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- Hydrodynamic analysis of different finger positions in swimming: a computational fluid dynamics approachPublication . Vilas Boas, J. Paulo; Ramos, Rui J.; Fernandes, Ricardo J.; Silva, António; Rouboa, Abel I; Machado, Leandro; Barbosa, Tiago M.; Marinho, DanielThe aim of this research was to numerically clarify the effect of finger spreading and thumb abduction on the hydrodynamic force generated by the hand and forearm during swimming. A computational fluid dynamics (CFD) analysis of a realistic hand and forearm model obtained using a computer tomography scanner was conducted. A mean flow speed of 2 m · s(-1) was used to analyze the possible combinations of three finger positions (grouped, partially spread, totally spread), three thumb positions (adducted, partially abducted, totally abducted), three angles of attack (a = 0°, 45°, 90°), and four sweepback angles (y = 0°, 90°, 180°, 270°) to yield a total of 108 simulated situations. The values of the drag coefficient were observed to increase with the angle of attack for all sweepback angles and finger and thumb positions. For y = 0° and 180°, the model with the thumb adducted and with the little finger spread presented higher drag coefficient values for a = 45° and 90°. Lift coefficient values were observed to be very low at a = 0° and 90° for all of the sweepback angles and finger and thumb positions studied, although very similar values are obtained at a = 45°. For y = 0° and 180°, the effect of finger and thumb positions appears to be much most distinct, indicating that having the thumb slightly abducted and the fingers grouped is a preferable position at y = 180°, whereas at y = 0°, having the thumb adducted and fingers slightly spread yielded higher lift values. Results show that finger and thumb positioning in swimming is a determinant of the propulsive force produced during swimming; indeed, this force is dependent on the direction of the flow over the hand and forearm, which changes across the arm's stroke.
- O efeito da profundidade no arrasto hidrodinâmico em nataçãoPublication . Ferreira, Rui Jorge Ramos; Marinho, Daniel AlmeidaO objectivo deste presente estudo passou por analisar o efeito da profundidade e da velocidade de nado na variação da força de arrasto hidrodinâmico (D) e do coeficiente de arrasto (CD), durante a fase de deslize subaquático passivo, após as partidas e viragens. Para esta análise, foi utilizada a metodologia de Dinâmica Computacional de Fluidos, através do software ANSYS® FLUENT®, tendo sido modelado um modelo tridimensional real de um nadador de elite na posição hidrodinâmica fundamental. Este modelo foi obtido através de uma tomografia axial computorizada (TAC) completa do corpo. As simulações foram efectuadas para as profundidades de 0, 0.25, 0.50, 0.75 e 1.0 metros, com três velocidades representativas diferentes, 1.5, 2.0 e 2.5 m/s. Os resultados obtidos revelaram que o arrasto hidrodinâmico diminuiu à medida que a profundidade aumentou, havendo uma tendência para a estabilização deste valor após os 0.75 m de profundidade. Contudo, a 0 m de profundidade, o valor de arrasto hidrodinâmico é menor do que a 1 m de profundidade. Verificou-se também que um aumento da velocidade levou a um aumento da força de arrasto e a uma diminuição do coeficiente de arrasto hidrodinâmico. Estes dados parecem sugerir que a selecção da profundidade adequada para a realização do deslize subaquático deve ser uma preocupação central dos nadadores e treinadores.
- The Effect of Depth on Drag During the Streamlined Glide: A Three-Dimensional CFD AnalysisPublication . Novais, Maria L; Silva, António; Mantha, Vishveshwar R; Ramos, Rui J.; Rouboa, Abel I; Vilas Boas, J. Paulo; Luís, Sérgio R; Marinho, DanielThe aim of this study was to analyze the effects of depth on drag during the streamlined glide in swimming using Computational Fluid Dynamics. The Computation Fluid Dynamic analysis consisted of using a three-dimensional mesh of cells that simulates the flow around the considered domain. We used the K-epsilon turbulent model implemented in the commercial code Fluent(®) and applied it to the flow around a three-dimensional model of an Olympic swimmer. The swimmer was modeled as if he were gliding underwater in a streamlined prone position, with hands overlapping, head between the extended arms, feet together and plantar flexed. Steady-state computational fluid dynamics analyses were performed using the Fluent(®) code and the drag coefficient and the drag force was calculated for velocities ranging from 1.5 to 2.5 m/s, in increments of 0.50m/s, which represents the velocity range used by club to elite level swimmers during the push-off and glide following a turn. The swimmer model middle line was placed at different water depths between 0 and 1.0 m underwater, in 0.25m increments. Hydrodynamic drag decreased with depth, although after 0.75m values remained almost constant. Water depth seems to have a positive effect on reducing hydrodynamic drag during the gliding. Although increasing depth position could contribute to decrease hydrodynamic drag, this reduction seems to be lower with depth, especially after 0.75 m depth, thus suggesting that possibly performing the underwater gliding more than 0.75 m depth could not be to the benefit of the swimmer.
- Relationships Between Vertical Jump Strength Metrics and 5 Meters Sprint TimePublication . Marques, MC; Gil, Maria Helena; Ramos, Rui J.; Costa, Aldo; Marinho, DanielThe aim of this study was to examine the relationship between short sprint time (5 m) and strength metrics of the countermovement jump (CMJ) using a linear transducer in a group of trained athletes. Twenty-five male, trained subjects volunteered to participate in the study. Each volunteer performed 3 maximal CMJ trials on a Smith machine. Peak instantaneous power was calculated by the product of velocity taken with the linear transducer. For sprint testing, each subject performed three maximum 5 m sprints. Only the best attempt was considered in both tests. Pearson product-moment correlation coefficients between 5 m sprint performance and strength metrics of the CMJ were generally positive and of clear moderate to strong magnitude (r = -0.664 to -0.801). More noticeable was the significant predictive value of bar displacement time (r= ∼0.70) to sprint performance. Nevertheless, a non-significant predictive value of peak bar velocity and rate of force development measurements was found. These results underline the important relationship between 5 m sprint and maximal lower body strength, as assessed by the force, power and bar velocity displacement. It is suggested that sprinting time performance would benefit from training regimens aimed to improve these performance qualities.