• 제목/요약/키워드: well diffusion

검색결과 1,349건 처리시간 0.031초

A new approach for calculation of the neutron noise of power reactor based on Telegrapher's theory: Theoretical and comparison study between Telegrapher's and diffusion noise

  • Bahrami, Mona;Vosoughi, Naser
    • Nuclear Engineering and Technology
    • /
    • 제52권4호
    • /
    • pp.681-688
    • /
    • 2020
  • The telegrapher's theory was used to develop a new formulation for the neutron noise equation. Telegrapher's equation is supposed to demonstrate a more realistic approximation for neutron transport phenomena, especially in comparison to the diffusion theory. The physics behind such equation implies that the signal propagation speed is finite, instead of the infinite as in the case of ordinary diffusion. This paper presents the theory and results of the development of a new method for calculation of the neutron noise using the telegrapher's equation as its basis. In order to investigate the differences and strengths of the new method against the diffusion based neutron noise, a comparison was done between the behaviors of two methods. The neutron noise based on SN transport considered as a precision measuring point. The Green's function technique was used to calculate the neutron noise based on telegrapher's and diffusion methods as well as the transport. The amplitude and phase of Green's function associated with the properties of the medium and frequency of the noise source were obtained and their behavior was compared to the results of the transport. It was observed, the differences in some cases might be considerable. The effective speed of propagation for the noise perturbations were evaluated accordingly, resulting in considerable deviations in some cases.

전개확산제트화염과 정체점 확산화염과의 유사성 (Similarity between a stagnant point diffusion flame and an evolving jet diffusion flame)

  • 박정;신현동
    • 대한기계학회논문집B
    • /
    • 제21권4호
    • /
    • pp.494-502
    • /
    • 1997
  • Experiments on corresponding jet flames with stagnant point diffusion flames have been carried out in initial injection periods. A compensated measurement of maximum flame temperature, which is based on the ion signal, has been employed to inspect flame responses to time-varying strain rates. The flame responses are obtained at two conditions for the slowly time-varying strain rate and the case of flame extinction, and analyzed to confirm similarity between a stagnant point diffusion flame and an evolving jet diffusion flame. Nonsteady effects are addressed via the comparison between several time scales. The time variation with low strain rates, in which illustrates the flame behavior of the upper branch far from extinction in the well-known S-curve, is confirmed to produce a quasi-steady flame response through the nonsteady experiments. The time variation with strain rates in the case of flame extinction indicates an unsteady effect of flame response. It is therefore found that the flame responses near jet tip depend on time histories of characterized strain rates in the developing process.

THERMAL CONDUCTION IN MAGNETIZED TURBULENT GAS

  • CHO JUNGYEON;LAZARIAN A.
    • 천문학회지
    • /
    • 제37권5호
    • /
    • pp.557-562
    • /
    • 2004
  • We discuss diffusion of particles in turbulent flows. In hydrodynamic turbulence, it is well known that distance between two particles imbedded in a turbulent flow exhibits a random walk behavior. The corresponding diffusion coefficient is ${\~}$ ${\upsilon}_{inj}{\iota}_{turb}$, where ${\upsilon}_{inj}$ is the amplitude of the turbulent velocity and ${\iota}_{turb}$ is the scale of the turbulent motions. It Is not clear whether or not we can use a similar expression for magnetohydrodynamic turbulence. However, numerical simulations show that mixing motions perpendicular to the local magnetic field are, up to high degree, hydrodynamical. This suggests that turbulent heat transport in magnetized turbulent fluid should be similar to that in non-magnetized one, which should have a diffusion coefficient ${\upsilon}_{inj}{\iota}_{turb}$. We review numerical simulations that support this conclusion. The application of this idea to thermal conductivity in clusters of galaxies shows that this mechanism may dominate the diffusion of heat and may be efficient enough to prevent cooling flow formation when turbulence is vigorous.

나노구조재료의 소성변형 성질의 변형률속도 의존성 (Strain Rate Dependence of Plastic Deformation Properties of Nanostructured Materials)

  • 윤승채;김형섭
    • 소성∙가공
    • /
    • 제14권1호
    • /
    • pp.65-70
    • /
    • 2005
  • A phase mixture model was employed to simulate the deformation behaviour of metallic materials covering a wide grain size range from micrometer to nanometer scale. In this model a polycrystalline material is treated as a mixture of two phases: grain interior phase whose plastic deformation is governed by dislocation and diffusion mechanisms and grain boundary 'phase' whose plastic flow is controlled by a boundary diffusion mechanism. The main target of this study was the effect of grain size on stress and its strain rate sensitivity as well as on the strain hardening. Conventional Hall-Petch behaviour in coarse grained materials at high strain rates governed by the dislocation glide mechanism was shown to be replaced with inverse Hall-Petch behaviour in ultrafine grained materials at low strain rates, when both phases deform predominantly by diffusion controlled mechanisms. The model predictions are illustrated by examples from literature.

A reaction-diffusion modeling of carbonation process in self-compacting concrete

  • Fu, Chuanqing;Ye, Hailong;Jin, Xianyu;Jin, Nanguo;Gong, Lingli
    • Computers and Concrete
    • /
    • 제15권5호
    • /
    • pp.847-864
    • /
    • 2015
  • In this paper, a reaction-diffusion model of carbonation process in self-compacting concrete (SCC) was realized with a consideration of multi-field couplings. Various effects from environmental conditions, e.g. ambient temperature, relative humidity, carbonation reaction, were incorporated into a numerical simulation proposed by ANSYS. In addition, the carbonation process of SCC was experimentally investigated and compared with a conventionally vibrated concrete (CVC). It is found that SCC has a higher carbonation resistance than CVC with a comparable compressive strength. The numerical solution analysis agrees well with the test results, indicating that the proposed model is appropriate to calculate and predict the carbonation process in SCC. The parameters sensitivity analysis also shows that the carbon dioxide diffusion coefficient and moisture field are essentially crucial to the carbonation process in SCC.

