• Journal of the Korean Society for Precision Engineering
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• v.29 no.12
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• pp.1331-1339
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• 2012

Safety valve used in LNG/LNG-FPSO ships is a high value valve, and it plays an important role in maintaining a fixed level of pressure by emitting LNG gas out of pipes in LNG piping system under the cryogenic and high-pressure condition when the pressure of the system connected with the LNG storage tank and pipes reaches over the set pressure. The structural stability is required for the inner pressure and thermal load because of the cryogenic and high-pressure condition, and a reliability of the safety valve is necessary for impact and deformation by opening the valve. But, the safety valve, which plays a key role for a safety of the transport and storage system, is depended on imports for over 90%, and in domestic production, the design of the valve is performed on the basis of experiences of the works without quantitative analysis for the inner operation characteristics and structural stability of the valve. In this study, impact velocity is calculated by theoretical analysis for obtaining the structural stability of the guide according to the impact load by opening the valve. The shape of the guide and the diaphragm for satisfying the structural stability are suggested and verified by using a thermal-structural analysis.

• Journal of Korea Water Resources Association
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• v.52 no.10
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• pp.719-728
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• 2019

Valve in water distribution network (WDN), that controls the flow in pipes, is used to isolate a segment (a part of WDN) under abnormal water supply conditions (e.g., pipe breakage, water quality failure event). The segment isolation degrades pressure and water serviceability in neighboring area during the water service outage of the segment. Recent hydraulic and water quality failure events reported encouraging WDN valve installation based on various abnormal water supply scenarios. This study introduces a scenario-based optimal valve installation approach to optimize the number of valves, the amount of undelivered water, and a shortest water supply path indicator (i.e., Hydraulic Geodesic Index). The proposed approach is demonstrated in the valve installation of Pescara network, and the optimal valve sets are obtained under multiple scenarios and compared to the existing valve set. Pressure-driven analysis (PDA) scheme is used for a network hydraulic simulation. The optimal valve set derived from the proposed method has 19 fewer valves than the existing valve set in the network and the amount of undelivered water was also lower for the optimal valve set. Reducing the reservoir head requires a greater number of valves to achieve the similar functionality of the WDN with the optimal valve set of the original reservoir head. This study also compared the results of demand-driven analysis (DDA) and the PDA and confirmed that the latter is required for optimal valve installation.

• 한국신재생에너지학회:학술대회논문집
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• 2010.11a
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• pp.75.1-75.1
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• 2010

This research presents a fuel cell simulator for control logic verification and operator training. Nowadays, power industries are focusing on clean energy as a response to new policy. The fuel cell can be the solution for clean energy, but operating technology is not well developed compared to other conventional power plans because of its short history. Therefore we need a simulator to verify the new control strategy and train operators, because the price of a real fuel cell system is too high and mechanically weak to be used for these kind of purposes. To develop the simulator, a 300 KW MCFC(Molten Carbonate Fuel Cell) system was modeled with stack, BOPs(pre-reformer, steam generator, etc) and mechanical components(valves, pipes, pumps, blowers, etc). The process model was integrated to emulated control system and HMI(Human Machine Interface). A static load and open loop tests were conducted for verifying the accuracy of the process model, since it is the most important part in the simulation. After verifying the process model, an automatic load change and start-up tests were conducted to verify the performance of a new control strategy(logic and functional loops).

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.905-910
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• 2004

Vibration characteristics of the FIV test loop for the Flow-Induced Vibration(FIV) study of a PWR partial(5x5) fuel assembly are investigated by the Finite Element(FE) analysis and the modal test. For the FE analysis, 3-D beam element is used for the pipes and the test section and mass element used for the valves and flanges. The 'U' restrainer stiffness determined by numerical simulation is used for the FE model. The result of the FE analysis is compared with that of the modal test. The higher mode similarity between the test and analysis is observed in a few low modes. After that, the mode similarity reduce as the mode goes high. It is concluded that the first to the third vibration modes are observed at the lower parts of the 6 inches restoring line, followed by a local mode at the test section, and the natural frequencies of the modes are 22.4 Hz, 26.0 Hz, 27.5 Hz and 31.4 Hz.

• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.162-162
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• 2019

Water Distribution Network (WDN) is a critical infrastructure to be maintained ensuring proper water supply to wide-spread consumers. The WDN consists of pipes, valves, pumps and tanks, and these elements interact each other to provide adequate system performance. If elements fail by internal or external interruptions, it may result in adverse impact to water service with different degree depending on the failed element. To determine an appropriate maintenance priority, the critical elements need to be identified and mapped in the network. In order to identify and prioritize the critical elements in WDN, an element-based simulation approach is proposed, in which all the elements composing the WDN are reviewed one at a time. The element-based criticality is measured using several resilience indexes that are newly developed in this study. The proposed resilience indexes are used to quantify the impacts of element failure to water service degradation. Here, three resilience indexes are developed, such as User Demand Severity, Economic Value Loss and Water Age Degradation, each of which intends to measure different aspects of consequences, such as social, economic, and water quality, respectively. For demonstration, the proposed approach is applied to a benchmark water network to identify and prioritize the critical elements.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2011.06a
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• pp.7-10
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• 2011

