• The Transactions of the Korean Institute of Electrical Engineers P
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• v.54 no.1
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• pp.34-40
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• 2005

This paper presents a frequency transfer function synthesis for simplifying a high-order model with time delay to a low-order model. A model reduction is based on minimizing the error function weighted by the numerator polynomial of reduced systems. The proposed method provides better low frequency fit and a computer aided algorithm. And in this paper, we present a design method of PID controller for achieving the desired specifications via the reduced model. The proposed method identifies the parameter vector of PID controller from a linear system that develops from rearranging the two dimensional input matrices and output vectors obtained from the frequency bounds.

• Journal of Institute of Control, Robotics and Systems
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• v.8 no.6
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• pp.439-444
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• 2002

In this paper, a new model reduction method is proposed to obtain a reduced order model in the frequency domain. The method is developed based on the second-order plus dead time modeling technique. The initial value of the reduced model parameters can be obtained using this method coinciding four point(0, -$\pi$/2, -$\pi$, -3$\pi$/2) on the Nyquist curve. The optimal parameters of the reduced model is obtained through calculation procedure with three steps. It is shown that Nyquist curves and unit step responses of the reduced models of numerical examples closely agree with those of original models.

• Journal of Power System Engineering
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• v.19 no.3
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• pp.55-62
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• 2015

This paper discusses a new model for investigating the micro-mechanical behavior of beam-like structures composed of various elastic moduli and complex geometries varying through the cross-sectional directions and also periodically-repeated along the axial directions. The original three-dimensional problem is first formulated in an unified and compact intrinsic form using the concept of decomposition of the rotation tensor. Taking advantage of two smallness of the cross-sectional dimension-to-length parameter and the micro-to-macro heterogeneity and performing homogenization along dimensional reduction simultaneously, the variational asymptotic method is used to rigorously construct an effective zeroth-order beam model, which is similar a generalized Timoshenko one (the first-order shear deformation model) capable of capturing the transverse shear deformations, but still carries out the zeroth-order approximation which can maximize simplicity and promote efficiency. Two examples available in literature are used to demonstrate the consistence and efficiency of this new model, especially for the structures, in which the effects of transverse shear deformations are significant.

• Carbon letters
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• v.7 no.3
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• pp.171-179
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• 2006

A carbonaceous sorbent was prepared from rice husk via sulphuric acid treatment. After preparation and washing, the wet carbon with moisture content 85% was used in its wet status in this study due to its higher reactivity towards Cr(VI) than the dry carbon. The interaction of Cr(VI) and the carbon was studied and two processes were investigated in terms of kinetics and equilibrium namely Cr(VI) removal and chromium sorption. Cr(VI) removal and chromium sorption were studied at various initial pH (1.6-7), for initial Cr(VI) concentration (100 mg/l). At equilibrium, maximum Cr(VI) removal occurred at low initial pH (1.6-2) where, Cr(III) was the only available chromium species in solution. Cr(VI) removal, at such low pH, was related to the reduction to Cr(III). Maximum chromium sorption (60.5 mg/g) occurred at initial pH 2.8 and a rise in the final pH was recorded for all initial pH studied. For the kinetic experiments, approximate equilibrium was reached in 60-100 hr. Cr(VI) removal data, at initial pH 1.6-2.4, fit well pseudo first order model but did not fit pseudo second order model. At initial pH 2.6-7, Cr(VI) removal data did not fit, anymore, pseudo first order model, but fit well pseudo second order model instead. The change in the order of Cr(VI) removal process takes place in the pH range 2.4-2.6 under the experimental conditions. Other two models were tested for the kinetics of chromium sorption with the data fitting well pseudo second order model in the whole range of pH. An increase in cation exchange capacity, sorbent acidity and base neutralization capacity was recorded for the carbon sorbent after the interaction with acidified Cr(VI) indicating the oxidation processes on the carbon surface accompanying Cr(VI) reduction.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.10
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• pp.1211-1222
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• 2011

It is necessary to use prestressed modal analysis to calculate the modal frequencies and mode shapes of a prestressed structure such as a spinning blade, a preloaded structure, or a thermally deformed pipe, because the prestress effect sometimes causes significant changes in the frequencies and mode shapes. When the finite element model under consideration has a very large number of degrees of freedom, repeated prestressed modal analyses for investigating the prestress effects might become too computationally expensive to finish within a reasonable design-process time. To alleviate these computational difficulties, a Krylov subspace-based model order reduction, which reduces the number of degrees of freedom of the original finite element model and speeds up the necessary prestressed modal analysis with the reduced order models (ROMs), is presented. The numerical process for the moment-matching model reduction is performed directly on the full order models (FOMs) (modeled in ANSYS) by the Arnoldi process. To demonstrate the advantages of this approach for performing prestressed modal analysis, the prestressed wheel and the compressor impeller under their high-speed rotation are considered as examples.

• 제어로봇시스템학회:학술대회논문집
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• 2002.10a
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• pp.75.1-75
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• 2002

Several model order reduction methods for large RLC circuits have been developed in the last few years. Krylop subspace based methods are extremely effective for generating the low order models of large system but there is no optimal theory for the resulting models. Alternatively, methods based truncated balanced realization have an optimality property but are too computationally expensive to use on complicated problems such as large RLC circuits. In this paper, we present a method for improving time domain response of reduced order RLC circuits. The method used here is based on combing Krylop subspace based method and truncated balanced realization method plus residualization. The metho...

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.18 no.6
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• pp.176-182
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• 2004

This paper proposes a frequency transfer function synthesis for simplifying a high-order model with time delay to a low-order model. The model reduction is based on minimizing the m function weighted by the numerator polynomial of reduced systems. The proposed methods provide a better fitness within low frequency. Four examples are given to illustrate the feasibilities of the suggested schemes.

• Korean Journal of Computational Design and Engineering
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• v.8 no.2
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• pp.109-114
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• 2003

In order to develop the reduced tire modal model for analyzing a full tire model, the Craig-Bampton method is utilized in this paper. When the tire contacts the road, the Abaqus solver extracts the condensed stiffness, coupled mass and mode shape matrix about the node, which contacts the road. The Abaqus full tire model is reduced using the substructure method utilizing Craig-Bampton algorithm. Then, the extracted matrices are interfaced with the superelement, which is fed to the Nastran reduction algorithm. Eventually, the reduced tire model is verified from experiment and various reduction parameters (i.e. modal number, reduction point, etc.) are studied for the effectiveness of the proposed paper.

• Journal of the Korean Institute of Intelligent Systems
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• v.16 no.2
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• pp.144-149
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• 2006

This paper deals with a balanced model reduction for uncertain nonlinear systems via T-S fuzzy approach. We define a generalized controllability/observability gramian and obtain a balanced state space model using generalized gramians which can be obtained from solutions of linear matrix inequalities. We present a balanced model reduction scheme by truncating not only state variables but also uncertain elements. An upper bound of the model reduction error will also be suggested. In order to demonstrate the efficacy of our method, a numerical example will be presented.

• Smart Structures and Systems
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• v.13 no.3
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• pp.343-352
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• 2014

Given a body undergoing a stress-strain status as consequence of external excitations, sensors can be deployed on the accessible lateral surface of the body. The sensor readings are regarded as input of a numerical model of reduced order (i.e., the number of sensors is lower than the number of the state variables the full model would require). The goal is to locate the sensors in such a way to minimize the deviations from the response of the true (full) model. One adopts either accelerometers as sensors or devices reading relative displacements. Two applications are studied: a plane frame is first investigated; the focus is eventually on a 3D body.