• 한국환경교육학회지:환경교육
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• 제17권2호
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• pp.10-25
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• 2004

This study aims to standardize and analyze the environmental teacher recruitment examination for secondary school. To achieve the purpose, the environmental teacher recruitment examinations, which were carried out for five times through the school year 2000 to 2004, were compared and analyzed. And then, based on the above analyses, we presented ‘the plan of standardization for the environmental teacher recruitment examination in secondary school.’ In addition, the propriety, reliance, and realistic suitability of the plan were confirmed by professors of environmental education department in universities, environmental education professionals, and environmental teachers in secondary school. By presenting ‘the plan of standardization for the environmental teacher recruitment examination in secondary school’ in this study, we expect that the curriculum design and management of environmental education teacher training universities can be standardized and improved, and that the teacher who have expert qualities in environment education is reasonably selected by the environmental teacher recruitment examination.

• Journal of Power Electronics
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• 제16권4호
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• pp.1375-1386
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• 2016

To decouple the secondary saliencies in sensorless permanent magnet synchronous machine (PMSM) drives, a repetitive control (RC) in the angle domain is proposed. In this paper, the inductance model of a concentrated windings surface-mounted PMSM (cwSPMSM) with strong secondary saliencies is developed. Due to the secondary saliencies, the estimated position contains harmonic disturbances that are periodic relative to the angular position. Through a transformation from the time domain to the angle domain, these varying frequency disturbances can be treated as constant periodic disturbances. The proposed angle-domain RC is plugged into an existing phase-locked loop (PLL) and utilizes the error of the PLL to generate signals to suppress these periodic disturbances. A stability analysis and parameter design guidelines of the RC are addressed in detail. Finally, the proposed method is carried out on a cwSPMSM drive test-bench. The effectiveness and accuracy are verified by experimental results.

• 상하수도학회지
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• 제24권1호
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• pp.41-50
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• 2010

The influent and effluent baffle configurations seriously affect the hydraulic characteristics of the secondary clarifier in wastewater treatment plant. In this study, those baffle configurations were optimized by computational fluid dynamics(CFD) analysis and particle image velocity(PIV) test in order to obtain uniform flow in inlet region and to minimize upflow velocity in outlet region of the secondary clarifier. Theoretical analysis using CFD showed that more uniform flow could be accomplished when the influent baffle was located closely to the inlet opening. Effects of effluent baffle configuration on the upflow velocity in the outlet region of the secondary clarifier were analyzed with four types of effluent baffles which are widely adopted for secondary clarifier design. From the CFD analysis, McKinney baffle(EB-2) was estimated to be the most effective for restraining the upflow velocity in the outlet region and these trends were identified by PIV tests. In addition, the McKinney baffle showed the most uniform overflow velocity distribution around the weir.

• 한국지진공학회논문집
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• 제24권2호
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• pp.87-93
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• 2020

Seismic responses due to the dynamic coupling between a primary structure and secondary system connected to a structure are analyzed in this study. The seismic responses are compared based on dynamic coupling criteria and according to the error level in the natural frequency, with the recent criteria being reliant on the error level in the spectral displacement response. The acceleration responses and relative displacement responses of a primary structure and a secondary system for a coupled model and two different decoupled models of two degrees-of-freedom system are calculated by means of the time integration method. Errors in seismic responses of the uncoupled models are reduced with the recent criteria. As the natural frequency of the secondary system increases, error in the natural frequency decreases, but seismic responses of uncoupled models can be underestimated compared to that of coupled model. Results in this paper can help determine dynamic coupling and predict uncoupled models' response conservatism.

• 상하수도학회지
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• 제24권2호
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• pp.219-230
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• 2010

Computer simulation has been widely used to design and optimize the operation of wastewater treatment plants since 1980. For secondary clarifiers, the simulation has been a tool to optimize the performance by providing dimensions for flocculation well. However, there has been no attempt to find the optimized geometrical parameters in circular secondary clarifier using simulation tools. In this study, three SVIs (Sludge Volume Indexes), two well types (feed and flocculation wells), 8 SWDs (Side Water Depths) and 9 bottom slopes were variables for simulation. Diurnal inflow and associated MLSS (Mixed Liquor Suspended Solid) concentrations were used for input loadings. When flocculation well was installed, 48% less concentration at lowest ESS (Effluent Suspended Solid) concentrations was produced and the diurnal ESS concentration range had been reduced by 52%. From these results, flocculation well must be installed to produce lower and stable ESS from circular secondary clarifiers. Under same loading conditions with $300m{\ell}$/g of SVI, The lowest ESS was produced when SWD was 4.5m with 4% of bottom slope. Therefore, SWD and bottom slope must not be deeper than 4.5m and must be near 4%, respectively, in circular clarifier with flocculation well to produce the lowest ESS concentration.

