整合式無線感測網路之結構健康監測系統 於建築與土木結構之研發

Abstract

本研究提出一整合式無線感測網路之結構健康監測系統架構並應用於建築與土木結構上。此架構主要包含了感測、資訊融合與管理以及決策診斷。在此架構目標下，本研究發展了一個整合式無線感測網路結構健康監測系統。此系統由多種無線節點所組成，包含感測結點、簇首節點、傳送節點與基地台。感測結點主要以Imote2平台為基礎，用來量測結構的動態反應或是環境參數。簇首節點為雙核心之設計結合了Imote2平台與額外之嵌入式系統。簇首節點含有額外之無線通訊模組與GPS來進行較長距離之資料接收、交換，並可以進行定位與同步之用。傳送節點可當作協調者並進行資料的跳躍傳送(Hopping)。基地台主要為接收所有回傳的感測資料與訊息，其硬體能力為所有結點中最高的。此系統亦包含了一個三層式的軟體架構，主要可以進行可靠的資料感測與傳輸、資料儲存、視覺化之使用者介面、資料分析與訊號處理等工作。在此軟體架構下，無線感測相關的結構健康監測的應用將可以很容易地被實行。此外，能源的消耗亦是無線感測的一個很重要的問題，因此，本研究發展了一個結合壓電、風車、與磁場的整合式能源擷取系統來改善能源消耗的問題。 結構健康監測可分為局部與全域之方法，然而，兩種方法各有其優缺點與應用之時機。因此本研究發展了一個整合式的結構損害評估方法整合全域與局部之結構損害評估法，應用於結構健康監測上。在全域結構損害偵測方面，本文分別提出了新的子結構頻率響應函數法來對結構進行大範圍之損害評估。接著，以電機阻抗為主之局部損害評估法則可以用來進行小範圍局部損害之評估。 在實驗與數值模擬研究中，數值模擬的結果發現本文所提出之結構損壞評估方法可以成功地找出結構發生損壞的位置。另外無線感測網路結構健康監測系統亦於一縮尺之建築模型上進行驗證，其實驗結果證實此系統可進行高質量的感測與資料傳輸並可以精確地獲得結構的相關動態反應參數。為驗證所發展之無線感測網路結構健康監測系統應用於實際土木結構上之可行性，將此系統佈設於一橋梁上進行驗證。實驗結果顯示，此系統於實際土木之結構上依然可以獲得相當好的感測結果，無線傳輸也可以達到預期的效果。在實際土木結構監測的佈設上更可以發現本系統之優點，在實驗過程中，平均一個節點的建置小於5分鐘，比起傳統有線的監測系統來說，在時間成本的節省上更顯現出本系統的優勢。在六層樓縮尺模型試驗中，亦可以證實本研究所提出之整合式的結構損害評估方法可以識別出結構之全域與局部之損害。

The main purpose of this dissertation was to propose a framework for an integrated wireless sensor network (WSN)-based structural health monitoring (SHM) system in buildings and civil infrastructures. In this framework, three main parts were considered: the physical sensing; information fusion and management; and inference and decision making. To achieve this goal, an integrated WSN-based SHM system was developed. This system consists of sensing nodes, cluster head nodes, transfer node, and base station. The sensing node measures structural response or environmental parameters. Each sensing node is controlled by an Imote2 platform comprised of a microprocessor, sensor module, and communication device. To exchange information or to trigger sensing tasks, the cluster head node can communicate with sensing nodes or cluster heads of neighboring communities. The cluster head has a dual-core design that combines the Imote2 platform with a second embedded device. The cluster head has an extra wireless module and GPS. The extra wireless module provides additional RF power needed for long-range wireless communication. The GPS is useful for synchronization and localization. The transfer node functions as a coordinating node for managing cluster heads and data hopping. The base station is the highest level end device and has the largest memory, the most powerful processor and the highest communication capability. The base station node is the gateway between smart sensor networks and the Host computer. A three-tier software framework is also developed in this work serving as reliable data-sensing and transmission, data logging and data storage, user interface, data analyzing, and signal processing. Based on this software framework, a SHM application for specific purpose can be easily developed. Power sources and power consumption are the critical issue in WSN if batteries have to be periodically replaced. Hence, a novel windmill-magnet integrated piezoelectric (WMIP) energy harvesting system was also proposed. Since local and global SHM have unique benefits and shortcomings, an integrated approach may be more effective than using either approach alone. This work developed a global-local-integrated damage detection approach for localizing damage. Substructure-based frequency response function approaches were proposed for global damage detection. Local damage was then identified by Electro-Mechanical-Impedance (EMI)-Based damage detection method. Numerical and experimental study is also conducted to complete this study. Numerical results reveal that the proposed global damage detection approach can successfully locate damage at a single site and at multiple sites. Experimental analysis confirms the proposed integrated WSN-based SHM system provides excellent data sensing and transmission quality for determining the structural dynamic properties. An experimental validation in building structure confirms that the proposed global SHM approach can indicate the approximate location of the damaged area in damaged floor and the EMI-based damage detection approach can check the component of building structure locally. Subsequently, the proposed WSN-based SHM system is employed in a bridge structure to test the feasibility in field. This experimental result confirms good-quality data collection by the proposed system. In experimental period, the system shows WSN-based SHM system outperforms conventional SHM system, especially in deploying sensors. Average time for deploying single node only takes within 5min.