Postprocessing techniques for 3D non-linear structures

How graphics postprocessing techniques are currently used to examine the results of 3-D nonlinear analyses, some new techniques which take advantage of recent technology, and how these results relate to both the finite element model and its geometric parent are reviewed

The Applicability of the Distribution Coefficient, KD, Based on Non-Aggregated Particulate Samples from Lakes with Low Suspended Solids Concentrations

Separate phases of metal partitioning behaviour in freshwater lakes that receive varying degrees of atmospheric contamination and have low concentrations of suspended solids were investigated to determine the applicability of the distribution coefficient, KD. Concentrations of Pb, Ni, Co, Cu, Cd, Cr, Hg and Mn were determined using a combination of filtration methods, bulk sample collection and digestion and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). Phytoplankton biomass, suspended solids concentrations and the organic content of the sediment were also analysed. By distinguishing between the phytoplankton and (inorganic) lake sediment, transient variations in KD were observed. Suspended solids concentrations over the 6-month sampling campaign showed no correlation with the KD (n = 15 for each metal, p > 0.05) for Mn (r2 = 0.0063), Cu (r2 = 0.0002, Cr (r2 = 0.021), Ni (r2 = 0.0023), Cd (r2 = 0.00001), Co (r2 = 0.096), Hg (r2 = 0.116) or Pb (r2 = 0.164). The results implied that colloidal matter had less opportunity to increase the dissolved (filter passing) fraction, which inhibited the spurious lowering of KD. The findings conform to the increasingly documented theory that the use of KD in modelling may mask true information on metal partitioning behaviour. The root mean square error of prediction between the directly measured total metal concentrations and those modelled based on the separate phase fractions were ± 3.40, 0.06, 0.02, 0.03, 0.44, 484.31, 80.97 and 0.1 μg/L for Pb, Cd, Mn, Cu, Hg, Ni, Cr and Co respectively. The magnitude of error suggests that the separate phase models for Mn and Cu can be used in distribution or partitioning models for these metals in lake water

Integrated force method versus displacement method for finite element analysis

A novel formulation termed the integrated force method (IFM) has been developed in recent years for analyzing structures. In this method all the internal forces are taken as independent variables, and the system equilibrium equations (EE's) are integrated with the global compatibility conditions (CC's) to form the governing set of equations. In IFM the CC's are obtained from the strain formulation of St. Venant, and no choices of redundant load systems have to be made, in constrast to the standard force method (SFM). This property of IFM allows the generation of the governing equation to be automated straightforwardly, as it is in the popular stiffness method (SM). In this report IFM and SM are compared relative to the structure of their respective equations, their conditioning, required solution methods, overall computational requirements, and convergence properties as these factors influence the accuracy of the results. Overall, this new version of the force method produces more accurate results than the stiffness method for comparable computational cost

Design sensitivity analysis of boundary element substructures

The ability to reduce or condense a three-dimensional model exactly, and then iterate on this reduced size model representing the parts of the design that are allowed to change in an optimization loop is discussed. The discussion presents the results obtained from an ongoing research effort to exploit the concept of substructuring within the structural shape optimization context using a Boundary Element Analysis (BEA) formulation. The first part contains a formulation for the exact condensation of portions of the overall boundary element model designated as substructures. The use of reduced boundary element models in shape optimization requires that structural sensitivity analysis can be performed. A reduced sensitivity analysis formulation is then presented that allows for the calculation of structural response sensitivities of both the substructured (reduced) and unsubstructured parts of the model. It is shown that this approach produces significant computational economy in the design sensitivity analysis and reanalysis process by facilitating the block triangular factorization and forward reduction and backward substitution of smaller matrices. The implementatior of this formulation is discussed and timings and accuracies of representative test cases presented

Compatibility conditions of structural mechanics for finite element analysis

The equilibrium equations and the compatibility conditions are fundamental to the analyses of structures. However, anyone who undertakes even a cursory generic study of the compatibility conditions can discover, with little effort, that historically this facet of structural mechanics had not been adequately researched by the profession. Now the compatibility conditions (CC's) have been researched and are understood to a great extent. For finite element discretizations, the CC's are banded and can be divided into three distinct categories: (1) the interface CC's; (2) the cluster or field CC's; and (3) the external CC's. The generation of CC's requires the separating of a local region, then writing the deformation displacement relation (ddr) for the region, and finally, the eliminating of the displacements from the ddr. The procedure to generate all three types of CC's is presented and illustrated through examples of finite element models. The uniqueness of the CC's thus generated is shown

