Showing papers on "Modal testing published in 2018"
TL;DR: In this article, a hybrid accelerometer/high-speed camera mode shape identification method was used to identify the eigenvalues, while the camera measurement is used to produce the full-field mode shapes close to 10 kHz.
75 citations
TL;DR: In this article, an integrative hinge fabricated by carbon fiber reinforced shape memory epoxy composites in the sequence of material selection, structure design and manufacture, material and structure experiments, and application is presented.
71 citations
TL;DR: In this article, a new approach based on modal decomposition is presented that directly links the fatigue-damage intensity with the dynamic properties of the system and thus offers a valuable insight into how different modes of vibration contribute to the total damage to the material.
58 citations
TL;DR: In this paper, a new surrogate assisted optimisation (SAO) method was proposed to predict the location and size of delaminations in fiber reinforced composite plates using natural frequency shifts as indicative parameters.
Abstract: Delamination is a frequently occurring type of damage in laminated fibre reinforced polymer (FRP) composites and causes substantial loss in structural stiffness and usable service life. The detection of delaminations in FRP composites is critical for the safe and reliable use of these materials in aeronautical and other industries. Structural Health Monitoring (SHM) techniques based on vibration measurements have proven to be promising towards this end. There have been comprehensive studies of FRP beams with through-width delaminations, but the damage assessment of FRP plates with embedded delaminations using frequency-based detection has not been extensively studied. To solve the inverse problem of determining size and location of delamination from changes in the natural frequencies, this paper presents a new surrogate assisted optimisation (SAO) method for predicting the location and size of delaminations in fibre reinforced composite plates using natural frequency shifts as indicative parameters. The proposed frequency-based delamination assessment method is validated using finite element models of FRP plates with embedded delaminations and by experimental modal analysis. Modal testing was conducted using scanning laser vibrometer on carbon/epoxy and glass/epoxy FRP plates that were manufactured with artificially induced delaminations. The proposed SAO algorithm was compared to an Artificial Neural Network (ANN) method in terms of database size, prediction accuracy and sensitivity to noisy data. The results show that the proposed inverse algorithm can predict the delamination parameters of location and size with good accuracy for numerically simulated frequency shift data but the prediction accuracy was reduced with experimental data. A comparison of the two inverse algorithms show that the SAO method has significant advantages compared to the ANN algorithm for delamination prediction.
54 citations
TL;DR: The purpose of this work is to overcome its present limitation to conservative nonlinearities by relying on the recently extended periodic motion concept, according to which nonlinear modes of damped systems are defined as family of periodic motions induced by an appropriate artificial excitation that compensates the natural dissipation.
43 citations
TL;DR: This article presents an extended ICA-based method called ICA -F, which establishes a BSS model in frequency domain, and shows that the proposed method can perform accurate modal identification for both light and high damping structures.
Abstract: Output-only modal identification methods are practical for large-scale engineering. Recently, independent component analysis (ICA) which is one of the most popular techniques of blind source separation (BSS) has been used for output-only modal identification to directly separate the modal responses and mode shapes from vibration responses. However, this method is only accurate for undamped or lightly damped structures. To improve the performance of ICA for high damping structures, this article presents an extended ICA-based method called ICA-F, which establishes a BSS model in frequency domain. First, the basic idea of BSS and ICA applied in modal identification is introduced in detail. The free vibration responses and the correlation functions of ambient responses can be cast into the frequency-domain BSS framework just by mapping the time history responses to frequency domain through fast Fourier transform (FFT). Then, an ICA-based method in frequency domain called ICA-F is proposed to accurately extract mode shapes and modal responses for both light and high damping structures. A simulated 3 degree of freedom mass-spring system and a 4-story simulated benchmark model developed by the IASC-ASCE Task Group in Health Monitoring are employed to verify the effectiveness of the proposed method. The results show that the proposed method can perform accurate modal identification for both light and high damping structures. Finally, the IASC-ASCE experimental benchmark structure is also utilized to illustrate the proposed method applied to practical structure.
31 citations
TL;DR: In this paper, a new method for estimating the modal mass ratios of buildings from unscaled mode shapes identified from ambient vibrations is presented based on the Multi Rigid Polygons (MRP) model in which each floor of the building is ideally divided in several non-deformable polygons that move independent of each other.
27 citations
TL;DR: In this paper, a modal force compensator is proposed to suppress vibration of flexible spacecraft during attitude maneuver, which can cancel out disturbance input to elastic dynamics using modal forces generated by gyroscope.
25 citations
TL;DR: In this paper, the authors applied the Bayesian spectral density algorithm to address the uncertainty of mode extraction from output-only response of a long-span suspension bridge and estimated the posterior most possible values of modal parameters and their uncertainties were estimated through Bayesian inference.
