Operational Deflection Shapes Research Articles

Influence of the variation of concrete properties in determining the vibration transmission index Kij

In this work, the influence of the modulus of elasticity, the loss factor and the density of reinforced concrete on the vibration transmission index ([Formula: see text]) of a reduced concrete bench was evaluated. An experimental modal analysis based on the Operating Deflection Shape (ODS) methodology is carried out on a reinforced concrete slab (1.20 × 0.80 × 0.20 m) supported on four concrete pillars, applying four sources of distinct impacts: mallets of 1 and 4 kg, impact machine and one person jumping. The experimental results served to validate the finite element bench model (FEM) considering both the first four modes of slab vibration and the adjustment of the elasticity and shear modulus, the loss factor and the density of the concrete using the NSGA genetic algorithm-II. The [Formula: see text] index between the slab and the columns was determined experimentally, numerically and analytically, according to the Gerretsen model. The FEM model showed a percentage difference in the frequencies of the vibration modes less than 10% concerning the tests for the [Formula: see text] index. The influence of density and the modulus of elasticity mainly in the direction perpendicular to the plane of the structure modify the values of the frequencies of the vibration modes by up to 10% without interfering in the modal forms of the structure. In addition, the internal loss factor alters the amplitude of the [Formula: see text] results by an average of 10 dB. Finally, it is shown that the stiffness varies according to the orthotropy of the material. It was possible to conclude that the computational model showed good convergence in results ([Formula: see text]%) when compared with the [Formula: see text] experiments, with the same varying along the frequency, different from what is proposed in the analytical and normative models. This fact proves the hypothesis raised that structural couplings in practice generate significant interference in the results, as happens in residential buildings, with the test bench being an important experiment for initial predictions with little interference from energy transmission to the environment.

Multi-damage detection of composite blades via the curvature modal shape approach in combination with surface interpolation and extreme learning machine

In recent years, there has been a rise in renewable energy, which has led to an increase in equipment maintenance. The damage detection technique for wind turbine blades (WTBs) can reduce maintenance costs. The majority are not immediately applicable to structures that are in an operating condition. Motivated by the current constraints, a novel two-stage multi-damage quantitative detection approach in WTBs during operation has been proposed. The multiple damage locations are first identified by calculating the curvature modal shape (CMS) difference for the WTBs after the interpolation of the operating deflection shape (ODS) using surface interpolation (SI). Then the relationship between the natural frequencies and damage severities for the WTBs is determined utilizing the finite element method (FEM). The established correlation provides a natural frequency database that can be utilized for identifying the corresponding damage severities through the application of the Extreme Learning Machine (ELM) method, upon measuring the natural frequencies of the damaged WTB. The efficacy of the suggested damage detection methodology has been confirmed through simulations conducted on WTBs featuring two or three instances of damage. Moreover, the ODS along with natural frequencies of the WTBs exhibiting two or three damages are experimentally assessed using a Scanning Laser Doppler Vibrometer. The simulation and experiment verify that the presented method has satisfactory effectiveness in damage detection.

Experimental modal identification of a pedestrian bridge through drive-by monitoring integrated with shared-mobility vehicles

In the context of improving resilience in transport infrastructure, an emerging approach of indirect structural health monitoring is gaining attention, known as drive-by monitoring, instrumenting a vehicle with sensors to evaluate the bridges it crosses. However, their effectiveness has predominantly been investigated in ideal scenarios, with actual real-world applications being quite scarce. The research presented in this paper explores the feasibility of combining two routes: (1) fleet emissions reduction and (2) transport resilience enhancement, through drive-by monitoring integrated with shared mobility, including electric mobility scooter and bicycle. The information from drive-by data collected from shared mobility can give valuable information on critical transport infrastructure (e.g., bridges) and such a drive-by database has the potential for network level infrastructure condition assessment. In this paper, two different drive-by roadmaps are investigated subject to the flexibility of the bridges, namely partially or fully drive-by monitoring. To validate the proposed roadmaps, a full-scale pedestrian bridge was chosen for drive-by testing, where smartphone sensors and specialised accelerometers are mounted on shared mobility for data acquisition. Experimental results demonstrate that (i) smartphone sensing can provide data with similar accuracy compared to specialised accelerometers, (ii) bridge frequencies can be easily obtained from temporarily parked shared mobility, with a maximum relative error of 1.05%, (iii) both the bridge frequencies and operational deflection shapes are successfully extracted from the moving shared mobility by using variational mode decomposition and filtering techniques, and shared mobility’s GPS data along with moving speeds are collected for potential vehicle positioning and drive-by database updating.

