• Nuclear Engineering and Technology
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• 제55권3호
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• pp.1140-1151
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• 2023

Fully Ceramic Microencapsulated (FCM) fuel is emerging advanced fuel material for the future nuclear reactors. The fuel pellet in the FCM fuel is composed of matrix and a large number of TRistructural-ISOtopic (TRISO) fuel particles which are randomly dispersed in the SiC matrix. The minimum layer thickness in a TRISO fuel particle is on the order of 10^-5 m, and the length of the FCM pellet is on the order of 10^-2 m. Hence, the heat transfer in the FCM pellet is a multi-scale phenomenon. In this study, three multi-scale heat conduction models including the Multi-region Layered (ML) model, Multi-region Non-layered (MN) model and Homogeneous model for FCM pellet were constructed. In the ML model, the random distributed TRISO fuel particles and coating layers are completely built. While the TRISO fuel particles with coating layers are homogenized in the MN model and the whole fuel pellet is taken as the homogenous material in the Homogeneous model. Taking the results by the ML model as the benchmark, the abilities of the MN model and Homogenous model to predict the maximum and average temperature were discussed. It was found that the MN model and the Homogenous model greatly underestimate the temperature of TRISO fuel particles. The reason is mainly that the conventional equivalent thermal conductivity (ETC) models do not take the internal heat source into account and are not suitable for the TRISO fuel particle. Then the improved ETCs considering internal heat source were derived. With the improved ETCs, the MN model is able to capture the peak temperature as well as the average temperature at a wide range of the linear powers (165 W/cm~ 415 W/cm) and the packing fractions (20%-50%). With the improved ETCs, the Homogenous model is better to predict the average temperature at different linear powers and packing fractions, and able to predict the peak temperature at high packing fractions (45%-50%).

• Nuclear Engineering and Technology
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• 제51권5호
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• pp.1241-1250
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• 2019

This study mainly focused on the neutronics modeling of bubbles in bubbly flow in boiling water reactors. The bubble, ring and homogenous models were used for radial void fraction distribution. Effect of the bubble and ring models on the infinite multiplication factor and two-group flux distribution was investigated by comparing with the homogenous model. Square pitch unit cell geometry was used in the calculations. In the bubble model, spherical and non-spherical bubbles at random positions, sizes and shapes were produced by Monte Carlo method. The results show that there are significant differences among the proposed models from the viewpoint of physical interaction mechanism. For the fully-developed bubbly flow, $k_{inf}$ is overestimated in the ring model by about $720{\pm}6pcm$ with respect to homogeneous model whereas underestimated in the bubble model by about $-65{\pm}9pcm$ with a standard deviation of 15 pcm. In addition, the ring model shows that the coolant must be separated into regions to properly represent the radial void distribution. Deviations in flux distributions principally occur in certain regions, such as corners. As a result, the bubble model in modeling the void fraction can be used in nuclear engineering calculations.

• Smart Structures and Systems
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• 제4권2호
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• pp.171-182
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• 2008

In this paper, a methodology for the estimation of masonry elasticity and shear moduli is presented, for linear elasticity considerations. The methodology is based on the assumption that for a "periodic" masonry wall, which is formed by the repetition of a basic unit containing blocks and mortar, the mechanical characteristics of the unit are representative of the characteristics of the entire wall. For their calculation, the finite element analysis method is used. A micro-model with finite elements simulating separately the blocks and the mortar is developed. An equivalent finite element model, using an homogenous material is also developed and assuming equivalence of strains for the two models, the homogenous material properties are estimated. The efficiency of the method and its applicability limits are investigated.

• Journal of applied mathematics & informatics
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• 제9권2호
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• pp.761-769
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• 2002

Due to the large scale application of software systems, software reliability plays an important role in software developments. In this paper, a software reliability growth model (SRGM) is proposed. The testing time on the right is truncated in this model. The instantaneous failure rate, mean-value function, error detection rate, reliability of the software, estimation of parameters and the simple applications of this model are discussed .

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2009년 추계학술대회논문집
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• pp.185-187
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• 2009

A density based method with homogeneous cavitation model to investigate cavitation-bubble collapsing behavior is proposed and applied to bubble-shock interaction problems. By applying this method, cylindrical bubbles located in the liquid and incident liquid shock wave are computed. Bubble collapsing behavior, shock-bubble interaction and shock transmission/reflection pattern are investigated.

