• 한국학교수학회논문집
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• 제4권1호
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• pp.103-114
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• 2001

The purpose of this study is to develop learning materials for functional concept on variable and to verify the effect of how well students could learn functional concept after they studied with those materials. To accomplish the purpose of this study, I developed learning materials and after teaching students with them. I have concluded the followings : First, there was little effect in teaching functional concept on variable between two experimental groups, whereas teaching functional concept had greater effect on forming functional concept in high level groups in those two experimental groups. Second, teaching functional concept on variable had little effect on students' understanding of functional concept and perfecting tables in Black box, graph, and mathematical problems, whereas there was much effect in students' understanding functional concept and solving relation formula, image, and range problems related to everyday life or general things. On the basis of the problems which appeared in the process of this study, the following can be suggested : First, we should develop learning materials fit for low level students so that they could understand functional concept. Second, we should continue to teach the basic problems like solving relation formula, image, and range, and understanding functional concept in graph until students are able to understand them exactly. Third, since the goals of Unit Function in a middle school textbook is to solve problems related to everyday life through functional thinking, there should be change in constructing systematic contents of Unit Function in a middle school textbook.

• Journal of Power Electronics
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• 제7권3호
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• pp.222-232
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• 2007

This paper presents the application of a single phase AC-to-DC converter using a three-phase series parallel (SPRC) resonant converter to variable speed dc-drive. The improved power quality converter gives the input power factor unity over a wide speed range, reduces the total harmonic distortion (THD) of ac input supply current, and makes very low ripples in the armature current and voltage waveform. This soft-switching converter not only possesses the advantages of achieving high switching frequencies with practically zero switching losses but also provides full ranges of voltage conversion and load variation. The proposed drive system is the most appropriate solution to preserve the present separately excited de motors in industry compared with the use of variable frequency ac drive technology. The simulation and experimental results are presented for variable load torque conditions. The variable frequency control scheme is implemented using a DSP- TMS320LF2402. This control reduces the switching losses and current ripples, eliminates the EMI and improves the efficiency of the drive system. Experimental results confirm the consistency of the proposed approach.

• 한국자동차공학회논문집
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• 제22권7호
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• pp.1-7
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• 2014

A variable displacement vane pump is possible to improve the fuel economy by varying the pump capacity with a vane mechanism according to the engine operating speed range and reducing its driving torque. In general the experimental evaluation of the vane pump for the transmission has been performed mainly not with the vehicle or dynamometer test rig but with component test rig due to the implementation and safety problems. In this paper, in order to evaluate the performance of the developed vane pump as well as the compatibility with other rotary and hydraulic components of the target transmission, the transmission dynamometer based test rig is implemented where the developed pump is built into it and then the variable pump capacity and effect of power reduction are investigated experimentally.

• 한국항공운항학회지
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• 제5권1호
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• pp.31-50
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• 1997

A new variable wing that can be swept back and forward synchronously were developed to enhance the aerodynamic and stability characteristics of a high speed airplane. The configuration of the new variable wing changes in such a way that inner part of the wing sweeps forward and outer part of the wing sweeps backward, the shift of aerodynamic center of the wing is small, therfore the static margin that is required for the stability of a airplane is not affected. In this study, various configurations of wing models by combined swept back and forward were designed and a wind tunnel tests were conducted to investigate the aerodynamic characteristics of these variable wings. The experimental results showed that the variable wing by combined swept back and forward has no effect on the pitching moment coefficient affecting on an aircraft stability margin and enhance the aerodynamic characteristics for a given approach angle of attack.

• 소성∙가공
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• 제15권1호
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• pp.47-56
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• 2006

It is well known that the family-mold has an advantage to reduce the cost for production and mold. However, defects are frequently occurred by over packing the smaller volume cavity during molding, especially when the family-mold has a volumetric difference between two cavities. In this study, the cavity-filling imbalance was confirmed by the temperature and the pressure sensors, and a variable-runner system was developed for balancing the cavity-filling. Experiments of balancing the cavity filling was carried out in the family-mold with the variable-runner system, and balancing the cavity-filling was confirmed by changing the cross-sectional area of a runner in the variable-runner system with the temperature and pressure sensors. The influence of the injection speed to the balancing-capability of the variable-runner system was also examined in the experiment.

