• Proceedings of the KSR Conference
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• 2007.05a
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• pp.675-679
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• 2007

The control method of programmable dynamometer for overall test of machine is to load reference torque which is computed from torque transducer into motor under test. But the torque information detected from torque transducer have a lot of noise when the load torque of moter is a small quantity or changing. Thus, torque transducer must have a low pass filter to detect a definite torque information. But The torque delay generated by filter with torque transducer occur a torque trouble for moter torque of programmable dynamometer. Therefore, this kind of system could not perform dynamic and nonlinear load. In this paper, the control method using the load torque observer without a measure for torque transducer is proposed. The proposed system improved the problem of the torque measuring delay with torque transducer, and the load torque is estimated by the minimal order state observer based on the torque component of the vector control induction moter. Therefore, the torque controller is not affected by a load torque disturbance.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.913-919
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• 2001

In this study, fiber orientation of stiffener was conducted to increase buckling load or failure load in each case with a different design value and a different objective function for stiffened laminated composite panel of I-type under compression loading. Regarding each of buckling load or failure load as objective function, optimum design was carried out. In respect of optimum design, it was investigated that optimum shape for buckling could improve fail load for postbuckling, because it was difficult to investigate the optimization of postbuckling which need long analysis times for nonlinear analysis.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.12
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• pp.1959-1963
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• 2012

Since electric railway load is variable largely due to starting and braking characteristics as well as various operation patterns, load modeling is not easy but complicated. For this reason, a simple technique for modeling of electric railway load of is required to analyze the AC substation system of electric railway. In this paper, a modeling technique of converter-based electric railway load is proposed and is tested using nonlinear loads on Matlab/Simulink.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.34 no.12
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• pp.491-497
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• 1985

An applicaton of the linear optimal control theory to the problem or load follow control in pressurized water reactors (PWR) is investigated. In order to perform the steady-state and load follow operation in PWR, a nonlinear model for the reactor and steam generator is derived and linearized at 50% rated power. Simulation tests are performed for 10% demanded load. Comparing the dynamic response of the newly developed optimal load follow controller with those of the integral error feedback controller proposed by Yang, the rise time of dynamic response of the former is about 15 seconds faster than those of the latter, thus the results indicate that the fast response of the optimal load follow controller is verified. The results of this work are directly applicable to the design of the load follow control systems for commercially operated PWRs.

• Structural Engineering and Mechanics
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• v.8 no.2
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• pp.137-150
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• 1999

This paper presents a numerical study on the flat plates in deep basements, subjected to floor load and in-plane compressive load due to soil and hydraulic lateral pressure. For nonlinear finite element analysis, a computer program addressing material and geometric nonlinearities is developed. The validity of the numerical model is established by comparison with existing experiments performed on plates simply supported on four edges. The flat plates to be studied are designed according to the Direct Design Method in ACI 318-95. Through numerical study on the effects of different load combinations and loading sequence, the load condition that governs the strength of the flat plates is determined. For plates under the governing load condition, parametric studies are performed to investigate the strength variations with reinforcement ratio, aspect ratio, concrete strength, and slenderness ratio. Based on the numerical results, the floor load magnification factor is proposed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.1 s.256
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• pp.18-25
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• 2007

Linear motor is easily affected by load disturbance, force ripple, friction, and parameter variations because there is no mechanical transmission to reduce the effects of model uncertainties and external disturbance. These nonlinear effects have been reduced for high-speed/high-accuracy position control either through the better motor design or via the better control algorithm that can compensate the nonlinear effects. In this paper, a nonlinear adaptive control algorithm is designed and applied for the position control of permanent magnet linear synchronous motor. In order to estimate and compensate the nonlinear effects such as friction and force ripple, the estimation and the nonlinear adaptive control laws are derived based on the virtual control input and a suitable Lyapunov function. The proposed controller is evaluated through the computer simulations. The control algorithm is also implemented to a DSP board and interfaced to the PMLSM for verifying the realtime control performance.

