輕航機之外型與結構最佳化分析

隨著航空產業的蓬勃發展，不僅軍用飛機或大型民航客機越來越普遍，輕型飛行載具的市場也日趨成熟，在輕航機逐漸成為民眾的一種休閒活動，但飛行事故卻頻傳的情況下，如何在飛行效率及飛航安全中達到平衡，就顯得非常重要。本研究應用有限元素軟體ANSYS對輕航機進行外型與結構耦合的最佳化，期望在達到最佳氣動力外型的同時，仍可以符合適墜性的最低安全標準。本研究使用Zenith公司的STOL CH701作為研究模型，以Pro/Engineer建立3D機身模型，機身結構以鋁合金作為材料，利用ANSYS中的Fluent進行流場分析後，再以Adjoint Solver完成外型最佳化；接著使用Static Structural進行結構模擬分析，再匯入Topology Optimization模組中，完成拓樸最佳化。本研究利用流場分析與墜撞模擬來比較原始模型與改良後模型的阻力值、座艙變形量與應變能的差異，探討其安全性的改變及效益是否提升。本研究之外型最佳化以最小阻力值為目標函數、機身外型為設計範圍，並以比例因子來調整外型變化程度；結構最佳化則以最小結構順從度為目標函數、座艙側板為設計範圍以及重量移除率為限制條件進行設定。邊界條件之撞擊速度設定以符合AGATE及ASTMF2245-11 4.4.4.1所規定的撞擊速度18 m/s以及CH701最大巡航速度38 m/s為基準；並以美國軍用法規MIL-STD-1290A規範之15%座艙壓縮量為適墜性安全標準。經過外型以及結構最佳化後，選擇在任何撞擊速度下，皆符合座艙壓縮量15%安全規範的模型。並以撞擊速度為18 m/s說明最佳化前後各項數據的改變：機身外型阻力值下降3.43%、結構重量下降14.44%，而應變能則增加53.21%，吸收能量能力提高。本研究結合外型與結構最佳化，使輕航機在機身外型與結構墜撞上都獲得改善，在達到最佳氣動力的同時，仍有符合適墜性的最低安全標準。

關鍵字

輕航機；外型最佳化；結構最佳化；適墜性

並列摘要

With the vigorous development of the aviation industry, not only military aircraft and civil aviation aircraft are becoming popular, but also the market of light sport aircraft is getting mature. In case of frequent light aircraft accidents, how to balance within flight efficiency and flight safety has become an important issue. This research use finite element software ANSYS to optimize the shape and structure of light sport aircraft, expected to receive the best aerodynamic shape and meet the minimum safety standard of crashworthiness simultaneously. This study use light sport aircraft STOL CH701 from Zenith Company as model, the fuselage material is aluminum alloy 6061-T6. The 3D model is established by Pro/E. Utilizes ANSYS Fluent to simulate fluid field and use Adjoint Solver to complete the shape optimization, which objective function is set as minimum resistance. After shape optimization, Static Structural and Topology Optimization are used to complete structure simulation and structure optimization. The objective function is the compliance and the constraint is weight reducing rate. This research then discusses the change and benefits of its safety and performance by resistance, deformation, and strain energy. After shape and structure optimization, this thesis chooses the model that comply the safety standard of MIL-STD-1290A, 15% cockpit reducing rate under any impact velocity. So that the result will be discuss with impact velocity 18 m/s. Compares to the original model, the optimum model has the resistance decreased by 3.43%, structure weight decreased by 14.44%, and the strain energy increased by 53.21% which prove that the absorption ability is increasing. This research combines shape and structure optimization let the light sport aircraft improve not only fuselage shape but aircraft structure successfully.