• Journal of the Korean Institute of Navigation
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• v.10 no.2
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• pp.83-96
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• 1986

In the restricted sea way such as fair way in harbor, narrow channel etc, the safe ship-handling is a very important problem, which is greatly related with turning ability of ships. It is of great importance that ship-handlers can grasp the position of pivoting point varying with time increase at any moment for relevant steering activities. Mean while, in advanced ship-building countries they study and investigated pivoting point related with turning characteristics, hut their main interest lies in ship design, not in safe ship controlling and maneuvering. In this regards it is the purpose of this paper to provide ship-handlers better under standing of pivoting point location together with turning characteristics and then to help them in safe ship-handling by presenting fact that pivoting points vary according to configuration of ships. The author calculated the variation of pivoting point as per time increase for various type of vessels, based on the hydrodynamic derivatives obtained at test of Davidson Laboratory of Stevens Institutes of Technology , New Jersey, U.S.A. The results were classified and investigated according to the magnitude of block coefficient , length-beam ratio, length-draft ratio, rudder area ratio ete, and undermentioned results were obtained. (1) The trajectory of pivoting point due to variation of rudder angle are all the same at any time, though the magenitude of turning circle are changed variously. (2) The moving of pivoting point is affected by the magnitude of block coefficient, length-beam ratio, length-draft ratio, however the effect by rudder area ratio might be disregarded. (3) In controlling and maneuvering of vessels in harbor, ship-handlers might regard that the pivoting point would be placed on 0.2~0.3L forward from center of gravity at initial stage. (4) The pivoting point of VLCC or container feeder vessels which have block coefficient more than 0.8 and length-beam ratio less than 6.5 are located on or over bow in the steady turning. (5) When a vessel intends to avoid some floating obstruction such as buoy forward around her eourse, the ship-handler might consider that the pivoting point would be close by bow in ballast condition and cloase by center of gravity in full-loaded condition.

• International Journal of Highway Engineering
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• v.11 no.4
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• pp.127-132
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• 2009

This study presents the test results on the compaction characteristics of warm mix asphalt mixtures that include the additive in 3 different mixtures(hot mix asphalt, SBS and SMA). The tests were conducted to find out the compaction characteristics on the compactability with varying compaction time, different amount of the warm mix additive and lowering the compaction temperature. The Superpave gyratory compactor was used to find out the variation of the density when the number of the gyration is varied. A dense mixture and 3 different warm mix additives were employed to find the relationship between compactability and compaction time. The comparison of the compactability with lowering the temperature was conducted using dense mixture, SBS polymer modified mixture and stone matrix asphalt mixture(SMA). The difference of the density of warm mix asphalt mixtures was not found due to the lowering of compaction temperature when it was compared with the standard mixture and the warm mix showed the stable condition in density. In the mean time, depending upon the different warm mix additive and mixture, the difference of density and the variation trend of compaction is found to be existed and shows the relationship between these two variables.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.225-225
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• 2015

Drought events usually evolve slowly in time and their impacts generally span a long period of time. This indicates that the sequence of drought is not completely random. The Hidden Markov Model (HMM) is a probabilistic model used to represent dependences between invisible hidden states which finally result in observations. Drought characteristics are dependent on the underlying generating mechanism, which can be well modelled by the HMM. This study employed a HMM with Gaussian emissions to fit the Standardized Precipitation Index (SPI) series and make multi-step prediction to check the drought characteristics in the future. To estimate the parameters of the HMM, we employed a Bayesian model computed via Markov Chain Monte Carlo (MCMC). Since the true number of hidden states is unknown, we fit the model with varying number of hidden states and used reversible jump to allow for transdimensional moves between models with different numbers of states. We applied the HMM to several stations SPI data in South Korea. The monthly SPI data from January 1973 to December 2012 was divided into two parts, the first 30-year SPI data (January 1973 to December 2002) was used for model calibration and the last 10-year SPI data (January 2003 to December 2012) for model validation. All the SPI data was preprocessed through the wavelet denoising and applied as the visible output in the HMM. Different lead time (T= 1, 3, 6, 12 months) forecasting performances were compared with conventional forecasting techniques (e.g., ANN and ARMA). Based on statistical evaluation performance, the HMM exhibited significant preferable results compared to conventional models with much larger forecasting skill score (about 0.3-0.6) and lower Root Mean Square Error (RMSE) values (about 0.5-0.9).

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.2
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• pp.219-225
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• 2013

In this study, the tribological characteristics of silver films that were deposited on a glass substrate by electroless plating were investigated. The electroless-plating method has many notable advantages. It is easy and economical to obtain solid films using this coating process, and it can be applied to both nonconducting and conducting substrates. In this study, silver was selected as the electroless-plating material because it is one of the most common materials used as a solid lubricant. The mechanical properties of silver electroless-plated specimens were investigated for various coating conditions. The thickness of the coating could be controlled by varying the electroless-plating time. The properties of the coatings were investigated using AFM, SEM, and a tribotester.