Cost effectiveness of treatments for wet age-related macular degeneration

Age-related macular degeneration (AMD) is a leading cause of blindness in people aged >= 50 years. Wet AMD in particular has a major impact on patient quality of life and imposes substantial burdens on healthcare systems. This systematic review examined the cost-effectiveness data for current therapeutic options for wet AMD. PubMed and EMBASE databases were searched for all articles reporting original cost-effectiveness analyses of wet AMD treatments. The Centre for Reviews and Dissemination and Cochrane Library databases were searched for all wet AMD health technology assessments (HTAs). Overall, 44 publications were evaluated in full and included in this review. A broad range of cost-effectiveness analyses were identified for the most commonly used therapies for wet AMD (pegaptanib, ranibizumab and photodynamic therapy [PDT] with verteporfin). Three studies evaluated the cost effectiveness of bevacizumab in wet AMD. A small number of analyses of other treatments, such as laser photocoagulation and antioxidant vitamins, were also found. Ranibizumab was consistently shown to be cost effective for wet AMD in comparison with all the approved wet AMD therapies (four of the five studies identified showed ranibizumab was cost effective vs usual care, PDT or pegaptanib); however, there was considerable variation in the methodology for cost-effectiveness modelling between studies. Findings from the HTAs supported those from the PubMed and EM BASE searches; of the seven HTAs that included ranibizumab, six (including HTAs for Australia, Canada and the UK) concluded that ranibizumab was cost effective for the treatment of wet AMD; most compared ranibizumab with PDT and/or pegaptanib. By contrast, HTAs at best generally recommended pegaptanib or PDT for restricted use in subsets of patients with wet AMD. In the literature analyses, pegaptanib was found to be cost effective versus usual/best supportive care (including PDT) or no treatment in one of five studies; the other four studies found pegaptanib was of borderline cost effectiveness depending on the stage of disease and time horizon. PDT was shown to be cost effective versus usual/best supportive care or no treatment in five of nine studies; two studies showed that PDT was of borderline cost effectiveness depending on baseline visual acuity, and two showed that PDT was not cost effective. We identified no robust studies that properly evaluated the cost effectiveness of bevacizumab in wet AMD

Kinetics and equilibria of ion-molecule association reactions : studied using temperature variable high pressure ion sources

Interest in termolecular association reactions of the type shown below, stems from their importance in the chemistry of planetary atmospheres, gas-cooled nuclear reactors and gas-phase cluster ions. This study is concerned with evaluating the rate constants of such X+ + X + M ------> X2+ + M k3 (1) reactions as both a function of temperature and of the third body M. The values of the third order rate constant k3 are expressed conventionally in terms of k3 = CT-m where T is the temperature and C and m are constants characteristic of the reaction which depend also on the nature of M. Literature now shows a general measure of agreement on values of C and m in several studies for which X=M, however, inconsistent values have been reported on the M=He system. This thesis describes an investigation of the two systems X=N2, CO and M= the reactant or a rare gas. Experiments were conducted in a conventional high pressure ion source and a pulsed drift ion source fitted to an updated Kratos MS9 mass spectrometer. Results obtained for the one component studies show good agreement with other literature values for the temperature dependence, m. In general, for both N2 and CO systems, He was found to have the same efficiency as the parent molecule as a third body at 300K, but the temperature dependence of k3 is markedly lower. Ar was found to behave very similarly to the parent molecule in both systems. For the CO system, although good agreement is found for the temperature dependence result with literature, there is still an uncertainty of about a factor of 2 in the room temperature values of k3

Performance of Major Flare Watches from the Max Millennium Program (2001-2010)

The physical processes that trigger solar flares are not well understood and significant debate remains around processes governing particle acceleration, energy partition, and particle and energy transport. Observations at high resolution in energy, time, and space are required in multiple energy ranges over the whole course of many flares in order to build an understanding of these processes. Obtaining high-quality, co-temporal data from ground- and space- based instruments is crucial to achieving this goal and was the primary motivation for starting the Max Millennium program and Major Flare Watch (MFW) alerts, aimed at coordinating observations of all flares >X1 GOES X-ray classification (including those partially occulted by the limb). We present a review of the performance of MFWs from 1 February 2001 to 31 May 2010, inclusive, that finds: (1) 220 MFWs were issued in 3,407 days considered (6.5% duty cycle), with these occurring in 32 uninterrupted periods that typically last 2-8 days; (2) 56% of flares >X1 were caught, occurring in 19% of MFW days; (3) MFW periods ended at suitable times, but substantial gain could have been achieved in percentage of flares caught if periods had started 24 h earlier; (4) MFWs successfully forecast X-class flares with a true skill statistic (TSS) verification metric score of 0.500, that is comparable to a categorical flare/no-flare interpretation of the NOAA Space Weather Prediction Centre probabilistic forecasts (TSS = 0.488).Comment: 19 pages, 2 figures, accepted for publication in Solar Physic