A coupled finite element-discrete element method for the modelling of brake squeal instabilities

The work presented here proposes a contribution on the analysis of brake squeal phenomenon using a transient coupled finite element-discrete element method (FEM-DEM) simulation with pad surface topography evolution. To build the coupled FEM-DEM model, a non-overlapping strong coupling is first employed between the FEM and DEM subdomains. Second, a new calibration methodology of the DEM microscopic properties is proposed based on the eigenvalue analysis of the full model. The results of the coupled FEM-DEM model show a good agreement in terms of unstable frequencies and the evolution of the pad contact state history when compared to full FEM models, both for new and worn pad topographies. The evolution of the pad surface topography during the transient analysis results in a complex frequency behaviour, with abrupt shifts of instabilities and new operating deflection shapes, in agreement with reported experimental results. The proposed coupled FEM-DEM model thus seems to be a valuable tool for a better understanding of the squeal triggering due to the evolution of the pad surface topography. This contribution paves the way to advanced numerical analyses of brake squeal phenomenon, which triggering conditions are still under investigation.

High precision full-field vibration measurement by LDV-induced stroboscopic fringe projection

A method for full-field vibration measurement that combines Fourier Transform Profilometry (FTP) and Laser Doppler Vibrometry (LDV) is proposed and validated experimentally on various structures. This technique projects sinusoidal fringe patterns onto the test sample using a flashing LED at an oblique angle, while a CCD camera captures the fringe images vertically. Vibration data is derived from 3-D phase maps generated by applying FTP to these images and is further calibrated using a motorized translation stage. To improve the precision of FTP and extend the measurable frequency range beyond that of normal-rate cameras, initial single-point vibration data from the test sample is obtained using LDV. This prior information enables noise decoupling and down-sampling techniques to be employed. The experimental results confirm that this method can precisely reconstruct the high-order operational deflection shapes of vibration on structures with different materials, achieving a precise measurement for vibration amplitude of around 500 nm (1/2000 of fringe spacing) on a 10 cm x 10 cm plastic plate and a 2 cm x 14 cm aluminum beam with approximately 1 mm fringe spacing and 26° projection angle.

An adaptive continuous scanning laser Doppler vibrometry technique for measuring vibrational mode shapes of structures with holes

Abstract Continuous Scanning Laser Doppler Vibrometry (CSLDV) enables fast and full-field vibration measurement in an intact area of a structure. This paper further proposes a novel adaptive CSLDV method that can obtain the Operational Deflection Shapes (ODS) and mode shape of structures with holes. Firstly, an adaptive path planning method is applied to the surface of the tested structure, which can automatically adapt to the size and position of round and square holes, as well as the resolution requirements for the measurement. Secondly, based on the symmetry and other characteristics of the planned path, the time domain signal is processed by delay optimization and demodulation to obtain the ODS of each vibration mode. Finally, a modal test is conducted on a flat structure with a square and circle holes as an example. A validation experiment is also performed using SLDV. The results show that the mode shapes obtained from both methods are consistent and the Modal Assurance Criterion (MAC) between them are all above 0.96. The method can realize CSLDV of flat plate structures with arbitrary square and round holes, and has the advantages of high efficiency and dense measurement points, which enhances its engineering applicability.

Validation of a model-based dual-band modal decomposition and expansion approach for fatigue monitoring of offshore wind turbine foundations

The fatigue limit state strongly drives the lifetime of offshore wind turbine support structures. Despite steady advancements in their design, the accumulation of fatigue damage over the lifetime of the structure remains uncertain; one way to improve certainty is to directly monitor structural loads at fatigue-critical locations, e.g., near or below the mudline. However, directly monitoring the loads at these locations is often not possible, since these locations do not allow for easy installation or retrofitting of sensors. To this end, model-based virtual sensing techniques can be employed to estimate the structural response at unmeasured locations based on vibration response data and a finite element model which can accurately describe the modal and operational deflection shapes of a specific turbine [1,2,3]. For this contribution, a modal decomposition and expansion (MDE) algorithm [4] will be used to predict strain time series at fatigue-critical locations, based on acceleration and strain data obtained from the tower of an operational OWT. Emphasis will be put on sparse data situations in which a realistic amount of sensor data is used as input. Fibre-optical strain gauges close to and below the mudline level (Fig 1) will be used for direct validation of the extrapolation capabilities. The required finite element model is built using an in-house developed and verified integrated FE model class [5,6], in combination with a unique database which contains all available geotechnical and structural data of offshore wind turbines (owimetadatabase) [7,8]. This combination allows us to generate fleet-wide, turbine-specific, finite elements models for several wind farms. The results will be presented in terms of time series (e.g., Fig. 2) and fatigue damage-related metrics. Preliminary results show that strain time series estimated with the MDE method show good agreement with the validation data.

