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Introduction
Published in Heung-Fai Lam, Jia-Hua Yang, Vibration Testing and Applications in System Identification of Civil Engineering Structures, 2023
Modal analysis, in general, is the technique used to calculate the modal parameters of a structural system by utilizing the measured dynamic data from vibration tests. If forced vibration tests are conducted (see Section 1.1.2), both the measured excitation and responses are available. Modal testing can be used to identify natural frequencies, mode shapes, and damping ratios of the system. However, both free and forced vibration tests are usually difficult to arrange for civil engineering structures, as discussed earlier. As a result, modal analysis for civil engineering structures is usually done with ambient vibration tests. As it is not necessary to apply external force or introduce disturbance to the target structure, the vibration test and the corresponding modal identification can be carried out under the operational condition of the structure, and therefore, this technique is called “operational modal analysis.” Operational modal analysis is convenient, as only structural responses (system output) are needed to be measured, and its implementation is cost-effective. As the vibration level under ambient excitation is usually very low, the identified modal parameters can only reflect the structural characteristic under low-level vibration. Furthermore, the accelerometer employed must be very sensitive due to the low vibration level. Without using the force information and the relatively low signal-to-noise ratio, the uncertainties associated with the operational modal analysis results are believed to be high.
Field Testing of Pedestrian Bridges
Published in Eva O.L. Lantsoght, Load Testing of Bridges, 2019
Darius Bačinskas, Ronaldas Jakubovskis, Arturas Kilikevičius
Identification of dynamic parameters of footbridges is generally much more complex in comparison to measurement of static deflection or strain at particular points of the structure. The dynamic behavior of a structure in a given frequency range can be modeled as a set of individual modes of vibration. Each vibration mode can be described by three modal parameters: mode shape, natural frequency, and modal damping. Modal parameters represent the inherent properties of a structure which are independent to the excitation source. Principally, determination of modal parameters (which is commonly referred as modal analysis) is the main task in the dynamic analysis of the footbridges. Modal analysis may be accomplished either through analytical, numerical or experimental techniques.
Vibration analysis
Published in C M Langton, C F Njeh, The Physical Measurement of Bone, 2016
Modal analysis is widely used in engineering and provides an understanding of the structural characteristics, operating conditions and performance of structures subject to vibration. Modal analysis determines the fundamental vibration mode shapes and the frequencies at which these occur. This can involve a relatively straightforward analysis for basic components of a simple system or an extremely complicated analysis when examining a complex device or structure exposed to time varying loading. Modal analysis is widely used in the design of many types of structure, including automotive structures, aircraft structures, spacecraft and of sports equipment such as hockey sticks, golf clubs and tennis racquets.
Computational analysis of the transportation phase of an innovative foundation for offshore wind turbine
Published in Ships and Offshore Structures, 2021
J. Cardoso, M. Vieira, E. Henriques, L. Reis
A modal analysis allows the determination of the vibration characteristics of a structure, that is, the determination of its natural frequencies and modes of vibration which depend on the stiffness of the structure, its mass and the way this mass is distributed. These two characteristics are important in the design of a structure subjected to dynamic loads to evaluate the risk of resonance (Nallayarasu and Senthil Kumar 2017). This would cause the system to oscillate at higher amplitudes than when the force is applied at other frequencies and from these large oscillations can result important deformations and structural damage, mainly due to fatigue (Challenges in Design of Foundations for Offshore Wind Turbines). It is therefore crucial to avoid that the main sources of excitation transmitted to the structure include frequencies of vibration close to their natural frequencies.
Seismic performance analysis of a wind turbine with a monopile foundation affected by sea ice based on a simple numerical method
Published in Engineering Applications of Computational Fluid Mechanics, 2021
Shuai Huang, Mingming Huang, Yuejun Lyu
Modal analysis is a method of studying the dynamic characteristics of a structure, and modal analysis can determine natural vibration frequencies and mode shapes at the natural vibration frequencies of the structure. The mode shapes can be used to indicate the most likely deformation of the wind turbine, and they can also reflect the deformation characteristics of the different parts, such as which parts are rigid and which parts are soft. The seismic deformation of the wind turbine is a superposition of the different modes, and the first two mode shapes are the most likely deformations of the wind turbine. Therefore, modal analysis is a critical step when analysing the seismic dynamics of wind turbines. First, we conduct modal analysis of the structure with and without sea ice. The order-1 and order-2 mode shapes of the wind turbine are illustrated in Figure 8, and their periods are listed in Table 5.
Research on the Dynamic Characteristics of the CFETR Vacuum Vessel Based on the Modal Synthesis Method
Published in Fusion Science and Technology, 2022
Haozhe Qiu, Kun Lu, Xiaojun Ni, Jianghua Wei, Songbo Han
Modal analysis is a common dynamic analysis method to study the vibration characteristics of structures. Through modal analysis, the weak parts of the system can be identified.15 If the modal frequency is close to the excitation load, it will easily cause resonance, which can result in structural fatigue fracture and parts failure. Compared with static analysis, more computational resources are required in modal analysis. The accuracy and the efficiency of the modal synthesis method were verified by comparing the results of substructure model with the conventional finite element model.