• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2012년도 제38회 춘계학술대회논문집
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• pp.555-561
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• 2012

Empirical Mode Decomposition(EMD)을 통한 Hilbert Huang Transform(HHT)은 시간-주파수 영역분석 방법 중 하나로 기존의 다른 분석 방법에 비해 비선형, 비정상 신호를 해석 가능하다는 등 여러가지 이점이 있다. 그러나 인접한 주파수를 분별하기 힘들고 잡음에 취약하다는 결점이 있다고 알려져 있다. 본 논문에서는 HHT와 정상신호 분석에 효과적인 Short-Time Fourier Transform(STFT)을 비교하여 각 방법의 장 단점을 분석하고 Rijke 튜브 실험에서 얻은 열음향학적 불안정 데이터에 적용하여 잡음에 취약한 점을 보완한 Improved HHT와 비교한다. 그 결과, EMD를 이용한 Original HHT보다 EEMD를 이용한 Improved HHT가 잡음의 영향을 적게 받아 보다 정확한 신호분석이 가능하다는 것을 알 수 있었다.

• Structural Engineering and Mechanics
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• 제36권6호
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• pp.697-714
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• 2010

This paper presents an improved version of the Hilbert-Huang transform (HHT) for the modal evaluation of structural systems or signals. In this improved HHT, a well-designed bandpass filter is used as preprocessing to separate and determine each mode of the signal for solving the inherent modemixing problem in HHT (i.e., empirical mode decomposition, EMD, associated with the Hilbert transform). A screening process is then applied to remove undesired intrinsic mode functions (IMFs) derived from the EMD of the signal's mode. A "best" IMF is selected in each screening process that utilizes the orthogonalization coefficient between the signal's mode and its IMFs. Through mode-by-mode signal filtering, parameters such as the modal frequency can be evaluated accurately when compared to the theoretical value. Time history of the identified modal frequency is available. Numerical results prove the efficiency of the proposed approach, showing relative errors 1.40%, 2.06%, and 1.46%, respectively, for the test cases of a benchmark structure in the lab, a simulated time-varying structural system, and of a linear superimposed cosine waves.

• 대한약침학회지
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• 제9권3호통권21호
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• pp.131-138
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• 2006

Objective : The aim of this study was to investigate the effect of HHT(Hwangryunhaedoktang Herbal-Acupuncture) on functional headache. Methods : 26 clinical experiment participants who experienced functional headache were gathered. The qualified patients were classified in two group, Normal saline injection group and Hwangryunhaedoktang Herbal-Acupuncture group. NS group was injected normal saline and HHT group was injected HHT at GB20, GB21, LI4. Treatment was applied 4 times every second day. The effects of both groups were analyzed using VAS scores and BPI(Brief Pain Inventory). Result : The VAS pain scores improved in both groups. the BPI scores decreased only in HHT group. The decrease rate of VAS scores and BPI scores was larger in HHT group. Conclusion : These results provided that HHT group is more effective than NS group. For clearly comparing the Effect of Hwangryunhaedoktang Herbal-Acupuncture on functional headache, it is need more sample's number and more treatment's duration.

• 한국식품영양학회지
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• 제9권2호
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• pp.181-188
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• 1996

Chemical compositions were investigated by harvested months and produced methods. The level of crude protein and crude ash of ginseng leaf tea harvested in July was slightly higher than it harvested in September. However, the level of crude fat and carbohydrate of ginseng leaf tea harvested in September were higher than it harvested in July. The results indicated that the harvest month influenced the chemical composition of the ginseng leaf tea. Also, the level of free sugar was increased when the ginseng leaf team harvested in September was produced by FHT(fermented and then hot-air dried) or HHT(heated and then hot-air dried). The results indicated that the subjects were preferred the color of ginseng leaf tea which was harvested in July. However, they were preferred the aroma and ginseng's aroma which was harvested and produced by HHT in September. Because they responded that the ginseng leaf tea tasted too bitter, it suggested that the taste of bitterness needed to remove. Also, the astringent, the savory, after aroma, and after say cry of the ginseng leaf tea was improved with FHT or HHT, and those results obtained from September's harvest rather than July's. Therefore, the overall quality of ginseng leaf tea which was harvested in September and produced with FHT or HHT were evaluated better than it of DHT(dried on the shade and then hot-air dried).

• Journal of Electrical Engineering and Technology
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• 제13권5호
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• pp.2134-2143
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• 2018

This work introduces a fault diagnosis method for transformer based on self-powered radio frequency identification (RFID) sensor tag and improved Hilbert-Huang transform (HHT). Consisted by RFID tag chip, power management circuit, MCU and accelerometer, the developed RFID sensor tag is used to acquire and wirelessly transmit the vibration signal. A customized power management including solar panel, low dropout (LDO) voltage regulator, supercapacitor and corresponding charging circuit is presented to guarantee constant DC power for the sensor tag. An improved band restricted empirical mode decomposition (BREMD) which is optimized by quantum-behaved particle swarm optimization (QPSO) algorithm is proposed to deal with the raw vibration signal. Compared with traditional methods, this improved BREMD method shows great superiority in reducing mode aliasing. Then, a promising fault diagnosis approach on the basis of Hilbert marginal spectrum variations is brought up. The measured results show that the presented power management circuit can generate 2.5V DC voltage for the rest of the sensor tag. The developed sensor tag can achieve a reliable communication distance of 17.8m in the test environment. Furthermore, the measurement results indicate the promising performance of fault diagnosis for transformer.

• Structural Engineering and Mechanics
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• 제22권3호
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• pp.351-370
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• 2006

In this study, the earthquake damage response of the concrete arch dams was investigated including dam-reservoir interaction. A continuum damage model which is a second-order tensor and includes the strain softening behavior was selected for the concrete material. Fluid-structure interaction problem was modeled by Lagrangian approach. Sommerfeld radiation condition was applied to the truncated boundary of reservoir. The improved form of the HHT-${\alpha}$ time integration algorithm was used in the solution of the equations of motion. The arch dam Type 5 was selected for numerical application. For the dynamic input, acceleration records of the 10 December 1967 Koyna earthquake were chosen. These records were scaled with earthquake acceleration scale factor (EASF) and then used in the analyses. Solutions were obtained for empty and full reservoir cases. The effects of EASF and damping ratio on the response of the dam were studied.

• 동력기계공학회지
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• 제16권4호
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• pp.12-16
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• 2012

In this paper, the equations of motions for planar multibody dynamics are established for considering the parallel programming based on GPU. Cartesian coordinates are used to formulate the equations of motion and implicit integration method called HHT-alpha is employed. Open chain multibody system is considered for computer simulation. CUDA toolkit is employed for establishing the GPU parallel programming. The exactness of the analysis is verified from the comparison with ADAMS. The results from parallel computing based on GPU are compared with the results from the sequential programming based on CPU in terms of calculation time. The multiple pendulum with bodies and joints is employed for the computer simulation. In the pendulum system that has 290 bodies, the parallel program indicates an improved efficiency of about 25.5 second(15.5% improvement). It is noted that the larger the size of system is, the time efficiency is better.