Beyond Dry Flocking: Shape-Dependent Hydrodynamic Alignment
Abstract
Flocking results from dynamical alignment among neighbors in a collection of active self-propelling objects. The intervening medium, typically a fluid, however, is not considered to be important for alignment, except for acting as a momentum sink. The flocking system is therefore described as momentum nonconserving "dry" active matter. Here we investigate a confined system of self-propelled Marangoni swimmers where feedback from the fluid medium, which crucially depends on the shape of the swimmers, influences their alignment. Using up to thirty partially camphor-coated triangular paper boats as polar swimmers, we uncover a disorder-to-order transition, and an unusual re-entrant order-to-disorder transition, as functions of camphor concentration and swimmer density, respectively. We reproduce these transitions by formulating a reaction-diffusion model for the camphor field, coupled to the swimmer dynamics, where propulsion forces arise from surface tension gradients. The shape-dependent hydrodynamic interaction discussed here could be central to efficient flocking in living organisms too.
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BibTeX
@misc{thakur2026beyond,
title = {{Beyond Dry Flocking: Shape-Dependent Hydrodynamic Alignment}},
author = {Abhishek Thakur and Taniya Khatun and Soumyadeep Kundu and Nitin Kumar and P. Parmananda and Anirban Sain},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.10709},
eprint = {2610.10709},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.10709},
}
RIS
TY - UNPB
TI - Beyond Dry Flocking: Shape-Dependent Hydrodynamic Alignment
AU - Abhishek Thakur
AU - Taniya Khatun
AU - Soumyadeep Kundu
AU - Nitin Kumar
AU - P. Parmananda
AU - Anirban Sain
PY - 2026
DA - 2026/10/07
PB - arXiv
DO - 10.48550/arxiv.2610.10709
UR - https://arxiv.org/abs/2610.10709
AB - Flocking results from dynamical alignment among neighbors in a collection of active self-propelling objects. The intervening medium, typically a fluid, however, is not considered to be important for alignment, except for acting as a momentum sink. The flocking system is therefore described as momentum nonconserving "dry" active matter. Here we investigate a confined system of self-propelled Marangoni swimmers where feedback from the fluid medium, which crucially depends on the shape of the swimmers, influences their alignment. Using up to thirty partially camphor-coated triangular paper boats as polar swimmers, we uncover a disorder-to-order transition, and an unusual re-entrant order-to-disorder transition, as functions of camphor concentration and swimmer density, respectively. We reproduce these transitions by formulating a reaction-diffusion model for the camphor field, coupled to the swimmer dynamics, where propulsion forces arise from surface tension gradients. The shape-dependent hydrodynamic interaction discussed here could be central to efficient flocking in living organisms too.
ER -