Experimental validation of flow and tracer-dispersion models in a four-strand billet-casting tundish

An exhaustive literature search indicates that, despite a large number of physical and mathematical model studies, very little efforts have been made to assess predicted flow and turbulence parameters in the tundish directly against equivalent experimental measurements until recently. Consequently, experimental measurements on the instantaneous velocity and residence-time distribution (RTD) were carried out in a scaled water model of a four-strand billet-casting tundish. While particle-image velocimetry (PIV) was applied to measure instantaneous flow, the electrical-conductivity measurement technique was applied to determine the RTD. Through PIV, the mean and the fluctuating components were derived along the central vertical plane of the tundish at two different liquid inflow rates: 1.55×10^?4 m³/s and 3.10×10^?4 m³/s, respectively. Similarly, RTD curves were obtained for tundish operations without and with a dam+turbulence inhibitor device (TID). Parallel to these operations, the flow and tracer dispersion were numerically predicted by FLUENT®. It is shown that the predicted time-average velocity components within the bath bear excellent correspondence with PIV measurements. On the assumption of isotropic fluctuations, turbulent kinetic energy was derived from experimental measurements, which agreed moderately with predictions. Furthermore, the experimentally derived fluctuating velocity components were compared with those obtained from the Reynolds stress model. This indicated very reasonable agreement between measurement and predictions (within ±20 pct). Despite such a difference, however, the extent of agreement between the measured and computed C curves was found to be excellent.     

Fuzzy Logic Based Group Maturity Rating for Software Performance Prediction

Driven by market requirements,software services organizations have adopted various software engineering process models (such as capability maturity model (CMM),capability maturity model integration (CMMI),ISO 9001:2000,etc.) and practice of the project management concepts defined in the project management body of knowledge.While this has definitely helped organizations to bring some methods into the software development madness,there always exists a demand for comparing various groups within the organization in terms of the practice of these defined process models.Even though there exist many metrics for comparison,considering the variety of projects in terms of technology,life cycle,etc.,finding a single metric that caters to this is a difficult task.This paper proposes a model for arriving at a rating on group maturity within the organization.Considering the linguistic or imprecise and uncertain nature of software measurements,fuzzy logic approach is used for the proposed model.Without the barriers like technology or life cycle difference,the proposed model helps the organization to compare different groups within it with reasonable precision.     

Experimental Investigation of Shear Capacity of Precast Reinforced Concrete Box Culverts

This study presents an experimental program to investigate the shear capacity of precast reinforced concrete box culverts. Each culvert was subjected to monotonically increasing load through a 254?mm×508?mm (10?in.×20?in.) load plate in order to simulate the HS20 truckload per AASHTO 2005. Instrumentation included strain gauges, high-resolution laser deflection sensor, and automated data acquisition. Four tests were conducted on 1.22?m×1.22?m×1.22?m (4?ft×4?ft×4?ft) box culverts. The location of the load plate was varied to identify the position, which introduces the maximum shear stresses. Laser sensor data and dial gauge readings were recorded to measure the deflection profile of the box culvert. Strain gauges were placed on the steel reinforcement to measure axial strain at locations of maximum positive and negative bending moments. The test results include reporting the loads at which each crack initiated and propagated. The displacement profile of the top slab from the laser instrumentation output along with the load versus maximum deflection for each culvert is also reported.     

‘Green’ composites Part 2: Characterization of flax yarn and glutaraldehyde/poly(vinyl alcohol) modified soy protein concentrate composites

In the present research, soy protein concentrate (SPC) was modified using glutaraldehyde (GA) and polyvinyl alcohol (PVA). The modified resin allowed to process soy protein polymer without any plasticizer. The modified resin also showed increased tensile properties, improved thermal stability and reduced moisture resistance as compared to SPC resin. Besides the tensile and thermal properties, modified SPC resin was also characterized for its dynamic mechanical properties. Unidirectional composites were fabricated using modified SPC and flax yarn. Composite specimens, approximately 1 mm thick, were prepared in both longitudinal and transverse directions. The composite specimens were characterized for their tensile and flexural properties. The fracture surface of the composite was also analyzed in both longitudinal and transverse directions. These composite specimens exhibited a fracture stress of 126 MPa and 2.24 GPa, respectively, in the longitudinal directions. The composite properties were also predicted using the rule of mixture in longitudinal direction. It was observed that the experimental values are lower than the predicted values for a variety of reasons.     

A comparative analysis of genetic algorithms and directed grid search for parametric optimization

In this paper, a comparative analysis of the performance of the Genetic Algorithm (GA) and Directed Grid Search (DGS) methods for optimal parametric design is presented. A genetic algorithm is a guided random search mechanism based on the principle of natural selection and population genetics. The Directed Grid Search method uses a selective directed search of grid points in the direction of descent to find the minimum of a real function, when the initial estimate of the location of the minimum and the bounds of the design variables are specified. An experimental comparison and a discussion on the performance of these two methods in solving a set of eight test functions is presented.     

