Parallel fem algorithms based on recursive spatial decomposition—I. Automatic mesh generation

This paper discusses an automatic meshing scheme that is suitable for parallel processing. Meshes derived from solid models through recursive spatial decompositions inherit the hierarchical organization and the spatial addressability of the underlying grid. These two properties are exploited to design a meshing algorithm capable of operating in parallel (concurrent) processing environments. The concept of a meshing operator for parallel processing is defined and algorithms for various stages of the automatic meshing scheme are presented. A systematic simulation of fine- and coarse-grain parallel configurations is used to evaluate the performance of the meshing scheme. A companion paper focuses on parallel processing for the analysis of these automatically derived meshes via hierarchical substructuring.     

Heat transfer and gas holdup studies in a bubble column: Air-water-sand system

Air-holdup and heat transfer coefficient data are reported for the air-water and air-water-sand system as a function of air velocity in the temperature range 297-343 K as measured in a 0.305 m diameter bubble column operating in semi-batch mode and equipped with either a five- or seven-tube bundle. A 65 μm average size sand powder is used at concentrations of 5 and 10 mass percent in the slurry. Available correlations of gas holdup and heat transfer coefficients are examined on the basis of these data. These are found inappropriate and inadequate for representing these experimental data. Gas holdup data are well represented by an approach based on Nicklin's (1962) work, and heat transfer data are adequately represented by a simple semi-empirical expression. Accurate experimental data on additional systems are needed to develop a reliable heat transfer theory particularly for process representation at temperatures higher than ambient.     

Predicting the life of high-temperature structural components in power plants

The concept of time-dependent fracture mechanics has been used to develop the quantitative life-prediction methodology and inspection criteria for high-temperature structural components. As an example, the methodology was applied to steam pipes. Leak-before-break analyses were utilized to determine the flaw inspection criteria of steam pipes. Both static and cyclic loading conditions were included in the life-prediction analyses. Increasing the frequency of shutdowns was found to decrease the remaining life. The effects of operating pressures and temperatures and material properties on the life of steam pipes were quantified.     

Dependence of Heat-Transfer coefficient for immersed surfaces in a gas-fluidized bed on pressure

The correlations and theories developed for the prediction of heat-transfer coefficients for immersed surfaces in fluidized beds are examined for their applicability and appropriateness at different pressures. It is found that the pressure dependence of minimum fluidization velocity and heat-transfer coefficient for ‘small’ and ‘large’ particle systems can be reconciled with an adequate interpretation of available correlations and model expressions on the basis of a recently proposed particle classification scheme. The latter utilizes the concept of Archimedes number to provide a particle classification scheme which interprets particles into different categories, keeping both hydrodynamic and thermal behaviors of the bed consistent with each other at the same time. Good agreement of the available experimental data with appropriate theories is demonstrated.     

Characterization of creep-fatigue crack growth behavior in 2.25 Cr-1 Mo steel using (C t)avg

Time-dependent creep-fatigue crack growth (CFCG) is an important consideration in the design and remaining life estimation of high temperature components. CFCG tests were carried out on compact type (CT) specimens of 2.25 Cr-1.0 Mo steel and its behavior, for hold times ranging from 10 seconds to 50 seconds, at 594°C (1100°F) was characterized using the average value of the C _t-parameter, (C _t)_avg. The trends in the creep-crack growth (CCG) data for this material are also compared with the CFCG data. The analytically estimated values of (C _t)_avg are compared with the experimental values of (C _t)_avg obtained from the measured values of load-line deflection rates. It is also shown that even in the absence of accurate creep deformation constants, accurate estimates of the measured values of (C _t)_avg can be obtained in CT specimens     

Hypertensive disorders of pregnancy and maternal and foetal outcome: a case controlled study

A case controlled prospective study of 250 cases of hypertension complicating pregnancy (study group) and 400 normal pregnant women (control group) was carried out to determine the effect of hypertension on maternal and foetal outcome. Pregnancy induced hypertension was present in 96% cases and chronic hypertension in 4% cases. Preterm delivery (28.8% versus 3%), labour induction rate (52.8% versus 3.25%), caesarean section rate (14.8% versus 3.5%), stillbirth rate (4.8% versus 0.25%) and overall perinatal mortality rate (14.8% versus 1%) were higher in study group compared to controls. In study group (40%) babies required special nursery care compared to controls (6.75%). From these results it can be concluded that maternal hypertension is associated with adverse pregnancy outcome.     

The relationship between microstructure and the J-R curve

A model is presented that establishes a quantitative relationship between the J _IC and the J-R curve and the microstructural parameters, such as inclusion size and spacing, and the plastic deformation properties of ductile materials, such as yield strength and strain hardening exponents. The model assumes that ductile crack growth occurs by void nucleation, growth, and coalescence. Each of these processes is modeled in the crack tip environment to complete the model. The proposed model is evaluated using tests performed on 303 stainless steel (SS) at room temperature and on 1Cr-Mo-0.25V steel at 565 °C. Satisfactory agreements are obtained between the experimentally obtained J-R curves and those predicted from the model. Limitations of the model are also discussed.