• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2005.03a
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• pp.277-283
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• 2005

Inelastic model of Second Jindo Bridge is investigated to perform nonlinear dynamic analyses with various earthquake ground motions. The modal analysis is performed to obtain dynamic characteristics of the bridge and verify the model. It proves that the model has an appropriate dynamic characteristic and its natural frequency is relatively low. Four ground motions are chosen for time history dynamic analyses; El Centro, Kobe, Taft, and Mexico earthquake. Each ground motion multiplied by specified factors to investigate damages of the structure. The analyses prove that responses of the bridge depend on the duration time and the frequency characteristics of ground motion, not only peak acceleration. Static push-over analysis of steel pylon shows that the dynamic analysis over-estimates the seismic behavior of steel pylon definitely. Nonlinear spring hinge model is suggest to improve the shortage of the inelastic model could not deliberate local buckling damage. According to the time history analysis of nonlinear spring hinge model, it is proved that the inelastic beam element analysis overestimate the seismic capacity of steel pylon unquestionably with a large amount of errors.

• Journal of Electrical Engineering and Technology
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• v.11 no.3
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• pp.662-669
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• 2016

In this work, nonlinear control of a three-phase shunt active power filter (SAPF) has been studied and compared to classical control based on proportional integral regulator. The control strategy is based on the direct current method using sliding mode control (SMC), where the aim is to regulate the average voltage across the dc bus of the inverter. Details are given for the control algorithm; the controller is comprised of a current loop which utilizes a hysteresis controller to generate the gating signals for the switching devices, and a nonlinear controller based on SMC law which is different from classical laws based on error between reference and measured output voltage of the inverter. Sliding surface applied in this work contains the whole of state variables, in order to ensure full control of the system behavior in the presence of disturbances that affect the supply source, the load parameters or the reference value. The designed controller offers advantage that it can gives the improvement of dynamic and static performances in cases of large disturbances. A comparison of the effects of PI control and SMC on the APF response in steady stat, under line variations, load variations, and different component variations is performed.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.1077-1078
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• 2008

The growing number of nonlinear loads such as static power converters has posed a problem on the quality of electric power supply. The active filters (AF) have been rapidly expanding with the advancement of power electronics technology. The purpose of the active filters is to compensate current harmonics and/or current imbalance. The authors have studied and introduced the PV-AF system; the PV power system, which is used widely as a dispersed source, including the function of active filter to compensate the harmonics caused by nonlinear loads. The PV-AF system has merits not only to compensate harmonics caused by nonlinear loads but also to increase the utilization of PCS. This paper describes the grid-connected single phase PV-AF system and the PSCAD/EMTDC simulation results.

• Smart Structures and Systems
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• v.26 no.2
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• pp.213-226
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• 2020

In this manuscript, static and dynamic behaviors of geometrically imperfect carbon nanotubes (CNTs) subject to different types of end conditions are investigated. The Doublet Mechanics (DM) theory, which is length scale dependent theory, is used in the analysis. The Euler-Bernoulli kinematic and nonlinear mid-plane stretching effect are considered through analysis. The governing equation of imperfect CNTs is a sixth order nonlinear integro-partial-differential equation. The buckling problem is discretized via the differential-integral-quadrature method (DIQM) and then it is solved using Newton's method. The equation of linear vibration problem is discretized using DIQM and then solved as a linear eigenvalue problem to get natural frequencies and corresponding mode shapes. The DIQM results are compared with analytical ones available in the literature and excellent agreement is obtained. The numerical results are depicted to illustrate the influence of length scale parameter, imperfection amplitude and shear foundation constant on critical buckling load, post-buckling configuration and linear vibration behavior. The current model is effective in designing of NEMS, nano-sensor and nano-actuator manufactured by CNTs.

