• 한국전산유체공학회:학술대회논문집
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• 2008.10a
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• pp.347-354
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• 2008

We introduce a series of studies on turbulent skin friction drag reduction in wall-turbulence. First, an identity equation relating the skin friction drag and the Reynolds shear stress (the FIK identity) is introduced. Based on the implication of the FIK identity, a new analytical suboptimal feedback control law requiring the streamwise wall-shear stress only is introduced and direct numerical simulation (DNS) results of turbulent pipe flow with that control is reported. We also introduce DNS of an anisotropic compliant surface and parameter optimization using an evolutionary optimization technique.

• The Korean Journal of Applied Statistics
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• v.25 no.4
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• pp.641-650
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• 2012

Spatial time series data can be viewed as a set of time series simultaneously collected at a number of spatial locations. This paper studies Bayesian inferences in a spatial time bilinear model with a Gibbs sampling algorithm to overcome problems in the numerical analysis techniques of a spatial time series model. For illustration, the data set of mumps cases reported from the Korea Center for Disease Control and Prevention monthly over the years 2001~2009 are selected for analysis.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.5 no.3
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• pp.36-42
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• 2006

The analytical realization of uncoupled system was introduced in this study using times series and its spectrum analysis. The ARMAX spectra of time series methods were compared with the conventional FFT spectrum. Also, the response of second order system uncoupled was solved using the Runge-Kutta Gill method. In this numerical analysis, the displacement, velocity and acceleration were calculated. The displacement response among them was used for the power spectrum analysis. The ARMAX algorithm in time series was proved to be appropriate for the mode estimation and spectrum analysis. Using the separate response of first and second mode, each modes were calculated separately and the response of mixed modes was also analyzed for the mode estimation using several time series methods.

• Journal of the Korean Society of Hazard Mitigation
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• v.8 no.1
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• pp.133-138
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• 2008

To analyze incident waves traveling from the deep ocean is very important in that it is based on resolving problems occurred in coastal areas. In general, numerical models and analytical solutions are used to analyze wave transformation. Although a numerical model can be applied to various bottoms and wave conditions, it may have some cumbersome numerical errors. On the other hand, an analytical solution has an advantage of obtaining the solution quickly and accurately without numerical errors. The analytical solution can, however, be utilized only for specific conditions. In this study, the analytical solution of the mild-slope equation has been developed. It can be applied to various conditions combing a numerical technique and an analytical approach while minimizing the numerical errors. As a result of comparing the obtained solutions in this study with those of the previously developed numerical model, A good agreement was observed.

• Journal of Soil and Groundwater Environment
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• v.13 no.5
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• pp.33-46
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• 2008

A series of three-dimensional numerical simulations using a generalized multidimensional hydrodynamic dispersion numerical model is performed to simulate effectively and to evaluate quantitatively impacts of fault existence on densitydependent groundwater flow and salt transport in coastal aquifer systems. A series of steady-state numerical simulations with calibration is performed first for an actual coastal aquifer system which contains a major fault. A series of steadystate numerical simulations is then performed for a corresponding coastal aquifer system which does not have such a major fault. Finally, the results of both numerical simulations are compared with each other and analyzed. The results of the numerical simulations show that the major fault produces hydrogeologically significant heterogeneity and true anisotropy in the actual coastal aquifer system, and density-dependent groundwater flow, salt transport, and seawater intrusion patterns in the coastal aquifer systems are intensively and extensively dependent upon the existence or absence of such a major fault. Especially, the major fault may act as a pathway for groundwater flow and salt transport along the direction parallel to its plane, while it may also behave as a barrier against groundwater flow and salt transport along the direction perpendicular to its plane.

• Journal of Korean Tunnelling and Underground Space Association
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• v.8 no.2
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• pp.151-163
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• 2006

Although various methods for effective modeling of pre-reinforced zones have been suggested for numerical analysis of large section tunnels, tunnel designers refer to empirical cases and literature reviews rather than engineering methods because ones who use commercial programs are unfamiliar with a macro-scale approach in general. Therefore, this paper suggests a simple micro-scale approach combined with the macro-scale approach to determine equivalent design parameters for effective numerical modeling of pre-reinforced zones in tunnel. This new approach is to determine the equivalent stiffness of pre-reinforced zones with combination of ground, bulb, and steel in series or/and parallel. For verification, 3-D numerical results from the suggested approach are compared with those of a realistic model. The comparison suggests that two cases make best approximation to a realistic solution: One is related to the series-parallel stiffness system (hereafter SPSS) in which bulb and steel are coupled in parallel and then connected to the ground in series, and the other is the series stiffness system (hereafter SSS) in which only bulb and steel are coupled in series. The SPSS is recommended for stiffness calculation of pre-reinforced zones because the SSS is inconvenient and time-consuming. The SPSS provides slightly bigger vertical displacement at tunnel crown in weathered rock than other cases and give almost identical results to a realistic model for horizontal displacement at tunnel spring line and ground surface settlement. Displacement trends on weathered rock and weathered soil are similar. The SPSS which is suggested in this paper represents the behavior mechanism of pre-reinforced area effectively.

