• Journal of Korea Water Resources Association
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• v.53 no.2
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• pp.141-154
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• 2020

The accidents of toxic chemical spill into rivers are increasing in recent years due to expansion of heavy industries in Korea. In order to respond to the chemical spills, accident response systems have been established for both main rivers and tributary rivers. However, since these accident response system adopted the water quality models imported from the foreign countries, it is difficult to acquire the model parameters and to calibrate and validate the water quality models. Therefore, this study developed a depth-averaged two-dimensional river water quality model to analyze the behavior of hazardous chemicals in rivers and proposed an efficient simulation execution framework by identifying the significant reaction mechanisms considering the characteristics of the toxic chemicals. The depth-averaged two-dimensional river water quality model CTM-2D was upgraded by adding reaction terms representing mechanisms of the adsorption, desorption, and volatilization of toxic chemicals. In order to verify the model, the analytical solution was compared with the numerical solution, and results showed that the error was less than 0.1%. In addition, the model was applied to a virtual scenario which is a water pollution accident at the confluence of the Nakdong River - Kumho River, and model results showed that an efficient simulation could be carried out by activating only significant reactions which were assessed by the sensitivity analysis.

• Journal of the Mineralogical Society of Korea
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• v.29 no.2
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• pp.79-87
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• 2016

Asian dust (Hwangsa) interacts with light, atmospheric gas, aerosol, and marine ecosystem, affecting Earth climate. Mineralogical properties are essential to understand the interaction between the dust and environments. In this study, we examined the mineralogical properties of Asian dust collected at Deokjeok Island, Incheon, Korea in February 22, 2015. X-ray diffraction (XRD) analyses showed that phyllosilicate minerals (62 wt%) dominate the Asian dust. Illite-smectite series clay minerals (55%) were common with minor chlorite (5%) and kaolinite (2%). Non-phyllosilicate minerals were quartz (18%), plagioclase (10%), K-feldspar (4%), calcite (4%), and gypsum (1%). Similar results were obtained by mineral quantification using scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS). Transmission electron microscopy combined with EDS confirmed illite-smectite series clay minerals as the dominant phyllosilicate type. Morphological analyses using SEM showed clay agglomerates, clay-coated quartz, feldspars, and micas. Gypsum grains were common on the particle surface, while calcite nanofibers, previously reported as common on the surface, were rare, indicating the reaction of calcite and acidic atmospheric pollutants to form gypsum. The analytical result of 2015 Asian dust would contribute to the establishment of mineralogical base for the modeling of the interaction between Asian dust and environments.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.11 no.3
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• pp.179-196
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• 1986

In this paper, the peformance of a statistical packet voice/data multiplexer is studied. In ths study we assume that in the packet voice/data multiplexer two separate finite queues are used for voice and data traffics, and that voice traffic gets priority over data. For the performance analysis we divide the output link of the multiplexer into a sequence of time slots. The voice signal is modeled as an (M+1) - state Markov process, M being the packet generation period in slots. As for the data traffic, it is modeled by a simple Poisson process. In our discrete time domain analysis, the queueing behavior of voice traffic is little affected by the data traffic since voice signal has priority over data. Therefore, we first analyze the queueing behavior of voice traffic, and then using the result, we study the queueing behavior of data traffic. For the packet voice multiplexer, both inpur state and voice buffer occupancy are formulated by a two-dimensional Markov chain. For the integrated voice/data multiplexer we use a three-dimensional Markov chain that represents the input voice state and the buffer occupancies of voice and data. With these models, the numerical results for the performance have been obtained by the Gauss-Seidel iteration method. The analytical results have been verified by computer simylation. From the results we have found that there exist tradeoffs among the number of voice users, output link capacity, voic queue size and overflow probability for the voice traffic, and also exist tradeoffs among traffic load, data queue size and oveflow probability for the data traffic. Also, there exists a tradeoff between the performance of voice and data traffics for given inpur traffics and link capacity. In addition, it has been found that the average queueing delay of data traffic is longer than the maximum buffer size, when the gain of time assignment speech interpolation(TASI) is more than two and the number of voice users is small.

