טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentBenarous Nir
SubjectNonlinear Energy Sink with Combined Nonlinearities
DepartmentDepartment of Mechanical Engineering
Supervisor Professor Oleg Gendelman
Full Thesis textFull thesis text - English Version


Abstract

Undesired oscillations are known in many fields of engineering. They can be caused by various reasons such as external shocks, internal and external resonances, self-excitation and etc. The undesired oscillations can reveal themselves in various mechanisms and structures such as a building in an earthquake, a wing of a plane undergoing flutter and more.

One of the ways suggested to deal with such oscillations is a Nonlinear Energy Sink (NES).

The NES is designed to mitigate vibrations in a primary system via passive targeted energy transfer (TET). A single degree of freedom (SDOF) NES can exhibit TET for a specific (often quite narrow) range of energies. The goal of this study is to suggest and explore a novel design for the NES, in order to achieve better TET performance than previously studied NES systems. The study of 2 degrees of freedom NES (2DOF NES) comes from the intention to increase the energy range and to improve the efficiency of the system while having the same relative mass and volume as with an SDOF NES.

The suggested NES design comprises two coupled essentially nonlinear elements: a cubic spring and an eccentric mass. Both masses are small compared to the primary mass and both are equipped with linear viscous damping.

First, we analyze the conservative dynamics of the separate NES itself with the help of analytic and numeric approaches. This system exhibits an interesting dynamical phenomenon called "Amplitude Locking". One of the nonlinear normal modes (NNM) of the system is characterized by constant amplitude of the cubic spring regardless of the energy in the system and any increase or decrease in the energy brings about in only a frequency shift. The novel phenomenon is studied in details.

We also investigate vibration suppression in the primary oscillator with the help of the 2DOF NES is studied. It is demonstrated that the 2DOF NES presents considerably better performance (in terms of characteristic range of energies of efficient suppression) than an SDOF NES with the same mass.