海底管線受海流引致沖刷過程之流場分析

NUMERICAL STUDY ON FLOW FIELD INVESTIGATION OF SCOUR PROCESSES AROUND SUBMARINE PIPELINES INDUCED BY OCEAN CURRENT

隨著全球推動能源轉型與淨零碳排，台灣燃氣發電占比持續上升。受限於地理與法規，陸上管線鋪設愈加困難，海底管線遂成為天然氣輸送的重要方式，目前已承擔超過50%的輸送量。海底管線多埋設於海床下，以避免直接暴露於海流並降低破壞風險，惟長期海流作用下仍可能造成局部淘刷，導致管線裸露或懸空。當海流流經懸空管線，將改變周圍流場並引發渦流脫落，進一步加劇沖刷並威脅結構安全。本研究運用FLOW-3D數值模擬，建立五種沖刷階段海床模型，於三種流速條件下分析海底管線周圍之流場變化。結果顯示，流速與間隙比對渦脫落的頻率與強度具明顯影響。

With the global promotion of energy transition and net-zero carbon emissions, the share of gas-fired power generation in Taiwan has steadily increased. Due to geographic and regulatory constraints, the installation of on-shore pipelines has become increasingly limited, making submarine pipelines an increasingly important means of transporting natural gas, now accounting for over 50% of Taiwan’s total gas transmission.
Submarine pipelines are typically buried beneath the seabed to prevent direct exposure to ocean currents and reduce the risk of third-party damage. However, under sustained ocean current action, local seabed scour may occur, causing sections of the pipeline to become exposed or suspended. The interaction between ocean currents and a suspended pipeline alters the surrounding flow field, potentially leading to vortex shedding. This phenomenon not only intensifies local scour but also poses a risk to pipeline structural integrity, potentially leading to deformation, damage, and reduced service life.
In this study, numerical simulations were conducted using FLOW-3D to investigate flow field variations around submarine pipelines. A series of five seabed configurations were developed to represent different scour stages, and simulations were performed under three different flow velocity. Results show that the pressure difference across the pipeline increases with flow velocity. Additionally, flow velocity significantly influences the period and intensity of vortex shed-ding. The gap ratio has a marked effect on the vortex shedding pattern and vorticity magnitude.