• 한국해양환경ㆍ에너지학회지
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• 제12권3호
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• pp.197-201
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• 2009

다상유동의 상분리 시뮬레이션 기법으로 Lattice-Boltzmann방법(LBM)을 이용하였다. 기체와 액체상사이의 경계면에서 마이크로한 상호교환을 LBM의 등가함수에서 취급하고 있으며, Van-der-Walls의 free energy를 도입하였다. 표면에너지에 따라 상경계면의 기울기의 변화, 온도에 따른 상분리 특성등을 조사하고, 일정 온도상에서 기체와 액체의 상분리 시뮬레이션을 수행하였다.

• Nuclear Engineering and Technology
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• 제29권1호
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• pp.7-14
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• 1997

Grain boundary diffusion plays a significant role in fission gas release, which is one of the crucial processes dominating nuclear fuel performance. Gaseous fission produce such as Xe and Kr generated during nuclear fission have to diffuse in the grain lattice and the boundary inside fuel pellets before they reach the open spaces in a fuel rod. These processes can be studied by 'tracer diffusion' techniques, by which grain boundary diffusivity can be estimated and directly used for low burn-up fission gas release analysis. However, only a few models accounting for the both processes are available and mostly handle them numerically due to mathematical complexity. Also the numerical solution has limitations in a practical use. In this paper, an approximate analytical solution in case of stationary grain boundary in a polycrystalline solid is developed for the tracer diffusion techniques. This closed-form solution is compared to available exact and numerical solutions and it turns out that it makes computation not only greatly easier but also more accurate than previous models. It can be applied to theoretical modelings for low bum-up fission gas release phenomena and experimental analyses as well, especially for PIE (post irradiation examination).

• 센서학회지
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• 제31권6호
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• pp.397-402
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• 2022

In this short review, we explore the recent progress in metal-based gas-sensing techniques. The strong interaction between the metal films and hydrogen gas can be considered to play a considerably important role in the gas-sensing technique. The physical and chemical reactions in Pd-Pd hydride systems were studied in terms of the phase transition and lattice expansion of the metals. Two types of represented detection, electrical and optical, were introduced and discussed along with their advantages.

• 한국세라믹학회지
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• 제33권7호
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• pp.802-808
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• 1996

PbTiO3 thin films were fabricated onto MgO(100) single crystal substrate by reactive D. C magnetron sput-tering of Pb and Ti metal in an oxygen and argon gas mixture. The annealing of the thin films resulted in the decrease of both the c-axis orientation ratio and the lattice parameter. It is well known that the c-axis lattice parameter of thin film is dependent on the Pb/(Pb+Ti)ratio and the residual stress in the film The PbTiO3 thin films with a Pb/(Pb+T) ratio ranging from 0.45 to 0.57 were fabricated and annealed. The structure of the film the c-axis orientation ratio and the lattice parameter were not dependent on the Pb/(Pb+Ti) ratio before and after annealing. These experimental results proved that the decrease of the c-axis lattice parameter under the annealing conditions was due to the relaxation of the intrinsic stress in the film. This relaxation of the intrinsic stress caused the decrease of the c-axis orientation ratio and this phenomenon can be explained by c-axis growth lattice model.

• Journal of Mechanical Science and Technology
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• 제16권10호
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• pp.1327-1335
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• 2002

The shock wave process represents an abrupt change in fluid properties, in which finite variations in pressure, temperature, and density occur over the shock thickness which is comparable to the mean free path of the gas molecules involved. This shock wave fluid phenomenon is simulated by using the finite difference lattice Boltzmann method (FDLBM). In this paper, a new model is proposed using the lattice BGK compressible fluid model in FDLBM for the purpose of speeding up the calculation as well as stabilizing the numerical scheme. The numerical results of the proposed model show good agreement with the theoretical predictions.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.1827-1832
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• 2003

In this research, the simulation method for acoustic sounds by a uniform flow around a two-dimensional circular cylinder by using the finite difference lattice Boltzmann model is explained. To begin with, we examine the boundary condition which determined with the distribution function $f_i^{(0)}$ concerning with density, velocity and internal energy at boundary node. Very small acoustic pressure fluctuation, with same frequency as that of Karman vortex street, is compared with the pressure fluctuation around a circular cylinder. The acoustic sound' propagation velocity shows that acoustic approa ching the upstream, due to the Doppler effect in the uniform flow, slowly propagated. For the do wnstream, on the other hand, it quickly propagates. It is also apparently the size of sound pressure was proportional to the central distance $r^{-1/2}$ of the circular cylinder. The lattice BGK model for compressible fluids is shown to be one of powerful tool for simulation of gas flows.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.561-564
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• 2002

For the reduction of fuel consumption of high speed, the aerodynamic drag must be reduced. In early vehicle design process, it is very important to have information about aerodynamic characteristics of design models. In this phase CFD methods are usually used to predict the aerodynamic forces. But commercial programs using turbulence models cannot give a good agreement with experimental result and have also problems with convergence. PowerFLOW employs a new technology called DIGITAL PHYSICS, which provides a different approach to simulating fluids. DIGITAL PHYSICS uses a lattice-based approach (extended from lattice-gas and lattice-Boltzmann methods) where time, space and velocity are discrete. This discrete system represents the Wavier-Stokes continuum behavior without the numerical instability Issues of traditional CFD solvers, such as convergence. In this paper, aerodynamic performance of vehicles are simulated using PowerFLOW by Exa and results are compared with experimental wind tunnel data.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.468-474
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• 2001

The shock process represents an abrupt change in fluid properties, in which finite variations in pressure, temperature, and density occur over a shock thickness which is comparable to the mean tree path of the gas molecules involved. The fluid phenomenon is simulated by using finite difference lattice Boltzmann method (FDLBM). In this research, the new model is proposed using the lattice BGK compressible fluid model in FDLBM for the purpose of shortening in calculation time and stabilizing in simulation operation. The numerical results agree also with the theoretical predictions.

• 한국해양공학회지
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• 제18권2호
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• pp.10-17
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• 2004

In this research, a numerical simulation for the acoustic sounds around a two-dimensional circular cylinder in a uniform flaw was developed, using the finite difference lattice Boltzmann model. We examine the boundary condition, which is determined by the distribution function concerning density, velocity, and internal energy at the boundary node. Pressure variation, due to the emission of the acoustic waves, is very small, but we can detect this periodic variation in the region far from the cylinder. Daple-like emission of acoustic waves is seen, and these waves travel with the speed of sound, and are synchronized with the frequency of the lift on the cylinder, due to the Karman vortex street. It is also apparent that the size of the sound pressure is proportional to the central distance to the circular cylinder. The lattice BGK model for compressible fluids is shown to be a powerful tool for the simulation of gas flaws.

• 한국표면공학회지
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• 제7권1호
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• pp.5-12
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• 1974

The interaction energy of water molecule over the surfaces of basal planes of silver iodide has been calculated , assuming 1-4-6--12 type potentials between the gas molecule and lattice ions in the silver iodide lattice. The heat of adsorption ranges from 12.25 to 12.75 kcal /mole at low coverage which is around the level of the latent heat of sublimaton of water.