• Nuclear Engineering and Technology
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• 제56권8호
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• pp.3450-3462
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• 2024

This paper presents a computational framework for drop time assessment of a control element assembly (CEA) under fuel assembly (FA) deformations. The proposed framework consists of three key components: 1) finite element modeling of CEA, 2) fluid-structure interaction to compute drag force, and 3) modeling of frictional contact between CEA and FA. Specially, to accommodate the large motion of CEA, beam elements based on absolute nodal coordinate formulation (ANCF) are adopted. The continuity equation is utilized to calculate the drag force, considering flow changes in the cross-sectional area during the CEA drop. Lastly, beam-inside-beam frictional contact model is employed to capture practical contact conditions between CEA and FA. The proposed framework is validated through experiments under two scenarios: free falls of CEA within FA, encompassing undeformed and deformed scenarios. The experimental validation of the framework demonstrated that the drop time of CEA can be accurately predicted under the complex coupling effects of fluid and frictional contact. The drop times of the S-shaped deformation case is longer than those of the C-shaped deformation case, affirming the time delay due to frictional force. The validation confirms the potential applicability to access the safety and reliability of nuclear power plants under extreme conditions.

• Wind and Structures
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• 제15권6호
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• pp.481-494
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• 2012

The greenhouse type metal structures are increasingly used in modern construction of livestock farms because they are less laborious to construct and they provide a more favorable microclimate for the growth of animals compared to conventional livestock structures. A key stress factor for metal structures is the wind. The external pressure coefficient ($c_{pe}$) is used for the calculation of the wind effect on the structures. A high pressure coefficient value leads to an increase of the construction weight and subsequently to an increase in the construction cost. The EC1 in conjunction with EN 13031-1:2001, which is specialized for greenhouses, gives values for this coefficient. This value must satisfy two requirements: the safety of the structure and a reduced construction cost. In this paper, the Navier - Stokes and continuity equations are solved numerically with the finite element method (Galerkin Method) in order to simulate the two dimensional, incompressible, viscous air flow over the vaulted roofs of single span and twin-span with eaves livestock greenhouses' structures, with a height of 4.5 meters and with length of span of 9.6 and 14 m. The simulation was carried out in a wind tunnel. The numerical results of pressure coefficients, as well as, the distribution of them are presented and compared with data from Eurocodes for wind actions (EC1, EN 13031-1:2001). The results of the numerical experiment were close to the values given by the Eurocodes mainly on the leeward area of the roof while on the windward area a further segmentation is suggested.

• The Korean Journal of Physiology
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• 제21권1호
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• pp.59-66
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• 1987

This study was aimed to investigate whether the conduction velocity of nerve impulses through the ventral afferent fibers is constant along their entire courses in dorsal as well as in ventral roots. Cats were anesthetized with ${\alpha}-chloralose$ (60 mg/kg, i.p.) and artificially ventilated. Laminectomies were done on L4-S1 spinal vertebrae to expose the lumbosacral spiral cord. Both ventral and dorsal roots of L7 or S1 spinal segments were isolated and cut near the spinal cord. Ventral roots were placed on 6-lead stimulating electrodes and stimulated with supra C-threshold intensity. Divided dorsal root fascicles were placed on bipolar recording electrodes and single fiber units activated by the stimulation of the ventral roots were identified. Followings are the results obtained: 1) A total of 27 VRA units were identified. 10 units of them conducted impulses slower than 2 m/sec. Conduction velocities of the remaining units were in the range of 3.11-20.91 m/sec. 2) In 12 Units conduction velocities Of the VRA units through dorsal$(CV_{DR})$ and venral root$(CV_{DR})$ were determined respectively. There was a tendency to conduct impulses faster through dorsal roots$(CV_{DR}=8.19{\pm}3.26\;m/sec)$ than ventral roots$(CV_{DR}=3.46{\pm}1.02\;m/sec)$. From the above results we confirmed that there exist nerve fibers in continuity between the spinal ventral and dorsal roots but we could not ascertain whether there is a change in conduction velocity through the entire course of ventral afferent unit.