25 citations
TL;DR: The numerical results exhibit the effectiveness of the proposed method for precisely determining the location and severity of multiple structural damages.
Abstract: To identify the location and severity of structural damages precisely, a two-stage damage detection method is proposed here. In the first stage, the most probable elements that maybe damaged are determined using the modal strain energy concept of structure. For such purpose, an efficient modal strain energy conversion-based index is proposed. In the second stage, the structural damage identification problem is defined as an optimization problem that to be solved by a modified genetic algorithm. In the optimization problem, the damage extents of structure’s elements which are determined in the previous stage are considered as the variables. An efficient objective function considering the first few modal frequencies of the structure, before and after damage occurrence, is utilized for optimization. The robustness of the proposed method is assessed by several benchmark examples. The numerical results exhibit the effectiveness of the proposed method for precisely determining the location and severity of multiple structural damages.
24 citations
TL;DR: In this paper, the authors demonstrate the effectiveness of a nondestructive diagnostic technique used to determine the location and size of delamination in laminated coatings of wind turbine blades.
Abstract: This paper demonstrates the effectiveness of a nondestructive diagnostic technique used to determine the location and size of delamination in laminated coatings of wind turbine blades. This is realized based on results of numerical and experimental investigations obtained by the use of the finite element method (FEM) and laser scanning vibrometry (LSV). The proposed method is based on the one-dimensional continuous wavelet transform of vibration parameters of a wind turbine blade. The investigations were conducted for a 1 : 10 scaled-down blade of a 36 m rotor wind turbine. Glass fibres and epoxy resin were used as laminate components. For numerical studies, a simple delamination model was proposed. The results obtained by the authors were used to determine the optimal set of parameters of the continuous wavelet transform. The application of high-quality LSV for experimental measurements allowed determining the optimal conditions of measuring procedures. At the same time the capabilities and limitations, resulting from the nature of the measurement method, were identified. In order to maximize the effectiveness of the detection method, preliminary signal processing was performed. Beside base wavelets also different waveform families were tested. The results obtained by the authors showed that it is possible to identify and localize even relatively small damage.
01 Apr 2018
TL;DR: In this article, an attempt was made to reduce tool vibration during turning of hardened steel using particle and mass impact dampers, which is an undesirable phenomenon which affects tool life, quality of machined surface and produces irritating noise.
Abstract: In the machine tools, tool vibration is an undesirable phenomenon which affects tool life, quality of machined surface and produces irritating noise. This tool vibration is due to the interaction between metal cutting process and forces acting on the machine tool. In this investigation, an attempt was made to reduce tool vibration during turning of hardened steel using particle and mass impact dampers. A mass impact damper used in this investigation consists of a concentrated mass made of copper mounted on the bottom of the tool holder and particle damper consists of copper particles of 3.5 mm diameter positioned along the axis of the tool holder. Particle size and its location were designed using computational analysis and impact hammer–based modal testing was performed for both dampers. When these dampers were mounted on the tool holder, particles will collide with each other and subdue the vibration produced in the tool holder. Cutting experiments were conducted to study the influence of mass and parti...
TL;DR: In this paper, the authors proposed a novel operational modal analysis (OMA) method based on the frozen-in coefficient method and limited memory recursive principal component analysis (LMRPCA) for linear weakly damped structures with slow time-varying characteristics under unmeasured stationary random ambient loads.
TL;DR: In this article, an efficient modal projection-based reduction method, which accounts for transient dynamic responses of structural system with multiple damping models, is proposed in the framework of a modified precise integration method.
TL;DR: A systematic three-step procedure to update the finite element models of machine tools with numerous uncertainties in connections is presented, which integrates statistical, numerical, and experimental techniques and gives rise to FE models whose dynamic responses closely agree with the experimental measurements, despite the large number of uncertainties.
Abstract: Accurate finite element models of mechanical systems are fundamental resources to perform structural analyses at the design stage However, uncertainties in material properties, boundary conditions, or connections give rise to discrepancies between the real and predicted dynamic characteristics Therefore, it is necessary to improve these models in order to achieve a better fit This paper presents a systematic three-step procedure to update the finite element (FE) models of machine tools with numerous uncertainties in connections, which integrates statistical, numerical, and experimental techniques The first step is the gradual application of fractional factorial designs, followed by an analysis of the variance to determine the significant variables that affect each dynamic response Then, quadratic response surface meta-models, including only significant terms, which relate the design parameters to the modal responses are obtained Finally, the values of the updated design variables are identified using the previous regression equations and experimental modal data This work demonstrates that the integrated procedure gives rise to FE models whose dynamic responses closely agree with the experimental measurements, despite the large number of uncertainties, and at an acceptable computational cost
TL;DR: In this article, the structure of a carbon fiber reinforced polymer floating raft frame and its vibration mode were analyzed. And a frame-based floating raft was designed, and two floating rafts were tested.
