• 소성∙가공
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• 제27권6호
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• pp.331-338
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• 2018

Electrohydraulic forming (EHF) process is a high speed forming process that utilizes the electric energy discharge in fluid-filled chamber to deform a sheet material. This process is completed in a very short time of less than 1ms. Therefore, finite element analysis is essential to observe the deformation mechanism of the material in detail. In addition, to perform the numerical simulation of EHF, the material properties obtained from the high-speed status, not quasi static conditions, should be applied. In this study, to obtain the parameters in the constitutive equation of Al 6061-T6 at high strain rate condition, a surrogate model using an artificial neural network (ANN) technique was employed. Using the results of the numerical simulation with free-bulging die in LS-DYNA, the surrogate model was constructed by ANN technique. By comparing the z-displacement with respect to the x-axis position in the experiment with the z-displacement in the ANN model, the parameters for the smallest error are obtained. Finally, the acquired parameters were validated by comparing the results of the finite element analysis, the ANN model and the experiment.

• Nuclear Engineering and Technology
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• 제54권8호
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• pp.2898-2914
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• 2022

When evaluating energy balance and temperature in reduced-scale fire experiments, which are conducted as an alternative to full-scale fire experiments, it is important to consider the similarity in the scale among these experiments. In this paper, a method considering the similarity of energy balance is proposed for setting the conditions for reduced-scale experiments of mechanically ventilated compartment fires. A small-scale fire experiment consisting of various cases with different compartment geometries (aspect ratios between 0.2 and 4.7) and heights of vents and fire sources was conducted under mechanical ventilation, and the energy balance in the quasi-steady state was evaluated. The results indicate the following: (1) although the compartment geometry varies the energy balance in a mechanically ventilated compartment, the variation in the energy balance can be evaluated irrespective of the compartment size and geometry by considering scaling factor F (∝h_effA_wR_T, where h_eff is the effective heat transfer coefficient, A_w is the total wall area, and R_T is the ratio of the spatial mean gas temperature to the exhaust temperature); (2) the value of R_T, which is a part of F, reflects the effects of the compartment geometry and corresponds to the distributions of the gas temperature and wall heat loss.

• Nuclear Engineering and Technology
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• 제54권7호
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• pp.2540-2549
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• 2022

For a pressurized water reactor power plant, the reactor coolant pump (RCP) is a kernel component. And for a canned motor RCP, the rotor system's properties determines its safety. The liquid coolant inside the canned motor RCP fills clearance between the metal shields of rotor and stator, forming a lengthy clearance flow. The influence of inlet preswirl on rotordynamic coefficients of clearance flow in canned motor RCP and their effects on the rotordynamic characteristics of the pump are numerically and experimentally investigated in this work. A quasi-steady state computational fluid dynamics (CFD) method has been used to investigate the influence of inlet preswirl. A vertical experiment rig has also been established for this purpose. Rotordynamic coefficients on different inlet preswirl ratios (IR) are obtained through CFD and experiment. Results show that the cross-coupled stiffness of the clearance flow would change significantly with inlet preswirl, but other rotordynamic coefficients would not change significantly with inlet preswirl. For the case of clearance flow between the stator and rotor cans, influence of inlet preswirl is not so significant as the IR is not large enough.

• 대한간호학회지
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• 제39권5호
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• pp.662-672
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• 2009

Purpose: This study was to examine the effects of self-foot reflexology on stress, fatigue and blood circulation in premenopausal middle-aged women. Methods: A quasi-experimental nonequivalent control group, pretest-posttest design was used. Participants were 59 premenopausal, middle-aged women in their 40s and 60s living in G city: 30 in the experiment group and 29 in the control group. Data were collected from May to August 2008. Self-foot reflexology was performed three times a week for 6 weeks for 40 min at each session. Results: The results showed that self-foot reflexology was effective in reducing perceived stress and fatigue and helped blood circulation in premenopausal middle-aged women. Conclusion: Self-foot reflexology may be an effective nursing intervention in reducing perceived stress and fatigue and in improving blood circulation.

