• Journal of the Earthquake Engineering Society of Korea
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• v.11 no.3 s.55
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• pp.63-72
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• 2007

The Emergency Diesel Generator (EDG) is a very important equipment for the safety of a Nuclear Power Plant (NPP). In this study, the operating vibration of three kinds of EDG systems was measured. The target EDG systems are Yonggwang 5 unit and Ulchin 2 and 3 units. The Yonggwang 5 and Ulchin 3 unit EDG systems are the same type but the foundation systems are different. One is an anchor bolt type and the other is a spring and viscous-damper type. The purpose of these measurements is for a verification of the vibration isolation effect depending on the foundation system. As a result, It can be said that the spring and viscous damper system of the EDG performed better for the vibration isolation than that of anchor bolt type.

• Nuclear Engineering and Technology
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• v.49 no.2
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• pp.426-433
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• 2017

This paper describes the development process, the innovative techniques used and insights gained from the latest integrated, full scope, multistate Level 2 PSA analysis conducted at the Leibstadt Nuclear Power Plant (KKL), Switzerland. KKL is a modern single-unit General Electric Boiling Water Reactor (BWR/6) with Mark III Containment, and a power output of $3600MW_{th}/1200MW_e$, the highest among the five operating reactors in Switzerland. A Level 2 Probabilistic Safety Assessment (PSA) analyses accident phenomena in nuclear power plants, identifies ways in which radioactive releases from plants can occur and estimates release pathways, magnitude and frequency. This paper attempts to give an overview of the advanced modeling techniques that have been developed and implemented for the recent KKL Level 2 PSA update, with the aim of systematizing the analysis and modeling processes, as well as complying with the relatively prescriptive Swiss requirements for PSA. The analysis provides significant insights into the absolute and relative importances of risk contributors and accident prevention and mitigation measures. Thanks to several newly developed techniques and an integrated approach, the KKL Level 2 PSA report exhibits a high degree of reviewability and maintainability, and transparently highlights the most important risk contributors to Large Early Release Frequency (LERF) with respect to initiating events, components, operator actions or seismic component failure probabilities (fragilities).

• Journal of Ocean Engineering and Technology
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• v.26 no.6
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• pp.86-92
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• 2012

An exploration well is drilled where oil or gas potential is shown by a seismic survey and interpretation. With the advance of drilling technology, most of the easily accessible oil had been developed by the end of the 20th century. To satisfy the ever increasing demand for oil, and bolstered by high oil prices, the major oil companies started to drill in deep water, which requires a deep offshore drilling unit. Offshore drilling units are generally classified by their maximum operating water depth. Many semi-submersible rigs have been purpose-designed for the drilling industry as the allowable drilling water depth has become deeper by the developed technics since the first semi-submersible was launched in 1963. Semi-submersible rigs are commonly used for shallow to deep water up to 3,000 m. Drilling equipment such as a top drive, blowout preventer, drawworks and power system, mud circulation system, and subsea wellhead system are explained to help with an understanding of offshore drilling procedures in the oil and gas fields. The objective of this paper is to introduce the main components of a semi-submersible rig and, by doing so, to raise the awareness of offshore drilling, which accounts for over 30% of the total oil production and will continue to increase.

• Journal of Korean Association for Spatial Structures
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• v.16 no.2
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• pp.79-88
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• 2016

Modular buildings are constructed by assembling modular units which are prefabricated in a factory and delivered to the site. However, due to a problem of noise between floors, concrete slab is usually poured at the top or bottom level of a modular unit in Korea. This greatly increases the weight of buildings, but designing vertical members of modular units to resist overall gravity loads is very inefficient. In this study, considering domestic building construction practices, feasible structural systems for tall modular buildings are proposed in which separate steel frames and reinforced concrete core walls are designed to resist gravity and lateral loads. To verify performance, a three-dimensional structural analysis has been performed with two types of prototype buildings, i.e., a residential building and a hotel. From the results, wind-induced lateral displacements and seismic story drifts are examined and compared with their limit values. Between the two kinds of buildings, the efficiency of the proposed system is also evaluated through a comparison of the weight of structural components. Finally, the effect of a floor diaphragm on the overall behavior is analyzed and discussed.

• Steel and Composite Structures
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• v.32 no.3
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• pp.347-359
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• 2019

Modular construction has been increasingly used for mid-to-high rise buildings attributable to the high construction speed, improved quality and low environmental pollution. The individual and repetitive room-sized module unit is usually fully finished in the factory and installed on-site to constitute an integrated construction. However, there is a lack of design guidance on modular structures. This paper mainly focuses on the evaluation of the initial stiffness of corrugated steel plate shears walls (CSPSWs) in container-like modular construction. A finite element model was firstly developed and verified against the existing cyclic tests. The theoretical formulas predicting the initial stiffness of CSPSWs were then derived. The accuracy of the theoretical formulas was verified by the related numerical and test results. Furthermore, parametric analysis was conducted and the influence of the geometrical parameters on the initial stiffness of CSPSWs was discussed and evaluated in detail. The present study provides practical design formulas and recommendations for CSPSWs in modular construction, which are useful to broaden the application of modular construction in high-rise buildings and seismic area.

