EVALUATION OF BODY MASS IS DUBIOUS

Kjendlie, P.-L., Alves, F., Berthelsen, A., Caspersen, C., Eik, M., Marinho, D., Pakozdi, C., Rouboa, A., Silva, A. J., & Vilas-Boas, J.-P. (2009). Added mass of human swimmers: A comparison of computational and experimental results. ** ACSM 56th Annual Meeting, Seattle, Washington.** Presentation Number 2561.

*"Added mass is the amount of water a swimmer has to accelerate in addition to his body during changes in velocity. It is an important concept in determining the total body drag of swimmers during unsteady motion, as well as propulsive forces acting from accelerating hands and feet."*

The aim of this study was to find added mass of a human body using experimental and computational methods, and to compare the two methods. For one male adult S, added mass was found experimentally using vertical oscillations. The S were connected to a 2.8m long bar with handles, springs, and a force cell. By oscillating this system vertically and registering the time period of oscillations it is possible to find the added mass of the swimmer, given the known masses of the bar and swimmer. Additionally the added mass was found using computational fluid dynamics calculations. The body surface and volumes of the S were determined using a computer tomography scan technique. The 3D body- and water-models were created using the Gambit software (Fluent®, Inc. Hannover, USA).

For the male swimmer, with a body mass of 81.6 kg, and a characteristic length of 2.39 m (reaching height) the added mass was found experimentally to be 21.6 kg, and using computational fluid dynamics to be 26.6 ± 4.3 kg.

**Implication**. The added body mass of male humans seems to be in the proximity of 26.5% or 32.5% using oscillation or computational fluid dynamics measurements respectively. There is a relatively close agreement between the two methods. The different actual measurement value is most probably due to S’s experimental conditions during oscillations involving small body posture movements, whereas with the computational fluid dynamics model the body was completely stiff. The results indicate that computational fluid dynamics can be used to estimate the added mass of human swimmers. For the future, unsteady effects of human swimming hydrodynamics should be investigated. [For this reviewer, the difference between the two measures/estimates of 22.5% is unacceptable.]

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