• Journal of the Korean Society for Nondestructive Testing
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• v.36 no.4
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• pp.273-280
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• 2016

The simulation of nondestructive testing has been used in the prediction of the signal characteristics of various defects and in the development of the procedures. CIVA, a simulation tool dedicated to nondestructive testing, has good accuracy and speed, and provides a three-dimensional graphical user interface for improved visualization and familiar data displays consistent with an NDE technique. Even though internal validations have been performed by the CIVA software development specialists, an independent validation study is necessary for the assessment of the accuracy of the software prior to practical use. In this study, time of flight diffraction signals of ultrasonic inspection of a calibration block for reactor vessel head penetrations were simulated using CIVA. The results were compared to the experimentally inspected signals. The accuracy of the simulated signals and the possible range for simulation were verified. It was found that, there is a good agreement between the CIVA simulated and experimental results in the A-scan signal, B-scan image, and measurement of depth.

• Journal of KIISE:Computing Practices and Letters
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• v.14 no.2
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• pp.181-185
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• 2008

Layered video multicast such as RLM Receiver-driven layered multicast) is a premising technique for delivering streaming video to a set of heterogeneous receivers over ALM(Application Layer Multicast) as well as over IP multicast. However, this approach may suffer from unnecessary fluctuation of video quality due to overlapped and failed join-experiments. Though a shared teaming scheme was introduced to resolve these problems, it may cause high control overhead and slow convergence problem when used with ALM. In this paper, we propose a new shared learning scheme for ALM-based layered video multicast which reduces control overhead and convergence latency while keeping the number of fluctuation reasonably small. The simulation results show that the proposed scheme performs better than an ALM-based layered video multicast with shared learning in terms of control overhead and convergence latency.

• Journal of the Korean Geotechnical Society
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• v.28 no.5
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• pp.67-76
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• 2012

This study is a research about cutter bits arrangement of shield-TBM and carried out a scale model test and numerical analysis according to a space of cutter bits. A cutter head pressures and an advance time are measured to be followed by the space of cutter bits with an advance speed through the scale model test. We conducted the numerical analysis to verify the result of the scale model test, and to compare with the scale model test. There are three cases of space : unification 1.0D and 1.5D. In case TBM is excavated and space is 1.0D, the advance speed is much faster than the other cases, and pressure of face of ground deformation and cutter head is maintained stably. If additional researches about bits arrangement of cutter head of sand ground based on the result of this research are performed, substantial results may be obtained.

• Tunnel and Underground Space
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• v.25 no.6
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• pp.496-504
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• 2015

Roadheader that excavates ground using pick cutters installed on the cutting head is one of the partial-face machines. A conical cutter among pick cutters is excavation tool decreasing the loss of cutter using tungsten carbide insert at the tip of the cutter and it has been widely used in the roadheaders. In this study, durability performance for three kinds of conical cutters was evaluated in copper mines composed of Manto and conglomerate. After field test, the visual inspection as well as the weight loss measurement of pick cutters was carried out to investigate the damage of pick cutters. In addition, CT scan and SEM were performed to check whether or not crack and apertures in pick cutters. As results, the conical cutter with hardfacing was evaluated as having the best durability performance and it was unable to find cracks in all cutters investigated.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.3
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• pp.419-430
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• 1999

Measurements of local blowing ratio and ammonia-diazo flow visualizations have been conducted for a shower-head film cooling on a first-stage turbine stator. In this study, six rows of normal holes are drilled symmetrically on the semicircular leading edge of a simulated blunt body. The measurements show that for an average blowing ratio based on freestream velocity, M, of 0.5, local average mass flow rate through the first two rows of the holes is less than those through the second and third two rows of the holes, and the fraction of mass flow rate through the first two rows to total mass flow rate has a tendency to increase with the increment of M. The flow visualizations reveal that the injection through the first two row results in inferior film coverage even In the case of M = 0.5, meanwhile the row of holes situated at farther downstream location provides higher film-cooling performances for all tested M. This is because film-cooling effectiveness depends on local mainflow velocity at the hole location as well as the mass flow rate through each row.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.2
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• pp.177-187
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• 2000

