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Elementary Aerodynamics
Published in Rama B. Bhat, Principles of Aeroelasticity, 2018
There are four types of drag: skin friction drag, form drag, induced drag, and wave drag. They can also be categorized in two ways: parasitic and induced. The sum of all the components of drag makes up the total drag force. Induced drag or drag due to lift is a small amount of excess (lift) force generated in the opposite direction of the motion. Wave drag generally only occurs when an airplane is flying near the speed of sound (transonic) or faster (supersonic). The form drag, also called pressure drag, is affected by the shape of the body. A smooth, streamlined shape generates less form drag than a blunt body. Automobiles are streamlined to increase gas mileage. Another type of drag, called interference drag, is a component of parasitic drag, which is caused by vortices. Whenever two surfaces meet at a sharp angle, the airflow has a tendency to form a vortex that contributes to drag.
Which variables may affect underwater glide performance after a swimming start?
Published in European Journal of Sport Science, 2022
Francisco Hermosilla, Inmaculada Yustres, Stelios Psycharakis, Jesús Santos del Cerro, Fernando González-Mohíno, José M. González-Rave
The maximum gliding depth was also an important predictor of gliding distance. Interestingly, group 1 (max depth under 125 cm) produced the shortest glide distances. The glide distances of groups 2 to 4 were very similar, suggesting that an increase in maximum depth beyond 165 cm may not benefit further the gliding distance. It may be possible that the drag coefficient reduces with increasing depth. For example, Marinho et al. (2010, 2009), used computational fluid dynamics simulations and determined that the drag coefficient and drag force is 44% greater in depths to 20 cm than to 250 cm. This was because a glide close to the surface contributes to the formation of surface waves, causing wave drag. Although the maximum depth of group 1 in the present study much more than 20 cm, it is perhaps more likely that this group has spent a longer time gliding closer to the surface at depths that are expected to increase drag (e.g. less than 40 cm). Therefore, it is recommended that average glide depth, as well as the time spent gliding closer to the surface, are both explored further in future studies. Lastly, it should also be mentioned that a deeper glide may increase the time back to surface, increase overall start time and reduce speed. Thus, the glides of groups 3 and 4 in the present study (165–245 cm) may not be beneficial to performance. Future research should, therefore, consider both the gliding distance and the swimmers’ underwater kicking and surface speed, for the purpose of optimising the combination of those factors in improving start performance.
Understanding the effects of training on underwater undulatory swimming performance and kinematics
Published in Sports Biomechanics, 2021
Jesús J. Ruiz-Navarro, Marta Cano-Adamuz, Jordan T. Andersen, Francisco Cuenca-Fernández, Gracia López-Contreras, Jos Vanrenterghem, Raúl Arellano
Maximisation of propulsive impulse and minimisation of resistive impulse are key variables when assessing technique to optimise swimming performance (Connaboy et al., 2009). Propulsion in UUS is generated by producing a ‘body wave’ that increases in amplitude as it travels caudally along the body (Gavilan et al., 2006; Ungerechts, 1983), resulting in a leg-dominated technique (A. J. Higgs et al., 2017). Resistive impulse is greatly affected by wave drag, a resistive force produced by the transfer of kinetic energy from the body to the water. The wave drag represents 50–60% of the total passive drag force at the surface in swimming; nevertheless, as depth increases the wave drag decreases noticeably (Vennell et al., 2006). This fact results in the potential for higher swimming velocity in UUS than in surface swimming.
Effect of wetted surface area on friction, pressure, wave and total drag of a kayak
Published in Sports Biomechanics, 2018
Beatriz B. Gomes, Leandro Machado, Nuno V. Ramos, Filipe A. V. Conceição, Ross H. Sanders, Mário A. P. Vaz, João Paulo Vilas-Boas, David R. Pendergast
The results of the present study suggest that the DF is the component of drag that contributes the most to the total DP, at velocities typical in international kayak sprint competitions and training. Also, present results support the importance of a kayak design selection that minimises the kayak’s drag for the individual weight of the kayaker, as it was previously reported by Gomes et al. (2015). In addition, this study contributes to increase knowledge and experimental accuracy of not only total drag, but importantly is components of friction, pressure and wave drag. These data can be applied to design approaches to guide kayak manufacturers to improve hull designs. The goal of new designs is to minimise DF, DPR and DW and consequently the total drag. Changes in hull design should take into consideration the effect of the kayaker’s weight to minimise the combined sum of DF, DPR and DW. This study has shown that the wetted surface area is an important consideration when designing hulls to reduce DF and DW.