• 전기의세계
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• v.45 no.5
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• pp.30-37
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• 1996

이 기술 논문의 목적은 플랜트 모델의 불확실성이 매개변수의 섭동으로 표현되는 제어계의 강인 안정도, 강인 제어성능, 강인 제어기 설계에 관한 최근의 연구결과들을 소개하는 것이다.

• The Journal of the Acoustical Society of Korea
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• v.17 no.5
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• pp.79-84
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• 1998

본 논문은 길이방향으로 조화함수 형태로 변화하는 단면적을 가진 원형단면의 탄성 막대에서 전파하는 비틂 탄성파의 전파속도에 대한 이론적 및 실험적 결과를 제시한다. 주 기적인 미소한 반경 변화를 섭동법에 의해 다루어 전파속도의 이론적 근사해를 구하였다. 그결과 전파속도는 반경 변화 폭의 제곱에 비례하는 양 만큼 감소하는 경향이 나타났다. 이 론적 경향을 검증하기 위한 실험은 자왜현상으로 비틂파를 전파시키고 나사면을 가진 탄성 도파관에서 전파속도를 측정하는 방법으로 행하였다.

• Journal of KSNVE
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• v.4 no.4
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• pp.435-442
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• 1994

Self-Compensating Dynamic Balancer (SCDB) is composed of a circular disk with a groove containing spherical balls and a low viscosity damping fluid. To investigate the stability of the motion equations these equations are perturbed and the resulting perturbation equations are analyzed further to determine whether the perturbations grow or decay with dimensionless time. Based on the results of stability investigation, ball positions that result in a balanced system are stable above the critical speed for .betha.' = 3.8. At critical speed the perturbed motion is said to be stable for .betha.' = 23. However, the system is unstable below critical speed in any case of .betha.'.

• The Journal of the Acoustical Society of Korea
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• v.31 no.1
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• pp.11-18
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• 2012

In this paper, the occurrence of a stopband phenomenon when an acoustic wave propagates through periodically corrugated ducts is discussed using theoretical and BEM analyses. A 2-D duct with sinusoidally corrugated upper and lower walls is considered. When the magnitude of the sinusoidal corrugation is sufficiently small compared to the duct's height, the wave equation is solved with the multiple scaling perturbation method. Then stopbands for Bragg and non-Bragg resonances are computed from the condition where frequency becomes a complex number. A 2-D BEM analysis is performed to compute insertion loss of the duct, and stopbands are confirmed as predicted by analytical analysis.

• Journal of the Korean earth science society
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• v.33 no.1
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• pp.11-31
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• 2012

Kaula's theory of satellite orbit and Kepler's law are re-visited. All the mathematical steps of derivation are thoroughly shown including the ones, which had been omitted in Kaula's original publication. Particularly in evaluations of the 15 independent Lagrange brackets, simplicity and clarity are attained by using orthogonal property of transformation matrix. Explanations of important physical concepts are included as well in the midway of derivation. One conceptual blunder of Kaula's is corrected.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.68-77
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• 2017

High-frequency combustion instability results from a feedback coupling between the unsteady heat release rate and the acoustic waves formed resonantly in the combustion chamber. It can be modeled as thermoacoustic problems with various degrees of the assumptions and simplifications. This paper presents numerical analysis of self-excited combustion instabilities in a variable-length lean-premixed combustor and designs of passive control devices such as baffle and acoustic resonators in a framework of 3-D FEM Helmholtz solver. Nonlinear behaviors such as steep-fronted shock waves and a finite amplitude limit cycle are also investigated with a compressible flow simulation technique.

• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.1
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• pp.16-24
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• 2008

Near-field scanning microwave microscope (NSMM) has been used to characterize the electromagnetic properties of samples based on a cavity perturbation technique. We used a NSMM using a waveguide cavity to couple a metallic probe tip as a point like evanescent field emitter. We explained the quality of our NSMM system by applying the cavity perturbation theory. First, to make a shape perturbation, we inserted linear and loop probes in the waveguide resonator. To check up electric and magnetic field distribution inside the waveguide resonator by shape perturbation, we confirmed the field distribution by using a HFSS simulation. Second, to make material perturbation, we located a dielectric sample in front of the probe tip and measured reflection coefficient $(S_{11})$. We found that the resonance frequency$(f_r)$ was changed linearly as the dielectric constant of resonator$({\varepsilon}_r)$ increased when ${\Delta}{\varepsilon}\;and\;{\Delta}{\mu}$ were small.

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.4
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• pp.106-113
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• 2002

A procedure to model and simulate control systems is presented using CADyna and MATLAB/Simulink computer codes. For the plant modeling, a technique for obtaining the state matrices from CADyna is presented. To obtain state matrices from CADyna models, perturbation theory is used. These state matrices are then used in NATLAB to design a controller for the plant. The controller design can subsequently be incorporated into the CADyna model and its closed loop performance is evaluated. Examples are presented to verify the developed methodology.

• Journal of Korea Water Resources Association
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• v.34 no.6
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• pp.651-657
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• 2001

The second-order long waves generated by short wave groups propagating over a step are theoretically investigated. The diffraction of short waves is firstly formulated and the governing equations of second-order long waves are then derived by using a multiple-scale perturbation method. It is observed that free and locked long waves are generated and propagated with different velocities.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.7 no.4
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• pp.161-166
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• 1982

In this paper, the intrinsic birefringence and twist-induced rotation of the single mode optical fiber have been investigated. On the analysis, the optical fiber has been modeled as a linear retarder and the intrinsic linear retardation of the single mode optical fiber is approximately found to be 2.57'/m from the measurement. Theoretically analyzing the twist-induce rotation by the purturbation theory, it is found that the magnitude of the twist-induced rotation varies linearly with the twisted angle. And this theorerical result has been in good accord with the experimental result.