An integrated approach for modelling the tensile behaviour of steel fibre reinforced self-compacting concrete

The present work resumes the experimental and numerical research carried out for the development of a numerical tool able of simulating the tensile behaviour of steel fibre reinforced self-compacting concrete (SFRSCC). SFRSCC is assumed as a two phase material, where the nonlinear material behaviour of SCC matrix is modelled by a 3D smeared crack model, and steel fibres are assumed as embedded short cables distributed within the SCC matrix according to a Monte Carlo method. The internal forces in the steel fibres are obtained from the stress–slip laws derived from the executed fibre pullout tests. The performance of this numerical strategy was appraised by simulating the tensile tests carried out. The numerical simulations showed a good agreement with the experimental results.     

An experimental approach for the analysis of early-age behaviour of high-performance concrete structures under restrained shrinkage

This paper presents a systematic approach for the experimental testing and analysis of the early-age thermo-mechanical behaviour of large prismatic high-performance concrete specimens under restrained autogenous shrinkage and realistic temperature conditions. The loading system can apply a partial degree of restraint in order to enable the characterisation of high-performance concrete specimens without premature termination of the test in case of significant restrained shrinkage. The instrumentation system can measure the strains and other parameters from the setting time with high accuracy and reliability. The analysis method takes into account the temperature effects on the measured properties and provides equations to determine the time-evolution of shrinkage, thermal expansion, stiffness and creep of the concrete. Results from the testing of 200 × 200 × 1000 mm specimens made with a 0.34 water-cement ratio concrete are presented, analysed and discussed in the paper to demonstrate the application of the proposed approach.     

An integrated knowledge-based approach for modelling biochemical reaction networks

This paper presents a new methodology for constructing cellular network topologies by searching for new binding species and new reactions catalysed by the enzymes present. Our technique is knowledge-based and integrates several steps. Starting from a pre-determined list of enzymes in the system it (i) generates lists of binding species, (ii) constructs a reaction network using these species and (iii) finds pathways through this network, which link different substrates (raw materials) with target metabolites (pathway products). Graph-theory-based analysis of the two-dimensional structures of known binding species is used to compute pharmacophores, the structures and functional groups binding at the corresponding enzymes’ sites. New binding species are obtained by searching in appropriate databases for existing compounds, which contain these pharmacophores. Reactions are constructed by generating all possible combinations of the binding species identified and by testing the feasibility (i.e. the ability to conserve atomic/molecular mass) of each constructed reaction. Generated reactions are required to be linearly independent in order to minimise the complexity of subsequent steps. Finally, pathways through the reaction network are computed to assess important reactions and metabolites for a given process. Our integrated procedure has been applied to two illustrative systems, the glycolysis and the citric acid cycle in Homo sapiens and Saccharomyces cerevisiae, respectively. New binding species and reactions were found for the enzymes involved. It was observed that some enzymes are very specific and only catalyse a small number of very similar reactions. Pathways were also constructed and analysed to demonstrate the relative importance of the metabolites involved.     

Multi-scales modelling for the behaviour of damaged concrete

The aim of this study is to investigate and to simulate damage mechanisms of concrete under fire conditions. A micro-mechanical model has been developed by coupling the effective moduli approach with a finite element model based on the representation of the heterogeneous materials random microstructure. Numerical simulations have been carried out in order to analyze the effective behaviour of confined concrete samples subjected to high temperatures coupled to compressive loads and to localize damage on the microstructure scale. These simulations show that the ‘transient thermal strain’, noticed during experimental tests, is due to the thermal damage of concrete.     

A statistical modelling approach for the analysis of TMD chronic pain data

This paper presents a discrete mixture model as a suitable approach for the analysis of chronic pain data, when they are expressed by means of ordered scores (ratings). The model is developed to allow for covariates effects; parameters estimation by maximum likelihood (using an E-M algorithm) and related inferential issues are discussed. A case-study concerning the assessment of pain (for a given pathology) and the effect of patients' covariates (e.g., gender, depression state) is illustrated. Besides, the same covariates are considered also for explaining the disruption in everyday lifestyle due to the chronic pain condition.     

