• Journal of the Korea institute for structural maintenance and inspection
• /
• v.13 no.1 s.53
• /
• pp.152-160
• /
• 2009

The pipe jacking method which is a non-excavation method is frequently used due to constructability and economical efficiency in a medium or small-sized pipeline construction. However, jacking process of the method still causes problems that the base ground is disturbed and loosen. These lead to surface settlement, strength decrease and leakage of water. Therefore, this study presents in-situ application of the steel pipe jacking with grouting, and it is that jacking and grouting are progressed simultaneously. To verify this, the steel pipe jacking with grouting and the existing steel pipe jacking have been constructed on the same ground condition. It has been proved that the steel pipe jacking with grouting is in-situ applicable according to results of monitoring surface settlement, in-situ density, GPR geophysical prospecting and large scale direct shear test.

• Economic and Environmental Geology
• /
• v.55 no.4
• /
• pp.317-338
• /
• 2022

Physicochemical characteristics and evaluation were studied by subdividing the concretes, bricks and earth pipes on the site of the Japanese Ministry of General Affairs in Joseon Dynasty, known as modern architecture, into three periods. Concretes showed similar specific gravity and absorption ratio, and large amounts of aggregates, quartz, feldspar, calcite and portlandite were detected. Porosity of the 1907 bricks were higher than those of 1910 and 1950 bricks. All earthen pipe is similar, but the earlier one was found to be more dense. Bricks and earthen pipes are dark red to brown in color within many cracks and pores, but the matrix of the earthen pipe is relatively homogeneous. Quartz, feldspar and hematite are detected in bricks, and mullite is confirmed with quartz and feldspar in earthen pipes, so it is interpreted that the materials have a firing temperature about 1,000 to 1,100℃. Concretes showed similar CaO content, but brick and earthen pipe had low SiO₂ and high Al₂O₃ in the 1907 specimen. However, the materials have high genetic homogeneity based on similar geochemical behaviors. Ultrasonic velocity and rebound hardness of the concrete foundation differed due to the residual state, but indicated relatively weak physical properties. Converting the unconfined compressive strength, the 1st extended area had the highest mean values of 45.30 and 46.33 kgf/cm², and the 2nd extended area showed the lowest mean values (20.05 and 24.76 kgf/cm²). In particular, the low CaO content and absorption ratio, the higher ultrasonic velocity and rebound hardness. It seems that the concrete used in the constructions of the Japanese Ministry of General Affairs in Joseon Dynasty had similar mixing characteristics and relatively constant specifications for each year. It is interpreted that the bricks and earthen pipes were through a similar manufacturing process using almost the same raw materials.

• Nuclear Engineering and Technology
• /
• v.55 no.5
• /
• pp.1802-1813
• /
• 2023

Conjugate heat transfer between liquid metal and solid is a common phenomenon in a liquid-metal-cooled fast reactor's fuel assembly and heat exchanger, dramatically affecting the reactor's safety and economy. Therefore, comprehensively studying the sophisticated conjugate heat transfer in a liquid-metal-cooled fast reactor is profound. However, it has been evidenced that the traditional Simple Gradient Diffusion Hypothesis (SGDH), assuming a constant turbulent Prandtl number (Pr_t,, usually 0.85 - 1.0), is inappropriate in the Computational Fluid Dynamics (CFD) simulations of liquid metal. In recent decades, numerous studies have been performed on the four-equation model, which is expected to improve the precision of liquid metal's CFD simulations but has not been introduced into the conjugate heat transfer calculation between liquid metal and solid. Consequently, a four-equation model, consisting of the Abe k - ε turbulence model and the Manservisi k_𝜃 - ε_𝜃 heat transfer model, is applied to study the conjugate heat transfer concerning liquid metal in the present work. To verify the numerical validity of the four-equation model used in the conjugate heat transfer simulations, we reproduce Johnson's experiments of the liquid lead-bismuth-cooled turbulent pipe flow using the four-equation model and the traditional SGDH model. The simulation results obtained with different models are compared with the available experimental data, revealing that the relative errors of the local Nusselt number and mean heat transfer coefficient obtained with the four-equation model are considerably reduced compared with the SGDH model. Then, the thermal-hydraulic characteristics of liquid metal turbulent pipe flow obtained with the four-equation model are analyzed. Moreover, the impact of the turbulence model used in the four-equation model on overall simulation performance is investigated. At last, the effectiveness of the four-equation model in the CFD simulations of liquid sodium conjugate heat transfer is assessed. This paper mainly proves that it is feasible to use the four-equation model in the study of liquid metal conjugate heat transfer and provides a reference for the research of conjugate heat transfer in a liquid-metal-cooled fast reactor.

• Journal of the Korean Geotechnical Society
• /
• v.37 no.6
• /
• pp.5-20
• /
• 2021

In this study, a modified empirical formula for estimating the bearing capacity of the steel pipe prebored and precast pile was proposed by performing 20 cases of real-scale field pile loading tests. The proposed formula will be based on expanded SPT N-value in order to consider the realistic condition of the surrounding soil. The formula is proposed based on a statistic approach of the data points from the field pile loading test, in order to ensure safe engineering practice while finding a reliable formula. The statistical analysis of the data points from the loading test indicated that the existing formula has been underestimated the bearing capacity of the prebored and precast pile. The proposed formula estimates 15% and 20% higher pile End bearing capacity (q_t=230P_driven(kN/m²)) and the shaft resistance (f_max=3.0N_s^E(kN/m²)) compared to the existing formula. The accuracy and the stability of the proposed formula was verified by comparing the estimated results with additional field test data. The verification process showed that the proposed formula was estimated to be more accurate than the existing formula.

