• Journal of the Computational Structural Engineering Institute of Korea
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• v.31 no.5
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• pp.235-241
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• 2018

The internal pressure is a critical parameter for designing a pressure vessel. The static pressure that a pressure vessel must withstand is usually determined according to the various codes and standards with simple formula or numerical simulations considering the geometric parameters such as diameter and thickness of a vessel. However, there is no specific codes or technical standards we can use practically for designing of pressure vessels which have to endure the detonation pressure. Detonation pressure is a kind of dynamic pressure which causes an impulsive pressure on the vessel wall in a extremely short time duration. In addition, it is known that the magnitude of reflected pressure at the vessel wall due to the explosion can be over twice the incident pressure. Therefore, if we only consider the reflected pressure, the design of the pressure vessel can be too conservative from the economical point of view. In this study, we suggest a practical method to evaluate the magnitude of maximum allowable pressure that the pressure vessel can withstand against the detonation inside a vessel. As an example to validate the proposed method, we consider the pressure vessel containing hydrogen gas.

• Journal of the Korean Society for Railway
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• v.14 no.2
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• pp.151-159
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• 2011

This study performed an experimental study for air-tightness performance evaluation of concrete tube structures with joints. The test specimens consist of a continuous concrete tube, a concrete tube with a joint in the middle, and a segmented concrete tube. The test is performed in such a way that the inner pressure of the tube is dropped down to 0.1atm and the increase of the pressure is monitored with time. An equivalent air permeability is then calculated based on the test results. The results show that, as expected, a structure with more joints or bonds tends to be less air-tight. A sensitivity study shows that the system air-tightness performance level becomes higher as either the diameter or the thickness of the tube increases. Moreover, the increase in the diameter or the thickness of the tube makes an effort to enhance the air-tightness more effective.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.4
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• pp.229-238
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• 2017

This study started to deduce a permeability relationship that can consider the geometric features of various porous media under different flow regimes. With reference to the previous works of Kozeny and Carman, the conventional Darcy-Weisbach relation (Darcy's friction flow equation) was reviewed and expanded for porous flow analysis. Based on the capillary model, this relation was transformed to the friction equivalent permeability (FEP) definition. The validity of the FEP definition was confirmed by means of comparison with the Kozeny-Carman equation. Hereby, it was shown that the FEP definition is the generalized form of the Kozeny-Carman equation, which is confined to laminar flow through a circular capillary. In conclusion, the FEP definition as a new permeability estimation method was successfully developed by expanding the Darcy-Weisbach relation for porous flow analyses.

• Journal of the Korean Society of Hazard Mitigation
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• v.3 no.1 s.8
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• pp.123-131
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• 2003

An experiment was carried out to investigate the mechanical behaviour of the circular hollow section reinforced concrete member with internal corrugated steel tube. A specimen, 50cm in diameter and 340cm in length, was made and tested by 3 points bending. The test load was increased slowly (quasi static) to the failure or unacceptable deformation. During the test, lateral displacement at mid point and longitudinal displacement of extreme fiber on compressive and tensile side of the specimen were measured. The measured data were analysed and compared with calculated results for the equivalent member without inserted corrugated steel tube. The comparison shows that the flexural strength and ductility of hollow section reinforced concrete members can be improved by inserting corrugated steel tubes inside.

• Journal of Korean Society of Steel Construction
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• v.13 no.2
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• pp.201-210
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• 2001

A numerical analysis and experimental study were performed to investigate the behavior and strength of tube-gusset connection subjected to axial and lateral forces. To investigate the behavior of the connections, experiment was conducted by applying three directional loads. Local buckling and local plastic bending deformation of the connection were observed from the test. Analytical results were compared with test results for the limited cases. Primary interests here are the effect of eccentricity on the strength of the connection. To suggest a formula for the strength of tube-gusset connection, lateral forces were replaced with equivalent wall moment and eccenrtric vertical component force of lateral force. Ultimate strength formula for the each force was proposed. Finally, nondimensionalized ultimate strength interaction relationships between the wall moment of tube($M_w$), vertical axial force($P_v$), and eccentric vertical component of lateral force($P_e$) were formulated through parametric study.

