• Bulletin of the Society of Naval Architects of Korea
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• v.24 no.3
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• pp.43-51
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• 1987

In this paper, dynamic elastic, plastic response of beam-columns is analysed using discrete models. composed of rigid bars and springs. The equation of motion is formulated including the shear deformation effect, and the stress change of yielding points is calculated with various yielding criteria. The effect of initial axial force is considered by two ways: (1) including the effect in interaction curve only. (2) including the effect directly in the equation of motion in terms of initial stiffness method is also used in nonlinear interaction procedure. It is found that this model is very effective in analysing not only the plastic response but the elastic response, and present method is more efficient than Finite Element Method from the viewpoint of calculation time and accuracy.

• International Journal of Aeronautical and Space Sciences
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• v.8 no.1
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• pp.115-121
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• 2007

The aeroelastic analysis of rotor blades with trailing edge flaps, focused on reducing vibration while minimizing control effort, are investigated using large deflection-type beam theory in forward flight. The rotor blade aerodynamic forces are calculated using two-dimensional quasi-steady strip theory. For the analysis of forward flight, the nonlinear periodic blade steady response is obtained by integrating the full finite element equation in time through a coupled trim procedure with a vehicle trim. The objective function, which includes vibratory hub loads and active flap control inputs, is minimized by an optimal control process. Numerical simulations are performed for the steady-state forward flight of various advance ratios. Also, numerical results of the steady blade and flap deflections, and the vibratory hub loads are presented for various advance ratios and are compared with the previously published analysis results obtained from modal analysis based on a moderate deflection-type beam theory.

• Proceedings of the KSME Conference
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• 2001.11a
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• pp.99-104
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• 2001

Effect of mean stress on the fatigue life of natural rubber for engine mount was investigated. Fatigue damage parameter based on the maximum Green-Lagrange strain was employed to account for the effect of mean stress. A procedure to predict the fatigue life of rubber components based on the maximum Green-Lagrange strain method was proposed. Nonlinear finite element analysis and fatigue test of jang-gu shape specimen were conducted to predict the fatigue life of engine mount. Predicted fatigue lives have a good agreement with tested lives within a factor of 3.

• Journal of Mechanical Science and Technology
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• v.14 no.7
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• pp.722-729
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• 2000

The goal of this paper is to describe an advanced method of a crack detection: a new way to localize position and to estimate depth of a crack on rotating shaft. As a first step, the shaft is physically modelled with a finite element method and the dynamic mathematical model is derived using the Hamilton principle; thus, the system is represented by various subsystems. The equations of motion of the shaft with a crack are established by adapting the local stiffness change through breathing and gaping from the crack to an undamaged shaft. This is the reference system for the given system. Based on a model for transient behavior induced from vibration measured at the bearings, a nonlinear state observer is designed to detect cracks on the shaft. This is the elementary NL-observer (Beo). Using the observer, an Estimator (Observer Bank) is established and arranged at the certain position on the shaft. When a crack position is localized, the procedure for estimating of the depth is engaged.

• Structural Engineering and Mechanics
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• v.35 no.6
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• pp.699-715
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• 2010

This paper investigates the structural responses of axially restrained steel beams under fire conditions by a nonlinear finite element method. The axial restraint is represented by a linear elastic spring. Different parameters which include beam slenderness ratio, external load level and axial restraint ratio are investigated. The process of forming a mid-span plastic hinge at the mid-span under a rising temperature is studied. In line with forming a fully plastic hinge at mid-span, the response of a restrained beam under rising temperature can be divided into three stages, viz. no plastic hinge, hinge forming and rotating, and catenary action stage. During catenary action stage, the axial restraint pulls the heated beam and prevents it from failing. This study introduces definitions of beam limiting temperature $T_{lim}$, catenary temperature $T_{ctn}$ and warning time $t_{wn}$. Influences of slenderness ratio, load level and axial restraint ratio on $T_{lim}$, $T_{ctn}$ and $t_{wn}$ are examined.

• Structural Engineering and Mechanics
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• v.31 no.5
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• pp.527-544
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• 2009

In this study, the periodic seismic performance evaluation scheme is proposed using a structural health monitoring system in terms of seismic fragility. An instrumented highway bridge is used to demonstrate the evaluation procedure involving (1) measuring ambient vibration of a bridge under general vehicle loadings, (2) identifying modal parameters from the measured acceleration data by applying output-only modal identification method, (3) updating a preliminary finite element model (obtained from structural design drawings) with the identified modal parameters using real-coded genetic algorithm, (4) analyzing nonlinear response time histories of the structure under earthquake excitations, and finally (5) developing fragility curves represented by a log-normal distribution function using maximum likelihood estimation. It is found that the seismic fragility of a highway bridge can be updated using extracted modal parameters and can also be monitored further by utilizing the instrumented structural health monitoring system.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.12
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• pp.1836-1842
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• 2012

Torque is proportional to the rate of change of inductance in a switched reluctance motor (SRM), and hence, phase inductance is an important parameter in determining the behavior of an SRM. Therefore, the accurate prediction of inductance with respect to rotor position makes a significant contribution to designing an SRM and its analytical approach is not straightforward due to nonlinear flux distribution. Although several different approaches using a finite element analysis (FEA) or curve-fitting tool have been employed to compute phase inductance [2-5], they are not suitable for a simple design procedure because the FEA necessitates a large amount of time in both modeling and solving with complexity for every motor design, and the curve-fitting requires the data of flux linkage from either an experimental test or an FEA simulation. In this paper, phase inductance is predicted by means of a permeance method, and the proposed approach is analytically verified in terms of the accuracy of estimated inductance compared to inductance obtained by FEA.

• Proceedings of the KIEE Conference
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• 2000.07b
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• pp.647-649
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• 2000

This paper presents a optimization procedure by using Response Surface Methodology(RSM) to determine design Parameters for reducing cogging torque in BLDC motor of Electric Power Steering (EPS). RSM is achieved through using the experiment design method in combination with Finite Element Method and well adapted to make analytical model for a complex problem considering a lot of interaction of these parameters. Moreover, Sequential Quadratic Problem (SQP) method is used to solve the resulting of constrained nonlinear optimization problem.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.51 no.2
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• pp.55-60
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• 2002

This paper presents an optimization procedure by using Response Surface Methodology(RSM) to determine design parameters for reducing cogging torque. RSM is achieved through using the experimental design method in combination with Finite Element Method and adapted to make analytical model for a complex problem considering a lot of interaction of these parameters. Sequential Quadratic Problem (SQP) method is used to solve the relsulting of constrained nonlinear optimization problem.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.1
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• pp.34-40
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• 2012

Flux linkage of phase windings or phase inductance is an important parameter in determining the behavior of a switched reluctance motor (SRM) [1-8]. Therefore, the accurate prediction of inductance at aligned and unaligned rotor positions makes a significant contribution to the design of an SRM and its analytical approach is not straightforward due to nonlinear flux distribution. Although several different approaches using a finite element analysis (FEA) or curve-fitting tool have been employed to compute phase inductance [2-5], they are not suitable for a simple design procedure because the FEA necessitates a large amount of time in both modeling and solving with complexity for every motor design, and the curve-fitting requires the data of flux linkage from either an experimental test or an FEA simulation. In this paper, phase inductance at aligned and unaligned rotor positions is estimated by means of numerical method and magnetic equivalent circuit as well, and the proposed approach is analytically verified in terms of the accuracy of estimated inductance compared to inductance computed by an FEA simulation.