• 대한토목학회논문집
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• 제14권1호
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• pp.39-48
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• 1994

본 연구는 3차원 층구조체의 복합이론 및 유한요소해석 프로그램의 개발에 목적이 있다. 3차원 층구조체는 선형, 탄성, 등방성의 작은 변위에 제한을 두었으며, 변위를 나타내기 위하여 global 좌표축외에 local 좌표축을 사용하는 multiscale 의 방법을 이용하였다. 유한요소법의 적용시 요구되는 주종속 변수들은 $C_o$ 연속성을 만족하도록 택하여 해석하였으며 그결과 해석이 아주 간편하였으며 계산과정이 매우 경제적이었다. 지금까지 개발되어온 대개의 복합이론은 중첩의 원리를 사용하여 비선형 해석에는 쉽게 적용될 수 없었으나 본 연구에서 개발한 복합이론은 비선형해석에 용이하게 적용할 수 있다. 본 연구에서 개발된 복합이론의 정당성과 사용성을 입증하기 위하여 2차원 및 3차원의 탄성받침을 해석하여 이산화해석의 결과치와 비교, 검토하였다.

• 대한토목학회논문집
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• 제14권1호
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• pp.29-38
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• 1994

본 연구는 축대칭 충구조체의 복합이론 및 유한요소해석 프로그램의 개발에 목적이었다. 연구대상인 축대칭 층구조체는 회전축에 수직으로 층을 이루고 있으며 선형, 탄성, 작은변형 및 축대칭 하중조건의 제한을 두었다. 개발된 복합이론은 multiscale의 방식을 사용하여 비균등질 층구조체를 등가 균등질로 취급할 수 있도록 하였으며 이 과정에서 주 변수들의 연속성만을 필요로 하였다. 그결과 종전에 시용되어온 비교적 복잡한 이론들과는 달리 $C_o$ 연속의 유한요소 프로그램의 개발이 가능하였으며 4 node isoparametric 요소를 사용하였다. 본 연구의 복합이론은 선형조건에 제한하였으나, 본 연구에서 제안한 multiscale 해석법을 이용하면 교량용 받침에 대한 연성재료의 비선형거동의 해석도 가능하게된다. 본 연구에서의 복합이론 및 유한요소해석의 타당함을 보이기위하여 두가지 하중조건 하에서 축대칭 층구조체를 해석하여 기존의 복합이론 및 이산화해석의 결과치와 비교하였다.

• Structural Engineering and Mechanics
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• 제68권4호
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• pp.385-398
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• 2018

In the present paper, we offer a new flat shell finite element. It is the result of the combination of a membrane element and a bending element, both based on the strain-based formulation. It is known that $C^{\circ}$ plane membrane elements provide poor deflection and stress for problems where bending is dominant. In addition, they encounter continuity and compliance problems when they connect to C1 class plate elements. The reach of the present work is to surmount these problems when a membrane element is coupled with a thin plate element in order to construct a shell element. The membrane element used is a triangular element with four nodes, three nodes at the vertices of the triangle and the fourth one at its barycenter. Each node has three degrees of freedom, two translations and one rotation around the normal. The coefficients related to the degrees of freedom at the internal node are subsequently removed from the element stiffness matrix by using the static condensation technique. The interpolation functions of strain, displacements and stresses fields are developed from equilibrium conditions. The plate element used for the construction of the present shell element is a triangular four-node thin plate element based on Kirchhoff plate theory, the strain approach, the four fictitious node, the static condensation and the analytic integration. The shell element result of this combination is robust, competitive and efficient.

• 대한영양사협회학술지
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• 제17권4호
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• pp.416-428
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• 2011

This study was carried out to investigate the effects of breakfast service on nutritional status, hematological status, and attentiveness of children in low-income families. The subjects were 19 boys and 13 girls between 7 and 11 years old. The subjects were divided into a control group and a breakfast service (BS) group, in which 12 boys and 5 girls received breakfast from February 1 to December 31, 2010. The results can be summarized as follows: intakes of energy, protein, carbohydrate, calcium, iron, zinc, vitamin A, vitamin $B_2$, niacin, and vitamin C in the BS group were significantly higher than those in the control group. In the BS group, the intakes of calcium, folic acid, and vitamin C were lower than 75% of recommended intake levels. There were no significant differences in the total blood protein level and total cholesterol level between the BS group and control group. A blood albumin level was significantly higher in the BS group than in the control group. Systolic blood pressure was higher in the BS group than in the control group, whereas the diastolic blood pressure showed no significant difference between the groups. A dietary attitude score increased according to breakfast service and nutritional education. No significant differences were found in the capacity value and continuity value between the two groups, but the control value was significantly higher in the BS group than in the control group. Therefore, to sustain the effect of breakfast service and improve nutritional status for children skipping breakfast in low-income families, nutrition intervention services, as well as legal and financial support by the government should be provided.

