engleski

Investigation of vibration characteristics of an energy saving device of pre-swirl stator type

Marine transportation is permanently oriented to the reduction of fuel consumption and nowadays this is even more pronounced due to stringent rules and regulations leading to the reduced ship environmental footprint. For this purpose, there are different technical solutions and operational strategies at disposal. Typical technical solution that reduces ship total power needs (particularly for the propulsion) is the Energy Saving Device (ESD), i.e. special hydrodynamically designed appendage installed on the ship aft body. There are different types of ESDs as for instance ducts, flow control fins (FCFs), pre swirl stators (PSSs), propeller boss cap fins, Costa bulbs, rudder fins, etc., and their design procedures differ from each one to another. If PSS is considered, from a structural point of view, beside its yielding and buckling capacities relevant dynamic properties should be ensured in order to reduce fatigue risks and probable damage accumulation. Energy saving devices could be exposed to different phenomena, as for instance Motion Induced Vibrations (MIV), Vortex Induced Vibrations (VIV) and Turbulence Induced Vibrations (TIV). Proper design from the vibration viewpoint includes natural vibration analysis of PSS fins and comparisons with relevant loadings in order to avoid frequency overlapping, i.e. resonant behavior. In this work the procedure is illustrated on the pre-swirl stator of a tanker. Several approaches to determine PSS fin natural frequencies were examined ranging from approximate procedures to sophisticated FEM approaches combined with different options to account for the effect of added mass. The obtained responses are compared with VIV frequencies and propeller blade frequencies. Special attention is paid to VIV frequency determination where approximate expressions are validated against computational fluid dynamics (CFD) approach.

Energy Saving Device ; Pre-Swirl Stator ; Added mass ; Dynamic response ; FEM ; Potential theory ; CFD

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