Structural Damage Detection Method Based on Decomposition of the Operating Deflection Shapes

Full-field measurement techniques such as the scanning laser Doppler vibrometer (LDV) and the electronic speckle pattern interferometry systems can provide a dense and accurate vibration measurement on structural operating deflection shape (ODS) on a relatively short period of time.The possibility of structural damage detection and localization using the ODS looks likely more attractive than when using traditional measurement techniques which address only a small number of discrete points.This paper discusses the decomposition method of the structural ODSs in the time history using principal component analysis to provide a novel approach to the structural health monitoring and damage detection.The damage indicator is proposed through comparison of structural singular vectors of the ODS variation matrixes between the healthy and damaged stages.A plate piece with a fix-free configuration is used as an example to demonstrate the effectiveness of the damage detection and localization using the proposed method.The simulation results show that:(1) the dominated principal components and the corresponding singular vectors obtained from the decomposition of the structural ODSs maintain most of all vibration information of the plate,especially in the case of harmonic force excitations that the 1st principal component and its vectors mostly dominated in the system;(2) the damage indicator can apparently flag out the damage localization in the case of the different sinusoidal excitation frequencies that may not be close to any of structural natural frequencies.The successful simulation indicates that the proposed method for structural damage detection is novel and robust.It also indicates the potentially practical applications in industries.     

Eulerian laser Doppler vibrometry: Online blade damage identification on a multi-blade test rotor

Laser Doppler vibrometry enables the telemetry-free measurement of online turbomachinery blade vibration. Specifically, the Eulerian or fixed reference frame implementation of laser vibrometry provides a practical solution to the condition monitoring of rotating blades. The short data samples that are characteristic of this measurement approach do however negate the use of traditional frequency domain signal processing techniques. It is therefore necessary to employ techniques such as time domain analysis and non-harmonic Fourier analysis to obtain useful information from the blade vibration signatures. The latter analysis technique allows the calculation of phase angle trends which can be used as indicators of blade health deterioration, as has been shown in previous work for a single-blade rotor.This article presents the results from tests conducted on a five-blade axial-flow test rotor at different rotor speeds and measurement positions. With the aid of artificial neural networks, it is demonstrated that the parameters obtained from non-harmonic Fourier analysis and time domain signal processing on Eulerian laser Doppler vibrometry signals can successfully be used to identify and quantify blade damage from among healthy blades. It is also shown that the natural frequencies of individual blades can be approximated from the Eulerian signatures recorded during rotor run-up and run-down.     

轮胎稳态运动学与六分力预报Ⅰ:理论与方法

提出一种新的轮胎运动学描述和六分力预报理论。滚动接触是汽车轮胎力学、轮轨动力学的核心问题,由于涉及刚体转动与有限变形,滚动接触运动学与动力学的描述与求解非常困难。用拉格朗日—欧拉混合描述法分析大变形滚动接触结构的速度场、加速度场和接触变形。以车轮定位角为卡尔丹角,用拉格朗日描述,得到了包含刚体转动和弹性变形的轮胎速度场。而接触区域的变形和受力用欧拉描述,通过欧拉网格和拉格朗日网格的信息传递,完成滚动结构动力学分析。所提出的理论可以退化到Fiala模型,并可以从理论上解释子午线轮胎的伪侧偏和伪侧倾现象。基于所建立的运动学理论和非线性有限元,建立轮胎六分力预报方法。针对某轿车子午线轮胎,分析轮胎接地面滑移速度、接地面积、接地压力、侧向剪力分布等随着侧偏角的变化规律,并研究该轮胎侧偏力和回正力矩随着胎面刚度和摩擦因数的参数敏感性。结果表明轮胎侧偏刚度和回正刚度主要受结构刚度控制,而峰值侧偏力和峰值回正力矩主要受摩擦因数控制。将利用所建立的方法和试验,探讨带束层结构对大规格子午线轮胎侧偏特性的影响规律,进一步验证所提出的理论和方法的正确性。所提出的理论和方法开辟了直接从轮胎设计预报轮胎六分力的新途径。     

System for measuring the coordinates of tire surfaces in transient conditions when rolling over obstacles: description of the system and performance analysis

This paper describes the development of a system for measuring surface coordinates (commonly known as "shape measurements") which is able to give the temporal evolution of the position of the tire sidewall in transient conditions (such as during braking, when there are potholes or when the road surface is uneven) which may or may not be reproducible. The system is based on the well-known technique of projecting and observing structured light using a digital camera with an optical axis which is slanted with respect to the axis of the projector. The transient nature of the phenomenon has led to the development of specific innovative solutions as regards image processing algorithms. This paper briefly describes the components which make up the measuring system and presents the results of the measurements carried out on the drum bench. It then analyses the performance of the measuring system and the sources of uncertainty which led to the development of the system for a specific dynamic application: impact with an obstacle (cleat test). The measuring system guaranteed a measurement uncertainty of 0.28 mm along the Z axis (the axial direction of the tire) with a measurement range of 250(X) x 80(Y) x 25(Z) mm(3), with the tire rolling at a speed of up to 30 km/h.     