Measurements of temperature fields and film-cooling effectiveness have been conducted for a shower-head film cooling on the leading edge of a blunt body, which simulates a first-stage turbine stator. In this study, three injection cases are employed for an average blowing ratio based on freestream velocity, M, of 0.5, 1.0 and 1.5. Two (Case 1), four (Case 2) and six (Case 3) rows of normal holes are symmetrically drilled on the three tested circular-cylinder leading edges. The measurements show that regardless of M, the film-cooling effectiveness increases as the injection row is situated at farther downstream location. In Case 1, the film-cooling effectiveness is highest for M = 0.5 and lowest for M = 1.5. On the contrary, in Case 3, the film-cooling effectiveness is highest for M = 1.0 and lowest for M = 0.5. When M = 0.5, the film coverage by the first row of the injection holes deteriorates as the number of the injection row increases. In particular, the film-cooling effectiveness due to the injection through the first row of the holes in Case 3, has a nearly zero value.

• Transactions of the Korean Society of Automotive Engineers
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• v.5 no.5
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• pp.178-187
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• 1997

For the experimental measurement of heat flux of DI diesel engine combustion chamber, the instantaneous temperature probes and data acquisition system were developed. By the analysis of measured temperatures at the cylinder head, the temperature at the point 3 which is located between intake and exhaust valve was higher than that of the other points. Temperatures at the point located mear the exhaust valve were higher than those of intake valve. The instantaneous and mean temperature at the cylinder head increases proportionally to the increase of the engine speed, while the temperature swing varies inversely. Temperature swings have influence on the maximum heat flux values from gas into head surface. It has been verified that these probes and data acquisition system perform well by the comparison of the trend of instantaneous temperature variation with that of measured combustion chamber pressure variation with respect to crank angle. It is presumed that these probes could be used in the measurement of other parts of combustion chamber as piston, cylinder wall etc. for the future study.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.1
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• pp.73-79
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• 2011

Inkjet printhead may have a lot of nozzles to increase productivity as a manufacturing tool. So, the uniformity of jetting performance among a lot of nozzles has been one of the key issues in inkjet technology In this study, we investigated the cross-talk effect which should be reduced for uniform jetting performance among a lot of nozzles. Due to the cross-talk, the jetting performance of a nozzle can be affected when neighboring nozzles are firing. For experimental study, we used commercial inkjet head SE-128 from Dimatix. To understand the cross-talk effect of SE-128 head, we measured the change in jetting speed of a nozzle when neighboring nozzles are jetting. The measured jetting speed was compared to the case of one nozzle jetting. Also, we used laser vibrometer to measure change in pressure wave due to cross-talk. As a result of the cross-talk, the jetting speed can become faster or sometimes slower depending on firing nozzle location. If the all nozzle are jetting, the jetting speed of a nozzle became slower because the pressure wave for jetting is reduced.

• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.5
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• pp.38-47
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• 2007

Based upon temperature calibration using the diffusion flame, the temperature and soot concentration of the turbulent flame in a visualized Diesel engine's turbulent flow of flame was qualitatively measured. Two different heads were used to judge the effect of swirl ratio within the combustion chamber. It was possible to measure the highest temperature of the non-swirl head visualized engine which is approximately 2400K, and that the swirl head engine managed up to 2100K. Also, the more the pressure of the spray increases the more the temperature increases due to the improved combustion situation with respect to the visualized diesel engine soot. This experiment also revealed that the KL factor was high where the fuel collided with the walls of the combustion chamber. Moreover the KL factor was high on parts of the chamber where the temperature dropped rapidly.

• Progress in Medical Physics
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• v.17 no.4
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• pp.224-231
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• 2006

The electron energy spectra for 6 MeV electron beam were calculated using a MCNPX code. The head of the linear accelerator (ML6M; Mitsubishi, Japan) was modelled for this study. The energy spectrum of the initial electron beam was assumed to be Gaussian and the mean energy was determined by evaluating the measured and calculated values of $R_{50}$ and dose profiles in air. The energy distributions for electrons and photons at the interested points in the head of the linear accelerator were calculated by appling the Initial beam parameters. The effect of contaminant photons on depth dose curves were estimated by the photon energy spectra at the end of the applicator.