ABSTRACT

This paper applies our in-house solver, naoe-FOAM-SJTU to simulate a fixed FPSO-shaped body in focused waves. This benchmark test follows the settings of experiments conducted in the Ocean Basin at Plymouth University's COAST Laboratory. The different headings are considered to figure out how the focused waves influence the fixed model. The values of wave height in different position of the empty wave tank are obtained through computations to compare with the experimental results. The scattered wave height and impact pressure on the hull are provided. The results of the wave and the corresponding pressure on the hull are in CCP-WSI Blind Test Workshop to ensure the accuracy of the method. It is found that the incident wave angle affects the maximum crest height and wave loading.

INTRODUCTION

As for offshore structures, it's essential to study those structures operating under the hostile environment. On the one hand, the designation and operation need to avoid structure damage and loss on work stoppage, thus the severe sea states must be considered. For example, the FPSO in deep sea may encounter with magnificent wave height, which may cause damage to ship bow. On the other hand, the wave-wave interaction may transfer high-frequency energy to the structure. Those wave-induced high-frequencies may cause nonlinear structure behaviors. Therefore, to investigate offshore structures in hostile sea states is necessary.

For the high cost and space limit for experiments, the numerical methods have its advantages to forecast the severe sea states and the wave-structure interactions. However, uncertainty still remains when considering the model fidelity. Thus the numerical simulation based on a benchmark test is required to ensure the accuracy of numerical methods and provide more details for future development of numerical modeling. Many researchers have discussed the nonlinear interaction between the steep waves and offshore structures (Kashiwagi, M., 2000). Yan, S. et al (2015) applied uni-directional focusing waves and a cylinder based on QALE-FEM (Quasi Arbitrary Lagrangian Eulerian Finite Element Method) with FNPT (fully nonlinear potential theory) and OpenFOAM coupled with potential theory. They compared those two methods when simulating the focusing waves and the cylinder. For the Floating Production Storage and Off-loading (FPSO) vessels are commonly used as oil storage and operate system, many studies have been done to discover the wave-structure interaction. Inoue, Y.et al (1993) used FPSO to investigate the effect of short crested waves on low frequency motions of moored tanker. Wu, G.X. and Hu, Z.Z (2004) applied the fully nonlinear potential flow formulation to study interaction between the FPSO and regular waves. As for the development of computer science, the CFD method has its ability to simulate some specific phenomenon. For example, the coupling effects between FPSO and sloshing tanks (Zhuang, Y. and Wan, D.C., 2016) and the extreme wave loading on offshore structures (Westphalen, J. et al., 2014). As the six DOF solving needs lots of cost, as well as to figure out the scattered wave and pressure on structure in detail, Mai, T. et al (2016), Hu, Z.Z. et al (2016) and Ma, Q.W. et al (2015) discussed the interaction between a fixed-body and focused waves.

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