• Journal of the Korean Geotechnical Society
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• v.34 no.3
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• pp.57-65
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• 2018

This study adopts high resolution 3D X-ray CT imaging technique to visualize and evaluate the internal structure of experimentally frozen soils. Temperature and elastic wave velocity are also measured during the freezing process. The X-ray images of frozen specimens reveal that no changes in internal structure are observed for sand specimen, whereas systematic growth pattern of pore ice is observed within clay specimen. The freezing patterns are then quantified by a set of X-ray images with the aid of two-point correlation method by computing characteristic length Lr. The results reveal that characteristic length for pore ice freezing pattern in clay linearly increases with respect to the distance from the cooling source, so that Lr at the bottom layer is 2.5 times greater than the top layer when freezing process is completed. Furthermore, during the freezing process, local temperature differences are not observed in sand, but observed in clay specimen due to its relatively low thermal conductivity.

• Bulletin of the Society of Naval Architects of Korea
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• v.26 no.4
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• pp.81-93
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• 1989

The present study attempts to develop the theoretical model for the damage estimation of offshore tubular members which are subjected to the accidental impact loads due to collision, falling objects and so on. For the reasons of the simplicity of the problem being considered, however, this paper postulates that the accidental load can be approximated to be the quasi-static one, in which dynamic effects are negelcted. Based upon the theoretical and experimental results which are obtained from the present study as well as the existing literature, the load-displacement relations taking the interaction effect between the local denting and the global bending deformation into account are presented in the explicit form when the concentrated lateral load acts on the tubular member whose end condition is supposed to be rotation ally free and axially restrained, in which membrane forces develop. Thus, the practical estimation of damage deformation for the local denting and the global bending damage of tubular members against the accidental loads is possible and also the collision absorption capability of the member can be calculated by performing the integration of the area below the given load-displacement curves, provided that all the energy is dissipated to the deforming the member itself.

• The Journal of Engineering Geology
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• v.17 no.1 s.50
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• pp.1-13
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• 2007

In order to evaluate the local site effects at two town fortress areas in Korea where stone parapets were col-lapsed by historical earthquakes, site characteristics were assessed using site investigations such as borehole drillings and seismic tests. Equivalent-linear site response analyses were conducted based on the shear ways velocity ($V_s$) profiles and geotechnical characteristics determined from site investigations. The study sites are categorized as site classes C and B according to the mean $V_s$ to 30 m ranging from 500 to 850 m/s, and their site periods are distributed in the short period range of 0.06 to 0.16 sec, which contains the natural period of fortress wall and stone parapet. From the results of site response analyses in the study areas, for site class C indicating most of site conditions, contrary to site class B, the short-period (0.1-0.5 sec) and mid-period (0.4-2.0 sec) site coefficients, $F_a$ and $F_v$ specified in the Korean seismic design guide, underestimate the ground motion in short-period band and overestimate the ground motion in mid-period band, respectively, due to the high amplification in short period range, which represent the site-specific seismic response characteristics. These site-specific response characteristics indicate the potential of resonance in fortress walls during earthquake and furthermore could strongly affect the collapse of parapets resulted from seismic events in historical records.

• The KIPS Transactions:PartB
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• v.16B no.2
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• pp.123-130
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• 2009

Motion estimation (ME) plays an important role in digital video compression. But it limits the performance of image quality and encoding speed and is computational demanding part of the encoder. To reduce computational time and maintain the image quality, integer pel and fractional pel ME methods are proposed in this paper. The proposed method for integer pel ME uses a hierarchical search strategy. This strategy method consists of symmetrical cross-X pattern, multi square grid pattern, diamond patterns. These search patterns places search points symmetrically and evenly that can cover the overall search area not to fall into the local minimum and to reduce the computational time. The proposed method for fractional pel uses full search pattern, center biased fractional pel search pattern and the proposed search pattern. According to block sizes, the proposed method for fractional pel decides the search pattern adaptively. Experiment results show that the speedup improvement of the proposed method over Unsymmetrical cross Multi Hexagon grid Search (UMHexagonS) and Full Search (FS) can be up to around $1.2{\sim}5.2$ times faster. Compared to image quality of FS, the proposed method shows an average PSNR drop of 0.01 dB while showing an average PSNR gain of 0.02 dB in comparison to that of UMHexagonS.

