The Spineless Swimmer

In wrapping up this blog about the extraordinary species, Hexabranchus sanguineus, I have decided to explore how the invertebrate sea slug is such a remarkable swimmer through the following research paper:

Title: Swimming Without a Spine: Computational Modeling and Analysis of the Swimming Hydrodynamics of the Spanish Dancer

Authors: Zhihua Zhou and Rajat Mittal

Journal: Bioinspiration & Biomimetics, 13(1), 015001

Hyperlink: https://iopscience.iop.org/article/10.1088/1748-3190/aa9392

Keywords:

Computational fluid dynamics (CFD): a method used to solve fluid flow problems numerically using computer simulations.

Hydrodynamics: The study of the motion of fluids and the forces acting on them.

Vortices: regions within a fluid where the flow is spinning or rotating around an axis

Drag reduction: the reduction of resistance to movement through a fluid

Lift generation: the creation of an upward force that opposes the force of gravity

Parapodia: fleshy protrusions along the sides of the Spanish Dancer’s body that are used for swimming

The study aims to analyze the unique swimming behavior of the Spanish Dancer, a marine gastropod that uses parapodia to swim, and investigate the hydrodynamics of its movement using computational modeling and analysis. The authors hypothesized that the vortices generated by the Spanish Dancer’s movement play a crucial role in reducing drag and increasing lift, which facilitates its efficient swimming behavior.

Their methods included using CFD simulations to model the hydrodynamics of the Spanish Dancer. They created a 3D model of the animal based on anatomical data, and simulated its swimming motions in water. The simulations allowed them to analyze the flow of water around the animal, including the formation of vortices and the resulting forces of lift and drag. To validate their simulations, the authors compared their results to experimental data from previous studies on the swimming of related animals. They also conducted sensitivity analyses to test the effects of variations in parameters such as swimming speed and body posture on the hydrodynamic performance of the Spanish Dancer. They found that the flapping motion of the parapodia generates complex vortical structures that provide lift and propulsion, while the body deformation helps to maintain stability and control. So the vortices generated by the animal’s movement were crucial in reducing drag and increasing lift. Additionally, the simulations demonstrated that the velocity and direction of water flow along the body of the animal differed depending on the phase of the swimming cycle, indicating that Hexabranchus sanguineus is able to adjust its hydrodynamics to optimize swimming performance. These hydrodynamic mechanisms are unique to the Spanish Dancer and enable it to swim effectively without a spine.The authors also suggest that the research could have implications for the development of new underwater propulsion systems inspired by the Spanish Dancer’s swimming behavior. The study sheds light on the unique and unusual swimming mechanics of the Spanish Dancer, which may inspire new approaches to underwater propulsion in robotics and other engineering applications. Further experiments could explore the specific biomechanics of the slug’s undulations, as well as the ecological factors that have driven the evolution of this unusual swimming behavior.

 

 

Citations

Zhou, Z., & Mittal, R. (2017). Swimming without a spine: computational modeling and analysis of the swimming hydrodynamics of the Spanish Dancer. Bioinspiration & biomimetics, 13(1), 015001. https://doi.org/10.1088/1748-3190/aa9392