• Journal of KSNVE
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• v.9 no.1
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• pp.131-140
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• 1999

A method to reconstruct the sound field around a Korean bell is developed. The sound radiation problem is formulated based on the boundary element method by using the algorithm of the acoustical holography. Sound pressures at the hologram surface are measured and used as input data for the analysis program that was developed in this study. An error minimization scheme is presented to overcome difficulties that arise in the backward reconstruction of the BEM-based acoustical holography In the model fictitious source surfaces were also introduced to reduce the complexity stemmed from the source shape. The sound field associated with the (4.0) vibrational mode of the Korean bell was visualized and verified experimentally.

• Journal of Industrial Technology
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• v.15
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• pp.71-75
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• 1995

A method of calculating the natural frequency corresponding to the first mode of vibration of beams and tower structures, with irregular cross-sections and with arbitrary boundary conditions was developed and reported by D. H. Kim in 1974. This method has been developed for two-dimensional problems including the laminated composite plates and was proved to be very effective for the plates with arbitrary boundary conditions and irregular sections. In this paper, the result of application of this method to the clamped composite plates with non-uniform cross-section and with attached point mass/masses is presented.

• Journal of Welding and Joining
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• v.19 no.2
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• pp.200-207
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• 2001

Three-diemnsional bead profile was measured using the biprism stereo vision sensor in GMAW, which consists of an optical filter, biprism and CCD camera. Since single CCD camera is used, this system has various advantages over the conventional stereo vision system using two cameras such as finding the corresponding points along the horizontal scanline. In this wort, the biprism stereo vision sensor was designed for the GMAW, and the linear calibration method was proposed to determine the prism and camera parameters. Image processing techniques were employed to find the corresponding point along the pool boundary. The ism-intensity contour corresponding to the pool boundary was found in the pixel order and the filter-based matching algorithm was used to refine the corresponding points in the subpixel order. Predicted bead dimensions were in broad agreements with the measured results under the conditions of spray mode and humping bead.

• Structural Engineering and Mechanics
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• v.52 no.3
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• pp.595-601
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• 2014

For analysis of the plates and membranes by numerical or analytical methods, the question of choice of the system of functions satisfying the different boundary conditions remains a major challenge to address. It is to this issue that is dedicated this work based on an approach of choice of combinations of trigonometric functions, which are shape functions of a bended beam with the boundary conditions corresponding to the plate support mode. To do this, the shape functions of beam vibrations for strength analysis of the rectangular plates by Kantorovich-Vlasov's method is considered. Using the properties of quasi-orthogonality of those functions allowed assessing to differential equation for every member of the series. Therefore it's proposed some new forms of integration of the beam functions, in order to simplify the problem.

• Journal of Advanced Navigation Technology
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• v.18 no.4
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• pp.371-375
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• 2014

In this paper, the solutions of TE(transverse electric) scattering problems by a resistive strip grating over a grounded dielectric layer are analyzed by applying the PMM(point matching method) known as a numerical method of electromagnetic fileld. The boundary conditions are applied to obtain the unknown field coefficients and the resistive boundary condition is used for the relationship between the tangential magnetic field and the induced surface current density on the resistive strip. The induced surface current density of resistive strip is obtained by difference of the up and down of the magnetic field in two boundary areas of the resistive strip. The numerical results for reflected power of zeroth order mode analyzed by according as the resistivity, the width and spacing of resistive strip, the relative permittivity and thickness of dielectric layer, and incident angles. The numerical results shown in good agreement compared to those of the existing papers using FGMM(fourier galerkin moment method).

