TY - JOUR
T1 - A constant parameter time domain model for dynamic modelling of multi-body system with strong hydrodynamic interactions
AU - Zou, Meiyan
AU - Chen, Mingsheng
AU - Zhu, Ling
AU - Li, Lin
AU - Zhao, Wenhua
PY - 2023/1/15
Y1 - 2023/1/15
N2 - It is well known that direct evaluation of the wave-induced dynamics of floating structures by Cummins equation is time-consuming due to the convolution integrals. Particularly, for a multi-body system, a complete matrix of the impulse response functions, namely the kernel of the convolution integral in Cummins equation, is required as the cross-coupling terms in the hydrodynamic matrices are important in accurately evaluating the dynamic responses, resulting in increased computation time. Rather than solving the convolution kernel, state-space models have been adopted as an alternative, working well for single body cases. However, it has the disadvantage of numerical instability, which may cause significant errors for strongly resonant phenomena, e.g. in the multi-body interactions. To overcome this issue, the practise is to introduce a damping lid to the free surface in the gap between multiple bodies in frequency domain. Based on the hydrodynamic coefficients obtained in the frequency domain, this study presents a time domain model that combines the damping lid method and statespace model, resulting in a Constant Parameter Time Domain Model (CPTDM). Due to the nature of the time domain model, it is possible to account for nonlinear viscous damping, wherever it is appropriate. The finding shows that the damping lid method helps to stabilize the numerical simulation of the multi-body system which undergoes gap resonances. It is found that a larger damping lid factor favors the decaying of the impulse response functions and the development of lower-order state-space models. The developed CPTDM is found to work well for different wave frequencies and wave headings, with better accuracy and higher efficiency than AQWA's timedomain simulations. Particularly, at the resonant frequency, the developed CPTDM still retains good accuracy as compared with the RAO-based responses.
AB - It is well known that direct evaluation of the wave-induced dynamics of floating structures by Cummins equation is time-consuming due to the convolution integrals. Particularly, for a multi-body system, a complete matrix of the impulse response functions, namely the kernel of the convolution integral in Cummins equation, is required as the cross-coupling terms in the hydrodynamic matrices are important in accurately evaluating the dynamic responses, resulting in increased computation time. Rather than solving the convolution kernel, state-space models have been adopted as an alternative, working well for single body cases. However, it has the disadvantage of numerical instability, which may cause significant errors for strongly resonant phenomena, e.g. in the multi-body interactions. To overcome this issue, the practise is to introduce a damping lid to the free surface in the gap between multiple bodies in frequency domain. Based on the hydrodynamic coefficients obtained in the frequency domain, this study presents a time domain model that combines the damping lid method and statespace model, resulting in a Constant Parameter Time Domain Model (CPTDM). Due to the nature of the time domain model, it is possible to account for nonlinear viscous damping, wherever it is appropriate. The finding shows that the damping lid method helps to stabilize the numerical simulation of the multi-body system which undergoes gap resonances. It is found that a larger damping lid factor favors the decaying of the impulse response functions and the development of lower-order state-space models. The developed CPTDM is found to work well for different wave frequencies and wave headings, with better accuracy and higher efficiency than AQWA's timedomain simulations. Particularly, at the resonant frequency, the developed CPTDM still retains good accuracy as compared with the RAO-based responses.
KW - Gap resonance
KW - Damping lid method
KW - Constant parameter time domain model
KW - Impulse response function
KW - State-space model
KW - SIDE-BY-SIDE
KW - OVER DECK INSTALLATION
KW - RELATIVE MOTIONS
KW - PERFORMANCE
KW - BARGES
KW - FORCES
KW - PISTON
KW - FLNG
UR - http://www.scopus.com/inward/record.url?scp=85143858554&partnerID=8YFLogxK
U2 - 10.1016/j.oceaneng.2022.113376
DO - 10.1016/j.oceaneng.2022.113376
M3 - Article
SN - 0029-8018
VL - 268
JO - Ocean Engineering
JF - Ocean Engineering
M1 - 113376
ER -