Cap Model Research Articles

Mass transfer of a rising spherical bubble in the contaminated solution with chemical reaction and volume change

In the present study, a systematic numerical study is conducted to investigate the mass transfer of a slightly contaminated spherical bubble under the effect of chemical reaction with the consideration of volume change of the bubble. The numerical approach is first validated by the benchmark tests, i.e., the dissolutions of a static bubble and a rising bubble. The numerical results are compared with the results from literatures and show very good agreements. Afterwards, the numerical method is utilized to study the chemical absorption process of a rising spherical CO2 bubble in the alkaline solution of NaOH. The shrinkage of the bubble and the decrease of bubble velocity during the chemical absorption process are taken into account, and the accumulation of the contamination on the bubble surface is also considered based on the stagnant cap model. The profiles of species concentration are presented in detail, and it can be found that the cap angle and the flow separation significantly influence the distribution of the concentration layers. The local mass transfer rate and reaction rate around the bubble surface are studied quantitatively, and the local mass transfer is found to be dominated by the chemical reaction directly. In additional, the supplement of the hydroxyl ion significantly affects the mass transfer which is mainly determined by the local velocity.

Experiment and finite element analysis of compaction densification mechanism of Ag-Cu-Sn-In mixed metal powder

Experiments and finite element analysis were performed to investigate the compaction densification mechanism of Ag57.6-Cu22.4-Sn10-In10 mixed metal powder. Firstly, the friction coefficient for lubricated and unlubricated die between the powder and die wall were determined experimentally. It is observed that the friction coefficient varies with the top punch pressure, and μ increases with the top punch pressure at low pressure regime (≤100MPa), while maintain constants at high pressure regime (>100MPa). The difference between the friction coefficients of lubricated/unlubricated die indicates that the lubrication (zinc stearate alcohol solution) could reduce the die wall friction greatly. Furthermore, the relative density distribution in the compacts for lubricated and unlubricated die compaction were characterized and mapped experimentally using the Vickers hardness method. Globally, the agreement between simulation calculation and experimental measurement of relative density distribution is reasonably good, indicating that the model parameters give an adequate description of the compaction behavior for the mixed metal powder. Moreover, a nonlinear compaction equation containing the die wall friction effect was proposed and established as: ln1−D1−D0=kP1−k1μ+b1−k2μP, k1 and k2 are correction coefficients related to the powder property. It is shown that the established nonlinear compaction equation could represent the relative density-compaction pressure relationship for the mixed metal powder under different die wall friction. At last, the influence mechanisms of die wall friction on the compaction behavior of mixed metal powder were detailedly analyzed in simulations using the modified Drucker-Prager Cap model. The results show that the friction induced inhomogeneous stress distribution and powder flows in compact during compaction, which caused density gradient and the occurrence of cracks and capping during ejection.

Modelling blast wave propagation in a subsurfacegeotechnical structure made of an evolutive porous material

In this study, a coupled thermo-hydro-mechanical-chemical (THMC)-viscoplastic cap model is developed to investigate the characteristics of blast wave propagation in a fill mass made of granular material (cemented backfill, CB) that is undergoing cementation under different curing conditions. The THMC model allows to evaluate its behavior and the changes in the material properties of the cementing granular material during the curing process, with rigorous evaluation of the coupled THMC factors. The THMC model is then coupled with a modified viscoplastic cap model to capture the nonlinear and rate-dependent behaviors of CB under blast loading. All of the material properties of CB required for the modified viscoplastic cap model are obtained from the THMC model. To validate the model, experiments carried out in high columns and impact testing on hydrating cemented backfill, as well as blast wave propagation experiments on soil and cemented backfill are adopted and simulated. A good agreement is found between the experimental and simulated results. Finally, by applying the coupled THMC-viscoplastic cap model, the effects of curing time, cement content, stope (mine cavity) size, initial backfill temperature, and filling rate on blast wave propagation in backfill mass are investigated. The obtained results provide new insight into blast wave propagation in fill mass under field curing conditions.

