Confinement Model Research Articles

Flow physics and sensitivity to RANS modelling assumptions of a multiple shock wave/turbulent boundary layer interaction

Reynolds Averaged Navier Stokes simulation (RANS) using the in-house CFD solver of Glasgow University is utilised to investigate the flow physics and the sensitivity to modelling assumptions of a multiple shock wave turbulent boundary layer interaction in a rectangular duct (Mr=1.61, Reδr=162000). Such interactions often occur in high-speed intakes. Two-dimensional simulations were first performed to investigate the required grid resolution. Then the sensitivity of the solution to different turbulence models is considered. Based on the required grid resolution a series of three-dimensional simulations were performed to investigate the effect of spanwise confinement and turbulence models. Lastly, using the best approach based on the above investigations, results from two additional test cases were compared to their experiments, and conclusions are drawn as to the best way to simulate multiple shock wave turbulent boundary layer interactions.

Electronic properties of Pb-I deficient lead halide perovskites.

The electronic structure evolution of deficient halide perovskites with a general formula (A,A')1+xM1-xX3-x was investigated using the density functional theory. The focus is placed on characterization of changes in the bandgap, band alignment, effective mass, and optical properties of deficient perovskites at various concentrations of defects. We uncover unusual electronic properties of the defect corresponding to a M-X vacancy filled with an A' cation. This defect "repels" electrons and holes producing no trap states and, in moderate quantities (x ≤ 0.1), does not hinder charge transport properties of the material. This behavior is rationalized using a confinement model and provides additional insight to the defect tolerance of halide perovskites.

Comparison of Two Parameters Models for clay brick masonry confinement

Masonry elements are often strengthened in order to improve their structural capacity. Generalized methods to assess the behavior of confined masonry columns are not available in the technical literature. They have been usually derived from concrete confinement models. However, concrete and masonry present several crucial differences due to their physical and mechanical properties. In fact, generalized models to assess the axial capacity of masonry columns were limited by the strong variability and heterogeneity of physical and mechanical properties. However, the recent scientific researches provided relevant information on the experimental behavior of confined masonry columns. In this paper, a confinement model has been proposed to assess the axial capacity of clay brick masonry strengthened using several strengthening systems. The model has been validated by means of comparisons with experimental results. In order to assess the potential of the proposed model, the comparison was carried out also with other available mechanical models.

Impurity-related optical response in a 2D and 3D quantum dot with Gaussian confinement under intense laser field

ABSTRACTUsing the two-dimensional (2D) diagonalisation method, the impurity-related electronic states and optical response in a 2D quantum dot with Gaussian confinement potential under nonresonant intense laser field are investigated. The effects of a hydrogenic impurity on the energy spectrum and binding energy of the electron and also intersubband optical absorption are calculated. The obtained numerical results show that the degeneracies of the excited electron states are broken and the absorption spectrum exhibits a redshift with the values of the laser field. The findings indicate a new degree of freedom to tune the performance of novel optoelectronic devices, based on the quantum dots and to control their specific properties by means of intense laser field and hydrogenic donor impurity. Using the same Gaussian confinement model, the electronic properties of a confined electron in the region of a spherical quantum dot are studied under the combined effects of on-centre donor impurity and a linearly polarised intense laser radiation. The three-dimensional problem is used to theoretically model, with very good agreement, some experimental findings reported in the literature related to the photoluminescence peak energy transition.

Numerical simulations of circular high strength concrete-filled aluminum tubular short columns incorporating new concrete confinement model

Abstract Concrete-filled aluminum tubular (CFAT) columns have the advantages of a lightweight, high resistance to corrosion, good appearance and ease of maintenance over concrete-filled steel tubular (CFST) columns. However, experimental and computational studies on the performance of CFAT columns have rarely been reported. This paper concerns with the fiber-based numerical analysis, structural behavior, and design of circular high strength CFAT stub columns loaded concentrically. A new concrete confinement model for computing the lateral pressures on the concrete core in CFAT circular columns is proposed and implemented in the computational model. The numerical analysis procedure is given for the determination of the nonlinear load-strain behavior of CFAT stub columns. The available experimental results of circular CFAT columns are used to assess the accuracy of the developed model. The computer model is employed to ascertain the significance of various geometric parameters in addition to material strengths on the responses of CFAT stub circular columns. The design equation based on Liang-Fragomeni's expression is proposed for quantifying the ultimate axial strengths of axially compressed CFAT short columns. The verification reveals that the computer modeling approach accurately quantifies the ultimate loads and nonlinear load-strain performance of CFAT columns with circular sections. The proposed design equation yields good calculations of the ultimate axial strengths of CFAT columns.

