  It is known that in a certain case, the secondary Bjerknes force, which is a
radiation force acting between pulsating bubbles, changes, e.g., from
attraction to repulsion as the bubbles approach each other. In this paper, a
theoretical discussion of this phenomenon for two spherical bubbles is
described. The present theory based on analysis of the transition frequencies
of interacting bubbles [M. Ida, Phys. Lett. A 297, 210 (2002)] provides an
interpretation, different from previous ones (e.g., by Doinikov and Zavtrak
[Phys. Fluids 7, 1923 (1995)]), of the phenomenon. It is shown, for example,
that the reversal that occurs when one bubble is smaller and another is larger
than a resonance size is due to the second-highest transition frequency of the
smaller bubble, which cannot be obtained using traditional natural-frequency
analysis.
