二維離散小波轉換應用於帶有加強材平板之破損偵測

Damage Detection of a Rectangular Plate with Stiffeners by Two-Dimensional Discrete Wavelet Transforms

本研究主要是利用小波包節點範數（wavelet packet node norm）來計算帶有加強材之鋁合金平板的第一模態振型值，並且利用二維離散小波分析來偵測裂縫之所在位置。在數值分析方面，利用有限元素法分析軟體（ANSYS），進行平板之模態振型分析，並以二維離散小波分析偵測裂縫位置，證明此方法之可行性。至於實驗模態分析方面，則利用激震器（Shaker）給予平板一個強制的外力，以加速規量測振動訊號，並利用小波包節點範數模擬出第一模態振型值，最後再藉山二維離散小波分析找出裂縫的位置。在船體複雜的結構中，加強材的應用（底板、船殼、隔艙壁、甲板等）更是扮演著舉足輕重的地位。本文所提出之帶有加強材之鋁合金平板的破損偵測方法，特別針對因焊接（應力集中處）而產生之裂縫進行偵測，對於單一或多個破壞程度之缺陷位置，均有不錯的檢測能力。 The main purpose of this study is to construct the first node shape of the aluminum alloy plate with stiffeners using the wavelet packet node norm (in experiment) and then detect the crack locations by the two-dimensional discrete wavelet transforms. In numerical analysis, the first mode shape of the damage plate with stiffeners is simulated by finite clement tool ANSYS and the damage locations of the plate with stiffeners are detected by two-dimensional discrete wavelet analysis. In experimental analysis, several accelerometers were used to measure the plate vibration signals which were excited by a shaker. The first mode shape of the plate with stiffeners is obtained by using the wavelet packet node norm. Finally, the damage locations of the plate are detected by two-dimensional discrete wavelet transform method. The applications of stiffeners and plates in assembling deck, bulkhead, sides anti bottom of a ship play a very important role in the construction of a complicated ship. The experimental results reveal that the proposed modal analysis and the discrete wavelet transforms can effectively identify the crack locations of stiffened plates with a single crack or multi-cracks.