• Journal of the Korean Geotechnical Society
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• v.20 no.3
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• pp.67-74
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• 2004

A case study was performed to verify the applicability of existing formulae for predicting bridge scour in cases where its piers are founded in fine-grained soils. The object of study was the Kanghwa Choji Bridge area where the streambed consists of mainly clayey soil. Site investigation included: direct measurement of scour depths around piers using an ultrasonic probe; and collection of undisturbed soil samples which were later used to determine geotechnical properties and scour rate under different stream velocities. Scour depth prediction was made by employing several conventional methods and compared with the measured value. All methods, not taking soil's intrinsic property against erosion into consideration, overestimated scour depth by a factor of 3.6 to 6.5. On the other hand, the SRICOS method yielded a reasonably acceptable overestimation by a factor of 1.7.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.7
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• pp.1869-1882
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• 1998

In this paper, we investigae convergence behaviors of a differential method for 2-D motion parameter estimation. While the differential method is widely studied for motion compensated prediction in video coding, little attention hs been paid to its convergence properties. Based on the nonseparable exponential covariance image model, we derive the estimates of update terms for the 2- and 6-parameter motion models. And, the effect of noise, spatial correlation, choice of spatial gradient measures, andthe size of a region, are quantitatively anlyzed in relation to the convergence speed. Some empirical results are presented to verify the analysis.

• Steel and Composite Structures
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• v.2 no.6
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• pp.441-460
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• 2002

In the design of bridges, it is important to consider the thermal stresses induced by the non-linear temperature distribution as well as the variation of effective temperature in the bridge deck. To cope with this, design temperature profiles are provided by design codes, which are normally based on extensive research work. This paper presents the results of a comprehensive investigation on the thermal behaviour of bridges in Hong Kong with special emphasis on composite bridges. The temperature distribution in bridges depends primarily on the solar radiation, ambient air temperature and wind speed in the vicinity. Apart from data of the meteorological factors, good estimates of the thermal properties of material and the film coefficients are necessary for the prediction of temperature distribution. The design temperature profiles for various types of composite bridge deck with bituminous surfacing and concrete slab of different thicknesses are proposed. The factors affecting the design effective temperature are also reviewed and suitable values for Hong Kong are proposed. Results are compared with recommendations of the current local code. The method facilitates the development of site-specific temperature profiles for code documents, and it can also be applied to create zoning maps for temperature loading for large countries where there are great climatic differences.

• Journal of the Korean Society of Marine Environment & Safety
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• v.17 no.2
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• pp.97-103
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• 2011

In this study, finite element analysis is performed for consolidation behavior prediction of drainage-installed soft deposits. Finite element analysis is performed under the two strain conditions as small strain with limited application and large strain for relatively thick layers, large deformation and non-linear material properties. The analysis conditions such as layer depth, loading conditions, smear effects are also changed and variation of consolidation behavior for each condition is estimated from ABAQUS program.

• Polymer(Korea)
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• v.30 no.5
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• pp.367-372
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• 2006

Electrochromic materials based on conducting polymers with pendant chromophores as well as their electrochromic properties are described. The conducting polymers described aye polypyrrole, polythiophene, poly(3,4-ethylenedioxythiophene), poly (cyclopentadithiophene), and poly (1,4-bis [2- (3,4-ethylenedioxy) thienyl] benzene). The chromophores described are viologen and perylenetetra-carboxylic diimide. When the wavelength ranges of absorption of the conducting polymer and the chromophore aye not overlapping, multiple electrochromism was achieved. When the wavelength ranges are largely overlapping, higher contrast was achieved. An easy method for prediction of the film thickness for maximum contrast of a given electrochromic material is also described.

• Polymer(Korea)
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• v.26 no.4
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• pp.452-461
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• 2002

In this study, the effect of various concentrations of antioxidants on thermo-oxidative degradation of polyamide 6 was investigated. Unstabilized and stabilized polyamides 6 were subjected to long-term oven aging in ambient atmosphere at 70~$160^{\circ}C$. All of specimens were discolored within 100 hr at temperature range of 70~$160^{\circ}C$. Optimum antioxidant concentration was determined from the data of mechanical properties, yellowness index and relative viscosity. The synergistic effect of each primary and secondary antioxidant concentrations was not observed. Yellowing phenomenon was explained by using NMR, IR and EA. Different carbonyl groups were detected by $^{13}C$/NMR. During thermooxidative degradation, oxygen consumptions were determined by EA. The lifetime after long-term aging was predicted using Arrhenius equation.

• Journal of the Society of Naval Architects of Korea
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• v.29 no.2
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• pp.60-65
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• 1992

The roll response of a ship to random beam seas is investigated in terms of the threshold crossing process. The non-white excitation process is modeled as an equivalent white-noise one based on the assumption that the upcrossing properties of the response can be approximately replaced by the excitation with a white noise process with a suitable intensity. Then the non-linear damping is reinstated. The reinstated equation of motion with the equivalent white-noise intensity is solved using the equivalent non-linear method to get the desired probability density function. The proposed scheme is tested extensively with varing coefficients.

• Journal of the Society of Naval Architects of Korea
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• v.33 no.3
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• pp.22-34
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• 1996

Regarding the plate bending process by line heating method, in this study a simplified numerical analysis is performed for a beam model to predict its residual deformation and stress distribution. Using the modified strip theory and beam finite element method, a PC-based simulation program is developed for a thermo-elastic-plastic beam. The plate bending problem can be approximately replaced by a beam model using distributed springs to account for the effect of adjacent strips. The spring constants are chosen as the best fit with experiments. In this paper, it is assumed that the temperature distribution is already given and the temperature-dependent material properties are considered. To verify the simulation program, the results using present numerical algorithm are compared with other published experimental results and similar numerical studies. The comparison shows good agreement. The present PC-based computer program also shows good efficiency in computing time.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.22 no.10
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• pp.710-718
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• 2010

A numerical study was performed to predict refrigerant charge amount in a mini-channel condenser for a R410A residential air-conditioning system. Multi-channel flat tubes with 12 mini-channels of 1.17 mm average hydraulic diameter for each tube were applied to the condenser. The condenser consisted of 3 passes, and the first, second, and third pass had 44, 19, and 11 tubes, respectively. Each pass was connected by a vertical header. In this study, the condenser was divided into 410 finite volumes, and analyzed by an $\varepsilon$-NTU method. With thermophysical properties and void fraction models for each volume element, the R410A amount distribution and a total charge amount in the condenser were calculated. The predicted total charge amount was compared with the experimentally measured charge amount under a standard ARI A condition. The developed model could predict the charge amount in the mini-channel condenser within prediction errors from -23.9% to -3.0%. Air velocity distribution at the condenser face was considered as non-uniform and uniform by the simulation model, and its results showed that the air velocity distribution could significantly influence the charge amount and vapor phase distribution in the condenser.

• Proceedings of the KSR Conference
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• 2008.06a
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• pp.65-70
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• 2008

This study aims to assess the field application of camber estimation for PC beams in the railroad bridge. Properties of two real-scaled PC beams were investigated by measuring material characteristics and sectional deformation of PC beams during tensioning procedure. The test results indicate that camber deflection was effectively predicted using the simplified analytical model. However, it is also emphasized that consideration on field conditions is required for reliable camber prediction.