• Earthquakes and Structures
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• v.14 no.2
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• pp.155-165
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• 2018

Methods based on nonlinear static analysis as simple tools could be used for the seismic analysis and assessment of structures. In the present study, capability of the N2 method as a well-known nonlinear analysis procedure examines for the estimation of the damage index of multi-storey reinforced concrete frames. In the implemented framework, equivalent single-degree-of-freedom (SDOF) models are utilized for the global damage estimation of multi-degree-of-freedom (MDOF) systems. This method does not require high computational analysis and subsequently decreases the required time of seismic design and assessment process. To develop the methodology, RC frames with period range from 0.4 to 2.0 s under 40 records are studied. The effectiveness of proposed technique is evaluated through numerical study under near- and far-field earthquake ground motions. Finally, the results of developed models are compared with two other simplified schemes along with nonlinear time history analysis results of multi-storey frames. To improve the accuracy of damage estimation, a modified relation is presented based on the N2 method results for near- and far-field earthquakes.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.26 no.1
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• pp.76-80
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• 1990

DC-servomotor acts an important role in robots and manipulatirs. But the precise control of DC-motor is difficult by a using usual linear controller because of the nonlinear characteristics of DC-motor. This study suggests the use of fuzzy controller in the control of DC-servomotor speed. The fuzzy controller is designed from a fuzzy model which can represent nonlinear systems very well. Hence the fuzzy controller is very useful in the control of nonlinear systems such as DC-motor. We construct a fuzzy model of DC-servomotor, design a fuzzy controller from the fuzzy model, and compare that with a linear controller. When we use the fuzzy controller, the static ripples are reduced and the rise time is required 20% less than in using a linear controller.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.1
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• pp.36-43
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• 2002

Thermopiezoelastic snap-through phenomena of piezolaminated plates are investigated by applying an are-length scheme to Newton-Raphson method. Based on the layerwise displacement theory and von Karman strain-displacement relationships, nonlinear finite element formulations are derived for the thermopiezoelastic composite plates. From the static and dynamic viewpoint, nonlinear thermopierzoelastic behavior and vibration characteristicx are stuied for symmetric and eccentric structural models with various piezoelestric actuation modes. Present results show the possibility to enhance the performance, namely thermopiezoelastic snapping, induced by the excessive piezoelectric actuation in the active suppression of thermally buckled large deflection piezolaminated paltes.

• Proceedings of the KIEE Conference
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• 1998.07b
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• pp.740-743
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• 1998

This paper presents an optimization algorithm for a stable Dynamic Neural Network (DNN) using genetic algorithm. Optimized DNN is applied to a problem of controlling nonlinear dynamical systems. DNN is dynamic mapping and is better suited for dynamical systems than static forward neural network. The real time implementation is very important, and thus the neuro controller also needs to be designed such that it converges with a relatively small number of training cycles. SDNN has considerably fewer weights than DNN. The object of proposed algorithm is to the number of self dynamic neuron node and the gradient of activation functions are simultaneously optimized by genetic algorithms. To guarantee convergence, an analytic method based on the Lyapunov function is used to find a stable learning for the SDNN. The ability and effectiveness of identifying and controlling, a nonlinear dynamic system using the proposed optimized SDNN considering stability' is demonstrated by case studies.

• Smart Structures and Systems
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• v.5 no.4
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• pp.495-505
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• 2009

Bridges form crucial links in the transportation network especially in high seismic risk regions. This research aims to provide a quantitative methodology for post-earthquake performance evaluation of the bridges. The experimental portion of the research involved shake table tests of a 4-span bridge which was subjected to progressively increasing amplitudes of seismic motions recorded from the Northridge earthquake. As part of this project, a high resolution long gauge fiber optic displacement sensor was developed for post-seismic evaluation of damage in the columns of the bridge. The nonlinear finite element model was developed using Opensees program to simulate the response of the bridge and the abutments to the seismic loads. The model was modified to predict the bent displacements of the bridge commensurate with the measured bent displacements obtained from experimental analysis results. Following seismic events, the tangential stiffness matrix of the whole structure is reduced due to reduction in structural strength. The nonlinear static push over analysis using current damaged stiffness matrix provides the longitudinal and transverse ultimate capacities of the bridge. Capacity loss in the transverse and longitudinal directions following the seismic events was correlated to the maximum displacements of the deck recorded during the events.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1990.10a
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• pp.47-54
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• 1990

Under external loads, large panel structures behave quite differently from monolithic wall structures, because of the distinct planes of weakness in the horizontal and vertical joints between panels. Study on the ultimate load and the failure mode of the large panel structures under extream lateral loads is therefore important. The purpose of this study is to predict the nonlinear behavior of the structure using the general purpose nonlinear computer program 'ANSR' being based on the quasi-static test results of the large panel structure(full scale in two story) and to examine the distribution and change mode of the internal forces which can not be obtained in the test.