• Journal of Korean Society of Steel Construction
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• v.18 no.6
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• pp.769-782
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• 2006

As the ambient vibration test (AVT) of railway bridges has a limited range of speed, it has a limitation in examining the dynamic behavior of bridges accordingto speed. Thus, in order to analyze the correlation between the speed of a train passing over a bridge and the bridge's dynamic response, we conducted a speed-increasing experiment using a real diesel locomotive. To analyze the acceleration response characteristics, we attached seven vertical accelerometers at equal intervals throughout the entire section of the bridge except the supports, and one horizontal accelerometer to the middle span. Linear variable differential transformers (LVDT) were installed at the bridge's center in both vertical and horizontal directions to investigate the vertical and horizontal behaviors. The test train was statically loaded at the center and at the end of the bridge. And its speed was increased from 5 km/h to 90 km/h. With data obtained from the experiment, the vibration level was evaluated in each direction by the filtering frequency, and the level of horizontal vibration was examined in comparison with vertical vibration. The displacement and wheel load variation was analyzed by speed.

• The Transactions of the Korea Information Processing Society
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• v.13 no.3
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• pp.130-139
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• 2024

Artificial intelligence models are being used to detect facility anomalies using physics data such as vibration, current, and temperature for predictive maintenance in the manufacturing industry. Since the types of facility anomalies, such as facility defects and failures, anomaly detection methods using autoencoder-based unsupervised learning models have been mainly applied. Normal or abnormal facility conditions can be effectively classified using the reconstruction error of the autoencoder, but there is a limit to identifying facility anomalies specifically. When facility anomalies such as unbalance, misalignment, and looseness occur, the facility vibration frequency shows a pattern different from the normal state in a specific frequency range. This paper presents an N-segmentation anomaly detection method that performs anomaly detection by dividing the entire vibration frequency range into N regions. Experiments on nine kinds of anomaly data with different frequencies and amplitudes using vibration data from a compressor showed better performance when N-segmentation was applied. The proposed method helps materialize them after detecting facility anomalies.

• The Journal of the Acoustical Society of Korea
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• v.43 no.3
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• pp.335-343
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• 2024

This paper came up with the theoretical modelling of the metrology for the acoustic power using ultrasonic radiation force and showed some theoretical results. In order to do this, a scattering model for a rigid circular cone based upon the Kirchhoff approximation was made, which was followed by the calculation of acoustic power, and then, was converted to the radiation force. From these works, it provided the accuracy and limitation of the conventional method using a circular cone, and the expanded metrology modelling that can be applied to a circular cone with arbitrary apex angle. Using these, this study provided the dependence of the metrology for the acoustic power using ultrasonic radiation force on the frequency and the size of the target. As a result, the correction was yielded in the value of the acoustic power calculated by the suggested International Electrotechnical Commission (IEC) method, which needs to be added when the frequency and the size of the target was considered.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.9
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• pp.859-866
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• 2010

Nonlinear dynamics of pulsating instability-diffusional-thermal instability with Lewis numbers sufficiently higher than unity-in counterflow diffusion flames, is numerically investigated by imposing a Damkohler number perturbation. The flame evolution exhibits three types of nonlinear behaviors, namely, decaying pulsating behavior, diverging behavior (which leads to extinction), and stable limit-cycle behavior. The stable limit-cycle behavior is observed in counterflow diffusion flames, but not in diffusion flames with a stagnant mixing layer. The critical value of the perturbed Damkohler number, which indicates the region where the three different flame behaviors can be observed, is obtained. A stable simple limit cycle, in which two supercritical Hopf bifurcations exist, is found in a narrow range of Damkohler numbers. As the flame temperature is increased, the stable simple limit cycle disappears and an unstable limit cycle corresponding to subcritical Hopf bifurcation appears. The period-doubling bifurcation is found to occur in a certain range of Damkohler numbers and temperatures, which leads to extend the lower boundary of supercritical Hopf bifurcation.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.9
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• pp.667-674
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• 2014

A ship's propulsion shafting system is subjected to varying magnitudes of intermittent loadings that pose great risks such as failure. Consequently, the dynamic characteristic of a propulsion shafting system must be designed to withstand the resonance that occurs during operation. This resonance results from hydrodynamic interaction between the propeller and fluid. For ice-class vessels, this interaction takes place between the propeller and ice. Producing load- and resonance-induced stresses, the propeller-ice interaction is the primary source of excitation, making it a major focus in the design requirements of propulsion shafting systems. This paper examines the transient torsional vibration response of the propulsion shafting system of an ice-class research vessel. The propulsion train is composed of an electric motor, flexible coupling, spherical gears, and a propeller configuration. In this paper, the theoretical analysis of transient torsional vibration and propeller-ice interaction loading is first discussed, followed by an explanation of the actual transient torsional vibration measurements. Measurement data for the analysis were compared with an applied estimation factor for the propulsion shafting design torque limit, and they were evaluated using an existing international standard. Addressing the transient torsional vibration of a propulsion shafting system with an electric motor, this paper also illustrates the influence of flexible coupling stiffness design on resulting resonance. Lastly, the paper concludes with a proposal to further study the existence of negative torque on a gear train and its overall effect on propulsion shafting systems.