• Journal of Korea Water Resources Association
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• v.41 no.8
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• pp.761-772
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• 2008

The object of this study is to develop the model that solves the numerically difficult problems in hydraulic engineering and to demonstrate the applicability of this model by means of various test examples, such as, verification in the gradually varied unsteady condition, three steady flow problems with the change of bottom slope with exact solution, and frictional bed with analytical solution. The governing equation of this model is the integral form of the Saint-Venant equation satisfying the conservation laws, and finite volume method with the Riemann solver is used. The evaluation of the mass and momentum flux with the HLL Riemann approximate solver is executed. MUSCL-Hancock scheme is used to achieve the second order accuracy in space and time. This study introduce the new and simple technique to discretize the source terms of gravity and hydrostatic pressure force due to longitudinal width variation for the balance of quantity between nonlinear flux and source terms. The results show that the developed model's implementation is accurate, robust and highly stable in various flow conditions with source terms, and this model is reliable for one-dimensional applications in hydraulic engineering.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.2A
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• pp.85-95
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• 2012

This paper presents an investigation on the ultimate behavior of steel cable-stayed bridges using nonlinear finite element analysis method. Cable-stayed bridges exhibit various geometric nonlinearities as well as material nonlinearities, so rational nonlinear finite element analysis should be performed for investigation of the ultimate behavior. In this study, ultimate behavior of steel cable-stayed bridges was studied using rational ultimate analysis method. Nonlinear equivalent truss element and nonlinear frame element were used for modeling the cable, girder and mast. Moreover, refined plastic hinge method was adopted for considering the material nonlinearity of steel members. In this study, the 2-step analysis method was used. Before live load analysis, initial shape analysis was performed in order to consider the dead load condition. For investigation of the ultimate behavior of steel cable-stayed bridges, analysis models which span length is 920.0 m were used. Radiating type and fan type were considered as the cable-arrangement types. With various quantitative evidences such as load-displacement curves, deformed shapes, locations of the yield point or region, bending moment distribution and so on, the ultimate behavior of steel cable-stayed bridges was investigated and described in this paper.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.38 no.2
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• pp.349-356
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• 2018

This paper attempts to develop a connection model based on FE analysis that can be applied to the evaluation of earthquake fragility of Steel Storage Racks lacking research in Korea. In order to accomplish this goal, shaking table tests, modal tests, and various member tests (8 case, push-over test) for structural members have been conducted to understand the behavior of steel storage racks. Based on the experimental results, detailed modeling of the joints was conducted using the NX-Nastran program in order to develop a connection model for Steel storage racks to be applied to the seismic vulnerability assessment. Especially, surface to surface contact element and spring element are applied to simulate the connection between the column member and the beam member connected by the simple latch method. Spring element model developed and applied ARX (Auto Regressive eXogenous) based mathematical model. The simulation results based on the FE model showed excellent reliability with a mutual error rate of less than 8% when compared with the member test results. As a result, it was confirmed that the FE model based connection model developed in the study can be applied to the analytical model for the seismic vulnerability assessment of Steel storage racks.

• International Journal of Highway Engineering
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• v.14 no.3
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• pp.151-162
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• 2012

It is not surprising to hear news about irresistible natural disasters all over the world due to climate change. Korean Government has focused on developing a variety of green technologies to reduce green house gasses, in particular, carbon dioxide. This study suggested 18 technology divisions for achieving green highway technology development in six different sub-sectors considering life-cycle of roadway and surveyed 29 highway and/or transportation professionals of three institutes using AHP(Analytical Hierarchy Process) analysis to construct "Green Highway"and realize carbon emission reductions and energy use efficiency in a road sector in Korea. Expert Choice Software was used to rank 18 technology divisions weighted by two-level choices. Transport Operating Infrastructure Improvement, Roadway Policy Implementation, Green Transportation(such as Pedestrian and Bicycle) were highly ranked by respondents according to results of the AHP modeling. Among the 18 divisions, technology policy for supporting R&D investments from development to commercialization was ranked as the most significant one to be focused. Green Transportation Facility Design/Construction/Operation and Eco-Friendly Roadway Plan were followed as expected since professionals have thought that the planning/design step of the life-cycle is a starting point to reduce carbon dioxide from roads more and more. Additionally, comparing the results with the Government investment trend 2006-2011 for the roads, it can be interpreted that the Government should invest to the R&D area more widely than before to promote element and core technology development for Green Highway Construction. Above all, small and mid-sized businesses have to be invested as well as encouraged to undertake green highwayrelated objects to accomplish the divisions which ranked high.

