• Journal of the Korean Society for Railway
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• v.10 no.5
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• pp.463-472
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• 2007

In this paper, the correlation between the vibration characteristics of the track components and the parameters affecting the vibration is analysed. To do it, the accelerations of each track component such as rails, sleepers and ballast are measured in Kyong-Bu high-speed line. The RMS values of the measured data are calculated and the pad stiffness, the longitudinal irregularity, running velocity and the corrugation, are considered as the parameters in the viewpoint of track. By using the linear regression, the correlation coefficient is calculated to analyse the relationship. Also, the 1/3 Octave analysis is calculated to analyse the dominant frequency band of tile vibrations of the track components.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.11
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• pp.1315-1321
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• 2013

This study presents a prognostic technique for the damage state of a ball bearing. A stochastic bearing fatigue defect-propagation model is applied to estimate the damage progression rate. The damage state and the time to failure are computed by using RMS data from noisy acceleration signals. The parameters of the stochastic defect-propagation model are identified by conducting a series of run-to-failure tests for ball bearings. A regularized particle filter is applied to predict the damage progression rate and update the degradation state based on the acceleration RMS data. The future damage state is predicted based on the most recently measured data and the previously predicted damage state. The developed method was validated by comparing the prognostic results and the test data.

• Journal of the Korean Society of Propulsion Engineers
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• v.24 no.6
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• pp.61-68
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• 2020

7-tonf turbopump real-propellant tests in Naro Space Center were conducted and high-frequency signals from an accelerometer and pressure sensors installed on the casing and the inlet/outlet pipeline of LOX pump were analyzed to estimate the structural and hydrodynamic stabilities. Waterfalls, frequency spectrums and RMS(Root Mean Square) values of the measured signals were calculated and characteristic instability frequencies by the rotating cavitation and the rear floating ring seal(F.R.S) were investigated. Static pressures of the inlet/outlet pipeline and an acceleration of the pump casing are strongly affected on pressure fluctuation induced by the rear floating ring seal in the leakage path. Despite the acceleration RMS value seems totally small, the rotating-speed-related synchronous frequency affecting the shaft instability is distinctly observed in the frequency contour.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.9
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• pp.731-740
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• 2014

Occupants induced floor vertical vibrations may cause other occupant's annoyance and lead to social loss. To help control such floor vibrations, several criteria have been developed mostly based on human perception tests and floor vibration tests. Floor vibration is evaluated by comparison with criteria and vibration parameters of subject floor, such as frequency, damping ratio, acceleration value, vibration duration time and occurrence frequency. Three acceleration value parameters are used in criteria; peak acceleration, rms acceleration and VDV, when a floor vibration serviceability is evaluated. Meanwhile rms acceleration and peak acceleration are adopted as vibration limit value in criteria and researches of human perception for vibration. Occupants induced floor vibration is transient rather than steady state. However, rms acceleration is not reliable parameter for evaluating transient vibration. The objective of this study is to investigate the characters of human perception level according to acceleration value parameters for vibration induced by heel impacts and walking activities.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.3
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• pp.437-443
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• 1987

An optimal design to improve the ride quality was performed with the time and frequency domain analysis based on both of deterministic and random road profiles. The objective function is established to minimize the absorbed power while the constraints are taken so as to satisfy the condition for the stability of vehicle. The result of the optimal design shows that the rms for the acceleration of a driver and his seat is within the critical values for the ride quality from ISO. The optimal values obtained show that the maximum absolute acceleration of the driver and his seat has significantly been reduced and the reference limits on the relative displacement have satisfied their feasibility. As the optimal value according to a specific speed is the results from the optimization process, a global optimum value should be determined to be the one which gives th minimum values of total sum of absorbed power with respect to various speed.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.1093-1098
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• 2017

High frequency signals are analyzed which are measured at the inlet / outlet pipeline and pump casing during cavitation tests of the LOx pump for the liquid rocket engine. RMS values of data are shown according to the cavitation number. RMS values of the synchronous frequency, its harmonic frequencies and frequencies of cavitation instabilities are also calculated. The pressure pulsations of the inlet and outlet pipeline are affected by cavitation instabilities. 3x component is predominant in the outlet pulsation sensor since 3x component generated at the inducer is amplified at the impeller. The cavitation instability is also found at the accelerometer signal of the casing.

