Analysis of a Nuclear Reactor Boilure Closure Unit Through Development of a 3D Parallel Finite Element Code

Three dimensional (3D) finite element analysis (FEA) allows the mechanical integrity of complex structures to be estimated with some confidence. This research is concerned with extending an existing parallel FEA code. This code has been run on up to 16 processors on Durham University’s high performance computing (HPC) cluster and two different parallel linear solvers have been compared. A key feature of the work has been to develop tools for structural analyses. An automatic mesh refinement program has been written, the Zienkiewicz and Zhu error estimator has been coded for 3D hexahedral meshes and post processing techniques have been used to calculate and visualise principal stress data and peak stress criteria. This project also reports on three peak stress envelopes used to assess the condition of a concrete sub-structure. The development of this parallel code has enabled the deformation behaviour of a key component of a nuclear rector vessel to be determined. The BCU is a prestressed cylindrical concrete vessel (depth of 1.73m and diameter of 3.37m) sealing the top of a boilers housed within the walls of the reactor. In recent years possible problems have been identified at the Hartlepool and Heysham I Advance Gas-Cooled nuclear reactors (AGR) with respect to the structural condition of the BCU (in particular the condition of the prestressed circumferential wires designed to maintain the BCU in a state of compression). This problem provides an interesting case study for this project. Four different BCU meshes have been used containing either 40201 or 321608 elements (the elements are either 8 or 20-noded hexahedral elements). Three different load cases have been used to model the BCU. The results of the analyses confirm that the circumferential pre-stressing is vital in order to keep the BCU is a state of compression and operating under safe working conditions. These results have been confirmed using principal stress plots and three different peak stress envelopes. The results show that when the pre-stressing is released approximately one quarter of the elements contain stresses at Gauss points which exceed the peak strength of the concrete. This suggests that under these extreme conditions the BCU’s structural integrity has been severely compromised, concrete rupture is possible and the nuclear reactor is no-longer safe to operate

ArticleRank: a PageRank-based alternative to numbers of citations for analysing citation networks

Purpose - The purpose of this paper is to suggest an alternative to the widely used Times Cited criterion for analysing citation networks. The approach involves taking account of the natures of the papers that cite a given paper, so as to differentiate between papers that attract the same number of citations. Design/methodology/approach - ArticleRank is an algorithm that has been derived from Google's PageRank algorithm to measure the influence of journal articles. ArticleRank is applied to two datasets - a citation network based on an early paper on webometrics, and a self-citation network based on the 19 most cited papers in the Journal of Documentation - using citation data taken from the Web of Knowledge database. Findings - ArticleRank values provide a different ranking of a set of papers from that provided by the corresponding Times Cited values, and overcomes the inability of the latter to differentiate between papers with the same numbers of citations. The difference in rankings between Times Cited and ArticleRank is greatest for the most heavily cited articles in a dataset. Originality/value - This is a novel application of the PageRank algorithm

A Finite State Constraint Grammar Parser

Proceedings of the NODALIDA 2011 Workshop Constraint Grammar Applications. Editors: Eckhard Bick, Kristin Hagen, Kaili Müürisep, Trond Trosterud. NEALT Proceedings Series, Vol. 14 (2011), 35–40. © 2011 The editors and contributors. Published by Northern European Association for Language Technology (NEALT) http://omilia.uio.no/nealt . Electronically published at Tartu University Library (Estonia) http://hdl.handle.net/10062/19231

Average structures of the disordered β-phase of Pigment Red 170: a single-crystal X-ray diffraction study

The [beta]-phase of the industrially important Pigment Red 170 ([beta]-P.R. 170) has a structure with severe layer stacking disorder. The single-crystal X-ray diffraction pattern consists of a difficult-to-disentangle mix of Bragg diffraction superimposed on rods of diffuse scattering which impede the estimation of accurate Bragg intensities. Two average monoclinic structure models with the same unit-cell dimensions, but different extents of disorder in the layers and different space groups seem plausible, one with the non-conventional space group setting B21/g (No. 14, Z' = 2) and one in P21/a (No. 14, Z' = 4). Disordered molecules related by a translation of 0.158b are present in all layers of the B21/g model and in every second layer of the P21/a model. Layer-to-layer contacts are practically the same in both models. According to order-disorder theory, both models are valid superposition structures. Structure-factor calculations show that the pattern of strong and weak Bragg reflections is very similar for the two models. R factors indicate that the B21/g model is the most economic representation of the average structure. However, given the limitations in data processing, the P21/a model should not be discarded and further insight sought from a detailed analysis of the experimental diffuse scattering. The difficulties encountered in this analysis raise the question of whether or not the concept of an average structure is applicable in practice to [beta]-P.R. 170

Users guide: Steady-state aerodynamic-loads program for shuttle TPS tiles

A user's guide for the computer program that calculates the steady-state aerodynamic loads on the Shuttle thermal-protection tiles is presented. The main element in the program is the MITAS-II, Martin Marietta Interactive Thermal Analysis System. The MITAS-II is used to calculate the mass flow in a nine-tile model designed to simulate conditions duing a Shuttle flight. The procedures used to execute the program using the MITAS-II software are described. A list of the necessry software and data files along with a brief description of their functions is given. The format of the data file containing the surface pressure data is specified. The interpolation techniques used to calculate the pressure profile over the tile matrix are briefly described. In addition, the output from a sample run is explained. The actual output and the procedure file used to execute the program at NASA Langley Research Center on a CDC CYBER-175 are provided in the appendices