• Transactions of the Korean Society of Automotive Engineers
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• v.2 no.5
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• pp.93-100
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• 1994

Friction-induced vibration characteristics of automotive brake lining pad are investigated on the basis of experimental observations from a pin-on-disk type friction-induced vibration experimental apparatus. The measured responses of the experimental apparatus show limit cycles of quasi-harmonics type and beat phenomena due to the velocity dependence of friction force. To deduce the friction coefficient vs. relative velocity Lienard method is adopted with least square fit. It shows Scurve which characterizes a quasi-harmonic vibration. The calculation of amplitudes and friquencies of the limit cycles is done using slowly changing phase and amplitude method. The theoretical and numerical results show fairly good agreements with those of experiments.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.710-711
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• 2014

In many cases, periodic noise occurs because most applications include motors, compressors and so on which have reciprocating motion. The noise usually contains tones at the fundamental frequency and at several higher harmonic frequencies in practice. For this type of noise, we developed a frequency-domain active noise control algorithm and determined that it's effective. However, the performance deteriorated for quasi-periodic noise. In this paper, we develop compensated frequency-domain active noise control algorithm for quasi-periodicity. And then, we implement computer simulation and compare the performance.

• Smart Structures and Systems
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• v.25 no.5
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• pp.543-557
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• 2020

This paper presents a series of experimental and numerical investigations on a vertical isolation system with quasi-zero stiffness (QZS) property. The isolation system comprises a linear helical spring and disk spring. The disk spring is designed to provide variable stiffness to the system. Orthogonal static tests with different design parameters are conducted to verify the mathematical and mechanical models of the isolation system. The deviations between theoretical and test results influenced by the design parameters are summarized. Then, the dynamic tests for the systems with different under-load degrees are performed, including the fast sweeping tests, harmonic excitation tests, and half-sine impact tests. The displacement transmissibility, vibration reduction rate, and free vibration response are calculated. Based on the test results, the variation of the transmission rule is evaluated and the damping magnitudes and types are identified. In addition, the relevant numerical time history responses are calculated considering the nonlinear behavior of the system. The results indicate that the QZS isolation system has a satisfactory isolation effect, while a higher damping level can potentially promote the isolation performance in the low-frequency range. It is also proved that the numerical calculation method accurately predicts the transmission character of the isolation system.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.690-695
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• 2005

Flexible circular cantilever beams when excited externally introduce a lot of dynamic characteristics. The non-linear elements that these flexible beams develop include non-linearity due to inertia terms, spring, and damping. They show different characteristics of motion from each other. In the modes of lower order, the non-linearity due to spring is prevalent, while the non-linearity due to inertia Is prevalent in the modes of higher order. To analyze these effects the non-linear phenomena are analyzed experimentally. When the response characteristics of non-linear vibration are analyzed using autospectrum, it is possible to analyze the subharmonic and superharmonic mot ion by comparison. The phase change is analyzed using the method of phase portrait and the non-linear characteristics of response characteristics that are developed in flexible structures can be predicted and applied to the stage of design.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.2
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• pp.47.1-47.1
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• 2019

We report the design and vibration analysis for the optomechanical structures of Linear Astigmatism Free - Three Mirror System (LAF-TMS). LAF-TMS is the linear astigmatism free off-axis wide-field telescope with D = 150 mm, F/3.3, and FOV = 5.51° × 4.13°. The whole structure consists of four optomechanical modules. It can accurately mount mirrors and also can survive from vibration environments. The Mass Acceleration Curve (MAC) is adapted to the quasi-static analysis. Modal, harmonic, and random vibration analysis have been performed under the qualification level of the launch system. We evaluate the final results in terms of von Mises stress and Margin of Safety (MoS).

• The Bulletin of The Korean Astronomical Society
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• v.45 no.1
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• pp.66.3-66.3
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• 2020

We present the optical design of Linear Astigmatism Free - Three Mirror System (LAF-TMS) D200 for UVO-Multiband Polarizing Imager System (UVOMPIS). LAF-TMS D200 is the off-axis wide-field telescope with EPD = 200 mm, F/2, and Field of View (FoV) = 2° × 4°. Its optical mirrors are optimized to freeform surfaces for high-quality optical performance over a wide FoV. The proposed mirror holder consists of four aluminum optomechanical modules that have applied for LAF-TMS D150 which is a prototype of the LAF-TMS system. It can accurately mount mirrors and also can sustain from vibration environments. As a feasibility study, quasi-static, modal, harmonic, and random vibration analyses have been performed to LAF-TMS D150 optomechanical structure under the qualification level of the Soyuz-2/Fregat launch system. We evaluate the vibration analysis results in terms of von Mises stress and Margin of Safety.

• Structural Engineering and Mechanics
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• v.88 no.3
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• pp.221-238
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• 2023

This paper developed and examined a novel passive vibration isolator (i.e., "X-inerter") motivated by combining a bio-inspired structure and a rack-pinion inerter. The bio-inspired structure provided nonlinear stiffness and damping owing to its geometric nonlinearity. In addition, the behavior was further enhanced by a gear inerter that produced a special nonlinear inertia effect; thus, an X-inerter was developed. As a result, the X-inerter can achieve both high-static-low-dynamic stiffness (HSLDS) and quasi-zero stiffness (QZS), obtaining ultra-low frequency isolation. Furthermore, the installed inerter can produce a coupled nonlinear inertia and damping effect, leading to an anti-resonance frequency near the resonance, wide isolation region, and low resonance peak. Both static and dynamic analyses of the proposed isolator were conducted and the structural parameters' influence was comprehensively investigated. The X-inerter was proven to be comparatively more stable in the ultra-low frequency than the benchmarking QZS isolator due to the nonlinear damping and inertia properties. Moreover, the inertia effect could suppress the bio-inspired structure's super- and sub-harmonic resonance. Therefore, the X-inerter isolator generally possesses desirable nonlinear stiffness, nonlinear damping, and unique nonlinear inertia, designed to achieve the ultra-low natural frequency, the anti-resonance property, and a wide isolation region with a low resonance peak.

• Structural Engineering and Mechanics
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• v.34 no.4
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• pp.507-523
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• 2010

Parametric and forced non-linear vibrations of an axially moving rotor both in non-resonance and near-resonance cases have been investigated analytically in this paper. The axial speed is assumed to involve a mean value along with small harmonic fluctuations. Hamilton's principle is employed for this gyroscopic system to derive three coupled non-linear equations of motion. Longitudinal inertia is neglected under the quasi-static stretch assumption and two integro-partial-differential equations are obtained. With introducing a complex variable, the equations of motion is presented in the form of a single, complex equation. The method of multiple scales is applied directly to the resulting equation and the approximate closed-form solution is obtained. Stability boundaries for the steady-state response are formulated and the frequency-response curves are drawn. A number of case studies are considered and the numerical simulations are presented to highlight the effects of system parameters on the linear and nonlinear natural frequencies, mode shapes, limit cycles and the frequency-response curves of the system.