Strain Modal Analysis Research Articles

Research on Damage Detection of Dual-Rotor Synchronous Excitation Mine Screen Beams Based on Strain Mode Difference Vibration Mode Analysis

The frame beam structure of the mine screen, subjected to various excitations, is a critical component of mining machinery. Its stress is intricate, the operational environment is severe, and damage can lead to catastrophic failures resulting in machinery destruction and fatalities. Based on the characterization of the vibration response of mine screen frame beams with varying degrees of damage at the same location and with the same degree of damage but at different locations, this paper develops a method of strain modal difference vibration pattern analysis and damage feature extraction for the detection of structural damage in beams. This method is based on the sensitivity of the sudden change in vibration strain modal difference to small deformations. This method solves the problem of using the conventional structural finite element analysis or experimental modal analysis methods to obtain the displacement mode, intrinsic frequency, and other characteristics, which make it difficult to effectively identify the actual engineering, with the damage conditions of the damage state and damage location of the mine screen frame beam problems. The feasibility and validity of the engineering application of the concept are demonstrated through instances.

Piezo sensor-based operational strain modal analysis of structures: Transition from lab to field application

This study evaluates piezo sensors for modal identification of a scaled-down prototype of a pedestrian foot-over bridge under pedestrian motions and further extends the application in real-life structures. The piezo sensors-based results are compared with the accelerometers-based displacement modal parameters. Pedestrian motions are adopted to simulate the operational conditions of a pedestrian footover bridge with different patterns of pedestrian motions. Piezo sensors are found to effectively capture the low amplitude dynamic strain response under pedestrian motions. Strain modal testing captures the modal parameters positively correlated with conventional acceleration modal testing. Staggered pedestrian motions are best suited for actuating the structure uniformly at all instrumented nodes. Piezo sensor-based modal testing is extended to modal testing of real-life footover bridges under low amplitude ambient pedestrian traffic. Piezo sensors successfully capture the bending and torsion modes with good correlation with accelerometers-based modes. The strain-based modal parameters are obtained with excellent repeatability and negligible deviation.

Quantification of Statistical Error in the Estimate of Strain Power Spectral Density Transmissibility for Operational Strain Modal Analysis

The use of strain modes in structural health monitoring has been constantly increasing because of their superior sensitivity to local structural anomalies. This study aims to investigate the applicability and robustness of power spectral density transmissibility (PSDT) in operational strain modal analysis (OSMA). By noting that OSMA in the frequency domain is vulnerable to the error of spectral estimates, uncertainty quantification stemming from strain spectral estimates and the error propagation analysis in OSMA are conducted from an analytical perspective. The main contributions include the following: (i) the mean and variance of strain PSDT estimates are asymptotically derived based on statistical moment theory and the statistics of PSD estimate error, (ii) the coefficients of variation (c.o.v.) of the strain PSDT estimate and strain spectral estimates are compared with each other through asymptotic analysis to elaborate the robustness of strain PSDT, and (iii) the variability of the strain mode shape is quantified based on the asymptotic formula of strain PSDT estimates tending to local minima of asymptotic zero variance at the resonances. The accuracy and efficiency of the quantification and propagation analysis are validated through numerical and experimental test data accompanied by various parametric studies.

Performance evaluation of piezo sensors with respect to accelerometers for 3D modal analysis of structures

Strain modal analysis, as a new domain in the health monitoring field, needs to be studied in depth for experimental modal testing. Towards this purpose, this paper experimentally investigates the efficacy of piezo sensors for structural identification for structural health monitoring under different excitations applicable to large-scale structures. The piezo sensors are evaluated against industry-standard accelerometers by experimental modal testing of a scaled-down model of a pedestrian foot over bridge. The model is excited under the impact hammer, electro-dynamic shaker-based sweep and random excitations, and pedestrian motion (PM)-based low-amplitude excitations. Piezo sensors are found to be capable of capturing the modal parameters (modal frequencies, damping ratios and mode shape vector) under all the excitations with excellent correlation with respect to accelerometer-based parameters. However, some modes are missed under the shaker and PM-based excitations compared to the impact hammer-based excitations for both accelerometers and piezo sensors. Modal parameters of lower modes are successfully extracted under low-level pedestrian excitations, the most efficient type of excitation acting in operational conditions. High modal assurance criteria values between the strain and the displacement mode shapes establish the piezo sensors as effective for strain-based vibration testing and structural identification.

