• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.255-258
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• 2005

The current ACI design code does not take into account the contribution of concrete for the torsional moment of reinforced concrete(RC) beams subjected to pure torsion. This code is not capable of evaluating the inter-effects between concrete and torsional reinforcement on the torsional resistance of the RC beams. In this study, 9 RC beams subjected to pure torsion were tested. The main parameter of the beams was the amount of torsional reinforcement and the angle of twist. Test results indicated that the current ACI code over-estimated the torsional strength of RC beams that had larger amount of torsional reinforcement.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.9A
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• pp.1313-1321
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• 2000

In recent years LEO(Low Earth Orbit) satellite communication systems have gained a lot of interest as high speed multimedia services by satellite are about to be provided. It is mandatory to use very efficient ECC(Error Correcting Code) to support high speed multimedia services over LEO satellite channel. Turbo codes developed by Berrou et al. in 1993 have been actively researched since it can achieve a performance close to the Shannon limit. In this paper, a LEO satellite channel model is adopted and the fading characteristics of LEO satellite channel are analyzed for the change of elevation angle in various propagation environments. The performance of turbo code is analyzed and compared to that of conventional convolutional code using the satellite channel model. In the simulation results using the Globalstar orbit constellations, performance of turbo codes shows 1.0~2.0dB coding gain compared to that of convolutional codes over all elevation angle and propagation environment ranges we have investigated. The performance difference resulting from the change of elevation angle in various propagation environments and the performance of different ECC are analyzed in detail, so that the results can be applied to choose an appropriate ECC scheme for various system environment.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.977-980
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• 1995

This paper proposes the look ahead algorithm with the trapezoidal velocity trajectory in each G-code block. The algorithm requires the information on the length of next trajectories and the connecting angle between each trajectiories. A method of generating the maximum corner velocity upon the connecting angle within the machining tolerance is developed and applied to the look ahead algorithm. Simulations and experiments witha machining center show the effectiveness of the methodology.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.35 no.3
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• pp.43-52
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• 2003

The new principle to measure a sizing degree by a contact angle was developed using an automatic determination of the 3-end point coordinates of the water droplet on a sheet, which could diminish the operator's bias during measurement. A constant amount of water was first placed on a sample sheet by a water dispenser, and then an image of the liquid droplet was captured by a digital camera and then transmitted to a computer. The program measuring for contact angle extracted a liquid contour by Gaussian function combined with a 8-direction chain code. The Euclidean equation was applied to the binary image of the liquid contour in order to measure the diameter of the contour. Finally, the contact angle of the liquid was calculated by using the diameter and the top coordinates. In addition, a surface free energy of the sample sheet and an elapsed time taken up to the complete absorption into the sheet were simultaneously measured with the contact angle.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.2 s.245
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• pp.161-169
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• 2006

The spray characteristics of liquid jet in cross flow with variation of injection angle are numerically studied. Numerical analysis was carried out using KIVA code, which was modified to be suitable for simulating liquid jet ejected into cross flow. Wave model and Kelvin-Helmholtz(KH)/Rayleigh-Taylor(RT) hybrid model were used for the purpose of analyzing liquid column, ligament, and the breakup of droplet. Numerical results were compared with experimental data in order to verify the reliability of the physical model. Liquid jet penetration length, volume flux, droplet velocity profile and SMD were obtained. Penetration length increases as flow velocity decreases and injection velocity increases. From the bottom wall, the SMD increases as vertical distance increases. Also the SMD decreases as injection angle increases.

• 한국전산유체공학회:학술대회논문집
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• 2009.11a
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• pp.19-26
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• 2009

The objective of this study is to investigate aerodynamic characteristics of a Horizontal-axis wind turbines(HAWT), using CFD method with a commercial code STAR-CCM+ version 3.06. To verify the reliability of the computations, the CFD results are compared with the experimental ones of the National Renewable Energy Laboratory(NREL) Phase Ⅵ HAWT. For the comparison and examination of aerodynamic characteristics, the existent shape with a predesigned twist angle was replaced by the one with one-dimensional linear twist angle. In this study, the pressure contour and stream line around the blade were analyzed as main focus. Through this study the more efficient shape of airfoil is suggested with consideration of manufacturing cost.

• Transactions of the Korean Society of Automotive Engineers
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• v.8 no.6
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• pp.9-21
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• 2000

In this study, the characteristics of high-pressure swirl injector have been studied using a commercial CFD code, STAR-CD and experiment to investigate the effect of the length of orifice and swirl port on the spray characteristics. Influences of swirl port angle and initial conditions have also been examined in terms of penetration depth and Sauter`s mean diameter. Computed results of the spray characteristics are compared with experimental results. The results show that the tangential velocity at the nozzle exit decreases, but the axial velocity increases as swirl port angle is increased. Hence, the static flow rate increases, but the initial spray angle decreases with increasing the swirl port angle. It is also shown that the values of the initial SMD used as input data for spray simulation influences the penetration depth and SMD. The spray pattern from the present numerical simulation agrees well with experimental result.

• Journal of Advanced Marine Engineering and Technology
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• v.32 no.6
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• pp.923-930
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• 2008

The butterfly valve is widely used in the industrial field as an on-off or a flow control valve. When the butterfly valve is used as a flow control valve. cavitation sometimes occurs in the range of high flow rate because of the small valve opening. Therefore. the pressure loss and the cavitation characteristics are investigated by use of a commercial CFD code. The results show that the possibility of cavitation occurrence in the cryogenic butterfly valve is very high in the case of valve opening angle below 10 degree and incident velocity over 6m/s. By increasing the inlet velocity at 10 degree of valve opening angle. the value of loss coefficient increased. However. by increasing the inlet velocity at 50 degree of valve opening angle. the value of loss coefficient decreased.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2003.10a
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• pp.479-486
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• 2003

The characteristics of harmonic phase angles and phase angle differences contained in earthquake ground motions such as El Centre 1940 NS, Taft1 1952 NS, Hachinohe 1968 NS and Mexico 1985 are figured, which have been mostly overlooked in contrast with the importance placed on harmonic amplitudes. Recently, performance based design method is used for seismic design and seismic retrofitting, which needs nonlinear response analysis, there must be earthquake ground accelerations which contain the phase angle, the phase angle difference and energy input spectrum characteristics of the zone considered to be constructed building structures. To make clear the importance of phase angle differences, responses of 4 recorded earthquake ground motions, 4-earthquake ground motions normalized by 110 gal and 4 artificial earthquake motions compatible to the seismic building code of Korea are compared.

• Journal of Korean Society of Steel Construction
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• v.10 no.4 s.37
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• pp.721-730
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• 1998

In this paper, an experimental study have been many studies on the joints of steel structure, for it has great influences on the safety of structures. Research on block shear rupture of the joint receiving pure tension have been done in foreign countries, but not in Korea. This study focuses on the propriety of block shear design code, according to limited state design criteria of steel structures recently established in Korea, by an experiment on the joint of angle tension members. The methods of this study were to compare other study results on block shear rupture mode and ultimate capacity, and to evaluate the propriety of the criteria design code. The result is that tension yield shear ruptures and shear yield tension ruptures happened at the joint, and the experimental rupture load was 15% higher than the capacity entered in the criteria design code. We conclude that it is necessary to revaluate the block shear design code presented by many studies on the limited state design criteria of steel structures.