• Nuclear Engineering and Technology
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• 제52권1호
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• pp.37-50
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• 2020

A passive containment cooling system (PCCS) has been developed as advanced safety feature for innovative power reactor (iPOWER). Passive systems are inherently less stable than active systems and the PCCS encountered the flashing-induced instability previously identified. The objective of this study is to develop stability maps for flashing-induced instability using MARS (Multi-dimensional Analysis of Reactor Safety) code. Firstly, we conducted a series of sensitivity analysis to see the effects of time step size, nodalization, and alternative MARS user options on the onset of flashing-induced instability. The riser nodalization strongly affects the prediction of flashing in a long riser of the PCCS, while time step size and alternative user options do not. Based on the sensitivity analysis, a standard input and an analysis methodology were set up to develop the stability maps of PCCS. We found out that the calculated equilibrium quality at the exit of the riser as a stability boundary above 5 kW/㎡ was approximately 1.2%, which was in good agreement with Furuya's results. However, in case of a very low heat flux condition, the onset of instability occurred at the lower equilibrium quality. In addition, it was confirmed that inlet throttling reduces the unstable region.

• 한국운동역학회지
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• 제30권1호
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• pp.7-16
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• 2020

Objective: It is to find factors related to stability through analysis of plantar pressure factors according to the level of instability when performing Snatch. Method: Foot pressure analysis was performed while 10 weightlifters performed 80% of the highest level of Snatch, and motion was classified and analyzed in 3 grades according to the level of instability. Results: First, in Bad Motion, the movement distance of the pressure center in the direction of ML and AP was larger significantly in Phase 2. Second, in Phase 2, the number of zero-crossing in the AP direction was larger statistically significantly in Good Motion. Third, in the bad motion in Phase 3, the number of zero-crossing in the ML direction showed a significantly larger value. Fourth, in Phase 4, it was found that the more stable the lock out motion, the greater the activity of foot controlling in the left and right directions. Fifth, Phase 3, the greater the Maximum/Mean foot pressure value, the more stable the pulling action. Sixth, in Phase 2, the foot pressure was concentrated with a wide distribution in the midfoot and rearfoot. Seventh, the triggering number of the forefoot region was small in the last pull phase. Eighth, the number of triggers in the toe area was significantly higher during Good Motion in Phase 4. Conclusion: Summarizing the factors of instability in Snatch, there was no significant difference in Phase 1 for each condition. In order to enhance the stability in Phase 2, the sensory control ability in the AP direction is required, and focusing the foot pressing motion with a wide distribution in the middle and rear parts increases the instability. In Phase 3, it was found that the more unstable, the more sensory control activity was performed in the ML direction, the stronger the forefoot pressing action should be performed for a stable Snatch. In Phase 4, It is important that the feet sensory control activity in ML directions and the control ability of the toes in order to have stable Lock out motion.

• 한국전산구조공학회논문집
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• 제18권4호통권70호
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• pp.347-360
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• 2005

경수로 원자로 하부구조물에서 발생되는 유포의 불균일성에 기인하는 교차류와 핵연료집합체의 수력저항의 차이에 의해 발생하는 교차류, 그리고 축류 등에 의해 유발되는 연료봉의 불안정성은 핵연료손상의 원인이 될 수 있으므로, 새로운 연료 개발 시 연료봉에 대한 진동 및 안정성 해석을 수행하여 연료봉 진동과 불안정성 발생 여부를 확인하고 있다. 본 연구에서는 새로 개발된 고리 2호기용 $16{\times}16$형 개량핵연료 집합체에 대한 연료봉의 진동 및 안정성 해석을 수행하여 지지격자 높이와 위치, 그리고 지지조건 등이 연료봉의 진동특성 및 안정성에 미치는 영향을 평가하였다 그리고 해석결과에 근거하여 개량연료 집합체에서 중간지지격자 높이와 각 지지격자의 위치를 제안하였다.

• Clinics in Shoulder and Elbow
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• 제19권2호
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• pp.78-83
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• 2016

Background: We investigated the risk factors for the recurrence of anterior shoulder instability after arthroscopic surgery with suture anchors and the clinical outcomes after reoperation. Methods: A total of 281 patients (February 2001 to December 2012) were enrolled into our study, and postoperative subluxation and dislocation were considered as recurrence of the condition. We analyzed radiologic results and functional outcome including the American Shoulder and Elbow Surgeons Evaluation Form, the Korean Shoulder Society Score, and the Rowe scores. Results: Of the 281 patients, instability recurred in 51 patients (18.1%). Sixteen out of 51 patients (31.4%) received a reoperation. In terms of the functional outcome, we found that the intact group, comprising patients without recurrence, had a significantly better functional outcome than those in the recurrent group. The size of glenoid defect at the time of initial surgery significantly differed between intact and recurrent group (p<0.05). We found that the number of dislocations, the time from the initial presentation of symptoms to surgery, and the number of anchor points significantly differed between initial operation and revision group (p<0.05). The functional outcome after revision surgery was comparable to intact group after initial operation. Conclusions: Eighteen percent of recurrence occurred after arthroscopic instability surgery, and 5.6% received reoperation surgery. Risk factors for recurrence was the initial size of glenoid defect. In cases of revision surgery, good clinical outcomes could be achieved using additional suture anchor.

