Modified wake oscillator model for vortex-induced motion prediction of low aspect ratio structures

ABSTRACT

Floating structures, such as Spar platform, are likely to experience significant motions while operation due to Vortex-induced Motion (VIM). The main features of VIM include aspect ratio and mass ratio of the structure. This paper focuses on further development of a previously published semi-empirical method called wake oscillator model (WOM) for VIM, which aims to derive a mathematical correlation in modelling all features of the phenomenon. Analytical solution is proposed to coupled WOM and structure oscillator model based on the Van der Pol equation by integrating mass ratio, m* = 4.36, and various low aspect ratios between 0.3 and 2.0. Additionally, a new approach was initiated to embed several empirical parameters linked to the aspect ratio in the existing WOM. It was found the aspect ratio parameter in the modified WOM significantly affected the performance of the model for estimation of VIM on floating structures.

KEYWORDS:

• Wake oscillator model
• vortex-induced motions
• low aspect ratio
• Van der Pol equation

Notes on contributors

Mohd Asamudin A Rahman is a senior lecturer at School of Ocean Engineering, Universiti Malaysia Terengganu. His expertise is on hydrodynamics of offshore structures, fluid structure interaction and computational fluid dynamics (CFD).

Wan Norazam Wan Hussin was a postgraduate student at Universiti Malaysia Terengganu. His study is on analytical modelling of vibration prediction on offshore structure.

Mohd Hairil Mohd is a senior lecturer at School of Ocean Engineering, Universiti Malaysia Terengganu. His research area is on subsea pipeline engineering.

Fatimah Noor Harun is a senior lecturer at School of Informatics and Applied Mathematics, Universiti Malaysia Terengganu. She involved in mathematical modelling, applied and computational mathematics.

Lee Kee Quen is a lecturer at MJIT Universiti Teknologi Malaysia. Her research area is on the vortex-induced vibrations (VIV).

Jeom Kee Paik is a Distinguished Professor of Marine Technology, Department of Mechanical Engineering, Univesity College London, UK. He is also a Professor of Safety Design and Engineering at Pusan National University, South Korea. He is currently Director of The Korea Ship and Offshore Research Institute (Lloyd's Register Foundation Research Centre of Excellence), Busan, Korea.

ORCID

Mohd Asamudin A Rahman http://orcid.org/0000-0001-9079-8498

Additional information

Funding

This work was supported by the Ministry of Higher Education Malaysia under Fundamental Research Grant Scheme FRGS/1/15/59416.