Effects of nonlinear FK (Froude- Krylov) and hydrostatic restoring forces on arctic-spar motions in waves

• Published in: International Journal of Naval Architecture and Ocean Engineering
• Main Authors: HaKun Jang, MooHyun Kim
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2020
• Subjects: Arctic spar; Conical platform; Nonlinear hydrostatic restoring force; Nonlinear froude-krylov forces; Mathieu instability; Ocean engineering; TC1501-1800; Naval architecture. Shipbuilding. Marine engineering; VM1-989; Arctic; Mathieu
• Online Access: https://doi.org/10.1016/j.ijnaoe.2020.01.002; https://doaj.org/article/65cd735a561e4053b0b61456a53d96eb

An Arctic Spar is characterized by its conical shape near the waterline. In this case, the nonlinear effects from its irregular hull shape would be significant if there is either a large amplitude floater motion or steep wave conditions. Therefore, in this paper, the nonlinear effects of an Arctic Spar are numerically investigated by introducing a weakly nonlinear time-domain model that considers the time dependent hydrostatic restoring stiffness and Froude-Krylov forces. Through numerical simulations under multiple regular and irregular wave conditions, the nonlinear behavior of the Arctic Spar is clearly observed, but it is not shown in the linear analysis. In particular, it is found that the nonlinear Froude-Krylov force plays an important role when the wave frequency is close to the heave natural frequency. In addition, the nonlinear hydrostatic restoring stiffness causes the structure's unstable motion at a half of heave natural period.