• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.6
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• pp.650-655
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• 2011

Analysis of two-dimensional Rayleigh wave scattering pattern by a surface defect is studied through modified boundary element method. BEM proposed in this paper has special treatment at each end of boundary which should have the Rayleigh wave go away without any generation of virtual reflections. It is shown that treatment for truncated boundary which is used to model two-dimensional Rayleigh waves' behavior in an elastic half-space is successfully implemented. To check numerical results' accuracy, time domain IFFT signal of the displacements is presented. Improvement on getting rid of unwanted influence of truncated boundary induced by 2-D Rayleigh waves on a flat surface of an elastic half-infinite medium is shown. As a final goal, the numerical results of Rayleigh wave scattering trend are plotted and they are compared with theoretical curves to prove its accuracy.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.1 s.118
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• pp.3-9
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• 2007

In this paper, a numerical case study is carried out on the hydroelastic vibration of rectangular plate with various fluid field. It is assumed that the tank wall is clamped along the plate edges. The VMM(virtual mass method) of Nastran is used for the simulation of fluid domain and calculating natural frequency of fluid-coupled structure. In this paper, natural frequencies are calculated and compared for rectangular plates with various fluid field such as infinite fluid and finite fluid, length change of finite fluid field and various fluid contacting conditions.

• Proceedings of the KSR Conference
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• 1999.05a
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• pp.352-357
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• 1999

During the cooling process of rail, residual stresses are produced due to the difference of the coefficients of thermal expansion between rail and inhomogeneous non-metallic inclusions such as sulphides and oxides. A micro-mechanical approach is used to obtain the stresses in the inclusions and matrix, After obtaining the stress of an elliptical inhomogeneous inclusion in an infinite domain, average stresses of randomly distributed spherical inclusions are obtained by use of Mori-Tanaka's self consistent method. The magnitude of the calculated residual stress is near to the yield stress of the matrix in case of the spherical inclusions.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.9 no.4
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• pp.483-490
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• 1998

The reflectivity of a grid ferrite electromagnetic wave absorber is analyzed using finite difference time domain (FDTD) method, which is usually used in anechoic chambers for EMI / EMS test. The frequency dispersive characteristics of ferrite medium and its boundary condition are modeled using magnetic flux in addition to E- and H-fields. By applying Floquets theorem, FDTD analysis of the grid ferrite absorber with periodic infinite array is simplified as a unit cell problem. The method of homogenization which is mainly utilized in the calculation of absorber reflectivity as a low frequency technique takes only into account volume fraction of the unit cell of the absorber except for the structure of medium geometry. However, the presented method in this paper can analyze the geometry effect of the unit cell with its medium characteristics up to high frequency region.

• Journal of the Korean Institute of Telematics and Electronics
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• v.25 no.12
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• pp.1625-1632
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• 1988

This paper aims not only to introduce the concept of linear singular systems, geometric structure, and feedback but also to provide applications of the multivariable linear singular system theories to electric circuits which may appear in some electronic equipments. The impulsive or discontinuous behavior which is not desirable can be removed by the set of admissible initial conditions. The output-nulling supremal (A,E,B) invariant subspace and the singular system structure algorithm are applied to this double-input double-output electric circuit. The Weierstrass form of the pencil (s E-A) is related to the output-nulling supremal (A,E,B) invariant subspace from which the time domain solutions of the finite and the infinite subsystems are found. The generalized Lyapunov equation for this application with feedback is studied and finally, the use of orthogonal functions in singular systems is discussed.

