Slab Configuration Research Articles

Optical analysis of the liquid layer combustion of paraffin-based hybrid rocket fuels

Liquefying hybrid rocket fuels (e.g. paraffin) enable higher regression rates due to the presence of an unstable melt layer on the fuel surface during combustion, which causes entrainment of liquid droplets into the oxidizer gas flow. In order to better understand the mechanism responsible for the droplets entrainment, the combustion behaviour of paraffin-based hybrid rocket fuels in combination with gaseous oxygen (GOX) was investigated in the framework of this research. Tests were performed in a 2D slab burner configuration at atmospheric conditions. High-speed videos were recorded and analysed with two different decomposition techniques, applied to the scalar field of the flame luminosity (the flame front is assumed to follow the liquid layer). The fuel slab composition and configuration and the oxidizer mass flow have been varied in order to study the influence of these parameters on the liquid layer instability process. The main focus of the research is to understand the relation between the unstable waves which enable the droplets entrainment process and the regression rate. The results show that the combustion is dominated by periodic, wave-like structures for all the analysed fuels. The frequencies and the wavelengths characterizing the liquid melt layer depend on the fuel viscosity and geometry and on the oxidizer mass flow. Moreover, a dependency of the regression rate on the most excited frequencies and longitudinal wavelengths was found. This is important to better understand the relation between the increased regression rate and the onset and development of the entrainment process, which is connected to the amplification of longitudinal unstable waves caused by the high velocity gas flow over the fuel surface.

Seismic reliability evaluation of tunnel form (box‐type) RC structures under the accidental torsion

In the tunnel form (box‐type) structural system, walls arrangement and mass distribution have important effect on the interactions of thinner shear walls and slab configurations. In the other words, despite the regularity of these buildings as well as symmetry in wall arrangement and mass distribution, the first mode of structural behavior in many cases is twisting. This characteristic is limited to the flexible torsional buildings, which are often sensitive to the mass eccentricity and rotational components of earthquake. According to the available guidelines for design and construction of tunnel form systems and emphasizing on regularity of these structural systems, it seems that the most probable mass irregularity of this type of structures is asymmetric distribution of live loads during service life. Therefore, in this paper, seismic behavior of box‐type (tunnel form) buildings is evaluated under the accidental torsion caused by asymmetric distribution of mass in stories. The incremental nonlinear dynamic analysis is used for this purpose. Despite the asymmetric distribution of mass in plan, the results demonstrate high capacity and appropriate seismic behavior of the tunnel form system. Therefore, an eccentricity equal to 10% of the plan dimension does not change the building performance level, which is higher than the immediate occupancy level under the design and maximum probable earthquake hazard levels.

Performance of reinforced concrete slabs under hydrocarbon fire exposure

This paper presents numerical results on the fire resistance of reinforced concrete (RC) slabs subjected to the severe hydrocarbon fire exposure. The hydrocarbon fire curve represents a possible fire scenario in parking structures, tunnels, and in petro-chemical facilities. A three-dimensional (3D) nonlinear finite element (FE) model is developed to simulate the thermo-mechanical response of a RC slab that incorporates temperature dependent thermal and mechanical properties of concrete and steel reinforcement, respectively. Transient thermal-stress analysis is performed to study the cross-sectional temperature distribution and resulting deflections in the slab during simultaneous application of heat exposure and sustained loading. The predicted temperature distribution within the slab and mid-span deflection are compared with published experimental data. The predicted FE results are in good agreement with the experimental data throughout entire fire exposure duration. The validated FE model is applied in a parametric study to study the fire resistance of RC slabs under different slab configurations and hydrocarbon fire exposure. The varied parameters included fire exposure scenario, service load level, aggregate type, and concrete cover thickness. Results from the numerical analysis showed that hydrocarbon fire exposure has a significant influence on the fire resistance of RC slabs. In particular, the fire resistance of a slab under hydrocarbon fire exposure is 22.4% lower than that of a slab under the standard ISO834 fire exposure. Further, load level has a major effect on the fire resistance of RC slabs under hydrocarbon fire.

