• Proceedings of the Korea Institute of Convergence Signal Processing
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• 2006.06a
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• pp.33-36
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• 2006

본 논문은 에지부분에서 뚜렷한 영상의 복원이 가능하도록 하는 칼라 영상의 비선형 보간 기법에 관한 것이다. 일반적으로 칼라영상을 구성하고 있는 성분중 휘도신호(Y)가 에지(edge)성분에 충실한 정보를 갖고 있다는 점에 착안하여 알고리즘 연구를 수행하였다. 일반적인 선형 보간 방법을 사용할 시 영상에서 고주파 대역의 손실을 일으키므로 영상의 화질 열화가 발생한다. 이를 보완하기 위해 본 논문에서는 비선형 보간법인 에지 방향성 보간 방법을 제안하였다 또한 조밀한 에지 영역에서의 에지 방향성 보간의 단점을 극복하기 위해 선형 보간과 에지방향성 보간 기법의 혼합을 통한 화질 열화 제거 기법을 제안한다.

• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.4
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• pp.352-357
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• 2008

The detection of micro cracks in materials at the early stage of fracture is important in many structural safety assurance problems. The nonlinear ultrasonic technique (NUT) has been considered as a positive method for this, since it is more sensitive to micro crack than conventional linear ultrasonic methods. The basic principle is that the waveform is distorted by nonlinear stress-displacement relationship on the crack interface when the ultrasonic wave transmits through, and resultantly higher order harmonics are generated. This phenomenon is called the contact acoustic nonlinearity (CAN). The purpose of this paper is to prove the applicability of CAN experimentally by detection of micro fatigue crack artificailly initiated in Aluminum specimen. For this, we prepared fatigue specimens of Al6061 material with V-notch to initiate the crack, and the amplitude of second order harmonic was measured by scanning along the crack direction. From the results, we could see that the harmonic amplitude had good correlation with COD and it can be used to detect the crack depth in more accurately than the common 6 dB drop echo method.

• Journal of the Korean earth science society
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• v.38 no.4
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• pp.263-268
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• 2017

The determination algorithm of the location of a line source with strike and dip using the gravity gradient tensor on a single profile is proposed. We already proposed the determination of strike and dip in the previous paper and then, now we improved the algorithm to locate a line source after determining strike and dip. The strike and dip of the line source can be determined by rotating the gravity gradient tensor matrix as reducing 2 independent components. Using the ratio of remaining 2 components, the location can be determined by the least square manner of the pointing vectors on each observation point. A synthetic model is tested for proving the usefulness of the proposed algorithm.

• The KIPS Transactions:PartB
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• v.16B no.3
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• pp.239-246
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• 2009

In this paper, we propose a Korean character recognition method from outboard signboard images. We have chosen 808 classes of Korean characters by an analysis of frequencies of appearance in a dictionary of signboard names. The proposed method mainly consists of three steps: feature extraction, rough classification, and coarse classification. The first step is to extract a nonlinear directional segments feature, which is immune to the distortion of character shapes. The second step computes an ordered set of 10 recognition candidates using a minimum distance classifier. The last step reorders the recognition candidates using a Fisher discriminant measure. As experimental results, the recognition accuracy is 80.45% for the first choice, and 93.51% for the top five choices.

• Proceedings of the Optical Society of Korea Conference
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• 2000.02a
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• pp.306-307
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• 2000

1962년 Armstrong 등에 의해 second harmonic generation(SHG) 의 이론이 완성된 후 SHG 효율을 높이기 위한 방법으로 비선형성이 큰 물질의 개발과 더불어 위상정합(phase matching)을 만족시키는 여러가지 방법이 연구 되었다. 특히 위상정합의 경우 지금까지는 복굴절을 이용하는 방법이 널리 사용되었으나 이 경우 입사광의 파장이 제한적이고, 많은 무기물 결정에서 비선형광학계수의 가장 큰 텐서 성분인 $d_{zzz}$를 사용할 수 없다는 단점을 가지고 있다. 반면 유사위상정합(Quasi-phase matching:QPM) 은 비선형광학계수( $d_{zzz}$)의 방향을 결맞음 길이(coherence length)마다 분극반전 시켜주어 2차 조화파의 진폭을 길이방향으로 계속 증가시키는 방법으로 구역반전된 길이를 조절하면 거의 모든 파장에 대해 비임계 위상정합( $d_{zzz}$ 사용)이 가능하고, 2차 조화파가 기본파의 전파경로에서 벗어나는 walk-off 현상이 없어 SHG 전환효율을 극대화할 수 있다. (중략). (중략)

• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.4
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• pp.376-387
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• 2012

Based on the nonlinear spring model coupled with perturbation method, 2nd harmonic waves generated by oblique incident ultrasound on nonlinear crack interface were calculated and investigated. Reflected and transmitted waves from the interface were determined and analyzed at various angle of incidence for the cracks with different interfacial stiffness in order to estimate the 2nd harmonic generation of incident ultrasound. It was shown in computer simulation that the 2nd harmonic components changed much with the increase of incidence angle in both reflected and transmitted wave, but became very small when the incident angle approached toward 90 degree. It can be concluded that the 2nd harmonic component of reflected wave has a meaningful amplitude as much as the transmitted 2nd harmonic wave from partly closed crack.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.25 no.12
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• pp.1817-1825
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• 2021

Omnidirectional mobile robots can be mobile in any direction without changing the robot's direction, making them easy to apply in many applications and providing excellent maneuverability. Omnidirectional mobile robots have non-linear dynamic components such as friction, making them difficult to model accurately. In this paper, we linearize the mobile robot system using the mobile robot's inverse dynamics and integral sliding mode control method to remove these nonlinear components. And the position and velocity gains are optimized using a genetic algorithm to realize the optimal performance of the proposed system control method. As a result of the performance evaluation, the genetic algorithm's control method showed superior performance than the control method with an arbitrary gain. And the proposed inverse dynamic and integral sliding mode control method can be applied to other control methods. It can be beneficial for designing a linear control system.

• Journal of the Korean Society for Nondestructive Testing
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• v.26 no.2
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• pp.77-83
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• 2006

Ultrasonic nonlinearity has been considered as a solution for the detection of microcracks or interfacial delamination in a layered structure. The distinguished phenomenon in nonlinear ultrasonics is the generation of higher-order harmonic waves during the propagation. Therefore, in order to quantify the nonlinearity, the conventional method measures a parameter defined as the amplitude ratio of a second-order harmonic component and a fundamental frequency component included in the propagated ultrasonic wave signal. However, its application In field inspection is not easy at the present stage because no standard methodology has yet been made to accurately estimate this parameter. Thus, the aim of this paper is to propose an advanced signal processing technique for the precise estimation of a nonlinear ultrasonic parameter, which is based on power spectral and bispectral analysis. The method of estimating power spectrum and bispectrum of the pulse-like ultrasonic wave signal used in the commercial SAM (scanning acoustic microscopy) equipment is especially considered in this study The usefulness of the proposed method Is confirmed by experiments for a Newton ring with a continuous air gap between two glasses and a real semiconductor sample with local delaminations. The results show that the nonlinear parameter obtained tv the proposed method had a good correlation with the delamination.

• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.185-188
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• 1999

수중에서 기포의 강한 비선형성을 이용하여 기포막상의 두 입사 음파의 상호작용 영역으로부터 산란된 차주파수 성분 음파의 확인과 두 입사 음파의 전파방향으로 차주파수 음파가 분포하고 있음을 관측하였다 본 논문에서는 기포막을 이용하여 두 입사 음파의 상호작용 영역으로부터 산란된 차주파수 성분 음파의 지향특성을 예측할 수 있음을 제시하였다.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.11 no.1
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• pp.20-33
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• 1999

The evolution of deep-sea waves is driven by energy input from wind, nonlinear energy transfer between wave components, and dissipation through whitecaps. A comparative study was implemented by the use of two wave models in which only the computation methods of nonlinear wave-wave interactions are different from each other. It was reaffirmed that the nonlinear interaction plays a central role in such phenomena that occurred during the spectral growth of wind-seas as down-shift of the spectral peak frequency, overshoot, undershoot, and formation of self-similar spectrum. Specifically, the directional distribution at high frequencies develops into bimodal form, which is attributed to the nonlinear interactions. As saturation stage is reached, spectral density at high frequencies becomes proportional to negative 4 power to the frequency. Perturbations introduced into the spectrum quickly vanished through the actions of the self-similar mechanism. Thus, the nonlinear transfer has important contribution to the stability of numerical ocean wave models.