• Journal of Korean Society of Coastal and Ocean Engineers
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• v.32 no.2
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• pp.95-105
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• 2020

In this study, using the CADMAS-SURF model, the characteristics of the wave pressures and the wave forces were analyzed according to the installation position of the parapet on top of the caisson, and the stability evaluation was carried out using estimated wave forces for the design wave condition. Numerical results show that adopting the rear-parapet reduces the front maximum wave pressures and wave forces, and the maximum wave pressure acting on the rear-parapet increases slightly compared to the front parapet, but the wave force acting on the rear-parapet has little effect on the stability of the breakwater due to the phase difference with the wave force acting on the front of the breakwater. In addition, impulsive wave pressures did not occur, as Yamamoto et al. (2013) pointed out the problem of the rear-parapet breakwater. As a result of the stability against sliding and overturning, it was estimated that the target safety factor of 1.2 could be secured by the self-weight of 13% less than the case of the front parapet. At this time, the maximum ground pressure was also reduced by 30%, and the applicability of the rear-parapet structure to the actual site was evaluated as high.

• Journal of Korean Society of Transportation
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• v.27 no.3
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• pp.161-168
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• 2009

The ubiquitous transportation system environments make it possible to collect each vehicle's position and velocity data and to perform more sophisticated traffic flow management at individual vehicle or platoon level through V2V and V2I communication. It is necessary to develop a new traffic management paradigm to take advantage of the ubiquitous transportation system environments. This paper proposed a preventive congestion management algorithm for uninterrupted flow, whose goal is to minimize the incident potential and maximize the productivity by maintaining traffic flow stability. The algorithm includes the following steps: Processing the raw data to produce the 3-dimension speed/flow/density profile and to produce the platoon profile and the shock wave profile, Determining the traffic state and the flow stability based on the processed data, Deciding the desirable speed the according the traffic flow state, and finally Providing the desirable speed information. It remains as further work to perform field experiments and calibrate the algorithm parameters.

• Journal of Korean Tunnelling and Underground Space Association
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• v.5 no.1
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• pp.13-21
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• 2003

To investigate the safety and stability of a concrete lining, numerous studies have been conducted over the years and several methods have been developed. Most signal processing techniques of NDT have been based on Fourier analysis. However, the application of Fourier analysis to analyze recorded vibrational signal shows results in the frequency domain only, and it is not enough to analyze transient waves precisely. In this study, Wavelet theory was employed for the analysis of non-stationary wave induced by mechanical impact on tunnel concrete lining. The Wavelet transform of transient signals provides a method for mapping the frequency spectrum as a function of time. To verify the availability of Wavelet transform as a time-frequency analysis tool, model experiments have been conducted and the thickness of the concrete lining was estimated based on the proposed theory. From this study, it was found that the contour map by Wavelet transform provides more distinct results than the power spectrum by Fourier transform and it was also found that Wavelet transform was also an effective tool for the analysis of dispersive waves in tunnel concrete linings.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.5
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• pp.1244-1253
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• 1990

Time-Marching methods solving Euler equations are used for calculation of two-dimensional, steady, inviscid flow through a stationary compressor cascade. Calculation method is based on the Denton`s opposed difference scheme. A smoothing in the axial direction is used to increase the stability of solution. The computational grid consists of quadrilateral elements, one of which has four nodes at each corner and the grid points on the upper periodic boundaries are located one pitch away from those on the lower boundaries to satisfy the periodicity condition. Results of calculation show good agreement with other computational and experimental results, proving that the present method of calculation should be applied with confidence for the cascade flow with shock wave.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.4
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• pp.87-99
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• 1993

The computer program, MFPD, which is used to backcalculate the layer moduli of asphalt concrete pavement system is modified by contemplating the depth to virtual bedrock in this study. An algorithm to estimate the depth to virtual bedrock is developed through the analysis of FWD impulse load duration and the compression wave velocity of ground. For verification of the modified MFPD, FWD is fabricated and then FWD field tests and verification tests are carried out at the test sites. Plate loading tests and surface wave propagation tests are performed at FWD test sites. Laboratory tests (Marshall stability tests, unconfined compression tests) for sampled asphalt concrete specimens are also carried out. From comparison analysis, the validity and applicability of the modified MFPD are verified.

• Journal of the Korean Society of Propulsion Engineers
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• v.17 no.1
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• pp.89-96
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• 2013

Combustion pressures were measured to study combustion stability for an oxygen rich preburner by both of static and dynamic pressure sensors. The resolutions of each static and dynamic pressure sensor are the 1,000 Hz and 25,600 Hz, respectively. The nominal combustion pressure of the preburner was 200 bar but 80 bar was used at the several initial tests for the safety reason. Two stage ignition was applied to reduce the ignition impact for every tests including the tests with 200 bar combustion pressure. The tests lasted for 10 sec. max. and a little fluctuations of pressure was observed during the main mode. The measured pressures were studied by FFT analysis and no noticeable frequency coupling was found. Thus the preburner can be regarded as stable and it can be utilized for further study on staged combustion cycle liquid rocket engine.

