Simulation numérique de l’écoulement du béton autoplaçant en tant que fluide(s) homogène(s) et matériel hétérogène pendant le processus de pompage

Le pompage est l'une des méthodes les plus couramment utilisées pour transporter le béton auto-plaçant (BAP). La prédiction de la baisse de pression de pompage est d'un intérêt particulier pour concevoir correctement les circuits de pompage et assurer un processus de pompage réussi compte tenu de l'application en cours. Cela est nécessaire pour répondre aux exigences de coulage, y compris le débit ciblé et l'homogénéité du béton respectivement pendant et après le pompage. Cette étude visait à prédire la pression requise pour pomper le BAP avec la caractérisation de la couche de lubrification formée près de la paroi du tuyau en utilisant des méthodes numériques. Bien que le processus de pompage du béton semble conceptuellement simple, le défi sous-jacent de la physique des matériaux est complexe et couvre une large gamme d'échelles de temps et de longueurs. Un autre défi vient de l'interaction entre la phase fluide et la diversité des tailles de particules dans le mélange de béton, ce qui résulte en différentes propriétés rhéologiques dans le béton à travers la section du tuyau. Cette étude a été menée en deux phases différentes et complémentaires. La phase 1 avait pour objectif principal de développer un modèle de calcul pour comprendre le circuit de pompage du béton en grandeur réelle. La perte de pression en fonction de la géométrie des tuyaux, des propriétés rhéologiques du béton et des caractéristiques d'écoulement de la couche de lubrification sont présentées et discutées. La méthode de dynamique des fluides computationnelle (CFD) a été utilisée pour prédire la pompabilité du béton et évaluer l'importance des paramètres d'influence, y compris les caractéristiques de la phase en suspension (c'est-à-dire le squelette granulaire), les propriétés rhéologiques de la matrice de pâte de ciment/mortier en suspension et les nombres de Reynolds de l'écoulement et des particules solides. Deux nouveaux modèles ont été introduits pour prédire la pompabilité des mélanges de béton et la caractérisation de la couche de lubrification et des zones de bouchage. De plus, une revue complète de la littérature sur les méthodologies numériques utilisées pour modéliser l'écoulement des tuyaux en béton a été effectuée, avec une comparaison des avantages et des inconvénients de ces différentes approches. En outre, des solutions potentielles ont été présentées pour les méthodes numériques les plus efficaces et les plus fiables pour prédire l'écoulement de béton dans des tuyaux. Les modèles informatiques basés sur la méthode des éléments discrets (DEM) et le couplage CFD-DEM ont été développés lors de la Phase 2. La migration de particules induite par cisaillement (SIPM), principal phénomène physique conduisant à la formation de la couche de lubrification, a été également étudiée. En conséquence, l'effet couplé de la distribution de taille des particules (PSD), de la concentration et du diamètre moyen des particules en tant que paramètres d'influence sur la couche limite, le SIPM et les hétérogénéités rhéologiques à travers le tuyau ont été étudié. Outre l'évaluation des paramètres d'influence sur la migration des particules, cette étude à plusieurs échelles a permis de proposer une bonne estimation de l'épaisseur de la couche de lubrification ainsi que des propriétés rhéologiques, y compris sa viscosité et son seuil d'écoulementAbstract: Pumping is one of the most commonly used methods to transport self-consolidating concrete (SCC). The prediction of pumping pressure drop is of particular interest to properly design the pumping circuits for successful pumping process given the application on hand. This is necessary to fulfil the targeted flow rate and ensure homogeneity of concrete during and after pumping, respectively. During the pumping process, a thin layer of highly fluid fine mortar enriched with high volume of cement paste and fine particles, namely lubrication layer (LL), is formed in vicinity of the pipe walls. It is revealed in literature that concrete pumpability is significantly controlled by the LL characteristics, in terms of thickness and flow properties, as well as the rheological properties of the bulk concrete (BC). This study firstly aims to predict the pressure required to pump SCC and to characterize the LL in large-scale pipelines using computational fluid dynamics (CFD). Although the concrete pumping process seems conceptually simple, the challenge underlying material physics is complex and covers a broad range of time and length scales. Another challenge comes from the interaction between suspending fluid phase (mortar) and diversity of particle sizes (aggregate) in concrete matrix, causing heterogeneous rheological behavior across the pipe section, and formation of the LL. The main mechanisms of LL formation, including the shear-induced particle migration (SIPM) and wall effects, were also simulated using multiphasic simulation techniques, including discrete element method (DEM) and coupled CFD-DEM. First, a comprehensive literature review on numerical methodologies used to model concrete pipe flow as well as their advantages and disadvantages was presented. In addition, potential solutions were introduced to predict concrete pipe flow given an application on hand in reasonable time and precision. This study was conducted in two complementary phases. The Phase 1 included developing computational models to predict the pressure loss in a full-scale concrete pumping circuit, as a function of the pipes’ geometry, rheological properties of BC, and the LL characteristics. Two novel tri-viscous models were developed to simulate the presence of the LL and BC as a homogeneous fluid with variable rheological properties across the pipe, corresponding to the BC and LL, using OpenForam software. In the second phase, the main mechanisms of LL formation, including the wall effect and SIPM, were simulated using DEM and coupled CFD-DEM approaches. The pipe flow of concrete was simulated as a biphasic suspension to evaluate the coupled effect of characteristics of the suspended particles (i.e., granular skeleton) and the suspending cement paste/mortar matrix. The interaction of the suspended particles and suspending fine mortar was simulated by considering the collision of particles with different particle-size distributions (PSD) and concentrations (and pipe wall), as well as the suspending fluid’s drag force. A multiscale soft-sphere discrete element method (DEM) and its four-way CFD-DEM coupling were employed in Phase 2 to simulate the rheological heterogeneity across the pipe and formation of the LL. Accordingly, the coupled effect of PSD, concentration, and mean diameter of particles, as well as the rheological properties of the suspending fluid and flow Reynolds number on wall effect, SIPM, and rheological heterogeneities across the pipe was evaluated. The LL of the investigated mixtures were eventually characterized in terms of the thickness and rheological properties

