• Journal of international Conference on Electrical Machines and Systems
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• 제3권2호
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• pp.190-199
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• 2014

In the last years, fault problem in power electronics has been more and more investigated both from theoretical and practical point of view. The fault problem can cause equipment failure, data and economical losses. And the analyze system require to ensure fault problem and also rectify failures. The current errors on these faults are applied for identified type of faults. This paper presents technique to detection and identification faults in three-phase voltage source inverter (VSI) by using time-frequency distribution (TFD). TFD capable represent time frequency representation (TFR) in temporal and spectral information. Based on TFR, signal parameters are calculated such as instantaneous average current, instantaneous root mean square current, instantaneous fundamental root mean square current and, instantaneous total current waveform distortion. From on results, the detection of VSI faults could be determined based on characteristic of parameter estimation. And also concluded that the fault detection is capable of identifying the type of inverter fault and can reduce cost maintenance.

• 한국포장학회지
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• 제21권2호
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• pp.61-65
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• 2015

Agricultural products packaged for transportation are put in the various dangerous environments owing to the damage factors like vibration, shock, compression, climate etc. under the distribution process. On fruits packaging for transportation, especially, the shock and vibration is considered as the most important damage factors. A major cause of shock damage to fruits is drops during manual handling. Especially, the damages of fruits during the parcel delivery service are very serious. The parcel delivery services of fruits are increasing and contribute to increasing of farm house earning. Also, the freight vehicle is mostly used to transport the fruits. Shock and impact generated by the freight vehicle may give serious damage to fruits. The optimum packaging design of parcel delivery service of fruits during transportation is required to reduce the fruits damages. In order to design the packaging system for parcel delivery service of fruits considering the transportation environment, the comprehension of characteristics for vibration and shock generated by manual handling and acting on transportation vehicles under various road conditions and loading methods is required. This research was performed to analyze the shock characteristics, acceleration level and power spectral density (PSD) during the parcel delivery service of fruits. The overall level of recommended PSD profile in a specific transportation of parcel delivery service for fruits was $0.63G_{rms}$.

• Smart Structures and Systems
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• 제21권5호
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• pp.591-600
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• 2018

The probabilistic characterization of wind field characteristics is a significant task for fatigue reliability assessment of long-span railway bridges in wind-prone regions. In consideration of the effect of wind direction, the stochastic properties of wind field should be represented by a bivariate statistical model of wind speed and direction. This paper presents the construction of the bivariate model of wind speed and direction at the site of a railway arch bridge by use of the long-term structural health monitoring (SHM) data. The wind characteristics are derived by analyzing the real-time wind monitoring data, such as the mean wind speed and direction, turbulence intensity, turbulence integral scale, and power spectral density. A sequential quadratic programming (SQP) algorithm-based finite mixture modeling method is proposed to formulate the joint distribution model of wind speed and direction. For the probability density function (PDF) of wind speed, a double-parameter Weibull distribution function is utilized, and a von Mises distribution function is applied to represent the PDF of wind direction. The SQP algorithm with multi-start points is used to estimate the parameters in the bivariate model, namely Weibull-von Mises mixture model. One-year wind monitoring data are selected to validate the effectiveness of the proposed modeling method. The optimal model is jointly evaluated by the Bayesian information criterion (BIC) and coefficient of determination, $R^2$. The obtained results indicate that the proposed SQP algorithm-based finite mixture modeling method can effectively establish the bivariate model of wind speed and direction. The established bivariate model of wind speed and direction will facilitate the wind-induced fatigue reliability assessment of long-span bridges.

• Journal of information and communication convergence engineering
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• 제5권2호
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• pp.164-170
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• 2007

In this paper, the new method alternating with the method for forming the symmetrical distribution of power and local dispersion in high bit-rate WDM system with optical phase conjugator (OPC) is proposed. The proposed method is carried by finding out the optimal values of OPC position offset and fiber dispersion offset. It is assumed to be that NRZ-formatted 24-channels of 40 Gbps are simultaneously propagated in WDM system with non zero - dispersion shifted fiber (NZ-DSF) of 1,000 km. It is confirmed that the compensation extents of overall WDM channels are more improved by applying the induced optimal values into WDM system than those in WDM system with the conventional mid-span spectral inversion (MSSI) technique, and the searching procedure of the optimal values makes little difference of performance if the optimal value of one parameter related with another parameter. And, it is confirmed that the flexible design of WDM system with OPC is possible by effectiviely using by these optimal values. Thus, it is expected that the proposed method alternate with the forming method of the symmetrical distributions of power and local dispersion.

