本文探討平板結構單側部分浸泡於流體時之流固耦合振動與暫態響應，並進一步分析水下火花放電所產生之脈衝壓力波對平板動態行為的影響。為兼顧理論分析之物理意義，以及有限元素法處理複雜幾何與邊界條件之彈性，本文建立一套結合有限元素計算與理論解析之半解析方法。此方法先求得平板在空氣中的自然頻率與模態形狀，以及各模態振動所產生的流體壓力分布，再計算流固耦合系統之共振頻率、模態形狀與暫態位移。 在振動與暫態分析方面，本文分別透過共振量測與鋼珠落擊實驗進行驗證，並比較半解析方法、完整有限元素模擬與實驗量測結果。結果顯示，所建立之方法可準確預測不同水深下的共振頻率、模態形狀及暫態響應，應用於不同平板與流場幾何時亦具有良好適用性。此外，半解析法在較長時間之暫態分析中可有效降低計算成本。 針對流體內部之水下波源，本文同時考慮波源直接產生並於流體中傳播的壓力波，以及平板振動推動周圍流體所形成的反作用壓力，建立水下脈衝壓力波作用下之流固耦合暫態分析方法。實驗方面，利用汽車點火線圈建置水下火花放電系統，使電極間水介質瞬間擊穿，產生近似水下點波源之脈衝壓力波，並以雷射位移計量測平板面外暫態位移。由於火花放電之波源歷時難以直接量測，本文將其表示為參數化函數，並結合有限元素模型與Levenberg-Marquardt最佳化方法，由平板位移反算等效波源歷時。結果顯示，多觀測點反算可提升波源歷時之空間代表性，且所建立模型能合理描述不同水深、量測位置及電極間距條件下之平板暫態響應。綜合而言，本文所提出之半解析法、水下火花放電實驗系統與波源反算方法，可有效應用於部分浸泡平板流固耦合系統之動態分析。;This study investigates the fluid–structure interaction vibration and transient responses of a plate partially submerged in fluid on one side， with further emphasis on the dynamic behavior induced by impulsive pressure waves generated through underwater spark discharge. To combine the physical interpretability of theoretical analysis with the flexibility of the finite element method in handling complex geometries and boundary conditions， a semi-analytical method based on finite element calculations and modal theory is developed. The natural frequencies and mode shapes of the plate in air， together with the fluid-pressure distributions induced by each structural mode， are first obtained and then used to calculate the coupled natural frequencies， mode shapes， and transient displacements. The proposed method is validated through resonance measurements and steel-ball impact experiments by comparison with fully coupled finite element simulations and experimental results. The method accurately predicts the natural frequencies， mode shapes， and transient responses under different water-depth conditions and maintains good applicability for different plate and fluid geometries. Because the precomputed modal data can be reused， the method also reduces the computational cost of relatively long transient analyses. For underwater excitation generated within the fluid domain， the analysis considers both the pressure wave directly generated and propagated by the underwater source and the reaction pressure produced when plate vibration displaces the surrounding fluid. Based on these two physical mechanisms， a transient fluid–structure interaction framework is established. An underwater spark discharge system using an automotive ignition coil is constructed to produce impulsive pressure waves approximating an underwater point source， while the out-of-plane transient displacement of the plate is measured using a laser displacement sensor. Because the source-time history of the spark discharge is difficult to measure directly， it is represented by a parameterized function and reconstructed from the measured plate displacement using a finite element model combined with the Levenberg–Marquardt optimization method. The results show that inversion using multiple observation points reduces dependence on a single measurement location and improves the spatial representativeness of the reconstructed source. When applied to the finite element model， the reconstructed source-time history reasonably reproduces the transient plate responses under different water depths， measurement positions， and electrode gaps. Overall， the proposed semi-analytical method， underwater spark-discharge experimental system， and source-time-history inversion procedure provide an effective framework for the dynamic analysis of partially submerged plate–fluid interaction systems.
