基于总体最小二乘准则旋转不变子空间法的叶尖定时欠采样信号分析

考虑到传统的应变法无法同时测量所有叶片的振动且存在一定的安全隐患,故利用叶尖定时技术对叶片振动进行监测。由于该方法得到的信号属于严重欠采样信号,且实际获得的信号存在噪声干扰,传统的傅里叶分析无法得到叶片的真实振动频率。研究基于总体最小二乘准则(TLS)的旋转不变子空间法(Esprit)对存在噪声干扰的欠采样信号进行频率估计,并以估计结果作为先验知识对欠采样信号进行重构。通过仿真信号分析及高速旋转叶片试验台验证方法的有效性。结果表明,所提方法可以有效地对含噪欠采样信号进行处理并估计出叶片的真实频率信息,具有很好的工程应用价值。     

Improved independent component analysis based modal identification of higher damping structures

Structural modal parameter identification under ambient excitation has strong engineering value and theoretical significance. As the most popular tool for solving Blind Source Separation (BSS) problems, Independent Component Analysis (ICA) is able to directly extract the time-domain modal parameters, including frequencies, damping ratios and modal shapes. ICA, however, has a fatal flaw of failing to identify structures with higher damping. To overcome the flaw above, the paper proposes a new method named “ICA + IDT”. Firstly, free vibration response of a structure is obtained from structural outputs under ambient excitation. Inverse damping transfer (IDT) is employed to turn a highly damped signal into a low damping response signal without changing of frequencies and mode shapes. Then, structural modal parameters are extracted from the low damping response signal by ICA. Finally, the identified damping ratios are adjusted to eliminate the impact of IDT. To verify the effectiveness and applicability of IDT + ICA proposed herein, two numerical simulations—mass-spring model and simply supported concrete beam—and an experiment model of three-story steel frame are built, and the analysis results reveal that presented method can identify structures with higher damping effectively.     

叶盘结构频率转向特征及失谐敏感性实验研究

搭建了用于失谐叶盘结构固有特性及失谐敏感性研究的实验平台,对谐调叶盘结构的频率转向现象进行了实验研究,验证了以往理论分析和有限元仿真中发现的频率转向特征和模态振型转换现象;通过在叶尖粘贴不同的质量块,模拟了三种典型的叶片失谐形式,实验研究了失谐叶盘结构的模态局部化问题;针对同一叶片失谐形式下不同的模态密度区域,实验研究了模态密度对失谐敏感性的影响规律。实验结果与有限元实验仿真结果吻合较好。     

叶尖定时信号趋势项自适应拟合

叶尖定时测量是航空发动机叶片振动监测关键技术,趋势项拟合作为定时信号预处理中的重要研究内容,是高精度叶片振动参数辨识的基础与前提。在航空发动机连续变工况运行条件下,当前趋势项拟合方法无法自适应调整拟合窗宽度,导致消除趋势项效果差,严重影响后续叶片振动分析。针对变工况条件下定时信号趋势项拟合难题,以相关系数作为趋势项拟合效果评价指标,提出趋势项自适应调节窗宽度拟合方法。采用航空发动机高压压气机叶尖定时试验数据进行验证,结果表明,所提方法由于能够自适应调节拟合窗宽度,可保证趋势项拟合效果最优,在满足有效去除趋势项的前提下能够完全保留原始振动信息,对实现高精度叶片振动参数辨识具有重要意义。     

汽轮机叶片——叶轮系统耦合振动特性的理论计算和实验研究

对汽轮机叶片—叶轮系统（轮系）耦合振动特性进行了理论和实验研究。首先介绍了一种简便实用的计算轮系振动特性的数值积分方法。此方法考虑了叶片的剪切变形、转动惯量、叶轮轮孔处支承柔度、叶片和叶轮连接处的叶根柔度及离心力等影响轮系振动的各种主要因素，给出了焊拉筋和松拉筋的处理方法，可供计算各种结构轮系振动的静、动频谱和相应的振型。其次，本文利用锤击法对叶片—叶轮系统模型进行了模态分析和参数识别，得到系统各阶固有频率和振型，理论计算结果与实验值的比较较为吻合。     

叶端定时测量方法及关键技术研究

研究了叶端定时测量方法及其实时监测系统的关键技术——叶端定时传感器、高速叶端脉冲信号采集系统和叶端定时信号的实时分析和处理。采用叶端定时测量系统在实验现场对某发动机的首级叶片振动进行实时测量，获得了满意的结果。     

Experimental and computational investigations of thermal modal parameters for a plate-structure under 1200 °C high temperature environment

