• Proceedings of the Korea Water Resources Association Conference
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• 2016.05a
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• pp.63-63
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• 2016

자연 하천은 연속적인 곡선 흐름을 가지고 있으며, 하천의 흐름을 해석하는 것은 복잡하고 어려운 일이다. 게다가 자연하천에서는 유사이송에 의해 하상변동이 발생하며 이를 정확하게 예측하는 것은 공학적 문제 해결에 중요한 역할을 한다. 곡선 흐름에서의 하상변동양상은 원심력에 의한 이차류로 인하여 유사가 하천의 내측으로 이동하게 되고, 하천의 외측에는 침식, 내측에는 퇴적이 된다. 이와 같은 현상은 원심력뿐만이 아니라 하천의 곡선에 의해 발생하게 되는 박리 또한 중요한 원인으로 이야기 되고 있으며, 선행 연구자들에 의해서 박리의 영향이 작지 않음을 알 수 있다. 자연하천에서의 정확한 하상변동을 예측하기 위해서는 원심력에 의한 이차류와 박리의 현상을 정확히 모의할 수 있어야하며, 이를 위해 3차원 모형이 필요하다. 따라서 본 연구에서는 3차원 unsteady RANS 모형을 이용하여 곡선수로에서 박리가 발생하는 현상을 모의하고자 한다. 곡선수로를 모의하기 위해서 곡선좌표계를 사용하였으며, 난류모형으로는 standard $k-{\varepsilon}$과 $k-{\omega}$ SST을 사용하였다. 또한 fractional step method를 이용하여 유속과 압력 커플링을 하였다. 그 결과 곡선수로의 흐름모의에서 레이놀즈 수가 큰 경우 박리가 발생하는 것을 확인하였으며, 두 난류모형 모두 곡선 흐름에서의 박리 현상을 모의할 수 있었다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.11
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• pp.3014-3021
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• 1995

This study is carried out in order to evaluate the performances of the Reynolds stress turbulence models such as SSG and GL models in the calculation of separated flow over backward-facing stepp.In addition, two slow return-to-isotropy models, YA and Rotta models combined with rapid part of SSG model are also tested. The finite volume method is used to discretize the governing differential equations, and the power-law scheme is used to approximate the convection terms. The SIMPLE algorithm is used for pressure correction in the governing equations. The results show that SSG model gives the better prediction near the reattachment point than GL model. In cases that the rapid term of SSG model is combined with Rotta and YA slow models, the results show the better predictions of stress components in recirculation zone, but indicate inaccuracy in the predictions of mean velocity.

• Journal of Chest Surgery
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• v.37 no.1
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• pp.43-49
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• 2004

Background: Acute thoracic aortic dissections involving the aortic arch differ in diagnosis, surgical procedures, and operative results compared to those that do not involve the aortic arch. In general cerebral perfusion under deep hypothermic circulatory arrest (HCA) is performed during the repair of the aortic arch dissection. Here, we report our surgical results of the aortic arch dissection repair using retrograde cerebral perfusion (RCP) and its safety. Material and Method: Between January 1996 and June 2002, 22 consecutive patients with aortic arch dissection underwent aortic arch repair. In 20 of them RCP was performed under HCA. RCP was done through superior vena cava in 19 patients and by systemic retrograde venous perfusion in 1, in whom it was difficult to reach the SVC. When the patient's rectal temperature reached 16 to 18$^{\circ}C$, systemic circulation was arrested, and the amount of RCP amount was 481.1 $\pm$292.9 $m\ell$/min with perfusion pressure of 20∼30 mmHg. Result: There were two in-hospital deaths (4.5%) and one late death (9.1%). Mean circulatory arrest time (RCP time) was 54.0$\pm$ 13.4 minutes (range, 7 to 145 minutes). RCP time has no correlation with the appearance of consciousness, recovery of orientation, or ventilator weaning time (p=0.35, 0.86, and 0.92, respectively). Ventilator weaning was faster in patients with earlier recovery of consciousness and orientation (r=0.850, r=926; p=0.000, respectively). RCP of more than 70 minutes did not affect the appearance of consciousness, recovery of orientation, ventilator weaning time, exercise time, or hospital stay (p=0.42, 0.57, 0.60, 0.83, and 0.51, respectively). Conclusion: Retrograde cerebral perfusion time under hypothermic circulatory arrest during repair of aortic arch dissection may not affect recovery of orientation, ventilator weaning time, neurologic complications, and postoperative recovery.

• Journal of Chest Surgery
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• v.34 no.8
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• pp.604-610
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• 2001

Stanford type A aortic dissection after graft replacement of ascending aorta and/or aortic arch required careful follow-up due to progression of the enlarged false lumen or the recurrence of dissection. From June 1984 to June 200, 124 patients underwent operations for type A aortic dissection. Among them, 6 patients underwent reoperation due to recurred aneurysm or dissection. We evaluated that the causes of reoperation, including Marfan syndrome, the approach and result of reoperation, and strategy to reduce the risk of reoperation. Material and method: The first operation was done on acute stage in 4 cases, and chronic stage in 2 cases. There were Marfan syndromes in 3 cases. The entry site was the ascending aorta for all cases except one who underwent Bentall operation(n=3) or ascending aorta graft replacement(n=2). In one case, Bentall operation and total arch replacement was performed due to chronic type A dissection with multiple fenestrations. Mean interval of reoperation was 67.6months(range 5 months to 14 year 4months) after the first operation. Reoperations were performed with recurrence of dissection(n=4), threatening aneurysmal evolution of persisting dissection(n=1), and false aneurysm with infection(n=1). The redo operation involved the hemiarch in 1 case, distal ascending to total arch and descending thoracic aorta in 4 cases, and only descending thoracic aorta in 1 case. Result: There were Marfan syndromes in 18 patients. The mean age in type A dissection was 56.7 years and that in the first operation of reoperationc ases was 32.2 years. Especially in 3 patients with Marfan syndrome, the mean age was 29 years.

