Scholarly Publications - Mechanical Engineering

Permanent URI for this collectionhttps://hdl.handle.net/11693/115626

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Browsing Scholarly Publications - Mechanical Engineering by Author "Akay, Adnan"

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    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.
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    Noise control engineering and education
    (2021) Akay, Adnan
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    Targeted energy pumping using a linear complex attachment
    (ISMA, 2012-09) Roveri, N.; Carcaterra, A.; Akay, Adnan
    The present paper considers the problem of realizing an effective targeted energy pumping from a linear oscillator to a plurality of ungrounded linear resonators, attached to it in parallel. Theoretical as well as numerical results demonstrate the efficacy of using a complex attachment as a passive absorber of broadband energy, injected into the primary structure. The paper unveils also the existence of an instantaneous frequency associated to the master response characterized by intermittency: a rather surprising result for a linear autonomous system. A comparative analysis with a nonlinear energy sink demonstrates that the two systems present some analogies in this respect and that the complex attachment is a very efficient energy trap.
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    Uncertainty and dissipation
    (Katholieke Universiteit Leuven, 2012-09) Carcaterra, A.; Akay, Adnan
    This paper discusses the question of the energy confinement in mechanical structures in the light of the uncertainties affecting the natural frequencies of the system. More precisely, recent studies have shown that energy can be introduced to a linear system with near irreversibility, or energy within a system can migrate to a subsystem nearly irreversibly, even in the absence of dissipation, provided that the system has a particular natural frequency distribution. In this paper, the case of uncertainties in the system's natural frequencies is discussed and a remarkable statistical property of the natural frequency is derived for permanent energy confinement within a part of the system. The results demonstrate the existence of a special class of linear non-dissipative dynamic systems that exhibit nearly-irreversible energy confinement (IEC) if they satisfy a minimum-variance-response (MIVAR) property. In this case, if the probability density function of the natural frequencies has a special distribution, the conservative system shows an unexpected decaying impulse response. © (2012) by the Katholieke Universiteit Leuven Department of Mechanical Engineering All rights reserved.