A STUDY OF THE ADDED MASS OF VIBRATING CYLINDRICAL SHELL IN WATER

A method for determining the added mass of cylindrical shells, such as of propeller-duct structures, vibrating in water is discussed. The velocity potentials of the surrounding water are calculated both analytically and numerically using a finite element program. The added mass of an elastic body can be expressed as a generalized mass so that the total kinetic energy of vibrating water might be equivalent. The dependence of the added mass on the vibration modes may be considered by introducing J factors that are similar to the three-dimensional correction factors conventionally used in the analysis of ship hull vibration. A modeling of the added water using a lumped mass system combined with J factors has been applied to the eigen-value analysis of a simple cylindrical shell and a MIDP (Mitsui Integrated Duct Propeller). The proposed procedure has proven to give enough accurate natural frequencies comparable to those given by direct coupled modeling of fluid-structure interaction. The calculated vibration modes and frequencies of the MIDP agreed fairly well with the measured values.