• 한국해양공학회지
• /
• 제12권2호통권28호
• /
• pp.147-152
• /
• 1998

In this study turbine flowmeters were used to predict volumetric flow rate of each phase in two-phase, gas-liquid, flowing in a vertical tube. To determine volumetric flow rates of two-phase, air-water, flowing vertically upward through the polycarbonate tube(57mm ID-inside diameter), two turbine flow meters were used. For void fraction measurements, two gamma densitometers were used at each location of the turbine flow meter, one at the upstream and the other at the downstream. It was determined that the turbine flowmeter's outputs were a function of actual volumetric flow rate of each of the two phases. A two-phase flow model was developed.

• 한국정보통신학회논문지
• /
• 제10권2호
• /
• pp.298-302
• /
• 2006

전원 잡음에 의한 링발진기의 위상잡음과 jitter의 모델을 제시하고 시뮬레이션을 수행하여 모델의 타당성을 확인하였다. 링발진기의 전원 잡음은 협대역 위상변조에 의해 중심 주파수 양측면에 잡음 주파수만큼 간격을 두고 출력 잡음 신호가 나타나는 위상잡음으로 나타났다. 또한 전원 잡음에 의한 jitter의 선형 모델을 제시하였고, 시뮬레이션에 의해 jitter가 잡음 진폭의 크기에 비례하여 발생하는 것을 확인하였다.

• 전기학회논문지
• /
• 제61권7호
• /
• pp.937-943
• /
• 2012

Most of faults occurred in transmission lines are single-phase to ground faults and transient faults. Single-phase auto reclosing is an appropriate scheme to maintain the system stability and restore the system effectively when those faults are occurred. In single-phase auto reclosing scheme, the secondary arc is generated after faulted phase is tripped to eliminate the fault and it is sustained by the capacitive and inductive coupling to the healthy phases. It is important to reclose the faulted phase after fully extinction of secondary arc because of the damage applied to system. Therefore, it is necessary to research on the detection of secondary arc extinction to ensure high success rate of reclosing. In this step, firstly, the accurate modelling of secondary arc should be performed. In this paper, the modelling of secondary arc is performed by using EMTP-RV and the simulation results show that the implemented model is correct and effective.

• 전기학회논문지
• /
• 제58권4호
• /
• pp.655-664
• /
• 2009

This paper, Part 1, describes the effective dual-input PSS parameter design procedure for the IEEE Type PSS2A against the Dangjin 612 MVA thermal plant's EX2000 excitation system. The suggested tuning technique used the model-based PSS tuning method and consisted of three steps: 1) generation system modeling; 2) determination of PSS2A model parameters using linear, time-domain transient and 3-phase simultaneous analyses, and 3) field testing and verification, which are described in Part 2. The effective PSS2A model parameters of EX2000 system in the Dangjin T/P #4 were designed according to the suggested procedure, and verified by using three analyses.

• The Korean Journal of Ceramics
• /
• 제6권2호
• /
• pp.129-133
• /
• 2000

Boron nitride films were synthesized with $N_2$ion flux of low energy, up to 100 eV, at different substrate temperatures of no heating, 200, 400, 500, and $800^{\circ}C$, respectively. Boron was supplied by e-beam evaporation at the rate of $1.5\AA$/sec. For all the conditions, hexagonal BN (h-BN) phase was mainly synthesized and high resolution transmission electron microscopy (HRTEM) showed that (002) planes of h-BN phase were aligned vertical to the Si substrate. The maximum alignment occurred around $400^{\circ}C$. In addition to major h-BN phase, transmission electron diffraction (TED) rings identified the formation of cubic BN (c-BN) phase. But HRTEM showed no distinct and continuous c-BN layer. These results suggest that c-BN phase may form in a scattered form even when h-BN phase is mainly synthesized under small momentum transfer by bombarding ions, which are not reconciled with the macro compressive stress model for the c-BN formation.

• Journal of Electrical Engineering and Technology
• /
• 제12권2호
• /
• pp.654-664
• /
• 2017

This paper proposed an unified dual-phase-shift (UDPS) control for dual active bridge (DAB) converters in order to improve efficiency for a wide output power range. Different operating modes of UDPS are characterized with respect to the reactive current distribution. The proposed UDPS has the same output power capability with conventional phase-shift (CPS) method. Furthermore, its implementation is simple since only the change of the leading phase-shift direction is required for different operating power range. The proposed UDPS control can minimize both the inductor rms current and the circulating reactive current for various voltage conversion ratios and load conditions. The optimal phase-shift pairs for two bridges of DAB converter are derived with respect to the comprehensive reactive power loss model, including the reactive components delivered from the load and back to the source. Simulation and experimental results are illustrated and explained with details. The effectiveness of the proposed method is verified in terms of reactive power losses minimization and efficiency improvement.

