Numerical Investigation of Water-Entry Problems Using IBM Method
- Liang Yang (City University London) | Hao Yang (City University London) | Shiqiang Yan (City University London) | Qingwei Ma (City University London)
- Document ID
- International Society of Offshore and Polar Engineers
- International Journal of Offshore and Polar Engineering
- Publication Date
- June 2017
- Document Type
- Journal Paper
- 152 - 159
- 2017. The International Society of Offshore and Polar Engineers
- computational fluid dynamics (CFD), Immersed Boundary Method (IBM), Water entry, numerical simulation
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- 54 since 2007
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This paper presents a systematic numerical investigation of the water-entry problems associated with dropping triangular wedges or ship sections that uses an incompressible Immersed Boundary Method (IBM). In the IBM, the solid bodies are treated as an additional phase, and their motions are solved by a unified equation similar to those governing the air and water flows; a level-set technique is used to identify the air-water interface, and a projected Heaviside function is developed to identify the fluid-solid interface. For the purpose of comparison, a corresponding numerical simulation with or without consideration of the compressibility of the fluids is also carried out by using OpenFOAM. All results are compared with the experimental data provided by the comparative study of ISOPE 2016. The results suggest that the unified equation in the IBM can well predict the motion of the dropping bodies; the IBM can capture the entrapped air and produce an impact pressure and local and global forces that agree fairly well with the experimental data.
The water entry is a complex and nonlinear fluid-structure interaction (FSI) problem involving many physical phenomena such as air trapping, spray, and extreme free-surface deformation. A large impulsive pressure and slamming forces possibly lead to the damage of the offshore structure and are of interest for engineering purposes. Both numerical modelling and experiments have been conducted for the prediction and validation of the water-entry problems, in particular the effect of the compressibility, aeration, and hydro-elasticity (Miyamoto and Tanizawa, 1985; Okada and Sumi, 2000; Huera-Huarte et al., 2011; Ma et al., 2014, 2015; Mai et al., 2015). Against such a background, the International Hydrodynamic Committee of the International Society of Offshore and Polar Engineers has proposed a comparative numerical study of such an issue, in which the experimental data from the third iteration of the Wave Induced Loads on Ships (WILS) Joint Industry Project (MOERI, 2013) are provided. This paper presents our numerical results for the comparative study, and therefore only relevant reviews of numerical approaches have been given herein.
Great effort has been devoted to deriving analytical solutions and empirical formulas to predict the slamming forces associated with the water-entry problems, e.g., Wagner (1932), Dobrovol’skaya (1969), Armand and Cointe (1986), and Cointe (1991), which benefit the design practices although such solutions may be suitable only for simple-geometry or wedge-type bodies. However, the body shapes and impact angles, in particular the structures with a small deadrise angle, are important for the impact pressure development and free surface formation near the impact surface, as observed by the experiment (Okada and Sumi, 2000; Huera-Huarte et al., 2011). Due to the limitation of the analytical and empirical methods, the numerical methods have been utilised to solve the engineering problems with more complex geometry.
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