一种新的轮胎印痕测量及压力分布数据处理方案

介绍了一种基于压阻阵列成像方法的轮胎外圈表面花纹磨损检测技术,该技术通过检测轮胎在特定载荷下印痕的变化来估计轮胎的质量与使用寿命。在介绍测量原理的基础上,重点介绍了印痕图像处理技术与评价方法,针对轮胎花纹与地面接触产生的印痕图像确定边界与接触面积,研究了一种基于圆模板滚边的方法来获取图像外包络线的算法。研究表明该方法能有效处理凸壳与非凸壳图形,自动获取带凹槽图形的外包络区域,具有较好的鲁棒性和较高的精度。     

汽车轮胎橡胶摩擦试验研究

介绍了所开发的轮胎橡胶摩擦试验台,提出了轮胎橡胶摩擦试验方法。在该试验台上进行了干水泥路面、冰面等工况下的轮胎橡胶块摩擦试验,对所得试验结果进行了分析、处理。初步掌握了路面、温度、垂直压力和滑移速度等因素对摩擦因数的影响。在此基础上把动摩擦的概念引入轮胎半经验模型,对现有模型进行了改进。提出了应用轮胎低速试验数据预测高速下轮胎特性的方法。     

A novel mixed Eulerian–Lagrangian finite-element method for steady-state hot rolling processes

For the finite-element analysis of steady-state rigid-viscoplastic forming processes in hot rolling of steel, a new and efficient mathematical model was developed. The method is based on a mixed Eulerian–Lagrangian formulation, using an Eulerian co-ordinate in the rolling direction, while employing Lagrangian co-ordinates in the direction of the thickness and width of the strip. This approach leads to an efficient algorithm, where the time is eliminated as an independent variable and the velocity components in the Lagrangian directions are replaced by displacement components as independent field quantities. Due to this concept, the free surface deformations can be accounted for directly and the problems encountered with pure Eulerian or Lagrangian models now appear with reduced complexity and can thus be tackled more easily. The new model is based on a finite-element formulation, modified to account for a mixed treatment of velocity and displacement components.     

A new method for processing impact excited continuous-scan laser Doppler vibrometer measurements

A scanning laser Doppler vibrometer (LDV) can acquire non-contact vibration measurements from a structure with high spatial detail in an automated manner; one only need redirect the laser via computer-controlled mirrors to acquire measurements at additional points. However, since most LDV systems are only capable of measuring one point at a time, conventional scanning vibrometry cannot be effectively employed in some situations, for example when the time record is long at each measurement point or when the structure changes with time. Conventional scanning LDV systems are also difficult to employ with impact excitation because there is considerable variation in the impact location, angle and the character of the impacts, which leads to errors in the mode shapes that are extracted from the measurements. This paper presents a method by which one can determine the mode shapes, natural frequencies and damping ratios of a structure from as little as one response record by sweeping the laser continuously over the vibrating structure as the measurement is acquired. A novel resampling approach is presented that transforms the continuous-scan measurements into pseudo-frequency response functions, so they can be processed using standard identification routines to find the modal parameters of the structure. Specifically, this work employs a standard multi-input–multi-output identification routine and the complex mode indicator function to the continuous-scan laser Doppler vibrometry (CSLDV) measurements. The method makes no assumptions regarding the shape or properties of the surface and only requires that the laser scan periodically and that the structure vibrate freely. The method is demonstrated experimentally on a free–free beam, identifying the first nine mode shapes of the beam at hundreds of points from a few time histories. For this system, this represents a two-order of magnitude reduction in the time needed to acquire measurements with the LDV.     

Velocity correction of the Janus configuration laser Doppler velocimeter

The error of laser Doppler velocimeter (LDV) based on Janus configuration is analyzed as the vehicle inclines. Analysis shows that the error of the Janus configuration LDV depends on the vertical velocity to horizontal velocity ratio (VHR) only. But the measurement accuracy of the Janus configuration LDV will be not high enough to meet the requirement of vehicle self-contained navigation system, if the VHR of the vehicle is overlarge in powerful rough ground. The error of the Janus configuration LDV is corrected through an inclinometer whose precision of angle needed is only 2%. Simulation shows that the error of the Janus configuration LDV after correction can be limited below 0.1% even as the VHR reaches 0.3 and pitch angle is 15°.     

