• 대한기계학회논문집A
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• 제20권9호
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• pp.2894-2900
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• 1996

The stream generator tubes represent an integral part of a major barrier against the fission product release to the environment. So, the rupture of these tubes could permit flow of reactor coolant into the secondary system and injure the safety of reactor coolant system. Therefore, if the crack was detected during In-Service Inspection of tubes the cracked tube should be evaluated by the pulgging criteria and plugged or not. In this study, the fracture mechanics evaluation is carried out on the thru-wall axial crack due to Primary Water Stress Corrosion Cracking in the roll transition aone of steam generator tube to help the assurence the integrity of tubes and estabilish the plugging criteria. Due to the Inconel which is used as tube material is more ductile than others, the plastic instability repture theory was used to calculate the critical and allowable crack length. Based on Leak Before Break concept the leak rate for the critical crack length and the allowable leak rate are compared and the safety of tubes was given.

• International Journal of Fluid Machinery and Systems
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• 제2권4호
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• pp.286-294
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• 2009

Hydroelectric power plants are known for their ability to cover variations of the consumption in electrical power networks. In order to follow this changing demand, hydraulic machines are subject to off-design operation. In that case, the swirling flow leaving the runner of a Francis turbine may act under given conditions as an excitation source for the whole hydraulic system. In high load operating conditions, vortex rope behaves as an internal energy source which leads to the self excitation of the system. The aim of this paper is to identify the influence of the full load excitation source location with respect to the eigenmodes shapes on the system stability. For this, a new eigenanalysis tool, based on eigenvalues and eigenvectors computation of the nonlinear set of differential equations in SIMSEN, has been developed. First the modal analysis method and linearization of the set of the nonlinear differential equations are fully described. Then, nonlinear hydro-acoustic models of hydraulic components based on electrical equivalent schemes are presented and linearized. Finally, a hydro-acoustic SIMSEN model of a simple hydraulic power plant, is used to apply the modal analysis and to show the influence of the turbine location on system stability. Through this case study, it brings out that modeling of the pipe viscoelastic damping is decisive to find out stability limits and unstable eigenfrequencies.

• Tribology and Lubricants
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• 제36권5호
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• pp.253-261
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• 2020

In this paper, we present an experimental investigation of the frequency characteristics and a visual inspection of an oxidizer pump with a modified rear-floating ring seal for a 7-tonf turbopump. An oxidizer pump typically operates at high rotational speeds and under cryogenic conditions. Despite its low hydraulic efficiency, the floating ring seal is frequently employed as a leakage control solution for turbomachinery because it effectively reduces abrasion by friction. When the oxidizer pump starts up, the floating ring moves excursively but locks up stably against the pump casing when the contact pressure increases. The compressive force on the floating ring depends on the hydrodynamic forces induced by the flow through the floating ring. This force is controlled by the nose position of the floating ring. Based on a validation test for a 7-tonf turbopump with two types of floating rings, we concluded that the floating ring with a small diameter nose can move easily with a low contact pressure in the cooling path. This leads to instability of the pressure fluctuation around the floating ring. In contrast, a floating ring with a large diameter nose has a high contact pressure and attaches strongly to the casing, which causes wear and frictional oxidation between the contact surfaces of the impeller and the floating ring.

• 동의생리병리학회지
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• 제19권4호
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• pp.903-907
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• 2005

Many naturally occurring plant extracts are studied for their beneficial effects for health and particularly on cancer. Apoptosis, or programmed cell death, occurs in both normal and pathological conditions, including cancer Dysregulation of apoptosis allows transformed cells to continually and uninhibitedly enter the cell cycle, thus perpetuating the sequence of mutation, genomic instability and, finally, oncogenesis. To investigate the apoptosis-inducing effect of the extract of Fructus Trichosanthis (EFT) on leukemic HL-60 cells and its mechanism, HL-60 cells in vitro in culture medium were given different doses of the extract. The inhibitory rate of cells were measured by microculture tetrazolium assay, cell apoptotic rate was detected by flow cytometry, morphology of cell apoptosis was observed by DAPI fluorescence staining, and the activations of caspases and PARP were detected using Western blotting analysis. The extract could activate the caspase-3 and caspase-8, induce PARP cleavage, inhibit growth of HL-60 cells, and cause apoptosis significantly The suppression was in dose-dependent manner. Marked morphological changes of cell apoptosis including condensation of chromatin and nuclear fragmentation were observed clearly by DAPI fluorescence staining especially. These results will provide strong laboratory evidence of EFT for clinical treatment of acute leukemia.