• ETRI Journal
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• 제38권5호
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• pp.941-951
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• 2016

In this paper, cognitive radio and simultaneous wireless information and power transfer (SWIPT) are effectively combined to design a spectrum-efficient and energy-efficient transmission paradigm. Specifically, a novel SWIPT-based primary-secondary cooperation model is proposed to increase the transmission rate of energy/spectrum constrained users. In the proposed model, a multi-antenna secondary user conducts simultaneous energy harvesting and information forwarding by means of power splitting (PS), and tries to maximize its own transmission rate under the premise of successfully assisting the data delivery of the primary user. After the problem formulation, joint power splitting and beamforming optimization algorithms for decode-and-forward and amplify-and-forward modes are presented, in which we obtain the optimal PS factor and beamforming vectors using a golden search method and dual methods. Simulation results show that the proposed SWIPTbased primary-secondary cooperation schemes can obtain a much higher level of performance than that of non-SWIPT cooperation and non-cooperation schemes.

• 동력기계공학회지
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• 제18권4호
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• pp.17-22
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• 2014

In this paper, the performance characteristics of R404 indirect refrigeration system using R744 as a secondary refrigerant were investigated experimentally to obtain a optimum design data for this system. First, for the constant experimental conditions, the COP of R404A indirect refrigeration system using R744 as secondary refrigerants decreases with respect to the increases in R404A condensation temperature and temperature difference in R744 cooler. And, the COP of indirect refrigeration system using R744 as secondary refrigerants decreases slightly with decreasing the mass flowrate of R744.

• 과학교육연구지
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• 제45권3호
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• pp.364-378
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• 2021

본 연구는 융합 인재 교육 경험을 오랫동안 해 온 교사들의 공학적 설계에 대한 인식을 탐색한 것이다. 본 연구에 참여한 교사들은 융합 인재 교육 경험을 5년 이상 해 온 초·중등 교사 12명으로 진행하였으며, 반구조화된 인터뷰를 통해서 진행되었으며, 면담은 1~2회에 걸쳐 60~90분 정도로 진행되었다. 면담 질문은 융합 인재 교육 경험과 공학적 설계에 대한 인식, 공학적 설계의 교육과정 반영 여부, 공학적 설계를 도입한 융합 인재 교육의 실제사례 등을 중심으로 진행하였다. 본 연구의 결과로는 과학, 기술, 공학에 대한 개념의 동일시 그리고 혼재, 공학적 설계는 창의적 설계를 위해 필요한 요소들의 적절한 조합, 공학적 설계는 창의적 설계에 유용성과 경제성을 추구했을 때 가능, 공학적 설계는 이공계 진로를 선택한 학생들만을 위한 것으로 인식하고 있었다. 본 연구를 토대로 과학, 기술, 공학에 대한 올바른 개념을 정립하여 제시하고 과학적 문제 해결을 위한 공학적 설계에 대한 내용을 교육과정에 포함시키는 노력이 필요하다. 또한, 공학적 설계가 포함된 융합 인재 교육 프로그램을 개발하고 확산하여 현장에 적용해야 할 것이다. 이를 통해 교사와 예비 교사들의 과학, 공학 융합 프로그램과 공학적 설계에 대한 인식을 개선시킬 수 있는 구체적인 실행 방안을 모색해야 할 것이다.

• Journal of international Conference on Electrical Machines and Systems
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• 제3권1호
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• pp.78-82
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• 2014

Power Transformers with more than one secondary winding are not uncommon in industrial applications. But new classes of applications where very large number of independent secondaries are used are becoming popular in controlled converters for medium and high voltage applications. Cascade H-bridge medium voltage drives and Pulse Step Modulation (PSM) based high voltage power supplies are such applications. Regulated high voltage power supplies (Fig. 1) with 35-100 kV, 5-10 MW output range with very fast dynamics (${\mu}S$ order) uses such transformers. Such power supplies are widely used in fusion research. Here series connection of isolated voltage sources with conventional switching semiconductor devices is achieved by large number of separate transformers or by single unit of multi-secondary transformer. Naturally, a transformer having numbers of secondary windings (~40) on single core is the preferred solution due to space and cost considerations. For design and simulation analysis of such a power supply, the model of a multi-secondary transformer poses special problem to any circuit analysis software as many simulation softwares provide transformer models with limited number (3-6) of secondary windings. Multi-Secondary transformer models with 3 different schemes are available. A comparison of test results from a practical Multi-secondary transformer with a simulation model using magnetic component is found to describe the behavior closer to observed test results. Earlier models assumed magnetising inductance in a linear loss less core model although in actual it is saturable core made-up of CRGO steel laminations. This article discusses a more detailed representation of flux coupled magnetic model with saturable core properties to simulate actual transformers very close to its observed parameters in test and actual usage.

• 태양에너지
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• 제18권3호
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• pp.95-105
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• 1998

In this study, basic design data which were required for development of highly efficient ice storage system with low temperature latent heat were experimentally obtained. The ice storage system considered in this study was the one that has been widly used in the developed country and called the ice-on-coil type. Using the system, the ice storage performance for various design parameters which were the flow direction and the inlet temperature of the secondary fluid was tested. In addition, the timewise variation of the interface profiles between the solid and the liquid were visualized, and the heat transfer characteristics of the Phase Change Material(PCM) in the ice storage tank were Investigated. During the freezing processes in the ice storage tank with several vertical tubes, decrease of the heat transfer area and the heat resistance of the ice layer made the increasing rate of ice packing factor(IPF) less. The total freezing energy for the upward flow of the secondary fluid was higher than that for the downward flow. The average ice storage efficiency for the upward flow of the secondary fluid was higher than that for the downward flow.