The key to stable coupling is matching physical response times and numerics. A simple rule of thumb:
$$\tau_c \approx \frac{\Delta t}{\zeta}$$
Where $\Delta t$ is the coupling step and $\zeta$ is your relaxation factor.
Tutorials
ICFD to FSI in LS-DYNA: Part 3 - Coupling Stability
Set the timestep and relaxation to avoid oscillation.
Related posts
FSI Basics: From Interfaces to Data Transfer
Foundation steps for a reliable fluid-structure coupling.
Simulation Smells: Early Warning Signals
Small cues that suggest a model is headed for instability.
Time Step Sanity Checks
A quick workflow for evaluating dt before expensive runs.