Bidirectional coupling of immersed structures, such as colloidal particles or polymer chains, to the surrounding fluid flow has been studied extensively; however, thermal fluctuations in the fluid equations are not usually considered even though they are responsible for Brownian motion. Achieving discrete fluctuation-dissipation balance in the coupled fluid-structure system is not trivial and requires special care in both the fluid solver and the fluid- structure coupling. I will review some approaches, including a hybrid particle- continuum approach that we have developed, and discuss some of the remaining theoretical and numerical challenges.

Joint work with Florencio Usabiaga Balboa and Rafael D. Buscalioni (UAM), and Boyce Griffith (NYU)