Eventos Anais de eventos
COBEM 2023
27th International Congress of Mechanical Engineering
Design of a Viscoelastic Pendulum Absorber for Enhancing Fatigue Life in Dynamically Excited Structures
Submission Author:
Leonardo de Castro Ferreira dos Santos , PR
Co-Authors:
Leonardo de Castro Ferreira dos Santos, Carlos Alberto Bavastri
Presenter: Leonardo de Castro Ferreira dos Santos
doi://10.26678/ABCM.COBEM2023.COB2023-0086
Abstract
Low frequency vibrations are a significant contributor to fatigue damage within dynamically excited structures. However, designing a slender body that can withstand these vibrations is a challenging task, due to dynamic amplification caused by the body's natural frequencies. In many cases, designers try to avoid the superposition of excitation and natural frequencies, including a proper safety margin, that reduces the response of the structure. On the other hand, when design requirements are tight, it may not be possible to make sufficient changes in mass and stiffness to ensure structural integrity. In such cases, external devices like dynamic absorbers can be used to suppress vibration responses. It can be done by tuning them according to the system’s modal parameters, reducing the stresses on the structure and enhancing its fatigue life. This article proposes a viscoelastic pendulum absorber design, tuned to the first natural frequency of a cantilever beam, based on the Fixed Points Theory. A Finite Element Model of the system is built and submitted to a random force, with white noise characteristics, exciting the structure with a constant density power between 0 and 500 Hz. Fatigue analyses are performed using Rainflow Cycle Counting in the frequency domain, based on Lalanne’s approach and the statistical properties of the stresses histories. The viscoelastic material used in the absorber has a complex Shear Modulus, with the loss factor directly related to damping, that is used to dissipate vibration energy from the system. To represent this behavior, a fractional derivative model is chosen, where the Complex Shear Modulus is represented as a function of the frequency and temperature. Finally, the fatigue evaluation is performed for both primary (cantilever beam) and composite (cantilever beam with the tuned absorber) structures. The analyses showed promising results, with the designed viscoelastic pendulum absorber reducing almost 20 dB of vibration amplitude in the first natural frequency and improving the fatigue life of the structure by 60 times.
Keywords
Random Fatigue, passive control vibration, Viscoelastic Dynamic Vibration Neutralizers, Random vibrations, low frequency vibration, pendulum tuned mass damper, Finite Element Method, structural dynamics, modal reduction, frequency domain analysis
