• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.8C
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• pp.827-834
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• 2003

In this paper, we implemented an optical information security system using computer generated hologram based on the principle of interference and BaTiO$_3$that is photorefractive material. First of all, we would generate binary phase hologram which can reconstruct the original image perfectly, and regard this hologram as the image to be encrypted. And then applying the interference rule to the hologram, encrypted and reference (fkey information) images are generated. In the decrypting process, we can get an interference intensity by interfering the reference image and the encrypted image in the Mach-Zehnder interferometer. and transforming interference intensity information into phase information using LCD(liquid crystal display) and finally recover original image by inverse Fourier transforming the phase information. In this process, the Intensity information generated by interference of two images is very sensitive to external vibrations. So, we get a stable interference using the characteristic of SPPCM(self pumped phase conjugate mirror) of BaTiO$_3$that is photorefractive material. The proposed method has an advantage of double image encryption by encrypting the hologram of the image instead of original image.

• Journal of Korean Society of Steel Construction
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• v.21 no.2
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• pp.165-173
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• 2009

Hanger cables in suspension bridges are constrained by the horizontal clamp. So, the accuracy of estimated tension of hange cable using existing methods based on the simple mathematical model of singel cable decreases as the length of cable decreases because of the flexural rigidity. Therefore, back analysis and system identification techniques based on the finite element model are proposed recently. In this paper, the applicability of the back analysis and system identification techniques are compared using the hanger cable of Gang-An Bridge. The experimental results show that the back analysis and system identification techniques are more reliable than the existing string theory and linear regression method in the view point of the error of natural frequencies. However, the estimation error of tension can be varied according to the accuracy of finite element model in the model based methods. Especially, the boundary condition is more affective when the length of cable is short, so it is important to identify the boundary condition through experiment if it is possible. The tension estimation method using system identification technique is more attractive because it can easily consider the boundary condition and it is not sensitive to the number of input measured natural frequencies.

• Journal of the Korean GEO-environmental Society
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• v.10 no.1
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• pp.49-54
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• 2009

The seismic slope stability is most often evaluated by the pseudo-static limit analysis, in which the earthquake loading is simplified as static inertial loads acting in horizontal and/or vertical directions. The transient loading is represented by constant acceleration via the pseudostatic coefficients. The result of a pseudostatic analysis is governed by the selection of the value of the pseudostatic coefficient. However, selection of the value is very difficult and often done in an ad hoc manner without a sound physical reasoning. In addition, the maximum acceleration is commonly estimated from the design guideline, which cannot accurately estimate the dynamic response of a slope. There is a need to perform a 2D dynamic analysis to properly define the dynamic response characteristics. This paper develops a new hybrid pseudostatic method that links the modified one-dimensional seismic site response analysis and the pseudostatic algorithm. The modified site response analysis adjusts the density of the layers to simulate the change in mass and weight of the layers of the slope with depth. Multiple analyses were performed at various locations within the slope to estimate the change in seismic response of the slope. The calculated peak acceleration profiles with depth from the developed procedure were compared to those by the two-dimensional analyses. Comparisons show that the two methods result in remarkable match. The calculated profiles are used to perform pseudostatic analysis. The results show that use of peak or a fraction of acceleration at the surface can seriously underestimate or overestimate the factor of safety, and that the proposed procedure significantly enhances the reliability of a standard procedure.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.37 no.4
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• pp.251-258
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• 2024

This study investigated the effect of bearing aging on the seismic response of a three-span continuous concrete girder bridge with pot bearings installed. The pot bearings were modeled as elastic springs in the longitudinal, transverse, and vertical directions of the bridge to reflect the stiffness of fixed and movable supports. The effect of bearing aging on the seismic response of the bridge was examined by considering two factors: a decrease in the horizontal stiffness of the fixed bearings and an increase in the horizontal stiffness of the movable bearings. The finite element model of the three-span continuous girder bridge was validated by comparing its numerical natural frequencies with the designed natural frequencies. Using artificial ground motions that conform to the design response spectrum specified by the KDS bridge seismic design code, the seismic responses of the bridge's girders and bearings were calculated, considering the bearing stiffness variation due to aging. The results of a numerical analysis revealed that a decrease in the horizontal stiffness of the fixed bearings led to an increase in the absolute maximum relative displacement of the bearings during an earthquake. This increases the risk of the mortar block that supports the bearing cracking and the anchor bolt breaking. However, an increase in the horizontal stiffness of the movable bearings due to aging decreased the absolute maximum shear on the fixed bearings. Despite the shear reduction in the fixed bearings, the aging of the pot bearings change could cause additional tensile bending stress in the girder section above the free bearings, which could lead to unexpected structural damage to the continuous bridge during an earthquake.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.1
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• pp.61-70
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• 2013

This paper presents the response calibration method based on quality control range, which is established from the concept and method of statistical quality control for natural frequency ratio and response ratio. To this end, statistical analysis including descriptive statistics analysis, normality test, ANOVA were performed for response characteristics obtained from loading tests and structural analysis for more than hundred and thirty well-conditioned bridges. Suggested method is based on real structural integrity evaluation case studies and statistical quality control approach, in this respect it is expected to provide scientific criteria and systematic procedure for response calibration and load carrying capacity assessment.

