• Nuclear Engineering and Technology
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• 제56권8호
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• pp.2948-2957
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• 2024

High-order harmonic techniques can be used to recreate neutron flux distributions in reactor cores using the neutron diffusion equation. However, traditional source iteration and source correction iteration techniques have sluggish convergence rates and protracted calculation periods. The correctness of the implicitly restarted Arnoldi method (IRAM) in resolving the eigenvalue problems of the one-dimensional and two-dimensional neutron diffusion equations was confirmed by computing the benchmark problems SLAB_1D_1G and two-dimensional steady-state TWIGL using IRAM. By integrating Galerkin projection with Proper Orthogonal Decomposition (POD) techniques, a POD-Galerkin reduced-order model was developed and the IRAM model was used as the full-order model. For 14 macroscopic cross-section values, the TWIGL benchmark problem was perturbed within a 20% range. We extracted 100 sample points using the Latin hypercube sampling method, and 70% of the samples were used as the testing set to assess the performance of the reduced-order model The remaining 30% were utilized as the training set to develop the reduced-order model, which was employed to rebuild the TWIGL benchmark problem. The reduced-order model demonstrates good flexibility and can efficiently and accurately forecast the effective multiplication factor and neutron flux distribution in the core. The reduced-order model predicts k_eff and neutron flux distribution with a high degree of agreement compared to the full-order model. Additionally, the reduced-order model's computation time is only 10.18% of that required by the full-order model.The neutron flux distribution of the steady-state TWIGL benchmark was recreated using the reduced-order model. The obtained results indicate that the reduced-order model can accurately predict the k_eff and neutron flux distribution of the steady-state TWIGL benchmark.Overall, the proposed technique not only has the potential to accurately project neutron flux distributions in transient settings, but is also relevant for reconstructing neutron flux distributions in steady-state conditions; thus, its applicability is bound to increase in the future.

• 천문학회보
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• 제37권1호
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• pp.90.2-90.2
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• 2012

Geosynchronous electron flux dropouts are most likely due to fast drift loss of the particles to the magnetopause (or equivalently, the "magnetopause shadowing effect"). A possible effect related to the drift loss is the radial diffusion of PSD due to gradient of PSD set by the drift loss effect at an outer L region. This possibly implies that the drift loss can affect the flux levels even inside the trapping boundary. We recently investigated the details of such diffusion process by solving the diffusion equation with a set of initial and boundary conditions set by the drift loss. Motivated by the simulation work, we have examined observationally the energy spectrum and pitch angle distribution near trapping boundary during the geosynchronous flux dropouts. For this work, we have first identified a list of geosynchronous flux dropout events for 2007-2010 from GOES satellite electron measurements and solar wind pressures observed by ACE satellite. We have then used the electron data from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft measurements to investigate the particle fluxes. The five THEMIS spacecraft sufficiently cover the inner magnetospheric regions near the equatorial plane and thus provide us with data of much higher spatial resolution. In this paper, we report the results of our investigations on the energy spectrum and pitch angle distribution near trapping boundary during the geosynchronous flux dropout events and discuss implications on the effects of the drift loss on the flux levels at inner L regions.

• Nuclear Engineering and Technology
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• 제21권1호
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• pp.56-61
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• 1989

Borresen의 1.5군 소격 확산이론에 의거하여 2군 중성자 속에 대한 adjoint 함수를 근사적으로 계산할 수 있는 한가지 간단한 방법을 제안하였다. 이 방법에서는 열 중성자 속에 대한adjoint 함수의 누설항을 1.5군 이론의 원리에 입각하여 기하학적 buckling에 의해 근사적으로 기술하게 되는데 이때 그 기하학적 buckling은 속중성자속의 adjoint 함수로부터 구하게 된다. 한편 제안된 계산 방법의 정확도를 알기 위해 adjoint함수 계산에 대한 KIDD 전산코드의 계산결과와 제안된 방법의 계산결과를 비교하였으며 이로부터 제안된 방법이 정확도면에서 만족스런 adjoint함수를 예측 할 수 있다는 것을 보였다. 뿐만 아니라 이 방법은 섭동 이론과 관련하여 반응도 평가에 유용하게 이용될 수 있다는 것도 보였다.

• 에너지공학
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• 제17권4호
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• pp.233-240
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• 2008

최근 새로운 2계 자기 수반형(self-adjoint) 중성자 수송 방정식으로 기존의 우성 및 기성 수송 방정식 외에 SAAF(Self-Adjoint Angular Flux) 수송 방정식이 소개되어, 이에 대한 적절한 경계조건, 수치해법, 정확도 등에 관한 논의가 활발히 진행되고 있다. 본 연구에서는 SAAF 수송 방정식의 수학적, 물리적 의미를 고찰하고 기존의 우성 및 기성 수송 방정식과의 연관성을 명확히 하였으며, Boltzmann 수송 방정식의 1계 차분식에서 2계의 SAAF 수송 방정식의 차분식을 유도하는 방법을 확산 가속법(diffusion synthetic acceleration method)과 함께 소개하였다. 유도된 SAAF 차분법이 계산 효율성과 수송해의 정확도를 증가시킴을 수치결과로 확인하였다.