• Journal of Korean Society of Steel Construction
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• v.21 no.1
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• pp.63-70
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• 2009

Failure modes result in fracture or tearing, which may cause deterioration of resistance and reduction of inelastic deformation capacity. The potential failure modes for Special Concentrically Braced Frames (SCBFs) include fracture or tearing of the brace, net section fracture of the brace or gusset plate, fracture of the gusset plate welds, shear fracture of the bolts, block shear, excessive bolt bearing deformation, and buckling of the gusset plate. HSS tubular braces are commonly used in SCBFs, and net section fracture of the tubular brace may also occur through the brace net section at the end of the slot cut into the tube to slip over the gusset plate. This failure mode is categorized as a tension failure mode, and may cause dramatic loss of resistance and brittle behavior. Net section reinforcement is required according to AISC design specifications (AISC 2001). In this paper, the need to reinforce the net section area was discussed. Initially, the results of the net section fracture tests done by the University of California in Berkeley were presented with the modeling of these tests using FE models. To investigate the possibility of net section fracture in an actual frame, the slot end hole model was adapted to the frame FE model, and alternate near-fault histories were applied with tension-dominated cycles, since previous analyses showed that loading history was the most critical factor in net section fracture. The need for this reinforcement (cover plate) and the tension-dominated near-fault history were investigated.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.19 no.4 s.74
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• pp.429-440
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• 2006

This paper comprises two specific objectives. The first is to examine the applicability of ordinary kriging interpolation(OK) to the p-adaptivity of the finite element method that is based on variogram modeling. The second objective Is to present the adaptive procedure by the hierarchical p-refinement in conjunction with a posteriori error estimator using the modified S.P.R. (superconvergent patch recovery) method. The ordinary kriging method that is one of weighted interpolation techniques is applied to obtain the estimated exact solution from the stress data at the Gauss points. The weight factor is determined by experimental and theoretical variograms for interpolation of stress data apart from the conventional interpolation methods that use an equal weight factor. In the p-refinement, the analytical domain has to be refined automatically to obtain an acceptable level of accuracy by increasing the p-level non-uniformly or selectively. To verify the performance of the modified S.P.R. method, the new error estimator based on limit value has been proposed. The validity of the proposed approach has been tested with the help of some benchmark problems of linear elastic fracture mechanics such as a centrally cracked panel, a single edged crack, and a double edged crack.

• Journal of Korea Technology Innovation Society
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• v.14 no.1
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• pp.22-39
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• 2011

This study examines the wage level from a viewpoint of major-job match as part of an analysis on the skill mismatch problem in 4-year college graduates. The empirical analysis explicitly incorporate the sample selection bias as an econometric problem not only suggested but merely introduced in the earlier studies. This study also set up a major-job match variable, which was usually handled as a binary variable for analytical convenience, as a polychotomous choice variable in selection equation as provided by the survey. In particular, it considered multi-cohort survey on graduates of the years 1982, 1992, and 2002 for the empirical analysis. As a result of empirical analysis, the wage premium of a major-job match was identified. This result was consistent after the consideration of a sample selection bias and also after modeling the major-job match variable as polychotomously selective. Through an analysis classified by the major, this study identified a relatively high wage premium among Social Science, Engineering, and Science majors. However, there was a difference in the effect of selection among these majors. Also, by assessing cohort effects this study found that the skill mismatch had rapidly progressed in 1992, while difference between 1992 and 2002 cohorts are insignificant. The analysis suggests that wage level is better understood within the context of both sample selection and major-job match, and regardless of model specification the major-job match affects wage strongly.