Transforming growth factor-β-induced gene product-h3 inhibits odontoblastic differentiation of dental pulp cells

ObjectiveThe aim of this study was to investigate transforming growth factor-β-induced gene product-h3 (βig-h3) expression in dental pulp tissue and its effects on odontoblastic differentiation of dental pulp cells (DPCs). DesignA rat direct pulp capping model was prepared using perforated rat upper first molars capped with mineral trioxide aggregate cement. Human DPCs (HDPCs) were isolated from extracted teeth. βig-h3 expression in rat dental pulp tissue and HDPCs was assessed by immunostaining. Mineralization of HDPCs was assessed by Alizarin red-S staining. Odontoblast-related gene expression in HDPCs was analyzed by quantitative RT-PCR. ResultsExpression of βig-h3 was detected in rat dental pulp tissue, and attenuated by direct pulp capping, while expression of interleukin-1β and tumor necrosis factor-α was increased in exposed pulp tissue. βig-h3 expression was also detected in HDPCs, with reduced expression during odontoblastic differentiation. The above cytokines reduced βig-h3 expression in HDPCs, and promoted their mineralization. Recombinant βig-h3 inhibited the expression of odontoblast-related genes and mineralization of HDPCs, while knockdown of βig-h3 gene expression promoted the expression of odontoblast-related genes in HDPCs. ConclusionsThe present findings suggest that βig-h3 in DPCs may be involved in reparative dentin formation and that its expression is likely to negatively regulate this process.

Constitutive modeling of indentation cracking in fused silica

AbstractFused silica shows three distinct regimes during nanoindentation, that is, plastic deformation, inelastic densification, and cracking. Cohesive zone FEM is used to study these regimes for different indenter geometries. In a three‐dimensional model, the median/radial cracking is considered by introducing cohesive element planes that are aligned along the indenter edges perpendicular to the indented surface. In addition to comparing indentation cracking data with experimental data, the role of densification on indentation crack growth is critically examined using a pressure independent von Mises and a pressure dependent Drucker‐Prager Cap constitutive model. The results show that the Drucker‐Prager Cap model delivers an accurate description of the elastic‐plastic deformation conditions for all examined indenter geometries. Material densification leads to shorter crack lengths and thus the approach by Lawn et al. (J Am Ceram Soc, 1980;63:574‐581) results in larger indentation‐based fracture toughness values. Once the crack was initiated its propagation is comparable for blunt indenter geometries (Berkovich), while densification leads to a slower crack propagation for sharper indenter geometries.

Research of Dynamic Constitutive Model of Reinforced Concrete Based on LS-DYNA

Bridge structure in life span, in addition to the need to withstand permanent and variable action, there may be large or small under dynamic loading, such as impact, explosion, earthquake etc. In order to get the real response of the structure under dynamic load, based on reasonable dynamic constitutive model, a nonlinear finite element analysis is needed. In this paper, several commonly used models of concrete dynamic constitutive model for ship collision with bridges are introduced: Reinforced concrete damage model (RC damage model), Elastic-Plastic Cap model, HJC model and Elastic model. Then the simulation analysis of two impact tests of rigid beads strike the target concrete walls and hammer strike the RC beams are carried out by using the analysis software LS-DYNA for nonlinear dynamic analysis. In the analysis, the influence of the various dynamic constitutive models on the impact structure is compared, and the calculated dynamic impact force-time curve and displacement-time curve are compared with the experimental data. It is found that the RC damage model can better simulate the change of concrete damage, and can simulate the development of structural cracks more realistic, and can consider the influence of reinforcement ratio on the impact force. Based on this, a multi parameter sensitivity analysis is made on the RC damage constitutive relationship, and the practical formula of the impact force is put forward. Research shows that the maximum impact force increases with the increase of the ratio of reinforcement, and the impact of the ship bridge collision analysis should be considered.