• Archives of Plastic Surgery
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• 제41권5호
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• pp.466-471
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• 2014

Background Bleeding can be a problem in wound debridement. In search for an effective hemostatic agent, we experimented with a chitosan film combined with the recombinant human epidermal growth factor (rh-EGF), hypothesizing that it would achieve effective hemostasis and simultaneously enhance arterial healing. Methods Forty-eight Sprague-Dawley rats were used, and 96 puncture wounds were made. The wounds were divided into the following four groups: treated with sterile gauze, treated with gelatin sponge, treated with chitosan, and treated with chitosan combined with rh-EGF. Immediate hemostasis was evaluated, and arterial healing was observed histologically. Results Groups B, C, and D showed a significant rate of immediate hemostasis as compared to group A (P<0.05), but there were no significant differences among groups B, C, and D. Histologically, only group D showed good continuity of the vessel wall after 1 week. It was the only group to show smooth muscle cell nuclei of the vessel wall. Conclusions We observed that chitosan has an effective hemostatic potential and the mix of rh-EGF and chitosan does not interfere with chitosan's hemostatic capabilities. We also identified enhanced healing of vessel walls when rh-EGF was added to chitosan. Further research based on these positive findings is needed to evaluate the potential use of this combination on difficult wounds like chronic diabetic ulcerations.

• Structural Engineering and Mechanics
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• 제70권5호
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• pp.551-562
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• 2019

In the present study, a suitable mathematical model considering parabolic transverse shear strains for dynamic analysis of laminated composite skew plates under different types of impulse and spatial loads was presented for the first time. The proposed mathematical model satisfies zero transverse shear strain at the top and bottom of the plate. On the basis of the cubic variation of thickness coordinate in in-plane displacement fields of the present mathematical model, a 2D finite element (FE) model was developed including skew transformations in the mathematical model. No shear correction factor is required in the present formulation and damping effect was also incorporated. This is the first FE implementation considering a cubic variation of thickness coordinate in in-plane displacement fields including skew transformations to solve the forced vibration problem of composite skew plates. The effect of transverse shear and rotary inertia was incorporated in the present model. The Newmark-${\beta}$ scheme was adapted to perform time integration from step to step. The $C^0$ FE formulation was implemented to overcome the problem of $C^1$ continuity associated with the cubic variation of thickness coordinate in in-plane displacement fields. The numerical studies showed that the present 2D FE model predicts the result close to the analytical results. Many new results varying different parameter such as skew angles, boundary conditions, etc. were presented.

• Structural Engineering and Mechanics
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• 제86권3호
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• pp.291-309
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• 2023

This paper addresses the finite element modeling of functionally graded porous (FGP) beams for free vibration and buckling behaviour cases. The formulated finite element is based on simple and efficient higher order shear deformation theory. The key feature of this formulation is that it deals with Euler-Bernoulli beam theory with only three unknowns without requiring any shear correction factor. In fact, the presented two-noded beam element has three degrees of freedom per node, and the discrete model guarantees the interelement continuity by using both C⁰ and C¹ continuities for the displacement field and its first derivative shape functions, respectively. The weak form of the governing equations is obtained from the Hamilton principle of FGP beams to generate the elementary stiffness, geometric, and mass matrices. By deploying the isoparametric coordinate system, the derived elementary matrices are computed using the Gauss quadrature rule. To overcome the shear-locking phenomenon, the reduced integration technique is used for the shear strain energy. Furthermore, the effect of porosity distribution patterns on the free vibration and buckling behaviours of porous functionally graded beams in various parameters is investigated. The obtained results extend and improve those predicted previously by alternative existing theories, in which significant parameters such as material distribution, geometrical configuration, boundary conditions, and porosity distributions are considered and discussed in detailed numerical comparisons. Determining the impacts of these parameters on natural frequencies and critical buckling loads play an essential role in the manufacturing process of such materials and their related mechanical modeling in aerospace, nuclear, civil, and other structures.