According to the requirement of Res.MSC.285(86) for natural gas-fueled engine installations in ships, pump and compressor rooms should be fitted with effective mechanical ventilation system of the under pressure type, providing a ventilation capacity of at least 30 air changes per hour. It generally considered that gas leakage is more likely from a Fueled Gas Supply System(FGS) room as compared to other places, where installed in many kind of machinery or equipments like gas supply high-pressure pipes, valves, flanges and etc. Furthermore, leaked gas may be dispersed in a short time in an enclosed space, especially a FGS room, due to high pressure. However, the present requirement in Res.MSC.285(86) just considers the ventilating capacity of air changes per hour but the capacity of leaked gas. Hence, the current requirements may not meet effectively when enforcing the new propulsion systems as marine fuel. This study is conducted for the purpose of safety evaluation about the dispersion and ventilation efficiency with estimated leakage scenario. Numerical analysis predictions as the result of this paper are explained to know the features of flow pattern and the diffusion of natural gas concentration.

• Journal of the Korean Society of Propulsion Engineers
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• v.18 no.1
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• pp.16-25
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• 2014

The system analysis and design program of the liquid rocket engine has been developed for preliminary conceptual design process. The program consists of modular programs analyzing the main thruster, the gas-generator, turbo-pumps, the turbine, pipes, valves and so on. Each module has been developed in order to estimate performance, weight, and shape parameters of the components. The results of them have been verified with experimental data or other programs.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.52-57
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• 2012

A liquid rocket system consists of a combustion chamber, a gas generator, a turbo pump, and a turbine, etc. Each component is connected by supply components such as valves, pipes, and orifices. Since each component has a combined effect on engine performance, preliminary analysis for overall system must be required before the conceptual design stage. Comprehensive analysis program considered the supply system has not been developed yet. In this paper, a supply component model of the liquid rocket engine has been designed after verification of each component. The gas generator cycle with supply components has been composed. The results of the cycle has been compared to those of the F-1 engine with the representative gas generator cycle.

• Journal of Korea Water Resources Association
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• v.39 no.2 s.163
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• pp.89-98
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• 2006

To evaluate the pipe failure impact, current methodologies consider only a broken pipe as the impacted area. However, these approaches are accurate if the broken pipe is the only area isolated from tile system. Depending on the number and locations of on-off valves, more pipes which are adjacent to a broken pipe may be isolated. Using the concept of Segment suggested by Walski, the methodology evaluating the pipe failure impact incorporated with on-off valve locations has been suggested by Jun. However, a segment cannot account for all possible pipe failure impacted areas since it does not consider additional failures, namely the network topological failure and the hydraulic pressure failure. For this reason, a methodology which can consider the network topology and hydraulic pressure limitation as well as on-off valve locations is suggested. The suggested methodology is applied to a real network to verify its applicability As results, it is found that a single pipe failure can affect huge areas depending on the configuration of on-off valves and the network topology. Thus, the applicability of the suggested methodology for evaluating the pipe failure impacts on a water distribution network is proved.

• Nuclear Engineering and Technology
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• v.35 no.6
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• pp.507-514
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• 2003

Recently dry decontamination/surface-cleaning technology using plasma etching has been focused in the nuclear industry. In this study, the applicability of this new dry processing technique are experimentally investigated by examining the etching reaction of $UO_2$, Co, and Mo in r.f. plasma with the etchant gas of $CF_4/O_2$ mixture. $UO_2$ is chosen as a representing material for uranium and TRU (TRans-Uranic) compounds while metallic Co and Mo are selected because they are the principal contaminants in the used metallic nuclear components such as valves and pipes made of stainless steel or inconel. Results show that in all cases maximum etching rate is achieved when the mole fraction of $UO_2\;in\;CF_4/O_2$ mixture gas is $20\%$, regardless of temperature and r.f. power. In case of $UO_2$, the highest etching reaction rate is greater than 1000 monolayers/min. at $370^{\circ}C$ under 150 W r.f. power which is equivalent to $0.4{\mu}m/min$. As for Co, etching reaction begins to take place significantly when the temperature exceeds $350^{\circ}C$. Maximum etching rate achieved at $380^{\circ}C\;is\;0.06{\mu}m/min$. Mo etching reaction takes place vigorously even at relatively low temperature and the reaction rate increases drastically with increasing temperature. Highest etching rate at $380^{\circ}C\;is\;1.9{\mu}m/min$. According to OES (Optical Emission Spectroscopy) and AES (Auger Electron Spectroscopy) analysis, primary reaction seems to be a fluorination reaction, but carbonyl compound formation reaction may assist the dominant reaction, especially in case of Co and Mo. Through this basic study, the feasibility and the applicability of plasma decontamination technique are demonstrated.