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Browsing School of Civil & Environmental Engineering (ETDs) by Author "Thakadu, Katlego"

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    Passive Vibration Isolation Systems Integrated with Dynamic Vibration Absorber
    (University of the Witwatersrand, Johannesburg, 2023-02) Thakadu, Katlego; Li, Kuinian
    Isolating vibration using an isolator and/or vibration absorber are the two commonly used measures of vibration control in practice. The presented investigation explores multiple passive vibration isolator configurations, integrated with a dynamic vibration absorber, to improve the performance of vibration isolating. In the first section, A Passive vibration Isolator Integrated with a Skyhook and Groundhook Vibrational Absorber is investigated. The dynamic behaviour of the proposed isolators with the lumped mass, fixed to an inertial reference, is investigated using force, and displacement transmissibility equations. The force and displacement transmissibility equations are derived by modelling the dynamic system as a two-degree-of-freedom system. Derivations for both configurations of the isolator, integrated with a skyhook and groundhook are presented, including numerical simulations and parameter sensitivity analyses. The analysis conducted, indicates that both configurations, is indeed a passive linear isolator, which can support a static load whilst achieving significant vibrational isolation, employing a relatively low damping element. Additionally, the practical applications of the proposed configurations are plausible with the currently available material, which makes the research viable within the field of engineering. In the second section, A Passive vibration Isolator Integrated a Dynamic Vibration Absorber with Negative Stiffness Spring is investigated. The dynamic behaviour of the isolator supporting a lumped mass, is investigated using force and displacement transmissibility equations of the isolator. The force and displacement transmissibility are derived by modelling the dynamic system as a two-degree-of-freedom system. A unique constraint on the negative stiffness ratio, α, for the isolator’s stable operation, is developed. The optimal design of such an isolator was demonstrated with a design example. Extensive numerical simulation and parameter studies on the isolator were performed, which revealed attractive dynamic characteristics of the isolator. It is a passive linear isolator, without any non-linear elements, spring or damper. However, it can bear a large static load and, at the same time, achieve a greatly increased vibration isolation. These two effects are considered mutually exclusive in linear isolator and can be overcome in some extent by properly configured nonlinear isolators only. Moreover, numerical simulation and parameters study shows that the negative stiffness ratio and the mass ratio required can be very small, which makes the implementation of such an isolator in practice convenient. All these make the isolator attractive for engineering application. The third section of this research is on the optimal design of a two-stage isolator, a isolator integrated with another isolator. Performance of a passive two-stage vibration isolator and its design was rigorously evaluated and recorded in this study. It is revealed that the vibration isolating performance of a linear passive two-stage vibration isolator depends on the configurational parameters of the isolator. The transmissibility, a non-dimensional parameter used to quantify the effectiveness of an isolation system, of the passive two-stage vibration isolator was derived. A numerical optimization on the transmissibility of the isolator was developed and performed using the Minimax algorithm. It is demonstrated that an optimally designed linear passive two-stage vibration isolator produces significantly better isolating than a single-stage linear isolator at all frequencies, high and low. The proposed linear passive two-stage isolator is not only effective against high-frequency isolation, which used to be the primary use of a passive two-stage isolator but shows outstanding isolation performance at all frequencies. The proposed linear passive two-stage vibration isolator outperforms many complicated nonlinear isolators, including both single-stage or two-stage isolators. Parameter selection, dynamic performance driven optimal design and potential application of the proposed isolator were also investigated and presented.