• Nuclear Engineering and Technology
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• 제45권5호
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• pp.613-624
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• 2013

Multi-dimensional two-phase phenomena occur in many industrial applications, particularly in a nuclear reactor during steady operation or a transient period. Appropriate modeling of complicated behavior induced by a multi-dimensional flow is important for the reactor safety analysis results. SPACE, a safety analysis code for thermal hydraulic systems which is currently being developed, was designed to have the capacity of multi-dimensional two-phase thermo-dynamic phenomena induced in the various phases of a nuclear system. To validate the performance of SPACE, a two-dimensional two-phase flow test was performed with slab geometry of the test section having a scale of $1.43m{\times}1.43m{\times}0.11m$. The test section has three inlet and three outlet nozzles on the bottom and top gap walls, respectively, and two outlet nozzles installed directly on the surface of the slab. Various kinds of two-dimensional air/water flows were simulated by selecting combinations of the inlet and outlet nozzles. In this study, two-dimensional two-phase void fraction profiles were quantified by measuring the local gap impedance at 225 points. The flow conditions cover various flow regimes by controlling the flow rate at the inlet boundary. For each selected inlet and outlet nozzle combination, the water flow rate ranged from 2 to 20 kg/s, and the air flow rate ranged from 2.0 to 20 g/s, which corresponds to 0.4 to 4 m/s and 0.2 to 2.3 m/s of the superficial liquid and gas velocities based on the inlet port area, respectively.

• 암석학회지
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• 제27권1호
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• pp.17-24
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• 2018

백두산 화산으로부터 폭발성 분화에 의한 것으로 추정되는 1654년의 조선왕조실록에 기록된 화산재 구름 이동의 역사기록을 화산학적 견지에서 고찰하였다. 1654년 10월 21일에 백두산에서 분화된 화산재와 화산가스가 북풍~북동풍의 바람을 타고 낮은 고도로 운반되어 재구름과 함께 한반도 남쪽으로 내려온 화산재로 해석할 수 있다. 그 영향 지역이 북쪽으로 함경도 남쪽 경계부에도 출현하였다는 것은 그 북쪽 즉 백두산에서 한반도 남쪽으로 남하한 것으로 평가된다. 분화지점인 백두산으로부터 약 500 km 이상 떨어진 경기도 적성과 장단 지역에 재구름이 통과한 것은 당시 백두산에서 중규모의 플리니식 분화로 형성된 분연주가 탁월풍의 영향으로 굽어진 형태로 지면을 따라 재구름을 형성하여 이동한 결과로 해석된다. 이를 유사 기상 장에서 수치 모의하여 재현하였다.

• Nuclear Engineering and Technology
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• 제23권2호
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• pp.183-199
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• 1991

가압수형 원자로 가압기의 오동작 보조살수 과도시 용기벽에서의 온도분포에 대한 과도응답을 해석하였으며, 해석은 분무수적으로 젖게되는 용기벽면에서 나타나는 열응력에 대하여 보수적으로 수행되었다. 수적이 부딪혀서 흘러내리는 용기벽의 내부경계면에서 강제대류열전달계수를 결정하기 위하여, 분무수적들이 살수노즐을 떠나 수증기와 비응축성인 수소기체로 이루어진 혼합기로 채워져 있는 가압기 내부공간을 통하여 비행한 후에 용기내부벽면에 도달할 때의 수적들의 과도온도를 예측하였다. 용기벽에서의 과도온도분포는 유한요소법을 사용하여 구하였으며, 대표적인 결과들을 제시하였다. 열해석의 결과는 입력자료에 대한 묘사와 부합되며, 타당한 물리적 의미를 가짐 이 확인되었다.

