摘要:

AbstractIt has recently been argued that in planar geometry, P2theory is more accurate (but no more complex) than P1(diffusion) theory as an approximation to transport theory. This argument was based upon analytic comparisons as well as results from numerical test problems. On the analytic side, the P2fundamental decay length is more accurate than the corresponding P1decay length. One of the purposes of this paper is to show that the P2expansion is, in fact, the optimal choice taken from a large family of expansions in predicting this decay length. Further, P2theory exhibits scalar flux discontinuities at material interfaces, which can be considered as accounting for internal transport boundary layers. By contrast, the P1scalar flux is everywhere continuous. The main purpose of this paper is to present an entire family of diffusion equations that contain flux discontinuities at material interfaces All members of this family predict the exact transport fundamental decay length (the discrete Case eigenvalue). One preferred member of this family is shown to be exceedingly accurate in predicting various transport theory behavior for homogeneous source-free problems. The formalism used to derive these diffusion theories is the variational calculus, including boundary considerations that lead to the diffusive boundary conditions.

ISSN:0029-5639    

DOI:10.13182/NSE94-A19018

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractThe exponential characteristic spatial quadrature for discrete ordinates neutral particle transport in slab geometry is derived and compared with current methods. It is similar to the linear characteristic (or, in slab geometry, the linear nodal) quadrature but differs by assuming an exponential distribution of the scattering source within each cell, S(x) = a exp(bx), whose parameters are root-solved to match the known (from the previous iteration) average and first moment of the source over the cell. Like the linear adaptive method, the exponential characteristic method is positive and nonlinear but more accurate and more readily extended to other cell shapes. The nonlinearity has not interfered with convergence. We introduce the“exponential moment functions,”a generalization of the functions used by Walters in the linear nodal method, and use them to avoid numerical ill-conditioning. The method exhibits O(Δx4) truncation error on fine enough meshes; the error is insensitive to mesh size for coarse meshes. In a shielding problem, it is accurate to 10% using 16-mfp-thick cells; conventional methods err by 8 to 15 orders of magnitude. The exponential characteristic method is computationally more costly per cell than current methods but can be accurate with very thick cells, leading to increased computational efficiency on appropriate problems.

ISSN:0029-5639    

DOI:10.13182/NSE94-A19019

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractThe solution to the searchlight problem for monoenergetic neutrons in a semi-infinite medium with isotropic scattering illuminated at the free surface is obtained through the numerical evaluation of an analytical expression for the scalar flux at various positions within the medium. The sources considered are normally incident pencil beam and isotropic point sources as well as a longitudinal uniformly distributed source. The analytic solution is effected by a recently developed numerical inversion technique applied to the Fourier-Bessel transform. The transform inversion results from the solution method of Rybicki, where the two-dimensional problem is solved by casting it as a variant of a one-dimensional problem. The numerical inversion results in a highly accurate solution. Comparisons of the analytic solution with results from Monte Carlo (MCNP) and discrete ordinates transport codes (DORT, TWODANT, and SMARTEPANTS) show excellent agreement. These comparisons, which are free from any associated data or cross-section set dependencies, provide significant evidence of the proper operation of the transport codes tested.

ISSN:0029-5639    

DOI:10.13182/NSE94-A19020

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractThis research is motivated by the need to relax the strict boundary of numeric-based signal validation. To this end, the use of fuzzy logic for redundant sensor validation is introduced. Since signal validation employs both numbers and qualitative statements, fuzzy logic provides a pathway for transforming human abstractions into the numerical domain and thus coupling both sources of information. With this transformation, linguistically expressed analysis principles can be coded into a classification rule-base for signal failure detection and identification.

ISSN:0029-5639    

DOI:10.13182/NSE94-A19021

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

ISSN:0029-5639    

DOI:10.13182/NSE94-A19022

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor