• 한국항공우주학회지
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• 제43권4호
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• pp.304-310
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• 2015

핀틀추력기는 추력조절을 위해 노즐목면적을 조절하는 핀틀 스트로크 개념을 사용한다. 충남대학교에서 수행한 공압시험용 핀틀추력기에 대해 MATLAB을 사용하여 1-D 시뮬레이션 성능예측 기법을 연구하였고 전산수치해석과 1-D 시뮬레이션을 수행하여 결과를 비교하였다. 일차원 유동이론에 근거한 성능예측결과는 챔버압력에 대해 경향성 뿐만 아니라 계산값까지 유사한 것을 확인하였지만, 노즐벽면의 박리로 인해 추력에 대해서는 오차가 존재하였다. 수치해석 결과로 모든 핀틀 스트로크 구간에서 노즐의 확장부 부분의 설계 노즐목 부근에서 유동박리가 발생하는 것을 확인하였다. 엠피리컬(Empirical) 추력예측 법은 노즐벽면의 박리를 포함하며, 1-D 엠피리컬 시뮬레이션은 초기 핀틀 스트로크 구간에서 추력을 잘 예측하였다.

• 한국항공우주학회지
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• 제36권3호
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• pp.279-284
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• 2008

액체로켓추진시스템에서 추진제 가압시스템은 추진제가 저장되어 있는 탱크의 얼리지 공간에 가압제인 가스를 제어된 압력으로 공급하는 것이다. 이러한 추진제 가압시스템의 가장 중요한 설계변수는 극저온 추진제 탱크 내에 설치된 가압제 탱크에서 토출되는 가압제의 온도이며, 기체 상태인 가압제의 밀도는 토출되는 가압제의 온도에 따라 민감하게 변한다. 이전 연구에서는 상온 가압제와 상온 외부유체 간의 온도 상관성에 대한 연구가 수행되었으며, 본 연구에서는 현재 개발 중인 액체로켓추진 발사체의 가압시스템과 동일한 조건인 극저온 가압제(GHe)와 극저온 외부유체(LOX)를 적용하여 가압제 탱크에서 가압제 토출 시 강하되는 온도 변화를 실험 및 해석을 통하여 고찰하였다.

• 한국항공우주학회지
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• 제36권3호
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• pp.258-263
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• 2008

초음속 순항 엔진 연소기에 적용하기에 유리한 스크류형 선회기를 장착한 인젝터의 성능을 이론적, 수치적, 실험적 방법을 통해 밝혀 내었다. 인젝터의 성능은 유출계수와 분무각을 중심으로 살펴보았으며, 이에 영향을 미치는 형상 파라미터를 정의하고 기준 인젝터를 설계하여 형상계수에 따른 성능의 변화를 살펴보았다. 정의된 범위에서 인젝터의 성능은 이론적 예측에 의한 값보다 작은 값으로 나타났으며, VOF 방법을 사용한 수치해석에 의해 성능이 매우 잘 예측되는 것을 확인할 수 있었다. 점성장벽에 해당하는 특성은 나타나지 않았으며, 최소 0.05의 유출계수와 최대 104의 분무각을 얻을 수 있었다.

• Journal of Korean Neurosurgical Society
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• 제41권4호
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• pp.236-240
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• 2007

Objective : The aim of this study is to analyze on the external ventricular drainage [EVD] related ventriculitis, especially on their risk factors, management, and prevention. Methods : From January 2003 to December 2005, a total of 174 EVD catheters were placed in 112 patients at our institution. Of these patients, EVD-related ventriculitis were developed in 15 cases. Clinical variables such as age, sex, prior clinical diagnosis, placement of EVD insertion, duration of EVD, total numbers of EVD per person, and outcome were analyzed in theses cases to verify the risk factors, causative agents and outcomes. Results : Fifteen cases of EVD related ventriculitis were noted presenting infection incidence of 13.39 % per patient and 8.62% per procedure. Of these, five patients died from sepsis, seven patients were recovered from infection but neurological complications remained and three patients were recovered without any complications. Microbes were obtained from cerebrospinal fluid only in six patients. Acinetobactoer baumanii was the most common pathogen in our study [4 cases]. Among the various risk factors, only the prior clinical diagnosis showed the statistical significance. Patients who underwent decompressive craniectomy after severe brain trauma showed unfavorable outcome because of possible contaminative environment compared with other cases. Conclusion : EVD is considered as a safe procedure with good control of intracranial pressure if meticulous care is provided for EVD procedure and maintenance. With regards to risk factors and prevention, the higher incidence and unfavorable outcome was seen especially in patients with severe head trauma. Thus, special attention is required in these clinical settings.

