Browsing by Subject "Linear oscillator"

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Open Access
Damping mechanisms
(Springer, Vienna, 2014) Akay, Adnan; Carcaterra, A.; Hagedorn, P.; Spelsberg-Korspeter, G.
The term damping is used to describe the means by which oscillation amplitudes are reduced through irreversible removal of vibratory energy in a mechanical system or a component. Dissipation, on the other hand, refers to the mechanism by which irreversible energy transfer, from vibratory to thermal, takes place. In this sense, damping is a macro-scale manifestation of atomic-scale dissipation. High damping is desirable to attain low vibration and noise levels whereas low damping is desirable for increased sensitivity in sensors and certain precision instrumentation. Damping is most obvious at resonance where the stiffness and inertia forces become equal. As a result, damping is a key factor in predicting vibration response of structures. As we will see in the following sections, there are numerous paths to damping and in a complex structure several means of damping may take place simultaneously at different locations throughout the structure. Accordingly, in determining the response of a vibrating structure, the total effect of all types of damping that may be distributed throughout a structure must be taken into account. Measurements of damping normally indicate the total damping a system experiences. It is difficult to isolate a component or a subsystem or a material within a system and measure its damping. In describing the various damping mechanisms, we will examine each through its effect on a single-degree-of-freedom (sdof) oscillator. In this section, we will review the response of a simple oscillator and examine the role of damping on it and review the basic methods of measurement criteria for damping properties of structures. However, we will not consider here the role of damping in dynamic behaviors such as chaos, stability, etc. Dissipation of vibratory energy takes place in both fluid and solid media, initiated by a number of possible macro activities. Accordingly, we will consider damping methods to reflect the media in which dissipation takes place when addressing damping methods in the next section. Models of fundamental dissipation mechanisms that describe energy transfer from ordered energy to disordered or thermalized energy are briefly summarized in the last section.
Open Access
Vibration absorption using non-dissipative complex attachments with impacts and parametric stiffness
(Acoustical Society of America, 2009) Roveri, N.; Carcaterra, A.; Akay, A.
Studies on prototypical systems that consist of a set of complex attachments, coupled to a primary structure characterized by a single degree of freedom system, have shown that vibratory energy can be transported away from the primary through use of complex undamped resonators. Properties and use of these subsystems as by energy absorbers have also been proposed, particularly using attachments that consist of a large set of resonators. These ideas have been originally developed for linear systems and they provided insight into energy sharing phenomenon in large structures like ships, airplanes, and cars, where interior substructures interact with a master structure, e.g., the hull, the fuselage, or the car body. This paper examines the effects of nonlinearities that develop in the attachments, making them even more complex. Specifically, two different nonlinearities are considered: (1) Those generated by impacts that develop among the attached resonators, and (2) parametric effects produced by time-varying stiffness of the resonators. Both the impacts and the parametric effects improve the results obtained using linear oscillators in terms of inhibiting transported energy from returning to the primary structure. The results are indeed comparable with those obtained using linear oscillators but with special frequency distributions, as in the findings of some recent papers by the same authors. Numerically obtained results show how energy is confined among the attached oscillators. © 2009 Acoustical Society of America.