水彈性力學分析貨櫃輪之疲勞強度

Fatigue Strength Analysis of Container Ship by Hydro-Elastic Dynamics

吳政緯(Zheng-Wei Wu)

指導教授 ： 李雅榮

國立臺灣大學/工學院/工程科學及海洋工程學研究所/碩士(2013年)

https://doi.org/10.6342/NTU.2013.02764

摘要

本文以水彈性力學理論，以模態疊加法計算船體與波浪間的水彈性耦合作用，考量波浪負荷造成船體整體變形下的應力分佈情形，並求得船體在單位波高下的應力響應函數(Response Amplitude Operator, RAO)；利用頻譜疲勞分析法，針對船體應力集中區域，將海洋頻譜轉換為船體負荷應力頻譜，探討波浪作用下，水彈性力學之流固耦合現象，對船體結構疲勞損傷及壽命的影響。
船舶航行時，承受輕船重量、貨物壓載及海水壓力等靜態負荷，亦承受海浪不規則反覆作用的動態負荷；而動態負荷造成應力振幅的變動，係船體結構產生疲勞損傷的主因；加上近年來，由於船舶大型化及輕量化，使得剛體(Rigid Body)效應式微，船體自然振動頻率大幅降低，趨近至船舶與波浪的遭遇頻率區間，受流固耦合之共振影響，造成船體波振(Springing)現象明顯，引起額外的應力變動，導致因疲勞損傷而發生的海難事件層出不窮，故船體疲勞強度已成為新船結構設計的評估重點之一
本文計算工具採用法國驗船協會已開發之分析軟體，配合其訂定的頻譜疲勞分析基準及流程，包含S-N Curve及累積損傷法則的選定，以台灣國際造船公司所設計8,240 TEU貨櫃輪為參考船，針對容易產生疲勞損傷的應力集中區域進行頻譜疲勞分析，評估水彈性力學對疲勞壽命的影響程度，期待將本研究成果，做為日後設計大型貨櫃輪時，評估其疲勞壽命及尋求設計改善對策之依據。

關鍵字

疲勞壽命 ； 水彈性力學 ； 應力響應函數 ； 頻譜疲勞分析 ； 流固耦合 ； 累積損傷法則

並列摘要

In accordance with hydro-elastics (HE), this study uses the modal superposition method to examine the hydro-elastic effect from the interaction between ships and waves and the stress distribution of different deformations under a wave load. The study obtained the stress response amplitude operator (RAO) of stress concentrating area to transfer wave spectrum to structure stress spectrum, and then assessed structural fatigue damage and life.
A ship sailing on the sea is not only exposed to static pressure from water and weight of the ship and cargo but also dynamic load such as cycle-loading of irregular waves. The dynamic load will cause stress variations on ships and result in fatigue damage. In recent years, ships have become larger and lighter; thus, the rigid body effect has become much weaker. Because of the new materials and models used in ships, the springing phenomena has become more obvious and significantly reduced the natural frequency of the ship. This lower frequency can vibrate with the wave environment and cause increased vibrations in the ship. In consequence, the lower frequency causes extra stress variation. Ships are often wrecked due to fatigue damage; therefore, the assessment of fatigue strength in ship structures has become an important point of analysis in the ship designing process.
The analysis software and spectral fatigue analysis (SFA) process were developed by the Bureau Veritas classification society (BV). The reference ship was a 8,240 TEU container ship, which was built by CSBS Corp., Taiwan and used for the fatigue damage assessment and spectral fatigue analysis.

並列關鍵字

Hydro-elastic ； Cumulative damage rule ； Fatigue life ； Response amplitude operator (RAO) ； Spectral fatigue analysis (SFA) ； Fluid–structure interaction

參考文獻

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