• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.2
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• pp.387-393
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• 2021

In this study, finite element analysis was performed to evaluate a method of increasing the fatigue life of the pipe connection structure commonly used in the topside structure of offshore platforms. MSC Patran/Nastran, a commercial analysis program, was used, and the critical structural model was selected from the global analysis. To realize the stress concentration phenomenon according to the load, modeling using 8-node solid elements was implemented. The main loads were considered to be two lateral loads and a tensile load on a diagonal pipe. To check the hotspot stress at the main location, a 0.01 mm dummy shell element was applied. After calculating the main stress at the 0.5-t and 1.5-t locations, the stress generated in the weld was estimated through extrapolation. In some sections, this stress was observed to be below the fatigue life that should be satisfied, and reinforcement was required. For reinforcement, a bracket was added to reduce the stress concentration factor where the fatigue life was insufficient without changing the thickness or diameter of the previously designed pipe. Regarding the tensile load, the stress in the bracket toe increased by 23 %, whereas the stress inside and outside of the pipe, which was a problem, decreased by approximately 8 %. Regarding the flexural load, the stress at the bracket toe increased by 3 %, whereas the stress inside and outside of the pipe, which was also a problem, decreased by approximately 48 %. Owing to the new bracket reinforcement, the stress in the bracket toe increased, but the S-N curve itself was better than that of the pipe joint, so it was not a significant problem. The improvement method of fatigue life is expected to be useful; it can efficiently increase the fatigue life while minimizing changes to the initial design.

• Journal of Energy Engineering
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• v.18 no.1
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• pp.49-55
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• 2009

Occurrence of hydrogen embrittlement could be one of the main obstacles for using structural equipment under hydrogen environment. It is required to develop assessment methods of hydrogen embrittlement for the metals used in production, storage, transmission and application utilities of hydrogen. The most probable method of hydrogen mass transmission is using existing natural gas pipeline. Base or weld part of the pipeline can be damaged by mixed gas of hydrogen in the pipeline. In this study small punch (SP) testing was employed to evaluate the hydrogen embrittlement behavior for a line pipe steel (API X65) with electrochemically hydrogen charged specimens. Results showed that the SP test can be a good candidate test method for hydrogen damage evaluation method. Strength of steel is known to be decreased with the level of hydrogen charging. However, for API X65 steel base metal need in this study, the effect of hydrogen to strength was not significant. It can be negligible regardless of the hydrogen contents in the steel. With this test different strength levels with various hydrogen charging conditions were observed. It can also be anticipated that more sensitive evaluation of material behavior be obtainable by the SP test method.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.10
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• pp.379-385
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• 2020

This paper presents a design for preventing coolant leaks in the core part of a heater mounted in a combat vehicle. The heater is a device that makes heated coolant flow through the heater core in the crew room. A problem with coolant leaks in the heater core area during the operation of a combat vehicle was identified. This problem is caused mainly by high pressure at the junction of the tank and tube due to the vulnerability of this area. To solve this problem, an improved core was made by improving the welding method and changing the end region of the heater core to a structure that can withstand high pressure. When pressure was applied sequentially to the existing core and improved core, a leak occurred at 7.0 kgf/㎠ in the existing core while the improved core maintained its structure up to 17.0 kgf/㎠, highlighting the improvement. Finally, performance tests and environment tests were conducted to demonstrate the suitability of the improved structure. The improved heater will be applied to combat vehicles. This paper is expected to serve as a reference for improving defense capabilities by securing reliability as well as the design and analysis of failures of similar equipment.nse capabilities through securing reliability as well as the design and analysis of failures of similar equipment.

• 한국해양학회지
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• v.30 no.4
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• pp.237-249
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• 1995

To understand the cross-sectional structures of temperature, salinity and current across the Korea Strait, field measurements were carried out for the period of May 2 to 20, 1994. Using the R/V Tam Yang, detailed CTD profiles and ADCP records were obtained and used to examine the mean and variability field on two time scales (15 days and 25 hours). A sharp coastal front in the middle of the Korea Strait exists across which two different water masses, i.e., warm and saline water in the eastern side and cold and less saline water in the western side are neighboring. We observed highly variable field of T and S apparently caused by the westward movement of warm and saline water mass. Short-term fluctuations of T and S in the middle layer are remarkable and their importance was analysed as the first Eigen mode accounting for more than 50% of total variances. The currents in th Korea Strait are strongly influenced by tidal currents with spring and neap variation whose maximum speed ranges 80-90 and 60-70 cm/s respectively near the central portion of the channel. Strong southward tidal current could even mask the Tsushima Current completely. Results of harmonic analysis show that the magnitudes of semidiurnal, diurnal and mean components of currents are comparable to each other at spring and neap tide conditions. The volume transport across the western channel of the Korea Strait were estimated to be 2.1 Sv at neap tide condition and 3.4 Sv at spring tide condition.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.7
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• pp.2386-2396
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• 1996

A numerical simulation has been performed for isothermal and reacting flows in an exisymmetric, bluff-body research combustor. The present formulation is based on the density-weighted averaged Navier-Stokes equations together with a k-epsilon. turbulence model and a modified eddy-breakup combustion model. The PISO algorithm is employed for solution of thel Navier-Stokes system. Comparison between measurements and predictions are made for a centerline axial velocities, location of stagnation points, strength of recirculation zone, and temperature profile. Even though the numerical simulation gives acceptable agreement with experimental data in many respects, the present model is defictient in predicting the recoveryt rate of a central near-wake region, the non-isotropic turbulence effects, and variation of turbulent Schmidt number. Several possible explanations for these discrepancies have been discussed.