Analysis of Materials for Heat Transport in Tokamaks

Every nuclear power reactor, whether of fusion or fission, is essentially a thermal system that generates electricity. In this sense, there are several problems in relation to this heat transport. The model of plasma confinement by magnetic force, in the nuclear fusion (sterellator and tokamak), has only been 20 years and recently some success in the quality of the generated plasma has been achieved. However, due to the large amount of energy coming from the plasma, the choice of the material that will carry the generated energy is quite troublesome, due to the need to handle a very high temperature for the nuclear fission standards. Solutions are explored by the scientific community to transport the energy generated in the case of the primary circuit, after exceeding breakeven temperature and models that are based on the fission reactors of the fourth generation and those currently in operation, to search for solutions regarding the transport of heat generated for the generation of electric energy. Several materials such as pressurized water, sodium, helium and boron have been considered and studied to form the primary heat transfer circuit for the exchanger. A thorough analysis of these materials is necessary. This research looked at some of these materials for heat transport and power generation. Lithium and helium were found to be the probable materials for conveying heat and cooling in the blanket. The results show that research on blanket materials needs more attention. The quality of these materials needs to be improved by material research, with the ODS EUROFER alloy and other research to reduce material erosion by helium nano bubbles. Plasma quality needs to be improved to keep constant and free of impurities when using lithium in liquid form.

Impact of scaling laws on tokamak reactor dimensioning

A simple and comprehensive method is derived and used to quantify the impact of scaling laws on tokamak reactor dimensioning. Assuming prescribed geometrical coefficients, we find the ensemble of possible triplets R, B and normalized beta which allow one to reach target fusion gain Q and fusion power , at an arbitrary Greenwald fraction. The model is generic and derived for any scaling law of the energy confinement time. Using the IPB98(y,2) scaling law (ITER Physics Expert Group on Confinement and Transport and Confinement Modeling and Database and ITER Physics Basis Editors 1999 Nucl. Fusion 39 2175) leads to ITER specifications, as expected. The recently proposed new scaling law for H-mode plasmas (DS03, (Sips et al 2018 Nucl. Fusion 58 126010)) is shown to lead to modest changes to the dimensioning, except for B which could be significantly smaller for the same target performance. The impact on the dimensioning of critical exponents of the scaling law—both regarding engineer and dimensionless variables—is assessed, pushing for their determination with refined accuracy. Finally, the method is applied to a DEMO-like machine. The DS03 scaling law is found to have favorable consequences on the dimensioning as compared to IPB98(y,2), provided one is able to operate at larger , which can reveal challenging in a reactor aiming at zero disruption. Importantly, the opposite scaling of both scaling laws with respect to the aspect ratio are shown to have significant consequences on the optimal choice of this critical parameter.

Fibre-reinforced intumescent fire protection coatings as a confining material for concrete columns

This paper considers a novel, alternative application of fibre-reinforced epoxy-based intumescent coatings as potential materials for strengthening concrete columns. An experimental programme is presented examining the compressive behaviour of unreinforced concrete cylinders at ambient temperature that are confined with fibre-reinforced intumescent wraps. It is demonstrated that these advanced composite coatings can provide effective passive confinement to concrete, achieving ultimate axial strength and strain enhancements that are comparable to those of conventional FRP wraps. The enhancements are also shown to be reasonably predicted by existing confinement models for FRP-confined concrete. The results demonstrate the strong potential of these fire protection materials as alternative strengthening systems for reinforced concrete columns, potentially eliminating the need for additional passive fire protection that is common with conventional fire-rated FRP wrapping systems.

New model for confinement of reinforced concrete columns with an ultra-high strength close to 200 MPa

The objective of this work is to develop a new confinement model for ultra-high strength concrete columns confined by transverse reinforcement. First, the mechanism of confinement with transverse reinforcement of square and rectangular section columns has been described. In this context, the existing peak strength and corresponding strain of the stress-strain models, with normal strength (NSC) and high strength (HSC) are selected. Next, the assembled database covering 300 existing experimental data in the literature with an unconfined compressive strength ranging between 20 MPa and 200 MPa is exposed. In order to evaluate the performance of the existing confinement models, three statistical indicators were used, namely: the coefficient of determination (R2), root mean square error (RMSE) and standard deviation (SD). Afterward, the performance of 20 existing confinement models was implemented. According to this study, the proposed peak strength concrete and the corresponding axial strain showed a good performance compared with the 20 selected models. In addition, the expressions of the proposed models are simple and easy to use for design applications.

