• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.5
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• pp.458-463
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• 2010

Since the acoustic nonlinearity is sensitive to the minute variation of material properties, the nonlinear ultrasonic technique(NUT) has been considered as a promising method to evaluate the material degradation or fatigue. However, there are certain limitations to apply the conventional NUT using the bulk wave to thin plates. In case of plates, the use of Lamb wave can be considered, however, the propagation characteristics of Lamb wave are completely different with the bulk wave, and thus the separate study for the nonlinearity of Lamb wave is required. For this work, this paper analyzed first the conditions of mode pair suitable for the practical application as well as for the cumulative propagation of quadratic harmonic frequency and summarized the result in for conditions; (1) phase matching, (2) non-zero power flux, (3) group velocity matching, and (4) non-zero out-of-plane displacement. Experimental results in aluminum plates showed that the amplitude of the secondary Lamb wave and nonlinear parameter growed up with increasing propagation distance at the mode pair satisfying the above all conditions and that the ration of nonlinear parameters measured in Al6061-T6 and Al1100-H15 was closed to the ratio of the absolute nonlinear parameters.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.12 no.4
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• pp.62-69
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• 1998

The harmonics caused b th nonlinear operation of transmission equipments are not identified yet and have been seldom studied. Sources of harmonics in nonlinear circuit, especially caused by the nonlinear operation of transmission equipments, can be approximately modeled with Duffing's Equation which is often referred in nonlinear mechanical oscillation problem. In this study, a new analytic technique is proposed for the analysis of harmonics n nonlinear circuits using Duffing's Equation and compared with some conventional methods. Finally some case studies were performed to evaluate the performance of proposed method and conventional methods.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.17 no.6
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• pp.113-118
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• 2003

This paper characterizes typical nonlinear loads into two types of harmonic sources, i.e., harmonic voltage source and harmonic current source. A series resonant filter is very effective in harmonic reduction for harmonic voltage source type of nonlinear loads such as personal computer loads with smoothing dc capacitors. A parallel resonant filter is suited for current source type of nonlinear loads such as ac drives with smoothing dc reactors. General compensation characteristics and comparison of series and parallel resonant filters are given analytically and experimentally. Compliance with IEC Std 1000-3-2 has been evaluated for limiting harmonic distortion.

• Proceedings of the KIPE Conference
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• 2016.11a
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• pp.222-223
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• 2016

본 논문에서는 계통연계 인버터에서 비선형부하의 위치에 따라서 발생되는 고조파를 보상하기위한 전류제어 방식을 사용하였다. 비선형부하로 인해 발생되는 고조파는 계통 전압 및 전류의 THD에 많은 영향을 미치기 때문에 이를 보상하는 것이 본 논문의 목적이다. 비선형부하의 위치에 따라서 각각의 경우에 대해 두가지의 고조파 지령값을 선택하는 방식을 사용하였다.

• The Korean Journal of Rheology
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• v.9 no.3
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• pp.97-102
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• 1997

내피로성은 기계적 구조물로 사용되는 고분자재료에는 반드시 필요한 성질이며, 피 로거동은 재료특유의 비선형 동적 점탄특성과 아주 밀접한 관계가 있다. 본 연구에서는 피 로과정에서의 비선형 동적 점탄특성을 정량적, 연속적으로 측정할수 있는 시험 기기와 가해 준 변형에 대한 응답 응력파의 기본 응력파(선형적 응답)로부터의 차이를 직접 측정하여 이 를 규격화한 비선형 점탄성파라미터, NVP(Nonlinear Viscoelastic Parameter)라 명명한 새 로운 평가방법을 개발하였다. 그리고 고밀도 폴리에틸렌(HDPE) 배향물을 사용하여 그 평가 방법의 타당성을 조사한 결과 피로과정에서의 비선형동적 점탄특성을 나타내는 NVP가 증 가함에 따라 재료의 피로수명은 감소하였다. 따라서 NVP가 고분자재료의 내피로성을 평가 하는 척도로서 사용가능하다는 사실이 증명되었다. 또한 각 고조파 성분에대해 조사한 결과 인장형 피로시험양식에서는 고체입자 분산계의 전단변형에서 나타난 비선형 점탄성의 결과 와는 달리 2차 성분의 크기가 가장컸으며 NVP에의 기여도도 가장 크게 나타났다. 이는 변 형양식의 차이에 따른 결과를 볼수 있다.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.8 no.1
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• pp.95-102
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• 1996

