• Corrosion Science and Technology
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• 제9권6호
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• pp.281-288
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• 2010

This study examined the carbon corrosion at Pt/C interface in proton exchange membrane fuel cell environment. The Pt nano particles were electrodeposited on carbon substrate, and then the corrosion behavior of the carbon electrode was examined. The carbon electrodes with Pt nano electrodeposits exhibited the higher oxidation rate and lower oxidation overpotential compared with that of the electrode without Pt. This phenomenon was more active at $75^{\circ}C$ than $25^{\circ}C$. In addition, the current transients and the corresponding power spectral density (PSD) of the carbon electrodes with Pt nano electrodeposits were much higher than those of the electrode without Pt. The carbon corrosion at Pt/C interface was highly accelerated by Pt nano electrodeposits. Furthermore, the polarization and power density curves of PEMFC showed degradation in the performance due to a deterioration of cathode catalyst material and Pt dissolution.

• Current Optics and Photonics
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• 제5권2호
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• pp.141-146
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• 2021

We have evaluated the suppression effect of atmospheric-turbulence-induced optical scintillation in terrestrial free-space optical (FSO) communication systems using a gain-saturated erbium-doped fiber amplifier (EDFA). The variation of EDFA output signal power has been measured with different amounts of gain saturation and modulation indices of the optical input signal. From the measured results, we have found that the peak-to-peak power variation was decreased drastically below 2 kHz of modulation frequency, in both 3-dB and 6-dB gain compression cases. Then, the power spectral density (PSD) of optical scintillation has been calculated with Butterworth-type transfer function. In the calculation, different levels of atmospheric-turbulence-induced optical scintillation have been taken into account with different values of the Butterworth cut-off frequency. Finally, the suppression effect of optical scintillation has been estimated with the measured frequency response of the EDFA and the calculated PSD of the optical scintillation. From our estimated results, the atmospheric-turbulence-induced optical scintillation could be suppressed efficiently, as long as the EDFA were operated in a deeply gain-saturated region.

• Journal of Electrical Engineering and Technology
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• 제10권3호
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• pp.916-924
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• 2015

Electromagnetic Interference (EMI) is a system to system or environment to system phenomenon. The literature survey proved that the Randomized Pulse Width Modulation (RPWM) technique is a promising technique to reduce EMI. A new Constant Trailing Edge, Randomized Pulse Width Modulation (CTERPWM) technique is proposed in this paper. The effect of the proposed RPWM technique for mitigation of conducted-EMI on Cuk converter operating in Continuous Conduction Mode (CCM) is simulated and tested. In this paper, the analytical expressions for the Power Spectral Density (PSD) are derived for the proposed RPWM technique and are validated by experimental measurements. The effectiveness of the proposed RPWM technique on the mitigation of conducted-EMI is verified comparing simulation and experimental results and it is identified that both the results are almost similar with allowable experimental deviations. The comparative investigation proves that the proposed RPWM technique can mitigate and spread the dominant peaks of conducted-EMI over the complete spectrum for the Cuk converter. Based on the investigation the CTERPWM technique is recommended for adoption.

• Smart Structures and Systems
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• 제10권6호
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• pp.517-546
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• 2012

In this paper, vibration-based methods to monitor damage in foundation-structure interface of harbor caisson structure are presented. The following approaches are implemented to achieve the objective. Firstly, vibration-based damage monitoring methods utilizing a variety of vibration features are selected for harbor caisson structure. Autoregressive (AR) model for time-series analysis and power spectral density (PSD) for frequency-domain analysis are selected to detect the change in the caisson structure. Also, the changes in modal parameters such as natural frequency and mode shape are examined for damage monitoring in the structure. Secondly, the feasibility of damage monitoring methods is experimentally examined on an un-submerged lab-scaled mono-caisson. Finally, numerical analysis of un-submerged mono-caisson, submerged mono-caisson and un-submerged interlocked multiple-caissons are carried out to examine the effect of boundary-dependent parameters on the damage monitoring of harbor caisson structures.

• 대한조선학회논문집
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• 제47권6호
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• pp.813-820
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• 2010

The spread mooring system for FPSO is developed to explore deep sea area, in which swell is dominant. It is known that the tension response of mooring lines in this sea area shows bimodal spectrum. Assuming normal distribution of tension profile and Rayleigh distribution of tension amplitude, the power spectral density function (PSD) of the mooring tension under the bimodal stationary random process is applied for the calculation of spectrum fatigue. Three popular methods, which are simple summation method, combined spectrum method and Jioa-Moan method, are used to combine fatigue damages from bimodal spectrum characteristics. Each damage value is compared with damage using Rainflow Cycle Counting (RCC) method which is believed to be close to exact solution. Vanmarcke' parameter and RMS(Root Mean Square) ratio are employed to assess relative damage variations between from RCC method and from three combination methods. Finally the most reliable fatigue damage combining method for spread mooring system is suggested.

• 한국철도학회논문집
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• 제14권6호
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• pp.526-534
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• 2011

본 연구에서는 고속철도의 자갈궤도와 콘크리트궤도에서 열차 주행 안전 측면에서 관리해야 할 레일패드 강성의 상한값을 차량 및 궤도의 동특성과 운영환경을 고려하여 결정하는 방법을 제시하였다. 차량-궤도의 상호작용해석의 중요 입력 파라메타인 궤도틀림과 관련하여 프랑스 및 독일에서 제시한 고저틀림 PSD(파워 스펙트럼 밀도)와 경부고속철도 1단계 구간 자갈궤도 및 콘크리트궤도에서 계측한 고저틀림 자료를 통하여 얻은 PSD를 기초로 하여 넓은 범위의 주파수 영역에서 적용할 수 있는 자갈궤도와 콘크리트궤도의 고저틀림 PSD를 제시하였다. 제시된 PSD 기준 모델을 사용하여 시간 영역에서의 고저틀림 입력을 난수 생성(random number generation)을 통하여 구한 후 차량-궤도 상호작용 해석기법을 사용하여 레일패드 강성에 따른 윤중 감소율을 산정하였다. 산정된 윤중 감소율에 대하여 국내 철도차량 안전기준에 관한 규칙의 탈선계수 규정을 적용하여 주행 안전 측면에서 허용할 수 있는 레일패드 강성의 상한값을 제시하였다.