• Smart Structures and Systems
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• 제26권3호
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• pp.391-401
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• 2020

The present article reports the feasibility of the electrical energy generation from ambient low-frequency vibration using a piezoelectric material mounted on a bimorph cantilever beam actuator. A corresponding higher-order analytical model is developed using MATLAB in conjunction with finite element method under low-frequency with both damped and undamped conditions. An alternate model is also developed to check the material and dimensional viability of both piezoelectric materials (mainly focussed to PVDF and PZT) and the base material. Also, Genetic Algorithm is implemented to find the optimum dimensions which can produce the higher values of voltage at low-frequency frequencies (≤ 100 Hz). The delamination constraints are employed to avoid inter-laminar stresses and to increase the fracture toughness. The delamination has been done using a Teflon sheet sandwiched in between base plates and the piezo material is stuck to the base plate using adhesives. The analytical model is tested for both homogenous and isotropic material characteristics of the base material and extended to investigate the effect of the different geometrical parameters (base plate dimensions, piezo layer dimensions and placement, delamination thickness and placement, excitation frequency) on the model responses of the bimorph cantilever beam. It has been observed that when the base material characteristics are homogenous, the efficiency of the model remains higher when compared to the condition when it is of isotropic material. The necessary convergence behaviour of the current numerical model has been established and checked for the accuracy by comparing with available published results. Finally, using the results obtained from the model, a prototype is fabricated for the experimental validation via a suitable circuit considering Glass fibre and Aluminium as the bimorph material.

• Journal of applied mathematics & informatics
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• 제8권3호
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• pp.989-999
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• 2001

In this paper we show that certain notions of negative dependence are preserved under a bivariate homogenous poisson shock model in which two devices shocks form two independent poisson processes.

• Journal of Yeungnam Medical Science
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• 제10권1호
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• pp.58-67
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• 1993

1986년 5월부터 1991년 6월까지 약 5년간 영남대학교 외과대학 부속병원에 내원하여 혈액학적 소견상 빈혈이 동반된 환자 210명과 정상인 200명 도합 410명을 대상으로 Coulter Counter S-plus II로 일반혈액검사를 실시하여 MCV와 RDW 및 여러 적혈구 지수를 얻어서 빈혈의 새로운 분류를 시도하였고 외국인에 비하여 빈혈의 병인 양상이 다른 한국인의 혈액질환의 감별진단에 도움이 되는 가를 알아 보고자 본 연구를 시행하였다. 거의 모든 경우에 MCV의 증감은 MCH와 MCHC의 증감을 동반하였으나 RDW와는 무관하였다. 따라서 저색소성빈혈 혹은 정색소성빈혈등의 용어보다는 이질성빈혈 혹은 동질성빈혈의 용어를 사용함이 빈혈의 형태학적 분류에 더욱 의미있는 것으로 사료되었다. 이질성소구성빈혈에는 철결핍성빈혈이 속하였고 이질성정구성빈혈에는 급성백혈병과 골수로성빈혈이 여기에 속하였으며 이질성대구성빈혈에는 거대적아구성빈혈과 용혈성빈혈이 속하였다. 동질성소구성빈혈에는 만성질환에 의한 빈혈이 여기에 속하였으며 동질성정구성빈혈에는 급성출혈, 만성백혈병 및 다발성 골수종등에 의한 빈혈이 여기에 속하고 동질성대구성빈혈에는 재생활량성빈혈이 여기에 속하였다. 진단적인 의의가 큰 혈색소병은 본 연구에는 관찰되지 않았지만 한국인에 가장 많은 빈혈의 원인인 철결핍성빈혈과 만성질환에 의한 빈혈의 감별진단에 RDW가 유용한 것으로 생각되었다.

• Journal of Mechanical Science and Technology
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• 제18권8호
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• pp.1271-1287
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• 2004

In this article, vapor bubble nucleation in liquid and the evaporation process of a liquid droplet at its superheat limit were discussed from the viewpoint of molecular clustering (molecular cluster model for bubble nucleation). For the vapor bubble formation, the energy barrier against bubble nucleation was estimated by the molecular interaction due to the London dispersion force. Bubble nucleation by quantum tunneling in liquid helium under negative pressure near the absolute zero temperature and bubble nucleation on cavity free micro heaters were also presented as the homogenous nucleation processes.

• 소성∙가공
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• 제22권7호
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• pp.371-376
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• 2013

The shape defects such as edge waves and center buckles may be formed in the rolled strip because rolling can easily produce non-homogenous elongation across the strip width. The main purpose of tension leveling is to remove such defects by eliminating the differences in elongation. In this paper, a new approach for the optimization of the process conditions in tension leveling is presented. The approach consists of an analytic model for the prediction of the strip curvature and the force at each roll. The accuracy of the proposed model is examined through comparison with the predictions from a finite element model.