When a hypersonic aircraft flies at a high Mach number, the plate-like attitude control structures, such as the wings and rudders, will be exposed to an extremely high-temperature environment. To obtain the thermal modal parameters of a structure that are difficult to measure, a high-temperature transient heating test system and a vibration test system were combined to establish a test system that can perform the thermal/vibration test at 1200 °C. Infrared radiation heating was employed to generate a controlled time-varying high-temperature environment, and an exciter was used to exert vibration excitation on the free end of the cantilever rectangular plate. A self-developed extension configuration of a high-temperature-resistant ceramic pole was used to transfer the vibration signals of the structure to a non-high temperature zone, and the acceleration sensors were applied to identify the vibration signals. The test data were analyzed using a time-frequency joint analysis technique, and next, the key vibration characteristic parameters of structure in a thermal-vibration coupled environment up to 1200 °C (e.g., the modal frequency and modal vibration shape) were experimentally obtained. In addition, the numerical simulation on the thermal modal characteristics of a rectangular plate was performed. The calculated results coincide favorably with the test results, verifying the credibility and effectiveness of the experimental methods. The research results can provide an important basis for the dynamic performance analysis and safety design of structure under high-temperature thermal-vibration conditions for hypersonic flight vehicles.     

Tribological property investigation on a novel pneumatic actuator with integrated piezo actuators

Pneumatic piston–cylinder actuators are commonly used in industry for a variety of automation and robotics applications. In order to suppress leakage, these actuators comprise seal rings which unfortunately introduce friction and affect the positioning accuracy and output force. This article investigates vibrations of the seal generated by integrated piezo actuators to reduce friction force. For this, two piezoelectric stacks are integrated in the cylinder and used to excite vibration modes. This concept was studied in a compact cylinder pneumatic actuator with a bore diameter of 5 mm and a stroke of 10 mm. Dry friction measurement shows a 52% reduction from the original friction force at a driving frequency of 18.29 kHz and vibration amplitude of 0.05 μm. In the wet friction experiments, the friction force can be reduced by 54% from the original wet friction with vibrations at amplitude of 0.04 μm.     

失谐对叶片-轮盘结构振动特性的影响

研究了失谐对叶片—轮盘结构系统振动特性的影响。将叶片模拟为固定在轮盘上的悬臂梁模型,采用Hamilton变分原理和Galerkin方法,导出了系统的运动方程表达式。求解状态方程的特征值问题获得系统的特征向量。以一个含16个叶片的叶片—轮盘结构为例,分析了它的振动模态。结果表明,失谐会导致系统的振动模态出现局部化现象。分析了叶片的失谐量和轮盘的转速对结构振动模态局部化的影响。     

Measurements of dynamic properties of a medium span suspension bridge by using the wavelet transforms

The aim of this paper is to show the capabilities of the real-time kinematic (RTK) global positioning network system (GPS) to measure the low-frequency vibration of a medium span suspension bridge. In particular, this paper presents the results of studies conducted on the identification of modal parameters including natural frequencies, damping coefficients and mode shapes of a suspension bridge using ambient excitation loads. A real-time kinematic (RTK) global positioning system (GPS) was designed and installed on the Nottingham Wilford Bridge to provide long-term and real-time measurement of bridge deck movement. An approach to estimate modal parameters, from only output data in the time domain using the wavelet transform, is presented. Displacements responses of the bridge are used in the wavelet transform to identify its dynamic characteristics. The modal properties were extracted using a two-step methodology. In the first step, the random decrement method was used to transform random signals in free vibration responses. Secondly, a wavelets-based technique was used to extract natural frequencies and to determine the mode shapes of the structure. This method was compared with the well-established techniques eigensystem realisation algorithm showing a difference of 1% in the estimated first natural frequency.The efficiency of RTK–GPS was demonstrated in the full-scale measurement. In particular, the results showed that the RTK–GPS data can be used for extracting modal properties from in-service-loads induced low-frequency vibration (<5 Hz) by processing the signal with the wavelets transform.     

A reduced order model based on sector mistuning for the dynamic analysis of mistuned bladed disks

In this paper, a pre-existing reduction technique suitable for the analysis of mistuned bladed disk dynamics, the Component Mode Mistuning technique (CMM), originally developed exclusively for the use of blade frequency mistuning pattern, is extended in order to allow for the introduction of a sector frequency mistuning pattern. If either mistuning is not confined to the blades (i.e. blades-to-disk interface mistuning), or the blades can not be removed from the bladed disk (i.e. integral bladed disks), sector mistuning rather than blade mistuning is a more suitable choice to perturb the tuned system. As a consequence, the extension of the original technique is referred as Integral Mode Mistuning (IMM). After a theory review of the original technique, the modifications leading to the IMM are described. Finally, the proposed IMM technique is validated in terms of both modal parameters estimation and forced response calculation, by means of a dummy bladed disk developed at Politecnico di Torino.     