• Structural Engineering and Mechanics
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• 제25권4호
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• pp.445-466
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• 2007

As the LNG (Liquefied Natural Gas) tank contains cryogenic liquid, realistic thermal analyses are of a primary importance for a successful design. The structural details of the LNG tank are so complicated that some strategies are necessary to reasonably predict its temperature distribution. The proposed heat transfer model can consider the beneficial effects of insulation layers and a suspended deck on temperature distribution of the outer concrete tank against cryogenic conditions simply by the boundary conditions of the outer tank model. To this aim, the equilibrium condition or heat balance in a steady state is utilized in a various way, and some aspects of heat transfer via conduction, convection and radiation are implemented as necessary. Overall thermal analysis procedures for the LNG tank are revisited to examine some unjustifiable assumptions of conventional analyses. Concrete and insulation properties under cryogenic condition and a reasonable conversion procedure of the temperature-induced nonlinear stress into the section forces are discussed. Numerical examples are presented to verify the proposed schemes in predicting the actual temperature and stress distributions of the tank as affected by the cryogenic LNG for the cases of normal operation and leakage from the inner steel tank. It is expected that the proposed schemes enable a designer to readily detect the effects of insulation layers and a suspended deck and, therefore, can be employed as a useful and consistent tool to evaluate the thermal effect in a design stage of an LNG tank as well as in a detailed analysis.

• 대한전기학회논문지:시스템및제어부문D
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• 제55권6호
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• pp.264-273
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• 2006

In this paper, we propose a new architecture of Self-Organizing Fuzzy Polynomial Neural Networks (SOFPNN) by means of consecutive optimization and also discuss its comprehensive design methodology involving mechanisms of genetic optimization. The network is based on a structurally as well as parametrically optimized fuzzy polynomial neurons (FPNs) conducted with the aid of information granulation and genetic algorithms. In structurally identification of FPN, the design procedure applied in the construction of each layer of a SOFPNN deals with its structural optimization involving the selection of preferred nodes (or FPNs) with specific local characteristics and addresses specific aspects of parametric optimization. In addition, the fuzzy rules used in the networks exploit the notion of information granules defined over system's variables and formed through the process of information granulation. That is, we determine the initial location (apexes) of membership functions and initial values of polynomial function being used in the premised and consequence part of the fuzzy rules respectively. This granulation is realized with the aid of the hard c-menas clustering method (HCM). For the parametric identification, we obtained the effective model that the axes of MFs are identified by GA to reflect characteristic of given data. Especially, the genetically dynamic search method is introduced in the identification of parameter. It helps lead to rapidly optimal convergence over a limited region or a boundary condition. To evaluate the performance of the proposed model, the model is experimented with using two time series data(gas furnace process, nonlinear system data, and NOx process data).

• 한국해양공학회지
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• 제19권5호
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• pp.16-25
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• 2005

The effect of vertical riser support system on the dynamic behaviour of a classical spar platform is investigated. Spar platform generally uses buoyancy-can riser support system, but as water depth gets deeper the alternative riser support system is required due to safety and cost issues. The alternative riser support system is to hang risers off the spar platform using pneumatic cylinders rather than the buoyancy-can. The existing numerical model for hull/mooring/riser coupled dynamics analysis treats riser as an elastic rod truncated at the keel (truncated riser model), thus, in this model, the effect of riser support system can not be modeled correctly. Due to this reason, the truncated riser model tends to overestimate the spar pitch and heave motion. To evaluate more realistic global spar motion, mechanical coupling among risers, guide frames and support cylinders inside of spar moon-pool should be modeled. In the newly developed model, the risers are extended through the moon-pool by using nonlinear finite element methods with realistic boundary condition at multiple guide frames. In the simulation, the vertical tension from pneumatic cylinders is modeled by using ideal-gas equation and the vertical tension from buoyancy-cans is modeled as constant top tension. The different dynamic characteristics between buoyancy-can riser support system and pneumatic riser support system are extensively studied. The alternative riser support system tends to increase spar heave motion and needs damper system to reduce the spar heave motion.

• 대한기계학회논문집B
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• 제41권8호
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• pp.521-529
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• 2017

본 연구에서는 항공기 추진용 가스터빈 엔진의 고증속 터빈 제1단 정익 익렬을 새로이 구축하고, 이 정익의 기본 유동 특성에 대하여 연구하였다. 그 결과 본 연구에서 도입된 정익의 압력면에는 강한 순압력구배가 존재하는 반면, 흡입면에는 앞전에서 미드코드 근처까지 압력면보다 훨씬 더 심한 순압력구배가 존재하고 그 이후 역압력구배가 존재하였다. 두 종류의 유막법을 적용한 유동의 가시화 실험을 통하여, 정익 앞전 상류 영역에 4와류모델 말발굽와류 시스템이 존재함을 확인하였고, 입구 경계층 유동의 박리선과 재부착 유동의 박리선을 정확히 파악하였다. 이와 함께 이 고증속 정익 익렬 하류에서의 2차유동, 압력손실, 선회각, 등에 대한 데이터를 확보하였다.