• Journal of the Korean GEO-environmental Society
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• v.15 no.5
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• pp.23-29
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• 2014

So far, the grouting using pressure injection has been extensively used to avoid adverse effects such as soil disturbance. Whereas, the pressure injection to the limitations of the diffusion range, so that the kinks would last injection of cement particles by introducing a frequency oscillation effect improved injection method have been recently developed. In this study, a pilot test was performed to compare injection effects of the both methods. The injections using both methods were tested on the embankment which consists of core clay and weathered soil. Subsequently, the injected volume, SPT N values, in-situ permeability and electrical resistivity were measured to compare their effects. The vibration method showed more effective permeation comparing with the pressure method. Also, it showed more homogeneously improved ground than the existing method. For SPT results, the vibration method presented increase of mean N value as much as 17.4 % comparing with the conventional method. Higher electrical resistivity was presented in case of injecting with vibration method and it indicated the injection was extensively completed. Finally, it is expected that the economic feasibility will be improved by decrease of drilling spacing, when the existing method is replaced with vibration method.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.2
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• pp.84-91
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• 2006

A heavy duty hydrogen-natural gas fueled engine can obtain stable operation at ultra lean conditions and reduce emissions extremely. Reduction of $CO_2$ in its engine is one of the most benefit. In this study, rate of hydrogen addition($R_{dH2}$) and compression ratio($\varepsilon$) were investigated including performance of this engine. As results, it was found that phenomenon of pressure oscillation when increasing $R_{dH2}$ and $\varepsilon$, it means occurring knock. It consider that pressure oscillation was increased due to fast burning speed of hydrogen. Even if same compression ratio, pressure oscillation was remarkable increased according to increasing $R_{dH2}$. Therefore, limit compression ratio of knock occurring was reduced by increasing $R_{dH2}$.

• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.308-308
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• 2019

지구상 해양, 대기 및 대륙 상호간의 연속적인 물의 거동을 나타내는 물의 순환의 주요 과정 중 하나인 유량 자료는 경년부터 수십년간의 다양한 기상학적 변동성을 내포하며 해당 지역의 수문기상학적 특성을 반영한다. 이러한 기상학적 변동성 중에서 비교적 긴 시간 주기를 나타내는 저주파 진동은 전지구적 기후변화의 장기적 영향을 나타내며 해수면 상승, 홍수 또는 가뭄과 같은 극한 수문사상을 나타내는 매우 주요한 지표로 활용되고 있지만 관측된 수문 시계열의 짧은 자료길이로 인하여 통계적 분석의 신뢰성에 한계를 보여왔다. 따라서 과거 수문 시계열의 확장으로 인하여 부재의 영역으로 남아있던 자료 기간의 한계가 보완되면 보다 정확하고 신뢰도 있는 분석이 가능할 것이다. 나무나이테를 활용한 고기후 복원 등의 연구가 증가하고 있지만 공학 분야에서 이를 실제로 활용한 연구는 아직 미비하다. 따라서 본 연구에서는 과거 기후의 정보를 바탕으로 복원된 수문 시계열을 활용하여 수문 시계열에 내재된 장기 기후 변동성을 통계적으로 분석하기 위한 문헌들을 조사하고, 장기적인 시간 흐름에 내재된 잠재적인 경향 및 변동성을 통계적 분석을 파악하고자 한다. 이를 위해 주어진 수문 시계열에 내재된 저주파 신호을 추출하기 위한 경험적 모드분해법을 활용하여 수문 자료에 내재된 장기 변동성을 추출하였으며, 산업화 이전부터 연장된 수문 시계열의 공학적 활용성을 분석하고자 한다.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.227.1-227.1
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• 2016

플라즈마 방출광 진단법은 플라즈마에 특별한 영향을 주지 않으면서도 진단 정보를 안정적으로, 지속적으로 취득할 수 있는 우수한 진단 방법이다. 이러한 분광 진단의 신뢰성을 확보하기 위해서는 방출광의 정확한 측정과 해석이 중요하다. 방출광의 측정에 이용되는 분광 장비는 모노크로메터(monochromator)와 소형 스펙트로메터(spectrometer)가 주로 사용된다. 스펙트로메터의 경우 모노크로메터보다 분광 성능은 다소 부족하지만 가볍고 작은 크기로 인해 장비의 설치가 용이하고 가격이 저렴하다는 장점이 있다. 또한 모노크로메터에 비해 분광 성능이 낮은 대신 넓은 범위의 파장을 동시에 측정할 수 있는 장점이 있다. 따라서 스펙트로메터는 플라즈마의 모니터링에 주로 사용된다. 그런데 스펙트로메터의 기기적 선폭 증대(instrumental broadening)보다 조밀하게 위치한 스펙트럼들은 서로 중첩이 일어나 진단이 어려워진다. 특히 분자 띠 스펙트럼(molecular band spectrum)과 같은 경우 선 스펙트럼들이 매우 밀집된 형태를 이루고 있어 범용적인 스펙트로메터로 진단하기가 어렵다. 이러한 문제점을 해결하기 위하여 합성 스펙트럼 해석법(synthetic spectrum method)을 이용할 수 있다. 본 연구에서는 수소 플라즈마의 Fulcher-${\alpha}$ 띠 스펙트럼 해석에 합성 스펙트럼법을 적용하여 분자의 회전 온도가 측정 가능한지 확인하고, 고성능의 모노크로메터를 이용한 온도 측정 결과와 서로 비교하였다. 그리고 분자의 진동 상태(vibrational state)가 분자 회전 온도 측정에 미치는 영향과 이에 따른 측정의 한계 등을 제시하였다.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.17 no.6
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• pp.127-129
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• 2003

Recently. the efforts for the development of DVD concentrate on the high storage and multi-media. DVD has been manufactured by assembling many parts and it causes the vibration and noise. In this paper, one body rotor is proposed, which can make the nose and vibration be decreased. The injection mould for DVD rotor is designed by finite element analysis and the rotor is manufactured in the mould. The magnetic flux density is measured on the surface and it is compared with the design criteria.