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Dynamics of Structures
Published in Lingyi Lu, Junbo Jia, Zhuo Tang, Structural Mechanics, 2022
Lingyi Lu, Junbo Jia, Zhuo Tang
Structural Dynamics is a field of structural analysis which covers the responses of structures subjected to dynamic loading. Intuition may suggest that dynamic loads include wind, earthquakes and blasts impacting structures. However, the academic definition of dynamic loading is a bit complicated. If the inertial forces are important for the analysis of the structural response to a load, then it is called adynamic loading, and the problem involved is known as a structural dynamics problem. In contrast, if the acceleration of the structure can be ignored in the analysis, then it is a static problem and the load involved is referred to as static loading. As might be expected intuitively, a time-varying excitation is usually a dynamic load. For example, the sinusoidal excitation shown in Figure 8.1a is a dynamic load applied to the cantilever. However, in some cases, a time-varying loading may be taken as a static load.
System identification and model updating
Published in You-Lin Xu, Jia He, Smart Civil Structures, 2017
In this regard, this chapter first presents the mathematical model of a dynamic civil structure in three different coordinate systems. Structural dynamic characteristics are introduced through a modal analysis in the modal coordinate system. This chapter then illustrates modal identification methods in the frequency domain, time domain and frequency-time domain, in which how to extract dynamic characteristics of a structure from measurement data is demonstrated. In consideration of the subsequent chapters, this chapter also gives a brief introduction to force identification. The model updating methods, mainly the sensitivity-and-modal-based updating method, are then fully discussed. Finally, the model updating of a multi-scale FE model of a transmission tower is given in detail as a case study.
Operational modal analysis of light pole-viaduct system from video measurements using phase-based motion magnification
Published in Hiroshi Yokota, Dan M. Frangopol, Bridge Maintenance, Safety, Management, Life-Cycle Sustainability and Innovations, 2021
T.J. Saravanan, D.M. Siringoringo, Y. Fujino, S. Wangchuk
The structural vibration measurement is important for structural performance evaluation and health monitoring. Commonly, the modal analysis technique is utilized for analyzing the vibration measurements and forming structural dynamics models. Two classical methods for identifying modal parameters from the vibration measurement are experimental modal analysis (EMA) and operational modal analysis (OMA) methods. EMA use both input excitation and output response obtained (Ewins 2000) while OMA utilizes only output structural response (Brincker & Ventura 2015). Therefore, OMA is used for analyzing large infrastructures like bridges which is subjected to various input force excitations like traffic, wind and other dynamic loads.
Modification of an implicit approach based on nonstandard rules for structural dynamics analysis
Published in Mechanics Based Design of Structures and Machines, 2019
Khadijeh Askaripour, Mohammad Javad Fadaee
Structural dynamics refers to the analysis of structures subjected to dynamic loading. The object of the analysis is to compute displacement time history and its time derivatives. To that end, finite element (FE) technique is substantially used to calculate the mass, damping and stiffness matrices containing structural properties. Numerous conventional isoparametric and non-isoparametric FEs such as triangular, rectangular, tetrahedral, brick, plate, shell, and beam employed for various types of structures are virtually in use. One of the recently developed FE techniques is absolute nodal coordinate formulation (ANCF) proposed for multibody applications to prevent large deformations, in which rotations are not interpolated over the FE. For example, new ANCF-based triangular and tetrahedral elements, respectively, involving 6 and 12 coordinates per node have been developed while evaluating their performances compared to those of the conventional elements (Pappalardo, Wang, and Shabana 2017). Furthermore, rational ANCF plate FEs allowing for modeling of complex geometric cross sections, where are not describable through non-rational FEs, have been utilized to analyze curved geometries (Pappalardo, Wallin, and Shabana 2016; Pappalardo et al., 2017). After obtaining the matrices of structural properties, the equation of motion should be solved under dynamic loading.
The systems stance
Published in Civil Engineering and Environmental Systems, 2020
Building real aircraft needs plans and working drawings which collectively model the whole and individually model the aircraft’s parts. Most are to scale, though some could be full-size, laid out with splines on a lofting floor. And they could be held digitally. Digital structural models would explore the aircraft’s structural dynamics, producing numbers for strength and dynamic response.
A numerical insight into stress mode shapes of rectangular thin-plate structures
Published in Mechanics Based Design of Structures and Machines, 2023
Yadong Zhou, Weili Zeng, Youchao Sun, Yile Zhang
For the purpose of dynamic response prediction and vibration damage evaluation, it is highly desirable to accurately calculate both the locations and amplitude of dynamic stresses, e.g., in the notch stress method where the accurate calculation of local stress concentration is highly critical. But challenges still exist for real applications, e.g., large-scale aircraft and spacecraft structures, because in FEM analysis environments of structural dynamics, the computation burden and storage resource cannot be neglected even for today’s computational resources. Such burden will be much heavier for the digital twins of advanced aircraft in the future, which enable to virtually predict the service lifetime and can be updated to track the state changes or damage as the aircraft ages. For instance, mapping loads to fatigue by FEM structural dynamics, it will be time-consuming and computationally expensive in dealing with the time history data (Habtour et al. 2014); in the real time fatigue estimation of large-scale structures, the limited memory to store data sets and completing the computations sufficiently fast should be overcome (Ugras et al. 2019). Usually, more than half of the time and human resource are paid for the high-accuracy numerical modeling, such as pursuing for the generation of quadrilateral or hexahedron mesh. However, a high-fidelity but excessive resource-consuming FEM model will make it infeasible for dynamic stress design, and hence MOR procedures are required. By means of computational modal analysis, the vibration characteristics of thin-plate members can be achieved efficiently with numerical simulations, such as widely-used FEM modeling, which also allows for possible structural modification and re-analysis. To date, extensive studies have been conducted on the modal analysis and mechanics design of plate-type structures. However, the conventional modal analysis and dynamic design always aim at the global modal properties, e.g., the modal frequency, anti-resonant frequency, and displacement mode shapes (DMSs). In such a manner, it is difficult to manifest the contributed factors to the final dynamic stress in a direct way, because obtaining the final dynamic stress only will mask the calculation process in FEM software. For this reason, the SMSs have the advantage in giving an insight into the contributed factors (e.g., critical locations and predominant modes) for the final dynamic stress responses.