Structural Vibration Monitoring Research Articles

Sensor Layout of Hoisting Machinery Vibration Monitoring Based on Harmony Genetic Search Algorithm

With the construction of automated docks, health monitoring technology as a parallel safety assurance technology for unmanned hoisting machinery has become a hot spot in the development of the industry. Hoisting machinery has a huge structure and numerous welded joints. The complexity and nonlinearity of the welded structure itself makes the structural failure parts random and difficult to arrange for monitoring sensors. In order to solve the problem of effectiveness and stability of the sensor arrangement method for monitoring the structure of hoisting machinery. Using the global and local search capabilities enhanced by the complementary search mechanism, a structural vibration monitoring sensor placement algorithm based on the harmony genetic algorithm is proposed. Firstly, the model is established for modal analysis to obtain the displacement matrix of each mode. Secondly, the optimal parameter combination is established through parameter comparison, and the random search mechanism is used to quickly search in the modal matrix to obtain the preliminary solution, and then the preliminary solution is genetically summed The mutation operation obtains the optimized solution, and the optimal solution is retained through repeated iterations to realize the decision of the vibration sensor layout of the crane structure monitoring. Combining the comparison test of harmony genetic algorithm, harmony search algorithm and genetic algorithm, the fitness of harmony genetic algorithm in <i>X</i>, <i>Y</i> and <i>Z</i> directions were 0.0045, 0.0084 and 0.0058, respectively, which were all optimal. And the average probability of deviating from the optimal path is 1.10%, 19.34%, and 54.43%, which are also optimal. Harmony genetic algorithm has the advantages of simplicity, fastness and strong global search ability, and can obtain better fitness value and better search stability.

An air-pressure and acoustic fiber sensor based on graphene-oxide Fabry-Perot interferometer

A fibre optic sensor for both air-pressure and acoustic signal detection based on graphene-oxide Fabry-Perot interferometer (GO-FPI) is proposed and demonstrated. The GO-FPI consists of a cleaved single-mode fibre (SMF) and GO film with good uniformity and high surface evenness. As for air-pressure detection, the highest sensitivity is 3.81 nm/kPa. As for acoustic sensing, the frequency response ranges from 4 Hz to 20 kHz with good fidelity and extremely high linearity of ∼ 1, with capability of single-frequency and multi-frequency signal detection. Moreover, the GO-FPI can detect the acoustic signal both in air and underwater with high stability. The noise-limited minimum detectable pressure levels are 28.74 µPa/Hz1/2@20 kHz in air and 14.44 µPa/Hz1/2@13 kHz underwater. The proposed multi-parameter sensor with high compactness and stability has potential applications in structure health and vibration monitoring.

Drone-Based Vibration Monitoring and Assessment of Structures

This paper presents a novel method of procuring and processing data for the assessment of civil structures via vibration monitoring. This includes the development of a custom sensor package designed to minimize the size/weight while being fully self-sufficient (i.e., not relying on external power). The developed package is delivered to the structure utilizing a customized Unmanned Aircraft System (UAS), otherwise known as a drone. The sensor package features an electropermanent magnet for securing it to the civil structure while a second magnet is used to secure the package to the drone during flight. The novel B-Spline Impulse Response Function (BIRF) technique was utilized to extract the Dynamic Signature Response (DSR) from the data collected by the sensor package. Experimental results are presented to validate this method and show the feasibility of deploying the sensor package on structures and collecting data valuable for Structural Health Monitoring (SHM) data processing. The advantages and limitations of the proposed techniques are discussed, and recommendations for further developments are made.

Modal analysis of composite nozzle for an optimal design of a tidal current turbine

Monitoring of structural vibrations and operational modal analysis are clearly essential to effectively control structural safety and the operational behavior of tidal current turbines. In order to satisfy industrial requirements, generally related to a mass gain problem, hybridization provides an excellent method to improve the breaking strength of composite materials, while keeping adequate mechanical performance for marine renewable energy applications. In this context, this work aims to study the structural modal analysis of a tidal turbine nozzle and the effect of hybrid materials (carbon/Glass) on the natural frequencies and corresponding mode shapes of the three laminates. The modal analysis was calculated by the Finite Element Method using ABAQUS software. According to the results, the stacking sequence has a considerable impact on the natural frequency of the nozzle. Furthermore, it is also found that the resonance effect does not appear for the three laminates under investigation.

Performance of Optical Structural Vibration Monitoring Systems in Experimental Modal Analysis.

