• Journal of the Korean GEO-environmental Society
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• v.19 no.11
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• pp.5-14
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• 2018

Worldwide, soil compaction work is one of the most important activities that are carried out on civil engineering works sites. Compaction work, particularly in the area of road construction, is considered to be important, as poor compaction work is closely related with poor construction even after a construction is complete. Currently, the plate bearing test or the sand cone method relative to the unit weight of soil test are commonly used to measure the degree of compaction, but as these require a great deal of time, equipment and manpower, it is difficult to secure economic efficiency. The method that is used to measure the degree of compaction according to the penetration depth achieved by free fall objects through gravity is the Free-Fall Penetration Test (FFPT), which uses a so-called "portable compaction measuring meter (PCMM)." In this study, the degree of compaction was measured and a penetration depth graph was developed after the field test using the portable compaction measuring meter. The coefficient of determination was 0.963 at a drop height of 10 cm, showing the highest level of accuracy. Both horizontal axis and longitudinal axis were developed in a decimal form of graph, and the range of allowable error was ${\pm}1.28mm$ based on the penetration depth. The portable compaction measuring meter makes it possible to measure the degree of compaction simply, quickly and accurately in the field, which will ensure economic efficiency and facilitate the process management.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.4
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• pp.293-301
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• 2017

A Sub-kWe small-scale experimental test loop was manufactured to investigate characteristics of the supercritical carbon dioxide power cycle. A high-speed turbo-generator was also designed and manufactured. The designed rotational speed of this turbo-generator was 200,000 rpm. Because of the low expansion ratio through the turbine and low mass flowrate, the rotational speed of the turbo-generator was high. Therefore, it was difficult to select the rotating parts and design the turbine wheel, axial force balance and rotor dynamics in the lab-scale experimental test loop. Using only one channel of the nozzle, the partial admission method was adapted to reduce the rotational speed of the rotor. This was the world's first approach to the supercritical carbon dioxide turbo-generator. A cold-run test using nitrogen gas under an atmospheric condition was conducted to observe the effect of the partial admission nozzle on the rotor dynamics. The vibration level of the rotor was obtained using a gap sensor, and the results showed that the effect of the partial admission nozzle on the rotor dynamics was allowable.

• Nuclear Engineering and Technology
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• v.45 no.4
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• pp.513-522
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• 2013

The ODSCC detected in the TSP position of Ulchin 3&4 SGs are typical ODSCC of Alloy 600MA tubes. The causative chemical environment is formed by concentration of impurities inside the occluded region formed by the tube surface, egg crate strips, and sludge deposit there. Most cracks are detected at or near the line contacts between the tube surface and the egg crate strips. The region of dense crack population, as defined as between $4^{th}$ and $9^{th}$ TSPs, and near the center of hot leg hemisphere plane, coincided well with the region of preferential sludge deposition as defined by thermal hydraulics calculation using SGAP computer code. The cracks developed homogeneously in a wide range of SGs, so that the number of cracks detected each outage increased very rapidly since the first detection in the $8^{th}$ refueling outage. The root cause assessment focused on investigation of the difference in microstructure and manufacturing residual stress in order to reveal the cause of different susceptibilities to ODSCC among identical six units. The manufacturing residual stress as measured by XRD on OD surface and by split tube method indicated that the high residual stress of Alloy 600MA tube played a critical role in developing ODSCC. The level of residual stress showed substantial variations among the six units depending on details of straightening and OD grinding processes. Youngwang 3&4 tubes are less susceptible to ODSCC than U3 and U4 tubes because semi-continuous coarse chromium carbides are formed along the grain boundary of Y3&4 tubes, while there are finer less continuous chromium carbides in U3 and U4. The different carbide morphology is caused by the difference in cooling rate after mill anneal. There is a possibility that high chromium content in the Y3&4 tubes, still within the allowable range of Alloy 600, has made some contribution to the improved resistance to ODSCC. It is anticipated that ODSCC in Y5&6 SGs will be retarded more considerably than U3 SGs since the manufacturing residual stress in Y5&6 tubes is substantially lower than in U3 tubes, while the microstructure is similar with each other.