Determination of crystallite size of nanodiamond by Raman spectroscopy

Although the phonon confinement model (PCM) was claimed to be successfully used to accurately calculate the size of larger Si nanocrystals, quantitative size characterization by Raman spectra still remains a challenge in the case of nanodiamonds due to its complexity. Here, we find that a local-mode model of Raman spectra developed recently can be employed to determine the bond number of the ordered diamond core in nanodiamonds, and then furtherly determine the size of nanodiamonds. The Raman lines of nanodiamonds of 3.0 nm, 2.0 nm, 2.2 nm, 3.3 nm, 3.7 nm 4.42 nm and 6.3 nm are calculated. Results are in good agreement with the measured Raman spectra. It not only provides a new approach to predict the size of nanodiamonds accurately by Raman spectra, but also helps to clarify issues in Raman spectra of nanodiamond and other carbon nanomaterials.

Thermal radiation and inclusive production in the Kharzeev-Levin-Nardi model for ion-ion collisions

We show that in order to obtain a successful description of the transverse momenta distribution for charged particles in ion-ion collisions, one must include a thermal emission term. The temperature of this emission $T_{\rm th}$ turns out to be proportional to the saturation scale, $T_{\rm th} = 1.8/2\pi \,Q_s$. The formalism for the calculation of the transverse momenta spectra in CGC/saturation approach is developed, in which two stages of the process are seen: creation of the colour glass condensate, and hadronization of the gluon jets. Our calculations are based on the observation that even for small values of $p_T$, the main contribution in the integration over the dipole sizes stems from the kinematic region in vicinity of the saturation momentum, where theoretically, we know the scattering amplitude. Non-perturbativ corrections need to be included in the model of hadronization. This model incorporates the decay of a gluon jet with effective mass $m^2_{\rm eff} = 2 Q_s \mu_{\rm soft}$ where $\mu_{\rm soft}$ denotes the soft scale, with the fragmentation functions at all values of the transverse momenta. We use the KLN model which, provides a simple way to estimate the cross sections for the different centrality classes. Comparing the results of this paper with the transverse distribution in the proton-proton scattering, we see two major differences. First, a larger contribution of the thermal radiation term is needed, in accord with higher parton densities of the produced colour glass condensate. Second, even changing the model for the hadronization, without a thermal radiation term, we fail to describe the $p_T$ spectrum. Consequently, we conjecture that theexistence of the thermal radiation term is independent of the model of confinement.

Accretion-induced Collapse from Magnetic White Dwarf Binaries and Formation of Binary Millisecond Pulsars: Redbacks and Black Widows

Abstract Redbacks (RBs) and black widows (BWs) are two peculiar classes of eclipsing millisecond pulsars (MSPs). The accretion-induced collapse (AIC) of an oxygen/neon/magnesium composition white dwarf (WD) to a neutron star has been suggested as one possible formation pathway for those two classes of MSPs. However, it is difficult to produce all known MSPs with the traditional AIC scenario. In this study by using the MESA stellar evolution code, we investigate the detailed pre-AIC evolution of magnetized WD binaries with the magnetic confinement model where the high magnetic field strength of the WD can confine the accreted matter in the polar caps. We find that the initial donor mass and orbital periods in our model can be lower than that of previous traditional AIC models. We also present post-AIC evolution models to form RBs and BWs with and without the spin-down luminosity evaporation of MSPs. Under the magnetic confinement model and evaporative winds (with corresponding angular momentum loss from the surface of the donor star), the companion masses and orbital periods of all known RBs can be covered and a number of binaries can evolve to become BWs.

The Influence of Steel Fiber on the Stress-Strain Behavior of Confined Concrete

This paper presents the result of an experimental study of confined concrete to evaluate the stress-strain behavior of fiber-reinforced concrete, which includes strength and ductility. The effectiveness of steel fibers in influencing the stress-strain behavior was also evaluated by creating a conventional concrete as a control specimen. The experimental results showed that there was a decrease in the value of the increased strength of confined concrete (f’cc/f’co) when the compressive strength of the concrete increased. Reducing the spaces of lateral reinforcement spaces will also increase the strength and ductility of confined concrete. The comparison of experimental results with various confinement models shows that there are substantial differences in the peak stress and the descending behavior of confined fiber concrete.

