在全球減碳趨勢的推動下，再生能源已成為重要的研究方向。其中，波浪能具有能量密度高、資源分佈廣等優勢，被視為深具開發潛力之再生能源；然而其實際應用與商業化程度仍遠不及風能與太陽能，顯示能量擷取機制、系統動態行為與數值預測方法仍有深入研究之必要。
本研究依據線性疊加原理，將波浪與浮體之交互作用拆解為繞射與輻射問題分別處理，探討固定浮體於規則入射波作用下之繞射效應，並以 COMSOL Multiphysics 建立三維無限域繞射模型。模型利用鏡像對稱性降低網格數量與總自由度，且無需如前人數值水槽模型般完整模擬造波器運動，在計算資源與模擬時間上具有明顯優勢。繞射波場可進一步分解為入射波場與擾動波場，並對所得之受力與波高訊號進行傅立葉級數展開，取得代表性之振幅，進而探討福祿數變化對總受力、擾動受力及兩者與波高間相位差之影響。
此外，本研究亦初步測試三維非線性勢流模型，採用以非線性自由表面邊界條件漸近展開為基礎之固定網格法。統御方程式與邊界條件無因次化後可得非線性參數 ε，其值反映非線性效應之強度，ε=0 時模型即退化為線性問題；目前水槽模型可穩定計算之極限約為 ε=0.02，超過此值即出現數值不穩定並發散。由於三維非線性自由表面問題對邊界條件、網格品質與求解器耦合皆相當敏感，本文遂將研究重點聚焦於三維無限域繞射模型之建立與分析，並呈現初步之弱非線性成果，以作為後續建立輻射模型、分析浮體運動響應，乃至發展完整波浪獵能器數值模型之基礎。

Wave energy offers the highest energy density among options of renewable energy yet remains far less commercially mature than wind and solar power, motivating further study of its capture mechanisms and predictive numerical methods. Based on the linear superposition principle, the wave–body interaction is decomposed into diffraction and radiation sub-problems, with the fixed-body diffraction problem as the main subject. This work develops a three-dimensional, infinite-domain diffraction model in COMSOL Multiphysics for a submerged, fixed circular cylinder under regular incident waves. The incident wave is prescribed analytically from finite-depth linear wave theory, so no physical wavemaker needs to be simulated, and mirror symmetry halves the computational domain—substantial savings over conventional numerical wave tank (NWT) models. The diffraction wave field is split into incident and disturbance components, and the force and elevation signals are Fourier-expanded to examine how the Froude number governs the total force, the disturbance force, and their phase lags relative to the incident elevation. A weakly nonlinear three-dimensional potential-flow wave-tank model is also tested, using a fixed-mesh approach based on asymptotic expansion of the nonlinear free-surface conditions; the expansion introduces a nonlinearity parameter ε, the model reduces to the linear problem at ε = 0, and stable computation is attainable up to about ε = 0.02, beyond which the solution diverges. Because three-dimensional nonlinear free-surface problems are highly sensitive to boundary conditions, mesh quality, and solver coupling, the weakly nonlinear results are presented as preliminary groundwork for future radiation models, floating-body motion analysis, and a complete wave-energy-converter (WEC) numerical model.

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