A study on memory effect for ships manoeuvring and oscillating in waves

2019 Fiscal Year Final Research Report

• Project/Area Number: 17K14891
• Research Category: Grant-in-Aid for Young Scientists (B)
• Allocation Type: Multi-year Fund
• Research Field: Naval and maritime engineering
• Research Institution: National Institute of Maritime, Port and Aviation Technology
• Principal Investigator: Ryosuke Suzuki 国立研究開発法人海上・港湾・航空技術研究所, その他部局等, 研究員 (20711328)
• Project Period (FY): 2017-04-01 – 2020-03-31
• Keywords: 波浪中操縦運動 / 6自由度船体運動

Outline of Final Research Achievements

The researcher developed a numerical simulation method to estimate 6 degrees-of-freedom (DOF) motion for ships manoeuvring in waves by focusing on the influence of past ship motion: memory effect, on hydrodynamic forces as the reaction of the ship motion. The researcher clarified the following points by comparison with free-running model tests conducted in this study:
1.The neglection of the memory effect by approximating the hydrodynamic forces with those at a certain frequency is possible to deteriorate estimation accuracy of ship motion.
2.Memory effect functions represented by convolution integration of impulse response functions based on a linear theory, which is common in seakeeping problems, can improve the estimation of ship motion such as wave-induced oscillation, drifting of trajectory and the time-averaged value of speed decrease by waves .

Free Research Field

船舶海洋工学

Academic Significance and Societal Importance of the Research Achievements

これまでの研究は、その簡易性から、波浪中の操縦運動や船体動揺に対する流体による反力をある1つの周波数で代表して、準定常的に扱うことがほとんどであった。本研究の様に、実験との比較からその問題点ならびに、流体反力の過去の履歴の影響度合いを具体的・定量的に示された例はほとんどない。また、開発された波浪中操縦運動計算法は、波浪中において船が備えるべき操縦性能を評価するための基礎的手法になりえる。以上により、本研究で得られた成果は意義があり、重要と言える。