The fault feature extraction and classification of gear using principal component analysis and kernel principal component analysis based on the wavelet packet transform

The vibration signal of a gear system is selected as the original information of fault diagnosis and the gear system vibration equipment is established. The vibration acceleration signals of the normal gear, gear with tooth root crack fault, gear with pitch crack fault, gear with tooth wear fault and gear with multi-fault (tooth root crack & tooth wear fault) is collected in four kinds of speed conditions such as 300 rpm, 900 rpm, 1200 rpm and 1500 rpm. Using the method of wavelet threshold de-noising to denoise the original signal and decomposing the denoising signal utilizing the wavelet packet transform, then 16 frequency bands of decomposed signal are got. After restructuring the decomposing signal and obtaining the signal energy in each frequency band, the signal energy of the 16 bands is as the shortlisted fault characteristic data. Based on this, using the methods of principal component analysis (short for PCA) and kernel principal component analysis (short for KPCA) to extract the feature from the fault features of shortlisted 16-dimensional data feature, then the effect of reducing dimension analysis are compared. The fault classifications are displayed through the information that got from the first and the second principal component and kernel principal component, and these demonstrate they have a different and good effect of classification. Meanwhile, the article discusses the effect of feature extraction and classification that caused by the kernel function and the different options of its parameters. These provide a new method for a gear system fault feature extraction and classification.     

The vibration behavior of impeller blades in the five-axis CNC flank milling process

Today, in most cases, impellers of centrifugal compressors are produced by flank milling on five-axis CNC milling machines. The complex three-dimensional geometry of the very thin blades consists of ruled surfaces. The flank milling process allows a fast production of the impellers and the surface of the blades is of high quality. The limited strength of the very thin blades and also the thin outer radial part of the disk lead to a high sensitivity to static and especially dynamic forces that are caused by the instationary flow in the impeller. The dynamic forces of rotating stall and surge are the most dangerous excitations of the bladed disk. Coupled vibrations may occur and damage the impeller. The highest static load is caused by the centrifugal forces. Therefore, most of the high-loaded impellers are manufactured from aluminum alloy or titanium because of the low density of this light metals and the relatively high strength. Most of the interests and the investigations in the last years are paid to the vibration behavior and the dynamic loads of the impeller during operation. But sometimes, the highest stress may occur during the production process and damage the impeller or weaken the strength and so cause later problems. Especially, excitations from the dynamic forces during the flank milling process have to be taken under consideration. The vibration behavior of the impeller is very complex and is affected by the vibration behavior of the cutter and the milling machine. In this paper, the change of the vibration behavior of centrifugal compressor impeller blades during the manufacturing process is investigated. During the finishing of the thin blades, the blade thickness is continuously changing and also the strength and the corresponding eigenfrequencies of the blade. The dynamic forces acting on the blades are caused by the cutter, the milling machine, and the cutting process. The quantity of the forces and the frequency of the excitation are determined by the rotational speed of the cutter, the feed, the number of edges, and the chip thickness. The results described in this paper give useful information about the change of the vibration behavior of the centrifugal impeller blades during the flank milling process and possible interaction with the cutter and the machine.     

某型涡轮盘/叶片/轴的耦合振动分析

某型涡轮盘/叶片/轴的耦合振动分析为某型涡轮结构设计的一个重要工作内容。本文首先采用UG软件对某型涡轮盘/叶片以及某型涡轮盘/叶片/轴进行三维实体建模,导入ANSYS软件建立了其耦合振动分析的有限元模型,并分别对其进行了静频与动频的计算与分析。计算结果表明:在工作转速范围内,该型涡轮盘/叶片/轴不存在危险振动。本文的工作为某型涡轮转子的设计提供计算分析依据。     

Ambient vibration test of building base slab for different ground conditions

It is very important to know the dynamic behavior of base slabs of buildings in earthquake prone areas. The slabs are generally assumed as a rigid diaphragm in structural analysis and design. But their response is considerably affected from ground condition. In this study, the dynamic characteristics of a scaled base slab are determined for different ground conditions. The dimensions of the base slab model are 150 cm long, 100 cm wide and 5 cm thick. This model is designed to be smaller than 20 times from an actual building base. The base slab model is tested for the ground conditions of sand, gravel and clay–silt mixture by ambient vibration test. The dynamic characteristics, such as natural frequencies, modal damping ratios, mode shapes, are identified from collected signals by Operational Modal Analysis method. The first five modes are taken into consideration to compare the effect of ground conditions on the dynamic characteristics. It is observed that the natural frequencies, mode shapes and modal damping ratios are considerably affected from ground conditions. The highest natural frequency is obtained for the gravel ground case. The lowest natural frequency is identified for the clay–silt mixture ground case. The mode shapes changed randomly in each case. But the main modal behaviors are vertical mode and bending modes.     

