• Journal of the Korean Institute of Gas
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• v.7 no.4 s.21
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• pp.44-52
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• 2003

In this work dynamic heat transfer in a CPFS (cable penetration fire stop) system built in the firewall of nuclear power plants is three-dimensionally investigated to develop a test-simulator that can be used to verify effectiveness of the sealant. Dynamic heat transfer in the fire stop system is formulated in a parabolic PDE (partial differential equation) subjected to a set of initial and boundary conditions. First, the PDE model is divided into two parts; one corresponding to heat transfer in the axial direction and the other corresponding to heat transfer on the vertical planes. The first PDE is converted to a series of ODEs (ordinary differential equations) at finite discrete axial points for applying the numerical method of SOR (successive over-relaxation) to the problem. The ODEs are solved by using an ODE solver In such manner, the axial heat flux can be calculated at least at the finite discrete points. After that, all the planes are separated into finite elements, where the time and spatial functions are assumed to be of orthogonal collocation state at each element. The initial condition of each finite element can be obtained from the above solution. The heat fluxes on the vertical planes are calculated by the Galerkin FEM (finite element method). The CPFS system was modeled, simulated, and analyzed here. The simulation results were illustrated in three-dimensional graphics. Through simulation, it was shown clearly that the temperature distribution was influenced very much by the number, position, and temperature of the cable stream, and that dynamic heat transfer through the cable stream was one of the most dominant factors, and that the feature of heat conduction could be understood as an unsteady-state process.

• Journal of Korea Port Economic Association
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• v.25 no.3
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• pp.269-282
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• 2009

This study investigates the difference of behavioral patterns between the import container volume of all ports and that of Gwangyang port in Korea. All series span the period January 1999 to December 2008. I first test whether the series are stationary or not. I can reject the null hypothesis of a unit root in each of the level variables and of a unit root for the residuals from the cointegration at the 5 percent significance level. I hitherto make use of variance decompositions and impulse response functions, both of which have now been widely used to examine how much movement in one variable can be explained by innovations in different variables and how rapidly these fluctuations in one variable can be transmitted to another. The variance decompositions for the import container volume show that the proportions of the forecast error variance of import container volumes explained by themselves are 30 and 26 per cent after 12 months, respectively. As a result, innovations in exchange rate and business activity explain 70 and 74 per cent of the variance in the import container volume. All in all, innovation accounting indicates that import container volumes are not exogenous with respect to exchange rate and business activity. The impulse responses indicate that container volumes decrease sharply to the shocks in exchange rate and decay very slowly to its pre-shock level, while container volumes respond positively to the shocks in the business activity and disappear very slowly, showing that the shocks last very long. Furthermore Gwangyang port is more sensitive to the change of the exchange rate and the industrial production than all ports.

• Journal of Korea Water Resources Association
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• v.52 no.8
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• pp.555-563
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• 2019

Reduced thickness of the water pipes due to corrosion makes it difficult to perform the original functions since corrosion in metallic water pipes can occur over time. In this study, reliability model that can estimate the probability of pipe breakage is developed regarding corrosion depth increment according to service year. Probability of pipe breakage was calculated by FORM(First Order Reliability Method) and unsteady analysis was performed to analyze the statistical properties of water pressure. And KCIP(Korea Cast Iron Pipe) equation was adopted for the reliability function. Furthermore, change of pipe thickness was estimated by Nahal and Khelif equation and Romanoff equation. Therefore, pipe thickness was calculated due to change of corrosion depth and probability of pipe breakage was calculated and compared with 10, 20, 30 service years. From the results, probability of pipe breakage for network A is gradually increased from 6.8% to 8.6% according to service year of 10, 20, 30 when Nahal and Khelif equation is applied. And probability of pipe breakage for network A is also gradually increased from 6.4% to 8.9% according to service year of 10, 20, 30 when Romanoff equation is applied.

