S.V. Kiyashko1, V.O. Afenchenko2, A.V. Nazarovsky3

1-3 Institute of Applied Physics of RAS (Nizhny Novgorod, Russia)

In systems with instability and in the presence of nonlinearity, multistability can occur. During the study of processes that can occur in real environments, the problem arises of finding the conditions under which paths arise that lead to some kind of equilibrium state and the search for new stable states. In distributed systems, they can also differ in the spatial structure of the field.

The aim of this work is to experimentally determine the features of the generation of multi-armed standing spiral waves on the surface of a layer of a viscous fluid in an oscillating gravitational field.

The paper presents the results of an experimental study of the process of generation of multi-armed standing spiral waves on the surface of a viscous liquid layer placed in a cell with an inhomogeneous boundary. It has been experimentally shown that if the cell boundary contains triangular inhomogeneities in the form of ledges on the wall, then the excitation front will contain defects that will move towards the center of the cell, which leads to the formation of a multi-armed spiral wave. The process of generation of multi-armed spiral waves is studied depending on the parameters of the inhomogeneity at the boundary. It was found that the most effective inhomogeneity is with a ledge height close to the wavelength of the excited helical structures and at an inclination of the short side to the cell boundary close to a right angle. With an increase in the number of protrusions, spirals with a large number of turns appeared on the boundary. In this case, if the protrusions had the same orientation, then the number of runs is equal to the number of steps on the excitation front, and the direction of twisting of its arms depended on the orientation of the triangular protrusions at the cell boundary. If the protrusions on the boundary had different orientations, then when the excitation front approached the center of the cell, defects of different signs arose. Further, some of the defects annihilated when they encountered defects of a different sign, and as a result, a spiral wave arose with the number of arms equal to the number of remaining defects of the same sign.

It is assumed that the results obtained may be of interest in studying the processes of establishing stable regimes in active media with strong competition and the presence of complex boundaries, as well as in studying the formation of two-dimensional structures from conducting particles capable of scattering electromagnetic waves.

Kiyashko S.V., Afenchenko V.O., Nazarovsky A.V. Multi-armed spiral waves under parametric excitation in a cell with an
inhomogeneous boundary. Nonlinear World. 2022. V. 20. № 4. 2022. P. 30-37. DOI: https://doi.org/10.18127/j20700970-202204-03 (In Russian)

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