含腐蝕與疲勞裂縫效應散裝貨輪的可靠度分析

RELIABILITY ANALYSIS OF A BULK CARRIER WITH THE COMBINED EFFECTS OF CORROSION AND FATIGUE CRACKS

大型船體結構通常使用鋼材做為船殼主體，然而鋼材受不斷變化的波浪與嚴苛的環境下極易發生疲勞與腐蝕現象。本文旨在探討船舶因疲勞所產生的結構破壞同時，也考慮合併腐蝕與疲勞裂縫兩效應下之船舶結構可靠度分析。文中將疲勞裂縫之可靠度分析分為兩個破壞模式來討論，首先考慮已具有初始裂縫之疲勞裂縫成長的可靠度，其次為在初始裂縫未發生前之疲勞可靠度。同樣地腐蝕過程亦可分為二個層面來看，第一個過程為塗裝保護仍為有效的過程，第二個階段為塗層開始失效並開始發生腐蝕的過程。由於發生初始裂縫的時間與塗層失效的時間可視為隨機變數，故船舶結構之可靠度就必須考慮裂縫初始時與塗層失效之機率下的條件可靠度。最後依據上述兩效應的合併條件，來求得船體結構的可靠度或失效機率。 Generally, the structures of large ships are made of steel. The corrosion and fatigue of the steel may occur due tofluctuating waves and harsh environment. The purpose of this study is to assess the reliability of a ship under extremeloading condition and severe environment. The process of corrosion may be separated into two stages. The first phaseis the time period in which the corrosion protection is effective, and corrosion does not occur. The second one startswhen the effectiveness of the coating is lost, and general corrosion is developing. Fatigue and corrosion are inevitablein sea-going ships and offshore structures. In order to obtain the accurate reliability of a ship’s hull, one should takeaccount of the combined effects of fatigue and corrosion. Both coating life and the time it takes to have a crackinitiation are considered as random variables in this study. In the fatigue analysis of a ship’s hull, two stages are alsoinvestigated. First of all, the reliability is evaluated before the crack initiation. Afterwards, the reliability after crackinitiation is also calculated. Finally, based on the combined effects of fatigue and corrosion, the reliability or theprobability of failure of a bulk carrier is studied.