• 제어로봇시스템학회:학술대회논문집
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• 2001.10a
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• pp.151.5-151
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• 2001

Sliding mode control is investigated for a discrete-time system with uncertainties. The narrowest neighborhood of the sliding surface is shown in which the state can remain. The range is determined by the upper bound of the absolute value of the uncertainty and the equation of the sliding surface. A sliding mode control algorithm is proposed to keep the state there without requiring an enormous input. Under the presence of the system parameter variations, the origin is not always stable although the sliding surface represents the stable dynamics and the state is kept in this neighborhood. The condition for the origin to be stable is investigated. Furthermore, the problems occurring when a continuous-time sliding mode control being ...

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.646-651
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• 2002

The flow field around a symmetrical airfoil in a uniform flow under the generation of noise was studied by experiments and numerical simulation. The experiments are conducted by visualizing the surface flow over the airfoil with a shear-sensitive liquid-crystal coating and by measuring the instantaneous velocity field around the trailing edge of the airfoil. The results indicate that the discrete frequency noise is generated when the separated laminar flow reattaches near the trailing edge of the pressure side and the turbulent boundary layer is formed over the suction side of the airfoil near the trailing edge. The periodic behavior of vortex formation was observed around the trailing edge and it persists further downstream in the wake. The frequency of the vortex formation in the wake was consistent with that of the discrete frequency noise.

• Journal of Korean Association for Spatial Structures
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• v.19 no.3
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• pp.41-50
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• 2019

The stone pagoda continued to be damaged by weathering and corrosion over time, and natural disasters such as earthquake are accelerating the destruction of cultural properties. Stone pagoda has discontinuous structure behavior and is very vulnerable to the seismic load acting in lateral direction. It is necessary to analyze various design variables as the contact surface characteristics play an important role in the dynamic behavior of stone pagodas. For this purpose, contact surface characteristics of stone pagoda can be classified according to surface roughness and filler type, and representative model is selected and structural modeling and analysis are performed using the discrete element method. Also, the seismic load according to the repetition period is calculated and the dynamic analysis is performed considering the discontinuous characteristics of the stone pagoda. Finally, the seismic behavior characteristics can be analyzed by the evaluation of stresses, displacements and structural safety.

• Nuclear Engineering and Technology
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• v.52 no.6
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• pp.1137-1147
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• 2020

The discrete ordinates method (S_N) is one of the major shielding calculation method, which is suitable for solving deep-penetration transport problems. Our objective is to explore the available quadrature sets and to improve the accuracy in shielding problems involving strong anisotropy. The linear discontinuous finite-element (LDFE) quadrature sets based on the icosahedron (in short, ICLDFE quadrature sets) are developed by defining projected points on the surfaces of the icosahedron. Weights are then introduced in the integration of the discontinuous finite-element basis functions in the relevant angular regions. The multivariate secant method is used to optimize the discrete directions and their corresponding weights. The numerical integration of polynomials in the direction cosines and the Kobayashi benchmark are used to analyze and verify the properties of these new quadrature sets. Results show that the ICLDFE quadrature sets can exactly integrate the zero-order and first-order of the spherical harmonic functions over one-twentieth of the spherical surface. As for the Kobayashi benchmark problem, the maximum relative error between the fifth-order ICLDFE quadrature sets and references is only -0.55%. The ICLDFE quadrature sets provide better integration precision of the spherical harmonic functions in local discrete angle domains and higher accuracy for simple shielding problems.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.11
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• pp.3560-3572
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• 1996

This paper presents a new discrete-time fuzzy-sliding mode controller for robust vibration control of a smart structure featuring a piezofilm actuator. A governong equation of motion for the smart beam structure is derived and discrete-time codel with mismatched uncertainties such as parameter variations is constructed ina state space. A discrete-time sliding mode control system consisting of an equivalent controller and a discontinuous controller is formulated. In the design of the equivalent part, so called an equivalent controller separation method is adopted to achieve vzster convergence to a sliding surface without extension of a sliding region, in which the system robustness maynot be guaranteed. On the other hand, the discontinuous part is constructed on the basis of both the sliding and the convergence conditions using a time-varying feedback gain. The sliding moide controller is then incorporated with a fuzzy technique to appropriately determine principal control parameters such as a discountinuous feedback gain. Experimental implementation on the forced and random vibraiton controls is undertaken in order to demonstrate superior control performance of the proposed controller.

• Journal of Environmental Science International
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• v.11 no.12
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• pp.1195-1204
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• 2002

We calculated dose rate using radiative transfer equations to consider radiative processes distinctly. The dose rate at Pohang(36°02'N, 129°23'E) was calculated using measured ozone and meteorological data and two-stream approximations(quadrature, Eddington, delta Eddington, PIFM(practical improved flux method), discrete ordinate, delta discrete ordinate) are used in solving equation. The purpose of this study is to determine the most compatible radiative transfer approximation for simulating the radiative and photochemical processes of atmosphere through comparision between calculated and measured values. Dose rate of the biologically effective irradiance in the region 0.28-0.32 U m showed the highest value when quadrature and Eddington was used and lower value on condition that delta scaling was applied. Correlation coefficient between dose rate at surface using radiation transfer equation and measured UV-B at Pohang was 0.78, 0.79 and 0.81 when delta Eddington, PIFM and delta discrete ordinate were used. Also, in case of above approximations were used, MBE(Mean Bias Error) was within -0.3MED/30min and RMBE(Relative Mean Bias Error) was below 10% between 1200 LST and 1400 LST Approximations which are compatible in estimating radiative process are delta Eddington, PIFM and delta discrete ordinate. Especially, in case that radiative process is considered more detail, delta discrete ordinate increased the number of stream is proper.

• Journal of the Korean Chemical Society
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• v.51 no.2
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• pp.136-140
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• 2007

By using the discrete-dipole approximation, we computed the extinction spectrum of a gold-silver alloy nanoparticle. We have examined how the surface plasmon resonance changes with respect to the variation in the composition of the alloy particle. As the fraction of silver increases for a 10nm particle, the peak position of the extinction spectrum blue-shifts linearly. The intensity of the peak however increases exponentially with increasing the silver fraction. These results are in accord with the previous experimental results.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2009.10a
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• pp.241-242
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• 2009

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11a
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• pp.365.2-365
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• 2002

The flow field around a symmetrical airfoil in a uniform flow under the generation of noise was studied by experiments and numerical simulation. The experiments are conducted by visualizing the surface flow over the airfoil with a shear-sensitive liquid-crystal coating and by measuring the instantaneous velocity field around the trailing edge of the airfoil. The numerical simulation was carried out by LES. (omitted)

• Journal of Advanced Research in Ocean Engineering
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• v.2 no.1
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• pp.1-11
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• 2016

The objective of this paper is to present an analytical solution in deep water waves and verify the validity of the theory (Shin, 2015). Hence this is a follow-up to Shin (2015). Instead of a variational approach, another approach was considered for a more accurate assessment in this study. The products of two coefficients were not neglected in this study. The two wave profiles from the KFSBC and DFSBC were evaluated at N discrete points on the free-surface, and the combination coefficients were determined for when the two curves pass the discrete points. Thus, the solution satisfies the differential equation (DE), bottom boundary condition (BBC), and the kinematic free surface boundary condition (KFSBC) exactly. The error in the dynamic free surface boundary condition (DFSBC) is less than 0.003%. The wave theory was simplified based on the assumption tanh $D{\approx}1$ in this paper. Unlike the perturbation method, the results are possible for steep waves and can be calculated without iteration. The result is very simple compared to the 5th Stokes' theory. Stokes' breaking-wave criterion has been checked in this study.