使用重疊網格與體積力螺槳模型於OpenFOAM中進行具六自由度運動之自主式水下無人載具自航模擬

AUV SELF-PROPULSION SIMULATION WITH SIX-DOF MOTION IN OPENFOAM USING AN OVERSET MESH AND BODY-FORCE PROPELLER MODEL

本研究利用開源計算流體力學（CFD）軟體OpenFOAM，針對自主式水下無人載具（AUV）進行自航特性之數值模擬分析。計算模型採用大渦模擬（LES）紊流模型，結合流體體積法（VOF），以精確捕捉自由液面效應。模擬中採用動態重疊網格方法，建構四個網格區域：包含一固定背景區域、一個與船體固定之重疊區域，以及兩個對應垂直舵之旋轉重疊網格。垂直舵的運動以相對於船體之預設動作設定，整體AUV則在由libDynamicMeshMotion函式庫計算之水動力作用下，執行六自由度（6-DOF）運動。網格由snappyHexMesh工具產生，並與國立成功大學拖航水槽之實驗數據進行比對驗證。研究中亦執行自由浮力穩定性測試與自航模擬，以全面評估AUV的流體力學響應。模擬結果於穩定性與推進性能方面皆與實驗數據呈現良好一致性，驗證了重疊網格技術與體積力螺槳模型之可行性與有效性。此外，本文亦深入探討自航過程中之流場結構與水動力分佈，以解析AUV的運動行為。

This study investigates the self-propulsion characteristics of an Autonomous Underwater Vehicle (AUV) through detailed numerical simulations conducted using the open-source Computational Fluid Dynamics (CFD) software OpenFOAM. The computational model employs the Large Eddy Simulation (LES) turbulence model in conjunction with the Volume of Fluid (VOF) method to accurately represent free-surface effects. A dynamic overset mesh approach is adopted, comprising four mesh zones: a stationary background domain, a hull-attached overset region, and two rotating overset grids associated with the ver-tical rudders. Rudder motions are prescribed relative to the hull, and the entire AUV assembly undergoes six-degree-of-freedom (6-DOF) movement, driven by hydrodynamic forces calculated using the libDynamicMeshMotion library. Meshes are gener-ated using snappyHexMesh and verified against experimental results from the National Cheng Kung University (NCKU) tow-ing tank. The study includes free-floating stability tests and self-propulsion trials to comprehensively evaluate the AUV’s hy-drodynamic response. Simulation outcomes show good correlation with experimental data in both stability and propulsion performance, validating the effectiveness of the overset mesh technique and the body-force propeller model. Furthermore, detailed examinations of flow fields and hydrodynamic forces elucidate the behavior of the AUV during self-propulsion.