• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.30 no.7
• /
• pp.29-35
• /
• 2002

Aeroelastic characteristics of a deployable missile control fin have been investigated. A deployable missile control fin is modeled by a 2-dimensional typical section. Supersonic Doublet-Point method is used for the computation of supersonic unsteady aerodynamic forces and Karpel's Minimum-State approximation is used for the aerodynamic approximation. Root-locus method and time-integration method are used for the linear and nonlinear flutter analyses. For the nonlinear flutter analysis the deployable hinge is represented by a asymmetric bilinear spring and is linearized by using the describing function method. From the flutter analyses, the effects of nonlinear parameters on the aeroelastic characteristics are investigated.

• Journal of Biomedical Engineering Research
• /
• v.24 no.3
• /
• pp.151-158
• /
• 2003

Numerous studies of short-term, beat-to-beat variability in cardiovascular signals have used linear analysis techniques. However, no study has been done about the appropriateness of linear techniques or the comparison between linearities and nonlinearities in short-term, beat-to-beat variability. This paper aims to verify the appropriateness of linear techniques by investigating nonlinearities in short-term, beat-to-beat variability. We compared linear autoregressive moving average(ARMA) with nonlinear neural network(NN) models for predicting current instantaneous heart rate(HR) and mean arterial blood pressure(BP) from past HRs and BPs. To evaluate these models. we used HR and BP time series from the MIMIC database. Experimental results indicate that NN-based nonlinearities do not play a significant role and suggest that 10 technique provides adequate characterization of the system dynamics responsible for generating short-term, beat-to-beat variability.

• Proceedings of the KOR-KST Conference
• /
• 1998.10a
• /
• pp.196-205
• /
• 1998

교통신호에서 주로 고려되는 변수는 신호주기(cycle length), 녹색시간(green split), 옵셋(offset)그리고 좌회전 현시순서(left-turn phase sequence)로 구성된다. 기존의 대부분의 연동 모델들은 고정된 주기하에서 평균적인 유입 교통량을 측정한 후, 선형최적화 이론을 적용하여 최적 신호를 산출한다. 그러나 이 방법은 어디까지나 평균적인 데이터에 대해서 계산을 한 것이기 때문에 실시간 최적화를 제공하기가 어렵다. 본 연구에서는 평균 차량 통행량 대신 실시간으로 입력되는 차량 대기행렬, 차량 도착률을 기초로 대기차량을 최소화하는 동적 신호시간 산출 모델을 개발하였다. 본 모델에서는 Peytechew가 제안한 각 진입로에서의 대기 차량 예측 모델을 기초로 하여 다음 주기에서의 차량 대기 행렬을 예측한 후, 선형 최적화 이론을 적용하여 신호시간을 산출한다. 본 모델에서 산출된 신호주기와 녹색시간은 대기차량길이를 최소화하는 신호 시간으로서 교차로간의 연동효과를 고려하여 실시산 교통상황에 따라 주기별로 변화한다. 본 모델은 3개의 교차로로 구성된 네트워크를 대상으로 적용하였다. 실험 네트워크의 주도로 교통량은 부도로의 교통량 보다 많다고 가정하였으며 각 링크사이에서의 차량 진출입은 없다고 보았다.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.34 no.9
• /
• pp.45-52
• /
• 2006

In this study, a nonlinear control by feedback linearization method, one of nonlinear control schemes based on the nonlinear model, is proposed to suppress the flutter of a supersonic composite panel using piezoelectric materials. Most of the previous panel flutter controllers are the LQR(Linear Quadratic Regulator) which is based on the linear model. A nonlinear feedback linearizing controller proposed in this study considers the nonlinear characteristics of the system model. We use the actuator implemented by piezoceramic PZT. Using the principle of virtual displacements and a finite element discretization with the conforming four-node rectangular element, we first derive the discretized dynamic equations of motion, which are transformed into a nonlinear coupled-modal equations of motion of state space form. The effectiveness of the proposed method is also compared with the LQR based on the linear model through numerical simulations in the time domain using the Newmark method.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.33 no.2
• /
• pp.81-93
• /
• 2020

