Thermo-mechanical modelling of rock-like materials at very high temperature : application to ceramic refractories

Rock-like materials like ceramic refractories, in working conditions may be subject to large temperature variations. To simulate practical applications, bespoke constitutive modelling is required. In this work a general, thermodynamically consistent framework, able to incorporate key micromechanical features of the material behaviour, and applicable to a wide range of geomaterials, is formulated and validated. Different thermodynamic potentials are proposed to deal with both reversibility and irreversibility. A key advantage of this approach is the ability to freely choose the thermal dependency interpolation functions. Extensive model validation is provided by correctly reproducing both reversible and irreversible experimental trends of different materials under different loading conditions. It is found that even for simple materials, if a sample is subject to a large stress level, its thermal and mechanical responses become unexpectedly coupled. The proposed modelling framework is not limited to refractories and can be easily adapted to different types of rock-like materials

A computational framework for immiscible three-phase flow in deformable porous media

Several soil decontamination processes and enhanced oil recovery techniques involve the co-existence of three immiscible fluids, such as water, a nonaqueous phase liquid and a gas. In this work, a computational framework based on the individual mass balance of each phase is developed, aimed at simulating three-phase flow in a deformable rock through the finite element method, without resorting to specific simplifications that are usually required by standard numerical schemes. Key ingredients of the model are: expression of the residual in terms of mass contents, consistent lumping of the storage terms in the residual and algorithmic (tangent) matrix, consistent integration rules, the use of a minimum relative permeability and a time marching scheme based on trapezoidal integration. Special convective boundary conditions are adopted for pressures to be consistent with the assumed rock wettability properties during co-current imbibition. The resulting numerical scheme can deal with arbitrary saturation and/or pressure boundary conditions. The model is tested by simulating gas injection tests, and both co- and counter-current water imbibition tests, in a deformable core. To assess the performance and robustness of the whole framework, sensitivity analyses are performed upon varying key constitutive, loading and numerical parameters

A new modelling approach for piled and other ground heat exchanger applications

Pile heat exchangers have an increasing role to play in the delivery of renewable heating and cooling energy. Traditionally the thermal design of ground heat exchangers has relied upon analytical approaches which take a relatively simple approach to the inside of the heat exchanger. This approach is justified while the heat exchanger diameter remains small. However, as larger diameter piled foundations are used as heat exchangers, the transient heat transfer processes operating within the pile become more important. To increase our understanding of these processes and ultimately lead to improved thermal design approaches for pile heat exchangers it is important to examine the heat transfer within the pile in detail. To accomplish this, a new numerical approach has been implemented within the finite element software ABAQUS. Coupling of the convective heat transfer due to fluid flow within the heat transfer pipes and the heat transfer by conduction within the pile concrete is the most important facet of the model. The resulting modelling approach, which is ready to generalise to other geothermal applications and to assess thermo-mechanical couplings, has been validated against a multi-stage thermal response test carried out on a test pile in London Clay

Dynamical effects during compaction band formation affecting their spatial periodicity

Compaction bands (CBs) are responsible for significant anisotropy alterations of permeability in geological materials; hence, understanding their formation conditions appears of key importance to all applications involving fluid extraction/injection from/into the ground. While most of the available models to understand CB formation are focused on interpreting the onset of a single CB, little effort has been so far dedicated to understand the documented periodicity of CBs. In this paper, the role of dynamical effects in inducing the post onset evolution of CBs is analyzed by means of a dedicated model for porous media with compressible constituents, with reference to a horizontal layer of sandy, water-saturated material. Elastic waves are generated as a first CB occurs due to sudden, localized volumetric collapse. If the waves are reflected at the interface with a softer material or with a previously formed CB, they produce significant local effective stress concentrations, which can promote the formation of further CBs in a cascade fashion, according to a regular geometric pattern. The spatial distribution of dynamically generated CBs, as well as the extent of the phenomenon, depends on the geometry of the domain and on the material's permeability. Sensitivity analysis is also performed to assess the key properties that promote dynamical CB in situ formation, identifying as the most influential conditions large stratum stiffness (increasing with depth) and the presence of softer layers. In contrast, the presence of less permeable and/or stiffer layers is not believed to play a major role in the proposed mechanism

Some new insights in swelling and swelling pressure of low active clay

This paper presents a multidimensional chemo-mechanical model for saturated clay treated as a two-phase deformable and chemically reactive porous medium. The constitutive relation is an extension of the original chemo-mechanical model proposed by Gajo et al. (2002) and Loret et al. (2002), in which a q-p formulation was proposed with a Cam-Clay-like elastic response. A novel hyper-elastic law is proposed in which shear stiffness and bulk stiffness change with stress state and ion concentration in pore solution. The proposed constitutive model and the associated coupled finite element formulation are implemented in a 2D, commercial, finite element code (ABAQUS) in the form of user-defined external subroutines. The proposed framework is used to simulate the oedometer tests performed on a low activity clay extracted from Costa della Gaveta slope. The computed chemo mechanical behaviour of the material prepared with distilled water is compared with the experimental results obtained from reconstituted specimens. Moreover, swelling and swelling pressure are computed for the overconsolidated material reconstituted with 1 M NaCl solution and then exposed to distilled water. The comparison of simulations and experiments shows a good agreement

