In general, mechanical vibrations can be defined as oscillatory movements of bodies around a position of equilibrium [1]. These movements generate dynamic loads that can require great efforts from the acting structures. Learn about Kot Engenharia 's work in analyzing these vibrations and the dynamics of structures in this article.

The relevance of vibration analysis and structural dynamics has increased with the advancement of modern engineering. This is because before the industrial revolution, structures had a high mass of their own, so vibrations on parts were of a lower magnitude and the dynamic response in structures was low.

 The arrival of new materials such as cast iron, steel and aluminum, together with the evolution of knowledge about material properties and structural loads, resulted in a significant reduction in the mass of structures. In addition, machines have become more efficient and therefore have higher rotational speeds. This scenario justifies the increase in vibrations on structures. [2]

The vibration present in machines and structures is often undesirable, as it causes excessive noise, damaging movements and dynamic stresses that contribute to fatigue processes.

For a better understanding of the context, we have the following concepts:

• Resonance: every mechanical system has at least one natural vibration frequency that depends only on its own mass and rigidity. Resonance is the process that occurs when this system is excited with a frequency equal to one of its natural vibration frequencies, increasing the amplitude of its movements.
• Fatigue: the ASTM standard [ASTM-E 823-96, 2000] defines fatigue as: "A progressive and localized process of permanent structural changes occurring in a material subjected to conditions that produce cyclic stresses and strains that can culminate in cracks or fracture after a certain number of cycles.". This sequence of events is illustrated in Figure 1.

Figure 1: Process of crack formation and fatigue rupture. [3]

One of the classic cases of the need for vibration and dynamics analysis of structures is the collapse of the Tacoma Narrows Bridge. In 1940, the suspension bridge went into resonance when excited by wind loads and, for this and other reasons, failed. [4] Figures 2, 3 and 4 show the bridge in its natural state, under excitation and after the disaster, respectively.

Figure 2: Tacoma Narrows Bridge in its natural state. [5]

Figure 3: Tacoma Narrows Bridge during resonance. [6]

Figure 4: Collapse of the Tacoma Narrows Bridge. [7]

Fatigue, in turn, has even caused problems such as preventing the use of large aircraft turbines.

Kot can act to prevent these events by carrying out studies using the Finite Element Method (FEM), a tool widely used in the context of applied engineering. The company's experience includes numerous assets, such as vibrating screens, metal and civil structures, train tracks, wagons and passenger cars, wheelsets, tanks, conveyors, rotors, shafts and bearings, among others. 

Kot also applies the Vibration Analysis method using image processing, find out more about this application by clicking here. ahere! These analyses can bring benefits in addition to preventing collapses, the main ones being: 

• Prevention of unexpected machine downtime;
• Increased plant reliability and productivity;
• Presentation of a precise diagnosis of equipment and structures.

Conclusion

The analysis of the vibrations and dynamics of structures is an extremely important topic from an economic and safety point of view. Kot has the necessary knowledge to apply it, being able to evaluate different operating contexts and contribute to the results. Contact our team for more information!

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Referências

[1] Corneliu Cismasiu (n.d). Notes on Mechanical Vibrations. 

[3] Kot Collection.

[2] C. Beards (1996). Structural Vibration: Analysis and Damping.

[4] K. Yusuf Billah and Robert H. Scanian (1998). Resonance, Tacoma Narrows bridge failure, and undergraduate physics textbooks.

[5] Física Matemática Músicas e Filmes. Ponte de Tacoma. Disponível em: <https://engenharia360.com/o-incrivel-caso-da-ponte-de-tacoma/>

[6] – Magnus Mundi (2014). Ponte de Tacoma. Disponível em: <https://engenharia360.com/o-incrivel-caso-da-ponte-de-tacoma/>

[7] Kitsap Sun (s.d) Ponte de Tacoma. Disponível em: <https://engenharia360.com/o-incrivel-caso-da-ponte-de-tacoma/>