• International Journal of Fuzzy Logic and Intelligent Systems
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• 제6권2호
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• pp.116-120
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• 2006

This paper discusses an approach for detecting a new edge in color images. The color image is to be represented by a vector field, and the color image edges are detected as differences in the local vector statistics. This method is based on the calculation for the vector angle between two adjacent pixels. Unlike Euclidean distance in RGB space, the vector angle distinguishes the differences in chromaticity, independent of luminance or intensity. The proposed approach can easily accommodate concepts, such as variable template edge detection, as well as the latest developments in vector order statistics for color image processing. In this paper, it is used not a conventional fixed template operator but a variable template operator The variable template is implemented and experimental results for digital color images are included.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2008년도 하계종합학술대회
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• pp.983-984
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• 2008

This paper proposes a variable break that can offset prediction error as well as a pre-selection methods, based on the variable break, for enhanced unit selection. In Japanese, a sentence consists of several APs (Accentual phrases) and MPs (Major phrases), and the breaks between these phrases must predicted to realize text-to-speech systems. An MP also consists of several APs and plays a decisive role in making synthetic speech natural and understandable because short pauses appear at its boundary. The variable break is defined as a break that is able to change easily from an AP to an MP boundary, or from an MP to an AP boundary. Using CART (Classification and Regression Trees), the variable break is modeled stochastically, and then we pre-select candidate units in the unit-selection process. As the experimental results show, it was possible to complement a break prediction error and improve the naturalness of synthetic speech.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1991년도 한국자동제어학술회의논문집(국내학술편); KOEX, Seoul; 22-24 Oct. 1991
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• pp.468-468
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• 1991

The variable-frequency type water supply equipment, which adopts the variable-voltage and variable-frequency converter(VVVF converter) to govern automatically the rotating speed of a pump, can save 15-20% of power, as compared with a throttle-controlled pump device or an airpressurized water supply equipment, and is finding a wide application. However, it still has some disadvantages : greater pressure fluctuations during switching over the pump and prolonged low-effeciency running of the pump in the case of small consumption of water. Therefore, it is difficult to apply the equipment to the fire water supply system where the water should not be put into use unless a fire takes place, and the water pressure in pipelines should permanently remain constant. This paper introduces the automatic regulation principle of the variable-frequency type air-pressurized water supply equipment (hereafter referred to as simply BFQS equipment) for dual purposes of daily life and fire control, which combined both technologies of speed governing by a converter and air-pressurized water supplying, then discusses some problems related to automatic control, and finally gives the experimental results of an embodiment-BPQS-100-50 water supply equipment.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 추계학술대회 논문집 학회본부 A
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• pp.364-368
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• 1999

This paper suggests switching regulator technique to overcome the drawback of conventional variable linear power supply. Switching regulator technique can eliminate the extremely lossy operation and reduce the size and weight of variable linear power supply and provide nearly constant output power over the majority of output voltage range. The topology of variable switched mode power supply is employed active clamp forward converter with a current doubler rectifier and by using control of variable-frequency together with control of fixed-frequency, output voltage can be controled. Equivalent circuits pertinent to each operational mode of converter are derived, and an experimental 20V, 50A converter was designed and built. The converter operates from an output voltage of zero to 25 V, under 100 kHz switching frequency.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.2035-2040
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• 2004

A cone cylinder is used to obtain variable operation conditions for the sonic ejector-diffuser system. The cone cylinder is designed to move upstream and downstream to change the ejector throat area ratio, thus obtaining variable mass flow rates. The present study investigates the effects of ejector throat area ratio and operating pressure ratio on the entrainment of secondary stream for the variable sonic ejector system. In experiment, the ejector throat area is varied in the range from ${\psi}=11.88$ to 66.69, and the operating pressure ratio from $p_{0p}/p_a=1.25$ to 9.0. The results show that the variable sonic ejector system is suitable for a required entrainment ratio of secondary stream by altering the ejector throat area ratio and operating pressure ratio.