滚动轮胎侧倾接地性能有限元分析

建立子午线轮胎滚动分析的三维有限元模型,在模型中充分考虑轮胎材料和结构的复杂性,轮胎与轮辋过盈配合以及轮胎与轮辋、地面的接触摩擦等状况,研究轮胎侧倾滚动状态下的速度和外倾角对轮胎变形、接地区应力和帘线的应力分布规律的影响.     

Hydroplaning simulation for a straight-grooved tire by using FDM, FEM and an asymptotic method

Much research has been conducted to simulate the hydroplaning phenomenon of tires by using commercial explicit FEM (finite element method) codes such as MSC.Dytran and LS-DYNA. However, it takes a long time to finish such a simulation because its model has a great number of Lagrangian and Eulerian elements, and a contact should be defined between the two different types of elements. The simulation results of the lift force and the contact force are very oscillatory. Thus, in this study a new methodology was proposed for the hydroplaning simulation by using two separate mathematical models. An FDM (finite difference method) code was developed to solve Navier-Stokes and continuity equations and to obtain the pressure distribution around a tire with the inertial and viscous effects of water taken into account. An FE tire model was used to obtain the deformed shape of the tire due to the vertical load and the pressure distribution. The two models were iteratively used until a converged pressure distribution was obtained. Since the converged pressure distribution could not be obtained near or at the contact zone due to very shallow water, an asymptotic method was also proposed to estimate the pressure distribution. This new simulation methodology was applied to a straight-grooved tire, and its hydroplaning speed was finally determined for a water depth of 5 mm, 10 mm, 15 mm and 20 mm. Moreover, a new simulation methodology using LS-DYNA was proposed, and the two methodologies were compared in terms of accuracy and efficiency.     

Evaluation of substitution monopole models for tire noise sound synthesis

Due to the considerable efforts in engine noise reduction, tire noise has become one of the major sources of passenger car noise nowadays and the demand for accurate prediction models is high. A rolling tire is therefore experimentally characterized by means of the substitution monopole technique, suiting a general sound synthesis approach with a focus on perceived sound quality. The running tire is substituted by a monopole distribution covering the static tire. All monopoles have mutual phase relationships and a well-defined volume velocity distribution which is derived by means of the airborne source quantification technique; i.e. by combining static transfer function measurements with operating indicator pressure measurements close to the rolling tire. Models with varying numbers/locations of monopoles are discussed and the application of different regularization techniques is evaluated.     

Influence of upstream disturbances on performance of an LDV-based cryogenic flow meter standard – CFD modelling and preliminary measurements with air

Increasing trade of liquefied natural gas (LNG) imposes stringent requirements for accurate flow rate measurement of this high energy content fluid. To satisfy this demand, a flow meter has been developed by CEASAME Exadebit which is based on velocity measurement behind a contraction nozzle using Laser Doppler Velocimetry technique (LDV). For this instrument, a calibration factor is defined relating the measured velocity to the flow rate. This calibration factor depends on the Reynolds number and it can be sensitive to the velocity profile behind the nozzle outlet and to presence of upstream flow disturbances such as bends, valves, etc. when the meter is installed on-site. In this paper, CFD modelling, using OpenFoam software, was employed to analyse the sensitivity of the calibration factor to flow disturbances for two types of disturbing elements; a U-bend and half-plate orifice. The CFD model was validated by comparison with experimental data for the calibration factor and velocity profiles obtained from preliminary LDV measurements with air. Two measurement setups were considered where the velocity is measured either in one point at the nozzle axis or integrated along a line across the nozzle diameter. The results show that the considered disturbing elements cause deviations in the calibration factor in the order of tenths of percent and that the maximal sensitivity of the line-setup to these disturbances is approximately half of the maximal sensitivity of the point-setup. On the other hand, it was shown that the line-setup is more sensitive to the LDV positioning than the point-setup.     

Point-velocity methods for flow-rate measurements in asymmetric pipe flow

Laser Doppler velocimetry (LDV) is characterized by its ability to determine local fluid velocities with high accuracy. Therefore, LDV may also be used for precise flow-rate measurements of turbulent flow in circular ducts. The uncertainty of the measurement depends mainly on the asymmetry of the axial velocity distribution and on the point-velocity method chosen to estimate the flow-rate. LDV-measurements in conjunction with velocity-area methods have been performed under different asymmetric flow conditions yielding errors in the range of one per cent. The experimental data have been transformed into analytical flow profiles, in order to investigate combinations of single-point measurements. As a result, a new multi-point method with variable centre-point factor is introduced, that reduces both the effort and uncertainty in the measurement.     