• Journal of the Optical Society of Korea
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• v.12 no.2
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• pp.112-117
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• 2008

Single-mode propagation conditions of X-ray waveguides are investigated by numerical calculations in order to understand the importance of waveguide design parameters, such as core thickness and the optical constants of waveguide materials, on the transmission and coherence properties of the waveguide. The simulation code for mode analyzing is developed based on a numerical solution of the parabolic wave equation. The initial boundary value problem is solved numerically using a finite-difference scheme based on the Crank-Nicolson scheme. The E-field intensities in a core layer are calculated at an X-ray energy of 8.0 keV for air and beryllium(Be) core waveguides with different cladding layers such as Pt, Au, W, Ni and Si to determine the dependence on waveguide materials. The highest E-field intensity radiated at the exit of the waveguide is obtained from the Pt cladded beryllium core with a thickness of 20 nm. However, the intensity from the air core waveguide with Pt cladding reaches 64% of the Be-Pt waveguide. The dependence on the core thickness, which is the major parameter used to generate a single mode in the waveguide, is investigated for the air-Pt, and Be-Pt waveguides at an X-ray energy of 8.0 keV. The mode profiles at the exit are shown for the single mode at a thickness of up to 20 nm for the air-Pt and the Be-Pt waveguides.

• Journal of Power Electronics
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• v.19 no.1
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• pp.201-210
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• 2019

This paper proposes a multimode hybrid control strategy that can achieve zero-voltage switching of primary switches and zero-current switching of secondary rectifier diodes in a wide input voltage range for full-bridge LLC resonant converters. When the input voltage is lower than the rated voltage, the converter operates in Mode 1 through the variable-frequency control strategy. When the input voltage is higher than the rated voltage, the converter operates in Mode 2 through the VF and phase-shift control strategy until the switching frequency reaches the upper limit. Then, the converter operates in Mode 3 through the constant-frequency and phase-shift control strategy. The secondary-side diode current will operate in the discontinuous current mode in Modes 1 and 3, whereas it will operate in the boundary current mode in Mode 2. The current RMS value and conduction loss can be reduced in Mode 2. A detailed theoretical analysis of the operation principle, the voltage gain characteristics, and the realization method is presented in this paper. Finally, a 500 W prototype with 100-200 V input voltage and 40 V output voltage is built to verify the feasibility of the multimode hybrid control strategy.

• Journal of Power System Engineering
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• v.12 no.2
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• pp.35-40
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• 2008

This paper deals with the free vibrations of conical shells with linearly variable thickness by the transfer influence coefficient method. The classical thin shell theory based upon the Flugge theory is assumed and the governing equations of a conical shell are written as a coupled set of first order matrix differential equations using the transfer matrix. The Runge-Kutta-Gill integration method is used to solve the governing differential equation. The natural frequencies and corresponding mode shapes are calculated numerically for the conical shells with linearly variable thickness and various boundary conditions at the edges. The present method is applied to conical shells with linearly varying thickness, and the effects of the semi-vertex angle, the number of circumferential waves and thickness ratio on vibration are studied.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.8 no.2
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• pp.86-93
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• 1999

Ceramic/metal bonded joints have led to increasing use of structural materials such as automobiles and heat engines. A method of strength evaluation focussing on fracture criterion of mixed mode was investigated in {{{{ {Si }_{3 } {N }_{4 } }}}}/metal bonded joint, Also Fracture toughness tests of {{{{ {Si }_{3 } {N }_{4 } }}}}/metal bonded joints with an interface crack were carried out and the stress intensity factors of these joints were analyzed by boundary element method. Form the results the fracture criterion and method of strength evaluation by the fracture toughness were proposed in {{{{ {Si }_{3 } {N }_{4 } }}}}/Metal bonded joints

• Structural Engineering and Mechanics
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• v.9 no.5
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• pp.483-490
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• 2000

After manufacturing a structure, the assembly of structural components is often not as perfect as expected due to the immaturity of current engineering techniques. Thus the actual buckling load for an element is sometimes not consistent with that predicted in the design. For design considerations, it is necessary to establish an analytical method for determining the buckling load experimentally. In this paper, a dynamic method is described for determining the linear buckling loads for elastic, perfectly flat plates. The proposed method does not require the application of in-plane loads and is feasible for arbitrary types of boundary conditions. It requires only the vibrational excitation of the plate. The buckling load is determined from the measured natural frequencies and vibration mode shapes.