• Nuclear Engineering and Technology
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• 제36권6호
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• pp.559-570
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• 2004

A computational fluid dynamics model for predicting moderator circulation inside the Canada deuterium uranium (CANDU) reactor vessel has been developed to estimate the local subcooling of the moderator in the vicinity of the calandria tubes. The buoyancy effect induced by the internal heating is accounted for by the Boussinesq approximation. The standard $k-{\varepsilon}$ turbulence model with logarithmic wall treatment is applied to predict the turbulent jet flows from the inlet nozzles. The matrix of the calandria tubes in the core region is simplified to a porous media in which the anisotropic hydraulic impedance is modeled using an empirical correlation of pressure loss. The governing equations are solved by DFX-4.4, a commercial CFD code developed by AEA technology. The resultant flow patterns of the constant-z slices containing the inlet nozzles and the outlet port are "mined-type", as observed in the former 2-dimensional experimental investigations. With 103% full power for conservatism, the maximum temperature of the moderator is $82.9^{\circ}C$ at the top of the core region. Considering the hydrostatic pressure change, the minimum subcooling is $24.8^{\circ}C$.

• 한국유체기계학회 논문집
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• 제13권4호
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• pp.37-43
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• 2010

The purpose of this study is not only to investigate the effects of air layer in the turbine chamber on the performance and internal flow of the cross-flow turbine, but also to suggest a newly developed air supply method. Field test is performed in order to measure the output power of the turbine by a new air supply method. CFD analysis on the performance and internal flow of the turbine is conducted by an unsteady state calculation using a two-phase flow model in order to embody the air layer effect on the turbine performance effectively. The result shows that air layer effect on the performance of the turbine is considerable. The air layer located in the turbine runner passage plays the role of preventing a shock loss at the runner axis and suppressing a recirculation flow in the runner. The location of air suction hole on the chamber wall is very important factor for the performance improvement. Moreover, the ratio between air from suction pipe and water from turbine inlet is also significant factor of the turbine performance.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제50권6호
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• pp.281-287
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• 2001

In order to obtain guidelines for design and operation of a new plasma source by a magnetic neutral loop discharge(NLD), the electron behavior was studied experimentally and numerically. Experimentally, the magnetic field gradient was changed over a wide range, and it was found that there existed an optimum value for efficient plasma production. Analyses of the electron behavior were performed using a model that included effects of a three dimensional electromagnetic field configuration considering the spatial decay of the electric field, and the limitation to the motion of electron caused by the existence of walls and thus electron loss at wall surfaces. These three dimensional factors were found to explain the existence of the optimum magnetic field gradient. It was shown that the L dependence of the plasma production efficiency was firstly decided by the finite decay length of the electric field strength, which was further modified by electron elastic collisions with neutral atoms which drove the electron to walls. The latter effect tends to reduce the optimum value of L.

• Nuclear Engineering and Technology
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• 제52권1호
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• pp.185-191
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• 2020

Plant-specific analyses of an advanced reactor have been performed to assure the structural integrity of the reactor pressure vessel during transient conditions, which are expected to initiate pressurized thermal shock (PTS) events. The vessel failure probabilities from the probabilistic fracture mechanics analyses are combined with the transient frequencies to generate the through-wall cracking frequencies, which are compared to the acceptance criterion. Several sensitivity analyses are performed, focusing on the orientations and sizes of cracks, the copper content, and a flaw distribution model. The results show that the integrity of the reactor vessel is expected to be maintained for long-term operation beyond the design lifetime from the PTS perspective using the design data of the advanced reactor. Moreover, a fluence level exceeding 9×10¹⁹ n/㎠ is found to be acceptable, generating a sufficient margin beyond the design lifetime.

• Korea-Australia Rheology Journal
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• 제15권2호
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• pp.97-105
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• 2003

In the previous paper (Hyun et al.,2002), we have investigated the shape of storage modulus (G') and loss modulus (G") of complex fluids under large amplitude oscillatory shear (LAOS) flow. As the strain amplitude increases, owever, the stress curve becomes distorted and some important information may be smothered during data processing. Thus we need to investigate the stress data more precisely and systematically. In this work, we have obtained the stress data using high performance ADC (analog digital converting) card, and investigated the nonlinear response of complex fluids, 4wt% xanthan gum (XG), 2 wt% PVA/ 1 wt% Borax, and 1 wt% hyaluronic acid (HA) solutions, using Fourier transformation (FT) rheology. Comparing the strain signals in time domain with FT parameters in frequency domain, we could illustrate the sensitivity and importance of FT rheology. Diverse and unique stress patterns were observed depending on the material system as well as flow environment. It was found that they are not the outcome of experimental deficiency like wall slip but characteristics of the material system. When nonlinear response of complex fluids is analyzed, the intensity and phase angle of higher harmonic contributions should be considered together, and the shape of the stress signal was found to be strongly dependent upon phase angle.ngle.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2011년도 학술발표회
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• pp.50-54
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• 2011