On the Effect of Presumed PDF and Intermittency on the Numerical Simulation of a Diffusion Flame

  • Riechelmann, Dirk;Fujimori, Toshiro
    • 한국연소학회지
    • /
    • 제6권2호
    • /
    • pp.23-28
    • /
    • 2001
  • In the present work, the effect of PDF selection and intermittency on the result of the numerical simulation are examined by the simulation of a turbulent methane-air jet diffusion flame. As to the PDFs, beta-function and clipped Gaussian are considered. Results for the pure mixing jet are compared with experimental results. Then, the turbulent flame is calculated for the same conditions and the results obtained for the several models are compared. It is found that the clipped Gaussian distribution coupled with consideration of intermittency recovers the experimental data very well. As to the reacting flow results, the main overall properties of the turbulent jet diffusion flame such as maximum flame temperature are less affected by the choice of the PDF. Flame height and NO emissions, on the contrary, appear to be significantly influenced.

  • PDF

Mechanisms of sulfate ionic diffusion in porous cement based composites

  • Gospodinov, P.;Mironova, M.;Kazandjiev, R.
    • Computers and Concrete
    • /
    • 제4권4호
    • /
    • pp.273-284
    • /
    • 2007
  • The paper considers a theoretical model for the study of the process of transfer of sulfate ions in saturated porous media - mineral composites. In its turn, the model treats diffusion of sulfate ions into cement based composites, accounting for simultaneous effects such as filling of micro-capillaries with ions and chemical products and liquid push out of them. The proposed numerical algorithm enables one to account for those simultaneous effects, as well as to model the diffusive behavior of separate sections of the considered volume, such as inert fillers. The cases studied illustrate the capabilities of the proposed model and those of the algorithm developed to study diffusion, considering the specimen complex configuration. Computations show that the theoretical assumptions enable one to qualitatively estimate the experimental evidence and the capabilities of the studied composite. The results found can be used to both assess the sulfate corrosion in saturated systems and predict and estimate damage of structures built of cement-based mineral composites.

침적시험에 의한 콘크리트의 염소이온 확산계수 평가 (A Study on the Chloride Ion Diffusion Coefficient of Concrete by Submergence in Salt Water)

  • 김동석;양승규;정연식;유재상;이종열;본간건일
    • 한국콘크리트학회:학술대회논문집
    • /
    • 한국콘크리트학회 2003년도 가을 학술발표회 논문집
    • /
    • pp.297-300
    • /
    • 2003
  • A chloride is an important deteriorating factor which governs the durability of the reinforced-concrete structures under marine environments. Also, the main penetration mechanism of chloride ion into concrete is a diffusion phenomenon. In this study, It is evaluated the diffusion coefficient of chloride ion in non-steady state by Fick's second law. Submergence method in salt water carried out in this experiment. Two types of cement which is different in mineral composition were used. In addition, the effect of mineral admixtures of blast-furnace slag and meta-kaolin was studied. In conclusion, the diffusion coefficient of chloride ion is much affected according to cement type and mineral admixtures, also, it is proved that meta-kaolin as well as blast-furnace slag is effective in preventing penetration of chloride ion.

  • PDF

인터넷 패션정보 확산에서 네트워크 특성의 영향에 관한 연구 (A Study on the Influences of Network Features on the Diffusion of Internet Fashion Information)

  • 송기은;황선진
    • 복식
    • /
    • 제63권2호
    • /
    • pp.1-13
    • /
    • 2013
  • The purpose of this study is to examine how the features of network in the Internet fashion community affect the diffusion of fashion information to members in the online community with other variables (informative features, consumer features). Communities that actively exchange fashion information among their members were selected for the social network analysis and hypothesis verification. As a result, we found that a few information activists influenced most of the information receivers in the network features of fashion communities. Also, we found that the informative features (usefulness, reliability), consumer features (NFC, innovation) as well as the network features (connectivity, power), have a significant influence on the diffusion of Internet fashion information which verified the importance of the network features in the study on the Internet.

Kinetic Monte Carlo 시뮬레이션을 이용한 흡착 원자의 확산 계수 결정 (A method for determination of diffusion parameters of adatoms using kinetic monte calo simulation)

    • 한국진공학회지
    • /
    • 제9권4호
    • /
    • pp.419-427
    • /
    • 2000
  • 본 연구는 원자의 주변 환경에 따른 각각의 확산 속도를 구할 수 있는 기구를 제시하였다. STM 또는 HRLEED 등의 실험과 kinetic Monte Carlo(KMC) 시뮬레이션 계산과의 비교를 통하여 테라스 위 흡착 원자의 확산장벽, step 끝 부착 원자의 탈착 확산 장벽, 잘 알려진 Schwoebel 장벽을 포함한 각각의 확산 장벽을 구할 수 있었다. 팔-넓이, 군집 밀도, 거칠기 등이 시뮬레이션 계산과 실험 결과를 비교하는 데에 가장 적절한 원자단위의 구조변수들임을 확인하였고, 특히 아직 잘 사용되지 않은 구조 계수인 가지폭이 확산 장벽을 구별하여 구하는 데에 중요한 역할을 하는 것을 확인하였다.

  • PDF