• Journal of Advanced Research in Ocean Engineering
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• v.3 no.1
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• pp.41-52
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• 2017

This paper presents a numerical and experimental study of sloshing loads on liquefied natural gas (LNG) vessels. Conventional LNG carriers with membrane-type cargo systems have filling restrictions from 10% to 70% of tank height. The main reason for such restrictions is high sloshing loads around these filling depths. However, intermediate filling depths cannot be avoided for most LNG vessels except the LNG carrier. This study attempted to design a membrane-type LNG tank with a modified lower-chamfer shape that allows all filling operations. First, numerical sloshing analysis was carried out to find an efficient height of the lower-chamfer that can reduce sloshing pressure at partially filled conditions. The numerical sloshing analysis program SHI-SLOSH was used for numerical simulation; this program is based on SOLA-VOF. The effectiveness of the newly designed tanks was validated by 1:50-scale three-dimensional tank tests. A total of three different tanks were tested: a conventional tank and two modified tanks. As test conditions, various filling depths and wave periods were considered, and the same test conditions were applied to the three tanks. During the test, slosh-induced dynamic pressures were measured around the corners of the tank wall. The measured pressure data were post-processed and the pressures of the three different tanks were statistically compared in several ways. Experimental results show that the modified tanks were quite effective in reducing sloshing loads at low filling conditions. This study demonstrated the possibility of all filling operations for LNG cargo containment systems.

• Journal of Welding and Joining
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• v.14 no.1
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• pp.99-106
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• 1996

Development of an automatic TIG welding system incorporating a vision sensor and torch control mechanism leads to an improved welding quality and greater production efficiency. The automatic welding system should be greatly restricted in its size and weight for the LNG(Liquefied Natural Gas) storage tank and also provide a unique torch rotating mechanism which keeps the torch tip in the constant position while the angle is changed continuously to maintain the welding torch substantially perpendicular to the weld line. The developed system is driven by two translation axes X, Z and one rotational axis. A moving line window method is adopted to the image recognition of the corrugated membranes with specular reflection. This method decides original laser stripe patterns in image which is affected by multi-reflection. A self-teaching algorithm, which guides the automatic welding machine with the information provided by the CCD camera without any previous learning of a reference trajectory, was developed for tracking the corrugated membrane of the LNG tank along the weld line.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.3 s.174
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• pp.710-717
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• 2000

Tensile and fracture toughness tests of the cold-rolled STS 304 steel plate for membrane material of LNG storage tank were performed at wide range of temperatures, 11 IK(boiling point of LNG), 153K , 193K and 293K(room temperature). Tensile strength significantly increases with a decrease in temperature, but the yield strength is relatively insensitive to temperature. Elongation at 193K abruptly decreases by 50% of that at 293K, and then decreases slightly in the temperature range of 193K to 111K. Strain hardening exponents at low temperatures are about four times as high as that at 293K. Elastic-plastic fracture toughness($J_c$) and tearing modulus($T_{mat}$) tend to decrease with a decrease in temperature. The $J_c$ values are inversely related to effective yield strength in the temperature range of 111K to 293K. These phenomena result from a significant increase in the amount of transformed martensite in low temperature regions.

• Journal of Ocean Engineering and Technology
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• v.14 no.1
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• pp.23-28
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• 2000

The fatigue crack growth behavior of the cold-rolled STS 304 steel developed for membrane material of LNG storage tank was examined experimentally at 293K, 153K and 111K. The fatigue crack growth rate(do/dN) tends to increase as the stress ratio (R) increases over the testing temperature when compared at the same stress intensity factor range($\Delta$K). The effect of R on do/dN is more explicit at low temperatures than at room temperature. The resistance of fatigue crack growth at low temperatures is higher compared with that at room temperature which is attributed to the extent of strain-induced martensitic transformation at the crack tip. The temperature dependence of fatigue crack growth resistance is gradually vanished with an increase in $\Delta$K which correlates with a decreasing fracture toughness with decreasing temperature. Fractographic examinations reveal that the differences of the fatigue crack growth characteristics between room and low temperature are mainly explained by the crack closure and the strengthening due to the martensitic transformation.

