Numerical Model of Sarsia tubulosa Jellyfish
Developing a numerical model to explore efficient kinematics of the prolate Sarsia tubulosa jellyfish
E. van der Weide (TU Delft - Mechanical Engineering)
B. Font – Mentor (TU Delft - Ship Hydromechanics)
Artur K. Lidtke – Mentor (Maritime Research Institute Netherlands (MARIN))
A.J.L.L. Buchner – Graduation committee member (TU Delft - Fluid Mechanics)
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Abstract
Jellyfish are among the most energy-efficient swimmers in the animal kingdom, driven by unsteady interactions between bell deformation, velar control, and vortex formation. Accurately modelling these mechanisms remains challenging, as existing numerical approaches often rely on simplified geometries, reduced dimensionality, or neglect of velar kinematics, limiting their ability to capture realistic three-dimensional flow dynamics.
This study presents a three-dimensional numerical model of Sarsia tubulosa implemented in the CFD solver WaterLily. The geometry is represented using time-dependent NURBS-based control points, enabling biologically realistic bell deformation and active velar motion. A Cartesian grid combined with the Boundary Data Immersion Method avoids remeshing and allows efficient simulation of complex, time-varying kinematics. Hydrodynamic forces are obtained directly from the incompressible Navier–Stokes equations, avoiding reduced-order approximations.
The model reproduces key propulsion mechanisms, including jet formation and vortex shedding, but discrepancies in force and velocity indicate limitations in physical fidelity. In particular, the absence of fluid–structure interaction, elastic effects, and tentacle-induced drag leads to idealised dynamics and phenomena such as velocity overshoot. This highlights that prescribed kinematics alone are insufficient to fully capture jellyfish propulsion.
Overall, the model provides an efficient framework for analysing three-dimensional flow structures and kinematic trends in jellyfish swimming. However, its use for quantitative efficiency assessment is limited, and future work should focus on incorporating fluid–structure interaction and passive biological effects to improve physical realism.
Code is available in the reproducibility repository that was added as link.:
https://github.com/evanvanderweide/WaterLily-Sarsia-tubulosa-Jellyfish-Modelling