• 한국의류학회지
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• 제25권3호
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• pp.516-524
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• 2001

This dissertation has been intented to grasp the components of personal colors and classify personal colors. The Method of the study was quasi-experimental. In the experiment to evaluate personal colors, the subjects was 315 male and female college students in Taegu and Kyungbuk area. The evaluations were analyzed by SAS and the methods used were descriptive statistics, cluster analysis, T-test. The results obtained were as follows: First, the major components of subjects personal colors were found to be the colors of skin and hair. Secondly personal colors were classified into three types: warm, cool, and ambiguous. Third types of personal colors tended to be different between men and women.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 봄 학술발표회 논문집
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• pp.455-460
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• 2002

In this study, a numerical analysis that can effectively predict the effect of strengthening of cracked flexural members is developed using axial deformation link elements. Concrete and interface between concrete and repair material are considered as quasi-brittle material. Reinforcing bars and reinforcing steel plates are assumed to perform as elasto-plastic materials. Unloading behavior of axial deformation link element is implemented. In the developed numerical model, a flexural member is intentionally cracked by pre-loading, then, the cracked member is repaired using extra elements, and reloaded. The results from analysis of repaired flexural members agrees well with available experiment results. Also, it was shown that the effect of strengthening and the change of failure mode with respect to the time for strengthening and thickness of repair materials. Based on the results, it was determined that the developed numerical model has a good agreement for determining failure modes and effect of strengthening in cracked flexural members. By utilizing the developed numerical analysis, the time and dimension of external strengthening in an existing cracked flexural member with predition of failure mechanism can be determined.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 추계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.139-142
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• 2004

Recently the PDP is the most remarkable media for a next generation display device. In this paper, we proposed the PDP dedicated AC-DC converter using quasi resonant method because the PDP has a lot of power dissipation so we need to develope. The proposed converter using one transformer has soft switching and a advantage to lower voltage stress in switch and also is predicted to have high power efficiency, we proposed the principles and theory using the zero voltage switching and verified the validity through a experiment.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1998년도 춘계학술대회논문집; 용평리조트 타워콘도, 21-22 May 1998
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• pp.386-391
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• 1998

The effect of the changes in parameter angles(precone, droop, sweep) on the lead-lag damping was focused on. Experiment was made with hingeless 4-blade rotors and NACA 0012 airfoil. For the measurement of the rotating natural frequencies and lead-lag damping, non-rotating swash plate was oscillated at the regressing lag mode frequency and the data were acquired after the excitation was cut off. Analysis was made using a finite element formulation based on Hamilton's principle. The main blade is assumed as elastic beams. Quasi-steady strip theory is used to obtain aerodynamic forces, and non-circulatory forces are also included.

• 정보관리학회지
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• 제8권2호
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• pp.32-73
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• 1991

본 논문은 탐색자의 개인적 특성이 온라인 서지 데이터베이스 탐색과정 및 탐색 성 과에 미치는 영향을 구명하여 탐색 행태에 관한 모형을 구축하기 위한 것이다. 도서관학과 재학생들을 피험자(N=67)로 하여 측정한 적성, 성격, 정규 교육, 온라인 탐색 교육 효과, 탐 색 과정, 탐색 성과에 대한 29가지 요소를 기초로 하여 9개의 변인을 구성한 후, 12개의 가 설을 검증하여 영향인자를 식별하였고, 경로 분석을 수행하여 5가지의 인과 모형을 구축하 였다.

• 여성건강간호학회지
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• 제12권2호
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• pp.168-176
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• 2006

Purpose: This study was to investigate the effects of aromatherapy massage on pain, physical function, sleep disturbance and depression in elderly women with osteoarthritis. Method: The study design was a quasi-experiment design with a non-equivalent control group pre and post-test. The study pool included elderly female patients older than 65years old suffering from osteoarthritis. Results: Pain in the experimental group after the aromatherapy massage was significantly decreased than that in the control group. The physical disability in the experimental group after the aromatherapy massage was significantly decreased than that in the control group. The sleep disturbance in the experimental group after the aromatherapy massage was significantly decreased than that in the control group. The depression in the experimental group after the aromatherapy massage was significantly decreased than that in the control group. Conclusion: Aromatherapy may be adopted as an effective nursing intervention for osteoarthritis.