On the Cover: Experimental Modal Analysis and Operational Deflection Shape Analysis of a Cantilever Plate in a Wind Tunnel with Finite Element Model Verification

On the Cover: Experimental Modal Analysis and Operational Deflection Shape Analysis of a Cantilever Plate in a Wind Tunnel with Finite Element Model Verification

Cause Analysis and Mitigation Measures of Vertical Vibration of Head-Cover of a Pump-Turbine

Abstract The abnormal vertical vibration of the head cover of a 306 MW pump-turbine was found in the 150 to 240 MW part load region of generating condition. To reveal the causes and find mitigation measures, field tests on vibration and pressure pulsations, and the ODS (Operational Deflection Shape) analysis of the head cover were conducted. It was found that the vibration of the head-cover is transferred by means of the clearance water body from the runner vibration, which in induced by pressure pulsations. Several vibration reduction measures were analysed and injecting compressed-air into the clearance between the head-cover and the runner-crown was proposed. The field test showed that the abnormal vibration was effectively eliminated because the fluid characteristics between the head-cover and the runner can be changed by just adding a small amount of compressed-air, which destroys the critical conditions of inducing vibration. This first attempt is of reference values, because it is a simple, effective, and economical.

Operational Deflection Shape Measurements on Bladed Disks with Continuous Scanning Laser Doppler Vibrometry.

The continuous scanning laser Doppler vibrometry (CSLDV) technique is usually used to evaluate the vibration operational deflection shapes (ODSs) of structures with continuous surfaces. In this paper, an extended CSLDV is demonstrated to measure the non-continuous surface of the bladed disk and to obtain the ODS efficiently. For a bladed disk, the blades are uniformly distributed on a given disk. Although the ODS of each blade can be derived from its response data along the scanning path with CSLDV, the relative vibration direction between different blades cannot be determined from those data. Therefore, it is difficult to reconstruct the complete vibration mode of the whole blade disk. In order to measure the complete ODS of the bladed disk, a method based on ODS frequency response functions (ODS FRFs) has been proposed. While the ODS of each blade is measured by designing the suitable scanning paths in CSLDV, an additional response signal is obtained at a fixed point as the reference signal to identify the relative vibration phase between the blade and the blade of the bladed disk. Finally, a measurement is performed with a simple bladed disk and the results demonstrate the feasibility and effectiveness of the proposed extended CSLDV method.

A novel mirror-assisted method for full-field vibration measurement of a hollow cylinder using a three-dimensional continuously scanning laser Doppler vibrometer system

A novel general-purpose three-dimensional (3D) continuously scanning laser Doppler vibrometer (CSLDV) system was recently developed by the authors to measure 3D vibration of a structure with a curved surface. As a non-contact system, it can avoid the mass-loading problem in 3D vibration measurement using triaxial accelerometers. In previous studies, the 3D CSLDV system was used to measure 3D full-field vibration of a turbine blade with a curved surface and identify its operating deflection shapes (ODSs) and mode shapes. The 3D CSLDV system had the same level of accuracy as that with a commercial 3D scanning laser Doppler vibrometer system, but can measure many more points in much less time than the latter. However, the 3D CSLDV system can be limited by its field of view, which is a common problem for optical-based measurement devices. Moving the 3D CSLDV system to different positions to measure different parts of a test structure is not practical during 3D CSLDV measurement, since the system has to be re-calibrated once it has been moved, which can be time-consuming and introduce measurement errors. This work proposes a novel mirror-assisted testing methodology for 3D CSLDV measurement that aims to measure vibration of difficult-to-access areas of a structure without moving the 3D CSLDV system during the test, and stitch ODSs of its different parts together to obtain its panoramic 3D ODSs. The proposed methodology includes a novel scan trajectory design method that uses virtual areas of the structure behind the mirror to conduct continuous and synchronous scanning of three laser spots, and a novel velocity transformation method that uses virtual positions of three laser heads behind the mirror to stitch ODSs of different parts of the structure together. To demonstrate the proposed methodology, 3D CSLDV measurement is conducted on an aluminum hollow cylinder specimen, which has difficult-to-access areas such as its side and back surfaces, with the assistance of the mirror to obtain its panoramic 3D ODSs corresponding to its first two modes. Comparison between identified ODSs of the hollow cylinder specimen from the experiment and mode shapes from its finite element model is made and modal assurance criterion values are larger than 0.98.

