• Earthquakes and Structures
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• v.26 no.1
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• pp.59-75
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• 2024

This paper presents a dam-reservoir interaction model that includes, water compressibility, sloshing of surface water, and radiation damping at the far-end reservoir, to investigate the influence of concrete deterioration on seismic behavior along with seismic performance of gravity dams. Investigations on seismic performance of the dam body have been conducted using the linear time-history responses obtained under six real and 0.3 g normalized earthquake records with time durations from 10 sec to 80 sec. The deterioration of concrete is assumed to develop due to mechanical and chemical actions over the dam lifespan. Several computer programs have been developed in FORTRAN 90 and MATLAB programming languages to analyze the coupled problem considering two-dimensional (2D) plane-strain condition. According to the results obtained from this study, the dam structure shows critical responses at the later ages (75 years) that could cause disastrous consequences; the critical effects of some earthquake loads such as Chi-Chi with 36.5% damage and Loma with 56.2% damage at the later ages of the selected dam body cannot be negligible; and therefore, the deterioration of concrete along with its effects on the dam response should be considered in analysis and design.

• Journal of the Korea Concrete Institute
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• v.17 no.2 s.86
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• pp.201-212
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• 2005

A new strut-tie model using secant stiffness, Direct Inelastic Strut-Tie Model, was developed. Since basically the proposed design method uses linear analysis, it is convenient and stable in numerical analysis. At the same time, the proposed design method can accurately estimate the inelastic strength and ductility demands of struts and ties because it can analyzes the inelastic behavior of structure using iterative calculations for secant stiffness. In the present study, the procedure of the proposed design method was established, and a computer program incorporating the proposed method was developed. Design examples using the proposed method were presented, and its advantages were highlighted by the comparison with the traditional strut-tie model. The Direct Inelastic Strut-Tie Model, as an integrated analysis/design method, can directly address the design strategy intended by the engineer to prevent development of macro-cracks and brittle failure of struts. Since the proposed model can analyze the inelastic deformation, indeterminate strut-tie model can be used. Also, since the proposed model controls the local deformations of struts and ties, it can be used as a performance-based design method for various design criteria.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.2
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• pp.197-205
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• 2015

Offshore structures for the gas production are exposed to the risk of gas leaks, and gas explosions can result in fatal damages to the primary structures as well as secondary structures. To minimize the damage from the critical accidents, the study of the dynamic response of structural members subjected to blast loads must be conducted. Furthermore, structural dynamic analysis has to be performed considering relationships between the natural frequency of structural members and time duration of the explosion loading because the explosion pressure tends to increase and dissipate within an extremely short time. In this paper, the numerical model based on time history data were proposed considering the negative phase pressure in which considerable negative phase pressures were observed in CFD analyses of gas explosions. The undamped single degree of freedom(SDOF) model was used to characterize the dynamic response under the blast loading. A blast wall of FPSO topside was considered as an essential structure in which the wall prevents explosion pressures from the process area to utility and working areas. From linear/nonlinear transient analyses using LS-DYNA, it was observed that dynamic responses of structures were influenced by significantly the negative time duration.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2019.11a
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• pp.150-152
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• 2019

In this study, the effects of the wave field changes due to the coastal structure on the hydrodynamic performance of the OWC wave energy, converter are analyzed using a three-dimensional numerical wave tank technique (NWT). The OWC device is simulated numerically by introducing a linear pressure drop model, considering the coupling effect between the turbine and the OWC chamber in the time domain. The flow distribution around the chamber is different due to the change of reflection characteristics depending on the consideration of the breakwater model. The wave energy captured from the breakwater is spatially distributed on the plane of the front of the breakwater, and the converted pneumatic power increased when concentrated in front of the chamber. The change of the standing wave distribution is repeated according to the relationship between the incident wavelength and the length of the breakwater, and the difference in energy conversion performance of the OWC was confirmed.

• 전자공학회논문지 IE
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• v.43 no.4
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• pp.99-104
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• 2006

The Langmuir-Blodgett(LB) technique has attracted considerable interest in the fabrication of electrical and electronic devices. Maxwell displacement current (MDC) measurement has been employed to study the dielectric property of Langmuir-films. MDC flowing across monolayers is analyzed using a rod-like molecular model. A linear relationship between the monolayer compression speed u and the molecular area Am. Compression speed a was about 30, 40, 50mm/min. Langmuir-Blodgett(LB)layers of Arachidic acid deposited by LB method were deposited onto slide glass as Y-type film. The structure of manufactured device is Au/Arachidic acid/Al, the number of accumulated layers are 9$\sim$21. Also, we then examined of the Metal-Insulator-Metal(MIM) device by means of I-V. The I-V characteristics of the device are measured from -3 to +3[V]. The insulation property of a thin film is better as the distance between electrodes is larger.