Abstract: This paper mainly studies the structure of a carbon fiber reinforced polymer floating raft frame and analyzes its vibration mode. A frame-based floating raft frame is designed, and two floating raf...
TL;DR: In this article, the free vibration analytical solution of a composite sandwich plate consisting of woven carbon laminated faces and a viscoelastic foam core was analyzed using Navier's procedure.
TL;DR: A portable and automated phase controlled impact device is introduced in the effort to eliminate non-synchronous components with minimal possible impacts applied and a good correlation of modal extraction data with benchmark data shown in this study has highlighted the advantages of ISTA using the proposed device.
Abstract: This paper studies how to enhance frequency response function (FRF) estimation in the presence of harmonic disturbances during operational modal testing. A novel technique which utilizes impact-synchronous time averaging (ISTA) called impact-synchronous modal analysis (ISMA) was introduced where modal analysis can be performed in the presence of ambient forces. The phase angle information of the harmonic signal at the impact events is shown to be a key factor in enhancing the effectiveness of this technique. However, lack of knowledge and control of impact with respect to the phase angle of the disturbances using conventional impact hammer in ISMA has limited the effectiveness and practicality of this novel technique. A portable and automated phase controlled impact device is introduced in the effort to eliminate non-synchronous components with minimal possible impacts applied. This device makes use of the feeding phase angle information of responses from the cyclic load back to the device and imparts the impact at the correct time/phase which is always non-synchronous with respect to the phase of response from cyclic load. A reduced number of averages thereby expedite the overall modal testing procedure, an improved of FRF estimation and a good correlation of modal extraction data with benchmark data shown in this study has highlighted the advantages of ISTA using the proposed device.
TL;DR: In this article, the use of wireless Inertial Measurement Units (IMUs) for modal testing of civil engineering infrastructure is explored, and the results from the IMUs are compared with those from a conventional wired system to identify the limitations.
TL;DR: In this paper, the influence of contact stiffness and friction on bending frequencies of the rotor assembly of a high-frequency permanent magnet electrical machine has been analyzed in detail, based on the finite element method.
Abstract: For the high-frequency permanent magnet electrical machine, a reasonable mechanical aspect design is crucial to meet its stability and reliability. This study focuses on the accurate modelling and analysis of the natural frequencies and modes of the rotor assembly for a designed and manufactured 100 kW 32,000 r/min motor. The influence of contact stiffness and friction on bending frequencies is analysed in detail. To obtain the accurate results of first two bending frequencies, on the basis of the finite-element method, the optimisation method is carried out to acquire appropriate variables of the contact stiffness and friction. The optimised results show that the method proposed in this study can realise the accurate analysis of the rotor mode, which are verified by free-free modal testing of the rotor.
TL;DR: This work has shown that dynamic modal testing is an economical method of evaluating structural key stiffness, the accuracy of which relies on the determination of selected target modes.
Abstract: Dynamic modal testing is an economical method of evaluating structural key stiffness, the accuracy of which relies on the determination of selected target modes. Pretension deviations are u...
TL;DR: The application of the direct modal parameters estimation (DMPE) algorithm for active modal control design is presented and provides a solution with a great numerical stability and allows estimating models with a higher order.
Abstract: Modal active control is based on a state model that requires the identification of modal parameters. This identification can typically be done through a rational fraction polynomial algorithm applied in the frequency domain. This method generates numerical problems when estimating high-order models, particularly when moving from the basis of orthogonal polynomials for the modal basis. This algorithm must therefore be applied independently on multiple frequency ranges with a low order for each range. In this case, the controller design cannot be automated and requires a lot of human intervention, especially to build the state space model. To address this issue, this paper presents the application of the direct modal parameters estimation (DMPE) algorithm for active modal control design. The identification algorithm is presented in a simplified version with only positive frequencies. Unlike other classical identification methods in the frequency domain, the DMPE algorithm provides a solution with a great nu...
TL;DR: In this paper, two different methods, local and modal, are suggested to control systems with distributed parameters, each of them having its own advantages and drawbacks, and the aim of the present research is to carry out experiments aiming in comparison of these two methods for the problem of suppression of forced bending vibrations of a thin metal beam.