• Nuclear Engineering and Technology
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• v.25 no.1
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• pp.91-101
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• 1993

To predict accurately the thermal hydraulic behavior of light water reactors during normal or abnormal operation, the accurate estimation of the void distribution is required. Up to date, many techniques for predicting void fraction of two-phase flow systems have been suggested. Among these techniques, the drift-flux model is widely used because of its exact calculation ability and simplicity. However, to get more accurate prediction of void fraction using drift-flux model, slip and flow regime effects must be considered more properly In the drift-flux method, these two effects are accounted for by two drift-flux parameters ; $C_{o}$ and (equation omitted). At earlier stage, $C_{o}$ is measured in a circular tube. In this study, $C_{o}$ is experimentally determined by measuring local void fraction and vapor velocity distribution in a rectangular subchannel having 4 heating rods which simulates nuclear subchannels. The measurements are peformed with two-electrical conductivity probes which are known to be adequate for measuring local parameters. The experiments are performed at low flow rate and the system pressure less than 3 atmo spheric pressure. In this experiment, (equation omitted), is not measured, but quoted from well-known empirical correlation to formulate $C_{o}$. Finally, $C_{o}$ is expressed as a function of channel averaged void fraction. fraction.

• Journal of Korean Society of Steel Construction
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• v.17 no.3 s.76
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• pp.263-270
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• 2005

This paper presents a program for protecting vehicles against side winds on highways. The present study consists of three processes. The first one involves giving a guideline for evaluating driving safety in high winds. The second one involves making a guideline for determining the necessity of wind protection system for a certain road area. A reasonable procedure is suggested based on the probability model of wind data on weather stations and the correction of local topographical conditions. The third one involves design of wind barriers. Both CFD analyses and wind tunnel tests were performed to find the proper type of wind barrier considering vehicle controllability, structural safety, economical efficiency as well as driver's visibility. Performance of the designed wind fences was verified from field tests. The performance of the four different types of wind barrier installed at the elevated bridge were tested and some of the results were provided.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.8C
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• pp.1175-1183
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• 2004

This paper propose a method to trace a moving object based on the information directly obtained from MPEG-2 compressed video stream without decoding process. In the proposed method, the motion flow is constructed from the motion vectors involved in compressed video and then we calculate the amount of pan, tilt, zoom associated with camera operations using generalized Hough transform. The local object motion can be extracted from the motion flow after the compensation with the parameters related to the global camera motion. The moving object is designated initially by a user via bounding box. After then automatic tracking is performed based on the mean-shift algorithm of the motion flows of the object. The proposed method can improve the computation speed because the information is directly obtained from the MPEG-2 compressed video, but the object boundary is limited by blocks rather than pixels.

• Korean Journal of Agricultural Science
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• v.30 no.2
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• pp.164-174
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• 2003

This study was performed to suggest a rational method for the stability evaluation of agricultural reservoir in the very soft ground. The stability methods for agricultural reservoir was used to compare and analyze with various condition by limit equilibrium method. The behavior of settlement-displacement obtained by field monitoring system was used to compare and analyze with various stability methods, and to investigate the applicability of the methods for stability evaluation of agricultural reservoir. The horizontal displacement was abruptly increased when physical properties of soft clay reached its maximum values and therefore, the values of these properties could be used to the fundamental data for stability evaluation. The evaluation of the stability of agricultural reservoir was suggested to use the inclination of curve rather than critical line.

• Tunnel and Underground Space
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• v.25 no.5
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• pp.435-449
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• 2015

Physical and microstructural properties of Pungchon and Maggol limestone were investigated quantitatively during 50 cycles of artificial freezing and thawing test. There were decrease in dry weight and P,S-wave velocity, and increase in absorption rate in both rock types. Porosity, pore volume, equivalent diameter, throat thickness and pore orientation were analyzed using X-ray computed tomography images. Porosity increased, and initiation and expansion of pores were investigated as weathering progresses. Physical and microstructural variation in Maggol limestone was larger than that of Pungchon limestone because Maggol limestone has more pores and microcracks at initial state. As this study analyzes physical and microstructural properties of rock specimens comprehensively, it can be applied to further rock weathering study and can be used as fundamental data of construction and resource development in cold regions.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.38 no.2
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• pp.179-190
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• 2001

In this proposed study, observing and analyzing contrast enhanced abdominal CT images, we segmented the liver automatically. We computed the ratio of each gray value from the estimated gray value range. With the average value of mesh image, we distinguished the liver from the noise parts. We divided the region based on immersion simulation. The threshold value is determined from the mesh image which is generated from each gray value portion of the liver and is used in dividing the liver to the noise region. To get the outline of the liver, we generated template image which represents the lump of the liver, and subtracted it from the binary image. With the results we use the proposed algorithm using 8-connectivity instead of the present opening algorithm, to reduce the processing time. We computed the volume from the segmented organ size and presented a clinical demonstration with the animal experiment