• 한국포장학회지
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• 제21권2호
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• pp.61-65
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• 2015

Agricultural products packaged for transportation are put in the various dangerous environments owing to the damage factors like vibration, shock, compression, climate etc. under the distribution process. On fruits packaging for transportation, especially, the shock and vibration is considered as the most important damage factors. A major cause of shock damage to fruits is drops during manual handling. Especially, the damages of fruits during the parcel delivery service are very serious. The parcel delivery services of fruits are increasing and contribute to increasing of farm house earning. Also, the freight vehicle is mostly used to transport the fruits. Shock and impact generated by the freight vehicle may give serious damage to fruits. The optimum packaging design of parcel delivery service of fruits during transportation is required to reduce the fruits damages. In order to design the packaging system for parcel delivery service of fruits considering the transportation environment, the comprehension of characteristics for vibration and shock generated by manual handling and acting on transportation vehicles under various road conditions and loading methods is required. This research was performed to analyze the shock characteristics, acceleration level and power spectral density (PSD) during the parcel delivery service of fruits. The overall level of recommended PSD profile in a specific transportation of parcel delivery service for fruits was $0.63G_{rms}$.

• 한국운동역학회지
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• 제15권1호
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• pp.91-109
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• 2005

The goal of this research was to determine whether gender differences exist in impact force and impact shock variables at stance phase during a preferred running. Ten male and ten female subjects volunteered to participate in this study. Impact force was quantified by using a surface-mounted force plate. In addition, Axial accelerations of the tibias and mouth were measured using low-mass accelerometers. Comparison of parameters relating to impact force and impact shock which attained from time domain, and impact shock parameters which were analyzed in frequency domain were made between genders. The conclusions based on results were as follows; 1. There were no significantly differences in impact force, mouth and tibia acceleration peak in time domain between two genders. 2. The male group was greater in impact shock peak of PSD(power spectral density) at the tibia than female group(p<.05), but no differences in active impact of PSD at the tibia and the mouth between two genders. 3. Female subjects exhibited that a peak of impact shock attenuation analyzed in frequency domain moved toward a high frequency, but no difference in time domain between two genders.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2014년도 춘계학술대회 논문집
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• pp.216-216
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• 2014

과거 유체 유발 진동(FIV : Fluid Induced Vibration)은 배관계 설계 하중에 고려되지 않은 설계 하중이었다. 하지만, 원자력 발전소 또는 화력 발전소의 배관형상이 복잡하고 고온수가 배관 내부에서 유동하는 배관계에서 육안으로 관측이 가능한 배관진동이 발생하였다. 이에 배관 진동에 대하여 원인 분석과 배관 구조 건전성 평가에 관심을 가지게 되었다. 배관 진동은 배관 형상에 따라 배관 내부 난류 유동에 대한 압력 변동이 하나의 원인이며, 고온수가 유동하는 배관일수록 압력 변동에 대한 배관 진동이 크게 나타나는 것으로 분석되었다. 배관 내부 난류 유동에 대한 압력 변동을 불규칙 수력하중이라고 한다. 본 연구에서는 배관 내부에서 난류 유동으로 발생하는 불규칙 수력하중을 유동해석을 이용하여 PSD(Power Spectral Density)로 산출하고, PSD 하중을 이용하여 불규칙 구조 응답 해석을 수행하여 배관계 응력 분포에 대하여 연구하였다. 배관 내부 난류 유동에 대한 불규칙 수력하중은 DES 난류 모델을 사용하여 시간에 대한 배관 내부 표면의 유체 속도를 유동 해석으로 산출하였으며, 유체 속도를 동압으로 계산한 후 FFT(Fast Fourier Transform)를 수행하여 PSD 하중으로 산출하였다. 그리고 불규칙 구조 응답 해석에서 배관 내부 유체 영향에 대한 진동 감쇠를 표현하기 위하여 유체 질량을 산출하고, 배관 구조 해석 모델 표면에 질량을 입력하는 방법으로 배관 고유진동수 및 불규칙 구조 응답 해석을 수행하였다.

• 한국신뢰성학회지:신뢰성응용연구
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• 제18권3호
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• pp.213-219
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• 2018

Purpose: Satisfying the environmental regulations, the automobile manufacturer should install urea tank, which is a key component of the urea system. However, due to the limitations of existing layouts, it may be mounted which is disadvantageous to vibration and shock resulting in durability robust. analyze the factors affecting the durability life of urea tank and the vibration characteristics through RLDA. In this study, clarify the limit of the current practice test method of urea tank and analyze the possibility of the new vibration test method in the system unit reflecting the characteristics of actual use condition. Methods: Analyzing the factors affecting the durability life of urea tank and the vibration characteristics through PSD & FDS of RLDA that actual vehicle driving data on durability test road. Results: The limit of the uniform width/single frequency test method of urea tank is clarifed and the positive prospects of the new test method are discovered. Conclusion: The vibration durability test with PSD method in system unit effectively reflects the magnitude and frequency characteristics of field vibration.