INTRODUCTION: The motions of ski jumping are divided into four parts: in-run, takeoff, flight, and landing. The takeoff motion in which largely change jumpers` posture in a short time of about 0.2~0.3 seconds is considered to strongly affect the performance. However, suitable takeoff motions have not been biomechanically and aerodynamically identified. Therefore, in this study, we first constructed a simulation framework that can reproduce detailed posture changes during takeoff using markerless motion capture. Next, the various jumps are classified with principal component analysis. The purpose of this study is to clarify the relationship between postural change during takeoff and the unsteady aerodynamic forces using the constructed framework. METHODS: A total of 640 actual takeoff motions of 80 athletes were recorded. The 3D posture data were acquired using markerless motion capture application (Theia3D). Next, using the obtained motion data, a principal component analysis (PCA) was applied to the time series data of angle of attack (AOA) of trunk to classify the takeoff motion data. Finally, 3DCG animations of representative motions among the classified ones were created, and the unsteady aerodynamic forces acting during each takeoff were analyzed using Computational Fluid Dynamics (CFD) framework [1]. RESULTS/DISCUSSION: PCA showed that it is important to keep the displacement of the AOA of trunk within the certain range for exceeding the K point. And also, the takeoff motions for exceeding K point have the difference in the overall size of the AOA of trunk. Therefore, we selected several trials with different AOA of trunk among trials over K-point and analyzed the unsteady aerodynamic forces by CFD (Figure 1). As a result, it was found that different aerodynamic characteristics exist among the trials exceeding K-point. CONCLUSION: Through this study, it is concluded that suitable takeoff motion in ski jumping is closely related to AOA of trunk displacement, and differences in aerodynamic characteristics exist among suitable takeoff motions.
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