• 대한기계학회논문집B
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• 제28권1호
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• pp.72-80
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• 2004

Steady flow of an ER (electro-rheological) fluid in a two-dimensional electrode channel is studied by using FEM. Hydrodynamic interactions between the particles and the fluid are calculated by solving the Navier-Stokes equation combined with the equation of motion for each particle, where the multi-body electrostatic interaction is described by using point-dipole model. Motion of the particles in the ER fluid is elucidated in conjunction with the mechanisms of the flow resistance and the increase of viscosity. The ER effects have been studied by varying the Mason number and volume fraction of particles. These parameters have an influence on the formation of the chains resulting in the changes of the fluid velocity and the effective viscosity of ER fluids.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1996년도 추계학술대회 논문집
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• pp.270-273
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• 1996

This paper describes a type of piezoelectric transformer with improved design principles. It consists of a thin rectangular piezoelectric ceramic plate having two input electrodes and one output electrode. The length of each input and output electrode is nearly one third of that of piezoelectric transformer itself. In the driving section, the ceramic plate is poled in the thickness direction reversely with each other, and has electrodes on both main faces. The electric input near its fundamental resonance frequency is applied to the driving section in parallel and the output voltage from the generating section is connected to the resistor load. Its equivalent circuit is derived from the Mason\`s model. The frequency characteristics near the resonance frequency under no load have been investigated. Moreover, using this piezoelectric transformer we measured the LCD backlight characteristics.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1994년도 하계학술대회 논문집 C
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• pp.1283-1285
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• 1994

A three-layered piezoelectric ceramic transducer is fabricated with three piezoelectric ceramic disk transducers and two sheets of thin insulator. Its equvalent circuit is derived from the Mason's model of a thickness-driven piezoelectric transducer. We applied the electric input near its fundamental resonant frequency to the center transducer and connect the output voltages across the left and right transducers in series to the resistor load. Then we investigate the load characteristics at resonant frequencies under various resistor loads and the frequency characteristics near the resonant frequency under no load. Moreover, symbolic expressions for input impedances, voltage ratios, resonant frequencies, and bandwidths have been derived. The values calculated from those symbolic expressions are shown to agree well with the measurement values.

• Wind and Structures
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• 제10권5호
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• pp.437-462
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• 2007

A non-translating, long duration thunderstorm downburst has been simulated experimentally and numerically by modelling a spatially stationary steady flow impinging air jet. Velocity profiles were shown to compare well with an upper-bound of velocity measurements reported for full-scale microbursts. Velocity speed-up over a range of topographic features in simulated downburst flow was also tested with comparisons made to previous work in a similar flow, and also boundary layer wind tunnel experiments. It was found that the amplification measured above the crest of topographic features in simulated downburst flow was up to 35% less than that observed in boundary layer flow for all shapes tested. From the computational standpoint we conclude that the Shear Stress Transport (SST) model performs the best from amongst a range of eddy-viscosity and second moment closures tested for modelling the impinging jet flow.

• E2M - 전기 전자와 첨단 소재
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• 제9권1호
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• pp.24-29
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• 1996

A composite piezoelectric ceramic transducer is fabricated with three piezoelectric ceramic disk vibrators and two sheets of thin insulator. Its equivalent circuit is derived from the Mason's model of a thickness-driven piezoelectric vibrator. When the electric input near its fundamental resonance frequency is applied to the center vibrator and the output voltages across the left and the right vibrators are connected in series to the resistor loads, the load characteristics at resonance frequencies under the various resistor loads and the frequency characteristics near the resonance frequency without load are investigated. Furthermore, symbolic expressions for input impedances, voltage ratios, resonance frequencies, and bandwidths are derived. The data calculated from those symbolic expressions are agreed well with the measurement data.

• Journal of Information Technology Applications and Management
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• 제15권3호
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• pp.195-208
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• 2008

In an emergency management case, evaluating the economic value of information technology investments is a challenging problem due to the effects of decision making, uncertainty of disasters, and difficulty of measurements. Risk assessment and recovery process, one of the major functions in emergency management, consists of (1) measurement of damages or losses, (2) recovery planning, (3) reporting and approving budgets, (4) auctioning off recovery projects to constructors, and (5) construction for the recovery. Specifically and of our interest, measurement of damages or losses is often a costly and time-consuming process because the wide range of field surveys should be performed by a limited pool of trained agents. Managers, therefore, have to balance accuracy of the field survey against the total time to complete the survey. Using information technologies to support field survey and reporting has great potential to reduce errors and lowers the cost of the process. However, existing cost benefit analysis framework may be problematic to evaluate and justify the IT investment because the cost benefit analysis often include the long-run benefit of IT that is difficult to quantify and overlook the impact of managerial control upon the investment outcomes. Therefore, we present an alternative cost-centric control model that conservatively quantifies all cost savings to replace benefits in cost benefit analysis and incorporate the managerial control. The model provides a framework to examine how managerial decision making and uncertainty of disaster affect the economic value of IT investments. The current project in Emergency Agency in South Korea is introduced as a case to apply the cost-centric control model. Our work helps managers to better evaluate and justify IT-related investment alternatives in emergency management.