• Transactions of the Korean Society of Mechanical Engineers
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• v.8 no.5
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• pp.498-504
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• 1984

가열된 곡면에 의한 자연대류에서는 유동의 박리현상이 존재하지 않음이 알려져 있다. 이에 반해 날카로운 모서리를 갖는 가열된 정방형 수평실린더에 의한 자연대류에서는 그라소프 수가 4.66*$10^{4}$ 전후로 부착 혹은 박리현상이 윗쪽 양 모서리 부근에서 일어남을 광학간섭 계(Mach Zehnder Inter-ferometer)를 이용하여 온도장을 가시화하고 이를 이용하여 좌우 대칭 선상에서의 속도분포를 간단한 대수적인 방법으로 구하여 수평정방형 윗쪽 수평면 위에 유동의 박리현상을 시사하는 "쌍동이 소용돌이"의 존재를 입증하였고, 이에 의해 온도역전현상과 평균 열전달량의 급격한 증가를 설명 할 수 있다.설명 할 수 있다.

• Journal of the Korean Society of Propulsion Engineers
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• v.8 no.1
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• pp.61-69
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• 2004

This paper describes numerical efforts to characterize the flame-holding and air-fuel mixing process of model SCRamjet engine combustor, where a hydrogen jet injected into a supersonic cross flow and in a cavity Combustion phenomena in a model SCRamjet engine, which has been experimentally studied at University of Queensland and Australian National University using a free-piston shock tunnel, was observed around separation region of upstream of the normal injector and inside of cavity. The results show that the separation region and cavity generates several recirculation zones, which increase the fuel-air mixing. Self ignition occurs in the separation-freestream and cavity-freestream interface.

• Journal of Chest Surgery
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• v.35 no.10
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• pp.740-744
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• 2002

Retrograde cerebral perfusion under hypothermic circulatory arrest is a simple and useful adjunct to avoid cerebral ischemic injury in the treatment of aortic arch pathology. In the surgery of distal aortic arch and proximal descending aortic lesions through the left thoracotomy incision, right atrium-retrograde cerebral perfusion (RA-RCP) through a venous cannula positioned into the right atrium is simpler than retrograde cerebral perfusion through superior vena cava. The time limits for RA-RCP during aortic arch reconstruction have yet to be clarified. We, herein, present a case with uneventful recovery after RA-RCP of 94 minutes during reconstruction of aortic arch and descending aorta. These data suggest that RA-RCP, as an adjunct to hypothermic circulatory arrest, may prolong the circulatory arrest time and thus prevent ischemic injury of the brain, even when RA-RCP exceeds 90 minutes.

• Proceedings of the KTCVS Conference
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• 1995.10a
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• pp.139-139
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• 1995

• Journal of the Korean Society of Radiology
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• v.82 no.5
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• pp.1281-1286
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• 2021

Brainstem infarction due to vertebrobasilar insufficiency is a rare initial presentation of systemic lupus erythematosus (SLE) patients and small-vessel dissection as the direct cause of infarction has not been reported. We report the case of a 20-year-old female with acute infarction on the right side of the pons due to a small artery (pontine perforator) dissection, identified on digital subtraction angiography and high-resolution vessel wall MRI (vwMRI). She was diagnosed with SLE based on the presence of neurologic disorders and relevant laboratory findings. The pontine perforator-dissecting aneurysm had occluded and the right distal vertebral artery had resolved on subsequent vwMRI. She had a modified Rankin Scale (mRS) score of 1 at discharge with mild symptom improvement, and exhibited no further aggravation of symptoms at 3 or 12 months, maintaining an mRS score of 1.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.7
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• pp.239-244
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• 2018

Both arterial dissection and atherosclerosis are major causes of cerebral infarction and appear to be occlusion or stenosis in magnetic resonance angiography(MRA) and computed tomographic angiography(CTA). But there are differences in treatment because they have different mechanisms. Recently, as high resolution magnetic resonance image(HR-MRI) develops, the image of blood vessel wall can be confirmed non-invasively. Though HR-MRI has become a very useful method for patients with suspected arterial dissection, differential diagnosis of the two diseases has not yet been fully established due to differences in the findings according to stages of arterial dissection and atherosclerosis. We investigated the differences between vertebral artery dissection and atherosclerosis through HR-MRI in two patients and confirmed the diagnosis by CTA follow-up. In addition to the previously established diagnostic criteria, we determined that the long and severe stenosis and recanalization suggest arterial dissection. Characteristics of arterial dissection confirmed by HR-MR and additional studies will be helpful for the treatment.