• 한국초전도ㆍ저온공학회논문지
• /
• 제18권2호
• /
• pp.42-47
• /
• 2016

A free-piston reciprocating expander is a device which operates without any mechanical linkage to a stationary part. Since the motion of the floating piston is only controlled by the pressure difference at two ends of the piston, this kind of expander may indispensably require a sophisticated active control system equipped with multiple valves and reservoirs. In this paper, we have suggested a novel design that can further reduce complexity of the previously developed cryogenic free-piston expander configuration. It is a simple replacement of both multiple valves and reservoirs by a combination of an orifice valve and a reservoir. The functional characteristic of the integrated orifice-reservoir configuration is similar to that of a phase controller applied in a pulse tube refrigerator so that we designate the one as a phase controller. Depending on the orifice valve size in the phase controller, the different PV work which affects the expander performance is generated. The numerical model of this unique free-piston reciprocating expander utilizing a phase controller is established to understand and analyze quantitatively the performance variation of the expander under different valve timing and orifice valve size. The room temperature experiments are carried out to examine the performance of this newly developed cryogenic expander.

• 한국IT서비스학회지
• /
• 제4권2호
• /
• pp.1-22
• /
• 2005

The object of this study is to elicit major success factors along with the phases of implementing the BPR in case of public corporations. To obtain the goal of this research, (1) this study reviews and integrates the major previous BPR studies and shows critical success factors of implementing BPR projects coincided with the characteristics of the public organizations. (2) This study has analyzed and arranged the details of BPR projects of public corporations in South Korea through the literature survey, the questionnaire and the interview. (3) This study classifies 40 critical success factors which were identified in existing studies into ones belonging to 3 phases of BPR projects implementation: Introduction Phase, Execution Phase and Stabilization Phase. (4) This study has tested the relation between critical success factors on each stage of BPR projects implementation and the performance variables. It has proven that there is the statistically significant correlation between the success factors and the performance. The findings of this study are thought not only to be useful as a practical guideline in carrying out BPR project Implementation but also to provide significant basis for constructing the theoretical framework of effective BPR project implementation strategy.

• 지역사회간호학회지
• /
• 제32권2호
• /
• pp.205-219
• /
• 2021

Purpose: This concept analysis was conducted to clarify 'parents' treatment adherence for an epileptic child or adolescent'. Methods: The analysis used a hybrid model comprising three phases: theoretical phase, fieldwork phase, and integration phase. In the theoretical phase, fifty studies were reviewed. Interviews with four parents of epileptic children or adolescents were conducted during the fieldwork phase. In the integration phase, the results derived from prior phases were synthesized and clarified. All phases were performed cyclically. Results: The concept, 'parents' treatment adherence for an epileptic child or adolescent' was defined as parents' voluntary and goal-directed behavior towards the epilepsy treatment for their children: a collaborative decision-making process with health-care providers, establishing a support system, adaptability to the treatment plans, and appraisals of the child's health condition. Conclusion: This achievement is thought to contribute to improving the accuracy and validity of the concept measurement. It has implications for additional research on how the concept 'treatment adherence' differs in diverse health problems and other population groups than parents of children and adolescents with epilepsy.

• Journal of Power Electronics
• /
• 제15권3호
• /
• pp.712-720
• /
• 2015

A model predictive current control (MPCC) method that does not employ a cost function is proposed. The MPCC method can decrease common-mode voltages in loads fed by three-phase voltage-source inverters. Only non-zero-voltage vectors are considered as finite control elements to regulate load currents and decrease common-mode voltages. Furthermore, the three-phase future reference voltage vector is calculated on the basis of an inverse dynamics model, and the location of the one-step future voltage vector is determined at every sampling period. Given this location, a non-zero optimal future voltage vector is directly determined without repeatedly calculating the cost values obtained by each voltage vector through a cost function. Without utilizing the zero-voltage vectors, the proposed MPCC method can restrict the common-mode voltage within ± V_dc/6, whereas the common-mode voltages of the conventional MPCC method vary within ± V_dc/2. The performance of the proposed method with the reduced common-mode voltage and no cost function is evaluated in terms of the total harmonic distortions and current errors of the load currents. Simulation and experimental results are presented to verify the effectiveness of the proposed method operated without a cost function, which can reduce the common-mode voltage.