Head-on collision of longitudinal density pulses near phase transition: Insights from numerical simulations

Upon the head-on collision of two longitudinal pulses, the superposition principle breaks down when the system is driven close to a phase transition. This phenomenon has been demonstrated experimentally in lipid membranes and numerically in a van der Waals fluid model. To further investigate collision properties near a phase transition, this work numerically explores the dynamics of nonlinear pulse interactions across different regimes of the fluid model. We show that pulse annihilation does not result from the simplest (second-order) nonlinear approximation. Furthermore, even in the full nonlinear model, longitudinal pulses re-emerge but in a perpendicular direction. Additionally, we demonstrate that collision properties depend on both the stimulus amplitude and the distance between the two stimuli. Notably, an asymmetric collision site may arise when the two stimuli have different amplitudes.