Image-based optical vibration measurement is an attractive alternative to the conventional measurement of structural dynamics predominantly relying on accelerometry. Although various optical vibration monitoring systems are now readily available, their performance is currently not well defined, especially in the context of experimental modal analysis. To this end, this study provides some of the first evidence of the capability of optical vibration monitoring systems in modal identification using input–output measurements. A comparative study is conducted on a scaled model of a 3D building frame set in a laboratory environment. The dynamic response of the model to an impulse excitation from an instrumented hammer, and an initial displacement, is measured by means of five optical motion capture systems. These include commercial and open-source systems based on laser Doppler velocimetry, fiducial markers and marker-less pattern recognition. The performance of these systems is analysed against the data obtained with a set of high-precision accelerometers. It is shown that the modal parameters identified from each system are not always equivalent, and that each system has limitations inherent to its design. Informed by these findings, a guidance for the deployment of the considered optical motion capture systems is given, aiding in their choice and implementation for structural vibration monitoring.

Results of the study of vibrations of concrete structures of the hydropower plant building

The paper considers the results of studying vibrations of certain components of the hydropower plant building and their influence on the structure of the building as a whole. Vibration loads on various elements of the hydropower plant building which can cause damage to the building, thereby reducing the operational reliability of the whole structure and doing potential harm to the environment and human life support, is analyzed. The necessity for vibration monitoring of structures which should be conducted constantly or periodically to determine the present condition of structures is reasoned. Vibrations of the section concrete parts and vibrations of hydroelectric power plant units are considered. To detect the vibrational movements of the section as a solid body on an elastic base Section № 2of the hydropower plant building has been chosen. The recording of vibrations has been conducted for all three components: Z (vertical), H II (horizontal, parallel to the flow) and H ⊥ (horizontal, perpendicular to the flow) and the obtained data are given in this paper. The intervals of observed and dominant periods of vibrations are estimated. The research provides the data on amplitudes and accelerations of vibrations, as well as on the maximum recorded peak-to-peak swing. Based on the analysis of the received vibrograms, it is stated that the recorded vibrations are non-periodic and have a relatively narrow range of periods. In conclusion it is underlined that in order to determine the maximum possible amplitudes of section vibrations as well as to calculate the corresponding dynamic stresses in ceiling trusses it is necessary to observe vibrations when hydraulic units are operated simultaneously and the flow passes through the fully open bottom spillways of the inspected section.

Vision-Based Vibration Monitoring of Structures and Infrastructures: An Overview of Recent Applications

Contactless structural monitoring has in recent years seen a growing number of applications in civil engineering. Indeed, the elimination of physical installations of sensors is very attractive, especially for structures that might not be easily or safely accessible, yet requiring the experimental evaluation of their conditions, for example following extreme events such as strong earthquakes, explosions, and floods. Among contactless technologies, vision-based monitoring is possibly the solution that has attracted most of the interest of civil engineers, given that the advantages of contactless monitoring can be potentially obtained thorough simple and low-cost consumer-grade instrumentations. The objective of this review article is to provide an introductory discussion of the latest applications of vision-based vibration monitoring of structures and infrastructures through an overview of the results achieved in full-scale field tests, as documented in the published technical literature. In this way, engineers new to vision-based monitoring and stakeholders interested in the possibilities of contactless monitoring in civil engineering could have an outline of up-to-date achievements to support a first evaluation of the feasibility and convenience for future monitoring tasks.

Vision-Based Moving Mass Detection by Time-Varying Structure Vibration Monitoring

In recent years, vision-based vibration measurement methods have been widely used in the field of mechanical engineering for structural health monitoring and fault diagnosis. However, these current methods mainly focus on monitoring the stationary vibrations of time-invariant systems or structures, which cannot deal with the time-varying conditions. In this paper, a video camera is used to monitor the non-stationary vibrations of a time-varying structure for an unexplored usage of moving mass detection. In the study, the laboratory time-varying structure is a clamped beam with one or more masses sliding on. The general parameterized time-frequency transform is first introduced to extract the time-dependent instantaneous frequencies (IFs) from the video motions. Then a parameterized mathematical model is proposed to estimate the weight of the moving mass based on the extracted IFs. By optimizing the parameters in this model, the moving mass can be estimated with high precision. Besides, multi-moving masses can be also detected for abnormal mass classification and identification. Both the finite element method (FEM) and experiments are performed to demonstrate the performance of the proposed vision-based moving mass detection (VMMD) technique. The VMMD technique has valuable potential for online detection, localization and classification of inferior products with abnormal mass in industrial automation.

