• Journal of Korean Tunnelling and Underground Space Association
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• v.6 no.1
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• pp.51-59
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• 2004

The effectiveness of one dimensional critical velocity method for evacuation environment at 10MW fire size in a railroad tunnel have been investigated in this paper by three dimensional CFD method. It was performed to evaluate the evacuation environment in terms of temperature distribution, visible distance distribution and CO concentration at some tunnel inlet velocity, 1m/s, 2m/s (near critical velocity), and 3m/s. At all inlet velocity, passenger should give away downward the flow direction because the inlet velocity can not afford to sufficient evacuation environment for passengers. In case of 3m/s inlet velocity, however, the evacuation environment for passengers is better than the other cases. To provide more safe evacuation environment on fire situation, tunnel inlet velocity should be larger than critical velocity.

• Journal of the Korean Society for Nondestructive Testing
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• v.36 no.1
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• pp.27-34
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• 2016

The type of ultrasound transducer used influences the quality of a reconstructed ultrasound image. This study analyzed the effect of transducer type on ultrasound computed tomography (UCT) image quality. The UCT was modeled in an ultrasound simulator by using a 5 cm anatomy model and a ring-shape 5 MHz 128 transducer array, which considered attenuation, refraction, and reflection. Speed-of-sound images were reconstructed by the Radon transform as the UCT image modality. Acoustic impedance images were also reconstructed by the delay-and-sum (DAS) method, which considered the speed of sound information. To determine the optimal combination of transducers in observation, point-source, flat, and focused transducers were tested in combination as trasmitters and receivers; UCT images were constructed from each combination. The combination of point-source/flat transducer as transmitting and receiving devices presented the best reconstructed image quality. In UCT implementation, the combination of a flat transducer for transmitting and a point transducer for receiving permitted acceptable image quality.

• Economic and Environmental Geology
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• v.31 no.2
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• pp.127-139
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• 1998

A new technique of simultaneous inversion for 3-D seismic velocity structure by using direct, reflected, and refracted waves is applied to the southeast part of the Korean Peninsula including Pohang Basin, Kyongsang Basin and Ryongnam Massif. Pg, Sg, PmP, SmS, Pn, and Sn arrival times of 44 events with 554 seismic rays are inverted for locations and crustal structure. $6{\times}6$ with $0.5^{\circ}$ and 8 layers (4 km each layer) model was inverted. 3-D seismic crustal velocity tomography including eight sections from surface to Moho, ten profiles along latitude and longitude are analyzed. The results are as follows: 1) the average velocity and thickness of sediment are 5.04 km/s and 3-4 km, and the velocity of basement is 6.11 km/s. The shape of velocity in shallower layer is agreement with Bouguer gravity anomaly (Cho et al., 1997). 2) the velocities fluctuate strongly in the upper crust. The velocity distribution of the lower crust under Conrad appears basically horizontal. 3) the average depth of Moho is 30.4 km, and velocity is 8.01 km/s. 4) from the velocity and depth of the sediment, the thickness, velocity and form of the upper crust, and the depth and form of Moho, we can find the obvious differences among Ryongnam Massif, Kyongsang Basin and Pohang Basin. 5) the deep faults (a Ulsan series faults) near Kyongju and Pohang areas can be found to be normal and/or thrust faults with detachment extended to the bottom of the upper crust.

• Journal of the Earthquake Engineering Society of Korea
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• v.11 no.1 s.53
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• pp.45-57
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• 2007

The mean shear wave velocity to the depth of 30 m (Vs30) derived from the western Vs is the current site classification criterion for determining the design seismic ground motion taking into account the site amplification potential. In order to evaluate the Vs30 at a site, a shear wave velocity (Vs) Profile extending to at least 30 m in depth must be acquired from in-situ seismic test. In many cases, however, the resultant depth of the Vs profile may not extend to 30 m, owing to the unfavorable field condition and the limitation of adopted testing techniques. In this study, the Vs30 and the mean shear wave velocity to a depth shallower, than 30 m (VsDs) were computed from the Vs profiles more than 30 m in depth obtained by performing various seismic tests at total 72 sites in Korea, and a correlation between Vs30 and VsDs was drawn based on the computed mean Vs data. In addition, a method for extrapolating the Vs profile from shallow depth to 30 m was developed by building a shape curve based on the average data of all Vs profiles. For evaluating the Vs30 from the shallow Vs profiles, both the methods using VsDs and shape curve result in less bias than the simplest method of extending the lowermost Vs equally to 30 m in depth, and are usefully applicable particularly in the cases of the Vs profiles extending to at least 10 m in depth.

• Journal of the Korean Society of Hazard Mitigation
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• v.7 no.5
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• pp.167-178
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• 2007

Based on the kinematic wave equations, the influence of moving rainstorms on the surface runoff were analyzed with a focus on the rainfall distribution types. Applied hypothetical rainfall distribution types of moving rainstorms used are uniform, advanced, delayed and intermediate type. The moving rainstorm velocities applied in this study were $0.125{\sim}2.0m/s$ of moving upstream and downstream direction of plane surface. Simulations were undertaken by varying the rainfall distribution type, moving rainstorm velocity and moving direction, and the results were compared with that of stationary rainfall. The results indicate significant differences in peak discharges and hydrograph shapes for moving rainstorms of various rainfall patterns and moving directions. It shows that the moving rainstorms of downstream direction generate the largest peak runoff at all rainfall distributions. The sensitivity of runoff to rainfall distribution types decreases as storm velocity increases. It is clear that faster rainstorm velocity generates faster peak time and becomes thin hydrographs rapidly.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.6
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• pp.1613-1620
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• 1990

