• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.10
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• pp.983-989
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• 2004

In this paper, a modeling method for the vibration analysis of rotating structures employing multi-reference frames is presented. The geometric stiffening effect that results from centrifugal inertia force is considered. In most previous studies single reference frame has been employed for the analysis. In the present study, a modeling method employing multi-reference frames is presented, and the effects of employing multi-reference frames on the analysis accuracy are investigated through solving numerical examples.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.52 no.10
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• pp.475-483
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• 2003

In this paper, dynamic characteristics of the magnetic flux leakage(MFL) type non-destructive testing(NDT) are analyzed. Effects of a sensor speed in MFL PIG system and remanent magnetization of the gas pipeline are analyzed by using 3 dimensional nonlinear finite element analysis including eddy current and hysteresis characteristics. Results show that the speed of the sensor reduces the magnitude of the sensing signals where as the hysteresis of the pipeline distorts the sensing signals.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.54 no.2
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• pp.101-109
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• 2005

The newly developed speed sensorless control scheme is proposed to estimate both motor speed and rotor resistance simultaneously using variable rotor flux. The rotor flux is given as sinusoidal waveform with an amplitude and a frequency without affecting precise torque control. Especially the proposed method makes the simultaneous estimation of rotor resistance and speed with high precision even though at the low speed area including a few rpm. Moreover, on-line identification of rotor resistance can be performed simply without calculating troublesome trigonometric functions and complicated integral computation. Therefore, the proposed system can be accomplished by using very cheap microprocessors for several applications. The results of the numerical simulations and experiments demonstrate that this method is effective to estimate the speed and on-line identification of rotor resistance for sensorless induction motors.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.48 no.8
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• pp.408-416
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• 1999

The characteristics of permanent magnet synchronous motor are defined by airgap flux and circuit parameters. Interior Permanent Magnet Synchronous Motor(IPMSM) has a nonlinear characteristics due to structural speciality of rotor, so it is difficult to analyze circuit parameters and field-weakening characteristics of IPMSM. This paper presents the calculation of circuit parameters by using Finite Element Method(FEM) taken into consideration of nonlinear characteristics. Using the circuit parameters by FEM, IPMSM is analyzed to field-weakening characteristics and is compared with the Equivalent Magnetic Circuit(EMC) in which lumped parameter is consideration.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.26 no.4
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• pp.225-243
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• 2014

As the economic matters are involved, applying the WEC, which is used for controlling waves as well as utilizing the wave energy on existing breakwater, is preferred rather than installing exclusive WEC. This study examines the OWC mounted on a pressurized air chamber floating breakwater regarding the functionality of both breakwater and wave-power generation. In order to verify the performance as a WEC, the velocity of air flow from pressurized air chamber to WEC has to be evaluated properly. Therefore, numerical simulation was implemented based on BEM from linear velocity potential theory as well as Boyle's law with the state equation to analyze pressurized air flow. The validity of the obtained values can be determined by comparing the previous results from numerical analysis and empirically obtained values of different shapes. In the actual numerical analysis, properties of wave deformation around OWC system mounted on fixed type and floating type breakwaters, motions of the structure with air flow velocities are investigated. Since, the wind power generating system can be hybridized on the structure, it is expected to be applied on complex power generation system which generates both wind and wave power energy.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.3 s.357
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• pp.61-67
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• 2007

In Reed Solomon decoder, when there are more than 4 error symbols, we usually use Chien search machine to find those error positions. In this case, classical method requires complex and relatively slow digital circuitry to implement it. In this paper we propose New fast and cost effective Chien search machine design method using Galois Subfield transformation. Example is given to show the method is working well. This new design can be applied to the case where there are more than 5 symbol errors in the Reed-Solomon code word.

• Journal of KIISE:Software and Applications
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• v.26 no.2
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• pp.284-296
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• 1999