• Structural Engineering and Mechanics
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• v.37 no.1
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• pp.111-129
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• 2011

This paper presents a nonlinear analysis of reinforced concrete column with lap splice confined by FRP wrapping in the critical hinging zone. The steel stress-slip model derived from the tri-uniform bond stress model presented in the companion paper is included in the nonlinear frame analysis to simulate the response of reinforced concrete columns subjected to cyclic displacement reversals. The nonlinear modeling is based on a fiber discretization of an RC column section. Each fiber is modeled as either nonlinear concrete or steel spring, whose load-deformation characteristics are calculated from the section of fiber and material properties. The steel spring that models the reinforcing bars consists of three sub-springs, i.e., steel bar sub-spring, lap splice spring, and anchorage bond-slip spring connected in series from top to bottom. By combining the steel stress versus slip of the lap splice, the stress-deformation of steel bar and the steel stress-slip of bars anchored into the footing, the nonlinear steel spring model is derived. The analytical responses are found to be close to experimental ones. The analysis without lap splice springs included may result in an erroneous overestimation in the strength and ductility of columns.

• Structural Engineering and Mechanics
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• v.40 no.2
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• pp.257-277
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• 2011

In this paper the geometrically nonlinear continuum plate finite element model, hitherto not reported in the literature, is developed using the total Lagrange formulation. With the layerwise displacement field of Reddy, nonlinear Green-Lagrange small strain large displacements relations (in the von Karman sense) and linear elastic orthotropic material properties for each lamina, the 3D elasticity equations are reduced to 2D problem and the nonlinear equilibrium integral form is obtained. By performing the linearization on nonlinear integral form and then the discretization on linearized integral form, tangent stiffness matrix is obtained with less manipulation and in more consistent form, compared to the one obtained using laminated element approach. Symmetric tangent stiffness matrixes, together with internal force vector are then utilized in Newton Raphson's method for the numerical solution of nonlinear incremental finite element equilibrium equations. Despite of its complex layer dependent numerical nature, the present model has no shear locking problems, compared to ESL (Equivalent Single Layer) models, or aspect ratio problems, as the 3D finite element may have when analyzing thin plate behavior. The originally coded MATLAB computer program for the finite element solution is used to verify the accuracy of the numerical model, by calculating nonlinear response of plates with different mechanical properties, which are isotropic, orthotropic and anisotropic (cross ply and angle ply), different plate thickness, different boundary conditions and different load direction (unloading/loading). The obtained results are compared with available results from the literature and the linear solutions from the author's previous papers.

• Structural Engineering and Mechanics
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• v.58 no.3
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• pp.515-532
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• 2016

The elastoplastic response of functionally graded material (FGM) beams resting on a nonlinear elastic foundation to an eccentric axial load is investigated by using the finite element method. The FGM is assumed to be formed from ceramic and metal phases with their volume fraction vary in the thickness direction by a power-law function. A bilinear elastoplastic behavior is assumed for the metallic phase, and the effective elastoplastic properties of the FGM are evaluated by Tamura-Tomota-Ozawa (TTO) model. Based on the classical beam theory, a nonlinear finite beam element taking the shift in the neutral axis position into account is formulated and employed in the investigation. An incremental-iterative procedure in combination with the arc-length control method is employed in computing the equilibrium paths of the beams. The validation of the formulated element is confirmed by comparing the equilibrium paths obtained by using the present element and the one available in the literature. The numerical results show that the elastoplastic post-buckling of the FGM beams is unstable, and the post-buckling strength is higher for the beams associated with a higher ceramic content. Different from homogeneous beams, yielding in the FGM beam occurs in the layer near the ceramic layer before in the layer near metal surface. A parametric study is carried out to highlight the effect of the material distribution, foundation support and eccentric ratio on the elastoplastic response of the beams.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.20 no.5
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• pp.623-628
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• 2007

The accurate peak response estimation of a seismically excited structure with frictional damping system(FDS) is very difficult since the structure with FDS shows nonlinear behavior dependent on the structural period, loading characteristics, and relative magnitude between the frictional force and the excitation load. Previous studies have estimated that by replacing a nonlinear system with an equivalent linear one or by employing the response spectrum obtained based on nonlinear time history and statistical analysis. In the case that an earthquake load is defined with probabilistic characteristics, the corresponding response of the structure with FDS has probabilistic distribution. In this study, nonlinear time history analyses were performed for the structure with FDS subjected to artificial earthquake loads generated using Kanai-Tajimi filter. An equation for the probability density function (PDF) of the displacement response is proposed by adapting the PDF of the normal distribution. Finally, coefficients of the proposed PDF are obtained by regression analysis of the statistical distribution of the time history responses. Finally the correlation between PDFs and statistical response distribution is presented.