• Journal of the Korea Concrete Institute
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• v.20 no.1
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• pp.13-22
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• 2008

The initiation and growth processes of cyclic ice body in porous systems are affected by the thermo-physical and mass transport properties, as well as gradients of temperature and chemical potentials. Furthermore, the diffusivity of deicing chemicals shows significantly higher value under cyclic freeze-thaw conditions. Consequently, the disintegration of concrete structures is aggravated at marine environments, higher altitudes, and northern areas. However, the properties of cyclic freeze-thaw with crack growth and the deterioration by the accumulated damages are hard to identify in tests. In order to predict the accumulated damages by cyclic freeze-thaw, a regression analysis by the response surface method (RSM) is used. The important parameters for cyclic freeze-thawdeterioration of concrete structures, such as water to cement ratio, entrained air pores, and the number of cycles of freezing and thawing, are used to compose the limit state function. The regression equation fitted to the important deterioration criteria, such as accumulated plastic deformation, relative dynamic modulus, or equivalent plastic deformations, were used as the probabilistic evaluations of performance for the degraded structural resistance. The predicted results of relative dynamic modulus and residual strains after 300 cycles of freeze-thaw show very good agreements with the experimental results. The RSM result can be used to predict the probability of occurrence for designer specified critical values. Therefore, it is possible to evaluate the life cycle management of concrete structures considering the accumulated damages due to the cyclic freeze-thaw using the proposed prediction method.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.26 no.2
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• pp.165-171
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• 2013

Due to the difficulty in considering dynamic load in the view point of a computer resource and computing time, it is common that external load is assumed as ideal static loads. However, structural analysis under static load cannot guarantee the safety of design of the structures under dynamic loadings. Recently, the systematic method to construct equivalent static load from the given dynamic load has been proposed. Previous study has calculated equivalent static load through the optimization procedure under displacement constraints. However, previously reported works to distribute equivalent static load were based on ad-hoc methods. Improper selection of equivalent static loading positions may results in unreliable prediction of structural design. The present study proposes the selection method of the proper locations of equivalent static loads to dynamically applied loads when we consider transient dynamic structural problems. Moreover, it is appropriate to take into account the stress constraint as well as displacement constraint condition for the safety design. But the previously reported studies of equivalent static load design methods considered only displacement constraint conditions but not stress constraint conditions. In the present study we consider not only displacement constraint but also stress constraint conditions. Through a few numerical examples, the efficiency and reliability of proposed scheme is verified by comparison of the equivalent stress between equivalent static loading and dynamic loading.

• Proceedings of the KSR Conference
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• 2007.11a
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• pp.1330-1336
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• 2007

The purpose of the study was to verify deduction of each coefficient necessary to analysis on micro-pressure waves and reliability of the analysis result. The tunnel running train model testing device used in the test was manufactured by scale of 1:60 and the study used a train model with ten cars long according to specifications of KTX model. The study applied tunnels with cross sections of $107.9m^3\;and\;95.1m^3$ and applied tunnel extensions with 1km, 0.75km and 0.5km. Also, the study tested train speed by changing it into 275, 300, 325 and 350km/h. The test device was a hydraulic launch system composed of a train model, a hydraulic launcher, a tunnel model and a brake. The study measured speed of a model trainby a speed sensor installed in the point of each 1.2m from the front of tunnel entrance and a pithead of tunnel exit and measured pressure change of internal tunnel continuously by installing pressure sensors in the entrance part of tunnel, in the middle part of tunnel and in the exit part of tunnel. As the result of the measurement, it was known that pressure slope of pressure wave happened in the entrance part of tunnel was increased by a nonlinear effect while spreading the tunnel or its pressure slope was reduced by diffusion. Also, the study compared and analyzed micro-pressure waves happened in the exit part of the tunnel by installing each kind of hoods in the entrance part of the tunnel to prevent reduction of micro-pressure waves.

• Fire Science and Engineering
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• v.24 no.2
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• pp.38-43
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• 2010

The purpose of this study is to secure the basis for judgment on the cause of an accident by analyzing the melting characteristics of a blade type fuse used for vehicles due to overload. In order to increase the reliability of the test, it was conducted by connecting the electrical system with conditions similar to those of an actual vehicle to apply the load. Carbonization pattern experiment of fuse by outside flame applied Korean Standard (KS). The fuse melted by the overcurrent showed a smooth cross-section while the test terminals, clear plastic body, etc., burnt out by the external flame was badly deformed. When 185% of the rated current (27.8A) was applied to a cable of 15A rated current onto which an over-capacity fuse (20A) was installed, the fuse melting time was 217 seconds. In addition, when a load current of 28.8[A] (139%) was applied, the fuse's test terminal and terminal blade were not burnt out although foam was observed on some parts of the plastic body. When a load capacity of 28.2[A] (141%) was applied to a cable of 15A rated current onto which an over-capacity fuse (30A) was installed, the fuse melting time was approximately 10 seconds. When a load current of 35.8[A] (119%) was applied, the fuse's test terminal and terminal blade were not burnt out, although some parts of the plastic body was swelled. However, it was observed that the switch terminal melted if approximately six minutes lapsed under such conditions. When a load capacity of 39.4[A] (131%) was applied to a cable of 15A rated current onto which an over-capacity fuse (30A) was installed, the fuse melted in approximately 69 seconds, and the test terminal and terminal blade were not burnt.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.11
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• pp.18-23
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• 2018

FPSO consists of topside modularized plants for production of crude oil, and hullside structures that serve as support for the topside and storage of produced crude oil. The structural behavior of the FPSO topside module and its supporting hull depends on the interface structure that connects them, and the interface structure consists of a combination of individual unit support structures called Module Support Seat (MSS). Types of interface structures are various and, accordingly, the basic design of the FPSO topside module structure is greatly influenced, so various design methods should be considered from the initial design phase. Structural design of FPSO topside module requires consideration of the number of MSSs, connection type, and structural analysis options such as the range of finite element models, load conditions, and boundary conditions for verification of structural strength. In this study, the comparison combination cases for the above considerations were derived and the strength evaluation was performed, and the structural behavior characteristics of the topside module were compared and analyzed through a detailed review of the analysis results. The results of this study are considered to be a good reference for designing a more reliable topside module structure.

