• Computers and Concrete
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• 제1권2호
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• pp.189-209
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• 2004

Several extensions to the Thelandersson phenomenological model for concrete under transient high temperatures are explored. These include novel expressions for the temperature degradation of the elastic modulus and the temperature dependency of the coefficient of the free thermal strain. Furthermore, a coefficient of thermo mechanical strain is proposed as a bi-linear function of temperature. Good qualitative agreement with various test results taken from the literature is demonstrated. Further extensions include the effects of plastic straining and temperature dependent Poisson's ratio. The models performance is illustrated on several simple benchmark problems under uniaxial and biaxial stress states.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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• pp.1059-1060
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• 2006

The creep behavior of Al-5vol.% SiC composite was investigated. The composite powder was produced by mechanical milling and hot extruded at $450^{\circ}C$ at ratio of 16:1. A creep test was carried out at a constant load at 598, 648, and 673 K. Using the steady-state equations, the threshold stress and the stress exponent of the creep as a function of temperature were determined. The stress exponent was found to be 3 at the temperature of 673 K and 8 at 598 and 648 K. The dependency of the threshold stress to temperature obeys the Arrhenius relationship with the energy term of $29\;kJ\;mole^{-1}$.

• 한국농공학회지
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• 제40권1호
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• pp.106-117
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• 1998

The nature of stress-path dependency, the principle that governs deformations in granular soil, and the use of Lade's double work-hardening model for predicting soil response for a variety of stress-paths have been investigated, and are examined The test results and the analyses presented show that under some conditions granular soils exhibit stress-path dependent behavior. For stress-paths involving unloading or reloading, the stress-path with the higher average stress level produces the larger strains, whereas all stress-paths having the same intial states of stress, and involving only primary loading conditions, produce strains of similar magnitudes. Experimental evidence indicates that the stress- path dependent response obtained from the double work-hardening model is also observed for real soils. It is concluded that the influence of stress history on the friction angle is negligible and the strains increment direction is uniquely determined from the state of stress but is not perpendicular to the yield surface. The strains calculated from Lade's double work-hardening model are in reasonable agreement with those measured.

• 대한조선학회논문집
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• 제44권4호
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• pp.370-378
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• 2007

In this study. a numerical analysis has been performed for the turbulent flow around a 15,000TEU twin-skeg container ship using a commercial CFD code. FLUENT. The computed results have been compared with the model test data from MOERI. We investigated viscous resistance coefficient. wake distribution and characteristics of the shear flow according to the grid numbers. Although the free surface is approximated by the plane of symmetry in this work. the calculated axial velocity and transverse vector show a good agreement with the MOERI experimental data except for the region of 0.9 level of axial velocity at the propeller plane. The numerical analysis show that commercial CFD code is useful tool for the evaluation of complex hull form with twin-skegs.

• 전자공학회논문지B
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• 제29B권10호
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• pp.78-89
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• 1992

In this paper, a multiresolution edge detction algorithm for speckle images is proposed. Due to the signal dependency of speckle images, the number of edge points detected depends on the local average intensity. Thus the edge detection method independent of the average intensity is required to detect properly real significant changes in an original signal. In the proposed method, candidate area is first selected based on the statistical propeties of speckle images,i.e., based on the busyness measure such as the CoV(coefficient of variation) and the difference between the real and theoretical CDF(cumulative density function). Then the real edges are extracted in a multiresolution environment. Computer simulation with test images shows that the proposed method reduces significantly false edges in relatively homogeneous areas while detects fine details properly.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.524-527
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• 2004

Hybrid rocket had many advantage with compared to solid and liquid rockets. However, the engines have not yet been used in practical rocket systems, due mainly to the disadvantage of hybrid combustion, such as low fuel regression rate. In this study, lab-scale hybrid motor was designed and manufactured. And the methods of regression rate improvement were considered. Test firings with thrusts up to 300 N were conducted with GOX and transparent PMMA. Thrust was calculated with the pressure of the combustion chamber and the regression rate was measured in with variation of oxidizer flow rate. The regression rates showed a strong dependency on GOX mass flux. The frequency analysis technique of the bulk-mode oscillation of motor was applied to a hybrid rocket motor and was based on the principle that this frequency was inversely proportional to the square root of the chamber volume. Several problems and solutions of operating hybrid rocket were presented.

• Communications for Statistical Applications and Methods
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• 제13권2호
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• pp.297-307
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• 2006

Most methods for describing the relationship among random variables require specific probability distributions and some assumptions of random variables. The mutual information based on the entropy to measure the dependency among random variables does not need any specific assumptions. And the redundancy which is a analogous version of the mutual information was also proposed. In this paper, the redundancy and mutual information are explored to multi-dimensional categorical data. It is found that the redundancy for categorical data could be expressed as the function of the generalized likelihood ratio statistic under several kinds of independent log-linear models, so that the redundancy could also be used to analyze contingency tables. Whereas the generalized likelihood ratio statistic to test the goodness-of-fit of the log-linear models is sensitive to the sample size, the redundancy for categorical data does not depend on sample size but its cell probabilities itself.

• 대한산업공학회지
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• 제39권3호
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• pp.183-191
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• 2013

We address the power generation mix problem that considers not only nuclear and fossil fuels such as oil, coal and LNG but also renewable energy technologies. Unlike nuclear or other generation technologies, the expansion plan of renewable energy is highly uncertain because of its dependency on the government policy and uncertainty associated with technology improvements. To address this issue, we conduct a delphi survey and forecast the capacity of renewable energy. We further propose a stochastic mixed integer programming model that determines an optimal capacity expansion and the amount of power generation using each generation technology. Using the proposed model, we test eight generation mix scenarios and particularly evaluate how much the expansion of renewable energy contributes to the total costs for power generation in Korea. The evaluation results show that the use of renewable energy incurs additional costs.

• 한국IT서비스학회지
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• 제7권1호
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• pp.195-204
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• 2008

As the dependency to network system and demands of efficient storage systems rapidly grows in every networking filed, the current trends initiated by explosive networked data grow due to the wide-spread of internet multimedia data and internet requires a paradigm shift from computing-centric to data-centric in storage systems. Furthermore, the new environment of file systems such as SAN(Storage Area Network) is adopted to the existing storage paradigm for providing high availability and efficient data access. We describe the design issues and system components of $SANique^{TM}$, which is the cluster file system based on SAN environment. We, especially, present the comparative results of performance analysis for the intensive I/O test by using the DBMSs that are operated at the top of cluster file system $SANique^{TM}$, EXT3 and NFS respectively.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1998년도 추계학술대회 논문집 학회본부A
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• pp.97-99
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• 1998

This paper presents a numerical study of the behavior of the transformer winding, when stressed by the standard impulse voltage. The mathematical model of the transformer takes several points into the account. Capacitance of not adjacent winding as well as adjacent winding, eddy current loss caused by self and mutual inductance given as the functions of frequency. Not like the previous approach where calculation of capacitance is performed, in average sense. In this paper, capacitance of both adjacent and not adjacent winding is calculated using the numerical approach(B.E.M.), so they can get the more accurate value of capacitance. Because of frequency dependency of inductance, numerical-laplace-transform technique is required. Finally, to validate this approach, a simple test winding is simulated.