This paper is a study of a nonlinear dynamical system with 3/2 degrees of freedom consisting of a point vortex and an unsteady background flow. This background flow consists of two parts, a steady and a (quasi)periodic with two sinusoidal components with different frequencies and amplitudes. The considered system with a separatrix loop in the phase portrait is the simplest model of chaotic scattering of passive tracers on a topographic vortex, captured by a seamount, in the ocean. We have found that depending on variation of amplitudes of two sinusoidal components, the passive tracers enters and leaves the vortex region in portions. The frequency of escape and the size of such portions depend on the parameters of the background flow. It is shown that the structure of the fractal-like scattering function changes at low levels through the formation (disappearance) of segments according to two mechanisms, the action of which is determined by the relation between two frequencies of the perturbation.

本文研究了由点涡和非定常背景流组成的3/2自由度非线性动力系统。该背景流由两部分组成，一个是稳定的，一个是（准）周期性的，具有两个具有不同频率和幅度的正弦分量。所考虑的在相图中具有分离环的系统是无源示踪剂在海洋中由海山捕获的地形涡旋上的混沌散射的最简单模型。我们发现，根据两个正弦分量幅度的变化，无源示踪剂部分地进入和离开涡流区域。逃逸频率和这些部分的大小取决于背景流的参数。