THE STRUCTURAL RESPONSE TO WAVE SPECTRUM AND FATIGUE STRENGTH Of HIGH SPEED ALUMINUM TRIMARAN

本文以頻譜疲勞分析法，探討一高速鋁合金三體船在航行中遭遇不同狀況之波浪作用造成船體應力集中較大的艙間結構應力反應，探討船體服務生命週期在波浪外力作用下，結構件的疲勞損傷及疲勞壽命。 船舶近一生航行於海洋中，除承受船體重量、貨物重量與海水壓力外，波浪負載也為重要議題，船體重載與輕載交互作用，及波浪造成船舶的反覆負載。此反覆負載將造成船體構件的疲勞破壞。特別是鋁合金材料彈性模數約為鋼材之1/3，其疲勞強度遠低於鋼材，且鋁合金電焊周圍之熱效應區材料強度下降30%至50%，過去鋼船結構設計資料發展較為完整，鋁合金船體如參採鋼船結構資料時，除降伏強度以外，疲勞強度也須進一步分析，鋁合金船結構疲勞損傷與疲勞壽命為重要議題。 本文以一1,700噸之高速鋁合金三體船為研究對象，首先建立全船有限元素模型，進行靜態分析與模態分析，並利用法國驗船協會已開發水動力分析軟體，分析船體浸水部分之水動力壓力，透過流體固體介面資料轉為船體浸水面結構入力，進行擬靜態FE-結構分析，取出結構應力敏感區與波浪反應敏感區之應力RAO（Response Amplitude Operators, 反應振幅運算子），據以分析其疲勞強度。波浪頻譜負載之頻率分析範圍為0.2 rad/s至1.8 rad/s，間隔0.1 rad/s，航向角由0°至360°，間隔15°。求解各波頻、航向角下之應力反應振幅運算子RAO，配合北大西洋統計波浪頻度表（JONSWAP Wave Spectrum for North Atlantic Ocean）與ABS波浪分佈資料，搭配鋁合金結構之S-N Curve，以計算結構疲勞壽命。The use of aluminum alloy for ship structures has weight efficiency and good corrosion resistance. Nevertheless, the heat affected zone (HAZ) of aluminum alloy will reduced the material strength noticeably, the fracture toughness and fatigue life of aluminum alloy are much lower than steel. This paper investigated the structural response of a 1,700 tons aluminum alloy trimaran in ocean waves. For the spectral response analysis, we considered that the frequency of waves ranges from 0.2 rad/s to 1.80 rad/s, in increments with 0.1 rad/s; and the wave heading angle ranges from 0 degree to 360 degree, in increments with 15 degrees. In this study, the structural response will be analyzed by finite element method. The wave response sensitive zones of ship structures are examined. The wave loads on the trimaran were analyzed by the BV hydrodynamic code – HydroStar. Combining the calculated stress response amplitude operators (RAO) and spectral fatigue analysis (SFA) with the JONSWAP wave spectrum for North Atlantic Ocean and ABS wave scatter diagram, the statistic response of structural components were calculated for the fatigue assessment. In the service life of ship different variation of loads (e.g., variation of full load and light ship and dynamic pressures of wave loads) were considered