This paper addresses two important worldwide environmental concerns: disposal of waste tyres and attenuation of trains induced vibration. To this end, use of the waste materials in construction of ...railway concrete slabs for reduction of train induced vibration is investigated in this research. For this purpose, rubber tyre particles with different dosages were used in the concrete mixtures of test specimens. Extensive laboratory tests were conducted on the rubberized concrete specimens to measure their compressive strength, density and damping of the specimens. The effect of rubberized slab track on attenuation of vibration propagated from slab track was investigated by numerical modeling using results of laboratory tests as the input data. The laboratory results obtained indicate that adding rubber particles to the railway slab causes up to 96% increase in damping ratio (for concrete with 10% rubber). Results of numerical analysis elucidates that the rubberized slab track causes up to 21% reduction of the train induced vibration. By compromising between compressive strength and damping of vibration, it is shown that the optimum amount of crumb rubber in the concrete of railway slabs is 2.5% by which the best performance of the railway slabs is obtained.
•This paper addresses two important environmental challenges in the world.•A method for recycling waste tyres and reducing railway vibration is developed.•Optimum amount of crumb rubber integrated into railway concrete slab is derived.•Environment-friendly solution for mitigation of train induced vibration is derived.
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•A robust fuzzy-driven approach is derived for fully IO/OO automated modal analysis.•The methodology is applicable using any growing model-order identification method.•A new indicator ...called nMTN is derived for emphasizing weakly excited modes.•The efficiency of the strategy is demonstrated on actual shaking-table tests results.
A crucial step when identifying the modal signature of systems using growing order parametric methods consists in discriminating spurious modes from physical modes. In this paper, a three-stages clustering strategy is presented in a fuzzy framework for automating this selection process in the context of Input/Output and Output-Only identification. The novelty and strong point of the approach lies in the first stage where, after computation of single mode validation indicators, a modified fuzzy c-means clustering procedure is developed for performing a first partition. It is shown how the membership function obtained for the cluster of physical modes can be interpreted as a new synthetic modal indicator and helps with pole-splitting detection, outlier rejection and generally improves the final modal parameters estimation. The developed methodology does not involve any user-specified threshold and can be used for discriminating modes produced by any methodology consisting in fitting a growing order model to experimental data of any type. In this paper, accelerations measured during the SMART2013 shaking-table test campaign are processed using data-driven state-space identification algorithms. The automated selection process is used for tracking the modal signature of a trapezoidal shaped reinforced-concrete specimen using in turn stochastic and combined deterministic-stochastic algorithms, defining for the latter the movement of the shaking table as input. Variations in the modal signature are then correlated to the damage actually observed on the specimen and a comparison between Output-Only and Input/Output results is made in order to estimate the interaction between the specimen and the whole shaking table device.
The vibrational characteristics of the Hybrid III and NOCSAE headforms are not well understood. It is hypothesized that they may perform differently in certain loading environments due to their ...structural differences; their frequency responses may differ depending on the impact characteristics. Short-duration impacts excite a wider range of headform frequencies than longer-duration (padded) impacts. While headforms generally perform similarly during padded head impacts where resonant frequencies are avoided, excitation of resonant frequencies during short-duration impacts can result in differences in kinematic measurements between headforms for the matched impacts. This study aimed to identify the natural frequencies of each headform through experimental modal analysis techniques. An impulse hammer was used to excite various locations on both the Hybrid III and NOCSAE headforms. The resulting frequency response functions were analyzed to determine the first natural frequencies. The average first natural frequency of the NOCSAE headform was 812 Hz. The Hybrid III headform did not exhibit any natural frequencies below 1000 Hz. Comparisons of our results with previous studies of the human head suggest that the NOCSAE headform's vibrational response aligns more closely with that of the human head, as it exhibits lower natural frequencies. This insight is particularly relevant for assessing head injury risk in short-duration impact scenarios, where resonant frequencies can influence the injury outcome.
In this paper, the vibration correlation technique (VCT) has been used as a nondestructive method for predicting the buckling load of grid-stiffened composite conical shells. This technique is ...capable of predicting the buckling load of structures without reaching failure point through modal testing. The grid-stiffened composite conical shell has been fabricated using the filament winding process. To perform the experiment, the fundamental natural frequency of the specimen is measured under stepped axial compression loading. The procedure is followed up without actually reaching the instability point when the structure collapses and is no longer usable. A finite element model has been built using ABAQUS software considering the effect of geometric imperfection in order to determine the correlation between natural frequency and applied compressive load. A comparison of the experimental and numerical approaches indicated that the difference between numerical buckling loads and those obtained via the VCT is negligible. Moreover, the VCT has provided a reliable estimate of the buckling load, especially when the maximum applied load is greater than 67% of the experimental buckling load.
•VCT has been used as a nondestructive method for predicting the buckling load of grid-stiffened composite conical shells.•The fundamental natural frequency is measured under stepped axial compression loading during experimental test.•A finite element model has been used to determine the correlation between natural frequency and applied compressive load.•VCT has provided a reliable estimate of the buckling load especially when the maximum applied load is greater than 67% of the experimental buckling load.