• 천문학회지
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• 제44권2호
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• pp.49-58
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• 2011

We calculate the energy spectra of cosmic ray (CR) protons and electrons at a plane shock with quasi-parallel magnetic fields, using time-dependent, diffusive shock acceleration (DSA) simulations, including energy losses via synchrotron emission and Inverse Compton (IC) scattering. A thermal leakage injection model and a Bohm type diffusion coefficient are adopted. The electron spectrum at the shock becomes steady after the DSA energy gains balance the synchrotron/IC losses, and it cuts off at the equilibrium momentum $p_{eq}$. In the postshock region the cutoff momentum of the electron spectrum decreases with the distance from the shock due to the energy losses and the thickness of the spatial distribution of electrons scales as $p^{-1}$. Thus the slope of the downstream integrated spectrum steepens by one power of p for $p_{br}$ < p < $p_{eq}$, where the break momentum decreases with the shock age as $p_{br}\;{\infty}\;t^{-1}$. In a CR modified shock, both the proton and electron spectrum exhibit a concave curvature and deviate from the canonical test-particle power-law, and the upstream integrated electron spectrum could dominate over the downstream integrated spectrum near the cutoff momentum. Thus the spectral shape near the cutoff of X-ray synchrotron emission could reveal a signature of nonlinear DSA.

• 한국포장학회지
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• 제29권2호
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• pp.129-138
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• 2023

The proportion of agricultural products handled through the Agricultural Products Processing Center (APC) is also steadily increasing every year, and in the case of Seongju Korean melon, a total of 10 APCs of Nonghyup and farming association corporations are in operation, and the distribution ratio is about 60% based on total production. In this study, Seongju Korean melon was selected as a target to analyze the environment load during carrying (production farm ~ APC) in the production area and the transport environment load during distribution of domestic fruits, and to analyze the environmental load for handling at APC. The vertical average vibration intensity (overall G_rms of 1~250 Hz) of truck transport measured at three transport routes from Seongju Korean melon producer ~ APC, Seongju ~ Seoul and Seongju ~ Jeju was about three times larger than that in the lateral direction and 4.5 times larger than that in the longitudinal direction, respectively. The frequency of occurrence of high-amplitude events (G) in the vertical direction compared to the measuring time was deeply related to pavement conditions in the order of unpaved farm-roads, concretepaved farm-roads, and asphalt-paved main-roads, but overall G_rms for the entire frequency band is believed to have a greater impact on vehicle traveling speed than road conditions. On the other hand, the difference in the size and direction of the vibration intensity measured by the forklift truck's main-body and the attachment (fork carrier) during handling at Seongju Korean melon APC was clear, and the vibration intensity of the forklift truck's main-body was largely affected by the stiffness of the fork and the mast according to the handling weight. Based on the field-data of the transport environment during domestic distribution measured through this study, it is believed that it is possible to develop a lab-based simulation protocol for appropriate packaging design.

• 한국산학기술학회논문지
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• 제12권7호
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• pp.3207-3213
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• 2011

조명 변화에 관계없이 물체의 원래 색을 결정할 수 있는 색 항등성 기법은 저조도 환경에 적합하지 않다. 이러한 저조도 환경을 고려한 색 항등성 기법을 위해 우선적으로 다양한 저조도 환경의 영상이 필요하다. 본 논문에서는 분광 데이터에 기반한 저조도 합성 영상 집합과 저조도 자연 영상 집합을 생성한다. 합성 영상 집합은 380~780nm의 5nm 단위로 보간된 카메라의 센서 반응 함수, 일루미넌트 분광분포(SPD) 그리고 분광 반사율 곡선을 사용하여 생성되며, 52,000개의 영상들로 구성된다. 자연 영상 집합은 Ebner 데이터 집합과 일루미넌트의 SPD를 기반으로 생성한 4,970개의 영상들로 구성된다. 영상 집합은 실측 분광 데이터와 물리적인 영상 형성 모델을 바탕으로 생성되기 때문에 저조도 환경에서의 색 변화 및 분포를 객관적이고 정량적으로 분석하는 것이 가능한 장점을 갖는다. 또한, 이 영상 집합은 Ground Truth Data를 포함하고 있어 색 항등성 기법의 평가를 위해 사용될 수 있다.