• Journal of Software Assessment and Valuation
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• v.16 no.1
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• pp.65-79
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• 2020

As Programmable Logic Controllers (PLCs), popular components in industrial control systems (ICS), are incorporated with the technologies such as micro-controllers, real-time operating systems, and communication capabilities. As the latest PLCs have been connected to the Internet, they are becoming a main target of cyber threats. This paper proposes two sanitizers that improve the security of uC/OS-II based firmware for a PLC. That is, we devise BU sanitizer for detecting out-of-bounds accesses to buffers and UaF sanitizer for fixing use-after-free bugs in the firmware. They can sanitize the binary firmware image generated in a desktop PC before downloading it to the PLC. The BU sanitizer can also detect the violation of control flow integrity using both call graph and symbols of functions in the firmware image. We have implemented the proposed two sanitizers as a prototype system on a PLC running uC/OS-II and demonstrated the effectiveness of them by performing experiments as well as comparing them with the existing sanitizers. These findings can be used to detect and mitigate unintended vulnerabilities during the firmware development phase.

• Journal of the Korean Geotechnical Society
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• v.39 no.8
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• pp.29-39
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• 2023

The degree of saturation determines the connectivity of void space and the particle surface. Thus, it greatly affects the electrical conductivity of soils. This study aimed to analyze the electrical conductivities of coarse grains with a high relevance of pore water conduction and fine grains with a high relevance of surface conduction based on the degree of saturation. It also aimed to express the electrical conductivity of unsaturated soils as a combination of surface and pore water conductions using the modified Archie's equation. Samples were prepared in a plastic cell equipped with four electrodes, and the electrical conductivity was measured based on the porosity at various degrees of saturation (40%~100%). The results demonstrate that Archie's equation can be used to express the electrical conductivity of coarse grains, with a saturation exponent of ~1.93 regardless of the pore water conductivity. However, the saturation exponent of fine grains varied considerably with pore water concentration. This variation can be attributed to the relative magnitude of surface conduction with respect to the electrical conductivity of soils at different pore water concentrations. Thus, the degree of saturation has varying effects on pore water conduction and surface conduction. Therefore, different saturation exponents must be used for pore water conduction and surface conduction to predict the electrical conductivity of unsaturated soils using the modified Archie's equation.

• Journal of the Korean Geotechnical Society
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• v.23 no.4
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• pp.5-13
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• 2007

Many construction projects adopt grouting technology to prevent the leakage of groundwater or to improve the shear strength of the ground. Recognition as a feasible field procedure dates back to 1925. Since then, developments and field use have increased rapidly. According to improvement of grout materials, theoretical study on grout penetration characteristics is demanded. Fluid of grout always tends to flow from higher hydraulic potential to lower one and the motion of grout is also a function of formation permeability. Viscosity of pout is changed by chemical action while grout moves through pores. Due to the increment of viscosity, permeability is decreased. Permeability is also reduced by grout particle deposits to the soil aggregates. In this paper, characteristics of new cement grout material that has been developed recently are studied: injectable volume of new grout material is tested in two different grain sizes of sands; and the method to calculate injectable volume of grout Is suggested with consideration of change in viscosity and clogging phenomena. The calculated values are compared with injection test results. Viscosity of new grout material is found to increase as an exponential function of time. And lumped parameter $\delta$ of new grout material to be used for assessing deposition characteristics is estimated by comparing deposit theory with injection test results considering different soil types and different injection pressures. Injection test results show that grout penetration rate is decreased by the increase of grout viscosity and clogging phenomena.

• Journal of the Korean Geotechnical Society
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• v.22 no.5
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• pp.83-91
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• 2006

Recently, the intensive rainstorm possibly induced by global warming plays a key role on the instability of railway adjacent slopes. The instability of slopes results as covering and loss of railway lines induced by slided soil mass. According to the site investigation on the failed slopes triggered by rainfall, low types of slope failure were observed: shallow, intermediate, gully erosion, and soil-rock interface failures. The observation reveals the different characteristics of slope failure depending on the thickness of soil layer, morphological features of slope, etc. Based upon the observations, flume tests were conducted to analyze the sliding mechanism of each failure. The variables of flume test are soil layer thickness, rainfall intensity, and morphology of slope under the constant condition of the percentage of fine, initial soil moisture content, slope angle and compaction energy. Test results show that shallow failure was mostly observed from the surface of the slope and caused by the soil erosion; in addition, compared to the other types of failure, the occurrence of initial erosion is late, however, the development of erosion is fast. In gully erosion failure, the collected water from the water catchment area helps erosion of the upper soil layer and transfer of residual corestone, which impedes the erosion process once the upper soil layers are eroded and corestone are exposed. The soil-rock interface failure shows the most fast initial erosion process among the failure types. Interestingly, the common feature observed from the different types of failure was the occurrence of the initial deformation near the toe of slopes which implies the existence of surbsurface flow along the downslope direction.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.5D
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• pp.821-829
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• 2006