3D torsional experimental strain modal analysis for structural health monitoring using piezoelectric sensors

Modal analysis is a dynamic response-based experimental structural identification procedure widely used for condition assessment and structural health monitoring (SHM). Piezoelectric sensors are smart material-based dynamic strain sensors being progressively implemented in vibration-based monitoring techniques. However, these have been so far limited to preliminary investigations on 1D and 2D structures with regard to modal analysis. Strain modal analysis using piezoelectric sensors has so far utilized only lower bending modes for frequency and mode shape-based SHM. This paper aims to evaluate the piezoelectric sensors for modal response measurement, modal parameter identification, and structural health monitoring of 3D structures, especially using torsional modes. It reports a comparative experimental study between the piezoelectric sensors and the accelerometers for dynamic response measurement, modal parameter extraction and damage identification and localization. Experimental modal analysis using impact hammer-based excitation is performed on two lab-sized specimens under different boundary conditions. Displacement mode shapes from both the sensors are used to determine the location and the severity of the damage. Torsional and bending modes are studied distinctly for sensitivity towards damage monitoring. Modal assurance criteria (MAC), coordinated MAC (CoMAC), and modal strain energy (MSE) are adopted as damage indicators. Results of the study show that the piezoelectric sensors are equivalent to accelerometers for response measurements and modal parameter extraction. They possess enhanced sensitivity towards damage monitoring as compared to accelerometers. Torsional modes perform better than bending modes for damage localization and severity quantification. Bending modes from both sensors are ineffective in locating the damage precisely. Modal strain energy (MSE) based damage index from torsional modes acquired from piezoelectric sensor performs best in terms of sensitivity towards damage location and exhibits peak severity, especially for incipient damage. The study establishes piezoelectric sensors as reliable and cost-effective modal response sensors.

RETRACTED: Civil engineering stability inspection based on computer vision and sensors

A computer that combines the purchase of vision technology and remote cameras and drones offers a promising non-contact solution for the state evaluation of civil infrastructure. This system's ultimate goal is too automatically and reliably converted to actionable information image or video data. This white paper provides an overview of computer vision technology's latest development and applies it to the state evaluation of private infrastructure. Deep learning has been applied to various computer vision; deep learning course covers most of the application. Each application has its architecture, such as the input image and labels data loss function. To explain computer vision architecture in the following figure. Review of the work can be divided into two types: application checks and application monitoring. Review inspection applications include context identifiers, local and global features, visible damage, and changes in the reference image. Monitoring applications described herein include static and dynamic strain modal analysis measurement and displacement measurement. Next, several key challenges continue to move towards civilian infrastructure automation and monitoring of vision-based. Finally, aim to address some of the ongoing challenges in our work.

Research on the Beam Damage Diagnosis Method for a High-Speed Transplanter Based on the Strain Mode

Abstract. The vibration of agricultural machinery significantly influences driving comfort and operation reliability. In recent years, research on the vibrational characteristics of agricultural machinery has gradually expanded. To solve the problem of the obvious vibration of a high-speed transplanter under operating conditions, this article examines the method of beam damage diagnosis for high-speed transplanters based on the strain mode. Based on the modal theory, the displacement and strain modal analysis of the beam of the high-speed transplanter is performed. The analysis shows that the relative deviation of the modal frequencies of the same order before and after the beam is damaged is small. There is no obvious abrupt change in the displacement mode shape, while the strain mode shape has a sudden change peak after the beam is damaged. Thus, the strain mode change rate is constructed as a diagnostic index for beam damage. The analysis results show that the strain mode change rate increases with the increase in beam damage degree. Finally, the least squares method is used to fit the corresponding relationship between the two quantities. The results show that the strain mode change rate is sensitive and reliable as an index of damage diagnosis, which can better determine the location and degree of damage to the beam. Keywords: Beam, Damage, Diagnosis, Rice transplanter, Strain mode.

