• Structural Engineering and Mechanics
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• v.6 no.1
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• pp.63-76
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• 1998

This paper presents dynamic responses of structures with sliding base which limits the translation of external loads from ground excitation. A discrete element model based on the discontinuous deformation analysis method is proposed to study this sliding boundary problem. The sliding base is simulated using sets of fictitious contact springs along the sliding interface. The set of contact spring is to translate friction force from ground to superstructure. Validity of the proposed model is examined by the closed-form solutions of an idealized mass-spring structural model subjected to harmonic ground excitation. This model is also applied to a problem of a three-story structural model subjected to the ground excitation of 1940 El Centro earthquake. Analyses of both sliding-base and fixed-base conditions are performed as comparisons. This study shows that using this model can simulate the dynamic response of a sliding structure with frictional cut-off quite accurately. Results reveal that lowering the frictional coefficient of the sliding joint will reduce the peak responses. The structure responses in little deformation, but it displaces at the end of excitation.

• Geomechanics and Engineering
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• v.7 no.4
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• pp.431-458
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• 2014

Construction of a new cavern close to an existing cavern will result in a modification of the state of stresses in a zone around the existing cavern as interaction between the twin caverns takes place. Extensive plane strain finite difference analyses were carried out to examine the deformations induced by excavation of underground twin caverns. From the numerical results, a fairly simple nonparametric regression algorithm known as multivariate adaptive regression splines (MARS) has been used to relate the maximum key point displacement and the percent strain to various parameters including the rock quality, the cavern geometry and the in situ stress. Probabilistic assessments on the serviceability limit state of twin caverns can be performed using the First-order reliability spreadsheet method (FORM) based on the built MARS model. Parametric studies indicate that the probability of failure $P_f$ increases as the coefficient of variation of Q increases, and $P_f$ decreases with the widening of the pillar.

• Proceedings of the Korea Society for Simulation Conference
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• 1999.10a
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• pp.186-191
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• 1999

The coagulation process of PAN (poly(acrylonitrile)) wet-spinning was modeled and simulated based on the numerical analysis of the coagulation of a viscous polymer solution by diffusional interchange with a bath. Experiments were performed with gelled solutions of PAN in nitric acid to determine the diffusion rate of solvent and nonsolvent (water) during the coagulation. The experimental data were analyzed by using equations of diffusion coefficient which are the function of the solvent concentrations of the coagulation bath and the filament. The concentration profile of solvent in moving filament was predicted by solving the diffusion model equation numerically. A simplex method was used in the computation of the parameters of the diffusion equations to minimize the difference between the numerical results and experimental data.

• Journal of Aerospace System Engineering
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• v.9 no.4
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• pp.62-66
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• 2015

During the conceptual design of turboprop aircraft, the power effect driven from rotating propeller is typically obtained from empirical data. In the present paper, propeller power effect was obtained by using unsteady three-dimensional Navier-Stokes solver with $k-{\omega}$ turbulence model for the accurate prediction of turboprop aircraft performance. In order to simulate the relative motion between propeller and fuselage, unsteady sliding mesh method was used. During simulation, three flow conditions such as climb, cruise and descending flight were selected considering the flight envelop of the real turboprop aircraft. For the correction of aerodynamic coefficients, the thrust effect of engine exhaust gas was included based on the engine manufacturer's data. Using the computational results, the correction table for the aerodynamic coefficient of turboprop aircraft was suggested for the performance analysis of turboprop aircraft.

• Proceedings of the IEEK Conference
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• 2002.06a
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• pp.171-174
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• 2002

In this study, we proposed a specification which is able to estimate tile uncertainty more easily and quickly and also able to maintain a confidence level when measuring tile magnitude and phase of 1-port and 2-port transmission.reflection coefficient using a VNA and attached coaxial cable probes. This proposed specification is available when it needs extra special condition of uncertainty estimation and when there is no additional standard equipment like as beadless airline or mismatch standard at the measurement institute. We compared and examined this proposed uncertainty estimation method with recommended EA specification and Agilent specification. As a result, we think that this proposed specification can be used as a reference for uncertainty estimation and calculation of VNA system, that is, a reference based on the IS0/1EC 17025 requirements.

