• 한국대기환경학회지
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• 제19권4호
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• pp.397-414
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• 2003

The performance of one-particle stochastic Lagrangian models for passive tracer dispersion are evaluated against measurements in horizontally-homogeneous neutrally-stratified atmospheric surface layer. State-of-the-technology models as well as classical Langevin models, all in class of well mixed models are numerically implemented for inter-model comparison study. Model results (far-downstream asymptotic behavior and vertical profiles of the time averaged concentrations, concentration fluxes, and concentration fluctuations) are compared with the reported measurements. The results are: 1) the far-downstream asymptotic trends of all models except Reynolds model agree well with Garger and Zhukov's measurements. 2) profiles of the average concentrations and vertical concentration fluxes by all models except Reynolds model show good agreement with Raupach and Legg's experimental data. Reynolds model produces horizontal concentration flux profiles most close to measurements, yet all other models fail severely. 3) With temporally correlated emissions, one-particle models seems to simulate fairly the concentration fluctuations induced by plume meandering, when the statistical random noises are removed from the calculated concentration fluctuations. Analytical expression for the statistical random noise of one-particle model is presented. This study finds no indication that recent models of most delicate theoretical background are superior to the simple Langevin model in accuracy and numerical performance at well.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2002년도 유체기계 연구개발 발표회 논문집
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• pp.337-345
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• 2002

The present study addresses a computational result of unsteady gas flow through a critical nozzle. The axisymmetric, unsteady, compressible, Wavier-Stokes equations are solved using a finite volume method that makes use of the second order upwind scheme for spatial derivatives and the multi-stage Runge-Kutta integral scheme for time derivatives. The steady solutions of the governing equation system are validated with the previous experimental data to ensure that the present computational method is valid to predict the critical nozzle flows. In order to simulate the effects of back pressure fluctuations on the critical nozzle flows, an excited pressure oscillation with an amplitude and frequency is assumed downstream of the exit of the critical nozzle. The results obtained show that for low Reynolds numbers, the unsteady effects of the pressure fluctuations can propagate upstream of the throat of critical nozzle, and thus giving rise to the applicable fluctuations in mass flow rate through the critical nozzle, while for high Reynolds numbers, the pressure signals occurring at the exit of the critical nozzle do not propagate upstream beyond the nozzle throat. For very low Reynolds number, it is found that the sonic line near the throat of the critical nozzle remarkably fluctuateswith time, providing an important mechanism for pressure signals to propagate upstream of the nozzle throat, even in choked flow conditions. The present study is the first investigation to clarify the unsteady effects on the critical nozzle flows.

• 대한기계학회논문집B
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• 제29권10호
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• pp.1119-1129
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• 2005

A new measurement system of wall pressure fluctuations on a rotating machinery, composed of digital recording device, was developed and evaluated. The small-sized digital recording device was attached on the rotating machinery and then was detached for data reduction. In order to obtain the system transfer function of the digital recording system, a dynamic calibration was performed utilizing the signal from a 1/8 inch B&K microphone as input. The time history of the unsteady pressure was then reconstructed from the output of the sensor by using this transfer function. The reconstructed pressure signals showed good agreement with the reference signal in both temporal and spectral sense. This sensor was then used to measure the wall pressure fluctuations on a rotating blade. An array of microphones were installed on the blade in the circumferential and radial directions. Various statistical moments were obtained from the measurement data set. Comparison of these quantities with the existing studies demonstrated satisfactory agreement. These tests give credence to the relevance and reliability of this device for applications in more complicated turbulent rotating machineries.

• 대한예방한의학회지
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• 제11권2호
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• pp.87-99
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• 2007

Background : Most traditional Korean doctors use "Packed Herbal Medicine", which is made from boiling various herbs together. However, the current insurance system doesn't cover the act of making packed herbal medicine. Therefore it is urgent for these doctors to study and find the best and most logical insurance program to cover the Packed Herbal Medicine system. Objectives : The purposes of this study were to investigate whether Announced System of Herb Price is proper for stability of medical herbs's price. Methods : This study made these following results by studying medical herbs's price of KOMD(The korea oriental medicine distribution company) from 2004 March to 2007 March The results are summarized as follows ; The 50 most frequently used herbs were chosen from the 831 standard prescriptions according to 26 pre-determined specific diseases. These prescriptions are considered the most important for this study and insurance purposes. fluctuations of fifty medical herbs which were used much about a predetermined list of 831 prescriptions are multiple function not linear equation. fluctuations of fifty medical herbs which were used much about a predetermined list of 831 prescriptions are different according to time. Therefore, to notify medical herbs's price is valid method for stability of medical herbs's price.