• Journal of Sensor Science and Technology
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• v.31 no.5
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• pp.353-359
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• 2022

This study investigated via computational analysis the application utility of series-cascaded ring resonators based on silicon-on-insulator (SOI) slot optical waveguides in integrated optical biochemical sensors. The radii of the two rings in the series-cascaded ring resonators were 59.4 ㎛ and 77.6 ㎛ respectively, and the coupling distance was 0.5 ㎛. The series-cascaded ring resonators were computationally analyzed using FIMMProp and PICWave numerical software. The free spectral range (FSR), full width at half maximum (FWHM), sensitivity, and quality-factor (Q-factor) of the series-cascaded ring resonators were 12.2 nm, 0.134 nm, 4100 nm/RIU, and 11580, respectively, and the measurement range was calculated to be slightly smaller than 3×10^-3 RIU. Although the measurement range was smaller than that of the single ring resonator, upon considering other characteristic parameters, the series-cascaded ring resonators are found to be more effective as integrated sensors than single ring resonators.

• Journal of the Korean Society of Safety
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• v.12 no.4
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• pp.27-38
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• 1997

The effect of geometry factors on the combined mode stress intensity factor behaviors of a slant crack in a non-uniform thickness material was analysed by 2-dimensional theoretical analysis. The analysis is based on the Laurent's series expansions of complex potentials where the complex coefficients of the series are determined from the compatibility and the equilibrium conditions of the thickness interface and the stress free conditions of the crack surface. In numerical calculations the perturbation technique is employed. The expressions for the crack tip stress intensity factor are given in the form of power series of dimensionless crack length $\lamda$, and the function of crack slant angle $\alpha$ and thickness ratio $\beta$. The results of numerical calculations for each problems are represented as the correction factors F($\lamda$, $\alpha$, $\beta$). The results clearly show the following characteristics : The correction factors of the combined mode stress intensity factors for a non-uniform thickness material can be defined in the form of F($\lamda$, $\alpha$, $\beta$). The stress intensity factor values for a given crack length are decreased with increase of thickness ratio $\beta$.

• International Journal of Naval Architecture and Ocean Engineering
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• v.13 no.1
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• pp.50-56
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• 2021

An accurate evaluation of three-dimensional (3D) Time-Domain Green Function (TDGF) in infinite water depth is essential for ship's hydrodynamic analysis. Various numerical algorithms based on the TDGF properties are considered, including the ascending series expansion at small time parameter, the asymptotic expansion at large time parameter and the Taylor series expansion combines with ordinary differential equation for the time domain analysis. An efficient method (referred as "Present Method") for a better accuracy evaluation of TDGF has been proposed. The numerical results generated from precise integration method and analytical solution of Shan et al. (2019) revealed that the "Present method" provides a better solution in the computational domain. The comparison of the heave hydrodynamic coefficients in solving the radiation problem of a hemisphere at zero speed between the "Present method" and the analytical solutions proposed by Hulme (1982) showed that the difference of result is small, less than 3%.

• Structural Engineering and Mechanics
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• v.86 no.1
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• pp.69-83
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• 2023

Analytical solutions to problems are crucial because they provide high-quality comparison data for assessing the accuracy of numerical solutions. Benchmark analytical solutions for the vibrations of cracked functionally graded material (FGM) plates are not available in the literature because of the high level of complexity of such solutions. On the basis of first-order shear deformation plate theory (FSDT), this study proposes analytical series solutions for the vibrations of FGM rectangular plates with side or internal cracks parallel to an edge of the plates by using Fourier cosine series and the domain decomposition technique. The distributions of FGM properties along the thickness direction are assumed to follow a simple power law. The proposed analytical series solutions are validated by performing comprehensive convergence studies on the vibration frequencies of cracked square plates with various crack lengths and under various boundary condition combinations and by performing comparisons with published results based on various plate theories and the theory of three-dimensional elasticity. The results reveal that the proposed solutions are in excellent agreement with literature results obtained using the Ritz method on the basis of FSDT. The paper also presents tabulations of the first six nondimensional frequencies of cracked rectangular Al/Al2O3 FGM plates with various aspect ratios, thickness-to-width ratios, crack lengths, and FGM power law indices under six boundary condition combinations, the tabulated frequencies can serve as benchmark data for assessing the accuracy of numerical approaches based on FSDT.