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RISS 인기검색어
- 검색키워드
- 저자 : Lotfollahi-Yaghin, Mohammad Ali (검색결과 5 건)
- 무료
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- 유료
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On the absolute maximum dynamic response of a beam subjected to a moving mass
Lotfollahi-Yaghin, Mohammad Ali,Kafshgarkolaei, Hassan Jafarian,Allahyari, Hamed,Ghazvini, Taher Techno-Press 2015 Structural Engineering and Mechanics, An Int'l Jou Vol.54 No.1
Taking the mid-span/center-point of the structure as the reference point of capturing the maximum dynamic response is very customary in the available literature of the moving load problems. In this article, the absolute maximum dynamic response of an Euler-Bernoulli beam subjected to a moving mass is widely investigated for various boundary conditions of the base beam. The response of the beam is obtained by utilizing a robust numerical method so-called OPSEM (Orthonormal Polynomial Series Expansion Method). It is underlined that the absolute maximum dynamic response of the beam does not necessarily take place at the mid-span of the beam and thus the conventional analysis needs modifications. Therefore, a comprehensive parametric survey of the base beam absolute maximum dynamic response is represented in which the contribution of the velocity and weight of the moving inertial objects are scrutinized and compared to the conventional version (maximum at mid-span).
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On the absolute maximum dynamic response of a beam subjected to a moving mass
Mohammad Ali Lotfollahi-Yaghin,Hassan Jafarian Kafshgarkolaei,Hamed Allahyari,Taher Ghazvini 국제구조공학회 2015 Structural Engineering and Mechanics, An Int'l Jou Vol.54 No.1
Taking the mid-span/center-point of the structure as the reference point of capturing the maximum dynamic response is very customary in the available literature of the moving load problems. In this article, the absolute maximum dynamic response of an Euler-Bernoulli beam subjected to a moving mass is widely investigated for various boundary conditions of the base beam. The response of the beam is obtained by utilizing a robust numerical method so-called OPSEM (Orthonormal Polynomial Series Expansion Method). It is underlined that the absolute maximum dynamic response of the beam does notnecessarily take place at the mid-span of the beam and thus the conventional analysis needs modifications. Therefore, a comprehensive parametric survey of the base beam absolute maximum dynamic response is represented in which the contribution of the velocity and weight of the moving inertial objects are scrutinized and compared to the conventional version (maximum at mid-span).
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Mohammad Ali Lotfollahi-Yaghin,Mahdi Koohdaragh 대한토목학회 2011 KSCE JOURNAL OF CIVIL ENGINEERING Vol.15 No.3
Modern and efficient methods focus on signal analysis and have drawn researchers' attention to it in recent years. These methods mainly include Continuous Wavelet and Wavelet Packet transforms. The main advantage of the application of these Wavelets is their ability to analyze the signal position in different times and places. The frequency decomposition of this transform in location with high frequencies is very poor. Wavelet packet transform is more advanced form of continuous wavelet and can make a perfect level by level resolution for each signal. However, very few studies have been done in this field. In the present study, first there was an attempt to do a modal analysis on the structure by the ANSYS finite elements software, then using MATLAB, the wavelet was investigated through a continuous wavelet analysis. Finally, the results were displayed in 2-D location-coefficient figures. In the second form, transient dynamic analysis was done on the structure and to find out the characteristics of the crack, wavelet packet energy rate index was suggested. The results revealed that suggested index in the second form is both practical and applicable.
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Shahverdi, Sajad,Lotfollahi-Yaghin, Mohammad Ali,Asgarian, Behrouz Techno-Press 2013 Smart Structures and Systems, An International Jou Vol.11 No.6
Identification of damage has become an evolving area of research over the last few decades with increasing the need of online health monitoring of the large structures. The visual damage detection can be impractical, expensive and ineffective in case of large structures, e.g., offshore platforms, offshore pipelines, multi-storied buildings and bridges. Damage in a system causes a change in the dynamic properties of the system. The structural damage is typically a local phenomenon, which tends to be captured by higher frequency signals. Most of vibration-based damage detection methods require modal properties that are obtained from measured signals through the system identification techniques. However, the modal properties such as natural frequencies and mode shapes are not such good sensitive indication of structural damage. Identification of damaged jacket type offshore platform members, based on wavelet packet transform is presented in this paper. The jacket platform is excited by simple wave load. Response of actual jacket needs to be measured. Dynamic signals are measured by finite element analysis result. It is assumed that this is actual response of the platform measured in the field. The dynamic signals first decomposed into wavelet packet components. Then eliminating some of the component signals (eliminate approximation component of wavelet packet decomposition), component energies of remained signal (detail components) are calculated and used for damage assessment. This method is called Detail Signal Energy Rate Index (DSERI). The results show that reduced wavelet packet component energies are good candidate indices which are sensitive to structural damage. These component energies can be used for damage assessment including identifying damage occurrence and are applicable for finding damages' location.
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Sajad Shahverdi,Mohammad Ali Lotfollahi-Yaghin,Behrouz Asgarian 국제구조공학회 2013 Smart Structures and Systems, An International Jou Vol.11 No.6
Identification of damage has become an evolving area of research over the last few decades with increasing the need of online health monitoring of the large structures. The visual damage detection can be impractical, expensive and ineffective in case of large structures, e.g., offshore platforms, offshore pipelines, multi-storied buildings and bridges. Damage in a system causes a change in the dynamic properties of the system. The structural damage is typically a local phenomenon, which tends to be captured by higher frequency signals. Most of vibration-based damage detection methods require modal properties that are obtained from measured signals through the system identification techniques. However, the modal properties such as natural frequencies and mode shapes are not such good sensitive indication of structural damage. Identification of damaged jacket type offshore platform members, based on wavelet packet transform is presented in this paper. The jacket platform is excited by simple wave load. Response of actual jacket needs to be measured. Dynamic signals are measured by finite element analysis result. It is assumed that this is actual response of the platform measured in the field. The dynamic signals first decomposed into wavelet packet components. Then eliminating some of the component signals (eliminate approximation component of wavelet packet decomposition), component energies of remained signal (detail components) are calculated and used for damage assessment. This method is called Detail Signal Energy Rate Index (DSERI). The results show that reduced wavelet packet component energies are good candidate indices which are sensitive to structural damage. These component energies can be used for damage assessment including identifying damage occurrence and are applicable for finding damages' location.
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