• Proceedings of the Membrane Society of Korea Conference
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• 1998.06a
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• pp.113-133
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• 1998

In activated sludge process, sludge settling condition is affected by organic loading rate or operation condition, and if settling condition is getting worse, it is common that overall process fails due to wash-out of biomass causing low concentration in the aeration tank. Also activated sludge process has such several problems as requiring large area, consuming a lot of power and producing large volume of sludge. Increased public concern over health and the environment combined with a strong desire to reduce capital, operating and maintenance costs, have created a need for innovative technologies for building new high quality effluents which vail meet 21st century crkeria. MBR(Membrane Bioreactor) process consists of a biological reactor and ultrafiltration(UF) membrane system that replaces the conventional clarifier of an activated sludge process. The main operating advantages of this system are that the quality of the effluent is independent of the settleability of the mixed liquor and that the effluent is free of suspended solids in any operating condition. It is possible to eliminate clarifier and to reduce the volume of aeration tank because it can afford to accumulate high biomass concentration in the bioreactor(20, 000~30, 000mg/L), which would not be possible in a conventional activated sludge process. Therefore, this process reduces overall treatment plant area. In addition to those advantages, Longer SRT condition enables higher sludge digestion in MBR process so the sludge volume produced is 50 to 70% lower than that of conventional activated sludge process There are two kinds of MBR process according to the allocations of membrane. One is cross flow type MBR of which module is located outside of the bioreactor and mixed liquor is driven into the membrane module. The other is submerged type MBR process of which module is submerged in the bioreactor and mixed liquor is generally sucked from the lumen side. addition to that the cake layer is often removed by the uplifting flow of bubbling air. A submerged MBR process is superior to a crossflow MBR in regard to the power consumption because suction pressure of a submerged MBR is generally lower than that of a crossflow MBR which has recirculation pump. A submerged MBR, therefore, has the potential to be applied to small wastewater treatment plants that need low cost treatment systems.

• Membrane Journal
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• v.28 no.4
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• pp.279-285
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• 2018

The pervaporation separation of isopropanol/water mixture was carried out on a series of chemically cross-linked poly(vinyl alcohol)(PVA) composite membranes. The membranes were prepared by casting three kinds of PVA solutions with varying concentrations of PVA and GA onto polyacrylonitrile (PAN) support followed by thermal cross linking. As the PVA concentration increased, the flux decreased but separation factor was increased. It was confirmed that the composite membrane coated with PVA-3 (98~99% hydrolyzed) at a concentration of 7 wt% PVA and 20 wt% glutaraldehyde (GA) exhibited a flux of $209g/m^2h$ and a separation factor of more than 100. The submerged module test was carried out with controlled feed tank temperature and IPA concentration of the feed solution. The continuous concentration of IPA solution was increased from 90% to 99% after 60 h.

• Journal of Advanced Marine Engineering and Technology
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• v.32 no.8
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• pp.1192-1200
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• 2008

This paper is concerned with the thermal design of the $138,000m^3$ class membrane type LNGC. To predict the temperature distribution, BOG and BOR, 3-dimensional numerical calculation was carried-out for the quarter of No.3 LNG tank. These sequence analyses were performed under the standard conditions of IMO ship design condition, USCG ship design condition and the Korean flag LNGC's route condition according to the 6-voyage modes. As the results, temperature behavior, heat flux, total penetrating heat, BOG and BOR were obtained, and those were compared with the maneuvering results considering the real temperature variation of air and sea water temperature at noon time. For securing the safety of LNGC during the ballast voyage, optimum control patterns of pressure and temperature in LNG tank is suggested in this paper.

• Journal of the Society of Naval Architects of Korea
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• v.52 no.2
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• pp.125-134
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• 2015

Spherical type LNG carrier has many advantages, but has a demerit it is more expensive than membrane type one. Therefore, when calculating the initial estimate of spherical type LNG carrier, high accuracy calculation of tank weight has to be carried out. In this study the simplified analysis method which is able to calculate stresses of all the tank zones is established and has special feature to deal with static and dynamic loading. In order to verify the established method, the design results obtained through the method in this study have been compared with those of existing ship obtained from finite element analysis. As a result, the usability of simplified analysis method has been confirmed.

• Membrane Journal
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• v.25 no.3
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• pp.216-222
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• 2015

The method measuring LEP (liquid entry pressure) was optimized to evaluate the wettabilities of hydrophobic membranes which might affect long-term durability of membrane in MD (membrane distillation) process. Conductivity of the permeate was monitored to measure the LEPs of PE (polyethylene) and PVDF (polyvinylidene di-fluoride) hollow fiber membranes from highly concentrated synthetic feed water of 20 wt% NaCl. Holding time over 5 min and the ratio of membrane area to the tank volume more than $10m^2/m^3$ were required to ensure LEP value.

• 한국가스학회:학술대회논문집
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• 2001.10a
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• pp.35-44
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• 2001

Analytical and experimental studies have been performed to investigate the strength of the membrane and the reaction force at the anchor point. Using nonlinear FEM code and experiments, the stress analysis of the corrugated membrane related the cryogenic liquid pressure and thermal loading is performed to ensure the stability and fatigue strength of the membrane. This paper reports on the FEM results of membrane.