Abstract
Oil dampers are indispensable devices for vibration suppression, but their nonlinear behavior makes it difficult to theoretically determine their damping characteristics. For that reason, the damping coefficient for oil dampers has conventionally been handled by introducing an experimentally determined constant into theoretical equations. In other words, the characterization of oil dampers has ultimately relied on experimentation. Fortunately, if the damping oil is a Newtonian Žuid, the Navier-Stokes equations are able to accurately describe its movement. In our previous study,the Navier-Stokes equations were solved using the finite difference method and the damping coefficient was accurately calculated for an annular-channel-type oil damper. In this paper, we report the damping and added mass characteristics of the commonly used oil dampers, the piston-hole-type and bypass-pipe-type dampers, obtained using the finite difference method as in the previous report. The most basic design formula indicates that the damping coefficients for these dampers are the same when the Žow paths are equal in length; however, it was demonstrated in this study that the damping characteristics of these dampers differ greatly depending on the shape of the convective vortex generated in the cylinder. The immersed boundary method was used in the present numerical analysis because the boundary of the Žuid to be analyzed is surrounded by fixed and moving walls.