Schemes of local fitting for damage detection of bars using longitudinal operating deflection shapes measured by 3D laser scanning

Longitudinal operating deflection shapes (ODSs) of a bar can be measured by three-dimensional laser scanning. The difference between slopes of ODSs (SODSs) under damaged and intact statuses of the bar can be used to indicate and locate the damage. This study inspects ODSs in a multiscale manner, whereby multiscale ODSs (MODSs) and multiscale SODSs (MSODSs) are produced. Noise interference can be eliminated by increasing scale parameters to their satisfying values. In addition, two schemes of local fitting are applied to measured MODSs to generate locally fitted MSODSs under virtual intact statuses of the bars. By relying on differences between measured and locally fitted MSODSs, two individual damage indices (DIs) are established, namely the type-I DI and the type-II DI, in which damage-induced peaks can indicate and locate the damage. The capability of the two schemes of local fitting is theoretically verified and experimentally validated by detecting two-sided notches in bars.

Enhanced Design of Sunroof System through Parametric Study Considering Vibration Phenomenon during Vehicle Operation

Recently, performance development related to noise, vibration, and harshness in sunroof systems has attracted significant research attention. However, research thus far has been limited to analytical and experimental studies relating to structural improvement of the individual parts, rather than considering vehicle driving conditions. This study compared the experimental data from actual driving tests with simulation results to examine sunroof vibration characteristics under realistic conditions. Firstly, the characteristics of sunroof vibrations were investigated theoretically in order to derive equations of motion and the natural frequencies of the sunroof. Sunroof vibrations occurring during driving were analyzed through experimental modal analysis and operational deflection shape. A parametric study was conducted adapting design parameters such as the Young’s modulus, glass thickness, and bracket location. The vibration characteristics of the sunroof glass could be improved by changing the support points of the front and rear brackets, which represent the design elements that can achieve the greatest efficiency with minimal design changes.

Damage imaging in plates by evaluating local entropy in guided wavefield data

This paper presents a new algorithm called broadband entropy-based two-stage damage imaging (BE2DI) for the detection and imaging of defects in multi-layer plates.The method differentiates defects from either local scattering phenomena of propagating Lamb waves or locally increased vibrational activity for stimulated global plate resonances by exploiting the higher vibrational activity of full-field broadband vibration signals at defective regions and the distinct spatial behavior of defects and artifacts. Using these features, first, a candidate damage map is constructed by means of iterative thresholding based on descriptive statistics of broadband data. Afterwards, an adaptive regional damage index based on local entropy is introduced, which utilizes operational deflection shapes to process previously identified candidate regions and subsequently reveal both shallow and deep defects. BE2DI can be seen as an automated local defect resonance identification approach in the case of shallow defects. Multiple plates having various defect types with different sizes and depths are investigated. Broadband chirp signals are used to excite the plates using low-power piezoelectric actuators, and vibrational data is registered by 3D scanning laser Doppler vibrometry. The obtained results quantitatively and qualitatively demonstrate that the proposed method can effectively detect different kinds of damage, regardless of being shallow or deep.

Experimental verification of a data-driven algorithm for drive-by bridge condition monitoring

As the world’s transport infrastructure ages, the importance of bridge condition monitoring is becoming increasingly acknowledged. Large-scale deployment of existing inspection and monitoring techniques is infeasible due to cost and logistical challenges. The concept of using sensors located within vehicles for low cost ‘drive-by’ monitoring has become the focus of much attention in recent years. This paper presents a new data-driven approach for drive-by bridge monitoring. Machine learning techniques are leveraged to allow the influence of vehicle speed to be considered and the Operating Deflection Shape Ratio (ODSR) is presented as an alternative damage-sensitive feature to the commonly used frequency spectrum. Extensive laboratory experiments demonstrate that the method is capable of detecting midspan cracking and seized bearings. A statistical classification approach is adopted to classify damage indicators as either ‘damaged’ or ‘healthy’. Classification accuracy is seen to vary between 65-96% and is similar whether using the frequency spectrum or ODSR. Based on the results of the laboratory testing, it is expected that this approach could be implemented on a large scale to act as an early warning tool for infrastructure owners to identify bridges presenting signs of distress or deterioration.