• 한국통신학회논문지
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• 제27권7B호
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• pp.719-726
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• 2002

WRC-2000에서 3GHz 이상의 대역에서 운영할 성층권 통신 시스템(HAPS)의 이용에 관한 연구로 Resolution 734가 채택되었다. 이에 새로운 HAPS 시스템과 기존의 지구상의 고정 서비스간의 공유 가능성이 먼저 분석되어야 한다. 본 논문에서는 HAPS 시스템이 무선 중계국에 미치는 간섭 영향을 두 가지의 경우로 나누어서 분석한다. 한가지는 HAPS 비행선의 PFD(Power Flux Density)에 의한 간섭이며, 다른 한가지는 HAPS의 지구국으로부터의 간섭영향이다. 분석 결과 위성 시스템과는 다른 새로운 PFD 기준 설정이 필요하며, 기존의 FS 시스템과 새로운 HAPS 시스템의 공유를 위한 HAPS nadir 사이의 조정거리는 전송전력밀도가 -50dBW/MHz 일 때 최고 253km에서 최저 60km정도가 요구된다.

• 한국항행학회논문지
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• 제10권2호
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• pp.103-113
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• 2006

본 논문에서는 광 전송로로 비영 분산천이 광섬유 (NZ-DSF ; Non Zero-Dispersion Shifted Fiber)를 이용한 $8{\times}40$ Gbps WDM 시스템에서 모든 채널을 효과적으로 보상할 수 있는 광 위상 공액기 (OPC ; Optical Phase Conjugator)의 최적 위치와 광섬유의 최적 분산 계수 값을 도출하는 수치적 방법을 제안하였다. 이 방법의 유용성을 확인하기 위하여 도출된 두 최적 파라미터를 갖는 시스템에서의 비트 에러율 (BER ; Bit Error Rate) 특성을 현재 일반화된 MSSI (Mid-Span Spectral Inversion)에서의 BER 특성과 비교하였다. 최적 파라미터들은 구하는 순서에 크게 의존하지 않지만 서로 연관되어 있어야 한다는 것을 알 수 있었다. 본 논문에서 제안한 방법은 WDM 시스템에 OPC를 적용하고자 할 때 전제가 되어야 하지만 실제 광 전송 링크에서 구현하기 어려운 OPC를 중심으로 한 광 신호 전력과 총 분산 값의 대칭 문제를 해결해야 하는 방법을 대체할 것으로 예상된다.

• Wind and Structures
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• 제18권6호
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• pp.693-715
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• 2014

Stochastic processes are used to represent phenomena in many diverse fields. Numerical simulation method is widely applied for the solution to stochastic problems of complex structures when alternative analytical methods are not applicable. In some practical applications the stochastic processes show non-Gaussian properties. When the stochastic processes deviate significantly from Gaussian, techniques for their accurate simulation must be available. The various existing simulation methods of non-Gaussian stochastic processes generally can only simulate super-Gaussian stochastic processes with the high-peak characteristics. And these methodologies are usually complicated and time consuming, not sufficiently intuitive. By revealing the inherent coupling effect of the phase and amplitude part of discrete Fourier representation of random time series on the non-Gaussian features (such as skewness and kurtosis) through theoretical analysis and simulation experiments, this paper presents a novel approach for the simulation of non-Gaussian stochastic processes with the prescribed amplitude probability density function (PDF) and power spectral density (PSD) by amplitude modulation and phase reconstruction. As compared to previous spectral representation method using phase modulation to obtain a non-Gaussian amplitude distribution, this non-Gaussian phase reconstruction strategy is more straightforward and efficient, capable of simulating both super-Gaussian and sub-Gaussian stochastic processes. Another attractive feature of the method is that the whole process can be implemented efficiently using the Fast Fourier Transform. Cases studies demonstrate the efficiency and accuracy of the proposed algorithm.