Metaphors the East Is Othered by: A Critical-cognitive Study of Metaphor in Lady Sheil’s Travelogue Glimpses of Life and Manners in Persia

Regarding travel writing as the textual manifestation of the Self and the Other confrontation, travelogues provide interesting material for analyzing otherness discourse and various strategies of othering. Accordingly, this paper aims to study how metaphor functions as an othering device in travel writing. The travelogue which is the subject of this research is Glimpses of Life and Manners in Persia written by Lady Sheil in the mid-nineteenth century. The framework employed for analyzing metaphor in this text is Critical Metaphor Analysis which is amongst various approaches of cognitive poetics. The critical-cognitive analysis of metaphors in this travelogue implies that Sheil metaphorized Persia mainly as an Oriental Other which has a denigrated inferior position relative to the Occidental Self. In so doing, she has vastly used different stereotypical images of the East abundantly present in the Orientalist discourse. It can be argued that Orientalism as a discourse has exerted great influence on Sheil’s metaphorization of Persia as an Eastern Other via a number of conceptual metaphors which characterize the East as a unified object which has no diversity and should be studied by European scholars

Synthesis of three-dimensional calcium carbonate nanofibrous structure from eggshell using femtosecond laser ablation

<p>Abstract</p> <p>Background</p> <p>Natural biomaterials from bone-like minerals derived from avian eggshells have been considered as promising bone substitutes owing to their biodegradability, abundance, and lower price in comparison with synthetic biomaterials. However, cell adhesion to bulk biomaterials is poor and surface modifications are required to improve biomaterial-cell interaction. Three-dimensional (3D) nanostructures are preferred to act as growth support platforms for bone and stem cells. Although there have been several studies on generating nanoparticles from eggshells, no research has been reported on synthesizing 3D nanofibrous structures.</p> <p>Results</p> <p>In this study, we propose a novel technique to synthesize 3D calcium carbonate interwoven nanofibrous platforms from eggshells using high repetition femtosecond laser irradiation. The eggshell waste is value engineered to calcium carbonate nanofibrous layer in a single step under ambient conditions. Our striking results demonstrate that by controlling the laser pulse repetition, nanostructures with different nanofiber density can be achieved. This approach presents an important step towards synthesizing 3D interwoven nanofibrous platforms from natural biomaterials.</p> <p>Conclusion</p> <p>The synthesized 3D nanofibrous structures can promote biomaterial interfacial properties to improve cell-platform surface interaction and develop new functional biomaterials for a variety of biomedical applications.</p

Validity and Reliability of Behavioral Pain Scale in Patients With Low Level of Consciousness Due to Head Trauma Hospitalized in Intensive Care Unit

Background:: Estimating pain in patients of intensive care unit (ICU) is essential, but because of their special situation, verbal scales cannot be used. Therefore, to estimate the level of pain, behavioral pain scale was developed by Payen in 2001. Objectives:: The aim of this study was to investigate the validity and reliability of behavioral pain scale in patients with low level of consciousness due to head trauma hospitalized in ICU. Patients and Methods:: This descriptive prospective study was performed in Yazd in 2013. In this study, fifty patients, including thirteen women and thirty seven men, were involved. To collect the data a questionnaire including demographic and Glasgow coma scale (GCS) information as well as a list of behavioral pain scale (BPS) were used. SPSS software (version 18) was used to analyze the data. Results:: There was no significant difference in reliability proving of average score of BPS recorded by two day and night assessors (P > 5). Cronbach’s alpha was 85 for painful procedures and 76 for non-painful procedures. In addition, known groups’ technique (painful and non-painful procedures) was used to assess validity. The average scores were 7.75 during painful procedures and 3.28 during non-painful procedures (P = 0.001). The results stated that BPS scores during these two procedures were significantly different. Conclusions:: BPS in patients with low level of consciousness due to head trauma has strong reliability and validity. Therefore, this scale can be used for patients hospitalized in ICU to assess the level of pain