Bus Network Based Fleet Monitoring Towards Sustainable Transport Infrastructure

Since its first invention in 2004, drive-by structural health monitoring has been widely adopted to assess ageing infrastructures worldwide. In 2019, the European Union Joint Research Centre highlighted it as one of the most promising techniques for bridge monitoring. Recently, a fleet composed of different vehicles has been regarded to be more efficient in obtaining bridge information in contrast with a sole vehicle, as fleet monitoring can mitigate the annoying impact caused by undesired road components, and any uncertainty from a single passing vehicle. Conventional drive-by fleet monitoring builds on instrumented heavy trucks, whereas various mechanical properties of the tested trucks usually make it challenging to derive the bridge information for some scenarios, i.e., both the dominant frequency of the vehicle and the bridge located within the same range. Therefore, this paper proposes a novel drive-by fleet monitoring framework, where thousands of buses are generated by utilizing Monte Carlo Simulations. Latterly, bridge information, i.e., operating deflection shapes, is extracted by implementing the proposed algorithm from the measured bus accelerations for bridge damage detection and localization. Unlike the conventional drive-by monitoring, bus network-based fleet monitoring has proved to be more efficient because most of the mechanical properties of buses are identical, which further contributes more benefits in bridge information extraction. The proposed bus network-based drive-by fleet monitoring is validated with numerical experiments of a short-span concrete bridge.

Continuous Wavelet Transform based Crack Detection in a Metallic Shaft

In metals, the probability of fatigue crack initiation is significant in high load and high-speed machinery. Once the crack is initiated, it will grow with time and cause critical failure to the system. The condition based monitoring or predictive maintenance of the metallic shaft is essential before the crack reaches its critical size. The presence of excessive measurement noise increases the complexity to detect the crack; hence, there is a need of crack detection algorithm to detect the crack in the presence of excessive measurement noise. In the present work a Continuous Wavelet Transform (CWT) based algorithm is used to locate the crack in metallic shaft. Finite element analysis is used to generate the Operating Deflection Shape (ODS) of the shaft. The presence of crack in the shaft creates additional slope discontinuity in the shaft’s ODS. This slope discontinuity is more dominant near the first natural frequency. However, exciting the shaft near the first natural frequency is hazardous. In order to make the algorithm more robust the excitation nearby the natural frequency is avoided. The CWT-based algorithm is developed to locate the crack by using the ODS at very low excitation frequency.

Experimental and numerical investigations on the dynamic response of a power transformer

In the manufacturing unit, there is a need of an accurate and reliable numerical tool to predict noise radiation from transformer. The first step to achieve this is to have a proper modal analysis of the active part (winding+core+clamping system). An impact test was performed on a 30 MVA power transformer unit and resonance peaks were identified from the FFT plots. Also, Operational Deflection Shapes (ODS) were extracted to visualize the displacement pattern of the test object. Moreover, the transformer unit was electrically energized, and vibration levels were measured with Polytec 3D scanning laser vibrometer. A detailed numerical model was developed in COMSOL Multiphysics, and very good agreement was seen between the numerical and measurement results.

Experimental study on improving the noise and vibration characteristics of electric brake systems using order analysis

In this study, the occurrence of driving noise and vibration was analyzed through an understanding of the driving mechanism of an electric brake system, and research was conducted to derive insights into improving the noise, vibration, and harshness performance. Because a brake system consists of very complex parts, accurately determining the dynamic characteristics of the entire system is often difficult, but it is a crucial process. Therefore, the noise frequency generated during brake operation should be checked, and operational deflection shape information of the corresponding frequency band should be obtained. Through this, correlation can be confirmed by comparing the noise with the vibration level of each component. Additionally, order analysis using a color map is performed to understand the relationship between the rotational excitation of the motor and the system's response. When this rotational excitation component excites the natural frequency of the system, the response of the system increases. Thus, resonance may be avoided by changing the dynamic characteristics of the main vibration component, causing the natural frequency to move. Experimental results were verified through theoretical analysis of the motor and ball screw of the driving part.

Experimental Modal Analysis and Operational Deflection Shape Analysis of a Cantilever Plate in a Wind Tunnel with Finite Element Model Verification

Experimental Modal Analysis and Operational Deflection Shape Analysis of a Cantilever Plate in a Wind Tunnel with Finite Element Model Verification