• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.23 no.11
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• pp.957-965
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• 2013

This paper deals with analytical methods for low frequency and high frequency brake squeal noise on brake-rear caliper. In order to improve low frequency and high frequency squeal noise, we take survey caliper bracket shape parameters and housing shape parameters. Besides, using the combination of bracket and housing parameter were surveyed. Thus, using the combination of bracket Alt_05 and housing Alt_45 specifications, instability analysis and brake dynamo test were carried out. Based upon the two models, low and high frequency squeal noise of base model were improved. But, for 6.0 kHz frequency noise, which is not improved, it needs to additionally study on instability analysis and combination of the other brake components.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1998.04a
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• pp.678-683
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• 1998

Combustion instability by thermoacoustic feedback incite strong low frequency noise and vibration which damage the system and provoke the environmental problems. Therefore, it is necessary to control the thermoacoustic oscillation. In the way of controlling the instability, active control method using adaptive algorithm is applied. In this study, active noise control method using anti-sound technique is selected, whose principle is cancelling the noise with the addition of opposite phase sound. At first, simulation is performed to confirm the stability of controller, and after that control of combustion instability is carried out to get cancellation of 20-30dB SPL.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.6 s.123
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• pp.498-506
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• 2007

Using wind tunnel, experimental approaches were employed to investigate fluidelastic instability of tube bundles, subjected to uniform cross flow. There are several flow-induced vibration excitation mechanisms, such as fluidelastic instability, periodic wake shedding resonance, turbulence-induced excitation and acoustic resonance, which could cause excessive vibration in shell-and tube heat exchanges. Fluidelastic is the most important vibration excitation mechanism for heat exchanger tube bundles subjected to cross flow. The system comprised of cantilevered flexible cylinder(s) and rigid cylinders of normal square array, In order to see the characteristics of flow in tube bundles, particle image velocimetry was used. From a practical design point of view, Fluidelastic instability may be expressed simply in terms of dimensionless flow velocity and dimensionless mass-damping. The threshold flow velocity for dynamic instability of cylinder rows is evaluated and the data for design guideline is proposed for the tube bundles of normal square array.

• Transactions of the Korean Society of Automotive Engineers
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• v.24 no.5
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• pp.520-526
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• 2016

Squeal noise is a typical brake noise that is annoying to both passengers and pedestrians. Its frequency range is fairly wide from 1 kHz to 18 kHz, which can be distressful to people. The brake squeal noise occurs due to various mechanisms, such as the mode coupling of the brake system, self-excited vibration, unstable wear, and others. In this study, several parameters involved in the generation of a squeal noise are investigated experimentally by using a brake noise dynamometer. The speed, caliper pressure, torque, and friction coefficient are measured as functions of time on the dynamometer. The contact pressure and temperature distributions of the disc and the pad are also measured by using a thermal imaging camera and a pressure mapping system. As a result of the simultaneous measurement of the friction coefficient and squeal amplitude as functions of the velocity, it is found that the onset of the squeal may be predicted from the ${\mu}-v$ curve. It is also found that a non-uniform contact pressure causes instability and, in turn, a squeal. Based on the analysis results, design modifications of the pad are suggested for improved noise characteristics.

• Journal of KSNVE
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• v.8 no.5
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• pp.914-921
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• 1998

Combusion instability due to thermoacoustic feedback in a ducted combustor usually excites severe noise and vibration, which could lead to result in the failure of the system or environmental dispute. In the present study, an active noise control(ANC) method with an adaptive algotithm is hired to suppress instability which has very discrete behavior in the frequency domain. Especially a feedback system is composed to evade hot environment of the combustor, and as a preliminary, the performance and stability of the controller is chekced by simulating the real situation with harmonic waves. Application to the real combustor showed serious reductions in sound pressure level by 20∼30 dB. It was also shown that the selected control system was very stable and effective.

• 한국연소학회:학술대회논문집
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• 2012.04a
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• pp.79-81
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• 2012

Flame stabilization conditions and combustion noise characteristics induced by premixed flames in sudden expansion channels were experimentally investigated. Nozzle size and channel scale were varied continuously, and variation of flame behaviors was examined. Combustion noise was observed at specific configurational conditions, and their mechanism was investigated. This study will help understand premixed flame instability at the burner surface.

• Journal of the Semiconductor & Display Technology
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• v.19 no.4
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• pp.88-93
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• 2020

Based on the capture-emission energy (CEE) maps of CMOS devices, a physics-informed machine learning model for the bias temperature instability (BTI)-induced threshold voltage shifts and low frequency noise is presented. In order to incorporate physics theories into the machine learning model, the integration of artificial neural network (IANN) is employed for the computation of the threshold voltage shifts and low frequency noise. The model combines the computational efficiency of IANN with the optimal estimation of Gaussian mixture model (GMM) with soft clustering. It enables full lifetime prediction of BTI under various stress and recovery conditions and provides accurate prediction of the dynamic behavior of the original measured data.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.1
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• pp.50-55
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• 2004

In this study, slit-tones by plane impinging jet are investigated experimentally over the whole subsonic flow range, especially at low speeds, in order to obtain the instability behaviour of impinging plane jet. Slit-tones are generated at low speeds associated with laminar shear layer instability as well as at high speeds associated with turbulent instability. Most of low-speed slit-tones are induced by symmetric mode instability unless the slit is not so wide, in which case antisymmetric modes are induced like edge-tones. It is found that the frequencies at low speeds ate controled by the unstable condition of the vortex at the nozzle exit and its pairings by which the frequencies are decreased by half. In the case of symmetric modes related with low-speed slit-tones, frequencies lower than those associated with one-step pairings are not found.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.483-488
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• 2003

Frictional heating in brakes causes thermoelastic distortion of the contacting bodies and hence affects the contact pressure distribution. The resulting thermo-mechanical coupling can cause thermoelastic instability (TEI) if the sliding speed is sufficiently high, leading to non-uniform heating called hot spots and low frequency vibration known as hot judder. The vibration of brakes to the known phenomenon of frictionally-excited thermoelastic instability is estimated studying the interface temperature and pressure evolution with time. A simple model has been considered where a layer with half-thickness ${\alpha}$ slides with speed V between two half-planes which are rigid and non-conducting. The advantage of this properly simple model permits us to deduce analytically the critical conditions for the onset of instability, which is the relation between the critical speed and the growth rate of the interface temperature and pressure. Symmetrical component of pressure and temperature distribution at the layer interfaces can be more unstable than antisymmetrical component. As the thickness ${\alpha}$ reduces, the system becomes more apt to thermoelastic instability. Moreover, the evolution of the system beyond the critical conditions has shown that even if low frequency perturbations are associated with low critical speed, it might be less critical than high frequency perturbations if the working sliding speed is much larger than the actual critical speed of the system.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.636-640
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• 2002

Acoustic coupled combustion instability, which is one of the most undesirable phenomena in the development of liquid propellant rocket engine, can cause serious damage to a rocket itself, and must be avoided by all means. Unfortunately, KSR-III rocket went through combustion instability during engine start at the propulsion test article No.2. To resolve the problem, time sequence (cyclogram) has been changed, and baffle system has been applied. In consequence of change, stable combustion was achieved.