Magneto-Rayleigh–Taylor instability driven by a rotating magnetic field

In this paper, we analyze theoretically the magneto-Rayleigh–Taylor instability driven by a rotating magnetic field. Slab configurations of finite thickness are treated both with and without using the Wenzel–Kramers–Brillouin approximation. Regardless of the slab thickness, the directional rotation of the driving magnetic field contributes to suppressing these instabilities. The two factors of the finite thickness and directional rotation of the magnetic field cooperate to enhance suppression, with the finite thickness playing a role only when the orientation of the magnetic field is time varying. The suppression becomes stronger as the driving magnetic field rotates faster, and all modes are suppressed, in contrast to the case of a non-rotating magnetic field, for which the vertical mode cannot be suppressed. This implies that the dynamically alternate configuration of a Theta-pinch and a Z-pinch may be applicable to the concept of Theta-Z liner inertial fusion.

Verification of Acuros XB dose algorithm using 3D printed low-density phantoms for clinical photon beams.

The transport‐based dose calculation algorithm Acuros XB (AXB) has been shown to accurately account for heterogeneities primarily through comparisons with Monte Carlo simulations. This study aims to provide additional experimental verification of AXB for clinically relevant flattened and unflattened beam energies in low density phantoms of the same material. Polystyrene slabs were created using a bench‐top 3D printer. Six slabs were printed at varying densities from 0.23 to 0.68 g/cm3, corresponding to different density humanoid tissues. The slabs were used to form different single and multilayer geometries. Dose was calculated with Eclipse™ AXB 11.0.31 for 6MV, 15MV flattened and 6FFF (flattening filter free) energies for field sizes of 2 × 2 and 5 × 5 cm2. EBT3 film was inserted into the phantoms, which were irradiated. Absolute dose profiles and 2D Gamma analyses were performed for 96 dose planes. For all single slab configurations and energies, absolute dose differences between the AXB calculation and film measurements remained <3% for both fields in the high‐dose region, however, larger disagreement was seen within the penumbra. For the multilayered phantom, percentage depth dose with AXB was within 5% of discrete film measurements. The Gamma index at 2%/2 mm averaged 98% in all combinations of fields, phantoms and photon energies. The transport‐based dose algorithm AXB is in good agreement with the experimental measurements for small field sizes using 6MV, 6FFF and 15MV beams adjacent to various low‐density heterogeneous media. This work provides preliminary experimental grounds to support the use of AXB for heterogeneous dose calculation purposes.

Seasonality and Tectonic Influences on Subduction Zones for Ultra-Deep Earthquakes

Our previous research has found that deep or very deep earthquakes can be influenced by different seasons of the year. It also indicates that other factors may impact the seasonality in addition to these external parameters. This would explain why the response from Northern Hemisphere and Southern Hemisphere for the seasons is different. In the current research, we will focus on very deep earthquakes over a very long period, 1950-2017, which have high magnitude of M ≥ 6 with depth ≥ 500 km and named ultra-deep earthquakes (UDQ). We will separate such events by coordinates of each subduction area located in the Pacific Ring of Fire to find which effects the seasons have on these specific areas. Former tomographic studies in such regions pointed out that each area mentioned had systematic differences in the slab configuration along arcs. Our conclusions showed that those discrepancies may influence the enhancement of earthquakes in some seasons or months.

Effects of building typology on energy consumption in hot and arid regions

This article highlights results of an investigation which was set to determine the effects of residential buildings typology on the consumption of energy for heating and cooling under the specific climatic conditions of hot and arid regions. Five typologies similar in characteristics and living space layouts have been simulated using TRNsys version 17 code. The typologies are representative of actual urban developments constructed during the 80s in Biskra, Algeria.The results showed that compactness, orientation have a great impact on building energy consumption in cooling and heating. In addition, the slab configuration and semi attached one seem to reduce drastically the energy loads.

Near-field thermal upconversion and energy transfer through a Kerr medium.

We present an approach for achieving large Kerr χ(3)-mediated thermal energy transfer at the nanoscale that exploits a general coupled-mode description of triply resonant, four-wave mixing processes. We analyze the efficiency of thermal upconversion and energy transfer from mid- to near-infrared wavelengths in planar geometries involving two slabs supporting far-apart surface plasmon polaritons and separated by a nonlinear χ(3) medium that is irradiated by externally incident light. We study multiple geometric and material configurations and different classes of intervening mediums-either bulk or nanostructured lattices of nanoparticles embedded in nonlinear materials-designed to resonantly enhance the interaction of the incident light with thermal slab resonances. We find that even when the entire system is in thermodynamic equilibrium (at room temperature) and under typical drive intensities ~ W/μm2, the resulting upconversion rates can approach and even exceed thermal flux rates achieved in typical symmetric and non-equilibrium configurations of vacuum-separated slabs. The proposed nonlinear scheme could potentially be exploited to achieve thermal cooling and refrigeration at the nanoscale, and to actively control heat transfer between materials with dramatically different resonant responses.

