• Journal of the Korean Society for Nondestructive Testing
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• v.12 no.1
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• pp.9-15
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• 1992

Ultrasonic spectroscopy is likely to become a very powerful NDE method for detection of microfects and thickness measurement of thin film below the limit of ultrasonic distance resolution in the opaque materials, provides a useful information that cannot be obtained by a conventional ultrasonic measuring system. In this paper, we considered a thin film below the limit of ultrasonic distance resolution sandwitched between two substances as acoustical analysis model, demonstrated the usefulness of ultrasonic spectroscopic analysis technique using information of ultrasonic frequency for measurements of thin film thickness, regardless of interference phenomenon and phase reversion of ultrasonic waveform. By using frequency intervals(${\triangle}f$) of periodic minima from the ratio of reference power spectrum of reflective waveform obtained a sample to power spectrum of multiple reflective waves obtained interference phenomenon caused by ultrasonic waves reflected at the upper and lower surfaces of a thin layer, can measured even dimensions of interest are smaller than the ultrasonic wave length with simplicity and accuracy.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.1
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• pp.1-12
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• 1993

Tangent stiffness matrices are derived for the torsional and lateral stability analysis of the space beams and framed structures with the symmetric thin-walled section by using the principle of virtual displacement. In the cases of restrained torsion and unrestrained torsion, the elastic and geometric stiffness matrices are evaluated by using the Hermitian polynomials which represent the displacement field of the beam element in simple flexure. Numerical examples illustrate the accuracy and convergence characteristics of the derived formulations.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1993.10a
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• pp.475-481
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• 1993

The objective of this study is to develope the reliability prediction model for Float Rated Integrating Gyroscope( :FRIG) at maximum loading. The equation of motion for FRIG is firstly derived to set up the reliability prediction model. To analysis reliability or all parts of the gyro is not easy due to their complicated structure. Therefore the failure parts are chosen by Failure Mode Effective Analysis (:FMEA). F.E.M is utilized to calculate loads for the selseced rotating assembly and pivot / jewel. The technical reliability is calculated by applying reliability design theory with these results and the performance reliability is sought through distribution estimation with error test data. The bulk reliability of gyroscope is sought by applying the two results. The present prediction results are compared with the accumulation time in good agreement.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.752-755
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• 2001

In order to investigate the vibration characteristics of fluid-structure interaction problem, we modeled two rectangular identical plates coupled with bounded fluid. The fixed boundary condition along the plate edges and an ideal fluid are assumed. MSC/NASTRAN was used to perform finite element analysis and analytic solutions were compared with experimental solutions to verify finite element model. As a result, comparison of FEM and experiment show good agreement, and the transverse vibration modes, in-phase and out of-phase, were observed alternately in the fluid-coupled system. The effect of distance between two rectangular plates on the fluid-coupled natural frequency is investigated.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 1999.02a
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• pp.81-84
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• 1999

The purpose of this paper is to find the magnetic field distribution inside the motor in order to find out if the high-Tc superconducting tapes operate stably in actual motor operation. With this gola, magnetic field distribution in a detailed model of the actual motor was analyzed through F.E.M. (Finite Element Method). As a result, it has been proved that the high-Tc superconducting tapes can withstand 4 A of current with stability. 4 A was the amount of current needed to achieve 600 A ·turns which is required by the previous simulation aimed at developing this motor. Also, it has been observed that the flux damper reduces armature reactance during the motor operation and during load changes, helping the stable motor operation. But, it was observed that the flux damper generates loss by means of leakage flux and this decreases the output of the motor by about 5%.

• Progress in Superconductivity and Cryogenics
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• v.1 no.2
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• pp.25-29
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• 1999

The purpose of this paper is to find the magnetic filed distribution inside the motor in order to find out if the high-Tc superconducting tapes operate stably in actual motor operation in a detailed model of the actual motor was analyzed through F.E.M.(finite Element Method). As a result, it has been proved that the high-Tc superconducting tapes can with-stand 4 A of current with staility. 4 A was the amount of current with stability. 4 A was the amount of current needed to achieve 600 A·turns which is required by the previous simulation aimed at developing this the flux damper reduces armature reactance during the motor operation. But it was observed that the flux damper generates loss by means of leakage flux and this decreases the output of the motor by about 5%.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.569-574
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• 2005

The steel retaining wall(s.r.w) are not constructed broadly all over the world. So the method of the analysis and the estimation for the behavior of the s.r.w. the interactive behavior of the frame and the fill material. In this study, the numerical analysis using F.E.M. was made to analize the mutural relation of the frame and the fill material in prior to the s.r.w. model test.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.35 no.11
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• pp.479-486
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• 1986

It is necessary to consider a rotor movement in dynamic analysis on the flux distribution of electric machinery by FEM. Therefore, if air-gap domain was subdivided into triangular elements, computation results contain errors due to variation of element shape in air-gap because the nodal points corresponding to the rotor are displaced in analyzing domain for the time difference. In order to reduce this errors, the paper presents a application of a Macro Air-gap Element that interpolation function is obtained analytically and a means to join it with linear triangular elements in the rotating machine or in the linear machine. At the end of paper, setting up analytic domain model, it compares analytic solution with the computation results of Macro Air-gap Element appliction and that of linear triangular element subdivision only to each cases of nodal displacement. And it carries out that errors due to variation of element shape are reduced effectively by application of a Macro air-gap element.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.5
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• pp.1462-1471
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• 1991

본 연구에서는 미소 결함주위에서 발생, 전파하는 균열들에 미치는 초기 결함 깊이와 상호 간섭 영향을 검토하기 위하여 기존 재료가 갖고 있는 결함이나 비금속 개 재물로 대신할 수 있다고 생각되는 미소 원공의 크기를 변화시킨 모델에 대해 유한 요 소법을 이용하여 3차원적으로 응력을 해석하였다. 실제 사용하고 있는 부재에 결함 들이 존재할 경우 응력장의 간섭으로 피로 균열 진전이 가속화됨으로 미소 원공 주위 의 응력 분포 및 미소 원공사이의 응력장의 간섭과 미소 원공에서 발생, 전파하는 표 면 균열의 응력 확대 계수에 미치는 영향에 대하여 비교검토 하였다.

• Journal of the Korean Society for Precision Engineering
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• v.13 no.5
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• pp.30-37
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• 1996

The objective of this research is to explore the analysis and test method for the reliable design and fabrication of a high precision dynamically tuned gyroscope. The tuning frequency is decided by the calculation of mass moment of inertia of rotor and gimbal and the stiffness of flexures. Due to the complex geometry of the flexure, calculation of the stiffness of the suspension flexure is difficult. In this paper, three analytical methods for obtaining the stiffness of the flexure are porposed and a special testing method is used for checking the accuracy of the computed results.