水下管路之抗震分析

Shock Resistant Study of Submerged Pipeline Exposed to Underwater Explosion

水下隧道、輸油管、工業原料輸送管…等近岸結構，可能受到地震或石油、礦產開採之爆破工程中所產生震波所損壞，因此水下管路之抗震為水下結構安全防護重要課題之一。目前水下管路結構抗震能力改善大致有從管路材料、結構構型、外加防護殼以及外包覆材料等方式著手。本論文以外包覆方式增強水下管路之抗震能力為研究對象。首先，本論文以遠場側炸圓筒殼的動態反應為研究對象，應用非線性有限單元ABAQUS/USA軟體（6.4 version）中藕合有限元素及邊界元素法之雙向漸近近似法DAA2（Doubly Asymptotic Approximation, DAA2），進行數值模擬，並與1993年Kwon等人之實驗為驗設比較，其次，探討未包覆與包覆之水下管路結構承受爆震波之動態反應，研究內容包括（1）沒有任何防護結構的水下鋼管（2）外層包覆混凝土防護層之水下鋼管（3）埋入海床沙中之外包覆混凝土防護層的鋼管（4）理入海床沙中且在內部充滿水之外包覆混凝土防護層鋼管。研究結果發現：於海床上外部包覆混凝土比未包覆之水下管路，能降低最大有效應力值達28%；將外包覆混凝土水下管路徑入海床沙中，比置於海床上降低最大有效應力值18%；外包覆混凝土水下管路埋入海床沙中，內充滿水的管路比未充水的管路，能降低最大有效應力值14%；外包覆混凝土並埋入海床沙（管內充滿水）中比未包覆置於海床上（管內未充水）之水下管路，能降低近50%最大有效應力值；其中，以外部包覆混凝土之水下管路所提升的抗震能力最為顯著，其次為埋入沙中以及內部充滿水之情況。本論文之研究成果希能提供水下管路設計參考應用。 In many engineering situation concerning off shore structures of a great importance (pipelines, underwater tunnel crossings in oil industry), their resistance against the load produced by underwater explosions is an important component of the entire structure's safety. This paper is related to the analyses of an underwater pipeline protected by an external covered concrete subjected to an explosion close to the external protective structure. A computational approach is proposed, and the fluid structure interaction between the seawater and pipeline are handled using the coupled finite element and boundary element codes, based on the Doubly Asymptotic Approximation (DAA). The shock pressure transmitted from the sea water and sea bottom is calculated based on published empirical equations, which are incorprated into the couple fluid- structure code. At first, the nonlinear dynamic response of a cylinder subjected to a side-on, far-field underwater explosion was studied using the finite-element computer code ABAQUS/USA. This study showed the numerical results compared with 1993 K won et al experimental data. And then, the safety assessment of submerged pipelines, exposed to underwater shock was studied in detail. Four cases of pipeline configurations developed by 2000 Gong et al were modeled and simulated. The first case is a submerged empty pipeline without any cover, the second case is a submerged empty pipeline with concrete cover, the third case is an empty pipeline buried in sand and the fouth case deals with a fluid-filled pipeline buried in sand. The numerical results obtained for four pipeline configuration were compared and discussed in order to find the best protection.