數值模擬蘇澳港受長週期波動影響

蘇澳港位於台灣東北部宜蘭縣，當颱風波浪從外海入射時，風湧浪會侵入港內因而引起水位的振盪，除了風湧浪，港外還會產生長週期波浪，長週期波浪造成港內水位振盪是蘇澳港要面對的課題，為了港灣船舶停泊的安全管理，本文利用數值模式FUNWAVE-TVD，模擬強烈颱風正射入射蘇澳港口，探討颱風波浪經由非線性轉移到長週期亞重力波(20~200秒)和非常低頻波(200~1000秒)之情況，並檢視港內各位置水位變化及波譜特性，蘇澳港東北角之三仙台礁岩以及南外廓防波堤處採用吸收邊界或是碎波邊界，是否是造成蘇澳港港池共振在論文中探討。模式結果顯示，無淺礁地形會讓波浪能量更容易進入港內，且港外低能量區塊更加明顯；防波堤處設定為碎波邊界或吸收邊界，港內模式結果影響甚微。波浪二維平面分布呈港池共振型態，在北內防波堤、北外廓防波堤、南外廓防波堤與航道碎波堤處有高能量之亞重力波發生，在公務船渠、第三船渠與南方澳第三漁港處則出現高能量之非常低頻波。

關鍵字

蘇澳港；亞重力波；非常低頻波；港池共振

並列摘要

Suao Port is located in Yilan County, northeastern of Taiwan. When incident waves induced by typhoons are from the east, swell and wind waves would propagate into the port and cause water level oscillations. Long-period waves are generated outside and inside the port. Effects of long-period oscillations on the safety of ship berthing is an important issue for Suao Port. In the present study, a numerical model, FUNWAVE-TVD, is applied to simulate long-period waves in the harbour during typhoon events. Incident waves approximately normal to the harbour entrance are set in the model simulation. The modeling results show that wave energy transfer from the peak frequency to infragravity (20-200 s) and very low-frequency (200-1000 s) bands through nonlinear wave-wave interactions. Water surface elevations and spectral energy characteristics at various locations in the port are distinct. In additional, model results indicate that the terrain without shallow reefs will make it easier for wave energy to enter the harbor. Setting breaking boundary or absorption boundary along the south breakwater has a mirror effect on simulated waves inside the harbour.