Seismic behavior and fragility curves of replaceable steel coupling beams with slabs

Replaceable steel coupling beams (RSCB) have been proposed as an alternative to conventional reinforced concrete (RC) coupling beams for enhanced seismic resiliency of coupled wall systems. This paper presents a series of quasi-static tests conducted to examine the seismic behavior of RSCBs with RC slabs and to identify reasonable slab configurations that can minimize the damage to RC slabs. A total of five large-scale specimens were designed and tested. The first four specimens adopted the same end plate link-to-beam connection but adopted different types of RC slabs, including a composite slab, bearing slab, isolated slab or slotted slab. The fifth specimen adopted splice plate link-to-beam connection and a bearing slab. The test results indicate that all specimens developed a large inelastic rotation capacity of more than 0.05rad with stable hysteretic response. The presence of RC slabs is found to have limited effect on the shear strength and inelastic rotation capacity of RSCBs. Some types of RC slabs increased the initial elastic stiffness of RSCBs, but in the plastic stage, none of the slabs affected the loading or unloading stiffness. Among those four types of slabs, the composite slab suffered the most significant damage, as a result of pulling out of shear studs and subsequent pouching failure of the slab. Compared with the bearing slab or slotted slab, the isolated slab developed much fewer and smaller cracks, which should allow for easier repair. Based on the observations of this test and previous tests, four damage states for RSCBs were identified, corresponding to different repair methods. Fragility curves of RSCBs at various damage states were developed, which can provide the criteria for seismic performance assessment of RSCBs.

Effective Constitutive Parameters Retrieval Method for Bianisotropic Metamaterials Using Waveguide Measurements

An effective method for extraction of electromagnetic properties of bianisotropic biaxial omega-type metamaterial (MM) slabs from waveguide measurements is presented. The method relies on measurements of S-parameters of two MM slab configurations (transverse and longitudinal) to extract electromagnetic properties endowed with strong bianisotropic coupling. An uncertainty analysis is performed for examining the effect of geometrical parameters of the longitudinal configuration on its resonance characteristic. For verification of the proposed method, constitutive parameters of a polyethylene sample are extracted at the $X$ -band (8.2–12.4 GHz). Then, the method is applied for extraction of electromagnetic properties of an MM slab (square split-ring resonators over FR4 substrate) using simulated and measured S-parameters for the two configurations at the $X$ -band. It is noted that extracted electromagnetic properties obtained from measured S-parameters are in good agreement with those obtained from simulated S-parameters except for a small frequency shift and magnitude change, which could arise from fabrication tolerances, air gaps present between MM cells, and local irregular surface of the longitudinal configuration. For completeness, it is analyzed whether extracted properties satisfy the locality conditions.

Automatic Yield-Line Analysis of Practical Slab Configurations via Discontinuity Layout Optimization

AbstractThe yield-line method provides a powerful means of rapidly estimating the ultimate load that can be carried by a reinforced concrete slab. The method can reveal hidden reserves of strength ...

Modeling of equilibrium conformation of Pt2Ru3 nanoparticles using the density functional theory and Monte Carlo simulations

Abstract

Effect of casting flow defects on the crack propagation in UHPFRC thin slabs by means of stereovision Digital Image Correlation

