Investigations on vibration behaviors of railway track systems were attempted in this research. This was made by conducting a comprehensive field investigation into the free vibration of track systems and response of tracks to train moving loads. In-situ Modal analysis was used in a railway track field as an efficient method of investigating dynamic properties of railway track systems. Natural frequencies and mode shapes of the track system in different insitu track conditions were obtained for the fist time. The sensitivity of the natural frequencies of the track to the types of sleepers, fastening systems, ballast conditions, and rail joints were studied. Efficiency of rail welded joints in CWR tracks and the effects of replacing timber sleepers with concrete sleepers on dynamic behavior of a track were investigated. Advantages of flexible sleeper fastening system from the aspects of serviceability and passenger riding comfort were discussed. The effects of the track accumulative loading as a main indicator of ballast degradation on track dynamic behavior were studied. Rail deflections were calculated by using auto-spectra obtained from vibrations of the track under trainloads, leading to the development of a new mathematical expression for the calculation of the rail dynamic amplification factor.

This paper discusses an adaptation of Modal analysis concepts to time-varying periodic systems. It will be shown that the pseudo-Modal parameters preserve certain properties of the conventional Modal parameters defined for LTI systems. For this reason, after definition of pseudo Modal parameters for time varying systems, a new Modal analysis method will be introduced in time domain and it will be shown that these parameters can explain the nature of system. for periodic time varying systems, state transition matrices are formed by an ensemble set of responses which are obtained through multiple experiments on the system with the sometime varying behavior. In next step the pseudo natural frequencies of a beam with moving mass using introduced method will be extracted. Finally, it will be proved that for a linear time periodic system, the pseudo natural frequency treats periodic too.

This paper is concerned with the finite element analysis and Modal testing of an industrial radial flow impeller. The goal is to determine and verify the vibration characteristics of the impeller using both experimental and analytical techniques.The finite element model of the impeller with tapered blades was built using a 3D solid element. The convergence properties of the FE model was then verified by mesh refinement and mass distribution methods. Next, a pre-test plan was performed before conducting a Modal test in order to select the proper suspension points, driving point(s) and response points on the  impeller.Impact testing using hammer excitation and laser Doppler vibrometer (LDV) response measuring techniques were used to measure the vibration properties of the impeller. Using a scanning laser Doppler vibrometer enabled the backplate modes to be described in terms of their nodal diameter components. The nodal diameters versus natural frequencies graph was then compared with the same results obtained from FE and hammer testing and showed good agreement. Finally, a parametric study was conducted on disc thickness, blade thickness, blade trailing, leading edge profiles and blade mistuning. It was found that the effect of varying disc thickness on the lower modes of the impeller was not significant. However, significant natural frequency shifts were observed for the higher modes. It was also concluded that varying the blade leading edge position had a marked effect on the natural frequencies while the lower modes were somehow insensitive to the variation of trailing edge position.

In this paper, an alternative approach in operational Modal analysis is presented, utilizing image processing technique and transmissibility functions. Imaging sensors do not impose additional mass on the structure due to their non-contact nature, while transmissibility functions, independent of excitation type, can directly extract mode shapes. The innovation of this research lies in combining these two techniques to record dynamic responses and identify Modal properties. To capture the temporal response history from video signals, the block-matching method with sub-pixel accuracy was employed. Validation was conducted by recording the response of the tip of a cantilevered steel beam subjected to impact excitation, using a high-speed camera and a laser vibrometer, simultaneously. The RMSE plots in the time domain and the PSD in the frequency domain indicate high accuracy of this method. Using this approach, the displacement time histories of various points on the structure were extracted from the video signals, and the Modal properties, including natural frequencies, damping ratios, and mode shapes, were identified using the transmissibility matrix method. The results obtained from the proposed method were compared with the stochastic subspace identification (SSI) method and analytical solutions. The findings reveal the accuracy of the Modal identification approach introduced in this article. The highest relative error in estimating the natural frequencies of the first and second modes, compared to the values from the laser method, are 0.19% and 0.13%, respectively, and in comparison to the analytical values, they are 0.34% and 1.5%, respectively.