Structure-property relationship in sol-gel derived polymer/silica hybrid nanocomposites prepared at various pH

This paper reports a comparative study on structure-property relationship of acrylic rubber (ACM)/silica, epoxidised natural rubber (ENR)/silica and poly (vinyl alcohol) (PVA)/silica hybrid nanocomposites prepared by sol-gel technique under different pH levels (pH = 1.0–13.0), probably for the first time. The initial concentration of tetraethoxysilane (TEOS) (used as the precursor for silica) was kept at 45 wt%, and tetrahydrofuran (THF) for ACM/silica and ENR/silica while water for PVA/silica were taken as solvents. TEOS to water mole ratio was maintained at 1:2 for the rubber/silica systems to accomplish the sol-gel reaction. The structure of the resultant hybrid composites was determined by using electron microscopy, Fourier Transform infrared spectroscopy and solubility. Dynamic mechanical and mechanical properties were also investigated. The silica particles were found to exist as nanoparticles (average diameter <100 nm) at low pH (≤ 2.0) beyond which these aggregate, although the amount of silica generation was not strictly influenced by the various pH conditions in all the systems. These nanocomposites were optically clear and showed superior mechanical reinforcement over the micro-composites containing aggregated silica structures with lower optical clarity. The nanocomposites exhibited higher storage modulus both at the glassy and the rubbery regions as compared to those micro-composites. The loss tangent peak heights were also minimum and the Tg shifted to higher temperature for those nanocomposites. The maximum improvement of mechanical properties was observed with the PVA/silica nanocomposites due to higher level of interaction between the hydroxyl groups of PVA and the silanol groups of the silica phase.     

Thermal performance of plastic film solar air and water heaters

The results of measurements on a few solar air and water heaters of the same design, but made from different plastic materials, are reported for different climatic conditions. The experiments on the systems were made over a long time period, first in Germany in 1982 and then in India in 1984. An economic evaluation shows that the use of such collectors can bring down the cost of solar energy in the desired economic scale. Despite the drawback of UV degradation of plastic material resulting in shorter lifetime, the low initial investment cost keeps the cost of useful energy also low.     

On the displacement formulation of torsion of shafts with rectangular cross-sections

The use of warping displacement functions for the torsional stiffness representation of beams with rectangular cross-sections is studied. These functions can directly be employed in the displacement-based formulation of Hermitian and isoparametric three-dimensional beam elements for linear, elastic-plastic or large displacement/large rotation analysis. the results of some studies are given to demonstrate the applicability and use of the proposed functions.     

A rule-based availability-driven cosynthesis scheme

The co-synthesis of hardware–software systems for complex embedded applications has been studied extensively with focus on various qualitative system objectives such as high speed performance and low power dissipation. One of the main challenges in the construction of multiprocessor systems for complex real time applications is provide high levels of system availability that satisfies the users’ expectations. Even though the area of hardware software cosynthesis has been studied extensively in the recent past, the issues that specifically relate to design exploration for highly available architectures need to be addressed more systematically and in a manner that supports active user participation. In this paper, we propose a user-centric co-synthesis mechanism for generating gracefully degrading, heterogeneous multiprocessor architectures that fulfills the dual objectives of achieving real-time performance as well as ensuring high levels of system availability at acceptable cost. A flexible interface allows the user to specify rules that effectively capture the users’ perceived availability expectations under different working conditions. We propose an algorithm to map these user requirements to the importance attached to the subset of services provided during any functional state. The system availability is evaluated on the basis of these user-driven importance values and a CTMC model of the underlying fail-repair process. We employ a stochastic timing model in which all the relevant performance parameters such as task execution times, data arrival times and data communication times are taken to be random variables. A stochastic scheduling algorithm assigns start and completion time distributions to tasks. A hierarchical genetic algorithm optimizes the selections of resources, i.e. processors and busses, and the task allocations. We report the results of a number of experiments performed with representative task graphs. Analysis shows that the co-synthesis tool we have developed is effectively driven by the user’s availability requirements as well as by the topological characteristics of the task graph to yield high quality architectures. We experimentally demonstrate the edge provided by a stochastic timing model in terms of performance assessment, resource utilization, system-availability and cost. An erratum to this article is available at .     

Effect of polymer–clay interaction on solvent transport behavior of fluoroelastomer–clay nanocomposites and prediction of aspect ratio of nanoclay

Diffusion and sorption of methyl ethyl ketone and tetrahydrofuran through fluoroelastomer‐clay nanocomposites were investigated in the temperature range of 30–60°C by swelling experiments. Slightly non‐Fickian transport behavior was found for these nanocomposites, having variation of type of nanoclay and loading. Different transport parameters depend on the size and shape of the penetrant molecules. The results were used to study the effect of nanoclay on the solvent transport‐properties of nanocomposites and their interactions with solvents. The diffusion coefficient of methyl ethyl ketone at 30°C for neat rubber was 1.43 × 10^?8 cm² s^?1, while those of the unmodified and the modified clay filled samples at 4 phr loading were 0.24 × 10^?8 and 0.50 × 10^?8 cm² s^?1, respectively. At 8 and 16 phr loading of the unmodified clay, it was found to be 0.44 × 10^?8 and 0.64 × 10^?8 cm² s^?1, respectively. The samples were also reswelled after deswelling. Surprisingly, transport behavior became Fickian on reswelling. Interestingly, ratio of diffusion coefficients of the filled system to the neat system was found to be almost same for the first time swelling and reswelling experiments. The results showed that better polymer‐clay interaction in the case of the unmodified‐clay filled nanocomposites is responsible for enhanced solvent‐resistance property. From the permeation data, for the first time, aspect ratio of nanoclays in different composites was calculated and found to have good correlation with the morphology data obtained from transmission electron microscopy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007