For the purpose of the study on the spray characteristics of a coaxial nozzle, the measurement of the velocity and size of droplets, concentration, and the statistical correlation coefficient between the fluctuation of the velocity and that of the corresponding drop diameter have been carried out. Various method of simultaneous measurement of velocity and drop size have been developed from LDV techniques. The technique used here belongs to the method that supposed by Yule, Holve and Self. It has the advantages of making use of a standard LDV apparatus to which minor modifications have been brought, photomultiplier is equipped with a slit instead of a pinhole and observed the measuring volume at an angle of 90.deg.. The voltage supplied by the photomultiplier has undergone an appropriate analog and digital processing. The experimental results give a good idea of the two phase flow organization and can be helpful to find a drop diffusion model when suitable data are imput.

• Journal of Radiation Protection and Research
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• v.19 no.1
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• pp.13-22
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• 1994

The MCNP 4.2 code was used to calculate the thermal neutron flux distributions for $(n,\;{\gamma})$reaction in mainshell, annular plate, and subshell of the calandria of a CANDU 6 plant during operation. The thermal neutron flux distributions in calandria mainshell, annular plate, and subshell were in the range of $10^{11}{\sim}10^{13}\;neutrons/cm^2-sec$ which is somewhat higher than the previous estimates calculated by DOT 4.2 code. As an application to shielding analysis, photon dose rates outside the side and bottom shields were calculated. The resulting dose rates at the reactor accessible areas were below design target, $6 {\mu}Sv/h$. The methodology used in this study to evaluate the thermal neutron flux distribution for $(n,\;{\gamma})reaction$ can be applied to radiation shielding analysis of CANDU 6 type plants.

• Journal of the Korean Society of Propulsion Engineers
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• v.4 no.4
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• pp.18-25
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• 2000

A two-color particle image velocimetry (PIV) has been developed for measuring two dimensional velocity flowfields and applied to a Mach 2.0 supersonic nozzle. This technique is similar to a single-color PIV technique except that two different color laser beams are used to solve the directional ambiguity problem. A green-color laser sheet (532 nm: 2nd harmonic beam of YAG laser) and a red-color laser sheet (619 nm: output beam from YAG pumped Dye laser using Rhodamine 640) are employed to illuminate the seeded particles. A high resolution (3060${\times}$2036) digital color CCD camera is used to record the particle positions. This system eliminates the photographic-film processing time and subsequent digitization time as well as the complexities associated with conventional image shifting techniques for solving directional ambiguity problem. The two-color PIV also has the advantage that velocity distributions in high speed flowfields can be measured simply and accurately by varying the time interval between two different laser beams due to its high signal-to-noise ratio and thereby less requirement of panicle pair numbers for a velocity vector in one interrogation spot. The velocity distribution in the Mach 2.0 supersonic nozzle has been measured and the over-expanded shock cell structure can be predicted by the strain rate field. These results are compared and analyzed with the schlieren photograph for the velocity distributions and shock location.

• Korean Journal of Materials Research
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• v.6 no.1
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• pp.99-105
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• 1996

본 연구에서는 TIMA를 전구체로 하는 수직형 MOCVD 반응기를 대상으로 수학적 모델을 세우고 컴퓨터에 의한 수치모사를 수행하여 반응기 설계 변수 및 공정조건이 AI의 증착속도와 증착두께 분포에 미치는 영향을 알아보았다. 수학적 모델은 수직형 반응기를 축대칭으로 보아 2차원으로 수립하였으며 반응기내의 운동량전달, 열전달, 물질전달을 포함한다. 이 수학적 모델의 지배 방정식들에 대하여 Galerkin 유한요소법을 적용하여 수치적으로 반응기 내의 유체 흐름 구조, 온도분포와 반응물의 농도 분포를 구하였다. 수치모사 결과 AI의 증착속도는 반응기 압력이 0.47torr, 기판온도가 25$0^{\circ}C$, 유량이 7.5sccm일 경우, 190-230$\AA$/min로 나타났다.

• Proceedings of the Korea Water Resources Association Conference
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• 2005.05b
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• pp.649-653
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• 2005

유역형상의 변화에 따라서 이동강우가 유출에 미치는 영향을 운동파이론을 적용하여 분석하였으며, 유역형상은 신장형유역과 정4각형유역 및 장방형유역에 대하여 분석하였고, 이동강우 분포형은 균등분포형, 전진형, 지연형, 중앙집중형을 사용하였다. 이와 같은 형상의 유역에 대하여 다양한 이동속도를 가진 강우가 유역내 하천의 상류방향, 하류방향, 횡방향으로 이동할 때 강우분포형에 따르는 유출수문곡선을 모의하여 그 특성을 비교분석하였다. 유출수문곡선의 모양과 첨두시간, 첨두유량은 시간적, 공간적으로 변화하는 강우와 유역형상에 의하여 크게 영향을 받는다. 횡방향의 이동강우에서는 상류방향과 하류방향의 경우보다 더 큰 첨두유량이 발생하며, 하류방향 이동강우의 첨두유량은 상류방향의 첨두유량보다 더 크게 나타났다. 신장형유역의 경우 하류방향 이동강우의 첨두시간은 상류방향과 횡방향의 경우보다 더 지체되며, 수문곡선의 총유출량과 기저시간은 강우속도가 증가함에 따라 감소하였다.