• Proceedings of the Korea Water Resources Association Conference
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• 2009.05a
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• pp.647-650
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• 2009

본 연구는 기존댐의 효율적 이용을 위해 하류유황을 고려한 효율적 용수공급방안을 새로운 방법으로 제시하고자 하며 용수공급의 효율적 증대방안을 연구하는데 목적이 있다. 새로운 용수공급방안을 위하여 모의 적용되는 지역은 안동댐 유역을 선정하였으며 낙동강하류를 대표하는 진동지점의 유황특성을 파악하고 안동댐 실측운영자료를 기준으로 HEC-5 모형을 이용하여 안동댐 용수공급 신뢰도를 평가하여, 비홍수기에 추가 용수공급량에 대하여 방안별 용수공급능력을 평가하였다. 연구결과, 낙동강 유량이 풍부한 홍수기에 댐하류 공급량을 안동댐에 저장하였다가 비홍수기에 추가 공급하는 3가지 시나리오별로 분석하여 추가 용수 공급 가능량은 각 시나리오별로 $1.35m^3/s^{\sim}2.12m^3/s$정도로 평가하였으며, 이를 바탕으로 현시점에서 국내 기존댐에 대해 댐건설 당시 적용된 농업용수 사용량을 재조사하여 최적의 필요량을 공급하고 비홍수기에 공급할 수 있는 방안 등의 효율적인 용수공급증대 방안에 대하여 발전적인 연구와 실효성있는 댐운영을 기대한다.

• The KSFM Journal of Fluid Machinery
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• v.6 no.4 s.21
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• pp.14-20
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• 2003

In this study an analysis of the flow characteristics in three types of turbo-fans for a vacuum cleaner was performed by using CFD. The characteristics of three models calculated for various rotating speed for flow rates are obtained and compared with measured data. The mixing plane approach is applied to compute the flow between impeller and diffuser. The results show that the model that is modified to reduce fan noise gives stable flow characteristics in operating range than the original model, with both models show similar performance characteristics at the range of high flow rate. Since in the modified model it takes much longer for an impeller blade to pass a diffuser blade than in the original model, and the peak pressure at BPF can be relieved, it is anticipated that the modified model give much lower noise level with similar performance than the original one, which remains to be verified by unsteady computation and measurements. The good agreement between the predictions and measurement results confirms the validity of this study.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.9
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• pp.923-928
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• 2008

Pyrotechnic shock or pyroshock is characterized as a transient vibration phenomenon which shows large acceleration and high frequency range up to 10kHz during the operation of separation devices where explosives are used. During the flight of a launch vehicle, pyroshock is mainly generated at several events such as satellite separation, fairing separation and stage separation. In this paper, wiremesh isolators are introduced and several types of isolators are manufactured for the performance tests. For the investigation of typical characteristics of wiremesh isolators, compressive loading tests are basically performed and pyroshock tests are accomplished to confirm pyroshock isolation ability of each wiremesh isolator by using 4Kg dummy mass.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.631-634
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• 2002

The study of the flow characteristics in two types of turbo-fans for a vacuum cleaner was performed in a previous study. In present study an analysis of a new modified model to reduce fan noise was performed by using CFD. The characteristics of three models calculated for various rotating speeds and flow rates are obtained and compared with available measured data. The results show that the modified model gives stable flow characteristics in operating range than the original model, while both models show similar performance characteristics at the range of high flow rate. Since in the modified model it takes much longer for an impeller blade to pass a diffuser blade than in the original model, and thus the peak pressure at BPF can be relieved, it is anticipated that the modified model gives much lower noise level with similar performance than the original one, which remains to be verified by unsteady computation and measurements.

• Korean Journal of Materials Research
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• v.9 no.7
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• pp.670-674
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• 1999

Accurate measurements of elastic constants are important from the view points of both science and engineering. The measurement can be viewed from scientific principle as a service tools for analyzing and improving the understanding of the nature of bondings between atoms and between ions. Also, from engineering perspective it would became an important factor to be definitely considered for the design of machinery equipments. In this investigation, two dynamic experimental methods of vibrations (acoustic method and Impulse technique method) are utilized and the results from the both methods are compared to obtain elastic constants data with a high degree of accuracy. The resonance frequencies obtained from the two methods are applied to both Euler and Timoshenko beam equations respectively, to determine the sources for possible differences.