• Korean Journal of Remote Sensing
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• v.31 no.1
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• pp.21-28
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• 2015

The essential idea of de-noising is referring to neighboring pixels of a center pixel to be updated. Conventional adaptive de-noising filters use local statistics, i.e., mean and variance, of neighboring pixels including the center pixel. The drawback of adaptive de-noising filters is that their performance becomes low when edges are contained in neighboring pixels, while anisotropic diffusion de-noising filters remove adaptively noises and preserve edges considering intensity difference between neighboring pixel and the center pixel. The anisotropic diffusion de-noising filters, however, use only intensity difference between neighboring pixels and the center pixel, i.e., local statistics of neighboring pixels and the center pixel are not considered. We propose a new connectivity function of two adjacent pixels using statistics of neighboring pixels and apply connectivity function to diffusion coefficient. Experimental results using an aerial image corrupted by uniform and Gaussian noises showed that the proposed algorithm removed more efficiently noises than conventional diffusion filter and median filter.

• International Journal of Fluid Machinery and Systems
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• v.3 no.1
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• pp.29-38
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• 2010

This paper presents a procedure for the design optimization of a centrifugal compressor. The centrifugal compressor consists of a centrifugal impeller, vaneless diffuser and volute. And, optimization techniques based on the radial basis neural network method are used to optimize the impeller of a centrifugal compressor. The Latin-hypercube sampling of design-of-experiments is used to generate the thirty design points within design spaces. Three-dimensional Reynolds-averaged Navier-Stokes equations with the shear stress transport turbulence model are discretized by using finite volume approximations and solved on hexahedral grids to evaluate the objective function of the total-to-total pressure ratio. Four variables defining the impeller hub and shroud contours are selected as design variables in this optimization. The results of optimization show that the total-to-total pressure ratio of the optimized shape at the design flow coefficient is enhanced by 2.46% and the total-to-total pressure ratios at the off-design points are also improved significantly by the design optimization.

• Journal of Electrical Engineering and information Science
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• v.2 no.5
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• pp.114-120
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• 1997

A design method is newly presented for the creation of planar type filters which shapes will be nonuniform transmission line with continuously varying characteristic impedances. Those filters yield frequency characteristics of the bandstop filter in transmission, and have not nay discontinuities. The design is achieved by the control of wave propagation in view to both reflection an transmission properties on the dispersive nonuniform line within the desired frequency band. The developed algorithm is based on optimized perturbations of inherent nulls of lobes from the solution of first-order nonlinear differential equation for reflection coefficients of the nonuniform line, and an appropriate distribution of reflection coefficient which affects to filter length and bandwidth. Practical measurements for designed wideband microstrip and stop filter show very good agreement with theoretical results.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.55 no.7
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• pp.306-312
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• 2006

Support Vector Machine(SVM), of which the foundations have been developed by Vapnik (1995), is gaining popularity thanks to many attractive features and promising empirical performance. In this paper, we propose a new short-term load forecasting technique based on SVM. We discuss the input vector selection of SVM for load forecasting and analyze the prediction performance for various SVM parameters such as kernel function, cost coefficient C, and $\varepsilon$ (the width of 8 $\varepsilon-tube$). The computer simulation shows that the prediction performance of the proposed method is superior to that of the conventional neural networks.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.51 no.2
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• pp.83-91
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• 2002

This paper presents a new speed and position sensorless control method of permanent magnet synchronous motors based on the sliding mode observer. Since the parameter of the dynamic equation such as machine inertia or viscosity friction coefficient are not well known and these values can be easily changed generally during normal operation, there are many restrictions in the actual implementation. The proposed adaptive sliding mode observer applies adaptive scheme so that observer may overcome the problem caused by using the dynamic equation. Furthermore, using the Lyapunov Function, the adaptive sliding mode observer can estimate rotor speed as well as stator resistance. The feasibility of the Proposed observer is verified cia the experiments.