simulation result reveals lower velocity than the experimental one, the tendency of the higher velocity than the theoretical one for the narrow gap is qualitatively similar to that in the experiment. Thus, the present simulation also indicates the presence of the additional narrow-gap repulsive force.

For an undeformed spherical bubble at small but non-zero Reynolds numbers $0<{\rm Re}\ll 1$, using the solutions to the equation set (\[eq:cont\_st\])–(\[eq:far\_st\]), we can also evaluate the inertia effect on the migration velocity $V_{B3}={\rm Re}\ V_{B3}^{({\rm Re})}$ from $$F_M^{({\rm Re})}=
\frac{1}{2}
\int_{{\cal V}}\!\!\!{\rm d}^3{\bm x}\ 
({\bm e}_3-{\bm u})\cdot\{({\bm U}\cdot\nabla){\bm U}\},
\label{eq:fmre_st}$$ $$\frac{V_{B3}^{({\rm Re})}}{V_{B1}}=\frac{F_M^{({\rm Re})}}{F_{DC}},
\label{eq:vb3re_st}$$ where ${\cal V}$ stands for the entire volume of liquid around the bubble. The force expression (\[eq:fmre\_st\]) is theoretically justified for the case that the wall is placed within a Stokes expansion region, i.e., $O({\rm Re})< \kappa$ ([@vas1976]). Figure \[fig:migvel\_inert\] shows the inertia-driven migration velocity as a function of $\kappa$. The simulated profile is globally consistent with the analytical solution ([@mag2003]) even for the narrow gap $\kappa\sim 1$, as opposed to the profile of the deformation-induced migration velocity in figure \[fig:migvel\_comp\_exp\]. It should be noticed that the expression (\[eq:fmca\_st\]) of the deformation-induced lateral force is written in a surface integral 