Relevant issues of periodic vibration monitoring of buildings and structures

Introduction. The author proposes a new universal optimization approach to mechanical safety monitoring of buildings and structures in the process of their operation. The new approach involves periodic monitoring of mechanic vibrations.&#x0D; Materials and methods. The methodology of periodic monitoring performable within the framework of general monitoring is based on the analysis of changes in the first natural frequency of a building or a structure and the logarithmic decrement of its damping along three mutually perpendicular axes. The shape and position of resonance peaks of the amplitude spectrum are employed to analyze resonant frequencies and logarithmic decrements of damping. The analysis of those electronically archived parameters is performed, whose values change over time proportionately with vibrations of a monitored facility. The time dependence of the first resonant frequency of a structure is considered as a generalized characteristic of its mechanical safety.&#x0D; Results. The author has shown that findings of the spectral analysis performed in respect of the vibration process are irrespective of a measurement method, provided that the uniformity of external influences is ensured. The frequency dependence of the structure’s first mode of vibrations on time (per year) has two non-linear sections within the entire term of operation. Following the analysis of measurements taken at construction facilities exposed to wind loads, it’s been found that advanced monitoring instruments can identify changes in the value of the first resonant frequency and the damping decrement with a reasonable degree of accuracy. The author believes that this finding has great practical importance.&#x0D; Conclusions. Identification of a trend towards a change in frequency and damping decrement values for the first mode of natural vibrations can help to schedule actions for the improvement of the mechanical safety of an engineering structure, and in some cases it can prevent an upcoming accident.

Design and Validation of Android Smartphone Based Wireless Structural Vibration Monitoring System.

Vibration monitoring is one of crucial functions of structural health monitoring (SHM) systems. Traditional structural vibration monitoring usually relies on specialized sensors, data transmission and acquisition equipment, which are expensive and may not be easily available in urgently needed situations like post-disaster structural evaluation. Therefore, developing an affordable and efficient structural vibration monitoring technique becomes an important topic in SHM research. In this paper, the authors developed an android system APP that can easily convert multiple android smartphones into a wireless structural vibration monitoring system. To make the designed system reliable and easy to use, the server/client architecture is adopted. One smartphone is designated as the serve of the system to remotely control all other smartphones, which function as sensors to measure structural vibration. An efficient method is proposed herein to establish the smartphone-based structural vibration monitoring network, allowing the server smartphone to quickly and easily connect multiple sensor smartphones to form the wireless network for structural vibration monitoring. Additionally, a synchronization method is also proposed to synchronize different smartphones for simultaneously measuring structural vibration. To verify the time synchronization accuracy of the developed system, an experiment is designed and conducted. Moreover, a new analysis method of the time synchronization accuracy is also proposed, which verifies that the designed smartphone-based monitoring can achieve the millisecond-level time synchronization accuracy. Finally, a shaking table experiment is conducted on a three-story bench-scale structural model, the results of which demonstrate that the designed smartphone-based wireless structural vibration monitoring system can quite accurately identify the modal parameters of the tested structure.

Testing Walking-Induced Vibration of Floors Using Smartphones Recordings

Smartphone technology is rapidly evolving, adding sensors of growing accuracy and precision. Structural engineers are among customers who indirectly benefit from such technological advances. This paper tests whether accelerometers installed in new generations of smartphones can reach the accuracy of professional accelerometers created for vibration monitoring of civil engineering structures, and how they can be useful. The paper describes an experimental study designed to measure walking-induced vibrations of a slender prefabricated prestressed concrete slab. Both traditional, high-accuracy, accelerometers and those integrated into commercial smartphones were used for experimental data collection. Direct comparison of the recordings yielded two key findings: the accuracy of smartphone accelerometers largely depends on the specific smartphone model, and nevertheless is satisfactory for preliminary modal testing at the very least. Furthermore, the smartphone measured accelerations of the lower back were used successfully to indirectly measure pedestrian walking loads.

Pixel-based operating modes from surveillance videos for structural vibration monitoring: A preliminary experimental study

This paper presents a practical and cost effective method for vibration monitoring using multiple surveillance cameras distributed throughout (within) a building structure. Robust feature points in surveillance footage are identified and tracked frame-by-frame (with the Kanade-Lucas-Tomasi tracker) to extract the pixel motions. The relative pixel motions from multiple locations within the structure are analyzed in the frequency domain to estimate dynamic characteristics of the monitored structure (e.g., the dominant frequencies), as well as the pixel-based operating modes. These pixel-based modes importantly are in pixel units, eliminating the need to converted to engineering (physical) units. The method is verified through an experimental parametric study on a three-story lab-scale building structure (with three surveillance cameras) excited by broadband white noise signals. The accuracy and repeatability of the method are assessed to evaluate its application for structural health monitoring.

High-performance optical coherence velocimeter: theory and applications.