• Korean Journal of Optics and Photonics
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• v.15 no.3
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• pp.268-273
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• 2004

A finite model eye based on longitudinal spherical aberration is designed by an optimization method. Longitudinal spherical aberration for pupil diameter between 1 mm and 8 mm is graphed theoretically and compared with other model eyes. The chromatic dispersions are adjusted to fit experimentally observed chromatic aberration of the eye. This is a finite model eye with four a spheric refracting surfaces. It has an effective focal length of 15.842 mm. A designed reduced eye has an equivalent power of 63.12 Diopter, curvature radius of 5.281 mm, index of 1.33333, and axial length of 21.123 mm.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.565-568
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• 2002

A lot of rotating machines are being used in the industrial world and electric motor and generator take the most part of it. When it comes to the electric motor and generator, we can not help thinking about the eddy current because it brings a loss of electric and can be a important reason of the heat generation. To attenuate eddy current. laminated silicon steel sheets are being used in general. Especially, laminated rotor is being used for rotating part of the electric motor and generator and it decreases electrical loss and heat generation but we can be faced with another problem. In general, most of the motor and generator can be normally operated under 3600rpm because they are designed to have the first critical speed more than that speed. But nowadays, they should be operated more than the first critical speed as usual with the trend of high speed. large scale and high precision in industrial world. The critical speed can be determined from the inertia and stiffness for the rotor and bearing of rotating systems. The laminated rotor stiffness can be hardly determined because it can be derived a lot factors for instance rotor material and shape. lamination material and shape. insulation material. lamination force and so on. In this paper, the change of the natural frequency of the motor was examined with the change of the lamination force as an experimental method.

• Nuclear Engineering and Technology
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• v.26 no.2
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• pp.237-246
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• 1994

A high flow critical heat flux (CHF) correlation, based on the single-pin CHF experimental data for finned and unfinned heated rods, was developed for the thermal-hydraulic design and safety analysis of the Korea Multi-purpose Research Reactor (KMRR) core. The correlation consists of dimensionless parameters such as Reynolds number, thermodynamic equilibrium quality, liquid-to-vapor density ratio, and hydraulic equivalent diameter ratio. The fin effect was taken into account in the correlation by a finned-to-unfinned heated perimeter ratio. The effects of a cold wall and non-uniform axial power distribution ore discussed to verify the applicability of the single-pin based correlation to the KMRR fuel bundle. The correlation limit departure from nucleate boiling ratio (DNBR) was determined as 1.44 from the statistical analysis of the CHF data.

• Journal of the Korean GEO-environmental Society
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• v.14 no.9
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• pp.5-12
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• 2013

In this study, each top-down load test and bi-directional load test has been performed on the 480mm diameter of two rock socketed drilled shafts, which are located next to each other, and the results have been compared. The result shows that the settlement from the equivalent load-settlement curve of bi-directional load test is smaller than one from top-down load test, because elastic is not considered in equivalent load-settlement curve of bi-directional load test. Therefore elastic shortening should be considered to obtain appropriate equivalent load-settlement curve. Three existing methods used to obtain equivalent load-settlement curve with consideration of elastic shortening has been compared with the result of top-down load test. The result shows that those existing methods are sufficiently applicable to the design. In addition, result of comparison between top-down load test and bi-directional load test shows that bi-directional load test was found to overestimate bearing capacity because it does not consider pile body failure.

• Journal of Dental Rehabilitation and Applied Science
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• v.29 no.4
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• pp.377-383
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• 2013

This study examined the radiopacity of eight contemporary luting cements by direct digital radiography. Five disc-shaped specimens ($5mm{\times}1mm$) were prepared for each material tested (BisCem, Clearfil SA Luting, Duolink, Maxcem Elite, Multilink Speed, Panavia F 2.0, RelyX Unicem Clicker, V-link). The specimens were radiographed using a Kodak CS 7600 image plate (Carestream Health, Inc., Rochester, NY, USA) and an aluminum step wedge with a range of thicknesses (1.5 to 16.5 mm in 1.5 mm increments) and a 1 mm tooth used as a reference. A dental X-ray machine Kodak 2200 Intraoral X-ray System (Carestream Health, Inc., Rochester, NY, USA), operating at 70 kVp, 4 mA, 0.156 s and a source-to-sample distance of 30 cm, was used. According to international standards, the radiopacity of the specimens was compared with that of an aluminum step wedge using NIH ImageJ software (available at http://rsb.info.nih.gov/ij/).The data was analyzed by ANOVA and a Tukey's post hoc test. Maxcem Elite (5.66) showed the highest radiopacity of all materials, followed in order by Multilink Speed (3.87) and V-link (2.83). The radiopacity of Clearfil SA Luting (1.35), BisCem (1.33), Panavia F 2.0 (1.29) and Duolink (1.10) were between enamel (1.79) and dentin (0.19). RelyX Unicem Clicker (0.71) showed the lowest radiopacity, which was higher than that of dentin. All materials showed a radiopacity above the minimum recommended by the International Organization for Standardization and the American National Standards/American Dental Association with the exception of RelyX Unicem Clicker.