The skewness of near-bottom velocity distribution caused by the nonlinear interaction of the second order waves proposed by Wells (1967) has been re-evaluated. The direction of cross-shore sediment transport was related to the sign of the third moment (skewness) of velocity distribution, and a new concept of neutral depth which can explain the recovery of beach equilibrium after a disturbance is suggested. The seasonal change of beach profile due to the change of wave condition (storm-swell profile) is interpreted in terms of nonlinear interaction of the waves rather than the conventional wave steepness. The beach is eroded (storm profile) when the nonlinear interaction of the waves is strong (storm wave), whereas the beach is accreted (swell profile) when the nonlinear interaction is weak (swell wave).

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.6 no.3
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• pp.281-289
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• 1994

An equation set of nonlinear model for regular/irregular waves presented in this study can be applied to waves travelling from deep water to shallow water, which is different from the Boussinesq equations. The presented equations completely satisfy the linear dispersion relationship and when expanded, they are proven to be consistent with the Boussinesq equation of several types. In addition, the position of averaged velocity below the still water level is estimated based on the linear wave theory.

• Proceedings of the KIEE Conference
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• 2009.04b
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• pp.23-25
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• 2009

전력용 커패시터는 전압 보상 및 부하에 필요한 무효전력을 전원측을 대신하여 공급함으로서 역률을 향상시킬 수 있으며, 리액터와 직렬로 연결할 경우 비선형 부하에서 발생하는 고조파 성분을 흡수하여 전압 고조파 왜형을 줄이고 전류고조파를 흡수하는 필터로도 사용이 가능하다. 그러나 수용가 부하가 일정하지 않고 변동하거나 선형부하와 비선형 부하가 존재할 경우 커패시터가 고조파의 홉수 등으로 인해 고장이 나는 경우가 많은 편이다. 그래서 본 연구에서는 현장에서 각 부하기기에 고조파를 줄이는 장치의 부착과 부착 전후 커패시터에 미치는 영향을 측정 분석하여 커패시터 규정과의 비교도 실시하였다.

• Journal of Korea Water Resources Association
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• v.38 no.6 s.155
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• pp.429-438
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• 2005

In this study, a couple of ordinary differential equations which can describe random waves are derived from the Boussinesq equations. Incident random waves are generated by using the TMA(TEXEL storm, MARSEN, ARSLOE) shallow-water spectrum. The governing equations are integrated with the 4-th order Runge-Kutta method. By using newly derived wave equations, nonlinear energy interaction of propagating waves in constant depth is studied. The characteristics of random waves propagate over a sinusoidally varying topography lying on a sloping beach are also investigated numerically. Transmission and reflection of random waves are considerably affected by nonlinearity.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.04a
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• pp.13-16
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• 2007

Nonlinear acoustic damping of a half-wave acoustic resonator in a combustion chamber is investigated numerically. First, in a baseline chamber without any resonators, acoustic behavior is investigated over the wide range of acoustic amplitude from 80 dB to 150 dB. Decay rate increases nonlinearly with acoustic amplitude and nonlinearity becomes appreciable at acoustic amplitude above 125 dB. Next, damping effect of a half-wave resonator is investigated. Nonlinear acoustic excitation does not affect optimum tuning condition of the resonator, which is derived from linear acoustics. A half-wave resonator is effective even for acoustic damping of high-amplitude pressure oscillation, but its function of acoustic damper is relatively weakened compared with the case of linear acoustic excitation.