• Journal of the Korean Geotechnical Society
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• v.35 no.8
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• pp.17-30
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• 2019

Based on pile load test results for various pile types that were constructed in-situ and pile design data of prebored PHC piles, the ratio of skin friction to total capacity (SRF) was analyzed. A SRF distribution range from the pile load test results for pilot test prebored PHC piles was 42~99% regardless of relative penetration lengths, soil types, and pile load test types. However, a SRF distribution range from the pile design data for prebored PHC piles was 20~53% regardless of relative penetration lengths and pile diameters. Also, a SRF distribution range from the restrike dynamic pile load test results for pretest working prebored PHC piles was a scattered range of 4~83% regardless of pile diameters, relative penetration lengths and soil types. The scattered SRF of pretest working piles was caused to the quality control issue on the filling of cement milk around piles and this quality control issue should be improved. The average SRF calculated by the current design method was estimated to be 2.2 times lower than the average SRF of the pilot test piles. It is because skin friction resistance is calculated at a very low level. Therefore, a new design method for skin friction will be proposed based on this study.

• Environmental and Resource Economics Review
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• v.28 no.2
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• pp.277-306
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• 2019

Mackerel is one of the most widely consumed aquatic products in Korea. Concerns about the depletion of stocks have also arisen as the catch has decreased. The primary purpose of this study is to estimate the mackerel stock and derive the optimal level of catch in Korea. We apply a generalized maximum entropy econometric method to estimate the mackerel growth function, which does not require the steady state assumption. We incorporate a bootstrapping approach to derive the significance levels of parameter estimates. We found that the average ratio of catch to the estimated total stock was less than 30% before the 1990s but exceeded 40% in the 1990s. After 2000, it dropped back to about 36%. This finding indicates that mackerel may have been over-fished in the 1990s, but the government regulations introduced in the 2000s alleviated over-fishing problems. Nevertheless, our dynamic optimization analysis suggests that the total allowable catch may need to be carefully controlled to achieve socially optimal management of resources.

• Journal of the Korean Geotechnical Society
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• v.35 no.4
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• pp.15-26
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• 2019

The stability of the gravity quay wall against earthquakes is evaluated on the basis of the allowable displacement of the wall. To estimate the displacement caused by external forces, empirical equations based on the Newmark sliding block method or numerical analysis are widely used. In numerical analysis, it is possible to analyze precisely a complicated site and structure, but difficult to set the appropriate parameters and environments; there are limitations in obtaining reliable results, depending on one's level of expertise. The Newmark method, with only seismic motions, is widely used because it is simpler than numerical simulations when estimating permanent displacement. However, the empirical equations do not have any parameters for the response characteristics and sliding block of the structure, and sliding blocks being assumed as rigid bodies does not consider the nonlinear behavior of the soil and interaction with the structure. Therefore, in order to evaluate the seismic stability of the gravity quay wall, a newly-developed empirical equation is needed to overcome the above-mentioned limitations. In this study, numerical simulations are performed to analyze the response characteristics of the backfill of the structure, and to propose an optimal method of calculating the active area. For this purpose, finite element analyses were performed to analyze the response characteristics, and stress-strain relationships for various seismic motions. As a result, the response characteristics, sliding block, and failure surface of the backfill vary depending on the input seismic motions.

• Journal of the Society of Disaster Information
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• v.16 no.4
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• pp.796-805
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• 2020

Purpose: A static loading test was performed to evaluate the ultimate flexural strength of a girder in which 80MPa high-strength concrete was synthesized on the compressive flange of the I-shape steel girder. Method: This test is designed and fabricated two types of specimens with different shear-connection specifications, and evaluated their ultimate flexural behavior until reaching the extreme event limit states. In addition, the ultimate strength was evaluated by comparing the test results and the results of the strain compatibility method. Result: By confirming the displacement within 0.02mm as a result of the relative slip measurement, it was verified that the two specimens secured perfect bonding. Therefore, the difference in the shear specification does not have a great effect on the stiffness, and if the specimens are completely synthesized, there is no difference in the behavior until it reaches the extreme-event limit states. Conclusion: The girder to be tested has a working load within the elastic range and meets the usability requirements for allowable deflection. Therefore, even if a part of the casing is subjected to the tensile force at the level of cracking, the deck will first reach the compression failure due to the role of the reinforcing bar.

