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RISS 인기검색어
- 검색키워드
- 저자 : Morteza Gharib (검색결과 3 건)
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Mehran Vagheian,Dariush Rezaei Ochbelagh,Morteza Gharib 한국원자력학회 2019 Nuclear Engineering and Technology Vol.51 No.5
A new moving-mesh Finite Volume Method (FVM) for the efficient solution of the two-dimensionalneutron diffusion equation is introduced. Many other moving-mesh methods developed to solve theneutron diffusion problems use a relatively large number of sophisticated mathematical equations, andso suffer from a significant complexity of mathematical calculations. In this study, the proposed methodis formulated based on simple mathematical algebraic equations that enable an efficient mesh movementand CV deformation for using in practical nuclear reactor applications. Accordingly, a computationalframework relying on a new moving-mesh FVM is introduced to efficiently distribute the meshesand deform the CVs in regions with high gradient variations of reactor power. These regions of interestare very important in the neutronic assessment of the nuclear reactors and accordingly, a higher accuracyof the power densities is required to be obtained. The accuracy, execution time and finally visual comparison of the proposed method comprehensivelyinvestigated and discussed for three different benchmark problems. The results all indicated a higheraccuracy of the proposed method in comparison with the conventional fixed-mesh FVM.
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Large-amplitude flapping of an inverted flag in a uniform steady flow – a vortex-induced vibration
Sader, John E.,Cossé,, Julia,Kim, Daegyoum,Fan, Boyu,Gharib, Morteza Cambridge University Press 2016 Journal of fluid mechanics Vol.793 No.-
<P>The dynamics of a cantilevered elastic sheet, with a uniform steady flow impinging on its clamped end, have been studied widely and provide insight into the stability of flags and biological phenomena. Recent measurements by Kim<I>et al.</I>(<I>J. Fluid Mech.</I>, vol. 736, 2013, R1) show that reversing the sheet’s orientation, with the flow impinging on its free edge, dramatically alters its dynamics. In contrast to the conventional flag, which exhibits (small-amplitude) flutter above a critical flow speed, the inverted flag displays large-amplitude flapping over a finite band of flow speeds. The physical mechanisms giving rise to this flapping phenomenon are currently unknown. In this article, we use a combination of mathematical theory, scaling analysis and measurement to establish that this large-amplitude flapping motion is a vortex-induced vibration. Onset of flapping is shown mathematically to be due to divergence instability, verifying previous speculation based on a two-point measurement. Reducing the sheet’s aspect ratio (height/length) increases the critical flow speed for divergence and ultimately eliminates flapping. The flapping motion is associated with a separated flow – detailed measurements and scaling analysis show that it exhibits the required features of a vortex-induced vibration. Flapping is found to be periodic predominantly, with a transition to chaos as flow speed increases. Cessation of flapping occurs at higher speeds – increased damping reduces the flow speed range where flapping is observed, as required. These findings have implications for leaf motion and other biological processes, such as the dynamics of hair follicles, because they also can present an inverted-flag configuration.</P>
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Amini, Moharram,Zamzamian, Seyed Mehrdad,Fadaei, Amir Hossein,Gharib, Morteza,Feghhi, Seyed Amir Hosein Korean Nuclear Society 2021 Nuclear Engineering and Technology Vol.53 No.10
Applying the available neutron flux for medical and industrial purposes is the most important application of research reactors. The neutron radiography system is used for non-destructive testing (NDT) of materials so that it is one of the main applications of nuclear research reactors. One of these research reactors is the 5 MW pool-type light water research reactor of Tehran (TRR). This work aims to investigate on materials and location of the beam tube (BT) of the TRR radiography system to improve the index parameters of BT. Our results showed that a through-type BT with 20 cm thick carbon neutron filter, 1.2 cm and 9.4 cm of the diameter of inlet (D<sub>1</sub>) and output (D<sub>2</sub>) BT, respectively gives thermal neutron flux almost 25.7, 5.6 and 1.1 times greater than the former design of the TRR (with D<sub>1</sub> = 1.8 cm and D<sub>1</sub> = 9.4 cm), previous design of the TRR with D<sub>1</sub> = 3 cm and D<sub>1</sub> = 9.4 cm, and another design with D<sub>1</sub> = 5 cm and D<sub>1</sub> = 9.4 cm, respectively. Therefore, the design proposed in this paper could be a better alternative to the current BT of the TRR.
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