• Structural Engineering and Mechanics
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• 제12권5호
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• pp.507-526
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• 2001

In standard finite element algorithms, the local stability conditions are not accounted for in the formulation of the tangent stiffness matrix. As a result, the loss of the local stability is not adequately related to the onset of the global instability. The phenomenon typically arises with material-type localizations, such as shear bands and plastic hinges. This paper addresses the problem in the context of the planar, finite-strain, rate-independent, materially non-linear beam theory, although the proposed technology is in principle not limited to beam structures. A weak formulation of Reissner's finite-strain beam theory is first presented, where the pseudocurvature of the deformed axis is the only unknown function. We further derive the local stability conditions for the large deformation case, and suggest various possible combinations of the interpolation and numerical integration schemes that trigger the simultaneous loss of the local and global instabilities of a statically determined beam. For practical applications, we advice on a procedure that uses a special numerical integration rule, where interpolation nodes and integration points are equal in number, but not in locations, except for the point of the local instability, where the interpolation node and the integration point coalesce. Provided that the point of instability is an end-point of the beam-a condition often met in engineering practice-the procedure simplifies substantially; one of such algorithms uses the combination of the Lagrangian interpolation and Lobatto's integration. The present paper uses the Galerkin finite element discretization, but a conceptually similar technology could be extended to other discretization methods.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1991년도 한국자동제어학술회의논문집(국제학술편); KOEX, Seoul; 22-24 Oct. 1991
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• pp.1664-1670
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• 1991

For kinematically redundant manipulators, conventional dynamic control methods of local torque optimization showed the instability which resulted in physically unachievable torque requirements. In order to guarantee stability of the null space vector method which resolves redundancy at the acceleration level, Maciejewski[1] analyzed the kinetic behavior of homogeneous solution component and proposed the condition to identify regions of stability and instability for this method. 'In this paper, a modified null space vector method is first presented based on the Maciejewski's condition which is a function of a manipulator's configuration. Secondly, a new control method which is based on the concept of aspects is proposed. It was shown by computer simulations that the modified null space vector method and the proposed method have a common property that a preferred aspect is preserved during the execution of a task. It was also illustrated that both methods demonstrate a drastic reduction of torque loadings at the joints in the tracking motion of a long trajectory when compared with the null space vector method, and thus guarantee the stability of joint torque.

• 대한기계학회논문집A
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• 제38권7호
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• pp.779-784
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• 2014

본 연구에서는 볼 조인트 구조에서 가장자리 하중을 받고 있을 때의 마찰 소음을 이론적으로 연구하였다. 구형 베어링 구조체와 반구 형태의 소켓간 마찰접촉 모델을 수학적으로 유도하여 동역학적 운동방정식을 전개하였다. 그 결과 볼 조인트부 굽힘 모드가 마찰에 의해 불안정할 수 있음을 보였고, 축력 및 접촉강성이 볼 조인트 동적 불안정성에 크게 영향을 주고 있음을 보였다. 반면 소켓의 틸팅 각도는 동적 불안정성에 크게 기여하지 않음을 보였다.

• 대한기계학회논문집
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• 제12권3호
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• pp.397-408
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• 1988

본 연구에서는 세가지 형상비의 연강판타원벌지 시험에 대하여 다이반경부분 의 형상과 수직이방성을 고려하여 해석고 이에 따른 실험과 비교검토하여 타원벌지시 험에서의 변형특성에 대해 논의하고자 한다. 또 불안정현상이 일어나는 압력을 예측 하여 실험에서 구한 파괴압력과 비교하여 타원벌지 시험에서의 파괴특성을 고찰하고자 한다.

• 대한기계학회논문집B
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• 제28권1호
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• pp.16-23
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• 2004

Acoustic characteristics of unbaffled and baffled combustion chamber are experimentally investigated under atmospheric condition to preliminarily determine baffle for mitigation of combustion instability. To investigate the effect of the baffle which has several configurations such as radial baffles and hub/blade baffle, resonant-frequency shift and damping factors of the chamber were analyzed and compared quantitatively with those of the unbaffled combustion chamber. From a view of acoustic characteristics, radial baffles with several configurations have not much difference in resonant-frequency shift and damping factor ratio with each other. On the other hand, hub and blade baffle is very effective to suppress the first tangential mode which was found to be the most harmful acoustic mode in KSR(Korean Sounding Rocket)-III engine. But more study on design parameters such as hub size and axial length should be done for complete optimization of hub and blade baffle. The present study based on linear acoustic analysis is expected to be a useful confirming tool to predict acoustic field and design a passive control devices such as baffle and acoustic cavity.

• Journal of Microbiology and Biotechnology
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• 제10권3호
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• pp.321-326
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• 2000

To examine the feasibility of the long-term production of the human granulocyte colony stimulating factor (hG-CSF) using the $_{L}-arabinose$ promoter system of Escherichia coli, flask relay culture and cyclic fed-batch culture were performed. In the flask relay culture, it was found that the pismid was maintained stably up to about 170 generations in an uninduced condition, whereby the cells could also maintain the capability of expressing hG-CSF expression were maintained stably up to at least 100 generations. In contrast, in the cyclid fed-batch culture, segregational plasmid instability was observed within about 4 generations after induction, even though the cell growth and hG-CSF production reached their maximum balues, 78.0 g/l of dry cell weight and 7.0 g/l of hG-CSF, respectively. It would appear that, when compared to the flask relay culture, the high-cell density and high-level expression of hG-CSF in the cyclic fed-batch cultrure led to the segregational plasmid instability; in other words, a severe metabolic burden existe on the cells due to the high-level expression of hG-CSF. Accordingly, based on these long-term cultures, the segregational and structural plasmid instability was observed and a strategy to overcome such problems could be designed.