PSI - Issue 77

Job S. Silva et al. / Procedia Structural Integrity 77 (2026) 550–558 Author name / Structural Integrity Procedia 00 (2026) 000–000

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parameters even in the absence of known input excitation, making it particularly suitable for in-situ operational modal analysis (OMA), as well as for laboratory setups without measured input forces. Compared to PSD, SSI is more robust in noisy environments and enables clear discrimination between physical and spurious modes through stabilization diagrams. Nevertheless, it requires greater computational effort and careful interpretation of results. In this work, the two techniques were applied sequentially: PSD was first used for a quick visual identification of the main resonance peaks, while SSI provided a detailed and reliable estimation of modal parameters. This combined strategy ensured accurate modal characterization of the scaled freight wagon model despite the absence of measured This section describes the methodology adopted to characterize the dynamic response of the scaled freight wagon model. The process encompassed the design and assembly of a laboratory-scale physical model, the development of a FE numerical model, and the experimental procedures used for modal identification. 3.1. Reduced-scaled Model A 1:25 scale model of a freight wagon was designed to reproduce the essential structural configuration of a two platform vehicle supported by a shared bogie. The model components were built primarily in aluminium to ensure lightweight construction while preserving geometric similarity with the full-scale prototype. The suspension elements were represented by scaled steel springs, enabling realistic stiffness distribution between the bogie frame and the platforms. This simplification allowed focusing on the dynamic behaviour of the primary suspension, where energy dissipation through frictional interfaces is dominant. The scaled wheels were replaced by rigid supports that allowed axle rotation but restricted lateral and vertical motion. Each platform was mounted independently on the bogie through the spring system, ensuring dynamic coupling similar to that observed in the real configuration. A schematic of the scaled wagon configuration is shown in Fig. 3. excitation data. 3. Methodology

Fig. 3. Reduced-scaled freight wagon model.

3.2. Numerical Model A detailed FE model was developed to replicate the experimental configuration. Different types of elements were used depending on the component: beam elements (one-dimensional elements) for axles, shell elements (bi dimensional elements) for platforms, and solid elements (tri-dimensional elements) for axle boxes and bogie frame. Contact interfaces were modelled using both tied constraints (where slave nodes follow the corresponding master nodes rigidly) and frictional contacts (μ = 0.6) to account for nonli near interactions. Although friction introduces nonlinear behavior, the modal analysis was performed on the linearized model around the equilibrium configuration, assuming small-amplitude vibrations. This approach ensures consistency with classical modal analysis while preserving the main dynamic characteristics of the assembly. Appropriate boundary conditions were applied to constrain rigid body motion while preserving realistic suspension compliance. Modal analyses were carried out up to 1000 Hz to capture both global and local vibration modes. For this study, a Finite Element Model of the experimental reduced-scaled freight wagon was developed using the HyperMesh software. It features a simplified representation of three bogies and two platforms modelled with,

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