Okumura considered the free-interface flow problem using the SLG characteristic finite element method with the Hermite element and the surface tension effect by the CSF method. Murakawa treated a moving boundary problem with triple-junction points. He provided a weak formulation of the problem which implicitly involves the information of the moving boundaries. Moreover, he proposed and analyzed an efficient numerical method for caputuring the moving boundaries. Yamaguchi had by analytic semigroup theory that mind solution of the Cauchy problem of penalized Navier-Stokes equations converges to that of original problem when penalty parameter tends to zero.