Dynamic analysis of Sitar: A comparative study of operational and experimental modal analysis

Dynamic analysis of Sitar, an Indian string instrument, is important for better understanding of the instrument behavior during performance. Sitar has complex geometry, and most of its components have anisotropic material properties, which generate a lot of challenges in performing numerical modal analysis. Considering this, an experimental approach of operational modal analysis (OMA) is performed on Sitar to extract its natural frequencies using the Stochastic Subspace Identification method. Hammer or shaker excitation required for conventional experimental modal analysis (EMA) has huge limitations of using harder hammer tips and high magnitude force as the instrument is delicate. However, to validate OMA results, EMA is performed with extreme care using an instrumented hammer with soft tip and with a very low excitation force. PolyMAX algorithm is used in EMA. It is observed that most of the correlated OMA and EMA modes lie in the audible frequency range. The maximum absolute percent error observed for these frequencies is 2.14%. All the modes obtained in OMA are significant as the string excitation simulate close to the real-life performing situation. Most of these modes map to musical note frequencies. Considering the detrimental effect of excitation required for EMA, OMA is a recommended method for extracting modal characteristics of Sitar.

Experimental modal analysis for the plate structures with roving inertial shaker method approach

In this article, a new roving inertial shaker method approach, using an inertial shaker, is presented to obtain a steel plate’s modal parameters with bolt connections on four sides. It aimed to emphasize the superiority of the proposed roving shaker approach over the classical, traditional hammer method on the plate-like structures. The frequency response functions (FRF), obtained from both methods, are investigated using the stabilization diagram, and the superiority of the roving shaker method is presented based on high stabilization and detecting more modes. The accelerometer’s position effect on experimental modal analysis (EMA) is investigated in the roving shaker method, which is performed using accelerometers in two different places, and obtained modal parameters are compared with experimental modal analysis validation methods. Accordingly, the results for the two separate locations are very close to each other. Finally, the experimental and numerical results are investigated according to the TEST/FEA correlation for the traditional roving hammer method and the roving shaker method. As a result, the roving shaker approach gives a better result according to the TEST/FEA correlation success than the roving hammer test. In conclusion, the high stabilization, high TEST/FEA correlation rate, and the number of modes show the roving shaker approach’s superiority.

Vibration Analysis of the Drivetrain in Dependence on the Type of Gearbox Suspension Bushing

In the vast majority of technical applications, there is a necessity to transmit the torque from drive to driven machine together with the demand to overcome great distance between given devices. One of the solutions of this problem is the use of a cardan shaft. Operations of connecting shaft and drivetrain are accompanied by oscillations negatively influencing the driver comfort. Main subject of this article is the measurement of vibrations on different parts of a heavy truck and its evaluation by FFT analysis. Measurements are performed with two kinds of suspension bushing which are compared with to each other. Based on the previous measuring, influence of cardan shaft length was also investigated. First of all, dependency on the length of the cardan shaft on deflection angles for V arrangement was evaluated by analytical method. The theoretical introduction is followed by research of eigen frequency depending on the length of the cardan shaft. The results obtained by modal analysis in FEM are verified by experimental modal analysis [1].

Performance of Camera-Based Vibration Monitoring Systems in Input-Output Modal Identification Using Shaker Excitation

Despite significant advances in the development of high-resolution digital cameras in the last couple of decades, their potential remains largely unexplored in the context of input-output modal identification. However, these remote sensors could greatly improve the efficacy of experimental dynamic characterisation of civil engineering structures. To this end, this study provides early evidence of the applicability of camera-based vibration monitoring systems in classical experimental modal analysis using an electromechanical shaker. A pseudo-random and sine chirp excitation is applied to a scaled model of a cable-stayed bridge at varying levels of intensity. The performance of vibration monitoring systems, consisting of a consumer-grade digital camera and two image processing algorithms, is analysed relative to that of a system based on accelerometry. A full set of modal parameters is considered in this process, including modal frequency, damping, mass and mode shapes. It is shown that the camera-based vibration monitoring systems can provide high accuracy results, although their effective application requires consideration of a number of issues related to the sensitivity, nature of the excitation force, and signal and image processing. Based on these findings, suggestions for best practice are provided to aid in the implementation of camera-based vibration monitoring systems in experimental modal analysis.