An analysis of the viscous behaviour of polymeric solutions

Viscosity data of an aluminum soap solution, a polyisobutylene solution, a polyacrylamide solution, and ten polystyrene solutions have been analysed using two rheological models: the Carreau model A and the Ellis model. The model parameters were obtained by non-linear regression. The importance of the zero-shear viscosity for design purposes is illustrated by observing the appearance of a master curve in the representation of the dimensionless viscosity versus the product of the zero-shear viscosity by the shear rate. A linear relation is shown to exist between the logarithm of the zero-shear viscosity and the polymer concentration. It is asserted that either model should replace advantageously the commonly used power-law expression.     

An integrated approach to evaluate the leaching behaviour of silver from sulfide concentrates

The leaching rates of two different mineral concentrates with the same silver content were investigated by cyanide leaching with silver phases identified by scanning electron microscopy (SEM) and electrochemical analysis. The mineralogical characterization (SEM) of the concentrates showed that each contained the silver in different phases. After leaching, the disappearance of only one of the phases in each concentrate was detected. The remaining silver was contained in phases that are refractory to cyanidation. Simultaneously, an electrochemical method for the detection of the different leachable and refractory silver phases in concentrates and leach residues was developed. Cyclic voltammetry was employed with the concentrate-carbon paste electrodes (concentrate-CPE) in order to detect the oxidation of the different phases of silver contained in the mineral concentrates. The extreme sensitivity of this method allowed the rapid and reliable detection of small quantities of silver, as well as the evaluation of its refractory nature.     

Error analysis and modelling of non-linear stress-strain behaviour in measuring dynamic mechanical properties of polymers with the Rheovibron

The Rheovibron is widely used for measuring the dynamic mechanical properties of polymers. Poor reproducibility and data variation which have been considered inherent to the Rheovibron operation necessitate both instrument modifications and modelling of the instrument operation for quantitative interpretation of the experimental data. The instrument modifications that have been made in this study include electronic modifications, a new clamp design that eliminates sample mounting and slippage problems, and the design of an environmental chamber, which, along with a nitrogen purge, eliminates moisture condensation on the sample at low temperatures. A previously-developed mathematical model for the instrument has also been extended to account for the effect of the static stress and the stress rate imposed on the sample during measurement. Based on a simple constitutive relation for non-linear stress-strain behaviour of polymers, this model has been applied to a number of polymeric materials including polyethylene, polyimide, poly (ethylene terephthalate), and polypropylene, among others. The instrument modifications and modelling of the influence of static stress and the stress rate imposed on the sample during dynamic mechanical testing allows for reproducible (within 5%) and accurate use of the Rheovibron.     

An iterative modelling approach for improving the performance of a pulsed electric field (PEF) treatment chamber

An important component of the pulsed electric field (PEF) technology is the treatment chamber in which the food is exposed to high voltage pulses. Non-uniformity of the treatment, particularly with respect to the electric field distribution, is a common problem in continuous PEF treatment chambers. A previously developed and validated Multiphysics model of a pilot-scale PEF system with co-linear electrode configuration was simplified and embedded into an iterative algorithm, automatically modifying the model's treatment chamber geometry and dimensions, and evaluating the simulated process with respect to a set of performance indicators. The algorithm was capable of identifying configurations that were superior to the standard co-linear treatment chamber configuration. A 3D Multiphysics model with the identified geometrical properties was developed and a corresponding treatment chamber manufactured. The Multiphysics model was validated by comparing measured and predicted temperatures at various process conditions induced in NaCl solution and apple juice.     

Mixture modelling for cluster analysis

Cluster analysis via a finite mixture model approach is considered. With this approach to clustering, the data can be partitioned into a specified number of clusters g by first fitting a mixture model with g components. An outright clustering of the data is then obtained by assigning an observation to the component to which it has the highest estimated posterior probability of belonging; that is, the ith cluster consists of those observations assigned to the ith component (i = 1,..., g). The focus is on the use of mixtures of normal components for the cluster analysis of data that can be regarded as being continuous. But attention is also given to the case of mixed data, where the observations consist of both continuous and discrete variables.     

