This PhD project at Université Grenoble Alpes investigates the collective motions of aquatic organisms, focusing on the interplay between hydrodynamic forces and cognitive (social) behaviors across a wide range of Reynolds numbers. The research aims to bridge the gap between social models of fish schooling and hydrodynamic simulations by developing advanced numerical methods that couple cognitive behavior with full hydrodynamics computations, particularly using the Navier–Stokes equations. The project is highly interdisciplinary, involving three leading laboratories on the Grenoble campus: LIPhy (physics at disciplinary interfaces), ELAN at INRIA Grenoble (numerical modeling and simulation), and LEGI (fluid mechanics). The student will be administratively hosted at LIPhy but will collaborate closely with all three labs and participate in a two-month research stay at the University of Genoa in Italy. The research will address key questions such as how hydrodynamic interactions among individuals affect group organization, the transition between social and hydrodynamic dominance, the effects of limited perception on group cohesion, and the energetic optimization of collective swimming. The project will also develop efficient computational fluid dynamics (CFD) algorithms to simulate large groups of interacting swimmers. The position is funded for 36 months under the Marie Skłodowska-Curie COFUND PhD@Tec21 Programme, offering a competitive salary, full social security, health insurance, and additional benefits such as training, networking, and support for international students. Candidates should have a Master's degree in Physics (or equivalent), strong analytical and programming skills (C/C++), and a keen interest in interdisciplinary research at the interface of physics, applied mathematics, and computer science. The application deadline is February 28, 2026. For more information and to apply, visit the PhD@Tec21 website or contact the management board.