experimental and numerical studies are implemented in this work to investigate the Modal characteristics of three-layered viscoelastic sandwich beams and plates with a natural rubber core and distinct isotropic face layers. In this study, the material of face layers in both beams and plates is varied with uniform face thickness by keeping the core constant to maintain the constant volume. Through the use of the Impact Hammer Modal Testing technique, experimental Modal analysis is carried out with SAMURAI and ME' Scope software. The beams and plates are subjected to numerical analysis using ANSYS 19.2 Mechanical APDL Software, a finite element analysis (FEA) tool to evaluate the Modal characteristics. The Modal characteristics including natural frequencies and mode shapes of both beams and plates are evaluated under various boundary conditions, such as Clamped-Free (C–F), Simply-Supported (S–S), Clamped–Simply Supported (C–S), and Clamped-Clamped (C–C) for beams. Other plate boundary conditions that are taken into consideration for plates in this inquiry include C-F-F-F (Cantilever), S-S-S-S (All edges simply-supported), C-F-C-F (opposite edges clamped and other edges free), and C-C-C-C (All edges clamped). Ultimately, an excellent agreement is established when the outcomes of the experimental Modal analysis are compared to those from ANSYS. The research also investigates how varying face layer material densities and end conditions affect natural frequencies at constant volume.

As components of the car's dashboard, there is a support structure which is called cross-car beam (CCB). This beam bears the loads and respond to crash forces. Cross-car beam is essential, because its functions include safety, structural support of the instrument panel and passing sound, vibration and harshness (NVH) standards. If the natural frequencies of the cross-car beam overlap with one of the excitement frequencies, a phenomenon known as resonance occurs. According to the low stiffness of the cross-car beam, the Modal response of the cross-car beam should be studied and modified to avoid this destructive phenomenon. In this article, by changing the material of the cross-car beam from steel to polymer-based composite, the beam was redesigned and its vibration performance and stress analysis were performed. The simulations showed that changing the material of the metal beam to glass-epoxy composite, carbon-epoxy composite and fiber in metal laminate (FML) increased the natural frequency by 18%. In order to avoid resonance, more increasing is required for natural frequency amount. Therefore, several supports were added to connect beam to car body and reduce degree of freedom. Changing the material and increasing supports at the same time resulted 460% increasing for natural frequency. Because excessive increase of natural frequency will lead to increasing structure rigidity and as a result stress concentration, so numerical stress analysis was done and finally a suitable laminated composite was suggested for cross-car beam.

Given the inherently time-consuming nature of Incremental Dynamic analysis (IDA), which requires extensive computational resources to simulate multiple ground motions and assess various structural responses, it is essential to explore more efficient methodologies that maintain accuracy while reducing analysis time. The MPA-based IDA algorithm (MIDA) is being developed for various structures to address the limitations of IDA. In this study, six individual masonry structures were examined, including three walls with varying perforation dimensions and three three-dimensional buildings subjected to two retrofitting conditions. These structures were analyzed using 30 ground motion accelerations. The masonry structures, reinforced with either a shotcrete layer or a coating application, were evaluated as homogeneous and anisotropic materials using a finite element-based macro-modeling approach. Additionally, IDA was performed, and the maximum displacement of the masonry structures was compared to that of the MIDA. The results indicate that, except under high surcharge conditions, the MIDA procedure not only significantly reduces computational time but also provides reasonable accuracy compared to the IDA precision algorithm. Therefore, it can be concluded that the difference between the IDA and MIDA methods is influenced by the lateral stiffness of the masonry structures being analyzed

Modal analysis is one of the applicable methods used to identify the dynamic characteristics of structures. Inspection of structures to avoid resonance conditions can be achieved by extracting vibration modes using Modal analysis. Since every point of the vibrating structure has its own characteristics such as the displacement, speed and acceleration, the measurement of these parameters in a specific time interval can be used to extract Modal parameters. In this study, stereo vision as a noncontact measuring system is used to obtain the displacement of several points of the blade of a 2.5kW wind turbine with a length of 3m under the operational Modal condition. At first, the camera calibration process is performed and then the three-dimensional data of the turbine blade are extracted from images recorded during the test. Consequently, Modal parameters of the blade are calculated by analyzing the data. Finally, Modal parameters obtained by three different methods including the stereo vision system, the finite element analysis and the testing accelerometer are compared. The results show that visually obtained data are sufficiently accurate to find the natural frequency of the first mode of the blade. The first natural frequency mode extracted by the stereo vision system shows a difference of 10.36% and 2.67% compared to those obtained by finite element method and the accelerometer, respectively.