• 한국산학기술학회논문지
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• 제13권12호
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• pp.5661-5668
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• 2012

물 부족 시대에 양변기 절수는 물을 절약하는데 가장 효과적인 방법 중 하나이다. 본 연구에서는 고절수형 양변기 개발을 위한 이상유동 해석을 위해 VOF 기법을 이용하였다. VOF를 이용한 전체 모델의 해석은 많은 시간이 요구되므로 전체모델의 일부분만 고려하는 부분모델도 해석시간 단축을 위해 사용하였다. 유량배분 해석을 위해 4개의 서로 다른 림 모델을 고려하였는데 림 홀의 위치나 개수보다는 림 홀의 크기가 유량배분을 효과적으로 달성하기 위한 인자임이 본 연구를 통해 밝혀졌다. 또한, 전체모델 해석을 통해 사이펀 현상에 따른 이상유동의 속도 및 압력도 분석하였다. 따라서 본 연구는 고절수형 양변기 모델 개발을 위한 다양한 기초 데이터를 제공한다.

• 한국추진공학회지
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• 제3권4호
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• pp.58-66
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• 1999

초음속 이젝터 유동특성은 압축성, 비정상성, 충격파 둥으로 인하여 충분히 알려져 있지 않다. 종래의 이론적/실험적 연구결과들은 대부분 1차원 가정 하에서 얻어진 것들이며, 현재까지 수치계산법을 이용하여 이젝터 내부 유동장을 해석한 실례가 많지 않다. 뿐만 아니라 기존의 수치계산 결과들은 2차유동의 질량유량이 매우 작거나 없는 단순한 유동장에 대한 것들이었다. 본 연구에서는 초음속 이젝터-펌프 유동장을 수치적으로 해석하기 위하여 축대칭 수치계산 모델을 이용하였다. 수치계산은 축대칭 압축성 Navier-Stokes 방정식에 유한체적법을 적용하였으며, 표준형 $\kappa$ -$\varepsilon$ 난류모델을 이용하였고, 2차유동의 질량유량을 변화시켜 1차유동과 2차유동의 질량비의 변화에 따른 이젝터 내부 유동장의 변화를 조사하였다. 그 결과, 2차목을 가지지 않는 일정 단면적의 혼합부를 가지는 이젝터의 경우, 이젝터 내부의 유동장 특성은 2차유동의 질량유량의 변화와 거의 무관하게 나타났다. 그러나 2차목을 가지는 경우는 2차유동의 질량유량의 증가에 따른 노즐출구 주위에서 배압으로 인하여 이젝터 내부 유동장이 크게 변화하였다.

• Asian-Australasian Journal of Animal Sciences
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• 제13권11호
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• pp.1529-1535
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• 2000

The aim of the present study was to determine whether brain corticotropin-releasing factor (CRF) and a new peptide, urocortin (UCN) have a direct action in brain mechanisms controlling feed, water and salt intake in sheep. We gave a continuous intracerebroventricular (ICV) infusion of the peptide at a small dose of $5{\mu}g/0.2ml/hr$ for 98.5 hrs from day 1 to day 5 in sheep not exposed to stress. Feed and water intake during ICV infusion of CRF or UCN decreased significantly compared to those during artificial cerebrospinal fluid (CSF) infusion. NaCl intake during infusion of CRF or UCN was the same as that during CSF infusion. Mean carotid arterial blood pressure (MAP) and heart rate during ICV infusion of CRF or UCN were not significantly different from that during CSF infusion. On the other hand, the plasma glucose concentration during ICV infusion of CRF or UCN tended to be higher than that during CSF infusion. These observations indicate that decreased feed intake induced by CRF and UCN infusion is not mediated by the activation of both the pituitary-adrenal axis and the sympathetic nervous system. The results suggested that brain CRF and UCN act directly in brain mechanisms controlling ingestive behavior to decrease feed and water intake, but do not alter salt intake in sheep.