We proposed a high-performance optical coherence velocimeter (OCV) based on broadband optical interference which achieves spatial resolution from interference cancellation or enhancement of different components of the broadband light. There is a challengeable issue for OCV that the interference fringes become blurred when the velocity of detected object is relatively large, hindering the pace of OCV application in high-velocity field. To resolve this, the relationship between blurry coefficient and OCV system parameters (e.g., exposure time, central wavelength, bandwidth of source) was derived. It was found that blurry coefficient changed with oscillatory decay form and reached the minimum at each order blurry velocity. It showed that maximum measurable velocity of OCV systems could reach 10th order blurry velocity. The measurement of vibration of the loudspeaker driven by a function signal generator was employed to experimentally verify the velocity measurement performance of the system. The experiment demonstrated that the developed OCV can provide large velocity measurement ranges from static to 25.2 mm/s with nanometer-level precision and maximum measurable vibration frequency of up to 50 kHz. However, in theory, the theoretical maximum measurable velocity can be up to 1.06 m/s for current OCV configuration. The OCV has high precision, large dynamic range, and high-velocity measurement capability, making it attractive for applications in mechanical structure vibration monitoring and acoustic measurement.

(Invited) Diffusion Map Analysis of Multi-Channel Time Series Data

Sensor data often come in the form of multichannel time series, for example, ECG, EEG, and structural vibration monitoring to name a few. Conventionally, such multichannel time series data are analysed by using FFT for each channel, and/or by computing inter-channel correlations. Mathematically, however, these signals are better represented by dynamical systems, which are sets of differential equations. The behaviour of a dynamical system may be visualised as a trajectory in the so-called phase space. For example, the state of a weight suspended by a spring can be fully described by the weight’s position x and its velocity v, hence its temporal behaviour creates a trajectory in its phase space (x, v). It works similarly for real systems that produce time series data. From a single channel of time series x(t) it is possible to reconstruct the phase space trajectory using lagged variables x(t), x(t-1), x(t-2),…., x(t-n). It is, however, very difficult to find and analyse the trajectory because the dimensionality of the phase space is very large in general. In this presentation, we will show that a method called the diffusion map can extract the lower dimensional manifold in which the trajectory resides, and reveal the structure of the dynamics. Using some toy models we will demonstrate how our technique can be used to extract various useful information about the nature of the dynamics, including identification of anomalies, especially signs for imminent catastrophic changes such as phase transitions or structural collapse.

Monitoring of a controlled space flexible multibody by means of embedded piezoelectric sensors and cameras synergy

Interaction between elastic dynamics and attitude control is a serious problem in space operations, which often involve satellites with highly flexible appendages. Monitoring and eventually control of the vibrations are a major concern to avoid a decrease in the expected performance. In particular, the classic case of a central bus with two lateral appendages (solar panels) is considered. The design of a system for structural vibration monitoring is proposed both from a numerical and an experimental point of view. Piezoelectric devices are a usual solution for measuring the deformation of the structures. In the proposed work, optical sensors are also implemented: the combined use of the two sets allows for the monitoring of the elastic displacement of the solar panels and for the reconstruction of the modal shapes of the entire flexible multibody system.

Motion magnification analysis applied to the dynamic identification of historic constructions

We applied a new methodology, namely the motion magnification (MM), to the dynamic identification of historic constructions. MM acts like a microscope amplifying small motions in video sequences, therefore tiny motion patterns are made visible with the naked eye. This technique provides advantages of particular interest to the dynamic identification: no wires, no physical contact, simplicity and low costs. In this paper, we investigated the ambient vibration monitoring of historic structures in urban environments, which is a relevant issue for the health surveying and early damage detection, particularly for ancient buildings. We give an introduction to the MM methodology and describe its practical application to the frequency domain through two case-studies: the so-called Temple of Minerva Medica of Rome and the Ponte delle Torri of Spoleto. Since in the outdoor environment the MM is much more prone to noise because of the wind, shadows, atmospheric refraction, light reflection, distance from the object, weak vibration sources, the case study of the Ponte delle Torri represents a hard test-bed for MM. However, the MM estimates of the first modes showed a good agreement with the experimental data of contact velocimeters.

