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題 名 | 再論FFT本質相位與波浪模擬=A Discussion on Essential FFT Phases in Water Wave Simulations |
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作 者 | 許師瑜; 林俶寬; 林炤圭; | 書刊名 | 海洋工程學刊 |
卷 期 | 18:3 2018.11[民107.11] |
頁 次 | 頁169-190 |
分類號 | 351.941 |
關鍵詞 | 快速傅立葉轉換; 時間序列; 頻譜分析; 相位差; Fast Fourier transforms; FFT phase; Time series; Phase shift; |
語 文 | 中文(Chinese) |
中文摘要 | Hsu et al.(2018)透過進行一系列數值波譜分析模擬實驗後,提出本質相位的觀念,指出利用FFT 分析波動訊號時,在運算中會自動賦予每個成分波一個介於0到π之間與頻譜分頻呈線性變化關係的本質相位,真實相位可由分析相位扣除其所對應的本質相位而得。如用真實相位、頻譜分頻及振幅可直接以餘弦函數線性疊加在時間域重建再生波形,而不需透過頻率域的傅立葉逆轉換(iFFT)運算。為了找出造成本質相位問題的可能原因,Hsu et al.持續進行各種可能的測試,並確認本質相位的產生應是FFT分析中對假想波形的定義不明確,導致對再生波形的誤解,而以為相位有流失的問題。波形的重建應先確認其所使用的FFT庫存函數對虛擬波形的定義。 |
英文摘要 | In Hsu et al. (2018), an essential phase shift of the fast Fourier transform (FFT) was proposed via a series of numerical experiments on designed wave signals. The FFT automatically adds-in a phase shift which linearly distributes from 0 to π along the whole spectral components. After subtracting the essential phase shifts from the analyzed phases of each components to gain the true phases. The signal can be fully recovered in time domain from spectral component frequencies, amplitudes and the true phases with only acceptable differences. In order to investigate what causes such phenomenon, an excess experiment was done and confirmed that the key problem is caused by the unclear definition of the wave profile in FFT and leads to a misunderstanding of recovered profile. |
本系統中英文摘要資訊取自各篇刊載內容。