Integrated Analytical, Finite Element and Experimental Modal Analysis of Off-Road Electric Vehicle Frames for Mobility-Assist Applications

Purpose This study presents a comprehensive dynamic characterisation of three off-road electric vehicle frames designed to improve mobility for users with reduced physical capabilities. The objective is to assess the predictive accuracy of different modelling approaches and identify the main factors governing their vibrational behaviour. Methods A multilevel modelling framework is developed, combining analytical lumped-parameter formulations, three-dimensional rigid-body models, finite element (FE) simulations, and experimental modal analysis (EMA) conducted on physical prototypes. Analytical models ranging from two- and four-degree-of-freedom (DOF) representations to full six-DOF formulations are evaluated against FE predictions and experimental modal parameters obtained through impact testing and accelerometer measurements. Results Simplified analytical models accurately reproduce the first natural modes (below 12 Hz), whereas three-dimensional rigid-body and FE models capture more complex dynamic behaviour, including roll–pitch coupling and local structural effects. Experimental modal analysis supports the numerical predictions and highlights the influence of structural joints, tyre stiffness, and boundary conditions. Remaining discrepancies are primarily attributed to damping effects and weld imperfections not represented in the FE models. Conclusion The proposed multilevel methodology provides a reliable framework for dynamic characterisation and structural optimisation of lightweight off-road mobility vehicles. The findings demonstrate the applicability of simplified and advanced modelling approaches across different frequency ranges, contributing to improved vehicle comfort, stability, and safety.