Effect of sand dilation on distortions and pattern allowances during steel sand casting

Mechanical interactions between the sand mold and casting have a great impact on pattern allowances. In this study, the effect of core expansion on distortions during steel casting is investigated. A hollow steel cylinder is cast using silica and zircon sand cores. The evolution of the cylinder’s inner diameter is measured in situ using LVDTs. During solidification, core expansion is found to distort the inner diameter into a barrel-shaped profile, generating the largest expansion at the mid-height. The experiments are simulated using a sequential thermo-mechanical coupling. In the stress analysis, the steel and sand are modeled using an elasto-visco-plastic constitutive law and the Drucker–Prager Cap model, respectively. The simulations reveal that sand dilation due to shear stresses, as opposed to thermal expansion, accounts for the majority of the increase in the inner diameter. The measured and predicted pattern allowances are found to be in excellent agreement.

Verification of the spar model of a reinforced concrete beam

The paper presents the outcomes of the research aimed at the verification of the computational model simulating a reinforced concrete beam employing spar and 3D finite elements, with account taken of physical nonlinearity. Structural calculations involved in R&D and design effort must factor in non-linear structural behavior both of the material and of structural elements. In particular, this is valid for the analysis of special types of impact (seismic, accidental etc.). However, design models under development may incorporate significantly varying models of nonlinear materials as well as different kinds of finite elements, and both have to be verified. This article considers two models of a hinged (pinned) beam. In the first case, the modeling was based on 3D elements for concrete and on spar elements for reinforcement using Euler-Lagrange coupling of finite elements belonging to concrete and reinforcement (three-dimensional model). The second case the simulation based on spar finite elements (spar model). Both the spar model and 3D model allow for non-linear nature of concrete and reinforcement. In case of concrete the material was set using the Continuous Surface Cap Model, while the reinforcement was modeled involving a bilinear diagram of material behavior.

Fuzzy multi-objective, multi-item, multi-supplier, lot-sizing considering carbon footprint

Optimum order size plays a key role for minimising carbon footprint of a supply chain. However, managers often face difficulty in handling conflicting objectives like cost reduction and carbon emission reduction for supply chain operation. As of now, very few studies have reported multi-objective, multi-item, multi-supplier lot-sizing problem taking consideration of carbon emission under fuzzy environment. This study fills the gaps of earlier research and proposes a fixed carbon cap model incorporating carbon footprint factor. The model has been subsequently modified to carbon offset and multi-objective fuzzy models. The proposed models have been solved by using different methodologies (mixed integer programming, interactive fuzzy goal programming, additive interactive fuzzy goal programming, weighted goal programming, and interactive fuzzy ε constraint method) and their results are compared. As theoretical contribution, this study extends interactive fuzzy goal programming and ε constraint method to additive interactive fuzzy goal programming and interactive fuzzy ε constraint method, respectively. The effectiveness of the proposed models has been explained through illustrative examples and various scenarios have been generated by varying different model parameters. This study will help managers to take prudent decision in carbon constrained world.

Comparative analysis of results from experimental and numerical studies on concrete strength

Some results of numerical experiments of testing concrete cubes and prisms on unconfined compression, and the comparison of results obtained with experimental and specified data, are presented in the article. When performing calculations of structures in a nonlinear setting, it is very important to choose adequate deformation diagrams or material models. Because of the fact that there are no instructions how to use the diagrams of concrete and armature deformation in collaboration of steel and concrete, the simulation of reinforced concrete structures by finite elements of the same type without any assumptions is impossible. Numerical experiments have been performed in the LS-DYNA software package. This software package allows simulating the collaboration of concrete and steeling with the help of three-dimensional (for concrete) and rod (for the reinforcement) finite elements. As samples, a cube and a prism with dimensions of 150×150×150 mm and 150×150×600 mm, respectively, have been taken. The samples are simulated by solid finite elements. For the simulation of concrete, the non-linear CSCM (Continuous Surface Cap Model) material is used. The tests were carried out with samples of the following classes of concrete as for cylinder compressive strength: C12, C16, C20, C25, C30, C35. This corresponds to the following classes of cube compression strength: B15, B20, B25, B30, B37, B45. The tests have been carried out considering the friction coefficients between the plates of a testing machine, and a sample. The performed researches have shown that the destruction nature of the samples in a numerical experiment corresponds to the failure nature in real tests. The investigated model of CSCM concrete can be used in the calculation of concrete and reinforced concrete structures with acceptable accuracy for main classes of concrete.

