Investigation of a ship resonance through numerical simulation
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Investigation of a ship resonance through numerical simulation * S. S. Kianejad 1, Hossein Enshaei 1, Jonathan Duffy 1, Nazanin Ansarifard 1 1. Australian Maritime College, University of Tasmania, Launceston, TAS, 7250, Australia (Received October 14, 2018, Revised February 18, 2019, Accepted March 28, 2019, Published online April 19, 2019) ©China Ship Scientific Research Center 2019 Abstract: Understanding dynamic stability of a ship at a resonance frequency is important because comparatively smaller external forces and moments generate larger motions. The roll motion is most susceptible because of smaller restoring moments. Most studies related to the failure modes such as parametric roll and dead ship condition, identified by second generation of intact stability criteria (SGISC) are performed at a resonance frequency. However, the nature of resonance, where the model experiences an incremental roll motion, has not been well understood. In this study, nonlinear unsteady computational fluid dynamics (CFD) simulations were conducted to investigate the resonance phenomenon using a containership under a sinusoidal roll exciting moment. To capture the complexity of the phenomenon, simulations were conducted over a range of frequencies to cover the resonance frequency including lower and higher amplitudes. In addition to the resonance frequency, the phase shift between roll exciting moment and roll angle, as well as the phase difference between acceleration and roll angle, were found to have significant effects on the occurrence of resonance. Key words: Resonance, Harmonic excited roll motion, Natural frequency, Phase shift, Phase difference
Introduction A deep understanding of a ship’s responses in calm and regular wave conditions can assist predicting ship responses in a realistic irregular wave sea condition[1]. Nowadays, improvement of computational capabilities and advancement in non-linear ship dynamics, have enabled more complex analysis of dynamic stability. Second generation intact stability criteria (SGISC) were proposed by international maritime organization (IMO) which defined several failure modes. These phenomena are parametric roll, pure loss of stability, surf-riding and broaching, dead ship condition and excessive accelerations. Resonance can be experienced in some of the failure modes such as parametric roll and dead ship condition where a ship experiences an incremental roll angle and in the worst cases a large generated roll angle endangers safety of the ship. The parametric roll occurs in the head and following sea condition, where an encounter frequency is twice the ship’s roll natural frequency. However, in the quartering and beam sea Biography: S. S. Kianejad (1986-), Male, Ph. D., E-mail: [email protected] Corresponding author: S. S. Kianejad, E-mail: [email protected]
conditions, resonance occurs if the encounter frequency matches the ship’s natural frequency[2]. Investigation of the parametric roll and dead ship condition were performed at resonance frequ
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