• Journal of Ocean Engineering and Technology
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• v.18 no.4 s.59
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• pp.52-58
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• 2004

A Semi-Autonomous Underwater Vehicle (SAUV), capable of simple work on the seabed, is under development in KRISO-KORDI. This SAUV pressure vessel is composed of fiberglass reinforced plastic (FRP), and is also manufactured to carry electronic equipment. The objective of this paper is to describe the safety check for the pressure vessel. This is achieved fly conducting structural analysis and testing in a pressure tank. Strain and stress test results, under unit load, are obtained fly using ANSYS in linear structural analysis. Local buckling analysis are performed with NASTRAN at the middle oj the cylindrical hull. The first test, using linear structural analysis, is unsuccessful, as buckling occurred. During the second test, linear structural analysis, combined with local buckling analysis, is conducted. There is no buckling up to 250 m when both ANSYS and NASTRAN are used.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.7
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• pp.179-184
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• 2004

In this work, a copper-clad aluminum composite was fabricated using hot hydrostatic extrusion with various extrusion ratios (8.5, 19, 49) and semi-die angles (30, 45, 60 degree) at a temperature of 32$0^{\circ}C$, Material characteristics of copper-clad aluminum composites were determined from compression tests and hardness tests The results showed that for ER of 8.5, the optimum semi-die angle was below or equal to 30 degree and a pressure drop was about 31%. For ER of 19, the optimum semi-die angle was in the range of 40 to 50 degree and a pressure drop was about 38%. In the case of ER=49, the optimum semi-die angle was above or equal to 60 degree and a pressure drop was about 36%. Compressive yield strength was maximum for ER of 8.5 and semi-die angle of 30 degree and the value of maximum was 155 MPa. Uniform hardness distribution was obtained as the extrusion ratio increases and the semi-die angle decreases. In the case of ER=8.5 and semi-die angle of 30 degree, the lowest extrusion pressure and the maximum compressive yield strength was obtained. Therefor, it was concluded that the optimum extrusion condition for fabricated copper-clad aluminum composites under hydrostatic pressure environment was ER of 19 and semi-die angle of 30 degree.

• Advances in aircraft and spacecraft science
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• v.7 no.3
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• pp.203-214
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• 2020

In many applications like the aircraft or the rockets/missiles, the flow from a nozzle needs to be expanded suddenly in an enlarged duct of larger diameter. The enlarged duct is provided after the nozzle to maximize the thrust created by the flow from the nozzle. When the fluid is suddenly expanded in an enlarged duct, the base pressure is generally lower than the atmospheric pressure, which results in base drag. The objective of this research work is to optimize the length to diameter (L/D) ratio of the enlarged duct using the CFD analysis in the flow field from the supersonic nozzle. The flow from the nozzle drained in an enlarged duct, the thrust, and the base pressure are studied. The Mach numbers for the study were 1.5, 2.0 and 2.5. The nozzle pressure ratios (NPR) of the study were 2, 5 and 8. The L/D ratios of the study were 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10. Based on the results, it is concluded that the L/D ratio should be increased to an optimum value to reattach the flow to an enlarged duct and to increase the thrust. The supersonic suddenly expanded flow field is wave dominant, and the results cannot be generalized. The optimized L/D ratios for various combinations of flow and geometrical parameters are given in the conclusion section.

• Journal of the Korean Society of Industry Convergence
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• v.21 no.6
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• pp.429-437
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• 2018

The process gas piping of the offshore plant can cause a massive explosion if the gas leakage occurs during operation. For the purpose of precaution of gas leakage accident, an air pressure test is performed on the process equipment tests using a test pump as much as the power to the piping inner side, mix 99% nitrogen gas and 1% helium gas. The purpose of the air pressure test is to check the work conformity process by handling and regulation for initial piping process, assembly, installation of module, welding, center alignment of the pipes assembling flange gasket in an unrestrained free state. In this paper, the regulation of the problematic air pressure test was analyzed and the solution criteria were established. And leakage tests of existing equipment were performed applying these solution methods. As a result, it was confirmed that there was no problem.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.77.1-77.1
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• 2019

It has been proposed by Gunn & Gott (1972) that galaxies may lose their interstellar gas by ram pressure due to the dense intra-cluster medium while falling to the cluster potential. The observational evidence for this process, which is known as ram pressure stripping, is increasing, and it is believed to be one of the key environmental effects that can dramatically change the star formation activity of galaxies and hence their evolution. Intriguingly however, some cases with clear signs of ram pressure stripping are found in the environment which betrays our expectations (e.g. large clustercentric distances), and our understandings to the detailed working principle behind ram pressure stripping seem to be still lacking. As one of the ways to gain more theoretical insights into the conditions for ram pressure stripping process, we have been comparing the gas truncation radius which is predicted based on the simple Gunn & Gott's prescription with what is actually observed in a sample of carefully selected Virgo galaxies. In this work, we present the results of our comparisons between the theoretically predicted truncation radius and the observationally measured truncation radius for individual galaxies in the sample and discuss which additional conditions are needed in order to fully understand the observations.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.2
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• pp.145-151
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• 2012

Evaluation of the heart work is starting to emerge as a new diagnostic tool for arterial diseases. The aim of this study is to develop a mathematical model for the estimation of heart work utilizing the pulse waves between two points of a vessel. In order to calculate heart work, medical data such as blood pressure waveforms (which are measured using a cuff) are utilized. The heart work is calculated by employing the modified Windkessel model together with the viscosity models of Casson or Herschel-Bulkely (H-B). The results indicate that the compliance values at the proximal and distal locations differ for the Casson and H-B models.