An investigation into the effects of installation on the performance of insertion flowmeters

An electromagnetic and a turbine insertion flowmeter were tested in three different flow conditions inside a 0.590-m bore pipe inserted in the National Engineering Laboratory (NEL) large water flow measurement facility. The results were compared with velocity measurements obtained from a laser Doppler velocimeter (LDV). The advantage of using such a reference measurement is that LDV is non-intrusive and does not affect the velocity profile itself.Of the meters tested, one was supplied with a whole meter calibration factor and the other was supplied with a calibration factor for the D/2 position.For both meters, application of the respective manufacturer's blockage correction improved the velocity measurements, reducing the differences between the LDV and corrected insertion meter measurements and the difference between the integrated insertion meter measurements and the gravimetric measurements.Swirling and skew flow profiles were generated by the installation of the NEL designed swirl generator and flow disturber, respectively. Neither of these disturbed profiles affected the performance of either of the meters in terms of accuracy of measurement compared with the LDV readings. The profiles themselves, however, changed the velocities at the D/8 and 7D/8 points, making single point estimates of the mean velocity inappropriate. A complete 13-point traverse, integrated using the method of cubics as described in BS 1042 [1] (Section 2.3: Measurement of fluid flow in closed conduits, 1992), gave acceptable estimates of mean velocity in both swirling and skew flow for both probes.     

混合单频激励下连续扫描激光多普勒振动测试

提出了一种混合单频激励下激光连续扫描振动测试方法,提高了连续扫描激光多普勒振动测试效率。首先,基于单频激励下连续扫描激光多普勒振动测试的原理,研究了混合单频激励下连续扫描激光多普勒振动测试技术,提出了适合混合单频激励的结构工作变形提取方法;其次,通过仿真测试,从理论上验证了方法的有效性;最后,以悬臂梁结构为例,进行了连续扫描和离散点扫描测试的试验验证。结果表明,混合单频激励下的连续扫描激光振动测试及分析方法可准确获得结构工作变形,具有效率高、空间分辨率高等优点,对进一步的工程应用具有实用价值。     

Demonstration of a laser vorticity probe in turbulent boundary layers

A laser-based probe for the nonintrusive measurement of velocity gradient and vorticity was demonstrated in turbulent boundary layers. Unlike most other optical methods, the current technique provides an estimate of the velocity gradient, without having to first measure velocity at multiple points. The measurement principle is based on the heterodyne of coherent light scattered from two adjacent particles. The beat frequency of the heterodyne is directly proportional to the velocity gradient. The probe is assembled from commercially available, inexpensive optical components. A laser Doppler velocimeter (LDV) processor is used to analyze the heterodyne signal. A component of vorticity is obtained by using two appropriately aligned velocity gradient probes. The optical probes developed were used in turbulent boundary layers to measure local, time-frozen velocity gradients partial differential u / partial differential y, partial differential v / partial differential x, and partial differential v / partial differential y, as well as the spanwise vorticity. The measurements were compared to those inferred from LDV measurements in the same facility and to data available in the literature.     

薄板等离子弧三维成形的工艺方法

平面薄板的等离子弧成形提出了一种有效实用的工艺方法.方法的重要特征是它首先计算成形一个特定形状所需要的应变场,利用应变场矢量和扫描路径方向垂直的关系设计扫描路径.等离子弧热参数通过应变场与等离子弧功率和扫描速度的关系确定.此方法在成形两种不同双曲形状上的有效性已经被仿真和试验所验证.     

Note: Reflection-type micro multipoint laser Doppler velocimeter for measuring velocity distributions in blood vessels

We have developed a laser Doppler velocimeter (LDV) for measuring velocity distributions in blood vessels. We converted a transmission-based LDV into a reflection-based LDV to make it suitable for clinical applications. The velocity distribution image of a serpentine flow channel obtained could be qualitatively explained by the numerical results. Finally, we evaluated the system by using it to measure injection of blood into a glass tube by a syringe pump. The results obtained demonstrate that erythrocytes can be used as seeding particles for the reflection-type micro multipoint LDV. The results obtained are useful as basic data for clinical applications.     

轮胎胎面参数在线检测系统研究及应用

为了提高汽车轮胎生产过程中对胎面尺寸的测量精度,针对移动中的橡胶胎面设计了一种测量轮胎胎面参数的在线检测系统。选用3D激光传感器,根据传感器获得的坐标数据绘出胎面横截面轮廓,基于B样条曲线拟合方法,通过特征点测量计算胎面横截面数据;选用CCD图像传感器,设置两端基准线,根据现场亮度采用可调光源控制器,并采用OSTU算法对图像进行二值化处理,基于像素数和实际的尺寸存在线性对应关系,可获得胎面长度。现场实验结果表明,该测量系统的横截面参数测量精度小于1 mm,长度测量精度小于2 mm,能够满足生产工艺的测量要求,可实现胎面参数的在线动态测量,该测量系统具有安装方便、运行稳定等特点。