• Fire Science and Engineering
• /
• v.32 no.4
• /
• pp.17-24
• /
• 2018

This paper presents a numerical analysis of flow inside a water nozzle for fire fighting and observes the effect of the variation in primary components on internal flow. In order to observe the performance of water nozzles, they have been systematically designed and modelled, applying boundary conditions obtained from field experiments (inlet pressure at pump : 4 bar, and pressure outlet : atmospheric pressure). In addition, the governing equations were calculated to obtain velocity, pressure inside the nozzle. Two main parameters (the presence and length of sub-pipes) were considered with the aim to observe the detail internal flow characteristics. It is found that the base model is not significant on flow characteristics, but a negative effect (i. e. the reverse flow) at the entrance region of sub-pipe. On the other hand, the reverse flow was vanished when making the length of sub-pipe double.

• Proceedings of the Korean Nuclear Society Conference
• /
• 2002.05a
• /
• pp.131.2-131
• /
• 2002

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.10 no.4
• /
• pp.482-488
• /
• 2022

In this study, the durability of ultra rapid hardening mortar for sewage pipe was evaluated by type of mortar binder. As a result of analyzing the internal structure for each type of mortar, it was confirmed that Al₂(OH)₃ was generated in the internal structure of the CAC-based mortar, and its corrosion resistance was superior to that of other types of mortar. As a result of the compressive strength test, OPC had the tsmallest strength, followed by CAC100 > CAC100P > CAC80. This trend was similar to the previous study results. Chloride ion penetration resistance and freeze-thaw test showed similar trends. That is, CAC and C12A7 were better than OPC, and CSA was worse than OPC. This is mostly beacuse of cracks caused by expansion of CSA-based mortar. CAC100P mix showed the best chemical resistance. It is thought that this is because the alumina gel formed inside the mortar and the polymer combine to make the internal structure more dense.

• ETRI Journal
• /
• v.30 no.1
• /
• pp.81-88
• /
• 2008

The security threat posed by worms has steadily increased in recent years. This paper discusses the application of the optimal and sub-optimal Internet worm control via Pontryagin's maximum principle. To this end, a control variable representing the optimal treatment strategy for infectious hosts is introduced into the two-factor worm model. The numerical optimal control laws are implemented by the multiple shooting method and the sub-optimal solution is computed using genetic algorithms. Simulation results demonstrate the effectiveness of the proposed optimal and sub-optimal strategies. It also provides a theoretical interpretation of the practical experience that the maximum implementation of treatment in the early stage is critically important in controlling outbreaks of Internet worms. Furthermore, our results show that the proposed sub-optimal control can lead to performance close to the optimal control, but with much simpler strategies for long periods of time in practical use.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2023.05a
• /
• pp.169-169
• /
• 2023

Most distributed water is not used effectively due to water loss occurring in pipe networks. These water losses are caused by leakage, typically due to high water pressure to ensure adequate water supply. High water pressure can cause the pipe to burst or develop leaks over time, particularly in an aging network. In order to reduce the amount of leakage and ensure proper water distribution, it is important to apply pressure management. Pressure management aims to maintain a steady and uniform pressure level throughout the network, which can be achieved through various operational schemes. The schemes include: (1) installing a variable speed pump (VSP), (2) introducing district metered area (DMA), and (3) operating pressure-reducing valves (PRV). Applying these approaches requires consideration of various hydraulic, economic, and environmental aspects. Due to the different functions of these approaches and related components, an all-together optimization of these schemes is a complicated task. In order to reduce the optimization complexity, this study recommends a sequential optimization method. With three network operation schemes considered (i.e., VSP, DMA, and PRV), the method explores all the possible combinations of pressure management paths. Through sequential optimization, the best pressure management path can be determined using a multiple-criteria decision analysis (MCDA) to weigh in factors of cost savings, investment, pressure uniformity, and CO₂ emissions. Additionally, the contribution of each scheme to pressure management was also described in the application results.

• Journal of the Korean Geotechnical Society
• /
• v.35 no.12
• /
• pp.123-134
• /
• 2019

This study presents dynamic responses of circular pipe models as a part of fundamental studies on dynamic stability monitoring of the large circular steel pipe cofferdam with the ship collision. Small-scaled laboratory experiments are performed with a single and bolted circular steel pipes with a diameter, thickness, and height of 30, 0.4, 90 cm, respectively. The bolted circular steel pipe is configured with three segments of 30 cm in height. Circular steel pipe models are embedded in a soil tank, all 1 m in length, width, and height. The thickness of soil in the soil tank is set at 23 cm. The ship collision is simulated with a hammer impacting. The dynamic responses are investigated with different water levels of 25, 40, 55, and 70 cm. Experimental results show that a signal energy decreases with increasing water level. More sensitive reduction in the energy appears for the bolted circular steel pipe. A predominant frequency decreases with increasing water level for both single and bolted steel pipes. The minor reduction in the frequency appears for the bolted circular steel pipe under the water level of 70 cm. This study suggests that the signal energy and frequency response is useful for the dynamic stability monitoring of the large circular steel pipe cofferdam.