טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentStarosvetsky Yuli
SubjectVibration Protection Based on Nonlinear Energy Sinks:
Mathematical Description and Applications
DepartmentDepartment of Mechanical Engineering
Supervisor Professor Gendelman Oleg
Full Thesis textFull thesis text - English Version


Abstract

One of the serious problems facing engineering design is undesired vibrations which cause severe and often unpredictable damage and failures in various applications. Many investigations in the past and present centuries are devoted to vibration isolation. The objective of a vibration isolation design is to prevent unwanted vibrations generated in a system from being transferred to other neighboring connected systems. Few structural examples are isolation of aero-structures, vibrating machinery, or buildings, vehicle suspensions.

The most well known solution of the problem is a linear vibration absorber, where an additional linear degree of freedom is added to the existing linear or weakly nonlinear main system. The linear absorber has a major drawback since it is only effective in the neighborhood of a single frequency.

            As shown in earlier researches dealing with transiently excited systems strongly nonlinear vibration absorber may effectively absorb vibrations for each excited mode with remote frequencies. However, in spite of significant advantages in the use of strongly nonlinear vibration absorber it possesses also one major drawback. Due to the nonlinearity presenting in the system there exist additional undesired regimes with high-valued amplitudes.

            The first part of the research is devoted to the extensive study of a two-degree-of-freedom system comprising of the main linear oscillator coupled to a strongly nonlinear vibration absorber. New semi analytical approach is developed for precise estimation of the effective system regimes for vibration suppression.

            Moreover in this research we study and develop new tools for prevention of the system undesired regimes. Applications of strongly nonlinear vibration absorber on single and multi-degree-of-freedom linear systems subject to harmonic and initial excitations are addressed.  In the first hand the system of two linear, coupled oscillators with remote and incommensurate frequencies (subject to harmonic excitation) with the absorber attached to it is considered. It is shown that strongly nonlinear vibration absorber is of significant preference comparing to a well known tuned mass damper. Existence of internal resonances in the linear subsystem is also addressed in the study. However, system under investigation in this case is subject to initial excitation and not a harmonic one. Extensive analytical and numerical studies are performed for the three-degree-of-freedom systems and the methods developed for a two-degree-of-freedom case are successfully extended.