A deep knowledge of the behaviour of multi-component products for stone protection by an integrated analysis approach

The application of hydrophobic polymers to stone materials is an important treatment to preserve stone artefacts and protect cultural heritage from decay. To improve the characteristics and performance of water-repellent treatments, new solutions have been explored. In this research context, great attention has been paid to multi-component formulations that contain various monomers and copolymerise directly on stone. When they are obtained on inert rather than real substrates, such as stone, polymeric materials are often quite different in terms of their chemical and physical characteristics, polymerisation rate, and rheological properties. The stone's characteristics strongly influence its response to the application of conservation products; so different issues may be seen when applying the same treatment, depending on the interaction between the applied product and the stone support. Because of this, it is crucial to have the right tools to investigate how the substrate affects the monomers’ distribution of the applied mixtures and the resulting performance of the treatments. In this study, we followed an integrated approach based on the data collected by different analytical techniques (contact angle and colorimetric measurements, FT-IR analyses and ESEM-EDS analyses) to acquire a deeper knowledge of the behaviour of potential innovative water-repellents and their interaction with a stone support. This combined approach was used to evaluate the behaviour of methacrylate/vinyl-polysiloxane multi-component water-repellents applied on two calcareous stones displaying different microstructure and porosity: a compact limestone and a porous calcarenite.     

Phase behaviour modelling of Athabasca bitumen for in situ combustion applications

Phase behaviour modelling of reservoir fluid is a fundamental step for reservoir simulation. Furthermore, as the complexity of the recovery process increases, the fluid model plays a more important role in the reliability of the simulation outputs. Although the in situ combustion enhanced oil recovery method (ISC) is one of the most complex recovery techniques available in the petroleum engineering literature, for most of the simulation jobs related to this elaborate process only simple and rudimentary fluid characterization layouts are considered. In this work, the principal fluid properties of Athabasca bitumen with regard to the ISC process are recognized, extracted from the literature, validated for consistency, and used for the development of an inclusive and accurate fluid model. Then the fluid model is fully developed while considering the ISC reaction kinetics so that the model has both accuracy, indispensable for phase behaviour modelling, and consistency, essential for the reactions definitions.     

An analysis of the steady state thermal behaviour of electrolysers with recycle

A mathematical model, based on thermal balances and heat transport equations for the computation of steady state values of key temperatures and heat loss rates, is employed to analyse electrolyser performance. In particular, the effect of recycling rate and thermal insulation thickness are investigated from the viewpoint of cost-optimal operation.Notation A _E heat transfer loss area (electrolyser) - A _T heat transfer loss area (recycle line) - C _H specific cost of thermal energy - C _i specific cost of insulation (including labour and amortisation) - C specific heat capacity of electrolyte - d _i thickness of lagging on recycle line - F Faraday constant - f _R recycle ratio (Q _R/Q) - H height of electrolyser - H _E rate of heat loss from electrolyser - H _T rate of heat loss from recycle line - h ₀ outer-surface heat transfer coefficient - I electric current - k _i thermal conductivity of lagging - L _E length of electrolyser - L _R length of the recycle line - MU symbol of an arbitrary monetary unit - Q volumetric flow rate of inlet electrolyte - Q _R volumetric flow rate of recycle stream - R _E electrolyte resistance in electrolyser - r _i inner radius of recycle line - T _A ambient temperature - T _m temperature of electrolyte entering the electrolyser - T _R temperature of electrolyte leaving the recycle line - T ₁ temperature of fresh intake electrolyte - T ₂ temperature of electrolyte leaving the electrolyser - t _i thickness of insulation on electrolyser - U _E overall heat transfer coefficient (electrolyser) - U _T overall heat transfer coefficient (recycle line) - V _i volume of lagging - W width of electrolyser - z valency - H _R heat of reaction - T _LM log mean temperature (electrolyser) - _LM log mean temperature (recycle line) - symbol for time - density of electrolyte     

Rigorous and simplified approach to the modelling of continuous photoreactors

Photochemical reactions where the absorption of radiant energy occurs by the reacting species are considered. In this case the radiant energy balance equation can not be decoupled from the mass balance of the reacting species and a highly non linear integro-differential problem arises.Mathematical difficulties have been usually bypassed by modelling the radiation field on the basis of simplified models of questionable physical reliability. A rigorous modelling of the radiation field has not yet been considered for such a class of photochemical processes.An approach based on a rigorous modelling is therefore presented here, the solution being obtained through a transient approach. Results are compared with those obtained on the basis of simplified models in order to investigate the range of the significant parameters where such simple models, which are less computer-time demanding, can be conveniently used.     