• 열처리공학회지
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• 제17권3호
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• pp.173-179
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• 2004

In this study, the influence of heat treatment and Ca contents on the electrochemical behavior was investigated. Mg-Ca alloys, i.e., Mg-0.22wt%Ca, Mg-0.56wt%Ca, Mg-1.31wt%Ca are prepared by ingot metallurgy. As-cast Mg-Ca alloys exhibited better electrochemical properties than pure Mg. Especially, Mg-0.22wt%Ca alloy improves its anode efficiency up to 62% and lowers the OCP up to -1.72VSCE. Microstructure and XRD patterns of Mg-Ca alloys show that additive Ca element is mainly solid-solutioned. While, the others show the microstructure and XRD pattern with large $Mg_2Ca$ at grain boundary. To assess the effect of heat treatment on the as-cast Mg-alloy, the specimens were heat treated at $200^{\circ}C$ for 2 hours under $CO_2$ gas atmosphere. Although corrosion properties of Mg-Ca alloys are somewhat deteriorated by heat treatment at $200^{\circ}C$ Mg-0.22wt%Ca alloy with uniformly distributed nano-sized $Mg_2Ca$ phase in ${\alpha}$-Mg matrix show still better corrosion properties than pure Mg specimen.

• 대한금속재료학회지
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• 제50권8호
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• pp.569-573
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• 2012

In order to understand the difference in SiC deposition between the $CH_3SiCl_3-H_2$ and $C_3H_8-SiCl_4-H_2$ systems, we calculate the phase stability among ${\beta}$-SiC, graphite and silicon. We constructed the phase-diagram of ${\beta}$-SiC over graphite and silicon via computational thermodynamic calculation considering pressure (P), temperature (T) and gas composition (C) as variables. Both P-T-C diagrams showed a very steep phase boundary between the SiC+C and SiC region perpendicular to the H/Si axis, and also showed an SiC+Si region with a H/Si value of up to 6700 in the $C_3H_8-SiCl_4-H_2$, and 5000 in the $CH_3SiCl_3-H_2$ system. This difference in phase boundaries is explained by the ratio of Cl to Si, which is 4 for the $C_3H_8-SiCl_4-H_2$ system and 3 for the $C_3H_8-SiCl_4-H_2$ system. Because the C/Si ratio is fixed at 1 in the $CH_3SiCl_3-H_2$ system while it can be variable in the $C_3H_8-SiCl_4-H_2$ system, the functionally graded material is applicable for better mechanical bonding during SiC coating on graphite substrate in the $C_3H_8-SiCl_4-H_2$ system.

• Computers and Concrete
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• 제21권6호
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• pp.717-726
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• 2018

Concrete pipelines are the most efficient and safe means for gas and oil transportation over a long distance. The use of nano materials and nono-engineering can be considered for enhancing concrete pipelines properties. the tests show that $SiO_2$ nanoparticles can improve the mechanical behavior of concrete. Moreover, severe hazard for pipelines is seismic ground motion. Over the years, scientists have attempted to understand pipe behavior against earthquake most frequently via numerical modeling and simulation. Therefore, in this paper, the dynamic response of underwater nanocomposite submerged pipeline conveying fluid is studied. The structure is subjected to the dynamic loads caused by earthquake and the governing equations of the system are derived using mathematical model via Classic shell theory and Hamilton's principle. Navier-Stokes equation is employed to calculate the force due to the fluid in the pipe. As well, the effect of external fluid is modeled with an external force. Mori-Tanaka approach is used to estimate the equivalent material properties of the nanocomposite. 1978 Tabas earthquake in Iran is considered for modelling seismic load. The dynamic displacement of the structure is extracted using differential quadrature method (DQM) and Newmark method. The effects of different parameters such as $SiO_2$ nanoparticles volume percent, boundary conditions, thickness to radius ratios, length to radius ratios, internal and external fluid pressure and earthquake intensity are discussed on the seismic response of the structure. From results obtained in this paper, it can be found that the dynamic response of the pipe is increased in the presence of internal and external fluid. Furthermore, the use of $SiO_2$ nanoparticles in concrete pipeline reduces the displacement of the structure during an earthquake.