• 한국항공우주학회지
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• 제30권1호
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• pp.1-8
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• 2002

자유류 속도가 40 m/sec 이고 날개의 뿌리시위에 기준한 레이놀즈수가 1.76${\times}$10$^6$인 상태에서 옆미끄럼이 삼각 날개 와류에 미치는 영향을 실험적으로 연구하였다. 받음각 범위는 16$^{\circ}$에서부터 28$^{\circ}$까지 이었으며 옆미끄럼각은 0$^{\circ}$, -10$^{\circ}$, 그리고 -20$^{\circ}$이었다. 옆미끄럼각은 바람쪽과 바람 반대쪽 와류 모두의 강도를 감소시키고, 바람쪽 와류의 붕괴를 촉진시킴이 관찰되었다. 옆미끄럼각 -10$^{\circ}$에서 바람 반대쪽의 와류는 받음각이 증가함에 따라 그 강도가 증가하였다. 이와 같은 옆미끄럼 조건에서 날개 와류의 비대칭적인 발달과 붕괴는 삼각 날개의 롤링모멘트를 어느 특정한 높은 받음각에서 급격히 바뀌게 할 수 있으며, 이는 일종의 롤링 모멘트 불안정성으로 간주할 수 있다.

• Korean Journal of Acupuncture
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• 제23권2호
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• pp.47-57
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• 2006

Objectives: The aim of the present study was to widen a clinical use by investigating literatures about the acupoint of Pu-ryu(KI7) and Um-gok(KI10) concerning Kidney-Eum(vital essence of the kidney) and Kidney-Yang(vital function of the kidney). Methods: We investigated the first literature about $Pu-ryu(KI7)\;{\cdot}\;Um-gok(KI10)$ and a second name, a location and a characteristic of them. We made a comparative study about the chief virtue and combination of $Pu-ryu(KI7)\;{\cdot}\;Um-gok(KI10)$. Results: Pu-ryu(KI7) is the 7th acupoint of Kidney Meridian of Foot Soeum(少陰), which reinforces a meridian of belonging and has the efficacy of warming the Kidney Yang, clearing heat, excreting dump and regulating water passage. Um-gok(KI10) is the 10th acupoint of Kidney Meridian of Foot Soeum(少陰), which has the virtue of nurishing the Liver and Kidney Eum, promoting lower heater and marinating the free flow of Gi Conclusions: The chief virtue of Pu-ryu(KI7) is to remove edema due to disturbance in Gi activity by dificiency of Kidney-Yang because of warming Yang to induce diuresis. To Um-gok(KI10), it is to treat instability of Kidney-Gi by Eum dificiency of the Liver and Kidney because of nurishing the Liver and Kidney Eum.

• 수면정신생리
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• 제6권1호
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• pp.19-25
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• 1999

Sleep alters both breathing pattern and the ventilatory responses to external stimuli. These changes during sleep permit the development or aggravation of sleep-related hypoxemia in patients with respiratory disease and contribute to the pathogenesis of apneas in patients with the sleep apnea syndrome. Fundamental effects of sleep on the ventilatory control system are 1) removal of wakefulness input to the upper airway leading to the increase in upper airway resistance, 2) loss of wakefulness drive to the respiratory pump, 3) compromise of protective respiratory reflexes, and 4) additional sleep-induced compromise of ventilatory control initiated by reduced functional residual capacity on supine position assumed in sleep, decreased $CO_2$ production during sleep, and increased cerebral blood flow in especially rapid eye movement(REM) sleep. These effects resulted in periodic breathing during unsteady non-rapid eye movement(NREM) sleep even in normal subjects, regular but low ventilation during steady NREM sleep, and irregular breathing during REM sleep. Sleep-induced breathing instabilities are divided due primarily to transient increase in upper airway resistance and those that involve overshoots and undershoots in neural feedback mechanisms regulating the timing and/or amplitude of respiratory output. Following ventilatory overshoots, breathing stability will be maintained if excitatory short-term potentiation is the prevailing influence. On the other hand, apnea and hypopnea will occur if inhibitory mechanisms dominate following the ventilatory overshoot. These inhibitory mechanisms include 1) hypocapnia, 2) inhibitory effect from lung stretch, 3) baroreceptor stimulation, 4) upper airway mechanoreceptor reflexes, 5) central depression by hypoxia, and 6) central system inertia. While the respiratory control system functions well during wakefulness, the control of breathing is commonly disrupted during sleep. These changes in respiratory control resulting in breathing instability during sleep are related with the pathophysiologic mechanisms of obstructive and/or central apnea, and have the therapeutic implications for nocturnal hypoventilation in patients with chronic obstructive pulmonary disease or alveolar hypoventilation syndrome.

