Numerical method for the vibration analysis of pre-swirl stator

ABSTRACT

Marine transportation is continuously 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 such as ducts, flow control fins (FCFs), pre swirl stators (PSSs), propeller boss cap fins, Costa bulbs, rudder fins and so on, 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. 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 behaviour. 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 Vortex Induced Vibration (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.

KEYWORDS:

• Energy saving device
• pre-swirl stator
• added mass
• dynamic response
• FEM
• potential theory
• CFD

Acknowledgments

This research was supported by the Croatian Science Foundation under the project ‘Green Modular Passenger Vessel for Mediterranean (GRiMM)’ (Project No. UIP-2017-05-1253) and by the Hyundai Heavy Industries Co., Ltd. within the project ‘A study on the structural integrity of the Energy Saving Devices (ESD) of the type Pre Swirl Stator (PSS) and Flow Control Fin (FCF)’. Also, the funding within the international collaborative project ‘Global Core Research Center for Ships and Offshore Plants’ (GCRC-SOP, No. 2011-0030669), established by the Republic of Korea Government (MSIP) through the National Research Foundation of South Korea (NRF) is greatly acknowledged.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This research was supported by the Croatian Science Foundation (Hrvatska Zaklada za Znanost) under the project ‘Green Modular Passenger Vessel for Mediterranean (GRiMM)’, (Project No. UIP-2017-05-1253) and by the Hyundai Heavy Industries Co., Ltd. within the project ‘A study on the structural integrity of the Energy Saving Devices (ESD) of the type Pre Swirl Stator (PSS) and Flow Control Fin (FCF)’. Also, the funding within the international collaborative project ‘Global Core Research Center for Ships and Offshore Plants’ (GCRC-SOP, No. 2011-0030669), established by the Republic of Korea Government (MSIP) through the National Research Foundation of South Korea (NRF) is greatly acknowledged.