A systematic approach for modelling the affinity coefficient in the Dubinin-Radushkevich equation

An unbiased evaluation of predictive models for the affinity coefficient of the Dubinin-Radushkevich equation was performed. The first step involved the selection of a minimum number of representative and chemically diverse organic compounds, the training set. This set, isopropylamine, heptane, dichloromethane, 2-chloro-2-methylpropane, 2-butanone, 1-chloropentane, acetonitrile, and benzene, covering five compounds classes, was selected with the help of PCA and statistical design. Secondly, experimental affinity coefficients of the training set compounds were determined from adsorption isotherms on Norit R1 activated carbon. In a third step, 45 physico-chemical properties were assembled for the training set compounds. A model was developed, based on PLS analysis, which correlates the measured affinity coefficients and the physico-chemical properties. Finally the model was validated by comparing model predictions of the affinity coefficients with literature data for an external validation set of 40 compounds. It was found that the predictive power of this model (RMS error=0.090) is better than using traditional methods based on parachor, molar polarizability or molar volume. The proposed new model for the affinity coefficient is based on three parameters only, the molecular weight and VdW volume of the compound and the calculated energy of interaction between the compound and a graphite model surface.     

A modelling study of the visco-elastic behaviour of polyester-based coil coatings

The time and temperature dependence of the mechanical response of a series of polyester-based hexa(methoxymethyl)melamine cross-linked coil coatings was investigated. Small strain experiments such as dynamic mechanical analysis and stress relaxation are used to determine the parameters required for time–temperature superposition and for the determination of the relaxation spectra of the materials. Tensile tests at a range of temperatures and strain rates are used to show that time–temperature superposition can be successfully extended to cover the ultimate properties of the paints (i.e. those at fracture). Finally, a hybrid visco-elastic/hyper-elastic model is used to capture the tensile stress–strain response of the paints. The success of the visco-elastic component of the model is demonstrated at strains up to 5%, while at larger strains the model behaves best when the experimental behaviour of the material approaches that of rubber, with the fit becoming worse when the mechanical response is that of a ductile plastic.     

Molecular modelling of the stress-strain behaviour of elastomers in pure shear

It is demonstrated that experimental stress-strain data for several types of polymer network under pure shear display an approximately universal behaviour. The Monte-Carlo network-modelling method of Stepto, Taylor and Cail is extended to treat stress-strain behaviour in pure shear and its predictions are in good agreement with the experimental data. The predictions of Gaussian network theory are shown to be seriously in error.     

3-D comparative behaviour of discrete transfer and imaginary planes methods for furnace modelling

The discrete transfer and imaginary planes methods are compared for accuracy and computation time in cartesian and cylindrical enclosures filled with grey gas. The reference solutions are given by the classical zone method. Comparisons are done for surface heat fluxes and gas radiative sources. A wide range of surface emissivities and gas absorption coefficients is analysed. In general, the discrete transfer method reveals superior for accuracy but consumes more computation time. The imaginary planes method loses accuracy when a high number of spatial divisions is used, however it is easy to apply.     

Hydrodynamic modelling of the liquid-solid behaviour of the circulating particulate bed electrode

Experimental and modelling investigations of the hydrodynamics of the internal flow structure in the circulating particulate bed electrode (CPBE) are reported. The CPBE, a hybrid between an expanded packed bed and an entrained/fluidized bed, is particularly well suited for many electrochemical applications such as metal recovery and pollution treatments for metal containing effluents. This study deals with the fundamental hydrodynamics and particle dynamics of the CPBE. A mathematical model of the CPBE has been developed which successfully describes the motion of the particles and the fluid in the bed. It is shown that many of the flow characteristics of the circulating bed can be predicted using fundamental data. The validity of the proposed model was demonstrated by comparing predictions to experimental observations of several bed characteristics under various operating conditions.     

Characterization and modelling of the viscous behaviour of adhesives using the modified Arcan device

The non-linear behaviour of an epoxy adhesive has been studied thanks to the use of a modified Arcan test device. Multilevel creep tests have been performed in order to characterize the time-dependent behaviour. A visco-elastic model has been chosen to describe the behaviour of the adhesive. This model is based on the decomposition of the visco-elastic strain into elementary viscous mechanisms. The non-linear behaviour of the visco-elasticity is taken into account thanks to a non-linear function which depends on the stress. A specific identification procedure based on a single test has been proposed. Finally, the model has been validated using tests that have not been used for the identification. The model proposed in this paper enables the time-dependent non-linear behaviour of adhesives to be reproduced in a correct manner.