• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.1A
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• pp.59-67
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• 2008

Acceleration time history used in the seismic analysis of nuclear power plant structures should envelop a target power spectral density (PSD) function in addition to the design response spectrum in order to have sufficient energy at each frequency for the purpose of ensuring adequate load. The safety for complex long-span highway bridges cannot be over-emphasize. An alternative method to improve the seismic capacity is to ensure the minimum PSD function of the applied seismic load. This study proposes a technical scheme to obtain the reference power spectral density function by using artificial earthquakes which are compatible with the highway bridge design spectrum.

• Transactions of the Korean Society of Automotive Engineers
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• v.5 no.1
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• pp.136-145
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• 1997

To analyzed ride quality and to predict durability in vehicle dynamics, it is essential to describe a road surface profile precisely. This paper presents a technique to generate road surface profiles in a spatial domain by using a power spectral density function. A single track power spectral density function is proposed to describe a road surface profile, which is also applicable for multi-track vehicle response analysis, The derived road surfaces are compared to ISO(International Organization for Standardization) standards and classifications, proposed by the MIRA(Motor Industry Research Association). The methodology in this paper is also proposed to generate road roughness description with a limited external data. A small amount of external curve data is combined with an internal PSD function to generate road surface roughness in a spatial domain.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.5
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• pp.917-922
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• 2009

This paper presents a technique to generate road surface profiles in a spatial domain using a power spectral density function. A single track power spectral density function is proposed to describe a road surface profile, which is also applicable for multi-track vehicle response analysis. The roads in lateral direction makes the relation between the coherence of the lateral tracks. The derived road surfaces are compared to ISO(International Organization for Standardization) standards. Generated road profiles are in good agreements with the target road PSD shape and measured coherence relation.

• KOREAN JOURNAL OF PACKAGING SCIENCE & TECHNOLOGY
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• v.12 no.1
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• pp.21-25
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• 2006

Measurements of accelerometer levels transmitted from the floor in commercials truck shipments were carried out transportation of 300 Kg-load from Gyungbu Highway(Waegouan-Seoul) to 88 Highway(Gwangju-Daegu). Different characteristics were observed the values measured the vibration levels with directions in the two Highway's as a function of road condition and truck speed. The results showed that the vibration levels of the Gyungbu Highway is much higher than those of the 88 Highway. A following analysis on the obtained values was used to get the acceleration spectral density (ASD) and power spectral density (PSD). For the entire transit route, the results showed that the level of vibration to vertical direction was significant effects for damaging the products carried compared to other directions such as longitudinal and transverse. This paper provides an updated history of measured characteristics of vibration levels for highways using mainly in domestic area.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.485-488
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• 2011

본 연구에서는 경부고속철도의 콘크리트궤도에서 열차주행안전측면에서 관리해야할 레일패드강성의 상한값을 차량 및 궤도의 동특성과 운영환경을 고려하여 결정하는 방법을 제시하였다. 차량과궤도의 상호작용의 해석의 중요 입력파라메타인 궤도틀림과 관련하여 프랑스 및 독일에서 제시한 궤도틀림 PSD(Power Spectral Density)와 경부 1단계구간 콘크리트궤도에서 계측한 궤도틀림 자료를 통하여 얻은 PSD를 기초로 하여 넓은 범위의 주파수영역에서 적용할 수 있는 콘크리트궤도의 궤도틀림 PSD를 제시하였다. 제시된 PSD 기준모델을 사용하여 시간영역에서의 궤도틀림 입력을 Random Generation을 통하여 구한 후 개발된 차량-궤도 상호작용해석 기법을 사용하여 레일패드에 따른 윤중감소율을 산정하였다. 산정된 윤중감소율에 대하여 국내 철도차량 안전기준에 관한 규칙의 탈선계수 규정을 적용하여 주행안전측면에서 허용할 수 있는 레일패드강성의 상한값을 제시하였다.

• Structural Engineering and Mechanics
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• v.68 no.1
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• pp.39-51
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• 2018

In this study, a frequency domain model updating method is presented using power spectral density (PSD) data. It uses the sensitivity of PSD function with respect to the unknown structural parameters through a decomposed form of transfer function. The stiffness parameters are captured with high accuracy through solving the sensitivity equations utilizing the least square approach. Using numerically noise polluted data, the model updating results of a truss model prove robustness of the method against measurement and mass modelling errors. Results prove the capabilities of the method for parameter estimation using highly noise polluted data of low ranges of excitation frequency.

