水下爆炸引致巨大空蝕區造成船艦結構動態效應分析

Structural Responses of Ships Subjected to Bulk Cavitation Induced by Underwater Explosions

水下爆炸有兩個主要階段，分別為爆震波（Shock wave）與氣泡脈動（Bubble pulse）階段。本研究主要探討水下爆炸引致巨大空蝕區造成船艦結構墜落時之結構動態效應，水下爆炸發生後，於接近自由液面處，會構成一個爆炸「氣體－－水－－空氣」的系統，當爆震波與自由液面的交互作用下，會產生了巨大空蝕區（Bulk cavitation）。此巨大空蝕區效應對水面的船體結構具有一定的損傷程度，故水下爆炸後船體結構的整體效應分析，必須將巨大空蝕之影響納入考量。本文以巨大空蝕為研究對象，首先以Matlab軟體為工具，探討400公斤重的TNT炸藥，在水深68公尺處，計算其巨大空蝕區（Bulk cavitation）。其次利用ABAQUS有限元素軟體為工具，運用CEL（Couple Eulerian-Lagrangian）理論，並與Ramajeyathilagam和Vendhan[14]探討平板在受水下爆炸衝擊後，平板變形之實驗結果進行驗證；最後以某型船艦為對象，探討船體結構在巨大空蝕區墜落之損傷分析；本研究之成果可提供船艦結構設計者進行船體結構設計時使用。

An underwater explosion usually contains two stages: shock wave and bubble pulse stages. A shock wave and free surface interaction produces a bulk cavitation. At the bubble pulse stage, the bubble expands and contracts during the collapse phase of the bubble, and a high-speed jet is produced. Bulk cavitation and high-speed jets may severely damage the structure of a ship. Therefore, this paper presents a study on the effect of bulk cavitation on structures in an underwater explosion. To investigate the aforementioned problems, the Finite Element Method was applied. The Coupled Eulerian-Lagrangian technique embedded in ABAQUS software was used to determine the structural dynamic response of a ship subject to bulk cavitation induced by underwater explosion during a simulation. Furthermore, in this paper, the response of a plate to the shock wave induced by the underwater explosion is examined and verified according to the experimental study of Ramajeyathilagam [14]. To study the effects of bulk cavitation, a ship model was used as the study object. The numerical results in this study may provide helpful information for ship design.