| 研究生: |
林昱廷 Lin, Yu-Ting |
|---|---|
| 論文名稱: |
利用類神經網路訓練與可變步階簡易共軛梯度法進行史特靈引擎最佳化設計 Optimal Design of Stirling Engines by Neural Network Training Algorithm and Variable-Step Simplified Conjugate-Gradient Method |
| 指導教授: |
鄭金祥
Cheng, Chin-Hsiang |
| 學位類別: |
博士 Doctor |
| 系所名稱: |
工學院 - 航空太空工程學系 Department of Aeronautics & Astronautics |
| 論文出版年: | 2021 |
| 畢業學年度: | 109 |
| 語文別: | 英文 |
| 論文頁數: | 99 |
| 中文關鍵詞: | VSCGM 、最佳化 、設計方法 、史特靈引擎 、自由活塞式史特靈引擎 、Gamma型史特靈引擎 |
| 外文關鍵詞: | VSCGM, Optimization, Design algorithm, Stirling engine, Free-piston Stirling engine, Gamma-type Stirling engine |
| 相關次數: | 點閱:99 下載:6 |
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本研究發展一史特靈引擎設計的新穎最佳化方法,此方法結合可變步階簡易簡易共軛梯度法(VSCGM)及類神經網路。與現有的梯度導向方法相比,例如:共軛梯度法(CGM)、簡易共軛梯度法(SCGM),可變步階簡易共軛梯度法(VSCGM)具有較佳與較快的收斂性,同時也兼具可自訂目標函數格式之彈性。同時,本方法之強健性也在本研究中獲得證實。
本研究先以一低溫差Gamma型史特靈引擎作為最佳化的目標。以三維電腦輔助流場分析(CFD)產生之資料訓練一類神經網路作為求解器。結果顯示指示功與熱效率分別增進了102.93%及5.24%。
然而,由於自由活塞式史特靈引擎與傳統史特靈引擎的運作特性差異,原本的可變步階簡易共軛梯度法需要加入兩項搜尋策略:喚醒策略、逆比較策略。透過此最佳化設計方法,除了可以依據現有的自由活塞式史特靈引擎進行多參數最佳化,也可以任意給定參數,將原本無法運作的自由活塞式史特靈引擎調整至可運作區的最佳化參數組合。本研究忠實呈現將原本不會動的自由活塞式史特靈引擎調整至可成功運作並具有23.998公厘的移氣器穩定振幅。本設計方法與一般最佳化過程不同的地方在於,不會因為引擎落入不可運作區而停止搜尋,而是透過前述策略維持設計方法持續運作。同時,透過此方法也可以識別出自由活塞式史特靈引擎之可運作區與不可運作區,並提供做為應用設計或選定引擎的運作條件之參考。
This study is mainly focus on developing a novel optimization process and design for a Stirling engine by combining the variable-step simplified conjugate gradient method (VSCGM) and the neural network training algorithm. The VSCGM method is a modified version of conjugate gradient method (CGM) and the simplified conjugate gradient method (SCGM). Compared with existing gradient-based methods, VSCGM provides a greatly accelerated convergence speed and also maintains the flexibility related to defining the form of the objective function. Also, the robustness testing for the VSCGM method is carried out by showing the same optimal result with different initial guesses.
In the present study, the optimal design of a low-temperature-differential gamma-type Stirling engine and a free-piston Stirling engine were used as testing cases. For the gamma-type Stirling engine, a direct-solution provider was trained using a backpropagation neural network based on the simulation samples provided from the three-dimensional computational fluid dynamic simulation package (CFD). The optimal design of the gamma-type Stirling engine shows that the indicated power and thermal efficiency were increased by 102.93% and 5.24%, respectively.
Due to the different operating characteristics of free piston Stirling engines and traditional Stirling engines, for the free-piston Stirling engine, two strategies are added to the VSCGM: the wake-up strategy, and the backward-comparison strategy. Therefore, a novel design algorithm for a free-piston Stirling engine was completed. Through the use of this design algorithm, the optimization not only can starting from the existing free-piston Stirling engine design parameters, but also can search from an inoperable region or any arbitrarily given free-piston Stirling engine. In this study, a comparison of automatic tuning of a free-piston Stirling engine with a set of inoperable design parameters to an operable one with a steady displacer amplitude of 23.998mm is made. The advantage of this algorithm is that the search process for the optimal design parameters does not stop in the inoperable region. This algorithm can proceed and identify both operable and inoperable zones. The engine designer can also use this identification data as a reference to determine operating requirements for such engines.
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