ARMAX modal parameter identification in the presence of unmeasured excitation—II: Numerical and experimental verification

The performance of an autoregressive moving average with exogenous excitation (ARMAX) time-domain parameter estimation algorithm is assessed using data simulating the response of a two degree-of-freedom system and also experimental data obtained from a cantilever aluminium beam. The algorithm is aimed at identifying modal parameters in the presence of significant measurement noise and unmeasured sources of periodic and random excitation. The simulated system exhibits lightly damped modes and is excited with measured random excitation as well as unmeasured random and periodic excitation. A second case is considered where the modal frequencies of the simulated system are separated by 0.345 Hz and the frequency of an unmeasured periodic excitation is 0.257 Hz below the first modal frequency. Electrodynamic shakers as well as piezoceramic plates are used to apply multiple independent excitation forces, including measured random noise and also unmeasured random and periodic signals. Successful identification of modal parameters is achieved in the presence of up to 10% random measurement noise, as well as over 200% unmeasured periodic and random excitations. Results showed that the ARMAX algorithm achieved better results than ARX models estimated from experimental data corrupted by the effects of unmeasured excitations. The use of piezoceramic plates for structural excitation was demonstrated in experiments and the ability to excite modes was observed to be dependent on the deflection of a particular mode in the contact area of the piezoceramic plates.     

含呼吸式裂纹的失谐叶盘系统响应特性研究

含张开式裂纹的叶盘系统无法准确地反映其受迫振动响应特性,为此,基于细梁理论和线弹性断裂力学理论建立了含呼吸式裂纹的失谐叶盘系统数学模型,对比分析了呼吸式裂纹、张开式裂纹对失谐叶盘系统固有特性和振动响应的影响,揭示了呼吸式裂纹对叶盘系统振动响应局部化的影响规律。研究表明:呼吸式裂纹使得振动响应呈现复杂的非线性特征;此外,与张开式裂纹模型相比,基于呼吸式裂纹模型的叶盘系统对失谐更敏感。      

The inception of OMA in the development of modal testing technology for wind turbines

Wind turbines are immense, flexible structures with aerodynamic forces acting on the rotating blades at harmonics of the turbine rotational frequency. These harmonics are comparable to the modal frequencies of the structure. Predicting and experimentally measuring the modal frequencies of wind turbines have been important to their successful design and operation. Performing modal tests on wind turbine structures over 100 m tall is a substantial challenge, which has inspired innovative developments in modal test technology. For wind turbines, a further complication is that the modal frequencies are dependent on the turbine rotation speed. The history and development of a new technique for acquiring the modal parameters using output-only response data, called the Natural Excitation Technique (NExT), will be reviewed, showing historical tests and techniques. The initial attempts at output-only modal testing began in the late 1980s with the development of NExT in the 1990s. NExT was a predecessor to Operational Modal Analysis (OMA), developed to overcome these challenges of testing immense structures excited with natural environmental inputs. We will trace the difficulties and successes of wind turbine modal testing from 1982 to the present.     

Effectiveness of the floating slab track system constructed at Konya Light Rail

Ground-borne vibrations and noise, originated at the train/tram wheel–rail interface and transmitted through the rails to the ground, may cause significant disturbance to people passing by or residing alongside the railways. This paper presents a case study on the evaluation of the effectiveness for mitigating ground-borne vibration and noise by floating slab track system (FST). The underpass located at a major road junction in front of Konya Metropolitan Municipality building serves to thousands of people every day. The Konya Light Rail makes a curb right on top of the underpass, which generates considerable amount of noise and vibration to the environment. In this study, the noise and vibration acceleration measurements were taken before and after the FST system installment in order to evaluate the effectiveness of the isolation work. The collected acceleration data were analyzed and the resulting vibration velocity levels were compared. It was found that the vibrations and the ground-borne noise due to the passage of the trams were reduced considerably. The FST system was found to be quite successful in absorbing the vibrations. A noise level reduction up to 26 dBA was measured after replacing the old rail system with FST.