• 한국소음진동공학회논문집
• /
• 제23권1호
• /
• pp.65-72
• /
• 2013

This case study presents a practical method to reduce resonant vibration of large vertical pumps. The pumps are driven at 400 rpm rated speed by induction motor. The vibration was not significantly large when operated at this rated speed. Large vibration was occurred when the pump was operated below the rated speed for flow control. Due to the large vibration resonance, variable speed operation of the pump was not possible for several months at worst cases. To find an efficient vibration control method, the flexural responses of pumps for both normal and transient operations were measured. The measured modal characteristics were compared with those of finite element analysis. When the pump was operated at a specific rpm, the natural mode whose resonance frequency is twice the rotating angular speed induced the large vibration. The retrofit utilizing stiffeners to reduce this resonant vibration were performed. Effects of designed stiffeners on reducing vibration were validated through tests after actual installation.

• 대한기계학회논문집B
• /
• 제34권5호
• /
• pp.499-504
• /
• 2010

디젤 매연여과장치내 포집된 입자상물질의 재생 시기를 제어하기 위해서는 매연 포집량을 정확히 예측하는 것이 중요하다. 필터내 축적된 매연 포집량은 필터 전 후의 압력차와 배기유량에 의해 예측될 수 있다. 따라서 본 연구에서는 먼저, 디젤산화촉매와 디젤매연여과장치 전 후의 각각 압력차의 비로써 정의한 매연지수의 산출을 위해 효과적인 신호처리방법을 제시하였다. 이를 3L급 승용 디젤엔진에서 정상운전조건과 과도운전조건에서 비교한 결과, 매연지수와 매연 포집량에 있어서 일정 상관관계가 있음을 알 수 있었다.

• 대한기계학회논문집B
• /
• 제37권1호
• /
• pp.35-41
• /
• 2013

금형온도는 사출성형시 수지의 유동특성이나 성형품의 변형에 영향을 미치는 중요한 변수로서, 고온의 수지 주입과 냉각회로에 주입되는 냉각수의 영향을 받아 사출 사이클이 반복될수록 온도의 상승과 하강이 반복되는 주기적인 변화특성을 가지고 있다. 본 연구에서는 금형 냉각회로에 저온과 고온의 유체를 번갈아 주입하는 가변 금형온도 제어기법을 적용하여 성형전에는 금형온도를 높게 유지하고 성형후에는 낮게 유지함으로써 사출성형시 품질과 생산성을 동시에 높일 수 있는 연구를 수행하였다. 특히 열전달-유동해석을 연계한 다중사이클 사출성형 과도해석을 수행하여 수지와 금형, 냉각수간의 과도적인 온도변화를 수치적으로 고찰하였고, 기존 냉각방법과의 해석결과를 비교하여 제안된 가변 금형온도 제어기법의 가열 및 냉각과정에서의 효율성을 비교하였다.

• Nuclear Engineering and Technology
• /
• 제46권5호
• /
• pp.633-640
• /
• 2014

In this research, the surface roughness affecting the pressure drop in a pipe used as the steam generator of a PWR was studied. Based on the CFD (Computational Fluid Dynamics) technique using a commercial code named ANSYS-FLUENT, a straight pipe was modeled to obtain the Darcy frictional coefficient, changed with a range of various surface roughness ratios as well as Reynolds numbers. The result is validated by the comparison with a Moody chart to set the appropriate size of grids at the wall for the correct consideration of surface roughness. The pressure drop in a full-scale U-shaped pipe is measured with the same code, correlated with the surface roughness ratio. In the next stage, we studied a reduced scale model of a U-shaped heat pipe with experiment and analysis of the investigation into fluid-structure interaction (FSI). The material of the pipe was cut from the real heat pipe of a material named Inconel 690 alloy, now used in steam generators. The accelerations at the fixed stations on the outer surface of the pipe model are measured in the series of time history, and Fourier transformed to the frequency domain. The natural frequency of three leading modes were traced from the FFT data, and compared with the result of a numerical analysis for unsteady, incompressible flow. The corresponding mode shapes and maximum displacement are obtained numerically from the FSI simulation with the coupling of the commercial codes, ANSYS-FLUENT and TRANSIENT_STRUCTURAL. The primary frequencies for the model system consist of three parts: structural vibration, BPF(blade pass frequency) of pump, and fluid-structure interaction.

• 동력기계공학회지
• /
• 제12권1호
• /
• pp.13-19
• /
• 2008

In this study, a variable induction and exhaust system is applied to turbocharged diesel engine to improve the volumetric efficiency, especially, in a low and transient engine speed range where much of the pollutant matters are expelled out. The volumetric efficiency is known as one of the most important factor which affects significantly engine performance, fuel economy and further emission and noise level. As the torque increase with the engine speed up, the gas flow in an exhaust pipe become pulsating and then has an effect on boost up capacity of air charging into the cylinder and expelling capacity to atmosphere simultaneously. But at a low and idling speed, the pulsation effect was not so significant. Accordingly, resonator was employed to compensate their loss. The variable induction system consists of the secondary pipe, resonator, intercooler, and torque variance were examined with extended operating conditions. In the mean time, for interpretation and well understanding for the phenomena of wave action that arising during intake and exhaust process between turbocharger and variable intake system, the concept of the combined supercharging was introduced. Some of results are depicted which deal with a pressure history during valve events of induction process. Consequently, by the governing of these phase and amplitude of pulsating wave, it enables us to estimate and evaluate for the intake system performance and also, designing stage of the system layout.

