Measurement and Modeling of Unsteady Fluid Force Acting on the Trunk of a Swimmer Using a Swimmer Mannequin Robot

Abstract

The objectives of this study were to measure the unsteady fluid force acting on the trunk of a swimmer using the ‘swimmer mannequin robot’ and to model the fluid forces based on the formulation of the swimming human simulation model SWUM, which was developed by the authors’ group. The swimmer mannequin robot consisted of a swimmer mannequin and a driving mechanism. The scale of the swimmer mannequin was 1/2 (half scale) and the three-dimensional shape of an athlete swimmer taking the gliding position was reproduced in detail. The driving mechanism could move the mannequin in the pitching, heaving and rolling motions. Using the swimmer mannequin robot, the trunk motions of four strokes (crawl, breast, back and butterfly) were reproduced, and the unsteady fluid forces acting on the mannequin were measured by the dynamometers installed in the robot. On the other hand, the swimmer mannequin was modeled using the swimming human simulation model SWUM. The fluid force coefficients in the model were identified so that the simulated fluid forces became as consistent as possible with the experimental ones for each stroke case. The identified coefficients were then unified into ones which can be used for all cases. It was found that the precision of the model almost did not decrease as a result of the unification. It was also found that the overall performance of the simulation using the determined fluid force coefficients to predict the time variation of the fluid forces was satisfactory.