Sea snakes are air-breathing aquatic animals. They have lungs. When diving, the volume of their lungs changes with depth, making them non-neutrally buoyant at least for a part of the dive. Gravity-buoyancy imbalance has to be compensated by hydrodynamic means. Moreover, the center of buoyancy (xb) and the center of mass (xcm) may not coincide, and in this case the resulting couple has to be compensated by hydrodynamic means as well.
Similar to many other elongated swimmers, sea snakes propel themselves by lateral deformation waves propagating along their bodies (nose to tail) faster than they swim. As opposed to other elongated swimmers, sea snakes also twist their tails in coordination with the lateral wave. This study attempts to quantify the hydrodynamic lift and couple this type of propulsion can generate, utilizing the framework of elongated body theory originally developed by J. Lighthill.
The quantitative results are validated through the existing data of buoyancy states sea snakes can swim at, which appear to fit. The values of hydrodynamic couple cannot be validated due to absence of relevant data, however they appear to be too small. Additional methods of dealing with excessive pitching moment are proposed.
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