• 한국수학교육학회지시리즈C:초등수학교육
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• 제24권4호
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• pp.247-264
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• 2021

사다리꼴의 넓이는 수학적 사고와 역량을 기를 수 있는 중요한 개념이지만 다수의 학생은 사다리꼴의 넓이 공식을 도구적으로 이해하는 경향이 있다. 이러한 문제를 해결하는 실마리를 Dienes의 수학학습이론과 Watson과 Mason의 예 공간 개념에서 찾을 수 있었다. 본 연구는 사다리꼴의 넓이 교수학습에 관한 시사점을 얻고자 Dienes의 수학학습이론에 따른 사다리꼴의 넓이 학습에서 학생들이 구성한 예 공간을 분석하였다. 분석 결과, 학생들이 구성한 수학학습단계별 예 공간은 놀이 단계의 사다리꼴 변형에 대한 예 공간, 비교·표현 단계의 공통점 표현에 대한 예 공간, 기호화·형식화 단계의 사다리꼴 넓이 식에 대한 예 공간이었다. 단계별 예 공간을 구성하는 예의 종류, 생성, 비중, 관련성을 분석하고 예 공간의 구조를 맵으로 도식화하였다. 단계별 예 공간의 일반적인 예, 특수한 예, 관례적인 예를 분석하고 실제 사다리꼴의 넓이 교수학습실행에서 예와 예 공간을 활용하는 방안을 논의하였다. Dienes의 수학학습이론에 따른 사다리꼴의 넓이 학습수행의 유의미함을 논의하였고 본 연구의 내용은 사다리꼴의 넓이 학습의 한 모델이 될 수 있다.

• 수산해양기술연구
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• 제35권3호
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• pp.312-322
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• 1999

A ultrasonic transduce with a single acoustic matching layer has been designed as an attempt to increase the bandwidth of underwater transducer. The wideband resonance condition was accomplished by attaching a single matching layer on the front face of a ceramic resonator composed of a piezoelectric bar, a taper part and a head part. A modified Mason's model was used for the performance analysis and the design of transducers, and the constructed transducers were tested experimentally and numerically by changing the impedance and thickness of the matching layer in the water tank.The obtained results are summarized as follows:1. Measured resonant and antiresonant frequencies of the piezoelectric transducer with no matching layer in air were 24.7 kHz and 25.6 kHz, respectively. 2. Two resonant frequencies of the piezoelectric transducer with a single matching layer were 21.7 kHx and 26.9 kHz, respectively, in air and 21.4 kHz and 22.7 kHz, respectively, with a water load.3. Two distinct resonance peaks in the transmitting voltage response(TVR) of the developed transducer were observed at 22.0 kHz and 25.8 kHz, respectively, with center frequency of 24.0 kHz. The values of TVR at these frequencies were 130.1 dB re $1 \muPa$/V at 22.0 kHz and 128.5 dB re $1 \muPa$/V at 25.8 kHz, respectively.Reasonable agreement between the experimental results and the numerical values was achieved.

• 한국조리학회지
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• 제21권5호
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• pp.119-128
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• 2015

본 연구의 목적은 그린 호텔을 방문하는 고객의 가치와 그들의 태도가 그린 실천이나 환경에 대한 걱정, 그린 호텔의 방문 행동에 어떠한 관계가 있는지 고찰하는 것에 있다. 또한 본 연구에서는 각 요인들이 서로 어떠한 영향을 미치는지 파악함으로써 그린호텔을 방문하는 고객들에 대한 다양한 관점을 이해하는데 유용한 학술적 자료를 제공하였다는데, 다른 의의가 있다. 각 요인들에 대한 심층적인 분석과 그린 호텔에 대한 선행연구를 토대로 가치는 자기초월과 자기고양으로 분류되었고, 태도는 환경에 대한 걱정과 그린 호텔에 대한 심리적 태도의 관계로 설명하였으며, 마지막으로 행동은 방문의도, 구전효과, 그리고 추가지불의도로 분류할 수 있었다. 따라서 본 연구를 토대로 그린 호텔 마케터나 정책관련 담당자들은 소비자들의 심도 있는 관점을 이해할 수 있으며, 보다 현실적인 학문적 이해를 할 수 있을 것으로 기대된다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1997년도 추계학술대회 논문집
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• pp.254-257
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• 1997

In this paper, we investigated the effects of gap length and tip radius influenced in breakdown of mineral based insulation oil Electrode system was needle-plane geometry It is to model conductive extrusions in oil filled electrical power apparatus. The tip radius of needle electrode was 5, 10, 20 and 25${\mu}{\textrm}{m}$, respectively. We measured breakdown voltage for each of tip radius with increasing electrode gap, 2mm to 12mm. It was calculated electrical breakdown strength at tip using Mason\`s equation from breakdown voltage As gap lenght increased. breakdown strength increased linearly. But, as tip radius of needle increased, breakdown strength decreased exponentially. It can be explained by tole phenomenon that electron is easily injected, as tip radius increases, and effective work function decreases. When appling DC voltage. breakdown 7tr7ilgtll was higher wheal polarity of needle was negative than positive. It is because of the space charge effect ill accordance with the influence of liquid motion.