The fatigue characteristics of glass fiber reinforced plastic (GFRP) composites were studied under repeated loads using the finite element method (FEM). To realize the material characteristics of GFRP composites, Digimat, a mean-field homogenization tool, was employed. Additionally, the micro-structures and material models of GFRP composites were defined with it to predict the fatigue behavior of composites more realistically. Specifically, the fatigue characteristics of polybutylene terephthalate with short fiber fractions of 30wt% were investigated with respect to fiber orientation, stress ratio, and thickness. The injection analysis was conducted using Moldflow software to obtain the information on fiber orientations. It was mapped over FEM concerned with fatigue specimens. LS-DYNA, a typical finite element commercial software, was used in the coupled analysis of Digimat to calculate the stress amplitude of composites. FEMFAT software consisting of various numerical material models was used to predict the fatigue life. The results of coupled analysis of linear and nonlinear material models of Digimat were analyzed to identify the fatigue characteristics of GFRP composites using FEMFAT. Neuber's rule was applied to the linear material model to analyze the fatigue behavior in LCF regimen. Additionally, to evaluate the morphological and mechanical structure of GFRP composites, the coupled and fatigue analysis were conducted in terms of thickness.

• Journal of the Institute of Electronics Engineers of Korea SC
• /
• v.37 no.6
• /
• pp.15-24
• /
• 2000

This paper presents an output feedback robust H$\infty$ control problem for a class of uncertain nonlinear systems, which can be represented by an fuzzy dynamic model. The nonlinear system is represented by Takagi-Sugeno fuzzy model, and the control design is carried out on the basis of the fuzzy model. Using a single quadratic Lyapunov function, the globally exponential stability and disturance attenuation of the closed-loop fuzzy control system are discussed. Sufficient conditions for the existence of robust H$\infty$ controllers are given in terms of linear matrix inequalities(LMIs). Constructive algorithm for design of robust H$\infty$ controller is also developed. The resulting controller is nonlinear and automatically tuned based on fuzzy operation.

• Journal of the Korean Institute of Intelligent Systems
• /
• v.21 no.4
• /
• pp.423-429
• /
• 2011

This paper deals with the observer-based decentralized fuzzy controller design for nonlinear interconnected system for PEMFC. The nonlinear interconnected system is represented by a Takagi-Sugeno (T-S) fuzzy model. Based on T-S fuzzy interconnected system, the fuzzy observer and the decentralized fuzzy controller are designed. The stability condition of the closed-loop system with the proposed controller is represented to the linear matrix inequality (LMI) form, and the observer and control gain s are obtained by LMI. An example is given to show the verification discussed throughout the paper.

• Journal of the Korea Institute of Building Construction
• /
• v.11 no.1
• /
• pp.1-8
• /
• 2011

Linear scheduling method limits to present works of work breakdown structure as a form of lines and was often developed manually. In other words, linear schedule could not utilize activity, work breakdown structure, and etc. information of network schedule such as CPM(Critical Path Method) and has been used only for reporting or confirming construction master plan. Therefore, it is necessary to develop system which can automatically generating the linear schedule based on the network schedule having many accumulated and useful construction schedule information. Thus, this research has an effort to establish data process model, data flow diagram, and data model in order to make linear schedule. In addition, this research addresses the system solution structure, user interface class diagram and logic diagram, and data type schema. The results of this paper can be used as a preliminary research for developing linear schedule generating system prototype by utilizing the network schedule information.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.20 no.3
• /
• pp.83-92
• /
• 2016

The purpose of this study is to evaluate the seismic performance of domestic unreinforced masonry(URM) buildings using nonlinear dynamic analysis. For that, the nonlinear hysteresis models suggested in the previous research were validated for the dynamic analysis. The results of the shaking table test were compared with the dynamic analysis results using the suggested nonlinear hysteresis models. As a result, the nonlinear hysteresis models were expected to be applicable to the dynamic analysis of URM buildings. Based on the models, the dynamic analysis of domestic URM buildings varying the number of stories and opening ratio was carried out. The analysis results showed that most of the domestic URM buildings were very vulnerable to design earthquake in Korea.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.26 no.2A
• /
• pp.285-292
• /
• 2006

In this study, a method determining the local bond-slip model from pure shear test results of CFRP sheet-concrete adhesive joints is proposed and local bond-slip models are presented. Adhesive joints with a specific bond-slip model, which is assumed as multi-linear curve in order to represent arbitary function, are solved numerically. The difference between the solution and test results are minimized for finding the bond-slip model. The model with bilinear curve is also optimized to verify the improvement of multi-linear model. The selected test results are ultimate load-adhesive length curves from a series of adhesive joints and load-displacement curves for each joint. The optimization problem is formulated by physical programming, and the optimized bond-slip model is found using genetic algorithm.