A Comparative Study of the Generalized Wagner Model and a Free-Surface RANS Solver for Water Entry Problems
- Charles Charles Monroy (Bureau Veritas) | Sopheak Sopheak Seng (Bureau Veritas) | Louis Louis Diebold (Bureau Veritas) | Alexis Alexis Benhamou (Bureau Veritas) | Sime Sime Malenica (Bureau Veritas)
- Document ID
- International Society of Offshore and Polar Engineers
- International Journal of Offshore and Polar Engineering
- Publication Date
- June 2017
- Document Type
- Journal Paper
- 135 - 143
- 2017. The International Society of Offshore and Polar Engineers
- slamming, CFD, Water entry impact, free-surface RANS solver, generalized Wagner model
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- 36 since 2007
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Correct assessment of entry of a solid through a free surface is important in various hydrodynamic applications. It is especially crucial when dealing with ship motion behavior in high sea states where slamming impacts are likely to occur. There is a wide range of numerical methods designed to compute forces and pressures on the hull triggered by this phenomenon. However, from an industrial perspective, it is important to discriminate between them and find a compromise among CPU time, setup time (i.e., engineering time), and accuracy. This paper aims at comparing the merits of two different classes of methods: potential theory based on a Wagner model and computational fluid dynamics (CFD) based on a finite volume method with a volume-of-fluid (VOF) interface. The numerical results are compared against experimental data from a wave-induced loads on ships (WILS) campaign.
Wave-induced loads on ships (WILS III) was a joint industrial project conducted by the Korea Research Institute of Ships and Ocean Engineering (KRISO) with participation of several academic and industrial partners, including Bureau Veritas. In the frame of this project (see Hong et al., 2014), an experimental campaign was run in order to measure loads on different 2-D sections impacting calm water. This experimental data set is very useful in validating different numerical tools designed to assess slamming loads on a ship. Since the pioneering work of Bishop and Price (1979), the standard practice in ship hydroelastic computations involving slamming events consists of cutting the bow of the ship in several 2-D sections. 3-D computations are too time consuming and there is no adequate simplified model. An example of such a method can be found in De Lauzon, Benhamou, and Malenica (2015), which compares hydroelastic behavior of a ship against an experiment.
Potential flow remains the standard theoretical framework when it comes to assessing slamming loads on a 2-D section of a ship and integrating them in a hydroelastic computation. In De Lauzon, Benhamou, and Malenica (2015), the slamming model is based on a generalized Wagner model (GWM), and elements of this model are shown for the WILS test cases. Several other potential flow models with different levels of complexity and robustness exist (e.g., see Korobkin and Malenica (2005) for a description of the modified Logvinovich model). All the models in this class of methods are very fast, but in our opinion, the GWM model offers a good compromise among accuracy, robustness, and CPU time.
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