• Proceedings of the Korea Water Resources Association Conference
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• 2020.06a
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• pp.299-299
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• 2020

국내외 발생하는 재난 중 70% 이상이 물과 관련된 재해로 분류되며, 집중호우와 태풍으로 인한 하천범람 및 내수침수 등으로 많은 피해를 발생시키고 있다. 특히 최근 발생하는 피해 양상은 과거에 발생하지 않았던 극한 강우로 인해 돌발적으로 발생하는 경우가 빈번하게 발생하고 있어 이에 따라 사전에 예측하여 미리 대비하는 선제적인 홍수 대비 시스템이 요구되고 있다. 선제적인 홍수 대비 시스템의 구축 여부는 정확한 하천 흐름 예측을 필요로 한다. 하지만 하천의 흐름은 댐붕괴, 제방붕괴, 하천 하상의 변동 등 다양한 상황에서 급격한 흐름의 변동이 발생하며, 이는 하천 흐름 예측에 장애물로 작용하여 정확도를 떨어뜨리는 요인이 된다. 특히 국내에는 산악지형과 수공구조물에 의한 불연속 단면이 다수 존재하고 있어 그 예측 결과에 대한 정확성에 대한 요구가 더욱 부각되고 있다. 그렇기 때문에 해당 문제를 해결하기 위한 다양한 기법들이 개발되어 실무에 적용되고 있으나 어떤 기법이 국내 하천특성에 적합한지 파악할 수 없으며, 그 정확성과 안정성에 측면에서 여전히 많은 문제점을 가지고 있는 실정이다. 본 연구에서는 불연속 흐름이 빈번하게 발생하는 국내 하천 특성에 적합한 수치 기법을 확인하고자 유량보존특성을 만족하는 유한체적기법 중 국내외적으로 다수 사용되었던 기법들을 비교 및 평가하였다. 불연속 흐름의 대표적인 예제로서 'Dam-break problem'과 충격파 해석 및 홍수기와 갈수기에 따른 하천 하상의 마름/젖음에 대한 평가를 할 수 있는 Toro's Riemann problems에 적용하여 비교하였으며 그 결과 값을 정량적인 수치로 나타내었다. 이를 통해 국내 하천 특성에 적합한 수치 기법을 선정하였으며. 향후 국내하천 환경을 만족할 뿐만 아니라 하천 종사자들의 요구에도 부합한 하천흐름해석 모형의 개발 시 많은 기여가 될 것이라 판단된다.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2013.06a
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• pp.270-272
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• 2013

In order to protect coastal facilities mainly from wave and current actions, the self-locking bio blocks constituting component elements of protecting structures against scouring were designed. These blocks are adapted to the sloping bottom, coastal dunes, and submerged coastal base counteracting the destructive and erosive impulse action. A series of laboratory experiments is necessary to investigate the reflection of water waves over and against a train of protruded or submerged shore structures and compare the reflecting capabilities of incident waves including wave forces. In this study the hydraulic model experiment was conducted to identify the performance of newly designed water affinity bio blocks to keep the coast slope and bottom mound from scouring by reduction of the reflection coefficient and to convince stability of the placements. Revised design of each element of blocks were also tested for field conditions. From the result of experiment, the field applicability of the developed blocks and placement is to be discussed afterward.

• Journal of Korea Water Resources Association
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• v.38 no.5 s.154
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• pp.333-343
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• 2005

The upwind model is well known to simulate shockwaves, but it is rarely applied to natural rivers because of problems caused by the source terms. Although several methods have been developed to deal with the source terms, none of them has been applied to natural rivers. This paper deals with application of the upwind model to the natural river. An implicit upwind model is applied to a hypothetical irregular channel and a natural river with highly irregular bed, width, and hydraulic structures. Different types of the flows including steady-state flow, flood wave, dam-break wave, and bore are simulated to test accuracy and applicability of the implicit upwind model. It is proved that the model can simulate various types of flows in natural rivers with high accuracy and robustness.

• Journal of the Korean earth science society
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• v.23 no.4
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• pp.357-368
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• 2002

In this study we have tried to explain the barrel-shaped morphology for young supernova remnants considering the dynamical effects of the ejecta. We consider the magnetic field amplification resulting from the Rayleigh-Taylor instability near the contact discontinuity. We can generate the synthetic radio image assuming the cosmic-ray pressure and calculate the azimuthal intensity ratio (A) to enable a quantitative comparison with observations. The postshock magnetic field are amplified by shearing, stretching, and compressing at the R-T finger boundary. The evolution of the instability strongly depends on the deceleration of the ejecta and the evolutionary stage of the remnant. the strength of the magnetic field increases in the initial phase and decreases after the reverse shock passes the constant density region of the ejecta. However, some memory of the earlier phases of amplification is retained in the interior even when the outer regions turn into a blast wave. The ratio of the averaged magnetic field strength at the equator to the one at the pole in the turbulent region can amount to 7.5 at the peak. The magnetic field amplification can make the large azimuthal intensity ratio (A=15). The magnitude of the amplification is sensitive to numerical resolution. This mens the magnetic field amplification can explain the barrel-shaped morphology of young supernova remnant without the dependence of the efficiency of the cosmic-ray acceleration on the magnetic field configuration. In order for this mechanism to be effective, the surrounding magnetic field must be well-ordered. The small number of barrel-shaped remnants may indicate that this condition rarely occurs.