• Journal of Electrical Engineering and Technology
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• v.13 no.5
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• pp.1791-1797
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• 2018

Sub-Synchronous Resonance (SSR) is a phenomenon that harms turbine generator shafts because the phenomenon induces sub-synchronous wavering in the system. In the study presented in this paper, a dynamic resistance bank is used to mitigate the occurrence of sub-synchronous phenomenon. A fuzzy logic controller using rotor speed deviation and its derivative as inputs is implemented to damp sub-synchronous oscillations more efficiently. An eigenvalue technique is used to analyse the stability of the system, and a simulation in MATLAB is conducted, based on the IEEE Second Benchmark, to validate the effectiveness of the proposed method under a 3-phase fault condition at an infinite bus. The time-domain simulation and eigenvalues are used to observe the proposed method's superior ability to damp sub-synchronous oscillation.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1999.10a
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• pp.83-90
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• 1999

This paper presents a method of seismic analysis for a cylindrical liquid storage structure on horizontally layered half-space considering the effects of the interior fluid and exterior soil medium in the frequency domain. the horizontal and rocking motions of the structures are included in this study. The fluid motion is expressed in terms of analytical velocity potential function which can be obtained by solving the boundary value problem including the sloshing behavior of the fluid as well as deformed configuration of the structure. The effect of the fluid is included in the equation of motion as the impulsive added mass and a frequency-dependent convective added mass along the nodes on the wetted boundary with structure. The soil medium is presented using the 3-D axisymmetric finite elements and dynamic infinite elements. The present method can be applied to the structures embedded in ground as well as on ground since it models the soil medium directly as well as the structure. For the purpose of vertification dynamci characteristics of a tank on homogeneous half-space is analyzed. Comparison of the present results with those by others shows good agreement.

• Steel and Composite Structures
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• v.25 no.2
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• pp.187-196
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• 2017

In this work, transient thermo-piezo-elastic responses of an infinite functionally graded piezoelectric (FGPE) plate whose upper surface suffers time-dependent thermal shock are investigated in the context of different thermo-piezo-elastic theories. The thermal and mechanical properties of functionally graded piezoelectric plate under consideration are expressed as power functions of plate thickness variable. The solution of problem is obtained by solving the corresponding finite element governing equations in time domain directly. Transient thermo-piezo-elastic responses of the FGPE plate, including temperature, stress, displacement, electric intensity and electric potential are presented graphically and analyzed carefully to show multi-field coupling behaviors between them. In addition, the effects of functionally graded parameters on transient thermo-piezo-elastic responses are also investigated to provide a theoretical basis for the application of the FGPE materials.

• Journal of the Korean Mathematical Society
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• v.58 no.3
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• pp.703-722
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• 2021

Let G = (V, E) be a connected locally finite and weighted graph, ∆_p be the p-th graph Laplacian. Consider the p-th nonlinear equation -∆_pu + h|u|^p-2u = f(x, u) on G, where p > 2, h, f satisfy certain assumptions. Grigor'yan-Lin-Yang [24] proved the existence of the solution to the above nonlinear equation in a bounded domain Ω ⊂ V. In this paper, we show that there exists a strictly positive solution on the infinite set V to the above nonlinear equation by modifying some conditions in [24]. To the m-order differential operator 𝓛_m,p, we also prove the existence of the nontrivial solution to the analogous nonlinear equation.

• Structural Engineering and Mechanics
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• v.13 no.6
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• pp.615-638
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• 2002

This paper presents a method of seismic analysis for a cylindrical liquid storage structure considering the effects of the interior fluid and exterior soil medium in the frequency domain. The horizontal and rocking motions of the structure are included in this study. The fluid motion is expressed in terms of analytical velocity potential functions, which can be obtained by solving the boundary value problem including the deformed configuration of the structure as well as the sloshing behavior of the fluid. The effect of the fluid is included in the equation of motion as the impulsive added mass and the frequency-dependent convective added mass along the nodes on the wetted boundary of the structure. The structure and the near-field soil medium are represented using the axisymmetric finite elements, while the far-field soil is modeled using dynamic infinite elements. The present method can be applied to the structure embedded in ground as well as on ground, since it models both the soil medium and the structure directly. For the purpose of verification, earthquake response analyses are performed on several cases of liquid tanks on a rigid ground and on a homogeneous elastic half-space. Comparison of the present results with those by other methods shows good agreement. Finally, an application example of a reinforced concrete tank on a horizontally layered soil with a rigid bedrock is presented to demonstrate the importance of the soil-structure interaction effects in the seismic analysis for large liquid storage tanks.