Distinguished Seminar in Computational Science and Engineering

Distinguished Seminar in Computational Science and Engineering

May 16, 2024, 12 PM

Conference Room 45-432 in Building 45 or Zoom Webinar

 

Stochastic Dissipative Euler’s equations

Pep Español
Full Professor in Applied Physics
Departamento de Física Fundamental
Universidad Nacional de Educación a Distancia in Madrid

Abstract: 

The motion of a rigid body is described in Classical Mechanics with the venerable Euler’s equations which are based on the assumption that the relative distances among the constituent particles are fixed in time. Real bodies, however, cannot satisfy this property, due to elastic behaviour and, more subtly, thermal fluctuations. In this talk, Prof. Pep Español will show how one can use the theory of coarse-graining to generalize Euler’s equations for a free body in order to describe dissipative and thermal fluctuation effects in a thermodynamically consistent way. The resulting stochastic differential equations governing the evolution of the orientation and shape of the body predict a number of interesting effects: 1) A nanoscopic free body will explore all orientations with the principal axis performing a Brownian motion on the sphere — essentially, it “spins” without any angular momentum. 2) A spinning body will always end up spinning around the major axis, a phenomenon known as precession relaxation, that explains why the vast majority of asteroids are found in pure rotation. Precession relaxation is also responsible for killing the Dzhanibekov effect — the surprising flipping of orientation of a body spinning around the intermediate axis as predicted by classic Euler’s equations. 3) In a central gravitational field, a body will eventually achieve tidal locking, synchronizing its rotation period with its orbit period, as seen with the Moon always presenting the same face to Earth.

Bio:

As a theoretical physicist, Prof. Pep Español’s work bridges the gap between the detailed molecular understanding of matter and its simplified, mesoscopic representations. His research focuses on Soft Matter, complex fluids, and the development of coarse-grained models to capture the essence of complex molecular structures. He has experience in simulation particle methods, which he applies to the study of the hydrodynamics of both simple and complex fluids. One important contribution to the field has been the enhancement of the Dissipative Particle Dynamics method, a popular approach for simulating coarse-grained models of complex fluids. His passion lies in probing the theoretical foundations of these models and ensuring their thermodynamic consistency. This involves a meticulous examination of the principles underlying new simulation techniques that stem from coarse-graining processes. Recently, his interest has expanded towards understanding the dynamics of interacting bodies, particularly focusing on how their orientation and shape influence motion, through advanced coarse-graining theories.

Prof. Pep Español earned his PhD in Physics in 1992 from the Universidad Nacional de Educación a Distancia (UNED) in Madrid. Following this, he embarked on a postdoctoral stay at the University of Cambridge from 1993 to 1994, holding a Marie Curie Fellowship. During his time at Cambridge, he was part of the Polymer and Colloids Group at the Cavendish Laboratory. His academic career continued at UNED, where he served as an Assistant Professor from 1998 to 2010. In 2009, he took a sabbatical leave to join the Freiburg Institute for Advanced Studies (FRIAS) as a Senior Fellow. Since 2010, he has held the position of Full Professor in Applied Physcs in the Department of Fundamental Physics at UNED. Additionally, Prof. Pep Español lead a Research Group focused on “Fluids and Soft Matter” at UNED.

 

Dissipative Euler's equations
Pep Español
Full Professor in Applied Physics
Universidad Nacional de Educación a Distancia in Madrid