Implementing the simulation of a flexible fish fin using IBFE method

[SHfei Lee]

hello,

everyone.

I am currently simulating fish swimming using IBAMR. I have implemented self-propulsion  using eel3d, but in reality, structures like fish fins undergo passive deformation. I want to use IBFE to simulate a rigid fish body and flexible fish fins. However, on GitHub, I found that IBFE is not as straightforward as eel3d. I am confused about the meanings and functions of ex0-ex11 on GitHub's IBFE repository because each "ex" file contains both input2d and inout3d files. How should I interpret these contents? 

Thank you.

[Boyce Griffith]

For IBFE models of flexible structures, you will need to provide a mechanics model that is specified using a stress tensor. In IBFEMethod, this is done using the 1st Piola-Kirchhoff stress (which we usually call PP). You need to provide a function that evaluates PP as a point wise function.

To make the swimmer swim, you will need to make it generate some active deformations. I would think about this from the standpoint of modeling active muscle contraction. Standard approaches are so-called active stress and active strain models. Here is a paper: https://link.springer.com/article/10.1007/s10659-011-9351-4.

You could also take a look at some of the work by Alex Hoover, Laura Miller, and others using IBAMR to model jellyfish. Here is a representative paper: https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/quantifying-performance-in-the-medusan-mechanospace-with-an-actively-swimming-threedimensional-jellyfish-model/0BC2DFD5BE57E3C79563D89DC5AA7E30.

Let me know if there are specific questions that we can try to answer about setting up these kinds of models. It mostly boils down to specifying the geometry (mesh) and material properties (stress function). You might also want to include some extra body forces.

— Boyce

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