Finite element analysis for the vibration control of structures with dynamic vibration absorbers

• Main Author: Loh, Tian Wai
• Other Authors: Sellakkutti Rajendran
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2022
• Subjects: Engineering::Mechanical engineering
• Online Access: https://hdl.handle.net/10356/158853
• Institution: Nanyang Technological University

Dynamic vibration absorbers (DVAs) are commonly used to suppress vibrations of a system at a specified frequency, usually at the operating frequency or resonant frequencies of the system. This project evaluates the effectiveness and impact of DVAs on a fixed-fixed beam structure and a building structure. ANSYS Mechanical APDL Version 2021 R2 is used for modal and harmonic analyses of the structures. With macro coding, automation for generation of models in ANSYS is allowed and adjustments to the codes are made according to requirements of the analyses. The structures are first modelled in ANSYS and convergence studies are subsequently performed through modal analyses to evaluate the variations in results of natural frequencies due to mesh refinements. An optimal mesh density will be obtained from convergence studies of the respective structures. This optimal mesh density will then be used for the harmonic analyses of the structures with and without DVA. The optimal element edge lengths obtained from mesh convergence studies for the fixed-fixed beam and building is 0.1mm for both structures. Through harmonic analyses, amplitude-frequency responses of the structures without DVAs are studied and compared with the results from harmonic analyses of the same structures with DVA. By defining parameters such as natural frequencies ( ) from modal analyses and equivalent stiffness ( ) of DVAs via analytical approach, the DVAs will be designed for vibration control of the structures. The consequence of adding a DVA to both structures resulted in full suppression of vibration motion at the intended frequencies. Consequently, due to the addition of a DVA to the primary structures, two new resonant frequencies are introduced to the overall systems. Next, similar analyses are performed to evaluate the impact of introducing structural damping to the structures. Structural damping has an important impact on the overall amplitude response of the structure. With structural damping, it is observed that overall amplitude-frequency responses of the structures reduced. Lastly, studies on the amplitude-frequency response of the DVA’s masses are carried out to evaluate the impact of subjecting different modes of damping to the DVA. The results indicate that damping in the DVA has no impact on DVA’s mass at the frequency of interest.