• Journal of the Korean GEO-environmental Society
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• v.12 no.1
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• pp.13-26
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• 2011

Because the allowable current loading of buried electrical transmission cables is frequently limited by the maximum permissible temperature of the cable or of the surrounding ground, there is a need for cable backfill materials to be maintained at a low thermal resistivity during the service period. Temperatures greater than $50^{\circ}C$ to $60^{\circ}C$ may lead to breakdown of cable insulation and thermal runaway if the surrounding backfill material is unable to dissipate the heat as rapidly as it is generated. This paper describes the results of studies aimed at the development of backfill material to reduce the thermal resistivity. A large number of different additive materials were tested to determine their applicability as a substitute material. The results of Dong-rim river sand (relatively uniform) show that as water content level increases, thermal resistivity tends to decrease, whereas the thermal resistivity on dry condition is very high value($260^{\circ}C-cm/watt$). In addition, other materials(such as Jinsan granite screenings, A-2(sand and gravel mixture), E-1(rubble and granite screenings mixture) and SGFC(sand, gravel, fly-ash and cement mixture)) are well-graded materials with low thermal resistivity($100^{\circ}C-cm/watt$ when dry). Based on this research, 4 types of improved materials were suggested as the environmentally friendly backfill materials with low thermal resistivity.

• Journal of the Korean Institute of Rural Architecture
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• v.24 no.3
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• pp.23-30
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• 2022

In this study, in order to grasp the current situation of indoor environmental pollution and indoor ventilation in one-room around the university in the post-corona era, we analyzed the experimental data and conducted a questionnaire survey on university students. By analyzing the content, the effects of formaldehyde, dust and other pollution on the human body, which are usually not easily detectable, are digitized and more easily taken into account. Among the experimental results, the concentration of VOC and HCHO, gas pollutants among indoor pollutants, exceeded the recommended criteria of the Ministry of Environment in most studio apartments. Overall, the average CO₂ concentration was lower than the Ministry of Environment's maintenance standard (1000ppm), but it was relatively high in summer and winter, and it is believed to be caused by cooling and heating in an enclosed space. The levels of PM2.5 and PM10, particulate pollutants, increased in November and December, and it is believed that ventilation defects due to degradation in external temperature. There was no clear difference between the two types, and there was a very high correlation between PM2.5 and PM10, HCHO and VOC. It was found that temperature was closely correlated with all sources except CO₂, and humidity was closely correlated with all sources except PM2.5 and PM10. Health risk assessment was conducted for formaldehyde. The average ECR of studio R2 in May was 3.91E^-4, and the ECR figure in September was 3.65E^-4, which was very high compared to other residential spaces. The R2 level was calculated as 4 people per 10,000 people in the lifetime risk of cancer of residents, exceeding the allowable risk. R8 also showed higher ECR results than other spaces after R2, especially in October, 2.01E^-4, six times higher than R7 measured in October, and 1.87E^-4 in July, four times higher than R9.

• Journal of the Korea Convergence Society
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• v.13 no.2
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• pp.67-75
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• 2022

The purpose of this study is to present an appropriate management plan as a supplement to the scientific evidence of the currently operated distancing system for preventing COVID-19. The currently being used mathematical models are expressed as simultaneous ordinary differential equations, there is a problem in that it is difficult to use them for the management of entry and exit of small business owners. In order to supplement this point, in this paper, a method for quantitatively expressing the risk of infection by people who gather is presented in consideration of the allowable risk given to the gathering space, the basic infection reproduction index, and the risk reduction rate due to vaccination. A simple quantitative model was developed that manages the probability of infection in a probabilistic level according to a set of visitors by considering both the degree of infection risk according to the vaccination status (non-vaccinated, primary inoculation, and complete vaccination) and the epidemic status of the virus. In a given example using the model, the risk was reduced to 55% when 20% of non-vaccinated people were converted to full vaccination. It was suggested that management in terms of quarantine can obtain a greater effect than medical treatment. Based on this, a generalized model that can be applied to various situations in consideration of the type of vaccination and the degree of occurrence of confirmed cases was also presented. This model can be used to manage the total risk of people gathered at a certain space in a real time, by calculating individual risk according to the type of vaccine, the degree of inoculation, and the lapse of time after inoculation.