• Journal of Mechanical Science and Technology
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• 제17권12호
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• pp.1912-1921
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• 2003

This paper presents a global mode modeling of space structures and a control scheme from the practical point of view. Since the size of the satellite has become bigger and the accuracy of attitude control more strictly required, it is necessary to consider the structural flexibility of the spacecraft. Although it is well known that the finite element (FE) model can accurately model the flexibility of the satellite, there are associated problems : FE model has the system matrix with high order and does not provide any physical insights, and is available only after all structural features have been decided. Therefore, it is almost impossible to design attitude and orbit controller using FE model unless the structural features are in place. In order to deal with this problem, the control design scheme with the global mode (GM) model is suggested. This paper describes a flexible structure modeling and three-axis controller design process and demonstrates the adequate performance of the design with respect to the maneuverability by applying it to a large flexible spacecraft model.

• 대한교통학회지
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• 제24권3호
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• pp.17-27
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• 2006

미시교통류의 한 연구분야인 차량추종이론은 1950년대에 처음으로 제시되었고 1960년대에 활발히 진행되다가 자료수집의 한계로 인해 연구가 부진하다가 위성을 이용한 차량의 위치추적 기술의 발달과 컴퓨터의 이용이 보편화되면서 다시 활기를 띠고 있다. 최근에는 GPS(global positioning systems)의 수신자료를 이용한 연구가 많이 수행되고 있다. GPS 기술이 교통에 도입되면서 차량의 위치에 대한 실시간 추적이 가능하게 되었다. 위치정보는 시간상으로 연속적일 뿐만 아니라, 여러 대의 차량의 연속주행에 대해서도 동시 측정이 가능하다. 본 연구는 현실자료를 기반으로 한 국내 교통류에 적합한 차량추종모델 파리미터를 정산하기 위하여 수집장치로서 DGPS의 활용 가능성을 타진하는 실험을 반복 수행하였고, DGPS를 활용한 분석 프로세스를 정립하고, 오차에 관한 현장조사를 수행하며, DGPS 수신자료의 활용성을 판단하여 추가조사를 통하여 제한적이긴 하나 차량추종모델의 파라미터를 정산한 후 이 값을 기존 연구결과와 비교해 보는 과정으로 구성되었다. 또한 최근 미시적 시뮬레이션의 도입이 광범위하게 이루어지고 있고. 시뮬레이션에는 차량추종모델이 적용 되어있다. 파라미터 정산의 어려움으로 인해 외국의 Default 값을 수정 없이 사용하고 있는데 국내 운전행태가 외국의 경우와 다르므로 Default값을 사용하는 것은 분석의 문제 가능성을 내포하고 있다. 본 연구에서는 현장실험을 통해 수집된 DGPS 수신자료를 이용하여 제한적이나마 PARAMICS의 차량추종모델의 파라미터를 정산하는 것으로 현실에 맞는 파라미터 정산치 가능성을 판단하였다.

• Journal of Chest Surgery
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• 제20권4호
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• pp.643-654
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• 1987

The effect of prostacyclin[PGI, ] on myocardial preservation during global ischemia was studied in the isolating working rabbit heart model. Forty hearts underwent a 15 minute period of retrograde nonworking perfusion with Krebs-Henseleit buffer solution [37*C] and were switched over to the working mode for 15 minutes. After baseline measurement of heart rate, peak aortic pressure, aortic flow, and coronary flow, all hearts were subjected to 60 minutes of ischemic arrest at 10*C induced with St. Thomas Hospital cardioplegic solution: Group I had single dose cardioplegia, Croup II double dose, Croup III oxygenated double dose, and Group IV single dose with PCI, infusion [10ng/min./gm heart weight]. Hearts were then revived with 15 minute period of nonworking reperfusion at normothermia, followed by 30 minutes of working perfusion. Repeat measurements of cardiac function were obtained and expressed as a percent of the preischemic baseline values. Oxygen content of arterial perfusate and coronary effluent was measured by designed time interval. Leakage of creatine kinase was determined during post-ischemic reperfusion period. Finally wet hearts were weighed and placed in 120*C oven for 36 hours for measurement of dry weight. In the PGI, treated group [IV], heart rate increased consistently throughout the period of reperfusion from 100*5.0% [p<0.001] to 107*6.2% [p<0.001]. The percent recovery of aortic flow showed 95*5.7% [p<0.001] at the first 3 minute and full recovery through the subsequent time. Coronary flow was augmented significantly in the 3 minute [96*6.2%, p<0.001] and then sustained above baseline values. Among the Croup I, II, and III, all hemodynamic values were significantly below preischemic levels. PGI2 relatively increased oxygen delivery [1.22*0.19ml/min, p<0.001] and myocardial oxygen consumption [0.90*0.13ml/min, p<0.001] during reperfusion period. Leakage of creatine kinase in the PGI2 group was 9.3*1.58IU/15min [p<0.001]. This was significantly lower than Group I [33.0*2.68 IU/15min]. The water content of PCI2 treated hearts [81*0.9%, p<0.001] was also lower than the other groups.