大型貨櫃輪波振效應之探討

Study of Springing Effect on Large Container Vessel

廖柏凱(Po-Kai Liao)

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(2014年)

https://doi.org/10.6342/NTU.2014.01824

摘要

本文利用水彈性力學理論，以模態疊加法求解考慮波振效應之船體結構應力分佈，並求得船體於單位波高作用下之反應振幅運算子(Response Amplitude Operator, RAO)；利用頻譜疲勞分析法，針對選定熱點區域，探討波振效應對結構疲勞壽命之影響。
波振效應(Springing Effect)為當船舶航行時之波浪遭遇頻率接近船舶結構自然振動頻率時，船體結構與波浪交互作用之流固耦合現象。波振效應會對船體造成額外負荷，進而降低船舶之疲勞壽命。隨著貨櫃輪持續朝大型化發展及高張力鋼的大量使用，船舶結構自然振頻降低，與遭遇頻率重疊之機率上升，使波振效應成為探討大型船舶結構疲勞壽命之重要議題。
本文首先透過建立全船有限元素模型求解船體結構之自然振動模態及對應之模態振頻，並利用法國驗船協會開發之分析軟體以小板法進行水動力計算。針對台灣國際造船股份有限公司8,000 TEU貨櫃輪，首先建立兩種裝載狀況之全船有限元素結構模型、探討之熱點局部細網格模型及水動力網格模型，利用所建立之模型進行全船有限元素分析，配合局部細網格模型搭配熱點處所適用之應力評估法，選擇適當之應力，求解不同波高、波頻、航向角下結構熱點考慮波振之應力反應振幅運算子，與波浪頻度表(Wave Scatter Diagram)組合，配合適當之S-N Curve，以頻譜疲勞分析計算結構疲勞壽命，並探討波振效應之影響。
本文選定兩不同形式之熱點進行分析，針對選定之兩種裝載狀況、分別就兩種船速假定進行計算，最後以兩種不同波浪頻度表進行頻譜疲勞分析，探討不同環境設定下波振效應之影響。

關鍵字

波振效應 ； 流固耦合 ； 水彈性力學 ； 疲勞壽命 ； 頻譜疲勞分析

並列摘要

This study employs modal superposition method to conduct hydro-elastics analysis, and evaluates stress distribution on ship structure considering springing effect. With the calculated stress response amplitude operators (RAO), spectral fatigue analysis (SFA) is used to obtain the fatigue life of hot spot on ship structure.
Springing effect is the phenomenon of ship hull structure resonance induced by wave load, which will cause extra cyclic loads on ship structure, therefore, fatigue life of ship would be decreased. The natural frequency of ship structure becomes lower while the size of container vessel growing larger and the widely use of high tensile steels are applied considerably, thus it is more probable to have the encounter frequency of wave loads approaching the natural frequency of ship hull structure, which makes springing an important subject in large container vessel design.
This study considered the CSBC’s 8,000TEU container vessel with two different loading conditions. A spectral approach using hydroelastic software Homer and Springing tools which contributed by Bureau Veritas has been used to evaluate the springing effect. To perform spectral fatigue analysis, the stress RAOs of hot spot which obtained by FE analyses were further combined with the wave scatter diagram. Two hotspot positions were chosen to compare their fatigue lives with/without springing effect. In the spectral fatigue analyses, two different wave scatter diagrams and two ship speeds were also considered as parameters in order to compare springing effects under different operating conditions.

並列關鍵字

Springing effect ； Fluid-structure interaction ； Hydroelastics ； Fatigue life ； Spectral fatigue analysis

參考文獻

1. 吳政緯, 水彈性力學分析貨櫃輪之疲勞強度. 台灣大學工程科學及海洋工程研究所碩士論文, 2013.

21. 謝靜如, 以共同結構規範分析雙層船殼油輪疲勞強度之研究. 台灣大學工程科學及海洋工程研究所碩士論文, 民國99年.

22. 蔡思潔, 考慮水彈性效應之散裝貨輪頻譜疲勞分析. 台灣大學工程科學及海洋工程研究所碩士論文, 2012.

2. Heller S. R. and Abramson H. N., Hydroelasticity：A new naval science[J]. Journal of American Society of Naval Engineers, 1959(71(2)): p. 205-209.

6. Hirdaris, S.E., W.G. Price, and P. Temarel, Two- and three-dimensional hydroelastic modelling of a bulker in regular waves. Marine Structures, 2003. 16(8): p. 627-658.