• 한국가시화정보학회:학술대회논문집
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• 2004.12a
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• pp.1-13
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• 2004

A scanning stereo-PIV system was developed to measure the three-dimensional distribution of three-component velocity in a turbulent round jet. A laser light beam produced by a high repetition rate YLF pulse laser was expanded vertically by a cylindrical lens to form a laser light sheet. The light sheet is scanned in a direction normal to the sheet by a flat mirror mounted on an optical scanner, which is controlled by a programmable scanner controller. Two high-speed mega-pixel resolution C-MOS cameras captured the particle images illuminated by the light sheet, and stereoscopic PIV method was adopted to acquire the 3D-3C-velocity distribution of turbulent round jet in an octagonal tank filled with water. The jet Reynolds number was set at Re=1000 and the streamwise location of the measurement was fixed at approximately x = 40D. Time evolution of three-dimensional vortical structure, which is identified by vorticity, is visualized. It revealed that the existence of a group of hairpin-like vortex structures was quite evident around the rim of the shear layer of the jet. Turbulence statistics shows good agreement with the previous data, and divergence of a filtered (unfiltered) velocity vector field was $7\%\;(22\%)$ of root-me an-squared vorticity value.

• Transactions of the Korean Society of Mechanical Engineers
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• v.5 no.4
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• pp.320-328
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• 1981

Experimental study of a round. free air jet is accomplished using a crossed hot wire probe with a constant temperature hot wire anemometer. Mean velocity Profiles, Reynolds stresses, tubulent intensities, velocity probability densities and correlation functions are measured in the down tream region. These values are calculated and averaged inthe correlation and probability analyzer. The reults are interpreted by the output of te dual beam oscilloscope.

• The Korean Journal of Ceramics
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• v.4 no.4
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• pp.311-322
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• 1998

American Society for Testing and Materials (ASTM) standard test method PS 070-97 has been created for measuring fracture toughness of advanced ceramics. PS 070-97 includes three test methods which use beams in bending: chevron notch (CNB), single-edged precracked beam (SEPB), and surface crack in flexure (SCF). Supporting data has been collected through several Versailles Advanced Materials and Standards round robins. This paper discusses the evolution of the standard including the rationale for the choice of the three methods and the specifications in the standard. Progress on Standard Reference material 2100 which will have certified values of fracture toughness is presented.

• Proceedings of the Korea Concrete Institute Conference
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• 1997.10a
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• pp.569-574
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• 1997

This research has improved composite joint system of R/C column and steel beam developed at previous study. In this system, the shear force occurred at beam is transmitted by bearing resistance of stiffness and moment is resisted by tension capacity of coupling members. As the preliminary step of stress transfer tests of this system, welding performance test of coupling member such as round bar or square bar which has a role of moment transfer has been carried out. From the test, this element has a good welding performance and enough resistance capacity compared to design force.

• Korean Journal of Optics and Photonics
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• v.6 no.4
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• pp.288-295
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• 1995

We have studied about spatial wavefront analysis of a pulsed laser output beam by means of an imaging unstable ring resonator with an infinite Fresnel number. We have constructed a Newtonian telescope type NBUR (Negative Branch Unstable Ring) Nd:YAG laser with 4 plane mirrors. Provided that the NBUR resonator is under self imaging condition, the resonator could be reduced diffraction effects which were occuring to the beam transmitting through the circular aperture of scraper mirror in the resonator. We have observed enhancement in the spatial coherence of wavefronts of laser beam due to the iterative round trips of the self imaging beam inside the ring resonator. The information on the spatial wavefronts was determined by the fringe patterns from Mach-Zehnder interferometer and the fringe analysis by means of the Fourier transform method showed the distortion of wavefronts of less than 0.2), In comparison with a standing wave type resonator, we have confirmed that the spatial coherence of the NBUR Nd:YAG laser output beam was enhanced as much as 75%. s 75%.

• Journal of architectural history
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• v.21 no.3
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• pp.7-28
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• 2012

This study is intended to Mindori structure which is general private houses' structural type among traditional types and is a basic study to confirm structural characteristics of Hwatong connection which is general connection type of column-beam-cross beam. It is aimed to analyze how main member, column, such as size, figure, thickness of Sungetuk and Dugeup affect on structure. Following conclusions are drawn. 1. According to connection conditions, models with big coefficient of friction show stable hysteretic behavior until the angle rotation of member reaches 1/60 and models with small coefficient of friction show dramatical increase in load after the angle rotation of member reaches 1/24. After the angle rotation of member reaches 1/30, separation distance of members is identified physically and cracks are not observed. 2. Specimens with big coefficient of friction show similar inner force regardless of column size(except column size 150mm) and models with small coefficient of friction show increasing inner force as the column size increases. Specimens with same sectional area have similar inner force even though the column figures are different. The thickness of Sungetuk and Dugeup doesn't affect inner force greatly, however, when the thickness of Sungetuk is thin, it could lead to failure of structure as it breaks. 3. The bigger the size of column and the coefficient of friction are, the smaller Bending stiffness depreciation ratio is. 4. Energy Dissipation Efficiency differs from the coefficient of friction. When the coefficient of friction is big, square column shows bigger than round one and it is bigger when the thickness of Sungetuk and Dugeup is thicker. When the coefficient of friction is small, round column shows bigger than square one.

