SKM 2021 – scientific programme
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DY: Fachverband Dynamik und Statistische Physik
DY 4: Poster Session II: Nonlinear Dynamics, Simulations and Machine Learning
DY 4.3: Poster
Tuesday, September 28, 2021, 17:30–19:30, P
Interplay of viscosity and surface tension for ripple formation by external laser melting — •Klaus Morawetz1,2, Sarah Trinschek1, and Evgeny Gurevich1 — 1Münster University of Applied Sciences,Stegerwaldstrasse 39, 48565 Steinfurt, Germany — 2International Institute of Physics- UFRN,Campus Universitário Lagoa nova,59078-970 Natal, Brazil
A model for ripple formation on liquid surfaces exposed to an external laser or particle beam and a variable ground is developed. Starting from the Navier Stokes equation the coupled equations for the velocity potential and the surface height are derived with special attention to viscosity. Linear stability analysis provides the formation of a damped gravitation wave modified by an interplay between the external beam, the viscosity, and the surface tension. The resulting wavelengths are in the order of the ripples occurring in laser welding experiments hinting to their hydrodynamical origin. The stability due to the periodic time-dependence of the external beam is discussed with the help of Floquet multipliers showing that the ripple formation could be triggered by an external excitation with frequencies in the order of the repetition rate of the laser. The weak nonlinear stability analysis provides ranges where hexagonal or stripe structures can appear. The orientation of stripe structures and ripples are shown to be dependent on the incident angle and a minimal angle is reported. Two models are presented to couple the external current to the gradient of the surface. Numerical simulations confirm the findings. arXiv:2107.02651