• Smart Structures and Systems
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• v.24 no.3
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• pp.403-414
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• 2019

Offshore drilling has become a key process for obtaining oil. Offshore platforms have many applications, including oil exploration and production, navigation, ship loading and unloading, and bridge and causeway support. However, vibration problems caused by severe environmental loads, such as ice, wave, wind, and seismic loads, threaten the functionality of platform facilities and the comfort of workers. These concerns may result in piping failures, unsatisfactory equipment reliability, and safety concerns. Therefore, the vibration control of offshore platforms is essential for assuring structural safety, equipment functionality, and human comfort. In this study, an optimal multiple tuned mass damper (MTMD) system was proposed to mitigate the excessive vibration of a three-dimensional offshore platform under ice and earthquake loadings. The MTMD system was designed to control the first few dominant coupled modes. The optimal placement and system parameters of the MTMD are determined based on controlled modal properties. Numerical simulation results show that the proposed MTMD system can effectively reduce the displacement and acceleration responses of the offshore platform, thus improving safety and serviceability. Moreover, this study proposes an optimal design procedure for the MTMD system to determine the optimal location, moving direction, and system parameters of each unit of the tuned mass damper.

• Nuclear Engineering and Technology
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• v.55 no.3
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• pp.981-988
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• 2023

A seismic event caused an accident at the Fukushima Nuclear Power Plant, which further resulted in simultaneous accidents at several units. Consequently, this incident has aroused great interest in the safety of nuclear power plants worldwide. A reasonable safety evaluation of such an external event should appropriately consider the correlation between SSCs (structures, systems, and components) and the probability of failure. However, a probabilistic safety assessment in current nuclear industries is performed conservatively, assuming that the failure correlation between SSCs is independent or completely dependent. This is an extreme assumption; a reasonable risk can be calculated, or risk-based decision-making can be conducted only when the appropriate failure correlation between SSCs is considered. Thus, this study analyzed the effect of the failure correlation of SSCs on the safety of the system to realize rational safety assessment and decision-making. Consequently, the impact on the system differs according to the size of the failure probability of the SSCs and the AND and OR conditions.

• Journal of the Korean Society for Marine Environment & Energy
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• v.19 no.2
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• pp.137-143
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• 2016

The sedimentary environment and sediment were surveyed at the West-Northern site of Chagwi-do nearby Jeju Island for the design of the embedded suction anchor system of 10 MW-class floating wave-offshore wind hybrid power generation system. According to the classification scheme of Chough et al.[2002], the echo type of the seismic profiles using the chirp III was classified. As a results, the center and west-northern area of survey site were proved to be type I-3 where subbottom layer with thickness 5~15 m exists under the flat seafloor. On the other hands, the east-southern area were regarded to be type I-1, I-2 and III-1 where seafloor reflection is much stronger than type I-3. Also, the physical tests (unit weight, moisture content, grain size, liquid limit, specific gravity) were performed with samples taken from 8 fixed locations. It is found that the sand (SP), the sand blended with silt (SM) and the mixture of SP-SM are distributed uniformly on the survey area.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.1
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• pp.19-26
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• 2019

The masonry infill walls are one of the most popular components that are used for dividing and arranging spaces in building construction. In spite of the fact that the masonry infills have many advantages, the system needs to be used with caution when the earthquake load is to be considered. The infills tend to develop diagonal compression struts during earthquake and increase the demand in surrounding RC frames. If there are openings in the infill walls, the loading path gets even complicated and the engineering judgements are required for designing the system. In this study, a masonry infill system was investigated through finite element analysis (FEA) and the results were compared with the current design standard, ASCE 41. It is noted that the equivalent width of the compression strut estimated by ASCE 41 could be 32% less than that using detailed FEA. The global load resisting capacity was also estimated by 28% less when ASCE 41 was used compare to the FEA case. Rather than using expensive FEA, the adapting ASCE 41 for the analysis and design of the masonry infills with openings would provide a good estimation by about 25% conservatively.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.6 no.3
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• pp.142-151
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• 2001

Detailed interpretation of some high-resolution seismic profiles in Yosu Strait reveals that Late Quaternary deposits consist of three allostratigraphic units (UH, LH, PL) formed by fluvial and tidal controls. The top mud unit, UH, thins onshore, and overlies the backstepping modem Seomjin delta deposits, which is interpreted as a transgressive systems tract (757) related to Holocene relative sea-level rise. The unit LH below the unit UH is composed of delta, valley- and basin-fill facies. The delta facies (Unit $LH_1$) occurs only in Gwangyang Bay and shows two prograding sets retrogradationaly stacked, thus it is also interpreted as a transgressive systems tract(757). On the contrary, the valley- and basin-fill facies (Unit $LH_2$), interpreted as 757, occur between the units UH and PL (Pleistocene deposits) in Yosu Strait. The bounding surface between UH and $LH_2$ can be interpreted as a tidal ravinement surface on the basis of trends thinning toward inner bay and becoming young landward. Furthermore its geomorphological pattern is similar to that of recent tidal channels. This allostratigraphy in'ffsu Strait suggests that two 757 deposits (UH and $LH_2$), divided by tidal ravinement surface, have been formed in Yosu Strait, whereas in Gwangyang Bay backstepping delta deposits ($LH_1$) without tidal ravinement surface have been formed during Holocene sea-level rise. These characteristics indicate that different stacking patterns could be formed in these two areas according to different increasing rate of accommodation space caused by different geomorphology, sediment supply and tidal-current patterns even in the same period of Holocene sea-level rise.