• 한국추진공학회지
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• 제14권2호
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• pp.46-53
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• 2010

본 연구에서는 하이브리드 추진 연소에서 산화제의 상(Phase)에 따른 연소특성 변화를 연구하였다. 산화제는 $GN_2O$와 $LN_2O$를 사용하고 고체연료는 HDPE(High Density PolyEthlene)를 적용하여 연소실험을 수행하였고, 상에 따른 고체연료의 후퇴율과 압력선도, 연소효율의 변화 등을 조사하였다. $LN_2O$를 적용할 경우 액체 산화제의 기화에 필요한 잠열이 화염에서 발생되는 연소에너지에 비해 무시할 정도로 작아 $GN_2O$를 산화제로 사용했을 때의 고체연료 후퇴율과는 큰 차이가 없었지만, 추진 성능효율이 낮아짐을 확인하였고, 액체 산화제의 유량이 증가할수록 산화제의 기화에 필요한 열전달 증가로 인 해 연소 불안정성이 커짐을 확인하였다.

• 한국수자원학회논문집
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• 제32권4호
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• pp.417-426
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• 1999

횡유입이 없는 경우(sign곡선의 홍수파 유입)와 횡유입이 있는 경우(강우 유입)를 대상으로 선형과 비선형 Muskingum-Cunge법에 의한 단위폭 사면에서의 유출수문곡선의 특성을 비교·고찰하였다. 유출곡선은 선형법에서는 확산효과에 의해서 거의 대칭적으로 확산되나, 비선형법에서는 비선형효과와 확산효과의 상호작용을 의하여 상승부는 급하게 되고, 하강부는 완만하게 된다. 선형법은 유입된 질량을 정확히 보존하나, 비선형법은 질량의 증가나 손실을 초래한다. 비선형법에서 기저유량이 작고 유량변화의 비가 큰 경우, 완경사에서는 파형의 감쇠와 질량의 감소를 가져오나, 급경사에서는 kinematic shock의 생성과 함께 질량의 증가를 가져온다. 같은 특성을 갖는 사면의 경우, 유출곡선의 전파속도와 파형의 변화는 선형법에서는 단위폭당 기준유량에 좌우되나, 비선형법에서는 기저유량 및 유량 변화의 비(= 첨두유량/기저유량)에 좌우된다. 횡유입(강우)이 있는 비선형법의 경우 횡유입이 없는 경우와 마찬가지로, 사면경사가 완만하고 유량변화의 비가 클수록 첨두유량은 작아지고 파형은 확산되나, 질량의 손실은 거의 없다.

• 한국수자원학회논문집
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• 제48권9호
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• pp.743-756
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• 2015

효과적인 하천관리를 위해서는 준설과 각종 수리구조물의 영향에 의한 하상변화 양상을 파악하고 평가하는 것이 필수적이다. 특히 대규모 준설과 대형수리구조물의 건설은 본류뿐만 아니라 지류의 하상안정에도 영향을 미칠 수 있다. 본 연구에서는 금호강이 유입하는 낙동강 강정고령보~달성보 구간에 대해 하도준설과 보 건설 및 운영에 따른 본류와 지류에서의 장기하상변동 영향을 살펴보고자 하였다. HEC-6모형을 이용하여 유사이송 및 장기하상변동 양상을 모의하였으며, 그 결과 준설 및 보 운영으로 인해 본류뿐만 아니라 지류에서도 하상변화량이 증가하고 가속화되었다.