Traffic load comprise primary input to pavement design causing pavement damage. therefore it should be proceeded suitable traffic load distribution modeling for pavement design and analysis. Traffic load have been represented by equivalent single axle loads (ESALs) which convert mixed traffic stream into one value for design purposes. But there are some limit to apply ESALs to other roads because it is empirical value developed as part of the original AASHO(American Association of State Highway Officials) road test. There have been many efforts to solve these problems. Several leading country have implemented M-E(Mechanistic-Empirical) design procedures based on mechanical concept. As a result, they established traffic load quantification method using load distribution model known as Axle Load Spectra. This paper details Axle Load Spectra and presents axle load distribution model based on normal mixture distribution function using truck load data collected by WIM system installed in national highway. Axle load spectra and axle load distribution model presented in this paper could be useful for basic data when making traffic load quantification plan for pavement design, overweight vehicle permit plan and pavement maintenance cost plan.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.4B
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• pp.357-363
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• 2009

When yields the mean velocity of the closed conduit which is used generally, it is available to use Darcy Weisbach Friction Loss Head equation. But, it is inconvenient very because Friction Loss coefficient f is the function of Reynolds Number and Relative roughness (${\varepsilon}$/d). So, it is demanded more convenient equation to estimate. In order to prove the reliability and an accuracy of Chiu's velocity equation from the research which sees hereupon, proved agreement very well about measured velocity measurement data by using Laser velocimeter which is a non-insertion velocity measuring equipment from the closed conduit (Laser Doppler Velocimeter: LDV) and an insertion velocity measuring equipment and the Pitot tube which is a supersonic flow meter (Transit-Time Flowmeters). By proving theoretical linear-relation between maximum velocity and mean velocity in laboratory flume without increase and decrease of discharge, the equilibrium state of velocity in the closed conduit which reachs to equilibrium state corresponding to entropy parameter M value has a trend maintaining consistently this state. If entropy M value which is representing one section is determinated, mean velocity can be gotten only by measuring the velocity in the point appearing the maximum velocity. So, it has been proved to estimate simply discharge and it indicates that this method can be a theoretical way, which is the most important in the future, when designing, managing and operating the closed conduit.

• Journal of the Korean Wood Science and Technology
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• v.39 no.4
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• pp.359-369
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• 2011

The study was carried out to investigate the quality characteristics of pellets manufactured with adding soybean oil, waste soybean oil, ozonized soybean oil and ozonized waste soybean oil to Larix kaemferi Carr sawdust. The characteristics of pellet included moisture contents, heating value, ash contents, apparent densities, durabilities, absorption ratio and elementary analysis. Moisture contents were shown 7.66~9.48% which satisfied the first grade (less than 10%) of quality standard of wood pellets announced by Korea Forest Research Institute. The heating value of the manufactured wood pellets in this study exceeded the first grade of quality standard (more than 4,300 kcal/kg) and it appeared that the pellets manufactured with adding oils and ozonized oils had more heating value than the control pellets. Ash contents 0.34~0.42% also passed the first grade (less than 0.7%) of quality standard and apparent densities were adequate for the first grade (640 kg/$m^3$) on the quality standard. Durabilities of the pellets manufactured with adding soybean oil and ozonized waste soybean oil were shown over the first grade (97.5 kg/$m^3$) of quality standard. In the general results of durabilities, the pellets manufactured with additives had better values than the control pellets. After 24 hours absorption ratio experiment, absorption ratio of pellets manufactured with additives also appeared much lower moisture absorption than the control pellets and they still had the same results after 5days absorption ratio experiment. Elementary analysis of the sulfur content was satisfied the first grade (less than 0.05%) of quality standard of wood pellets and the nitrogen content was also adequate for the first grade (less than 0.3%) of quality standard of wood pellets.