Abstract: Summary
Two different methods, local and modal, are suggested to control systems with distributed parameters, each of them having its own advantages and drawbacks. The aim of the present research is to carry out experiments aiming in comparison of these 2 methods for the problem of suppression of forced bending vibrations of a thin metal beam. Two pairs of piezoelectric sensors and actuators are attached to the beam in each control system considered. Their locations are chosen so as to provide the most efficient measurement and excitation of the first and second vibration modes of the beam. Frequency methods of the automatic control theory are employed to design stable control systems that can efficiently suppress bending vibrations of the beam with the first and second resonance frequencies. As a result, control systems with the desired performance are created on the basis of both local and modal methods. The obtained modal system works efficiently for both resonances, whereas the local systems demonstrate appropriate performance either at the first or at the second resonance frequency only. This difference is due to the fact that in the case of modal control, each control loop corresponds to a particular vibration mode and can be designed to provide optimal performance at the required frequency. The performed benchmark study demonstrates the advantages of the modal method over the local one for the cases where it is necessary to suppress vibrations in the frequency range that contains more than one resonance frequency of the control object.
TL;DR: In this article, a model-updating approach based on an improved free-interface component synthesis method is proposed, where the perturbation for both the eigenvalues and eigenvectors of each component are used to formulate the synthesis equations containing the perturbing expression.
TL;DR: This work introduces an auto impact device to replace the manual impact hammer that allows significant improvement in FRF estimation and shows good correlation of modal extraction data with benchmark experimental modal analysis results.
Abstract: Previous study has shown that synchronization of phases between impacts and the cyclic load component should be avoided to improve the effectiveness of operational modal testing, i.e. impact-synchronous modal analysis in obtaining a cleaner frequency response function (FRF) estimation with fewer number of averages. However, avoiding the phase synchronization effect is rarely achievable with the current manual impact hammer because of the lack of control of the impact timing. We investigate how to improve FRF estimation in the presence of harmonic disturbances, such as those present in operating rotating machines. An auto impact device is therefore introduced to replace the manual impact hammer. This device ensures that impact intervals can be applied at non-synchronous instances with respect to the harmonic disturbance. We demonstrate that this new device is a viable option for operational modal testing. It allows significant improvement in FRF estimation and shows good correlation of modal extraction data with benchmark experimental modal analysis results.
TL;DR: In this article, the modal sensing behavior and modal vibration control effect of distributed PVDF patches laminated on the paraboloidal shell are investigated. And the amplitude suppression ratio of each mode controlled by the pole placement controller is calculated and compared with the results obtained by using a PPF controller.
TL;DR: In this article, three composite SSGSC samples were fabricated by the hand lay-up method using a silicon rubber die, and two metallic samples made of Aluminum 1050 and glass/epoxy were fabricated.
Abstract: Composite sandwich structures with a grid-stiffened core (SSGSC) are one of the new structural configurations employed in advanced industries, and therefore the knowledge of their dynamic characteristics is very important. Hence, in the present study, three composite SSGSC samples of glass/epoxy and carbon/epoxy were fabricated by the hand lay-up method using a silicon rubber die. Also, two metallic samples — a monolithic one and a SSGSC, made of Aluminum 1050, were fabricated. The core of the aluminum SSGSC was produced using the wire cutting process, and the face sheets were attached using a high-grade adhesive. Modal experiments were carried out on all the samples using B&K vibration equipment. The frequency, mode shape, and damping coefficients were obtained from each experiment. Finally, a numerical modal analysis was performed, and good agreement between experimental and numerical results was obtained.
TL;DR: In this article, a 3D Finite Element (FE) numerical model is presented to provide preliminary estimates of the expected modal characteristics for the examined structural system, which is then used to extract the natural frequencies and vibration modes of the system, according to conventional state-of-theart output-only modal parameter identification techniques.
Abstract: This paper reports on the dynamic characterisation of a Reinforced Concrete (RC) stadium grandstand module for the Sporting Stadium in Lisbon. To this aim, a three-dimensional (3D) Finite-Element (FE) numerical model, implemented according to the technical drawings of the structure, is first presented to provide preliminary estimates of the expected modal characteristics for the examined structural system. Ambient vibration tests are then carried out on the same grandstand, and used to extract the natural frequencies and vibration modes of the system, according to conventional state-of-the-art output-only modal parameter identification techniques. A sensitivity investigation and FE model updating study is hence presented for the grandstand, giving evidence of the major influencing parameters and key input data for the numerical fitting of the experimental modal testing results.
TL;DR: It is concluded that the connection rod failure is due to buckling at the presence of hydrolock phenomenon and provides vital information for the proper operation and maintenance of heavy duty Diesel engines.