• The Korean Journal of Physiology and Pharmacology
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• 제4권5호
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• pp.393-401
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• 2000

To define the postnatal changes in ANP secretion in response to mechanical stretch and atrial compliance, experiments have been done in perfused nonbeating rabbit atria with different ages: 1-day, 1-, 2-, 3-, 4-, and 8-wk-old. In 1-day-old-rabbits, an increase in intraatrial pressure resulted in an increase in atrial volume, which was higher than that in 1-wk-old rabbits. Increases in atrial volume stimulated the secretion of ANP with concomitant translocation of extracellular fluid (ECF) into the atrial lumen. However, mechanically stimulated ECF translocation was lower in 1-day-old rabbits than that in 1-wk-old rabbits. Therefore, positive relationship between mechanically stimulated ECF translocation and ANP secretion was shifted upward in 1-day-old rabbits, as compared to 1-wk-old rabbits. Changes in atrial volume and ECF translocation were gradually increased with aging and reached the peak value at 4 wk. The stretch-induced ANP secretion in terms of ECF translocation (the interstitial ANP concentration) was also increased with aging and reached the peak value at 4 wk. The interstitial ANP concentration was dependent on the atrial content of ANP. These data suggest that the higher level of atrial ANP secretion is related to the postnatal changes in atrial volume and unidentified factor.

• Journal of Korean Neurosurgical Society
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• 제39권5호
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• pp.335-339
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• 2006

Objective : The authors present eight cases of immediate post-operative epidural hematomas[EDHs] adjacent to the craniotomy site, describe clinical details of them, and discuss their pathogenesis. Methods : Medical records of eight cases were retrospectively reviewed and their clinical data, operation records, and radiological findings analyzed. Any risk factors of the EDHs were searched. Results : In 5 of 8 cases, adjacent EDHs developed after craniotomies for the surgical removal of brain tumors. Three cases of adjacent EDHs developed after a pterional approach and neck clipping of a ruptured anterior communicating artery aneurysm, a ventriculoperitoneal shunt, and a craniotomy for a post-traumatic EDH, respectively. In all eight cases, brain computed tomography[CT] scans checked immediately or a few hours after the surgery, revealed large EDHs adjacent to the previous craniotomy site, but there was no EDH beneath the previous craniotomy flap. After emergent surgical removal of the EDHs, 7 cases demonstrated good clinical outcomes, with one case yielding a poor result. Conclusion : Rapid drainage of a large volume of cerebrospinal fluid or intra-operative severe brain collapse may separate the dura from the calvarium and cause postoperative EDH adjacent to the previous craniotomy site. A high-pressure suction drain left in the epidural space may contribute to the pathogenesis. After the craniotomy for brain tumors or intracranial aneurysms, when remarkable brain collapse occurs, an immediate postoperative brain CT is mandatory to detect and adequately manage such unexpected events as adjacent EDHs.

• Journal of Korean Neurosurgical Society
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• 제30권3호
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• pp.366-370
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• 2001

Objective : The authors present three cases of brain tumors in which epidural hematomas(EDHs) were developed postoperatively in the remote areas from craniotomy sites. The preventive tactics as well as possible mechanisms of development of remote EDH are discussed. Material and Methods : The magnetic resonance imagings of three patients revealed a left lateral ventricular mass located just aside of foramen Monro in a 27-year-old male, a large cystic mass in the temporal lobe in a 35-year-old male, and a partially calcified pineal mass in a 27-year-old male patient. The surgical removals of these tumors were performed without any noticeable events during surgery via left frontal transcortical transventricular approach for lateral ventricular tumor, left temporal craniotomy for cystic temporal tumor, and right occipital transtentorial approach for pineal tumor. Results : Postoperative EDHs remote from the sites of craniotomy were detected by the immediate postoperative computerized tomographic scans. We obtained good outcomes without any morbidity in all three patients with emergent evacuation of the hematoma. The pathologic diagnoses were lateral ventricular ependymoastrocytoma, temporal craniopharyngioma and mixed germinoma of the pineal region. Conclusion : It is postulated that a sudden reduction of intracranial pressure(ICP) at the time of tumor removal may strip the dura from the inner table of the skull to cause EDH from the remote site of craniotomy. Gradual reduction of ICP with slow drainage of cerebrospinal fluid before tumor removal as well as lowering the head position of patient during surgery might be helpful for preventing this unusual complication.