Viscous Heating Effects on Heat Transfer Characteristics of an Explosive Fluid in a Converging Pipe

Viscous dissipation is the production of heat due to the slip of fluid layers and can raise the temperature of the fluid that is affected by&nbsp;high shear stresses. This raise of temperature in fluids with explosive properties can cause the explosion during the processing. The&nbsp;present paper investigates the temperature distribution of an explosive fluid beside the wall of a converging tube. This study has been done by using the computational fluid dynamics and OpenFOAM software. The studied cases contain the fluid with two viscosities (50 and 500 kg/m&nbsp;×&nbsp;s) and two inlet conditions (constant and developed velocity profile). The results of this study show that at the end of a converging pipe, duo to the viscous dissipation effects, the temperature rise for high viscosity fluid is more intensive and this is a dangerous fact for high viscosity explosive fluids discharging. Also, it has been considered that the constant inlet velocity is safer in comparison with the developed profile, as the slope of temperature rise is less

Children’s Health and Maternal Work Activities

I estimate the effect of poor child health on maternal labor force participation. Mothers of health-impaired children may decide not to work and stay at home to take care of their children. Alternatively, mothers may choose to enter the labor force to pay for these children’s additional resources. Which action dominates is the empirical question I answer in this paper. I control for the potential endogeneity of a child’s health status by using an instrumental variables approach. I find that if mothers have a child in poor health, the probability that the mother works is decreased by thirteen percentage points, and the work hours of employed mothers are reduced by approximately nine percent

General Extenders in Persian Discourse: Frequency and Grammatical Distribution

This study tries to investigate the frequency and grammatical distribution of general extenders in Persian. The analysis is based on a corpus of informal conversations. On some occasions, a comparison will also be made with the corpus of informal English compiled and analyzed by Overstreet (1999, 2005). The results of this study lay bare the fact that Persian speakers use adjunctive general extenders more frequently than disjunctive ones. It will also be demonstrated that Persian speakers use general extenders both at clause final and clause-internal positions. Finally, Persian general extenders will be examined with reference to their grammatical agreement requirements.Keywords: Discourse marker; frequency; general extender; grammatical distribution; Persia

Novel Tri-Viscous Model to Simulate Pumping of Flowable Concrete through Characterization of Lubrication Layer and Plug Zones

In this study, computational fluid dynamics (CFD) was employed to simulate the pipe flow of 18 self-consolidating and four highly workable concrete mixtures in a 30-m long pumping circuit. Pressure loss (ΔP) in 100- and 125-mm diameter (DP) pipelines was measured under low (1.2–6.2 l/s) and high (8.1–16.4 l/s) flow rates (Q). The numerical simulation was successfully carried out using a two-fluid model and a new variable-viscosity single-fluid approach, namely double-Bingham and tri-viscous models, respectively. The radial variation of rheological properties of the concrete across the pipe section, representing the plug flow, sheared concrete, and lubrication layer (LL) zones was successfully simulated based on a total of 404 pipe flow experiments. The relative LL viscous constant (ηLL) values obtained using numerical simulations-to-those obtained experimentally using a tribometer ranged between 30% and 200%. Moreover, the coupled effect of the characteristics of different flow zones, DP, and Q on ΔP was evaluated

Correlating with Local Variation in Collagen Level and Mechanical Properties of the Heart Tissues

The determination of the myocardium\u27s tissue properties is essential in constructing finite element (FE) models of the heart. To obtain accurate results, especially for functionally modeling the heart, we must determine the tissue properties in-vivo. The calculation of the heart tissue properties remains a challenging area as it is categorized as a heterogeneous, anisotropic, nonlinear soft tissue that undergoes large deformation. In this work, we tried to introduce and evaluated a finite element method to determine the mechanical properties of the cardiac tissue. The introduced method combined a finite element modeling with the experimentally obtained images from the left and right ventricles to develop a model for calculating the shear modulus, Young\u27s modulus, and the Poisson\u27s ratio of the ventricles leading to obtaining the constitutive matrices for each specimen. Tissue behavior was quantified under three different loading conditions: tensile loading in the x and y direction and shear loading. Statistical analysis reveals that the left ventricle demonstrates higher mechanical properties compared to the right ventricle. Additionally, the heart tissue\u27s mechanical properties were effectively used for studying the effects of the variation in the tissue\u27s composition, primarily collagen, on the myocardium behavior. Based on the obtained results, it was demonstrated that mechanical properties enhanced with increasing the collagen amount. The results indicated that the proposed model showed a good agreement with the previous studies and provided an ability to describe the heart tissue\u27s behavior precisely. It offers a new approach to the study of cardiac tissue properties, as it shows the cardiac tissue\u27s mechanical properties, including Young\u27s modulus, shear modulus, constitutive matrices, and their correlation with the change in the microstructure of the heart tissue