Large-area synthesis of monolayer MoTexSe2-x alloys by chemical vapor deposition

Great achievements have been made in the alloying of two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs), which can allow tunable bandgaps for practical applications in optoelectronic devices. However, telluride-based TMDs alloys were less studied due to the difficulties of sample synthesis. Here, in this work, we report the large-area synthesis of monolayer MoTexSe2-x alloys with a controllable Te composition by a modified alkali metal halide assisted chemical vapor deposition method. Photoluminescence (PL) spectra demonstrate that the bandgap changes from 1.55 to 1.38 eV with increasing Te concentrations. The behaviors of Raman modes of MoSe2 are well explained by a phonon confinement model. The density functional theory calculation provides insights into the atomic vibration images and better understanding of the Raman properties of MoTexSe2-x alloys. Our work provides a simple method to synthesize large-scale 2H phase Te-based 2D TMDs alloys for their further applications in near-infrared devices.

Prediction of triaxial behavior of recycled aggregate concrete using multivariable regression and artificial neural network techniques

A cost-effective design of concrete elements in compliance with sustainability principles requires to accurately predict the behavior of concrete under various loading conditions. Yet to date available approaches for the prediction and evaluation of recycled aggregate concretes (RAC) under triaxial load are very scarce, which may hinder the transition of such an eco-friendly concrete from lab-based technique to widespread applications. As a first attempt to iron out this issue, this study develops some reliable and accurate analytical tools on the basis of an experimental database containing the results of 193 cylindrical peak stress under axisymmetric triaxial load, 55 cubic peak stress under true triaxial load, 76 peak strains and 61 elastic moduli of RAC retrieved from an extensive review of the literature. First, a new empirical design-oriented model is presented refining the generic form of conventional confinement models for natural aggregate concrete while considering the impacts of RCAs. Then Grey Correlation Analysis (GCA) is conducted to look into the sensitivity of the key parameters that affect the triaxial behavior of RAC. The results of the GCA indicate that the triaxial behavior of RAC mainly depends on the effective water-to-cement binder ratio, aggregate-to-cement ratio, lateral stress conditions, exposure temperature, as well as the RCA replacement ratio. Having the input parameters identified by the GCA, three robust data-mining mathematic tools, namely Multiple Nonlinear Regression (MNR), Artificial Neural Network (ANN), and hybrid Genetic Algorithm Artificial Neural Network (GA-ANN) are employed to simulate the mechanical performances of RAC under triaxial load. The results demonstrate that the developed MNR equations and the neural network models satisfactorily predict the behavior of RAC under triaxial load; among those models (including the developed design-oriented one), the ANN optimized with GA performs the best. These arguably point to the possibility of the application of those models in the design and evaluation of structural members manufactured using RAC, especially for them under complex loading scenarios.

Experimental and analytical investigation on strengthening of heat damaged concrete by textile reinforced concrete (TRC)

Composites fabricated of textile as reinforcement and a fine-grained concrete as matrix are referred to textile reinforced concrete (TRC) which provides the opportunity to build thin and shell constructions and to repair and strengthen concrete and masonry structures. This paper aimed to exploit the repair potential of TRC through confinement of heat-damaged concrete columns. For this purpose, a two-phase approach was conducted, in the first phase of which the effect of elevated temperature on mechanical properties of concrete was examined. The main objective of the second phase, however, was to assess the efficiency of glass textile reinforced concrete (GTRC) in the confinement of heat-damaged concrete. This phase commenced with selecting a candidate mortar among commonly used TRC mortars to confine heat-damaged specimens. Experimental results revealed that the adopted confinement system is an efficient solution to enhance the load bearing capacity of even seriously heat-damaged specimens. Eventually, experimental results were compared with available prediction models from the literature for both of the load-bearing capacity and also the compressive strength of confined concrete. Then an analytical confinement model was proposed based on best-fit analysis exclusive to heat-damaged concrete confined by GTRC.

Influence of Li ion implantation on LO phonon broadening and bandgap opening in ZnO thin films

Doping of nonmagnetic impurities in technologically important ZnO has opened a new window for achieving room temperature ferromagnetism, p-type carrier conduction, and enhancement of ferroelectric properties. Here, we report on the confined optical phonon and bandgap engineering in highly oriented Li implanted ZnO thin films. Using resonance Raman scattering condition, the confined longitudinal optical phonon lineshapes in uniaxial hexagonal wurtzite crystal are analyzed in detail using the phonon confinement model. We have demonstrated that phonon confinement model can yield a meaningful result for the interpretation of resonance Raman lineshapes if one considers the contribution of both the E1 (LO) and A1 (LO) modes, particularly while dealing with oriented ZnO thin films. Furthermore, with the increase in Li dose, the bandgap of ZnO is found to show a blue shift, and such blue shift in bandgap is explained using first principles calculation.