• Nuclear Engineering and Technology
• /
• 제27권3호
• /
• pp.317-326
• /
• 1995

증기발생기의 수위제어시스템에 대해 특히 저출력시 수위제어의 문제점을 분석고찰하고 퍼지제어기 법을 기반으로 한 안정되고도 신속한 수위제어에 관한 연구가 주로 수행되었다. 문제해결의 한 방안으로서, 중요 제어변수임에도 불구하고 저출력운전시 저유량구간의 추정불량으로 인해 사용할 수 없는 유량신호를 대신하여 밸브개도를 이용한 대체정보를 채용하였으며 또한 소속함수크기의 유동적인 조정방법을 이용하여 수위오차가 크게 발생한 과도상태시에는 신속한 수위회복이 이루어지도록 하였다. 실제운전환경에서 제시된 제어기를 튜닝 하기 위한 방법으로서 제어성능지수 및 decent method를 이용한 소속함수의 self-tuning 기법을 제시하였다. 원자력 연구소의 연수원에 설치된 교육훈련용 시뮬레이터에서 수행된 실험결과는 제시된 제어기 및 튜닝방법의 안정되고 우수한 성능구현 및 실질적 인 유용성을 보여주고 있다.

• 멤브레인
• /
• 제27권1호
• /
• pp.77-83
• /
• 2017

무기실리카 입자로 구성된 고탁도 원수를 처리하는 침지식 정밀여과 운전에서 휴민산과 2가 양이온의 존재유무에 따라 시간에 따른 파울링 저항을 관찰하였다. 공기폭기로 인한 무기실리카 입자의 파울링 감소효과는 휴민산과 칼슘이 혼합으로 존재 시 감소하였다. 파울링층의 전자현미경 관찰결과 칼슘의 존재 시 휴민산의 무기실리카 입자 표면흡착이 관찰되었다. 이는 멤브레인 표면에 조밀한 파울링층을 형성시켜 공기폭기 효과를 감소시킨 것으로 판단된다. 용액의 조성에 따른 고탁도 원수의 탁도 제거율에는 큰 변화가 없었으나 공기폭기량에 따라 칼슘과 무기실리카 입자의 혼합 존재 시 유기물질의 제거율은 80% 이상으로 증가하였다. 이는 공기폭기 하에 무기실리카 입자 표면에 흡착된 일부 휴민산들이 멤브레인 표면으로부터 함께 역수송 되어 유기물질 제거율을 증가시킨 것으로 사료된다.

• 대한한의학회지
• /
• 제19권2호
• /
• pp.59-74
• /
• 1998

Clinical observation was done on 272 cases of patients who were diagnosed as CVA with brain CT, TCD, MRI scan and clinical observation. They were hospitalized in the oriental medical hospital of Kyung-Won University from 1st January to 31st December in 1997. 1. The cases were classified into the following kinds: cerebral infarction, cerebral hemorrhage. and transient ischemic attack. The most case of them was the cerebral infarction. 2. There is no significant difference in the frequency of strokes in male and female. And the frequency of strokes was highest in the aged over 50. 3. In cerebral infarction the most frequent lesion was the territory of middle cerebral artery, and in cerebral hemorrhage the most frequent lesion was the basal ganglia. 4. The most ordinary preceding disease was hypertension. and the next was diabetes. 5. The rate of recurrence was high in cerebral infarction. 6. The cerebral infarction occurred usually in resting and sleeping, and the cerebral hemorrhage in acting. 7. The common symptoms were motor disability and verbal disturbance. 8 The average time to start physical therapy was 1l.3rd day after stroke in cerebral infarction and it was 15.2th day after stroke in cerebral hemorrhage. 9. The common complications were urinary tract infection, pneumonia, myocardial infarction. 10. Hypercholesterolemia and hypertriglyceridemia are usually found more frequently in cerebral infarction than in hemorrhage. 11. In acute or subacute stage, the methods of smoothening the flow of ki(順氣), dispelling phlegm(祛痰), clearing away heat(淸熱) or purgation(瀉下) were frequently used. and in recovering stage, the methods of replenishing ki(補氣), tonifying the blood(補血) or tranquilization(安神) were frequently used.

• 수면정신생리
• /
• 제6권1호
• /
• pp.19-25
• /
• 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
• /
• 제11권5호
• /
• pp.60-71
• /
• 2007

액체로켓 엔진의 시동은 연소기와 가스발생기의 안정적인 점화는 물론 시동에 소요되는 시간을 단축하여 추력 발생과 상관없는 추진제 소모량을 줄이는 방향으로 전개되어야 한다. 특히 엔진시스템의 시동 순서나 규격을 모두 시험적으로 개발하는 데는 한계가 있으며, 안전상의 이유로 시험 조건이나 시동 cyclogram에 대한 해석적인 분석이 선행될 필요가 있다. 이에 본 연구에서는 가스발생기 사이클 액체로켓 엔진의 수학적 모델을 상용 1차원 유체시스템 해석 프로그램인 Flowmaster를 기반으로 개발하였으며, 이를 이용하여 안정된 엔진 시동을 위한 파이로시동기 규격이나 연소기 및 가스발생기 종단밸브의 열림시간 등을 구하는 방법론을 제시하였다. 아울러 해석 결과로 구한 시동특성을 해외 엔진의 시동 해석 결과와 정성적인 비교를 수행하여 비교적 잘 일치함을 파악하였다.