Numerical simulation of the slamming phenomenon of a wave-piercing trimaran in the presence of irregular waves under various seagoing modes

Abstract

Trimaran vessels have been of great interest to naval architects, due to their large deck space, low resistance at high speeds and stability. Meanwhile, determination of their slamming forces in the presence of highly nonlinear waves has always been a challenge for the structural designers. However, because of novelty and complexity of their hulls, there is insufficient information in this regard, which necessitates suitable effort in filling this gap. Accordingly, in this article, using Flow-3D, a commercial computational fluid dynamics code, seakeeping of a wave-piercing trimaran is simulated in the presence of irregular waves via standard Bretschneider spectrum in sea state 5 in various seagoing modes. These modes include two speeds and two waves with encountering angles of head sea and bow quartering sea. For validation purposes, seakeeping of a trimaran vessel and water entry of a wedge-shaped section are investigated and numerical results are compared against experimental and analytical data. Good compliance of the results confirms the accuracy of the proposed numerical model. In the slamming analysis of the considered trimaran, using the relative vertical velocity of the bow section from the seakeeping analysis, the water entry problem is investigated for the most severe slamming mode. Pressure distribution caused by water entry and instantaneous impact pressure, known as structural design pressure, is computed. The exerted slamming pressure on the bottom and bow flare region is determined to be 4300 and 2100 Pa, respectively. Results indicate that during slamming phenomenon, the maximum pressure exerted on the vessel’s floor occurs at the time of impact at which the pressure coefficient is 4.4. Accurate assessment of the vessel’s vertical velocity from the start of water entry until the water surface rise-up, and the utilized technique considered for slamming phenomenon in more realistic sea condition, can be considered as important features of this study.