• Journal of Society of Preventive Korean Medicine
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• v.14 no.3
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• pp.51-61
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• 2010

This study aimed to evaluate musculoskeletal workload associated with the work of hair designers, to identify the factors associated with work-related stress, depression and musculoskeletal symptoms in Hair Designers, and to check the painful areas based on patients who complained of musculoskeletal symptoms. The data were collected from 279 hair designers in Daegu metropolitan city from February 1 to August 31 of 2009. A summary of the results was as follows : According to work-related stress in study subjects, the degree of stress load was relatively higher in association with the working demand, the relational conflicts and the organizational culture, but the degree of stress was found to be relatively lower in association with the physical environment, work-related autonomy, an insufficient compensation and an occupational instability. People engaged for beauty business have gotten lots of stress because of the endless needs from customers, the pressure of the learning new skills and the uncomfortable working environment. These are able to cause the musculoskeletal disorder. Under this circumstance, small fries do not have any prevention managements for improving the musculoskeletal diseases and they are not afforded to have regular checkup. When teaching the people related with beauty business, it is necessary to provide accurate information like correct carriage to reduce musculoskeletal disorder stress.

• Journal of Information Technology Applications and Management
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• v.26 no.1
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• pp.77-93
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• 2019

Recently, office workers are increasingly aware of the right to disconnect because of the pressure from strong connections with Internet messengers. In this study, we examined the reason why the perception of the right to disconnect increases and how to deal with it. This research model is that smart working and psychological attachment from work affect right to disconnect, and that open communication and gender moderate the intensity of these effects. To verify this research model, survey questionnaires were distributed to workers in smart working environments, and 400 data were collected and analyzed using Smart-PLS. As results of data analysis, it was verified that smart working and psychological attachment from work had a significant influence on right to disconnect, that open communication group had a lesser effect of psychological attachment from work on right to disconnect than closed communication group, and that women had a lesser effect of psychological attachment from work on right to disconnect than men. Organizations need to maintain a desirable level of right to disconnect in order to improve the quality of working life. But, if it is impossible, They need to change the way of communication more openly so as to absorb the burden of strong connection by Internet. And they need to perform task assignment or stress relief policy reflecting gender characteristics.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.2
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• pp.325-335
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• 1992

In this work, direct contact 4-stage fluidized bed heat exchanger is experimentally studied to develop a new type of heat exchanger which recovers the energy contained in the high temperature waste gas exhausted from the industrial furnaces. A sand is used as a heat transfer medium in this experiment. To determine the optimum operating condition, 11 different perforated plates which have a different free area ratio with different hole diameter are used in the experiment. From the room temperature experiment, the pressure drop which is caused by fluidized bed formation is observed. The high temperature experiment is carried out to seek the optimum operating condition of high heat efficiency at low heat exchanger operation cost. The results of experiment are as following. The pressure drop in the high temperature condition can be predicted from the results of the room temperature experiment. And Nusselt number becomes smaller due to the increased interference between sand particles as Reynolds number increases when the dilute phase fluidized beds are formed in nigh temperature condition. But heat transfer amount through the total sand surface area become larger due to the large resident amount of sand. Considering the heat transfer amount and the heat exchanger operation cost, perforated plates which have either a 30% or 35% of free area ratio with 15mm of hole diameter are best fitted for our goal of this work. The values of .phi. which is a dimensionless number representing the absorption heat amount per unit sand rate are in the range from 0.4 to 0.5, when Reynolds number of waste gas ranges from 25-30 with these perforated plates.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.17 no.1
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• pp.8-17
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• 2021

The seat leakage test is required after the maintenance work on the valve seat. Either the test has been performed outside of the plant after cutting the valve from the pipe system or the simplified test has been performed so far. It was unable to perform the test at the plant site because it is hard to make a steady pressure on the valve inlet when it is installed in the pipe. This research aims to perform the leakage test in the nuclear power plant while it is installed in the pipe system. The mock-up test is performed by pressurizing the leak-off pipe on the valve body. The result is compared with traditional test result by pressurizing the valve inlet. Furthermore the chamber mock-up tests are performed under various conditions. The leak rate by the developed test using the leak-off pipe is found to be similar but greater than the leak rate by the existing test method. It implies that the test using the leak-off pipe is more conservative than the existing test. The methodology and the equipment which this paper suggests that on-site seat test is possible and the application of the technology could reduce the time and cost for the valve maintenance work significantly.