• 대한의용생체공학회:의공학회지
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• 제28권4호
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• pp.569-576
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• 2007

Ventricular Assist Device(VAD) has switched its goal from a short-tenn use for bridge-to-transplantation to a long-tenn use for destination therapy, With this goal, the importance of long-tenn reliability gets more interests and importances, H-VAD is an portable extracorporeal biventricular assist device, and adopts an electro-pneumatic driving mechanism. The pneumatic pressure to pump out blood is generated with compression of bellows, and is transmitted in a closed pneumatic circuit through a pneumatic line. The existing pneumatic VAD adopts a air compressor which can generate stable pressures but has defects such as a noise and a size problem. Thus, it is not suitable for being used as a portable device, These problems are covered with adopting a closed pneumatic circuit mechanism with a bellows which has a small size and small noise generation, but it has defects that improper pneumatic setting causes a failure of adequate flow generation. In this study, the pneumatic pressure regulation system is developed to cover these defects of a bellows-type pneumatic VAD. The optimal pneumatic pressure conditions according to various afterload conditions for an optimal flow rate were investigated and the afterload estimation algorithm was developed, The final pneumatic regulation system estimates a current afterload and regulate the pneumatic pressure to the optimal point at a given afterload condition. The afterload estimation algorithm showed a sufficient performance that the standard deviation of error is 8.8 mmHg, The pneumatic pressure regulation system showed a sufficient performance that the flow rate was stably governed to various afterload conditions. In a further study, if a additional sensor such as ultrasonic sensor is developed to monitor the direct movement of diaphragm in a blood pump part, the reliability would be greatly increased. Moreover, if the afterload estimation algorithm gets more accuracy, it would be also helpful to monitor the hemodynamic condition of patients.

• 한국수자원학회논문집
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• 제42권7호
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• pp.537-546
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• 2009

상수관망의 유지 관리를 위한 최적 압력 계측 위치 선정은 효율적인 상수관망 운영을 위해 필수적이다. 본 연구에서는 최적 압력 계측 위치 결정에 기존 연구의 단점을 보완하기 위하여 정보이론인 엔트로피 이론을 사용하였다. 기존의 방법은 실측자료를 이용한 검 보정이 필요로 하기에 체계적인 관리가 미흡한 지역에서는 적용이 어려운 단점이 있다. 또한 대부분의 연구가 상수관망 모형의 정확도를 높이며 측정비용을 최소화하는 절점을 제안하였으며, 이는 상수관망 유지 관리를 위한 압력 계측기 위치 결정목적과는 다소 차이가 있다. 본 연구에서 제안된 방법은 특정 절점에서의 유량변화에 의한 다른 절점에서의 압력변화를 정보량인 엔트로피로 정의하여 객관적이고 정량화된 기준을 제시하였다. 절점에서 비정상상태가 발생했을 때 전체 상수관에 미치는 영향 정도를 정량화된 수치인 엔트로피로 나타내며, 또한 각 절점에서 실제적으로 변동하는 압력을 반영하고자 EPANET의 에미터(emitter) 기능을 사용하여 실제 압력변화 패턴을 파악하였다. 최적 압력계 설치 지점은 엔트로피 기준에 의해 전체 시스템으로부터 제공받는 정보량이 가장 큰 절점을 우선으로 설치해야 한다고 제시하였으며, 제안된 모형을 branch형과 loop형 관망에 각각 적용하여 최적 압력 계측 위치를 선정하고 그 결과를 분석하였다. 분석 결과 현재 실무자의 경험적 판단에 의해 계측기를 설치 운영하고 있는 국내의 상수관리 시스템을 고려할 때, 엔트로피 이론을 통해 보다 객관적인 기준으로 상수관망에서의 압력계 설치 우선순위를 운영자에게 제시할 수 있을 것이며, 상수관망에 압력계를 설치하기 위한 효율적인 의사결정 기준으로 활용이 가능할 것으로 판단된다.

• 한국초전도ㆍ저온공학회논문지
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• 제6권3호
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• pp.56-61
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• 2004

An optimal cooling method for a long HTS power transmission cable was scrutinized by using theoretical models. Cooling length of HTS cable is determined by pressure range and temperature range of LN2 in the HTS cable. Results showed limitation from temperature range is stricter than that from pressure range. The well-known one-side cooling was modified to two-side cooling. It was shown that cooling length can be nearly doubled by adopting two-side cooling of the same capacity.

• Journal of Advanced Marine Engineering and Technology
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• 제28권2호
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• pp.269-276
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• 2004

A marine diesel engine should realize optimal efficiency operation while reducing NOx. Fuel injection systems by electronic control can become effective means for that. Although it would be able to get more precise engine control compared to the mechanical injection system, it needs some accurate and instant information in order to bring its ability into full play while sailing on the sea. Very important information of them is shaft torque and continuous combustion pressure of all cylinders. The system presented in this report can deliver those data.