The automotive industry must deal with significant challenges in the future. Consequently, predicting the Noise‐Vibration‐Harshness (NVH) in the early design and concept phase becomes essential. ...Especially dynamic seat behavior immediately affects ride comfort and hence customer acceptance. Therefore, it is necessary to have reliable finite element (FE) models for the simulation‐based prediction of the dynamic seat behavior. This study describes different aspects of the experimental‐ and simulation‐based modeling of a vehicle seat. The experimental modal analysis is used to characterize the seat system as well as the subsystem's seat backrest and frame. The structural dynamics of a seat depend on various sensitive parameters. We identified the dominant mode shapes below 100 Hz, which are lateral, fore‐and‐aft, and twisting modes. We could see that the seat backrest has a substantial mass influence. Besides, we showed that the twisting mode can be modified by varying cross‐direction stiffness. Thus, findings are utilized to improve the predictive power of simulation results.
This paper discusses the application of Dynamic Mode Decomposition (DMD) to the extraction of modal properties of linear mechanical systems, i.e., experimental modal analysis (EMA). First, ...theoretical background of the DMD is briefly reviewed and its relevance to the Ibrahim time-domain method is discussed. Second, DMD is applied to a single DOF system and multi-DOF discrete system to discuss the applicability and interpretation of the DMD as a method of EMA. Furthermore, the effects of measurement errors on the results of DMD are discussed. It is shown that with relatively small measurement errors, DMD can capture modal parameters accurately. However, with relatively large measurement errors, DMD fails to capture modal parameters. Finally, DMD is applied to experimentally-obtained displacement field of a cantilevered beam, and its modal parameters are extracted. It is shown that the modal parameters extracted by DMD are as accurate as the ones obtained by the existing modal parameter extraction method.
Camera-based Experimental Modal Analysis (EMA) is able to measure full-field vibration modes contactlessly. However, camera measurements still suffer from a lower sampling frequency and lower ...Signal-to-Noise Ratio (SNR) compared to accelerometers and laser vibrometers. Since regular sampling confines the results to the Nyquist frequency (i.e., half the frame rate of a camera), in a previous paper we have proposed an approach that exploits images randomly sampled in time, allowing to measure modes beyond the Nyquist frequency. In this paper we employ such an approach and we propose a novel excitation scheme to increase the SNR, i.e., the specimen under investigation is excited at selected resonance frequencies, which results in high amplitudes of the structural responses. These frequencies are measured by accelerometers during a pre-test, and a multi-sine signal containing these frequency components is generated as structural excitation through a shaker. Furthermore, as Rigid Body Motion (RBM) due to pseudo-free suspension is not desired for EMA, in this paper we also propose a novel optimization workflow for RBM compensation. The accuracy of the proposed approach with multi-sine excitation is first evaluated numerically by reconstructing steady-state response signals. Secondly, the whole workflow (i.e., multi-sine excitation and RBM compensation) is validated on an experimental case with a 3D component and a stereo camera setup. From a sequence of randomly sampled images equivalent to a frame rate below 50fps (corresponding to an equivalent Nyquist frequency below 25Hz), four modes up to 250Hz (i.e., ten times higher than the Nyquist frequency) are extracted, which correlate well with the modes predicted through a finite element simulation.
•We propose a multi-sine excitation method to improve SNR in the camera-based EMA.•The excitation contains the resonance frequencies of the specimen.•We propose a two-step approach to compensate for rigid body motion.•We adopt a random sampling scheme to go beyond the Nyquist frequency.•We obtain 3D spatially dense vibration mode shapes with a fast measurement campaign.
In this research, it is aimed to investigate the effect of boundary condition and variable shell thickness on the vibration behavior of grid-stiffened composite conical shells. In order to fabricate ...the stiffeners and shell for the experimental study, continuous and woven glass fibers have been used during a filament winding process, respectively. Due to the non-uniform distribution of the stiffeners in a stiffened conical shell, the equivalent thickness varies along the longitudinal axis. The stiffener and shell structures have been reduced into an equivalent shell using smeared method. The governing equations have been solved in order to evaluate the natural frequencies of the grid-stiffened conical shell by the use of first-shear deformation theory (FSDT) along with the power series method. In order to validate the analytical solutions, an experimental modal analysis have been carried out on a real grid-stiffened composite conical shell with uniform shell thickness. In addition, the finite element solution has been provided for further validations. Furthermore, the effects of various geometric parameters, variable shell thickness and boundary conditions have been discussed.
Due to the problems arising from impact damage in composite laminates, there is a need to develop fast, accurate, cost-effective and non-destructive testing methods to identify this type of damage at ...an early stage and thus enhance the service life of composite structures. This paper presents the results of an extensive experimental campaign conducted to investigate the feasibility of using vibration-based methods to identify damages sustained by composite laminates due to low-velocity impacts. The experimental programme included an evaluation of impact damage resistance and tolerance according to ASTM test methods, characterisation of induced damage by ultrasonic testing and quantification of the effects on the vibration response. The damage identification involved the detection, localisation, quantification and estimation of the remaining bearing capacity. Four damage indicators based on modal parameters were assessed by comparing pristine and damaged states. The results allowed for conclusions to be drawn regarding the capability and suitability of each damage indicator, including its ability to detect impact-induced damage, its precision in determining the location of damage, its sensitivity regarding damage extent and pertinent correlations with residual bearing capacity.
