• Korean Journal of Optics and Photonics
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• v.14 no.6
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• pp.588-593
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• 2003

A signal processor for interferometeric fiber optic sensors, which measure dynamic quantities of frequency up to 1 KHz with high sensitivity, is developed. It is a high-speed version of the all-digital phase tracking (ADPT) processor that was used to measure static or slowly-varying quantities. The processor was applied to a fiber optic Mach-Zehnder interferometer to evaluate the performance. The measured total harmonic distortion was near to -50 ㏈, which is the theoretical limit or the ADPT signal processing.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2021.11a
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• pp.208-209
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• 2021

In 2017, 100 aftershocks with a magnitude of 2.0~3.0 and 615 minor earthquakes in Pohang in Korea caused the collapse and destruction of aggregate, tile, glass, and other structural components of multi-family houses constructed as finishing materials for buildings, causing damage to vehicles and casualties. Based on this factor, seismic design standards were established for non-structural elements of buildings that were applied only to past structures. Therefore, this study reinterpreted various vibration response spectra transmitted to waterproof layers as well as the definition and concept of the waterproof layer demand response spectrum derived by developing various vibration response test evaluation devices through a new testing apparatus.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.105-105
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• 2021

본 연구에서는 2차원 비선형 천수모형과 수심평균된 스칼라 이송모형을 해석하는 수치모형에 대해 기술하였다. 수치모형의 정확성을 보장함과 동시에 안정성을 높이기 위해 유한체적법, 플럭스 재구성 및 minmod 제한자를 사용하였다. 비선형 천수방정식의 이송항과 바닥 경사항은 계산된 수심의 양수 보존과 흐름의 정상 상태를 보장하기 위한 second order well-balanced positivity preserving central-upwind method를 이용하여 수치적으로 이산화되었다. 마찬가지로, 이송-확산 방정식 내 이송항은 동일한 2차 풍상차분법을 통해 수치적으로 풀이하였다. 격자점 경계면에서의 불연속으로 인한 수치진동을 방지하기 위해 이송항의 계산에 포함된 보존항의 차이로 인해 발생하는 스칼라의 수치확산을 최소화하기 위해 무차원의 비소산함수를 도입하였다. 또한, 확산항은 유한차분법을 이용하여 이산화하였다. 제안된 수치모형은 시간미분항의 계산을 위해 오일러 기법을 적용하여 계산된 수심 및 스칼라의 양수 보존여부와 함께 정지된 흐름의 정상 상태의 보존여부를 확인하였다. 제안된 수치모형의 해석 정확성을 평가하기 위해 1, 2차원 공간 내 다양한 흐름 조건에서의 해석해를 이용한 3개의 벤치마크 테스트를 수행하였다. 평균 제곱근 오차(Root Mean Squared Error, RMSE)를 산정하여 수치모형의 성능을 정량적으로 평가하였으며, 비소산함수를 적용함에 따라 스칼라의 수치확산이 감소하게 되었음을 확인하였다. 또한, 세 차례의 벤치마크 테스트 결과는 공통적으로 수치모형에 의해 계산된 결과값이 비소산함수를 고려함에 따라 해석해와 잘 일치함을 확인하였다.

• Journal of the Korea Concrete Institute
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• v.21 no.6
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• pp.681-688
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• 2009

The railroad bridges have been usually experienced by vibration and impact in service state. With this reason, it is important that the effective strengthening capacity should be considered to resist the kind of service loading. In this study, NSM strengthening technique is recommended for the concrete railroad bridge because of its better effective resistance for dynamic loading condition and strengthening cost than the conventional externally bonded strengthening using fiber sheet. However, to widely apply NSM method for the concrete railroad bridge, it needs that the strengthening ratio has to be reasonably evaluated with geometrical and material uncertainties, especially for the concrete bridge under long-term service state without the apparent design history and detail information such as concrete compressive strength, reinforcing ratio, railroad characteristics. The purpose of this study is to propose the critical strengthening ratio of CFRP plate for the targeted concrete railroad bridge with uncertainties of deterioration of the structures. To do this, Monte Carlo Simulation (MCS) for geometrical and material uncertainties have been applied so that this approach may bring the reasonable strengthening ratio of CFRP plate considering probabilistic uncertainties for the targeted concrete railroad bridge. Finally, the critical strengthening ratio of NSM strengthened by CFRP plate is calculated by using the limit state function based on the target reliability index of 3.5.