Segmentation Analysis Techniques and Identifying Stress Ratio of Human Lumbar Spine Using ANSYS

The Finite Element Method [FEM] used to replicate the products and systems. In this method, the abnormality estimation of the spine has developed and presented in this paper. Spine injury found on vertebrae L1–L5 and its corresponding inter-vertebral disk. Different types of filters used to eliminate obtained noise, starting the MRI image at different levels. The noiseless image was segmented using differing Edge Detection Algorithm (EDA) such as Canny Edge Detection Algorithm (CEDA), Prewitt, Sobel, and Robert from the applied segmentation algorithm the best EDA identified and the 3D model for lumbar spine was created. After the segmentation algorithm, the FEA method utilized for examining images of the 3D human lumbar spine on different loads. The experiment conducted with the stress–strain relationship and Modal Analysis on Natural Frequency (NF) calculated. The entire analysis accomplished by real-time simulation software called ANSYS.

Clamp looseness detection using modal strain estimated from FBG based operational modal analysis

Clamps are widely used to fix and support the pipe in engineering community. Clamps looseness may further lead to the fatigue damage of the pipe, therefore the early detection of clamps looseness is very crucial. The robustness and the accuracy of damages detection have already been the greatest challenges in traditional methods in Structural Health Monitoring (SHM). Due to the higher sensitivity of Strain Mode Shape (SMS) to local damages and more effective performance of fiber Bragg grating (FBG) sensing technology for industrial and mechanical devices, present works focus on a new method to detect clamp looseness based on Strain Mode Shape Differences (SMSD) and FBG sensing technology. In order to estimate the SMSs online, a novel diagram of Operational Strain Modal Analysis (OSMA) with FBG sensing technology is also presented, in which a rational fraction composed by Forsythe Complex Orthogonal Polynomials (FCOP) is employed to fit the ‘Positive’ Strain Power Spectral Density (PSPSD) of a single output. Traditionally, the fitting of the all the outputs need to be conducted to obtain the SMSs, which increases the calculation cost. To further address this issue, an improved OSMA integrated with strain response transmissibility (SRT) is also proposed to calculate the SMSs by just fitting a single output. Firstly, the identified modal parameters based on the presented method is validated with simulation results. And then, the ability of the SMSD index is further investigated analytically and experimentally for clamp looseness detection under different locations and degrees, the results indicate that the clamp looseness can be detected by the SMSD index.

New approach based on operational strain modal analysis to identify dynamical properties of the high-speed reciprocating operation mechanism

A high-speed reciprocating operating mechanism with fast running and frequent stopping produces a certain vibration due to inertia. The inherent vibration of this mechanism becomes a key factor aff...

Research on dynamics of sorting arms with high frequency reciprocating motion

The characters of high frequency reciprocating equipment are quick starting and stopping, short range, high frequency and multi-freedom reciprocating motion. The inertia introduced by the high frequency reciprocating motion of a LED chip sorter has complicated effects on the positional accuracy. It is necessary to obtain dynamics of the sorting arm to suppress the vibration of the high frequency operation. The positioning precision and positioning time are affected by the natural vibration of the sorting arm by analyzing the displacement response. The paper verifies that the inherent vibration of the sorting arm has a crucial effect on its positioning precision and positioning time. Under static condition, due to the additional mass of the accelerometers, the research results show that there is no obvious difference in the experimental modal analysis (EMA) based on multi-type sensors. The modal parameters identified by accelerometers and strain gauges are very close. The modal parameters are obtained through the modal analysis method, which combines the strain modal analysis and operational modal analysis (OMA), under high frequency reciprocating motion. The paper verifies that the modal parameters of lightweight structure are very different in the static and operation. The key points of each mode are found by analyzing the modal amplitudes at different speeds which provide the guiding principle and basis for the dynamic optimization of the sorting arm mechanism.

