COMPUTER VISION BASED VIBRATIONAL DISPLACEMENT MEASUREMENT AND MODAL IDENTIFICATION

Abstract

Physical parameters such as displacements and modal parameters that are obtained from experimental tests contain crucial information about the current state of civil engineering structures. Identification of those parameters has been usually carried out by the time and the frequency domain analysis of the data obtained by means of accelerometers, velocity and displacement transducers. However, it is not always practical to obtain such experimental quantities via conventional methods. Recently, digital image processing techniques have made it Optical Flow Algorithmpossible to measure vibrational data in a way that is much cheaper and easier. In this study, computer vision based measurement of structural vibrations and identification of experimental modal parameters (natural frequency, mode shapes etc.) are emphasized. Three popular methods are introduced and tested on a 4-storey single-span laboratory structure, which is made of aluminum alloy. The investigated methods are KanadeLucas-Tomasi (KLT) algorithm, a correlation-based template matching method and an optical flow method, respectively. While the first two methods are used to measure the vibrational displacements, the last approach is suitable for velocity field measurements. In addition, all methods are capable of capturing vibrational quantities by tracking natural targets located on the structure. In this study, the presented methods are discussed and their performances are evaluated by comparing the results with conventional accelerometers and LVDT measurements

Keywords

• Computer vision processing, Operational modal analysis, Vision based template matching, Kanade-LucasTomasi algorithm

SAYISAL GÖRÜNTÜ İŞLEME İLE TİTREŞİM YER DEĞİŞTİRMELERİNİN ÖLÇÜMÜ VE MODAL PARAMETRE TAYİNİ

Abstract

İnşaat mühendisliği yapılarında deneysel yöntemler ile elde edilen yer değiştirme gibi fiziksel büyüklükler ile modal parametreler yapının mevcut durumu hakkında önemli bilgiler içermektedir. Bu parametrelerin tayini genellikle ivme, hız ve yer değiştirme ölçerler ile toplanan verilerin zaman veya frekans alanında analizi ile yapılmaktadır. Fakat bu verilerin alışılagelmiş yöntemler ile elde edilmesi çoğu kez pratik olmamaktadır. Son yıllarda ise sayısal görüntü işleme teknikleri titreşim verilerinin çok daha ucuz ve kolay bir şekilde toplanmasına olanak tanımaktadır. Bu çalışmada, sayısal görüntü işleme teknikleri ile yapı titreşimlerinin ölçülmesi ve deneysel modal parametrelerin (doğal frekans, mod şekilleri v.b.) tayini üzerinde durulmuştur. Alüminyum alaşımdan inşa edilmiş dört katlı tek açıklıklı model bir yapı üzerinde üç yöntem test edilmiştir. Bu yöntemler sırasıyla Kanade-Lucas-Tomasi (KLT) algoritması, korelasyon tabanlı şablon eşleştirme ve görsel akış yöntemleridir. İlk iki yaklaşımda, titreşim kaynaklı yer değiştirmeler ölçülürken diğer yaklaşımda hız büyüklükleri ölçülebilmektedir. Ayrıca tüm yöntemlerde doğal hedeflerin takibi ile bu büyüklükler bulunabilmektedir. Bu çalışma kapsamında yapısından ivmeölçerler ve LVDT yardımıyla toplanan veriler ile karşılaştırma yapılarak değerlendirilmiştir

Keywords

• Sayısal görüntü işleme, Operasyonel Modal Analiz, Görüntü tabanlı şablon eşletirme, Kanade-LucasTomasi algoritması, Görsel akış algoritması

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