• Journal of the Korean Society of Marine Environment & Safety
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• v.23 no.7
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• pp.948-955
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• 2017

Currently, porous materials (e.g., mineral wool) are the core materials used in offshore plant panels, but in spite of their superb acoustic performance, these items must be replaced for environmental reasons. A honeycomb structure is widely used throughout the industry because of its high strength-to-weight ratio. However, research in terms of noise and vibration is minimal. An acoustic study should be conducted by taking advantage of honeycomb structures to replace porous materials. In this study, a simulation was performed assuming that a honeycomb panel is a superposition of symmetric mode and antisymmetric mode. Reliability was verified by comparing a simulation results based on a theory with a experimental results, and the possibility of the panel as a core material was evaluated by studying the sound insulation characteristics of a honeycomb. As the panel thickness increased, the coincidence frequency shifted to low frequency. As the angle between horizontal line and oblique wall and cell-size decreases, the sound insulation performance is improved. And as the cell-wall thickness increased, the sound insulation performance improved.

• Journal of the Korean Society for Railway
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• v.18 no.3
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• pp.203-211
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• 2015

Ride comfort of a vehicle can be utilized to maintain the track geometry and track irregularities because ride comfort of the rolling stock is affected by the characteristics of the vehicle and track. Ride comfort was evaluated according to the measured floor acceleration data of vehicles for a Korean high speed line as well as European high speed lines using Continuous comfort method which can be applied to track maintenance. The exceedance distribution of the ride comfort was quantitatively analyzed by the vehicle speed, the ride comfort of the Korean high speed line was compared with that of European high speed lines. It is shown that the ride comfort of Korean high speed line is better than that of European high speed lines, which indicates that the Korean track geometry and track irregularities are properly maintained.

• Journal of the Earthquake Engineering Society of Korea
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• v.9 no.1 s.41
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• pp.33-42
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• 2005

Even in moderate to low seismic regions like Korean peninsular where wind loading usually governs the structural design of a tall builidng, the probable structural impact of the 500-year design basis earthquake (DBE) or the 2400-year maximum credible earthquake (MCE) on the selected structural system should be considered at least in finalizing the design. In this study, seismic performance evaluation was conducted for concentrically braced steel highrise buildings that were only designed for wind by following the assumed domestic design practice. It was found that wind-designed concentrically braced steel highrise buildings possess significantly increased elastic seimsic capacity due to the system overstrength resulting from the wind-serviceability criterion and the width-to-thickness ratio limits on steel members. The strength demand-to-strength capacity study based on the response spectrum analysis revealed that, due to the system overstrength factors mentioned above, wind-designed concentrically braced steel highrise buildings having a slenderness ratio of larger than six can withstand elastically even the maximum credible earthquake at the performance level of immediate occupancy.

• Journal of Korean Society of Steel Construction
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• v.25 no.6
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• pp.649-658
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• 2013

Recently, an urgent issue of the global environment in the 21st century is the well-established paradigm of a sustainable and circulatory system. In the field of construction, it is important to approach sustainablity issues from a structural engineering point of view. The reusable steel structural system, which can adapt to changes in socio-economic conditions and varied demands, realized that the consumption of natural resources was minimized, the environmental load was reduced as much as possible. In order to reuse and recombinant the structural members, removable PC slab connection was introduced. This paper investigates the structural performance and serviceability by the dynamic characteristics of the steel beam to concrete slab connection.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.2
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• pp.68-77
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• 2020

The purpose of the paper is to evaluate the pore structure and mechanical properties of early frost damaged concrete using electric arc furnace slag as aggregate. From the results, when the concrete is exposed to frost damage at an early age, the peak point of pores 100 to 150 ㎛ in diameter were transferred into larger one. When the freezing duration is not exceeded 24 hours, it is possible that the pore distribution of under the 200 ㎛ is maintained and pore size of over 500 ㎛ is not formed, and, the freezing resistance of concrete using EFG could be improved. When BFS was mixed in concrete using EFG as coarse aggregate, the relative strength is higher than that of natural coarse aggregate. Meanwhile, the elastic modulus and resonance frequency did not change significantly due to the early frost damage as compared with the compressive strength. So, it is necessary to analyze the correlation between the experimental results in order to evaluate the performance degradation due to early frost damage.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.6
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• pp.143-154
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• 2012

The wireless low-floored tram is an innovative transportation system which is environment-friendly and highly energy-efficient. In addition, the system has various advantages such as low construction cost, improvement of urban landscape, revitalization of surrounding commercial area, elevated convenience for passengers, etc. Therefore, more than ten local governments have proposed tram construction projects in Korea. Accordingly, many research and development projects are ongoing funded by government including the developments of tram vehicle, tram trackway, signal system, etc. The embedded rail system are commonly used in order to provide leveled roadway surface in urban area. It is effective to reduce the noise and vibration, caused at the interface between the wheel and track, to minimize the construction period, and to lower the maintenance cost. This paper investigated the design and construction processes for tram trackway and figured out the constructability for the test track with embedded rail system for the first time in Korea. The performance to reduce the noise and vibration were quantitatively measured in the test track with embedded rail system. In addition, the results were compared to the ones for track with conventional rail system.