ABSTRACT
Objective To explore characteristics of flow field around the athletes, change of net flow force, and influences of hip flexion angles at the end of extension kick on the submerged dolphin kick stroke. Methods The body shape data of a swimmer were obtained by three-dimensional (3D) scanning, and the data were reversely reconstructed to obtain the swimmer model. The joints of the swimmer model were separated, and each segment of the athlete was divided into independent rigid body, and simulation of the submerged dolphin kick stroke was realized by controlling movement of each independent rigid body. The computational fluid dynamics (CFD) software package ANSYS Fluent was used as the solver for calculation and solution. Results The vortex structures were shed off from the surface of the swimmer’s body in the area with a large velocity gradient in flow field, and the shedding of vortex structures was different at the stage of extension kick and flexion kick. Propulsion was mainly generated during extension kick phase. At the end of extension kick, the drag decreased as the hip flexion angle increased from 20° to 30°. Conclusions To some extent, increasing flexion angle of the hip joint at the end of extension kick will reduce the drag force and increase the swimming speed in process of the submerged dolphin kick stroke.
ABSTRACT
The purpose of this study is to analyze the biomechanics of ankle cartilage and ligaments during a typical Tai Chi movement-Brush Knee and Twist Step (BKTS). The kinematic and kinetic data were acquired in one experienced male Tai Chi practitioner while performing BKTS and in normal walking. The measured parameters were used as loading and boundary conditions for further finite element analysis. This study showed that the contact stress of the ankle joint during BKTS was generally less than that during walking. However, the maximum tensile force of the anterior talofibular ligament, the calcaneofibular ligament and the posterior talofibular ligament during BKTS was 130 N, 169 N and 89 N, respectively, while it was only 57 N, 119 N and 48 N during walking. Therefore, patients with arthritis of the ankle can properly practice Tai Chi. Practitioners with sprained lateral ligaments of the ankle joint were suggested to properly reduce the ankle movement range during BKTS.