船體振動之動態特性量測識別

Identification of Dynamical Characteristics of Ship Structures

本研究發展一套船體結構振動量測的等效系統運動方程式與模態參數的識別方法，藉由同時量測的多點輸入（激振力）輸出（結構動態反應）訊號的MIMO（多輸入輸出）系統來識別結構的動態特性。採用向量型後向自我回歸含外力對數模型（Vector Backward Auto-Regressive with eXogenous，簡稱VBARX）來描述動態系統在不同時步的輸出輸入資訊關係，據以建立離散時間狀態方程式，推導與量測自由度相對應的等效狀態運動方程式來估算結構的模態參數。本文以一貨櫃輸之有限元素動態分析與系統識別數值模擬為例，說明理論在應用上的可行性。另以與分析船相同的實船的部分量測資料為例，進行船體整體之動態特性識別，以檢討理論與實際應用之差異。 In this work, an efficient method has been developed to identity the equivalent system matrices and the modal parmeters of ship structures from the measured input force (or acceleration) and output response data in a multiple input/output measurement system. A vector type of backward auto-regressive with exogenous variable model, termed as VBARX model for short is adopted to set up an assembled state equation, which describes the relationship of the measured data among different time steps. From the eigen problem of this state equation the equivalent system matrices of structure can be extracted. The FEM modal analysis and numerical simulation of modal identification for a container ship have been carried out to show the applicability and effectiveness of the proposed method. Finally, the modal parameters were identified from on board measurement data of the same ship as experimental comparison study.