• Journal of the Earthquake Engineering Society of Korea
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• v.13 no.2
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• pp.59-68
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• 2009

For safe and economical design to provide strong earthquake resistance, the moment redistribution and plastic rotation of structures and their members needs to be evaluated. To achieve this, an earthquake design method was developed using secant stiffness analysis. To address the variation of member stiffness due to plastic rotation and moment redistribution, a structure was modeled with a beam-column element with non-rigid end connections (NREC element). Secant stiffness for the NREC element was determined based on the ductility demands of the structure and members. By performing a conventional linear analysis for the secant stiffness model, redistributed moments and plastic rotations of the members were computed. The proposed method was applied to a moment frame and two dual systems. The design results were verified using detailed nonlinear analyses.

• Journal of Electrical Engineering and Technology
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• v.12 no.6
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• pp.2388-2398
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• 2017

In this study, we propose a robust face recognition system to pose variations based on automatic pose estimation. Radial basis function neural network is applied as one of the functional components of the overall face recognition system. The proposed system consists of preprocessing and recognition modules to provide a solution to pose variation and high-dimensional pattern recognition problems. In the preprocessing part, principal component analysis (PCA) and 2-dimensional 2-directional PCA ($(2D)^2$ PCA) are applied. These functional modules are useful in reducing dimensionality of the feature space. The proposed RBFNNs architecture consists of three functional modules such as condition, conclusion and inference phase realized in terms of fuzzy "if-then" rules. In the condition phase of fuzzy rules, the input space is partitioned with the use of fuzzy clustering realized by the Fuzzy C-Means (FCM) algorithm. In conclusion phase of rules, the connections (weights) are realized through four types of polynomials such as constant, linear, quadratic and modified quadratic. The coefficients of the RBFNNs model are obtained by fuzzy inference method constituting the inference phase of fuzzy rules. The essential design parameters (such as the number of nodes, and fuzzification coefficient) of the networks are optimized with the aid of Particle Swarm Optimization (PSO). Experimental results completed on standard face database -Honda/UCSD, Cambridge Head pose, and IC&CI databases demonstrate the effectiveness and efficiency of face recognition system compared with other studies.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.3
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• pp.259-265
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• 2009

This paper studies the Element Connectivity Parameterization Method(ECP method) for topology optimization considering dynamic compliance. The previous element density based topology optimization method interpolates Young's modulus with respect to design variables defined in each element for topology optimization. Despite its various applications, these element density based methods suffer from numerical instabilities for nonlinear structure and multiphysics systems. To resolve these instabilities, recently a new numerical method called the Element Connectivity Parameterization(ECP) Method was proposed. Unlike the existing design methods, the ECP method optimizes the connectivities among plane or solid elements and it shows some advantages in topology optimization for both nonlinear structure and multiphysics systems. In this study, the method was expanded for topology optimization for the dynamic compliance by developing a way to model the mass matrix in the framework of the ECP method.

• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 2004.10a
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• pp.433-436
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• 2004

In this paper, we introduce a new Fuzzy Polynomial Neural Networks (FPNNS)-like structure whose neuron is based on the Fuzzy Set-based Fuzzy Inference System (FS-FIS) and is different from that of FPNNS based on the Fuzzy relation-based Fuzzy Inference System (FR-FIS) and discuss the ability of the new FPNNS-like structure named Fuzzy Set-based Polynomial Neural Networks (FSPNN). The premise parts of their fuzzy rules are not identical, while the consequent parts of the both Networks (such as FPNN and FSPNN) are identical. This difference results from the angle of a viewpoint of partition of input space of system. In other word, from a point of view of FS-FIS, the input variables are mutually independent under input space of system, while from a viewpoint of FR-FIS they are related each other. The proposed design procedure for networks architecture involves the selection of appropriate nodes with specific local characteristics such as the number of input variables, the order of the polynomial that is constant, linear, quadratic, or modified quadratic functions being viewed as the consequent part of fuzzy rules, and a collection of the specific subset of input variables. On the parameter optimization phase, we adopt Information Granulation (IC) based on HCM clustering algorithm and a standard least square method-based learning. Through the consecutive process of such structural and parametric optimization, an optimized and flexible fuzzy neural network is generated in a dynamic fashion. To evaluate the performance of the genetically optimized FSPNN (gFSPNN), the model is experimented with using the time series dataset of gas furnace process.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.5
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• pp.77-83
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• 1993

A modified Lanczos method combined with a substructure analysis technique was used for calculating natural frequencies and mode shapes of large structural systems. The method does not require generation and storage of stiffness and mass matrices of the entire structure. It only uses the stiffness and mass matrices of each substucture. No approximating assumptions are required other than the usual assumption of linear elastic system modelled by finite elements. Thus, natural frequencies and mode shapes for the finite element model employed are the same as those with or without the suhstructuring algorithm. To check the efficiency of the proposed method, first ten natural frequencies and the corresponding mode shapes of an open truss helicopter tail-boom structure are calculated by using it.