• Corrosion Science and Technology
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• v.8 no.5
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• pp.203-207
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• 2009

Electrochemical methods have been widely used to study the performances and mechanisms for the degradation of organic and inorganic coatings. In this study, EN(Electrochemical noise) measurement was applied to the protective properties and review the parameters analyzed noise signals in the time and in the frequency domain for epoxy resin based coated steels during exposure to hot sea water($40^{\circ}C$) and salt spray for 200 days. It was also found that $R_n$(Noise resistance), $R_{sn}$($f_{min}$)(Spectral noise resistance) and 2H(Hurst exponent) represented the performance of epoxy coated steels. $R_n$ can be determined as the ratio of the standard deviations of potential and current noise signals and is decreased to exposure time. Data qualities can be easily checked by PSD(Power Spectral Density) plot and $V_{psd}$, $I_{psd}$ and $R_{sn}$($f_{min}$) is useful to research the protective performances and mechanisms of coated steels. Hurst exponent represents the degradation of coated steels. But, it is difficult to directly apply the protective criterion to the evaluation of epoxy coated steels used the shipbuilding processes.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.2
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• pp.712-718
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• 2016

A heat exchanger tube array in a heat recovery steam generator is exposed to hot exhaust gas flow that can cause flow induced vibrations, which could damage the heat exchanger tube array. The characteristics of flow induced vibration in the tube array need to be established for the structural safe operation of a heat exchanger. Several studies of the flow induced vibrations of typical heat exchangers have been conducted and the nondimensional PSD (Power Spectral Density) function with the Strouhal number, fD/U, had been derived using an experimental method. The present study examined the results of the previous experimental research on the nondimensional PSD characteristics by CFD analysis and the basis for the application of flow induced vibration to the heat recovery steam generator tube array was determined from the present CFD analysis. The present CFD analysis introduced circular cylinder tube array and calculated using unsteady laminar flow for the tube array. The characteristics of lift and drag fluctuations over the cylinder tube array was investigated. The derived nondimensional lift and drag PSD was compared with the results of the previous experimental research and the characteristics of lift and drag PSD for a circular cylinder tube array was established from the present CFD study.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.10
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• pp.6641-6646
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• 2015

Heat exchanger tube array in a heat recovery steam generator is exposed to the hot exhaust gas flow and it could cause the flow induced vibration, which could damage the heat exchanger tube array. It is needed to establish the characteristics of flow induced vibration in the tube array for the structural safe operation of the heat exchanger. Several researches for the flow induced vibration of typical heat exchangers had been conducted and the nondimensional PSD(Power Spectral Density) function with the Strouhal number, fD/U, had been derived by experimental method. The present study examined the results of the previous experimental researches for the nondimensional PSD characteristics by CFD analysis and the basis for the application of flow induced vibration to the heat recovery steam generator tube array would be prepared from the present CFD analysis. For the previous mentioned purpose, the present CFD analysis introduced circular cylinder tube array and calculated with the unsteady laminar flow for the tube array. The characteristics of lift fluctuation over the cylinder tube array was investigated. The derived nondimensional PSD was compared with the results of the previous experimental researches and the characteristics of lift PSD for circular cylinder tube array was established from the present CFD study.

• Journal of Energy Engineering
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• v.24 no.4
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• pp.211-216
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• 2015

Heat exchanger tube array in a heat recovery steam generator is exposed to the hot exhaust gas flow and it could cause the flow induced vibration, which could damage the heat exchanger tube array. It is needed for the structural safe operation of the heat exchanger to establish the characteristics of flow induced vibration in the tube array. The researches for the flow induced vibration of typical heat exchangers have been conducted by using single cicular tube or circular tube array and the nondimensional PSD(Power Spectral Density) function with the Strouhal number, fD/U, had been derived by experimental method. From the present study, the basis for the application of flow induced vibration to the heat recovery steam generator tube array would be prepared. For the previous mentioned purpose, the present CFD analysis introduced a single fin tube and calculated with the unsteady laminar flow over the single fin tube. The characteristics of vortex shedding and lift fluctuation over the fin tube was investigated. The derived nondimensional PSD was compared with the results of the previous experimental researches and the characteristics of lift PSD over a single fin tube was established from the present CFD study.