Experimental strain modal analysis for beam-like structure by using distributed fiber optics and its damage detection

Modal analysis is commonly considered as an effective tool to obtain the intrinsic characteristics of structures including natural frequencies, modal damping ratios, and mode shapes, which are significant indicators for monitoring the health status of engineering structures. The complex mode indicator function (CMIF) can be regarded as an effective numerical tool to perform modal analysis. In this paper, experimental strain modal analysis based on the CMIF has been introduced. Moreover, a distributed fiber-optic sensor, as a dense measuring device, has been applied to acquire strain data along a beam surface. Thanks to the dense spatial resolution of the distributed fiber optics, more detailed mode shapes could be obtained. In order to test the effectiveness of the method, a mass lump—considered as a linear damage component—has been attached to the surface of the beam, and damage detection based on strain mode shape has been carried out. The results manifest that strain modal parameters can be estimated effectively by utilizing the CMIF based on the corresponding simulations and experiments. Furthermore, damage detection based on strain mode shapes benefits from the accuracy of strain mode shape recognition and the excellent performance of the distributed fiber optics.

Damage Identification and Fatigue Residual Life Prediction of Vibrating Screen Beam Based on Strain Modal Analysis

Damage Identification and Fatigue Residual Life Prediction of Vibrating Screen Beam Based on Strain Modal Analysis

Strain modal analysis and fatigue residual life prediction of vibrating screen beam

The displacement and strain modal analysis of vibrating screen beam is carried out, the results show that the relative deviation of the modal frequencies between intact and damaged beam is small, the displacement mode shapes of the damaged beam have no obvious variation, but the strain mode shapes have mutation peaks at the damaged location for the damaged beam. Therefore, a damage index is defined as the rate of strain modal change between damaged and intact beam. The rate of strain modal change increases with the increasing damage extent of the beam. The initial fatigue crack length is related to the damage extent of the beam; the fatigue crack propagation residual life of the beam is predicted by the Paris law. The results show that the rate of strain modal change is a sensitive and reliable damage index for indicating the damage location and damage extent. The predictions of the damage extent and the crack propagation residual life of the vibrating screen beam are beneficial to dynamic optimization design, which can improve the service life of the vibrating screen.

On the use of strain sensor technologies for strain modal analysis: Case studies in aeronautical applications.

This paper discusses the use of optical fiber Bragg grating (FBG) and piezo strain sensors for structural dynamic measurements. For certain industrial applications, there is an interest to use strain sensors rather than in combination with accelerometers for experimental modal analysis. Classical electrical strain gauges can be used hereto, but other types of strain sensors are an interesting alternative with some very specific advantages. This work gives an overview of two types of dynamic strain sensors, applied to two industrial applications (a helicopter main rotor blade and an F-16 aircraft), FBG sensors and dynamic piezo strain sensors, discussing their use and benefits. Moreover, the concept of strain modal analysis is introduced and it is shown how it can be beneficial to apply strain measurements to experimental modal analysis. Finally, experimental results for the two applications are shown, with an experimental modal analysis carried out on the helicopter main rotor blade using FBG sensors and a similar experiment is done with the aircraft but using piezo strain sensors instead.

Strain Modal Analysis of Small and Light Pipes Using Distributed Fibre Bragg Grating Sensors.

Vibration fatigue failure is a critical problem of hydraulic pipes under severe working conditions. Strain modal testing of small and light pipes is a good option for dynamic characteristic evaluation, structural health monitoring and damage identification. Unique features such as small size, light weight, and high multiplexing capability enable Fibre Bragg Grating (FBG) sensors to measure structural dynamic responses where sensor size and placement are critical. In this paper, experimental strain modal analysis of pipes using distributed FBG sensors ispresented. Strain modal analysis and parameter identification methods are introduced. Experimental strain modal testing and finite element analysis for a cantilever pipe have been carried out. The analysis results indicate that the natural frequencies and strain mode shapes of the tested pipe acquired by FBG sensors are in good agreement with the results obtained by a reference accelerometer and simulation outputs. The strain modal parameters of a hydraulic pipe were obtained by the proposed strain modal testing method. FBG sensors have been shown to be useful in the experimental strain modal analysis of small and light pipes in mechanical, aeronautic and aerospace applications.

