Enhancing the prediction accuracy of EKASTOS with individual parameter tuning

Abstract

Whole-body vibration strongly influences perceived ride comfort, particularly in automated vehicles, where limited visual cues and unpredictable movements introduce a “surprise factor” that challenges postural stabilization. Conventional seat-to-head transmissibility assessments rely on simplified, linear assumptions that insufficiently represent multi-axis biomechanical responses and neglect inter-individual variability. More detailed and individualized modelling approaches are therefore required. This study, employs Ekastos, a computationally efficient 3D full-body dynamic model developed in Simscape MATLAB, to evaluate its ability to reproduce experimental anterior-posterior whole-body vibration responses across three distinct anthropometries with regards to body size. A hierarchical multi-objective evolutionary optimization framework is implemented to identify model postural control parameters and benchmarked against a gradient-based method. Average (response and anthropometry) seat-to-head frequency-response functions are first compared between experimental data and model responses obtained using the two optimization methods. Model performance is assessed using metrics for head, trunk, and pelvis motion in both X-translation and pitch, comparing model responses against (i) average and (ii) across minimum-maximum range of individual experimental responses. Afterwards, individualization is examined for two subjects by comparing (a) average-optimized postural control parameters with individualized anthropometry and (b) subject-specific postural control parameters with individualized anthropometry. Under average-response conditions, the multi-objective approach reduced objective metrics by 9-31%. Applying average anthropometry and parameters to individuals increased errors by 18–650% (>1000% in extreme cases), whereas anthropometry adaptation and subject-specific tuning reduced errors by up to 47%. These results highlight the necessity of robust optimization and individualization for accurate prediction of seated human dynamic responses under whole-body vibration.

Keywords: EKASTOS, Computational Human Body Model, Anthropometry, Individualization, Whole-body Vibration, Postural Control

DOI: 10.54941/ahfe1007701