Documents disponibles écrits par cet auteur

Flexible videogrammetric technique for three-dimensional structural vibration measurement / C. C. Chang in Journal of engineering mechanics, Vol. 133 N°6 (Juin 2007) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 133 N°6 (Juin 2007) . - pp.656–664. Titre : Flexible videogrammetric technique for three-dimensional structural vibration measurement Type de document : texte imprimé Auteurs : C. C. Chang, Auteur ; Y. F. Ji, Auteur Année de publication : 2007 Article en page(s) : pp.656–664. Note générale : Applied mechanics Langues : Anglais (eng) Mots-clés : Photogrammetry  Vibration  Dynamic  response  Measurement  Imaging  techniques. Résumé : A videogrammetric technique is proposed for measuring three-dimensional structural vibration response in the laboratory. The technique is based on the principles of close-range digital photogrammetry and computer vision. Two commercial-grade digital video cameras are used for image acquisition. To calibrate these cameras and to overcome potential lens distortion problems, an innovative two-step calibration process including individual and stereo calibration is proposed. These calibrations are efficiently done using a planar pattern arbitrarily shown at a few different orientations. This special characteristic makes it possible to perform an on-site calibration that provides flexibility in terms of using different camera settings to suit various application conditions. To validate the proposed technique, three tests, including sinusoidal motion of a point, wind tunnel test of a cross-section bridge model, and a three-story building model under earthquake excitation, are performed. Results indicate that the proposed videogrammetric technique can provide fairly accurate displacement measurement for all three tests. The proposed technique is shown to be a good complement to the traditional sensors for measuring two- or three-dimensional vibration response in the low-frequency range. ISSN : 0733-9399 En ligne : http://ascelibrary.org/action/showAbstract?page=656&volume=133&issue=6&journalCo [...] [article] Flexible videogrammetric technique for three-dimensional structural vibration measurement [texte imprimé] / C. C. Chang, Auteur ; Y. F. Ji, Auteur . - 2007 . - pp.656–664. Applied mechanics Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 133 N°6 (Juin 2007) . - pp.656–664. Mots-clés : Photogrammetry  Vibration  Dynamic  response  Measurement  Imaging  techniques. Résumé : A videogrammetric technique is proposed for measuring three-dimensional structural vibration response in the laboratory. The technique is based on the principles of close-range digital photogrammetry and computer vision. Two commercial-grade digital video cameras are used for image acquisition. To calibrate these cameras and to overcome potential lens distortion problems, an innovative two-step calibration process including individual and stereo calibration is proposed. These calibrations are efficiently done using a planar pattern arbitrarily shown at a few different orientations. This special characteristic makes it possible to perform an on-site calibration that provides flexibility in terms of using different camera settings to suit various application conditions. To validate the proposed technique, three tests, including sinusoidal motion of a point, wind tunnel test of a cross-section bridge model, and a three-story building model under earthquake excitation, are performed. Results indicate that the proposed videogrammetric technique can provide fairly accurate displacement measurement for all three tests. The proposed technique is shown to be a good complement to the traditional sensors for measuring two- or three-dimensional vibration response in the low-frequency range. ISSN : 0733-9399 En ligne : http://ascelibrary.org/action/showAbstract?page=656&volume=133&issue=6&journalCo [...]

Nontarget stereo vision technique for spatiotemporal response measurement of line-like structures / Y. F. Ji in Journal of engineering mechanics, Vol. 134 n°6 (Juin 2008) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 134 n°6 (Juin 2008) . - pp.466–474. Titre : Nontarget stereo vision technique for spatiotemporal response measurement of line-like structures Type de document : texte imprimé Auteurs : Y. F. Ji, Auteur ; C. C. Chang, Auteur Année de publication : 2008 Article en page(s) : pp.466–474. Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Measurement  Imaging  techniques  Displacement  Structural  response Résumé : With continuous advancement in optical, electronics, and computer technology, commercial digital cameras now are equipped with a high pixel resolution at a reasonable cost. Image sequences recorded by these cameras contain both spatial and temporal information of the target object; hence they can be used to extract the object’s dynamic responses and characteristics. This paper presents a nontarget stereo vision technique to measure response of a line-like structure simultaneously in both spatial and temporal domain. The technique uses two digital cameras to acquire image sequences of a line-like structure. It adopts a simple nondimensional length matching approach and the epipolar geometry to establish point correspondences within an image sequence and between two image sequences, respectively. After reconstructing a spatio-temporal displacement response from the two image sequences, wavelet transform is then used to extract the modal characteristics of the structure. The technique is illustrated using two free vibration tests: a steel cantilever beam and a bridge stay cable. Results show that the technique can measure the spatiotemporal responses, natural frequencies, and mode shapes of the two structures quite accurately. This image-based technique is a low-cost and simple-to-use approach that not only can complement current response measurement sensors but also offer special advantages which are hard to obtain using these traditional sensors. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A6%2846 [...] [article] Nontarget stereo vision technique for spatiotemporal response measurement of line-like structures [texte imprimé] / Y. F. Ji, Auteur ; C. C. Chang, Auteur . - 2008 . - pp.466–474. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 134 n°6 (Juin 2008) . - pp.466–474. Mots-clés : Measurement  Imaging  techniques  Displacement  Structural  response Résumé : With continuous advancement in optical, electronics, and computer technology, commercial digital cameras now are equipped with a high pixel resolution at a reasonable cost. Image sequences recorded by these cameras contain both spatial and temporal information of the target object; hence they can be used to extract the object’s dynamic responses and characteristics. This paper presents a nontarget stereo vision technique to measure response of a line-like structure simultaneously in both spatial and temporal domain. The technique uses two digital cameras to acquire image sequences of a line-like structure. It adopts a simple nondimensional length matching approach and the epipolar geometry to establish point correspondences within an image sequence and between two image sequences, respectively. After reconstructing a spatio-temporal displacement response from the two image sequences, wavelet transform is then used to extract the modal characteristics of the structure. The technique is illustrated using two free vibration tests: a steel cantilever beam and a bridge stay cable. Results show that the technique can measure the spatiotemporal responses, natural frequencies, and mode shapes of the two structures quite accurately. This image-based technique is a low-cost and simple-to-use approach that not only can complement current response measurement sensors but also offer special advantages which are hard to obtain using these traditional sensors. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A6%2846 [...]