문자 인식 및 영상 인식 분야의 대부분의 연구들은 이진영상(binary image)을 바탕으로 이루어진다. 하지만, 입력영상에서 보다 많은 정보를 얻기 위해 명도영상(grayscale image) 으로 입력받아 필요한 정보를 추출한후 이진영상으로 변환하여 처리하는 방법도 많이 사용되고 있다. 이런 경우, 명도영상으로부터의 보다 깨끗한 이진영상의 획득 여부는 시스템의 성능과도 밀접한 관계가 있다. 본 논문에서는 기존의 대부분의 이진화 방법과는 달리, 실제 이진화를 수행하기 이전에 여러 가지 필터링 기법을 사용하여 영상의 질을 개선시키는 영상개선기법을 사용한후, 기존의 이진화방법을 사용하여 명도영상을 이진화하는 방법을 제안하고자 한다. 영상의 질을 개선시키기 위해서 BM 필터링, 경게선 개선 필터링, Erosion필터링 방법을 사용하였으며 , 기존의 이진화방법으로는 전역적 이진화 방법중 하나로써 클래스간 분산을 이용한 Ostu 방법[1]을 사용하였다. 다양한 종류의 문서를 대상으로 실험하였는데 평가실험에 사용된 영상은 문서 특성에 따라 균일하지 않은 배경을 가진 영상, 순수하게 텍스트로만 구성된 영상, 선성분이 많으며 명도값이 다양하게 나타나는 영상, 텍스트와 선성분이 함께있는 영상 등 크게 4가지 부류로 구분하였고, 평가대상 영상에 대해 매개변수의 개수, 끊어진/잃어버린 /뭉게진 물체가 적은 정도, 실행속도, 매개변수 결정의 용이성, 잡영이 적은 정도를 평가기준으로 선정한 후, 정량적인 평가가 어려운 항목에 대해서는 9개의 등급으로 나누어 이진화 된 영상의 특성을 분석, 평가하였다.

• Journal of the Institute of Convergence Signal Processing
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• v.20 no.4
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• pp.199-204
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• 2019

In the boundary layer, vortical system has been analyzed by the statistical methods to identify the vortex interaction. However, there are the limitations in explaining vortices by the mean velocity or the standard deviation. This paper proposed a method to establish a frequency analysis by Fourier transform in order to simultaneously investigate various scale vortices. For this purpose, the flow visualization conducted to reveal a standing vortex, a hairpin vortex and a wake region around a hemisphere attached on a flat plate in a water channel. In addition, the velocity where the hairpin vortex was being generated in the wake region was measured by a hot-film anemometer. To observe changes in the vortex interaction, suction was applied through a hole in front of the hemisphere. For the evaluation of the proposed frequency analysis, the existing statistical results were compared to the frequency analysis that corresponds to the qualitative results of the flow visualization.

• The Journal of the Acoustical Society of Korea
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• v.18 no.6
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• pp.77-83
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• 1999

H.263 is an international standard of ITU-T that can makes the service such as video phone, video conference in the transmission line less than 64Kbps. This recommendation draft has used motion estimation/compensation, transform coding and quantizing methods. TMN5 used for the performance estimation of H.263 has fundamentally used DCT in transform coding method and presented quantizer for quantizing the DCT transform coefficient. This paper is presenting adaptive quantizer effectively able to quantize DCT coefficient considering the human visual sensitivity while the structure of TMN5 is maintaining. As quantizer that proposed DCT-based H.263 could make transmit more frame than TMN5 in a same transfer speed, it could lower the frame drop effect. And the luminance signal appeared the difference of -0.3 ～ +0.7dB in the average PSNR for the estimation of objective image quality and the chrominance signal appeared the improvement in about 1.5dB in comparision with TMN5. As a result it can attain the better image quality compared to TMN5 in the estimation of subjective image quality.

• The Journal of the Acoustical Society of Korea
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• v.30 no.1
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• pp.56-62
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• 2011

In the present study, the phase velocities of guided ultrasonic waves such as the first arriving signal (FAS) and the slow guided wave (SGW) propagating along the long axis on the 12 tubular cortical bone samples in vitro were measured and their correlations with the cortical thickness were investigated. The phase velocities of the FAS and the SGW were measured by using the axial transmission method in air with a pair of unfocused ultrasonic transducers with a diameter of 12.7 mm and a center frequency of 200 kHz. The phase velocity of the FAS measured at 200 kHz exhibited a very high negative correlation with the cortical thickness and that of the SGW arriving after the FAS showed a high positive correlation with the cortical thickness. The simple and multiple linear regression models with the phase velocities of the FAS and the SGW as independent variables and the cortical thickness as a dependent variable revealed that the coefficient of determination of the multiple linear regression model was higher than those of the simple linear regression models. The phase velocities of the FAS and the SGW measured at 200 kHz on the 12 tubular cortical bone samples were, respectively, consistent with those of the S0 and the A0 Lamb modes calculated at 200 kHz on the cortical bone plate.