二維扁平流線型仿生載具動態地面效應之參數模擬研究

Abstract

本研究建立二維比目魚型水下載具模型在水中特定高度下與地面效應之模擬，為了讓水下載具能長時間的在水中做動，藉由計算流體力學工具ANSYS-FLUENT進行流場的分析找出較省能的運動模式，此比目魚型之模型設計參考真實比目魚外型及水下潛體的幾何特性，分別為剛性的本體和軟性的胸鰭，本文主要針對比目魚型二維波動胸鰭與地面之高度變化進行探討，比較在不同高度下推力係數及輸入功率係數的差別，藉由模擬結果分析流場的變化，進而探討地面對比目魚型載具游動時所產生的影響。模擬結果顯示比目魚型載具游動時，在理想流體中，二維波動胸鰭對流場產生的地面效應與使用勢流理論所推導之數學式相符合，證實比目魚型載具在某特定高度能有較佳游動效率，然而在具有黏性之流場狀況下，根據本文結論，所有不同運動模式下靠近牆壁的效率均較高，但不同運動模式之最有效率高度不同。本研究結果證明藉由分析出比目魚型載具在不同運動模式下的省能的游動高度，可以方便未來控制比目魚型載具運動時能在最佳高度下游動，達到節能的目的。

In this study, a simulation study on the kinematic parameters of a two-dimensional flatfish-shaped biomimetic autonomous underwater vehicle (BAUV) under specific height in water is performed. The flow field is analyzed by a computational fluid dynamics tool ANSYS-FLUENT, and the design of the BAUV is based on the biological flatfish to mimic the geometric characteristics of the submerged bodies. The flatfish model is divided into two parts, rigid body and flexible pectoral fin. Mathematical formula is derived to describe the motion of the flexible fin. The distribution of the pressure field and velocity field when the flatfish-shaped BAUV swimming at different height above the ground is compared. The simulation results show that the ground effect of the flow field coincides with the derived formula from the potential theory, and it is confirmed that the optimal swimming efficiency can be obtained at a specific multiple of the characteristic length of the BAUV. The optimization of swimming-height above the ground can be obtained by simulation. In the future applications, the flatfish BAUV can be controlled at a specific height to ground to achieve the purpose of most energy-saving.