AVALIAÇÃO DA COMPOSIÇÃO QUÍMICA E CARACTERÍSTICAS SENSORIAIS DE BEBIDAS LÁCTEAS FERMENTADAS ELABORADAS COM LEITE DE OVELHA

A manufatura de bebida láctea fermentada pode ser uma excelente alternativa para utilização industrial de leite de ovelha e fornecimento de um alimento altamente nutritivo, pois este leite possui em sua composição química, constituintes de considerável valor nutricional que podem ser preservados na elaboração destes produtos. Este trabalho teve como objetivo avaliar a composição química das bebidas lácteas fermentadas com adição de polpa e diferentes concentrações de soro, fabricados a partir de leite de ovelha. Os produtos foram elaborados na planta piloto de Laticínios do Departamento de Ciência dos Alimentos da Universidade Federal de Lavras. As análises foram realizadas no Laboratório de análises de leite e Laboratório de análise sensorial, ambos do mesmo departamento da mesma instituição. As concentrações de adição do soro de leite de ovelha (proveniente da fabricação de queijo Minas padrão) foram nas proporções de 25%, 35% e 45%. Sensorialmente, quanto ao sabor, não apresentaram diferença signi? cativa pelo teste Scott-Knott (p<0,05), todavia os tratamentos com maior adição de soro (35% e 45%) obtiveram, sensorialmente, maior nota no atributo: intenção de compra. Os resultados para as bebidas lácteas com 25%, 35% e 45% de soro foram respectivamente: lipídeos: 3,5g/100mL, 3,3g/100mL e 2,5g/100mL, proteína: 5,7g/100mL, 5,1g/100mL e 4,98g/100mL, carboidratos: 15,16g/100mL, 14,94g/100mL e 13,74g/100mL, extrato seco total: 25,04g/100mL, 24,01g/100mL e 21,81g/100mL. O processo de fermentação foi acompanhado através dos valores de pH, sendo em torno de 4,6 o pH fi nal para todos os produtos. Conclui-se que as bebidas lácteas apresentaram diferenças em suas composições e preferência sensorial no atributo intenção de compra nos diferentes tratamentos aplicados

Motivation for or from bilingual education? A comparative study of learner views in the Netherlands

Teaching and Teacher Learning (ICLON

A polymorphic variant of the insulin-like growth factor 1 (IGF-1) receptor correlates with male longevity in the Italian population: a genetic study and evaluation of circulating IGF-1 from the "Treviso Longeva (TRELONG)" study

<p>Abstract</p> <p>Background</p> <p>An attenuation of the insulin-like growth factor 1 (IGF-1) signaling has been associated with elongation of the lifespan in simple metazoan organisms and in rodents. In humans, IGF-1 level has an age-related modulation with a lower concentration in the elderly, depending on hormonal and genetic factors affecting the IGF-1 receptor gene (<it>IGF-1R</it>).</p> <p>Methods</p> <p>In an elderly population from North-eastern Italy (<it>n </it>= 668 subjects, age range 70–106 years) we investigated the <it>IGF-1R </it>polymorphism G3174A (<it>rs2229765</it>) and the plasma concentration of free IGF-1. Frequency distributions were compared using χ²-test "Goodness of Fit" test, and means were compared by one-way analysis of variance (ANOVA); multiple regression analysis was performed using JMP7 for SAS software (SAS Institute, USA). The limit of significance for genetic and biochemical comparison was set at α = 0.05.</p> <p>Results</p> <p>Males showed an age-related increase in the A-allele of <it>rs2229765 </it>and a change in the plasma level of IGF-1, which dropped significantly after 85 years of age (85+ group). In the male 85+ group, A/A homozygous subjects had the lowest plasma IGF-1 level. We found no clear correlation between <it>rs2229765 </it>genotype and IGF-1 in the females.</p> <p>Conclusion</p> <p>These findings confirm the importance of the <it>rs2229765 </it>minor allele as a genetic predisposing factor for longevity in Italy where a sex-specific pattern for IGF-1 attenuation with ageing was found.</p

A laboratory study of anisotropic geomaterials incorporating recent micromechanical understanding

This paper presents an experimental investigation revisiting the anisotropic stress–strain–strength behaviour of geomaterials in drained monotonic shear using hollow cylinder apparatus. The test programme has been designed to cover the effect of material anisotropy, preshearing, material density and intermediate principal stress on the behaviour of Leighton Buzzard sand. Experiments have also been performed on glass beads to understand the effect of particle shape. This paper explains phenomenological observations based on recently acquired understanding in micromechanics, with attention focused on strength anisotropy and deformation non-coaxiality, i.e. non-coincidence between the principal stress direction and the principal strain rate direction. The test results demonstrate that the effects of initial anisotropy produced during sample preparation are significant. The stress–strain–strength behaviour of the specimen shows strong dependence on the principal stress direction. Preloading history, material density and particle shape are also found to be influential. In particular, it was found that non-coaxiality is more significant in presheared specimens. The observations on the strength anisotropy and deformation non-coaxiality were explained based on the stress–force–fabric relationship. It was observed that intermediate principal stress parameter b(b = (σ2 − σ3)/(σ1 − σ3)) has a significant effect on the non-coaxiality of sand. The lower the b-value, the higher the degree of non-coaxiality is induced. Visual inspection of shear band formed at the end of HCA testing has also been presented. The inclinations of the shear bands at different loading directions can be predicted well by taking account of the relative direction of the mobilized planes to the bedding plane