• 한국연소학회:학술대회논문집
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• 한국연소학회 제26회 KOSCO SYMPOSIUM 논문집
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• pp.143-150
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• 2003

The synthesis gas generated in waste pyrolysis melting process which consists of pyrolysis of waste and melting process of ash is known to be an alternative fuel. Since the compositopn of synthesis gas is much different from other synthesis gases, the fundamental combustion characteristics are analyzed in this study. The radiation heat heat flux is used to estimate the heat flux from flames made by many combinations of fuel and oxidant supply. The results show that the synthesis gas needs much more amount of oxidant for equivalent heat flux to methane flame and the inverse diffusion flame type for synthesis gas burner is suitable for better radiation heat transfer.

• 한국전산유체공학회지
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• 제8권4호
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• pp.34-40
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• 2003

The effect of nose radius on aerodynamic heating is investigated by using the Navier-Stokes code extended to thermochemical nonequilibrium airflow, Spherical blunt bodies, whose nose radius varies from 0.O03048 m to 0.6096 m, flying at Mach 25 at an altitude of 53.34 km are considered. Comparison of heat flux at stagnation point with the solution of Viscous Shock Layer and Fay-Riddell are made. Results show that the flow for very small radius is in a nearly frozen state, and therefore the heat flux due to diffusion is smaller than that due to translational energy. As the radius becomes larger, the portion of heat flux by diffusion becomes greater than that of heat flux by translational temperature and approaches to a constant value.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2002년도 춘계 학술대회논문집
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• pp.109-114
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• 2002

The effect of nose radius on aerodynamic heating are investigated by using the Wavier-Stokes code extended to thermochemical nonequilibrium airflow. A spherical blunt body, whose radius varies from 0.003048 m to 0.6096 m, flying at Mach 25 at an altitude of 53.34 km is considered. Comparison of heat flux at stagnation point with the solution of Viscous Shock Layer and Fay-Riddell are made. Obtained result reveals that the flow chemistry for very small radius is nearly frozen, and therefore the contribution of heat flux due to chemical diffusion is smaller than that of translational energy. As the radius becomes larger, the portion of diffusion heat flux becomes greater than translational heat flux and approaches to a constant value.

• 한국초전도ㆍ저온공학회논문지
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• 제5권2호
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• pp.66-70
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• 2003

Transient magnetic diffusion process in a melt-cast Bi2Sr2CaCu20X(Bi-2212) tube was studied by experimental and numerical analyses. The transient diffusion partial differential equation is transformed into an ordinary differential equation by integral method. The penetration depth of magnetic field into a superconducting tube is obtained by solving the differential equation numerically. The results show that the penetration depth as a function of time which is somewhat different from the results by Bean's critical state model. The reason of the difference between the present results and that of Bean's model is discussed and compared in this paper. This experiment measure the magnetic flux density in the supercondutor after supply direct-current of Bi-2212 rounded by copper coil. This study was discussed of valid of a previous numerical solution which is compared by the penetrate time and the magnetic flux density difference of between the present results and the numerical solution.

• 천문학회보
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• 제45권1호
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• pp.70.3-70.3
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• 2020

Previous numerical simulations on planet-disk interactions revealed a lot of interesting phenomena including the planetary migration and the formation of many sub-structures inside the disks. However, these simulations were limited to an isothermal or adiabatic equation of state which does not account for various heating and cooling processes in the disks. Recent studies showed that the behavior of the planet-disk interaction can be significantly influenced by the disk thermodynamics. We develop a radiative diffusion module based on the two-temperature flux-limited diffusion approximation accounting for viscous heating and the accretion feedback. In this presentation, we describe our radiative diffusion solver, present some test results, and discuss potential applications of the module to planet-disk interactions,

• 한국안광학회지
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• 제8권2호
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• pp.1-11
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• 2003

확산에 관한 Fick 법칙 및 연속법칙을 사용하여 액체(눈물)-콘택트 렌즈-눈물 층을 통하여 각막으로 유입되는 산소 flux 및 각막 표면의 산소 분압을 계산할 수 있는 일련(一連)의 방정식을 세우고 이들 식에 의거하여 피팅에 따른 눈물 층의 두께, 콘택트 렌즈의 Dk 및 두께 변화가 각막에 유입되는 산소 flux에 어떠한 영향을 미치는가를 예측하였다. 본 모델을 사용하여 적절한 피팅 조건에 부합하고 또한 각막 표면의 산소 분압이 보장되는 콘택트 렌즈의 Dk 및 두께를 결정할 수 있다. 대단히 높은 Dk값을 지닌 콘택트 렌즈라도 너무 flat 또는 tight하게 피팅된 경우 콘택트 렌즈의 주변부와 각막 사이 눈물 층의 간격이 커짐으로 인하여 각막 주변부에 도달하는 산소 flux 및 각막 주변부 표면의 산소 분압이 급격히 감소하게 될 수 있다.