• 대한기계학회논문집A
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• 제26권1호
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• pp.23-30
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• 2002

Abstract The optimization is performed to reduce the mass of CNG pressure vessel reinforced with composite materials in the hoop direction. An axisymmetric shell element which takes into account the layered liner and hoop composite materials is thus developed and incorporated into a program Axicom. The accuracy of the program is then verified using the 4 noded element in ANSYS. Three different cases of optimization are then performed using the Axicom: (1) uniform hoop thickness, (2) varying hoop thickness, and (3) varying the ply angles and accordingly the thickness. Compared with a traditional method, cases (2) and (3) were found to be very effective in reducing the thickness and cost of the hoop composite materials by about 80% without sacrificing the safety factors.

• 대한기계학회논문집A
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• 제31권5호
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• pp.556-561
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• 2007

The rapid thermal response(RTR) molding is a novel process developed to raise the temperature of mold surface rapidly in the injection stage and then cool rapidly to the ejection temperature by air or water. The objectives of this paper are to investigate the effect of mold temperature, pressure and thickness of micro pattern molding and to provide a optimization of RTR injection molding for micro pattern from Moldflow simulation. Optimal minimum temperature and pressure was found without shortcut according to thickness. Filling percentage was influenced by glass transition temperature with the kinds of resin. Optimal temperature is slightly higher than glass transition temperature irrespectively of pressure, thickness, the kinds of resin in the micro pattern molding.

• 한국자동차공학회논문집
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• 제9권4호
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• pp.121-130
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• 2001

For the purpose of optimal control of anti-lock brake systems, precise dynamic characteristics analysis of hydraulic modulator, especially solenoid valve is necessary. However, most of researches so far have dealt with dynamic characteristic analysis of valve itself, and the results have been restrictively applied to the actual ABS modulator, where hydraulic pressure is acting. In this study, mathmatical modeling and experimental analysis were peformed in order to evaluate the valve dynamic characteristics when the hydraulic pressure is applied. High pressure on the master cylinder that affects on the valve dynamic characteristics have been analyzed quantitatively, and performance improvement methods have been suggested through parameter study. Consequently, results of solenoid valve dynamic characteristics analysis derived in the study can be utilized as criteria for the optimal control of anti-lock brake systems.

• 한국소음진동공학회논문집
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• 제15권5호
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• pp.612-619
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• 2005

In this work. two dynamic absorbers are introduced and designed to reduce the vibration of the large-size pressure vessel of a reactor for a petrochemical plant. The vibration modes and harmonic responses of the vessel are firstly analyzed by the finite element method. On the basis of the analyzed results, two dynamic absorbers are designed by a simple design theory. Furthermore, an optimization process is executed and an optimal design of the dynamic absorber is obtained to improve performance and structural safety of the vessel. As a result, the maximum displacement and stress of the vessel is decreased about $85\%$ and $65\%$ respectively, the design criteria being satisfied.

• 한국분말재료학회지
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• 제1권2호
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• pp.198-207
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• 1994

In order to find an optimal friction-welding condition for Ni-base ODS alloy (MA 754) produced by mechanical alloying, joint experiments were performed with various conditions of friction pressures (50~500 MPa), friction times (1~5 sec) and upset pressures (50~600 MPa). The optimal friction pressure and upset pressure must be above 400 MPa and 500 MPa, respectively, which are determined by tensile strengths and fracture features of as-welded joints. A maximum stress설h of 975 MPa could be obtained under these pressure conditions at friction time of 2 sec. Microstructural features of bonded interface by optical microscope and SEM revealed that the interface regions of all specimens are consisted with three distinct regions and defects such as voids, cracks and wavy interfaces exist in the joints produced under not-optimized conditions. EDS results showed that these defects include oxides composed with elements of Al, Y and Ti. The hardness on the bonded interface was higher than in the base metal region. Specimens fractured in bonded interface region had lower strength values compared to those fractured in base metal region. Surfaces of the former showed a typical intergranular fracture.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1987년도 정기총회 및 창립40주년기념 학술대회 학회본부
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• pp.296-299
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• 1987

The purpose of this paper is to increase the lamp efficacy by filling the optimal Nitrogen gas pressure in the outer enclosure of metal halide lamp. This study presents a new model of Langmuir in the outer enclosure of discharge lamp. In this paper, in the first place, the diameter of Langmuir sheath and the total gab loss were calculated. Secondly, the each gas loss was computed if the arbitrary gas pressure is filled, With the calculated data, flash over which affects the lamp efficacy, lamp life and color rendering was considered. In case of the established discharge lamp, the gab pressure has been filled by experience only roughly. The gas loss is converted into the radiation output. Therefore, the lamp efficacy is improved by reducing the gas loss.