공극률, 슬릿 수 및 두께가 다양한 오리피스 구조물을 대상으로 개수로 수리실험을 진행하여 유공벽의 벽두께에 따른 에너지 손실계수의 변화 및 메커니즘을 연구하였다. 오리피스의 개수로 수리실험을 수행하였으며 다양한 유속조건에서 오리피스의 벽두께에 대한 에너지 손실계수를 측정한 뒤 결과를 권 등(2010)의 관수로 실험결과와 비교하였다. 실험결과 전체적으로 유속에 따라 에너지 손실은 변화하였으며 유속이 감소할수록 에너지 손실은 크게 증가함을 보였다. 유속이 작은 층류구간에서 유속이 감소할수록 에너지 손실은 증가하는 반비례 관계를 보였고 에너지 손실량은 관수로 실험결과와 서로 비슷하였다. 그러나 유속이 강한 난류 구간에서는 에너지 손실이 유속과 무관하게 일정한 관수로 결과와는 달리 유속에 따라 변화하였다. 또한 유속이 약한 흐름에서는 오리피스의 두께 및 슬릿 수에 따라 에너지 손실은 각각 다르게 측정되었지만 유속이 강한 흐름에서는 벽두께 변화와 상관없이 에너지 손실은 거의 비슷하였다. 이 결과로부터 개수로 오리피스의 경우 유속이 강한 구간에서는 오리피스의 벽두께 효과 보다 상 하류 수위차로 발생하는 개수로 효과가 더 큰 영향을 주는 것으로 확인되었다.

• Earthquakes and Structures
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• 제9권2호
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• pp.431-453
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• 2015

A destructive earthquake, the magnitude of this earthquake was 7.2, hit Van, Turkey on October 23, 2011. After this devastating earthquake, a moderate earthquake which had 5.7 magnitude on November 9, 2011 occurred in Edremit, Van. These earthquakes caused heavy damages and collapses in many reinforced concrete buildings with loss of lives. In this paper, characteristics of ground motions of these earthquakes were studied and, deficiencies in structural elements and engineering faults such as poor workmanship and quality of construction, soft and weak stories, strong beam-weak column, short column, large overhang, hammering and unconfined gable wall were investigated. According to the observations, it was seen that, low quality of structural materials, lack of engineering services, inappropriate design and construction with insufficient detailing of the structural elements were the main reasons of heavy damages.

• 설비공학논문집
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• 제21권7호
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• pp.417-423
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• 2009

Air curtains are widely used for gates of shopping mall, warehouse, cold stores and refrigerated display cabinets. The purpose of the air curtain is to reduce the infiltration of outdoor air and heat loss from the air conditioning space to ambient air. Design data for the air curtain given by previous researchers do not mention the influence of wind speed. Thus, this paper presents a performance of single jet air curtain in heating space when the wind blows toward the opening space of the building. A numerical simulation is used to study the influence of various parameters on the efficiency of the downward-blowing air curtain device which is installed inside of the wall above the door. The performance of the air curtain is evaluated by sealing efficiency which provides the assessment of the energy savings. A new safety factor is also proposed for determination of air curtain jet velocity under the various wind conditions.

• 한국임상수의학회지
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• 제35권6호
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• pp.302-307
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• 2018

This report describes the unusual ultrasonography features of chronic hypertrophic pyloric gastropathy in two dogs - a 12-year-old neutered male Pekingese (case 1) and an 11-year-old spayed female Shih Tzu (case 2) - with chronic vomiting and weight loss. Chronic hypertrophic pyloric gastropathy can be observed as the focal thickening of the pyloric wall with normal layers on ultrasonography images. However, in case 1, gastric neoplasia could not be ruled out because of the presence of regional lymph node enlargement; in case 2, an intussusception was tentatively diagnosed because of a mass within the pylorus, which appeared to be connected to the descending duodenum on the longitudinal image. In both cases, focally thickened pyloric walls were demonstrated through exploratory laparotomy, and the histopathological diagnosis of chronic hypertrophic pyloric gastropathy was made. Ultrasonography is useful for imaging the gastrointestinal tract, and the typical ultrasonographic features of chronic hypertrophic pyloric gastropathy have been reported. However, the possibility, that chronic hypertrophic pyloric gastropathy can present unusual ultrasonographic findings similar to those of tumors or intussusception, should also be considered.

• Earthquakes and Structures
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• 제16권6호
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• pp.727-741
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• 2019

A reinforced concrete water tank is a typical functional liquid storage structure and cracks are the greatest threat to the liquid storage structure. Tanks are readily cracked due to seismic activity, thereby leading to the leakage of the stored liquid and a loss of function. In order to study the effect of cracks on liquid storage tanks, self-healing and leakage tests for bending cracks and through cracks in the walls of a reinforced concrete water tank were conducted. Material performance tests were also performed. The self-healing performance of bending cracks in a lentic environment and through cracks in a lotic environment were tested, thereby the self-healing width of bending micro-cracks in the lentic environment in the short term were determined. The through cracks had the capacity for self-healing in the lotic environment was found. The leakage characteristics of the bending cracks and through cracks were tested with the actual water head on the crack. The effects on liquid leakage of the width of bending cracks, the depth of the compression zone, and the acting head were determined. The relationships between the leakage rate and time with the height of the water head were analyzed. Based on the tests, the relationships between the crack characteristics and self-healing as well as the leakage were obtained. Thereby the references for water tank structure design and grading earthquake damage were provided.