Percorrer por autor "Kjendlie, Per L."
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- Computational fluid dynamics applied to competitive swimming: the role of finger positionPublication . Marinho, D.A.; Barbosa, Tiago M.; Kjendlie, Per L.; Reis, Victor M.; Vilas-Boas, João Paulo; Machado, Leandro; Rouboa, Abel; Silva, A.J.The best fingers’ relative position during the underwater path of the stroke cycle in swimming seems to be an unclear issue. Even in elite level swimmers, different relative positions of thumb and finger spreading can be observed. The aim of the current abstract was to present the hydrodynamic characteristics of a true model of a swimmer’s hand with different fingers’ positions using computational CFD.
- Modelling hydrodynamic drag in swimming using computational fluid dynamicsPublication . Marinho, D.A.; Barbosa, Tiago M.; Kjendlie, Per L.; Mantripragada, Narendra; Vilas-Boas, João Paulo; Machado, Leandro; Alves, Francisco B.; Rouboa, Abel; Silva, A.J.In the sports field, numerical simulation techniques have been shown to provide useful information about performance and to play an important role as a complementary tool to physical experiments. Indeed, this methodology has produced significant improvements in equipment design and technique prescription in different sports (Kellar et al., 1999; Pallis et al., 2000; Dabnichki & Avital, 2006). In swimming, this methodology has been applied in order to better understand swimming performance. Thus, the numerical techniques have been addressed to study the propulsive forces generated by the propelling segments (Rouboa et al., 2006; Marinho et al., 2009a) and the hydrodynamic drag forces resisting forward motion (Silva et al., 2008; Marinho et al., 2009b). Although the swimmer’s performance is dependent on both drag and propulsive forces, within this chapter the focus is only on the analysis of the hydrodynamic drag. Therefore, this chapter covers topics in swimming drag simulation from a computational fluid dynamics (CFD) perspective. This perspective means emphasis on the fluid mechanics and CFD methodology applied in swimming research. One of the main aims for performance (velocity) enhancement of swimming is to minimize drag forces resisting forward motion, for a given trust. This chapter will concentrate on numerical simulation results, considering the scientific simulation point-of-view, for this practical implication in swimming. In the first part of the chapter, we introduce the issue, the main aims of the chapter and a brief explanation of the CFD methodology. Then, the contribution of different studies for swimming using CFD and some practical applications of this methodology are presented. During the chapter the authors will attempt to present the CFD data and to address some practical concerns to swimmers and coaches, comparing as well the numerical data with other experimental data available in the literature.
- Swimming propulsion forces are enhanced by a small finger spreadPublication . Marinho, D.A.; Barbosa, Tiago M.; Reis, Victor M.; Kjendlie, Per L.; Alves, Francisco B.; Vilas-Boas, João Paulo; Machado, Leandro; Silva, A.J.; Rouboa, AbelThe main aim of this study was to investigate the effect of finger spread on the propulsive force production in swimming using computational fluid dynamics. Computer tomography scans of an Olympic swimmer hand were conducted. This procedure involved three models of the hand with differing finger spreads: fingers closed together (no spread), fingers with a small (0.32 cm) spread, and fingers with large (0.64 cm) spread. Steady-state computational fluid dynamics analyses were performed using the Fluent code. The measured forces on the hand models were decomposed into drag and lift coefficients. For hand models, angles of attack of 0°, 15°, 30°, 45°, 60°, 75°, and 90°, with a sweep back angle of 0°, were used for the calculations. The results showed that the model with a small spread between fingers presented higher values of drag coefficient than did the models with fingers closed and fingers with a large spread. One can note that the drag coefficient presented the highest values for an attack angle of 90° in the three hand models. The lift coefficient resembled a sinusoidal curve across the attack angle. The values for the lift coefficient presented few differences among the three models, for a given attack angle. These results suggested that fingers slightly spread could allow the hand to create more propulsive force during swimming.
- Swimming simulation: a new tool for swimming research and practical applicationsPublication . Marinho, D.A.; Barbosa, Tiago M.; Kjendlie, Per L.; Vilas-Boas, João Paulo; Alves, Francisco B.; Rouboa, Abel; Silva, A.J.Swimming is one of the major athletic sports and many efforts are being made to establish new records in all events. To swim faster, thrust should be maximized and drag should be minimized. These aims are difficult to achieve because swimmers surge, heave, roll and pitch during every stroke cycle. In addition, measurements of human forces and mechanical power are difficult due to the restrictions of measuring devices and the specificity of aquatic environment.