• Journal of the Earthquake Engineering Society of Korea
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• v.7 no.1
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• pp.31-40
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• 2003

Due to the random nature of earthquake, the definition of the input excitation is one of the major uncertainties in the seismic response analysis. Furthermore, ground motions that correspond to a limited number of design parameters are not unique. Consequently, a brood range of response values can be obtained even with a set of motions, which match the same target parameters. The paper presents a practical probabilistic approach that can be used to systematically model the stochastic nature of seismic loading. The new approach is based on energy-based RMS hazard and takes account for the uncertainties of key ground motion parameters. The simulations indicate that the new RMS procedure is particularly useful for the rigorous probabilistic seismic response analysis, since the procedure is suitable for generation of large number of hazard-compatible motions, unlike the conventional procedure that aim to generate a small number of motions.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.18 no.10
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• pp.60-67
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• 2019

Recently, lightweight materials such as Ti alloys have been used increasingly in the aerospace and high-tech industries for weight loss and fuel efficiency. Because of built-up edges and workpiece deflection due to low stiffness, the Ti alloys have poor machinability. In our study, systematic experiments were conducted to investigate the milling characteristics of the Ti alloy (Ti-6A1-4V) with endmills. The independent variables in the experiment were spindle speed, feed per tooth, and axial depth. Cutting force, acceleration RMS, and surface roughness were measured. Using the response surface method, the optimal cutting conditions were analyzed to improve machining quality and productivity.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1990.10a
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• pp.143-147
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• 1990

자동차는 주행시에 노면가진으로 인하여 진동을 받게 되는 데 이러한 진동 은 운전자의 승차감을 저하시킬 뿐만 아니라 화물과 차량 부품을 파손시키 는 원인이 되기도 한다. 노면가진력은 주로 현가장치를 통하여 차량에 전달 되어 차량의 진동을 유발하게 되므로 승차감을 향상시키려면 노면가진을 효 과적으로 차단할 수 있도록 현가장치를 설계하여야 한다. 이를 위하여 본 논 문에서는 차량을 현가장치의 형식에 따라 3가지 종류로 구분한 다음 각각을 12자유도로 모델링하여 노면이 불규칙(random)한 도로를 주행할 때의 승용 차의 진동을 해석하고, 현가스프링의 강성과 쇼크 압소바의 감쇠 값이 자체 수직 가속도 유효치(rms value)와 현가장치 유효행정(rms stroke length)에 미치는 영향을 분석하였다. 차량의 운동방정식은 현가장치의 비선형 특성을 고려하였기 때문에 미소 각 운동의 가정에도 불구하고 비선형 방정식이 된 다. 운동 방정식의 해는 4차 Runge-Kutta 적분법을 사용하여 수치해석으로 구하였다.

• Proceedings of the Korea Information Processing Society Conference
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• 2014.04a
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• pp.252-255
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• 2014

구조적인 한계로 인해 전통적인 진동 측정 시스템의 구축이 곤란할 경우나, 고가의 데이터 수집 시스템을 사용하기가 어려운 상황에 대비하여, 언제 어디서나 용이하게 진동 데이터를 측정하기 위해 휴대용 무선 측정 시스템을 개발한다. 이 연구를 통해 개발한 시스템을 기반으로 기능들을 업그레이드하면 철로 주변의 진동 환경 평가 등을 포함한 다양한 분야에 사용될 수 있으며, 근/원거리 진동 데이터 무선 모니터링 시스템의 개발에 적용될 수 있다.