Owing to their outstanding compressive strength and considerable cracking resistance, Ultra High Performance Fibre Reinforced Concrete (UHPFRC) have been recently successfully applied to thin bi-dimensional elements, e.g., plate and shells. As a critical aspect of UHPFRC technology,is work aims at experimentally investigating the effect of fibre orientation on the damage behaviour of UHPFRC 2-way thin slabs by means of stereovision digital image analysis. To this aim, the fibre orientation was perturbed by introducing a simple divider line as a temporary barrier to the casting flow of fresh concrete. The casting flow defect affected the fibre distribution by creating a weakened plane with a strong discontinuity. By varying the line direction and the position of the concentrated load position, six different slab configurations were fabricated and tested under punching load with hyperstatic boundary conditions. Then, the 3-D deformation field was measured by means of stereovision-based Digital Image Correlation (DIC). The results showed the critical importance of the fibre distribution on the microcracking growth and the structural ductility. The casting flow defect had a major impact on the observed microcrack pattern and growth especially before the peak load. When the defect crossed the loading point, the microcracks did not fully develop with an important reduction of the load-carrying capacity and the structural ductility. Finally, a simplified application of yield line theory allowed estimating the effect on the fibre distribution of the casting flow defects.

Interaction of Hydrogen with Au Modified by Pd and Rh in View of Electrochemical Applications

Hydrogen interaction with bimetallic Au(Pd) and Au(Rh) systems are studied with the density functional theory (DFT)-based periodic approach. Several bimetallic configurations with varying concentrations of Pd and Rh atoms in the under layer of a gold surface(111) were considered. The reactivity of the doped Au(111) toward hydrogen adsorption and absorption was related to the property modifications induced by the presence of metal dopants. DFT-computed quantities, such as the energy stability, the inter-atomic and inter-slab binding energies between gold and dopants, and the charge density were used to infer the similarities and differences between both Pd and Rh dopants in these model alloys. The hydrogen penetration into the surface is favored in the bimetallic slab configurations. The underlayer dopants affect the reactivity of the surface gold toward hydrogen adsorption in the systems with a dopant underlayer, covered by absorbed hydrogen up to a monolayer. This indicates a possibility to tune the gold surface properties of bimetallic electrodes by modulating the degree of hydrogen coverage of the inner dopant layer(s).

Abnormal seismological and magmatic processes controlled by the tearing South American flat slabs

The influence of flat slab subduction on the formation of intra-slab earthquakes, volcanic activities and mantle seismic velocity anomalies remains unclear. We attempt to better understand these processes by simulating the two flat slabs in Peru and Chile using data-orientated geodynamic models. Our results successfully reproduce the observed flat slabs as mainly due to two subducting aseismic ridges. In contrast to the traditional view of flat-slab subduction, we find that these slabs are internally torn, as is due to the 3D nature of the subducting buoyancy features. This broken slab configuration, confirmed by regional tomography, naturally explains the abnormal distribution of and stress regimes associated with the intermediate-depth earthquakes. We further show that the slab tearing process could also better explain the formation of adakitic and ore-forming magmatism, the evolution of the magmatic arc, and the enigmatic mantle seismic structures beneath these regions. We propose that slab tearing may represent a common result of buoyancy feature subduction and that the resulting mantle processes could affect the long-term geodynamic evolution of continents.

Verification of BOUT++ by the method of manufactured solutions

BOUT++ is a software package designed for solving plasma fluid models. It has been used to simulate a wide range of plasma phenomena ranging from linear stability analysis to 3D plasma turbulence and is capable of simulating a wide range of drift-reduced plasma fluid and gyro-fluid models. A verification exercise has been performed as part of a EUROfusion Enabling Research project, to rigorously test the correctness of the algorithms implemented in BOUT++, by testing order-of-accuracy convergence rates using the Method of Manufactured Solutions (MMS). We present tests of individual components including time-integration and advection schemes, non-orthogonal toroidal field-aligned coordinate systems and the shifted metric procedure which is used to handle highly sheared grids. The flux coordinate independent approach to differencing along magnetic field-lines has been implemented in BOUT++ and is here verified using the MMS in a sheared slab configuration. Finally, we show tests of three complete models: 2-field Hasegawa-Wakatani in 2D slab, 3-field reduced magnetohydrodynamics (MHD) in 3D field-aligned toroidal coordinates, and 5-field reduced MHD in slab geometry.