Flow Behavior and Drag Coefficients of Spherical Bubbles in Surfactant-laden Carreau Model Fluids

The flow and drag phenomena of contaminated spherical bubbles in columns filled with surfactant-laden Carreau model fluids is numerically investigated using a computational fluid dynamics based commercial solver, COMSOL Multiphysics 4.3b. The effect of contaminants is incorporated in the solver by the use of the spherical stagnant cap model. The numerical solver is thoroughly benchmarked through extensive validation with the existing literature results. Further new simulations are performed over wide range of the conditions as the Reynolds number (Re) varying in the range of (0-100), the power law index (n) ranging between (0.2-0.8), the Carreau number (Λ) varying in the range of (1-100) and the degree of contamination (α) ranging between (0-180°). Briefly, the results indicate that recirculation wakes behind the bubbles are observed for all values of Carreau number ranging between 1-100 if the bubble is at least partially contaminated, i.e., for α > 30°. The total drag coefficient decreases with the increasing Carreau and/or Reynolds numbers and/or with the decreasing power-law index and/or with the decreasing cap angle.

Modeling Mass Transfer During Single Organic Droplet Formation and Rise

Copper reactive extraction from ambient aqueous solution to organic droplets using single droplet experiments was performed. Extractant was Agorca M5640 hydroxyoxime in Exxsol D80. An image analysis based method was used to determine droplet concentration directly after droplet formation and rise. Mass transfer during formation is correlated using literature. Level Set interface tracking method was used to find formation hydrodynamics and as a result the assumption of non-circular velocity field could be validated. This was also supported by the circulation criteria based on needle Reynolds number. A model to estimate extraction rate as function of droplet Fourier number was based on a literature correlation and it was found that a model where the interface effect was described using interface mobility parameter was able to predict satisfactorily mass transfer. For a rising droplet stagnant cap model was used. Stagnant cap volumes were estimated from droplet images. A CFD model of a non-deforming rising droplet with rigid interface was used to fit interfacial reaction kinetic constant. Fitted value was much lower than experimentally determined by high a shear reactor. Mass transfer coefficients calculated from CFD model and estimated using literature correlations agreed well. By applying a two-film model it was shown that major part of the resistance is located at the interface between the phases.

The Application of Numerical Analysis in Determining the State of the Rock Mass Around Directional Wells

Drilling directional and horizontal wellbores plays an important role in the exploitation of hydrocarbons. In the case of long operated and unconventional fields the importance of this type of drilling is fundamental. The horizontal and directional drilling technologies are also applicable in other fields. Directional and horizontal holes are among other various types of drilling under buildings, microtunnels, injection and storage holes. This technology is also used in obtaining coal-bed methane and in underground coal gasification methods.Compared to holes with vertical axes, directional drilling is a much more complex issue. The curvature of the wellbore's axis, passing through the horizontally stratified rock mass, causes the conditions around its cross section to be strongly anisotropic. Not infrequently, the same rock material of each layer exhibits anisotropic properties. Ensuring the stability of the well is very difficult under such conditions.The proper determination of the state of stress, strain and displacement of the rock mass around the hole is critical in the design of directional holes. Numerical analysis tools which take into account the structure of the rock mass and the mechanical properties of rocks along the well trajectory are used for this purpose.The article presents numerical simulations of changes of the rock mass state around a directional well. The calculations were conducted with various material models of rock: the linear-elastic model, the linear-elastic with regard to pore fluid flow model, the elastic – plastic model, the Drucker-Prager cap model with pore fluid flow, the concrete damage plasticity model (CDP), and the cracked material model. The impact of primary pressure, lamination and anisotropy of the rock mass are also included in the calculation. Based on the results of the calculations we analyze the impact of the behavior of rocks on the wellbore's stability.

