Simulation of a swimming dogfish shark

Abstraction: Julia/WaterLily.jl CFD simulation of fish locomotion using immersed boundary

Key points:

• WaterLily.jl uses an immersed boundary method with automatic differentiation; only a signed distance function (SDF) is needed — no mesh generation required
• Shark geometry is modeled via Lighthill's slender-body theory: a thickness distribution plus a lateral traveling wave with wavelength ~1.4x body length and Strouhal number St=0.3
• Reynolds number Re=1e4 sets fluid viscosity; simulation shows vorticity trailing only from the tail, indicating efficient locomotion with no mid-body eddies
• Force measurement via surface integral ∮nds reveals thrust force at double the swimming frequency (peak each time tail crosses centerline) and side force at the base frequency
• Entire notebook runs in Julia with WaterLily, StaticArrays, Interpolations, Plots, and Images; Pluto notebook available for interactive exploration

Connections: Julia · Waterlily Jl · Computational Fluid Dynamics · Scientific Computing · Numerical Simulation

Source: https://julialang.org/blog/2021/08/sharks/