Structural vibration monitoring and operational modal analysis of offshore wind turbine structure

In order to reduce the structural failure and accident occurrence of the offshore wind turbine, the researches on structural operational safety of offshore wind turbine based on the measured data during the operation periods should be carried out and considered as the key way to solve these problems. However, the current researches are only focused on numerical simulation, model experiment and theoretical analysis and ignore the structural vibration characteristics analyzed from condition monitoring and prototype observation data from the actual wind turbine structure. To compensate for this study defect, the structural vibration displacement signals of one Chinese offshore wind power prototype under different conditions were obtained based on a long-term prototype observation in order to achieve the comprehensive and systematic research on vibration response characteristics and operational modal analysis of measured structure. Considering the complicated operational environment of offshore wind turbines, the structural response regular pattern and vibration safety are also discussed emphatically under different conditions such as standstill, normal operational, startup, shutdown and extreme typhoon status. Simultaneously, the integral operational modal identification method of offshore wind turbine in the range of full power is proposed based on traditional and modified stochastic subspace identification technologies, and further the modal identification results and the relationship between structural modal parameters and environmental/operational factors are also illustrated in this paper. The researches on the structural vibration characteristics and operational modal analysis of offshore wind turbine not only provide powerful data and technology support for the operation safety evaluation, but also provide the necessary theoretical and practical bases for the design and maintenance of wind turbine structures.

Vision-based measurement system for structural vibration monitoring using non-projection quasi-interferogram fringe density enhanced by spectrum correction method

A non-projection fringe vision measurement system suitable for vibration monitoring was proposed by using the concept of a 2D optical coherence vibration tomography (2D-OCVT) technique. An artificial quasi-interferogram fringe pattern (QIFP), similar to the interferogram of the 2D-OCVT system, was pasted onto the surface of a vibrating structure as a sensor. Image sequences of the QIFP were captured by a high-speed CMOS camera that worked as a detector. It was possible to obtain both the in-plane and out-of-plane vibration simultaneously. The in-plane vibration was obtained by tracking the center of the imaged QIFP using an image cross-correlation method, whilst the out-of-plane vibration was obtained from the changes in period density of the imaged QIFP. The influence of the noise sources from the CMOS image sensor, together with the effect of the imaging distance, the period density of the QIFP and also the key parameters of the fringe density enhanced by the spectrum correction method on the accuracy of the displacement measurement, were investigated by numerical simulations and experiments. Compared with the results from a conventional accelerometer-based measurement system, the proposed method was demonstrated to be an effective and accurate technique for measuring structural vibration without introducing any extra mass from the accelerometer. The significant advantages of this method include its simple installation and real-time dynamic response measurement capability, making the measurement system ideal for the low- and high-frequency vibration monitoring of engineering structures.

Data-base with in-situ vibration frequencies of bridges in Portugal

A data-base of 285 bridges in Portugal was composed with information about the geometric characteristics like largest span length, height and cross-section, as well as the main vibration frequencies with special emphasis on the frequency of first vertical mode. This data-base includes different bridge typologies ranging from reinforced concrete (RC) box girders and RC beam bridges, steel girder bridges, steel truss bridges, RC arch and stone bridges, cable-stayed bridges and suspension bridges. Each one of the bridges was subjected to an in situ test with a single 3-component accelerometric station and its main natural frequencies were determined. Very good correlation of the vertical frequency with largest span length was obtained for the first four typologies above referred. Good correlations were obtained for the transversal frequency with the total length of long span cantilever RC bridges. Numerical modelling was performed for six long span cantilever RC bridges and comparison with in situ frequencies in the vertical and transversal directions was made. Further discussion was made on the value of frequency estimation, in view of the uncertainties in methods and analysis, the changes that are observed along the lifetime and the corresponding interpretations. This last point is related to the continuous vibration monitoring of structures which is very important in damage detection.

The Interferometric Use of Radar Sensors for the Urban Monitoring of Structural Vibrations and Surface Displacements

In this paper, we propose a combined use of real aperture radar (RAR) and synthetic aperture radar (SAR) sensors, within an interferometric processing chain, to provide a new methodology for monitoring urban environment and historical buildings at different temporal and spatial scales. In particular, ground-based RAR measurements are performed to estimate the vibration displacements and the natural oscillation frequencies of structures, with the aim of supporting the understanding of the building dynamic response. These measurements are then juxtaposed with ground-based and space-borne SAR data to monitor surface deformation phenomena, and hence, point out potential risks within an urban environment. In this framework, differential interferometric SAR algorithms are implemented to generate short-term (monthly) surface displacement and long-term (annual) mean surface displacement velocity maps at local (hundreds m2) and regional (tens km2) scale, respectively. The proposed methodology, developed among the activities carried out within the national project Programma Operativo Nazionale MASSIMO (Monitoraggio in Area Sismica di SIstemi MOnumentali), is tested and discussed for the ancient structure of Saint Augustine compound, located in the historical center of Cosenza (Italy) and representing a typical example of the Italian Cultural Heritage.