• International Journal of Automotive Technology
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• v.8 no.6
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• pp.697-704
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• 2007

Recently, a variable valve timing system has been widely adopted in internal combustion engine in order to improve the fuel economy and torque at low engine speed. In addition, it is known that varying valve timing according to the various engine operations could reduce exhaust gas, especially NOx, because of residual gas by valve overlap. In this study, to improve the low exhaust gas and fuel economy at part load condition, the residual gas and back flow of exhaust gas due to valve overlap were calculated computationally. Moreover, the characteristics of engine performances and NOx formations were investigated with the experiment of combination of intake and exhaust valve timing condition. Under these various valve operating conditions, the effects of both the positive valve overlap and negative valve overlap(valve underlap) were examined simultaneously. Finally, the characteristics of cyclic THC emission were analyzed by using Fast Response FID(FR-FID) in the cylinder, intake port and exhaust port positions. Besides, the effect of the different gradients of the valve timing change on engine performance was investigated and an optimum control strategy was suggested.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.22 no.6
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• pp.369-374
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• 2010

A refrigerant-subcooling refrigeration system consisted of a typical single vapor-compression refrigeration cycle, a subcooler, and an ice storage tank. The degree of subcooling at the exit of the condenser can be increased by the heat exchange between the subcooler and the ice storage tank. The cold heat in the ice storage tank was stored by using the refrigeration cycle during night time and then used to absorb the heat from the subcooler during daytime. The performance of the refrigerant-subcooling refrigeration system was measured by varying the degree of subcooling. In addition, the performance characteristics of the present system were compared with those of a conventional refrigeration system. The mass flow rate of the present system was higher than that of the conventional system due to the increase in the degree of subcooling. Generally, the refrigerant-subcooling system showed superior performance to the conventional refrigeration system.

• Journal of Environmental Science International
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• v.26 no.3
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• pp.363-371
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• 2017

This study evaluates the adsorption properties of Sr ions in an aqueous solution of the synthetic zeolite (Z-Y1) prepared using coal fly ash generated from a thermal power plant. In order to investigate the adsorption characteristics, the effects of various parameters such as the initial concentrations of Sr ion, contact time, and solution pH were investigated in a batch mode. The Langmuir and Redlich-Peterson model fitted the adsorption isotherm data better than the Freundlich model. The maximum adsorption capacity of Sr ions, as determined the Langmuir model, was 181.68 mg/g. It was found that by varying the Sr ion concentration, pH, and temperature, the pseudo-second-order kinetic model describes the adsorption kinetics of the Sr ion better than the pseudo-first-order kinetic model. The calculated thermodynamic parameters of ${\Delta}H^0$ and ${\Delta}G^0$ showed that the adsorption of Sr ions on Z-Y1 was occurred through a spontaneous and an endothermic reaction. We found that the adsorption of Sr ions by Z-Y1 was more affected by pH than by temperature and Sr ion concentration.

• ETRI Journal
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• v.31 no.1
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• pp.1-9
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• 2009

Frequency domain analysis is a fundamental procedure for understanding the characteristics of visual data. Several studies have been conducted with 2D videos, but analysis of stereoscopic 3D videos is rarely carried out. In this paper, we derive the Fourier transform of a simplified 3D video signal and analyze how a 3D video is influenced by disparity and motion in terms of temporal aliasing. It is already known that object motion affects temporal frequency characteristics of a time-varying image sequence. In our analysis, we show that a 3D video is influenced not only by motion but also by disparity. Based on this conclusion, we present a temporal anti-aliasing filter for a 3D video. Since the human process of depth perception mainly determines the quality of a reproduced 3D image, 2D image processing techniques are not directly applicable to 3D images. The analysis presented in this paper will be useful for reducing undesirable visual artifacts in 3D video as well as for assisting the development of relevant technologies.

• Journal of computational fluids engineering
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• v.21 no.1
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• pp.86-93
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• 2016

In this paper, heat transfer characteristics of pulsating heat pipes are investigated with the diameter and the number of tubes through the computational analysis of thermal flow. The numerical simulation includes the phase change precess with VOF model using OpenFOAM software. The numerical code is modified for the phase change to occur with saturation temperature. The numerical results are compared with the previous ones to validate the present code. The resonable results have been obtained based on the mass transfer time relaxation parameter considering the density ratio. When the ratio of length to diameter and the number of tubes are on the decrease, the thermal resistances also tends to decrease in the pulsating heat pipes. These numerical results will supply the base line data to design and to manufacture the pulsating heat pipe.

• Journal of Korean Society for Atmospheric Environment
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• v.17 no.6
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• pp.463-474
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• 2001

In this study, the concentrations of major anthropogenic volatile organic compounds(VOCs) which include benzene, toluene, m, p-xylene, o-xylene, and ethylbenzene were measured at the Nan-ji-do landfill site during the spring and fall season of 2000. the temporal distribution characteristics of these VOCs were investigated over varying time scale. According to our study, the mean concentration of those species were computed to be 1.65$\pm$2.68(benzene), 9.62$\pm$9.32(toluene), 1.84$\pm$2.90(m, p-xylene), 0.83$\pm$1.43(o-xylene), and 1.17$\pm$1.21 ppb(ethylbenzene). The VOCs levels in the study area are not distinctively higher than the level typically found in urban area that can be subject to the influence of various anthropogenic source processes. Inspection of their temporal trends exhibited various patterns for the diurnal(and seasonal) cycle. Although each species showed distinctive patterns in temporal distribution trends, we were able to find the strong correlations among most concurrently measured VOCs except for benzene.