Behaviour of CFRP wrapped RC square columns under eccentric compressive loading

This paper presents the effects of carbon fibre reinforced polymer (CFRP) volumetric ratios on structural and failure behaviour of CFRP wrapped reinforced concrete (RC) square columns under concentric, eccentric and flexural loadings. The CFRP volumetric ratio is considered as the ratio of volume of CFRP to the volume of concrete. The applicability of existing confinement models to predict the load-moment interaction diagrams of such columns in eccentric loadings is also presented in this paper. Total 20 columns were tested. Dimensions of all columns were 175x175x800 mm with 20 mm rounded corners. Variable considered in this study were number of CFRP layers (e.g. 0, 1, 2 and 3 layers) which corresponds to CFRP volumetric ratio of 0, 0.3, 0.6 and 0.9%, respectively, increasing eccentricities (e.g. 0, 25, 35 and 50 mm) of the applied load and pure flexural loading. Results show that ultimate load capacity and axial deformation increase with increase in CFRP volumetric ratios irrespective of eccentricities. However, load capacity and deformation decrease with increasing eccentricities for any given CFRP volumetric ratio. Hoop strains also increase with increase in CFRP volumetric ratios and eccentricities. Stiffness of CFRP wrapped columns also increases with increase in CFRP volumetric ratio up to 0.6% and decreases with increase in eccentricities. Ductility of CFRP wrapped columns increases with increase in CFRP volumetric ratios and eccentricities. The algorithms for calculation of critical points for load-moment (P-M) interaction diagrams using analytical as well as numerical stress integrations are developed and compared to those of the column tests. P-M interaction diagram developed using existing confinement models agree well with the experimental P-M interaction diagrams of CFRP wrapped RC square columns under eccentric loading.

Experimental studies and theoretical models for concrete columns confined with FRP composites: a review

PurposeAdvanced fibre-reinforced polymer (FRP) composites have been increasingly used over the past two decades for strengthening, upgrading and restoring degraded civil engineering infrastructure. Substantial experimental investigations have been conducted in recent years to understand the compressive behaviour of FRP-confined concrete columns. A considerable number of confinement models to predict the compressive behaviour of FRP-strengthened concrete columns have been developed from the results of these experimental investigations. The purpose of this paper is to present a comprehensive review of experimental investigations and theoretical models of circular and non-circular concrete columns confined with FRP reinforcement.Design/methodology/approachThe paper reviews previous experimental test results on circular and non-circular concrete columns confined with FRP reinforcement under concentric and eccentric loading conditions and highlights the behaviour and mechanics of FRP confinement in these columns. The paper also reviews existing confinement models for concrete columns confined with FRP composites in both circular and non-circular sections.FindingsThis paper demonstrates that the performance and effectiveness of FRP confinement in concrete columns have been extensively investigated and proven effective in enhancing the structural performance and ductility of strengthened columns. The strength and ductility enhancement depend on the number of FRP layers, concrete compressive strength, corner radius for non-circular columns and intensity of load eccentricity for eccentrically loaded columns. The impact of existing theoretical models and directions for future research are also presented.Originality/valuePotential researchers will gain insight into existing experimental and theoretical studies and future research directions.

BED TEMPERATURE IN COMPOST BARNS TURNED WITH ROTARY HOE AND OFFSET DISC HARROW

ABSTRACT The success of confinement for dairy cattle in the compost barn model depends mainly on the management of the bed and consists of its turning. This paper characterises the spatial variability of the bed temperature in the compost barn confinement model, as well as verifying whether there was an effect on efficiency from turning the bed with different agricultural implements. The experiment was conducted during the summer and winter of 2016, with 8 days of collection in each period. Data were analysed with descriptive statistics methods and geostatistical modelling with semivariograms and kriging maps. The results of the t-test at a5% significance level indicated that, after turning the bed with the plough or rotary hoe, the temperature values were significantly lower. There was an efficient on bed turning based on different agricultural implements. Spatial dependence was observed on the data, with a better adjustment given by a Gaussian model. Kriging maps allowed the characterization of the spatial variability of bed temperature and the visualization across the compost barn bed at the superficial layer and 0.15 m in depth.