• Computers and Concrete
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• 제8권3호
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• pp.243-278
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• 2011

The paper presents simulations of the Brazilian test using two numerical models. Both models are regularized in order to obtain results independent of discretization. The first one, called gradient damage, is refined by additional averaging equation which contains gradient terms and an internal length scale as localization limiter. In the second one, called viscoplastic consistency model, the yield function depends on the viscoplastic strain rate. In this model regularization properties are governed by the assumed strain rate. The two models are implemented in the FEAP finite element package and compared in this paper. Parameter studies of the split test are performed in order to point out the features of each model.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2010년도 춘계 학술논문 발표대회 1부
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• pp.101-104
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• 2010

Development and practical emerging construction technologies has been studied as one of key solution for overcoming these barriers. Many literatures indicated that effective performance evaluation methodologies are demanding for efficient applications of new technologies. This paper presents a performance evaluation methodology using construction simulation technique and introduces studies of two cases where the steel staircase system, as an new technologies was applied and where the conventional method of staircase concrete works. Productivity was measured and calculated by site observation and construction simulations. This results show the quantified influence of new technology to site personnels and assist them to make various decisions for using or not using the technology depending on their own situations.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1992년도 하계학술대회 논문집 A
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• pp.453-456
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• 1992

A Data-based Covariance Matrix(DCM) is introduced in the Eigenvector(EV) method, among subspace methods of estimating multiple sinusoidal frequencies from finite white noisy measurements. It is shown that the EV with the DCM can obtain the true. frequencies from finite noiseless data Some asymptotic results and further improvement on the DCM are also presented mathematically. Monte-carlo simulations are statistically conducted from the view-points of means and standard deviations in the EV's of DCM and Conventional Covariance Matrix(CCM). Simulations show a great promise for using the DCM, particularly for the cases of short data records, closely spaced frequencies and high signal-to-noise ratios.

• 전자공학회논문지D
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• 제34D권11호
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• pp.37-47
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• 1997

Utilizing 2-dimensional device simulations incorporating lattic eheating models, we analyzed in detail the DC breakdown characterisics of NMOS trasistors with different structures, which are commonly used as ESD protection transistors. The mechanism leading to device failure resulting from electrostatic discharge was explained by analyzing the 1st and 2nd breakdown characteristics of LDD devices. Also a criteria for more robust designs of NMOS transistor structures against ESD was suggested by examining the characteristics changes with changes in structural parameters such as the LDD doping concentration, the drain junction depth, the distance between source/drain contacts, and the source junction area.

• 한국전산유체공학회지
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• 제1권1호
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• pp.19-25
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• 1996

A multiblock grid generation has been developed to be reliably used for a Navier-Stokes simulation of the turbomachinery flow-fields A multiblock structure simplifies the creation of structured H-grids about complex turbomachinery geometries and facilitate the creation of a grid in the tip flow region. The numerical algorithm adopts the combination of the algebraic and elliptic method to create the internal grids efficiently and quickly. The grid refinement process is enhanced by developing strategies to utilized Bezier curves and splines along with weighted transfinite interpolation technique and by formulating the grid-imbedding method for the viscous boundary-layer meshes. For purposes of illustration, the grid generator is applied to the high turning turbine rotor blades. Two different types of computational grids are provided to be compared with respect to the grid adaptation to the flow simulations. Extension to three-dimensions was done to show the possibility of its application to the tip-flow simulations. The grid quality of the multiblock structure is good in the passages, with gloval orthogonality and adequate smoothness.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2004년도 추계학술발표대회 논문집
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• pp.147-150
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• 2004

In order to describe the mechanical behavior of highly anisotropic and asymmetric materials such as fiber­reinforced composites, the elastic-plastic constitutive equations were used here based on the recently developed yield criterion and hardening laws. As for the yield criterion, modified Drucker-Prager yield surface was used to represent the orthotropic and asymetric properties of composite materials, while the anisotropic evolution of back­stress was accounted for the hardening behavior. Experimental procedures to obtain the material parameters of the hardening laws and yield surface are presented for 3D Circular Braided Glass Fiber Reinforced Composites. For verification purpose, comparisons of finite element simulations using the elastic-plastic constitutive equations, anisotropic elastic constitutive equations and experiments were performed for the three point bending tests. The results of finite element simulations showed good agreements with experiments, especially for the elastic-plastic constitutive equations with yield criterion considering anisotropy as well as asymmetry and anisotropic back stress evolution rule.

• 대한기계학회논문집
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• 제17권2호
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• pp.426-437
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• 1993

The flowfield of Weis-Fogh type ship's Propulsion is visualized by numerical simulations using the discrete vortex method and by the hydrogen bubble technique. The simulations are performed by assuming that the separations occur at the trailing edge of the wing. The streak lines and time lines are calculated by introducing the tracers at adequate intervals. They agree well with experimental results. The flowfield is unsteady and complex, but the properties of the flow are clarified by numerical and experimental visualization.

• 한국기계가공학회지
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• 제11권5호
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• pp.121-128
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• 2012

The optimization of cooling system parameters for designing injection mold is very important to acquire the highest part quality. In this paper, the integration of computer simulations of injection molding and Analysis of Variance(ANOVA) with orthogonal array was used as a design tool to optimize the cooling system parameters aimed at minimizing the part warpage. The design optimizer was applied to find the optimum levels of cooling system parameters for a dustpan. This optimization resulted in more uniform temperature distribution over the part and significant reduction of a part warpage, showing the capability of present method as an effective design tool. The whole optimization process was performed systematically in a proper number of cooling simulations. The design optimizer can be utilized effectively in the industry practice for designing mold cooling system with less cost and time.

• Journal of Mechanical Science and Technology
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• 제16권1호
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• pp.102-108
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• 2002

Numerical simulations of 1, 2 dichloroethane(EDC) pyrolyisis are conducted to understand the process in the production of the vinyl chloride monomer (VCM) and by-products. A chemical kinetic mechanism Is developed, with the adopted scheme involving 44 gas-phase species and 260 elementary forward and backward reactions. Detailed sensitivity analyses and the rates of production analysis are performed on each of the reactions and the various species, respectively. The concentrations of EDC, VCM, and HCI predicted by this mechanism are in good agreement with those deduced from experiments of commercial and laboratory scale. The mechanism is found to accurately predict the EDC yield an(1 the production of by-products by varying the ranges of pyrolysis temperature, residence time, and pressure which impact on the pyrolysis of 1, 2 dichloroethane. The influence of reactions related to H atom on the relative sensitivity of EDC becomes important as the residence time increases. The pyrolysis of EDC mainly occurs through C$_2$H$_4$Cl$_2$+Cl=CH$_2$CICHI+HCI.

• Wind and Structures
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• 제19권1호
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• pp.75-88
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• 2014

The computational fluid dynamic is used to explore new aspects of the hill flow. This analysis focuses on flow dependency and the comparison of results from measurements and simulations to show an optimization turbulent model and the possibility of replacing measurements with simulations. The first half of the paper investigates a suitable turbulence model for determining a suitable site for a wind turbine. Results of the standard k-${\varepsilon}$ model are compared precisely with the measurements taken in front of the hilltop, The Reynolds Stress Model showed exact results after 1.0 times of hill steepness but the standard k-${\varepsilon}$ model and standard k-${\omega}$ model showed greater underestimation. In addition, velocity flow over Pha Taem hill topography and the reference geometry shape were compared to find a suitable site for a turbine in case the actual hill structure was associated with the trapezoid geometric shape. Further study of geometry shaped hills and suitable sites for wind turbines will be reported elsewhere.