autonomous Car Parking System

The use of hand gestures can be the most intuitive human-machine interaction medium.The early approaches for hand gesture recognition used device-based methods....     

The laboratory simulation of abrasive wear

Abrasive wear has long been recognised as one of the most potentially serious tribological problems facing the operators of many types of plant and machinery; several industrial surveys have indicated that wear by abrasion can be responsible for more than 50% of unscheduled machine and plant stoppages. Locating the operating point of a tribological contact in an appropriate operational ‚map’︁ can provide a useful guide to the likely nature and origins of the surface degradation experienced in use, though care must be exercised in choosing the most suitable parameters for the axes of the plot. Laboratory testing of materials and simulations of machine contacts are carried out for a number of purposes; at one level for the very practical aims of ranking candidate materials or surface hardening treatments in order of their wear resistance, or in an attempt to predict wear lives under field conditions. More fundamentally, tests may be aimed at elucidating the essential physical mechanisms of surface damage and loss, with the longer term aim of building an analytical and predictive model of the wear process itself. In many cases, component surface damage is brought about by the ingress of hard, particulate matter into machine bearing or sealing clearances. These may be running dry although, more usually, a lubricant or service fluid is present at the interface. A number of standardised wear test geometries and procedures have been established for both two- and three-body wear situations, and these are briefly described. Although abrasive wear is often modelled as following an ‚Archard’︁ equation (i.e. a linear increase in material loss with both load and time, and an inverse dependence on specimen hardness) both industrial experience and laboratory tests of particularly lubricated contacts show that this is not always the case: increasing the hardness differential in an abrasively contaminated lubricated pair may not always reduce the rate of damage to the harder surface.     

Limits of topographic measurement by the scanning tunnelling and atomic force microscopes

Parameters describing the topographic character of a surface (height, surface wavelength, slope and curvature) can be derived from equivalent sinusoidal profiles. The response of a surface-measuring instrument may be modelled in terms of instrument parameters such as stylus radius, and scanning range and resolution. The performance of the instrument may then be mapped as a zone in amplitude-wavelength (AW) space to show the sinusoidal profiles it is capable of measuring. In a first-order analysis the STM and AFM are considered as equivalent to contact-stylus instruments with a notional stylus radius equal to the tip radius plus the gap. Comparisons between different instruments and types of instrument are readily made by mapping in AW space. The error arising from convolution of the sinusoidal profile with that of the finite tip may be quantified and plotted as contours in AW space.