A frequency and spatial domain decomposition method for operational strain modal analysis and its application

Operational modal analysis (OMA), where only the responses are utilized, has been applied to various engineering problems more commonly due to its advantages in real life implementations. A frequency and spatial domain decomposition method for operational modal analysis making use of strain measurements is presented in this paper. With the proposed algorithm, accurate global characteristics of a structure can be obtained from only the measured strain responses. Singular value decomposition, power spectrum enhancement, and the least square fitting techniques are adopted to decouple and obtain the strain modes one by one. Strain modal analysis and acceleration modal analysis are conducted simultaneously to extract the modal parameters of a four-span bridge model with a pair of heavily coupled modes. The processes and the results are carefully compared with each other. Starting from the abnormal strain modes observed, the accidental change of a boundary condition of the bridge model is successfully detected, and also accurately located by the correlation calculation of strain mode shapes.

Structural Identification by Processing Dynamic Macro Strain Measurements

In contrast to traditional modal identification methods processing structural accelerations for modal parameter identification, a multiple reference impact testing method using long-gauge fiber optical sensors and the related data processing approach are proposed. First, macro strains of key structural elements during the impact testing are measured through long-gauge fiber optic sensors, which subsequently are used to estimate the strain frequency response functions (FRFs) of the structure. Second, an approach is proposed to estimate strain mode shapes from the strain FRFs, and corresponding displacement mode shapes are calculated by applying an improved conjugate beam method. Finally, the strain flexibility character of the structure is identified by using the identified strain and displacement mode shapes with normalization. The advantage of long-gauge fiber optic sensors measuring averaged strains in a long length (e.g., 1 meter) provides the opportunity for strain modal analysis. The output of the proposed method, strain flexibility, is meaningful for static strain prediction and structural capacity evaluation. Examples investigated successfully verified the effectiveness of the proposed method for structural strain flexibility identification.

A comparison of strain and classic experimental modal analysis

This research is focused on a comparison of classic and strain experimental modal analysis (EMA). The modal parameters (the natural frequencies, the displacement mode shapes (DMSs) and the damping) of real structures are usually identified with classic EMA, where the responses are measured with motion sensors (e.g. accelerometers). Strain EMA is a special approach in the field of EMA, where the responses are measured with strain sensors. Classic EMA is the preferred method, but strain EMA offers advantages that are important for particular applications: for example, the direct identification of strain mode shapes (SMSs), which is important in the vibration-fatigue and damage-identification models. The next advantage is that strain EMA can sometimes be used, for experimental/geometrical reasons, where classic EMA cannot. There are also drawbacks: for example with strain EMA only, the mass-normalization of the DMSs and SMSs cannot be performed. This study researches the theoretical similarities and differences of both EMA approaches. Furthermore, the accuracy of both approaches for the case of a free–free supported beam and a free–free supported plate is investigated. Classic and strain EMA were performed with a piezoelectric accelerometer and the piezoelectric strain gauges, respectively. The results show that the accuracy of strain EMA results (the natural frequencies, DMSs and the damping) is comparable to the accuracy of classic EMA.

Research on Structural Damage Diagnosis Based on Strain Modal

The damage diagnosis theory and method of engineering structure is one of the hot issues concerned by the engineering circles at present. Based on the strain modal analysis theory, it expounds the connection among displacement mode, strain mode and curvature mode, with a heavy rubber as the material to make a cantilever beam, and establishing the different damage conditions of the cantilever beam, studying about dynamic structural damage identification under the incentive, which provides the theoretical basis and technical support for the research on damage detection of large engineering structure.