• International Journal of Industrial Entomology and Biomaterials
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• 제19권1호
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• pp.155-164
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• 2009

The most important factors in environment that influence the physiology of insects are temperature and humidity. Insects display a remarkable range of adaptations to changing environments and maintain their internal temperature (thermoregulation) and water content within tolerable limits, despite wide fluctuations in their surroundings. Adaptation is a complex and dynamic state that widely differs in species. Surviving under changing environment in insects depends on dispersal, habitat selection, habitat modification, relationship with ice and water, resistance to cold, diapause and developmental rate, sensitivity to environmental signals and syntheses of variety of cryoprotectant molecules. The mulberry silkworm (Bombyx mori) is very delicate and sensitive to environmental fluctuations and unable to survive naturally because of their domestication since ancient times. Thus, the adaptability to environmental conditions in the silkworm is quite different from those of wild insects. Temperature, humidity, air circulation, gases and photoperiod etc. shows a significant interaction in their effect on the physiology of silkworm depending upon the combination of factors and developmental stage affecting growth, development, productivity and quality of silk. An attempt has been made in this article to briefly discuss adaptation in insects with special emphasis on the role of environmental factors and their fluctuations and its significance in the physiology of mulberry silkworm, B. mori.

• Journal of Power Electronics
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• 제10권5호
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• pp.498-504
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• 2010

The output power fluctuations of renewable energy power plants such as wind turbine generators and photovoltaic systems result in frequency deviations and terminal voltage fluctuations. Furthermore, these power fluctuations also affect the turbine shaftings of diesel generators and gas-turbine generators which are the main power generation systems on isolated islands. Therefore, it is important to achieve torsional torque suppression. Since the measurement of torsional torque is technically difficult, and there is an uncertainty in the mechanical constants of the shaft torsional system. This paper presents an estimation system that estimates torsional torque by using a developed $H_{\infty}$ observer. In addition to the above functions, the proposed shaft torque observer incorporates a parameter identification system that aims to improve the estimation accuracy. The simulation results validate the effectiveness of the proposed $H_{\infty}$ observer and the parameter identification.

• 한국전산유체공학회지
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• 제17권2호
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• pp.85-92
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• 2012

Flows over a square cylinder with and without plasma actuation are numerically investigated to see whether plasma actuation can effectively modify vortex shedding from the cylinder and reduce the drag and lift fluctuations. In this study, a plasma synthetic jet actuator is mounted on the rear side of cylinder as a means of direct-wake control. The effect of plasma actuation is considered by adding a momentum forcing term in the Navier-Stokes equations. Results show that the reduction of mean drag and lift fluctuations is obtained for both steady and unsteady actuation. However, the steady actuation is better than the unsteady one in terms of mean drag as well as drag fluctuations. With the strong steady actuation considered, the interaction of two separating shear layers from rear corners is effectively weakened due to the interference of synthetic jets. It results in a merging of synthetic-jet and shear-layer vortices and the increase of vortex shedding frequency. On the other hand, the unsteady actuation generates pulsating synthetic jets in the near wake, but it does not change the vortex shedding frequency for the actuation frequencies considered in this study.

• Journal of Electrical Engineering and Technology
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• 제12권4호
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• pp.1357-1368
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• 2017

The lack of controllability over the wind causes fluctuations in the output power of the wind generators (WGs) located at the wind farms. Distribution Static Compensator (DSTATCOM) equipped with Battery Energy Storage System (BESS) can significantly smooth these fluctuations by injecting or absorbing appropriate amount of active power, thus, controlling the power flow of WGs. But because of the component aging and thermal drift, its harmonic filter parameters vary, resulting in performance degradation. In this paper, Quantitative Feedback Theory (QFT) is used as a robust control scheme in order to deactivate the effects of filter parameters variations on the wind power generation power smoothing performance. The proposed robust control strategy of the DSTATCOM is successfully applied to a microgrid, including WGs. The simulation results obviously show that the proposed control technique can effectively smooth the fluctuations in the wind turbines' (WT) output power caused by wind speed variations; taking into account the filter parameters variations (structural parameter uncertainties).

• 조명전기설비학회논문지
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• 제20권8호
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• pp.48-53
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• 2006

제철소에서 사용되고 있는 전기로는 전력계통에 전압 변동을 일으키며 시간에 따라 변하는 비선형 부하이다. 플리커는 전압 변동의 크기에 따라 램프의 방출 변화에 의한 인간의 지각 효과로 정의된다. 플리커 레벨은 전압 변동의 크기, 주파수 및 기간에 의해 결정된다. 본 논문에서는 전기로 부하로 인한 154[kV] 시스템에서의 전압 변동 문제를 측정하고, 플리커 저감을 위한 SVC 적용 결과를 분석하고, IEC 61000-3-7에 의하여 플리커를 평가하였다.

• 한국통신학회논문지
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• 제14권5호
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• pp.472-485
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• 1989

광대역 화상정보신호(TV방송파)의 이동수신에 의한 화상품질영화는 고정수신의 경우와는 전혀 다른 상황을 타나내며, 이동체의 이동과 더불어 시시각각 복잡하게 변화한다. 본 논문에서는 야외 및 실내에서의 기초적 실험에 의해 텔레비 이동수신에서 Fluttering ghost가 화상품질열화원인중 가장 중요하다고 생각하여, 그 발생원인과 특성을 조사했다. Fluttering ghost는 텔레비 수상기에서 재생되는 수평동기펄스의 동기시각이 다중파간섭 페이딩에 의해 불안정하게 변동하므로서 발생한다는 것을 알았다. 따라서, H-sync pulse timing의 다중파 조건에 대한 변화를 이론적으로 해석하고 그 특성을 밝혀 동기시간변동의 조건과 원인을 밝혔다.