TH-AB-BRA-05: Lung Cannot Be Treated as Homogeneous in Radiation Transport Simulations in Magnetic Fields

Purpose: Magnetic fields in MRgRT are known to induce dose perturbations near lung-tissue interfaces. The goal of this study is to determine if the heterogeneous structure of the lung influences the dose distribution in a magnetic field. Method: The dose distribution from a 4 cm X 4 cm 6 MV photon beam in a 0, 0.6, or 1.5 T magnetic field in a homogeneous lung density (0.333 g/cm3) geometry is compared to that in a heterogeneous segmented slab configuration. The heterogeneous phantom is composed of 2/3 water vapour and 1/3 liquid water such that the overall density of the lung regions in the two phantoms are equivalent. The EGSnrc DOSXYZnrc user code is used with a previously implemented magnetic field transport code. Results: For water vapour gap thickness of 2 mm, compared to the homogeneous lung case (which already exhibits significant dose perturbations in a magnetic field) differences as large as 12.3 ± 0.2 % are observed for a 0.6 T field and 9.3 ± 0.1 % for a 1.5 T field at the tissuelung interface, and on the order of several percent within the lung-like tissue region for both magnetic fields. Thicker gaps produced larger deviations while a gap thickness of 0.2 mm does not result in notable differences. Regardless of gap thickness, the heterogeneities had little effect on the 0 T simulations. Further, using smaller scoring regions revealed that dose averaging effects could obscure dose differences as large as 10 – 20 % within the heterogeneous structures of the lung-like media. Conclusions: This simple model demonstrates that media heterogeneities can play an important role in MRgRT dose distributions, and care must be taken in setting up any dose calculation in the lung in the presence of a magnetic field, especially for air regions larger than 2 mm.

Adhesive and adhesiveless contact mechanics of elastic layers on slightly wavy rigid substrates

The behavior of an elastic layer in contact with a wavy rigid substrate is analyzed depending on layer thickness, substrate geometry, energy of adhesion, for given value of remote applied load or penetration. Two different slab configurations are considered: (i) a free layer with uniform pressure acting on the upper boundary, and (ii) a confined layer with uniform displacement assigned to the upper boundary. These two different geometries have been considered as exemplar cases which are of great relevance in a large number of applications of crucial importance as structural adhesives, pressure sensitive adhesives, coatings and protective adhesives. Our study shows that the layer thickness affects the contact behavior differently depending on the constraints configuration. In particular, reducing the thickness of the layer makes the latter more or less compliant depending on the considered configuration. Thus, the free layer becomes more sticky and, as the layer thickness is reduced, an increasingly large amount of external work needs to be provided to detach the layer from the substrate. On the contrary, the confined layer significantly stiffens by decreasing the layer thickness. This leads to an increase of the pull-off force for detachment accompanied by a decrease of the energy needed to bring the layer and substrate apart.

The effects of grain size and grain boundary characteristics on the thermal conductivity of nanocrystalline diamond

Molecular dynamics simulation was used to study the effects of each grain dimension and of grain boundary characteristics on the inter-grain thermal boundary resistance (TBR) and intragrain thermal conductivity of nanocrystalline diamond. The effect of the grain boundaries perpendicular to the heat flow was studied using a multiple slab configuration, which greatly reduced the artifacts associated with the heat source/sink. The TBR between the slabs was found to be more sensitive to the atomic arrangement at the boundary than to the tilt angle between the slabs. When the atomic arrangement at the interface was altered from the minimum energy configuration, the TBR increased by a factor of three, suggesting that a sub-optimal interface quality between the grains could play a large role in reducing the thermal conductivity of nanocrystalline diamond. The thermal conductivity between the boundaries was found to be similar to the bulk value, even when the boundaries were only 25 nm apart. The effect of grain boundaries parallel to the heat flow was found to have a large dependence on the microstructural details. Parallel boundaries which were 2 nm apart reduced the thermal conductivity of defect-free diamond by between one third and a factor of ten.

Broadband fractional total internal reflection quasi phase matching based second harmonic generation in reverse tapered isotropic semiconductor considering the effect of nonlinear reflection

This paper analyzes a highly efficient broadband second-harmonic generator in the mid infrared region using an isotropic reverse tapered semiconductor slab configuration, using fractional total internal reflection quasi-phase matching technique. A computer aided simulation has been performed using ZnTe as the nonlinear material which provides an extremely high conversion efficiency of 22.94% with a 3[Formula: see text]dB bandwidth of 200[Formula: see text]nm. Effect of varying the slab dimensions on the performance parameters has also been analyzed. Finally, the catastrophic effect caused by destructive interference due to nonlinear law of reflection has also been incorporated in the analysis thereby giving more accurate results.