| Objective:The study of hydrodynamic characteristics of swimming is the main way to optimize the swimming movement.The relationship between position,water depth and swimming performance of undulating underwater swimming is one of the main concerns of scholars.Therefore,the aim of this study is to analyze the swimming performance of three different undulatory underwater swimming positions under various swimming depth using a numerical simulation method based on multi-body motion.Methods:Using a numerical simulation method based on multi-body motion,we analyzed the performance of three different undulating underwater swimming positions.The simulation was conducted using 3D incompressible Navier–Stokes equations using the RNG k-ε turbulence closure equations,and in combination with the VOF method so we could include the water surface in our calculations.Different swimming depths based on the distance from the shoulder joint center to the initial water surface were considered.The velocity of the shoulder joint center was captured with a swimming motion monitoring system(Ki Swim)and compared with the calculated results.Results:1)The validity of the numerical swimming velocity was demonstrated by com-paring the computed results with the experimental data,which were in accord.2)The swimmer can generate a lot of propulsive force in a full sea guinea pig kick cycle,either bending kick or stretching kick.3)In the stage of flexion and kicking,the soles of the feet form a high-pressure area,and the calves and instep form a low-pressure area.Stretch kick stage,the soles of the feet form a low-pressure area,the calf and instep form a high-pressure area.When the swimmer completed a flexion kick,the flows at the cross section of the toe produced a strong downward jet stream.Two counter-rotating vortices were generated in the wake of the swimmer s feet,and the water flows converged at the place where the feet had been together.When the swimmer completed an extension kick,the water flowed up to the cross section of the toe and produced a strong upward jet stream.5)The hydrodynamic performance of the three UUS positions was basically the same when the water depth was lower than 0.5 m.This suggested that the effect of wave drag had decreased to the minimum value,which would be desirable for efficient UUS at the start of a lap and when turning.Conclusion:This study examined UUS as the research object.A rigid-body simulation strategy for UUS was established,which simulated the complex dynamics of UUS swimming.With regard to the impact of water depth on UUS,the influence of different positions as well as the effect of the water surface on the hydrodynamic characteristics of UUS was discussed.The main conclusions are as follows:1)The validity of the numerical swimming velocity was demonstrated by com-paring the computed results with the experimental data,which were in accord;There was a significant difference in the hydrodynamic characteristics of the three UUS positions when swimming near the water surface,and the difference decreased as the swimming depth increased.It is,therefore,recommended that swimmers travel at least 0.5 m below the surface in any UUS position in order to avoid excessive drag forces.2)As the swimmer approaches the water surface,the swimmer should use the lateral position,which has more swimming velocity and hydrodynamic advantage than the other two UUS positions.3)The numerical results showed that the flexion kick can also generate significant propulsion as well as the extension kick.Therefore,competitive swimmers should focus on optimizing the timing and amplitude of their flexion kick while working to strengthen the required musculature. |
PDF Full Text Request