• Proceedings of the Korean Society of Medical Physics Conference
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• 2003.09a
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• pp.64-64
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• 2003

Objectives: Patient dose verification is clinically the most important parts in the treatment delivery of radiation therapy. The three dimensional(3D) reconstruction of dose distribution delivered to target volume helps to verify patient dose and determine the physical characteristics of beams used in intensity modulated radiation therapy(IMRT). We present Beam Intensity Scanner(BInS) system for the pre treatment dosimetric verification of two dimensional photon intensity. The BInS is a radiation detector with a custom made software for relative dose conversion of fluorescence signals from scintillator. Methods: This scintillator is fabricated by phosphor Gadolinium Oxysulphide and is used to produce fluorescence from the irradiation of 6MV photons on a Varian Clinac 21EX. The digitized fluoroscopic signals obtained by digital video camera will be processed by our custom made software to reproduce 3D relative dose distribution. For the intensity modulated beam(IMB), the BInS calculates absorbed dose in absolute beam fluence, which are used for the patient dose distribution. Results: Using BInS, we performed various measurements related to IMRT and found the followings: (1) The 3D dose profiles of the IMBs measured by the BInS demonstrate good agreement with radiographic film, pin type ionization chamber and Monte Carlo simulation. (2) The delivered beam intensity is altered by the mechanical and dosimetric properties of the collimating of dynamic and/or static MLC system. This is mostly due to leaf transmission, leaf penumbra, scattered photons from the round edges of leaves, and geometry of leaf. (3) The delivered dose depends on the operational detail of how to make multileaf opening. Conclusions: These phenomena result in a fluence distribution that can be substantially different from the initial and calculative intensity modulation and therefore, should be taken into account by the treatment planing for accurate dose calculations delivered to the target volume in IMRT.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.11 no.2
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• pp.20-24
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• 2015

During refueling Outage, In-service inspections(ISIs) for the Nuclear Power Plant components are mandatory requirement in accordance with ASME Code Sec. XI. Especially, in current ultrasonic testing is one of the most important NDT techniques that are used for volumetric examination methods for nuclear power plant components, and accurate sizing of flaw indication by UT is essential to assure the integrity of the components. However, ASME code specifies minimum requirement for vessel examination procedure, and so far many different flaw sizing approaches have been tried to apply. Through the Round Robin Test(RRT), the accuracy of ultrasonic flaw sizing using DAC techniques was measured with the mock-ups simulating typical pressure vessel welds. These mock-ups contain artificially introduced flaws of known size and location. This paper shows experimental comparison data on the accuracy of techniques using such as 6dB drop, 50%DAC, 20%DAC and 20%DAC with beam spread correction, and also shows that diverse DAC techniques can be effectively applied to the assessment of the flaw sizing for pressure vessel welds in the stage of welding and fabrication.

• Journal of the Optical Society of Korea
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• v.6 no.3
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• pp.121-127
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• 2002

The operating principal of a ring laser gyroscope depends on the phase difference for the counter-propagating waves within a closed path. The reflecting mirrors mounted on the monoblock form the traveling waves. The manufacturing accuracy of the monoblock influences the traveling path of ray, the sensitivity of laser resonator for misalignments, and diffraction losses. A 3 $\times$ 3 ray transfer matrix was derived for optical components with centering and squaring errors in a ring resonator. The matrix can be utilized to predict the optical ray paths on the basis of the manufacturing errors of the monoblock as well as the misalignment of mirrors. Then the distance and orientation (o. slope) at the arbitrary plane inside the resonator along the ideal optical path can be calculated from the chain multiplication of the ray transfer matrix for each optical component in one round trip. We also show that the counter-propagating rays In a ring resonator with errors does not coincide in each round trip, which results in gain difference between two beams, and how these errors can be adjusted through the alignment procedure. Finally this 3 $\times$ 3 ray matrix formalism can be used to calculate the beam size and its displacement from the optical axis and the deviation at the diaphragm.

• Tunnel and Underground Space
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• v.20 no.5
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• pp.378-389
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• 2010

Submarine tunnels are affected by the surrounding environments more than regular tunnels. Especially, they are often vulnerable to damage by salt in seawater. Seawater is more likely to affect reinforcing rods and steel fibers than concrete. Recently the usage of anti-corrosive fibers increases in the tunnel which is subject to the possibility of damage. By comparing the capability of polypropylene fibers with that of steel fibers, the proper mixture ratio is decided and the supporting capability of polypropylene fibers was tested using round panel and beam specimens. The results of this study can be of great use in selecting the fiber material and designing of fiber reinforced shotcrete of submarine tunnels.