• Journal of Korean Tunnelling and Underground Space Association
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• v.21 no.1
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• pp.177-188
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• 2019

The purpose of the optimization of the installation of supply/exhaust ports for tunnels with transverse ventilation system is to supply fresh air from outside to inside of tunnels uniformly and exhaust pollutant from tunnels properly for creating safe and clean environment for tunnel users. For this purpose, a ventilation port area optimization program was developed to obtain a uniform supply or exhaust air volume inside a great depth double deck tunnel with transverse ventilation system. In order to area optimize the developed port sizing program, the wind velocity was measured in the duct of the currently operated tunnel with semi-transverse ventilation. Also 3D cfd was performed on the same tunnel and cfd results were compared to the measured value. As a result, the error rate between the predicted value from the program and measured value was 6.72%, while the error rate between the predicted value from the program and 3D cfd analysis value was 4.86%. Both of comparison results show less than 10% of error rate. Thus It is expected that supply/exhaust port optimization design of transverse ventilation tunnel can be possible with using this large exhaust port area optimization program.

• Journal of the Korean Institute of Gas
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• v.4 no.3 s.11
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• pp.39-45
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• 2000

In general, most of the GIS only deal with materials and geometric data which just include position, radius, length of the structure. Therefore it's hard to get corrosion data from it. But the one that an owner of metallic structures want to know is the integrity of the structure. Cathodic Protection System can not protect corrosion on the underground facilities perfectly but protect corrsion effectively. It therefore is necessary to monitor the facilities continually So, we need the development of GIS interconnected a corrosion prediction system on the view point of the efficiency of operation and the protection for a big accident. The results of the development of its system are described in this paper. It can do life prediction and interference analysis and also newest corrosion data should be updated regularly.

• Korean Journal of Optics and Photonics
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• v.33 no.4
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• pp.167-176
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• 2022

Adaptive optics (AO) systems compensate for atmospheric disturbance, especially phase distortion, by introducing counter-wavefront deformation calculated from real-time wavefront sensing or prediction. Because AO system implementations are time-consuming and costly, it is highly desirable to estimate the system's performance during the development of the AO system or its parts. Among several techniques, we mostly apply statistical analysis, computational simulation, and optical-bench tests. Statistical analysis estimates performance based on the sum of performance variances due to all design parameters, but ignores any correlation between them. Computational simulation models every part of an adaptive optics system, including atmospheric disturbance and a closed loop between wavefront sensor and deformable mirror, as close as possible to reality, but there are still some differences between simulation models and reality. The optical-bench test implements an almost identical AO system on an optical bench, to confirm the predictions of the previous methods. We are currently developing an AO system for a 1.6-m ground telescope using a deformable mirror that was recently developed in South Korea. This paper reports the results of the statistical analysis and computer simulation for the system's design and confirmation. For the analysis, we apply the Strehl ratio as the performance criterion, and the median seeing conditions at the Bohyun observatory in Korea. The statistical analysis predicts a Strehl ratio of 0.31. The simulation method similarly reports a slightly larger value of 0.32. During the study, the simulation method exhibits run-to-run variation due to the random nature of atmospheric disturbance, which converges when the simulation time is longer than 0.9 seconds, i.e., approximately 240 times the critical time constant of the applied atmospheric disturbance.

• Journal of Korean Society of Steel Construction
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• v.15 no.4 s.65
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• pp.341-358
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• 2003

This paper proposed a general formulation of Life-Cycle Cost (LCC) models and LCC effective design system models of steel bridges suitable for practical implementation. An LCC model for the optimum design of steel bridges included initial cost and direct/indirect rehabilitation costs of a steel bridge as well as repair/replacement costs, loss of contents or fatality and injury losses, road user costs, and indirect socioeconomic losses. The new road user cost model and regional socioeconomic losses model were especially considered because of the traffic network. Illustrative design examples of an actual steel box girder and an orthotropic steel deck bridge were discussed to demonstrate the LCC effectiveness of the design of steel bridges. Based on the results of the numerical investigation, the LCC-effective optimum design of steel bridges based on the proposed LCC model was found to lead to a more rational, economical, and safer design compared with the initial cost-optimum design and the conventional code-based design.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.3D
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• pp.431-436
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• 2008

Recently, the rapid development of GIS technology has made it possible to handle a various data associated with spatially hydrological parameters with their attribute information. Therefore, there has been a shift in focus from lumped runoff models to distributed runoff models, as the latter can consider temporal and spatial variations of discharge. In this research, a distributed rainfall-runoff model based on physical kinematic wave for analysis of surface and river flow was used to simulate temporal and spatial distribution of long-term discharge. The snowfall and melting process model based on Hydro-BEAM was developed, and various hydrological parameters for input data of the model was extracted from basic GIS data such as DEM, land cover and soil map. The developed model was applied for the Shonai River basin(532) in Japan, which has sufficient meteorological and hydrological data, and displayed precise runoff results to be compared to the hydrograph.