Fuzzy multi-objective, multi-item, multi-supplier, lot-sizing considering carbon footprint

Optimum order size plays a key role for minimising carbon footprint of a supply chain. However, managers often face difficulty in handling conflicting objectives like cost reduction and carbon emission reduction for supply chain operation. As of now, very few studies have reported multi-objective, multi-item, multi-supplier lot-sizing problem taking consideration of carbon emission under fuzzy environment. This study fills the gaps of earlier research and proposes a fixed carbon cap model incorporating carbon footprint factor. The model has been subsequently modified to carbon offset and multi-objective fuzzy models. The proposed models have been solved by using different methodologies (mixed integer programming, interactive fuzzy goal programming, additive interactive fuzzy goal programming, weighted goal programming, and interactive fuzzy e constraint method) and their results are compared. As theoretical contribution, this study extends interactive fuzzy goal programming and e constraint method to additive interactive fuzzy goal programming and interactive fuzzy e constraint method, respectively. The effectiveness of the proposed models has been explained through illustrative examples and various scenarios have been generated by varying different model parameters. This study will help managers to take prudent decision in carbon constrained world.

Reduced order numerical modeling for calibration of complex constitutive models in powder pressing simulations

Numerical simulations of different ceramic production phases often involve complex constitutive models, with difficult calibration process, relying on a large number of experiments. Methodological developments, proposed in present paper regarding this calibration problem can be outlined as follows: assessment of constitutive parameters is performed through inverse analysis procedure, centered on minimization of discrepancy function which quantifies the difference between measurable quantities and their computed counterpart. Resulting minimization problem is solved through genetic algorithms, while the computational burden is made consistent with constraints of routine industrial applications by exploiting Reduced Order Model (ROM) based on proper orthogonal decomposition. Throughout minimization, a gradual enrichment of designed ROM is used, by including additional simulations. Such strategy turned out to be beneficial when applied to models with a large number of parameters. Developed procedure seems to be effective when dealing with complex constitutive models, that can give rise to non-continuous discrepancy function due to the numerical instabilities. Proposed approach is tested and experimentally validated on the calibration of modified Drucker-Prager CAP model, frequently adopted for ceramic powder pressing simulations. Assessed values are compared with those obtained by traditional, time-consuming tests, performed on pressed green bodies.

SEARCH FOR DIFFERENCES BETWEEN RADIO-LOUD AND RADIO-QUIET GAMMA-RAY PULSAR POPULATIONS WITH FERMI-LAT DATA

ABSTRACT Observations by the Fermi-Large Area Telescope (LAT) have enabled us to explore the population of non-recycled gamma-ray pulsars with a set of 112 objects. It was recently noted that there are apparent differences in the properties of radio-quiet and radio-loud subsets. In particular, the average observed radio-loud pulsar is younger than the average radio-quiet one and is located at lower Galactic latitude. Even so, the analysis based on the full list of pulsars may suffer from selection effects. Namely, most radio-loud pulsars are first discovered in the radio band, while radio-quiet ones are found using the gamma-ray data. In this work we perform a blind search for gamma-ray pulsars using the Fermi-LAT data alone, using all point sources from the 3FGL catalog as the candidates. Unlike our previous work, the present catalog is constructed with a semi-coherent method based on the time-differencing technique and covers the full range of characteristic ages down to 1 kyr. The search resulted in a catalog of 40 non-recycled pulsars, 25 of which are radio-quiet. All pulsars found in the search were previously known gamma-ray pulsars. We find no statistically significant differences in age or in distributions in Galactic latitude for the radio-loud and radio-quiet pulsars, while the distributions in rotation period are marginally different with a statistical probability of . The fraction of radio-quiet pulsars is estimated as . The results are in agreement with the predictions of the outer magnetosphere models, while the polar cap models are disfavored.

Is socially responsible investment useful in Mexico? A multi-factor and ex-ante review

The present paper continues the firsts reviews made to socially responsible investment in Mexico. We extended these reviews by using a non-parametric multivariate equality test, along with a multi-factor market cap model, and a Monte Carlo simulation. Our results show that the IPCS index, the IPCcomp and the IPC have a statistically equal mean-variance performance, suggesting that this sort of investment style (SRI) is a good substitute of the broad market investment style in the long term. Among the causes of this finding is the fact that the IPCS and the IPCcomp indexes have almost the same large and small cap stock concentration and the IPC index (a large-cap one) is not as diversified and mean-variance efficient as the former.

Effects of heating rate, quartz particle size, viscosity, and form of glass additives on high‐level waste melter feed volume expansion

AbstractNuclear waste can be vitrified by mixing it with glass‐forming and ‐modifying additives. The resulting feed is charged into an electric glass melter. To comprehend melting behavior of a high‐alumina melter feed, we monitored the volume expansion of pellets in response to heating at different heating rates. The feeds were prepared with different particle sizes of quartz (the major additive component) and with varied silica‐to‐fluxes ratio to investigate the glass melt viscosity effects. Also, we used additional melter feeds with additives premelted into glass frit. The volume of pellets was nearly constant at temperatures <600°C. After a short period of volume shrinkage at ~600°C‐700°C, foam generation produced massive volume expansion. The low heat conductivity of foam hinders the transfer of heat from molten glass to the reacting feed. The extent of foaming increased with faster heating and higher melt viscosity, and decreased with increasing size of quartz particles and fritting of the additives. Volume expansion data are needed for the mathematical modeling of the cold cap.

A density-dependent modified Drucker-Prager Cap model for die compaction of Ag57.6-Cu22.4-Sn10-In10 mixed metal powders

Due to the bad plastic workability, silver based brazing filler metals with high proportions of additional elements such as Zn, Sn, In, Ga, are very brittle and difficult to be made into thin sheets using conventional manufacturing processes. A novel process method that combine powder compaction and sintering, can fabricate thin sheets of the fragile silver based filler metals. In this work, the densification mechanism of Ag57.6-Cu22.4-Sn10-In10 (wt.%) mixed metal powders was investigated, and a modified density-dependent Drucker-Prager Cap (DPC) model was introduced to describe its compaction behavior based on the equivalent density method. The powder compact was considered as a continuum, and a linear elasticity law as a function of relative density was then used to express the elastic behavior of the powders. An instrumented die with force transducers has been designed to determine the material parameters of the modified DPC model. The elastic and plastic material parameters such as E, υ, β, d, pa, R and pb were then determined experimentally. The friction coefficient between the powders and the die wall with a lubricated die was determined based on the Janssen–Walker theory in the instrumented die experiments. Furthermore, the modified DPC model with the linear elasticity law was validated using finite element simulation method in ABAQUS with a user subroutine (USDFLD). A good agreement between the simulations and experimental results was obtained, indicating the feasibility and applicability of the introduced modified models to describe the die compaction behavior of the mixed metal powders.

Note on the Use of Diametrical Compression to Determine Tablet Tensile Strength

The diametrical compression (DC) test, as defined in United States Pharmacopeia <1217> and in American Society for Testing and Materials testing standard D 3967, has been used extensively to derive the tensile strength (TS) of pharmaceutical tablets from the measured breaking force. DC-derived TSs provide a good approach to measuring the consistency of tablet mechanical properties from one batch to the next. For these quality control type applications, method precision is required, but accuracy is not. In addition, DC has been used to calibrate parameters of the Druker Prager Cap model, a yield criterion expressing the failure of a powder compact under arbitrary 3D loading conditions. For this application, the DC method must not only provide suitable precision but also provide accuracy. In this work, we explore the accuracy of the DC method by comparing TS results to those of the 3-point bend test method (also defined in United States Pharmacopeia <1217>). We conclude that the true TS of a powder compact is approximately double the DC-derived value. Although historical literature assumes that tablets fracture under tension along the centerline of the tablet, analysis of the stress state suggests that tablets are likely to fracture under shear. The impact of this ∼50% error should be considered when accuracy of the TS result is required.