Search Results (130)

We review some aspects of accretion disks physics, spacetime photon shell and photon orbits, related to retrograde (counter-rotating) motion in Kerr black hole (BH) spacetimes. In this brief review, we examine the counter-rotating components of the Kerr BH shadow boundary, under the influence of counter-rotating accretion tori, accreting flows and proto-jets (open critical funnels of matter, associated with the tori) orbiting around the central BH. We also analyze the redshifted emission arising from counter-rotating structures. Regions of the shadows and photon shell are constrained in their dependence of the BH spin and observational angle. The effects of the counter-rotating structures on these are proven to be typical of the fast-spinning BHs, and accordingly can be observed only in the restricted classes of the Kerr BH spacetimes. This review is intended as a concise guide to the main properties of counter-rotating fluxes and counter-rotating disks in relation to the photon shell and the BH shadow boundary. Our findings may serve as the basis for different theoretical frameworks describing counter-rotating accretion flows with observable imprints manifesting at the BH shadow boundary. The results can eventually enable the distinction of counter-rotating fluxes through their observable imprints, contributing to constraints on both the BH spin and the structure of counter-rotating accretion disks. In particular, photon trajectories and their impact parameters can manifest in the morphology of the BH shadow. Such features, when accessible through high-resolution imaging and spectral or polarization measurements, could provide a direct avenue for testing different theoretical models on accretion disk dynamics and their BH attractors. Full article

Water and sand inrush is frequently accompanied by surface subsidence, which severely constrains the sustainable development of coordinated coal mining and ecological environment. This study investigated four key influencing factors based on a water and sand inrush test system: fracture width, aquifer thickness, sand particle size composition and stratigraphic sedimentary structure. It obtained the morphological evolution characteristics of collapse funnels and revealed the evolution mechanism of collapse funnels induced by water and sand inrush. The results indicate that fracture width and aquifer thickness mainly affect the range of collapse funnel, and both show a positive correlation with the radius of collapse funnels. Sandy particle size composition plays a dominant role in the morphology of collapse funnels induced by disasters: as the size of the soil skeleton particles increases, the morphology of collapse funnels changes sequentially from a bowl shape to an inverted cone shape and then to a funnel shape with a sunken center and raised slopes. The stratigraphic sedimentary structure has a significant impact on the morphology and damage induced by disasters in collapse funnels. The upper clay layer of the underlying aquifer inhibits the water and sand inrush processes to some extent. An increase in the thickness and number of clay layers effectively prevents the water and sand mixture from flowing into the fracture channel from the lateral direction. This reduces the damage range of collapse funnels and decreases the rate of water and sand inrush. This study clarifies the formation mechanism of surface collapse funnels under the influence of the disaster-causing factors of water and sand inrush, and provides theoretical guidance for the prevention and control of such disasters. Full article

To better understand the relationship between meniscus instabilities and the high levels of turbulence in the fluid dynamics of a continuous medium slab mold, this study investigates the magnitudes of meniscus dynamics distortions and their fluid dynamic origin using a full-scale water modeling experiment and mathematical simulations. The three-dimensional mathematical model is composed of the continuity and momentum equations, together with the standard k-ε turbulence model and the volume of fluid model, to track the dynamics of the steel interface. The results show that the medium slab mold shares flow patterns common to both conventional slab molds and funnel thin slab molds, making its fluid dynamics more complex. Despite this, the fluid dynamics within the mold do not develop a dynamic distortion phenomenon but induce upward stream flows with instability and high velocities, which generate an unstable meniscus behavior characterized by significant surface oscillations, variations in velocity, and high deformations. These latter flow characteristics are the origin of meniscus dynamic distortion (MDD), which shows a constant frequency with non-constant periodicity and different median lifecycle ranges. Full article

Hydrogen-based direct reduction of iron ore is a promising route to reduce CO₂ emissions in steelmaking, where uniform particle flow inside shaft furnaces is essential for efficient operation. In this study, a full-scale three-dimensional Discrete Element Method (DEM) model of a shaft furnace was developed to investigate the effects of a diverter device on granular flow. By systematically varying the radial width and top/bottom diameters of the diverter, particle descent velocity, residence time, compressive force distribution, and collision energy dissipation were analyzed. The results demonstrate that introducing a diverter effectively suppresses funnel flow, prolongs residence time, and improves radial flow uniformity. Among the tested configurations, the smaller central diameter diverter showed the most favorable performance, achieving a faster and more uniform descent, reduced compressive force concentration, and lower collision energy dissipation. These findings highlight the critical role of diverter design in regulating particle dynamics and provide theoretical guidance for optimizing shaft furnace structures to enhance the efficiency of hydrogen-based direct reduction processes. Full article

In the digitally saturated hospitality environment, research on digital transformation remains dominated by macro-level adoption trends and user-generated content, while the potential of micro-level web-behavioural data remains largely untapped. Recent systematic reviews highlight a fragmented body of literature and note that hospitality studies seldom address first-party behavioural data or big-data analytics capabilities. To address this gap, we collected clickstream, navigation and booking-funnel data from five luxury hotels in the Mediterranean and employed big-data analytics integrated with simulation modelling—specifically fuzzy cognitive mapping (FCM)—to model causal relationships among digital touchpoints, managerial actions and customer outcomes. FCM is a robust simulation tool that captures stakeholder knowledge and causal influences across complex systems. Using a case-study methodology, we show that first-party behavioural data enable real-time insights, support knowledge-based decision-making and drive digital service innovation. Across a 12-month panel, visitor volume was strongly associated with search traffic and social traffic, with the total-visitors model explaining 99.8% of variance. Our findings extend digital-transformation models by embedding micro-level behavioural data flows and simulation modelling. Practically, this study offers a replicable framework that helps managers integrate web-analytics into decision-making and customer-centric innovation. Overall, embedding micro-level web-behavioural analytics within an FCM framework yields a decision-ready, replicable pipeline that translates behavioural evidence into high-leverage managerial interventions. Full article

Background/Objectives: Optimizing drug deposition to the olfactory region is key in Nose-to-brain drug delivery strategies. However, findings from computational fluid dynamics (CFD) studies remain inconsistent concerning the parameters influencing olfactory deposition, limiting clinical translation and device optimization. This systematic review aims to identify robust CFD parameters for optimizing drug delivery to the olfactory region. Methods: A systematic review and meta-analysis were conducted following PRISMA guidelines, selecting studies reporting CFD simulations of nasal drug delivery with evaluation of olfactory deposition efficiency. The primary outcome was the correlation between each CFD parameter and olfactory deposition rate. Parameters included particle size, impaction parameter, flow rate, spray cone angle, insertion angle, injection velocity, head position, release position, and breathing pattern. Data were extracted and standardized, and statistical methods were used to assess correlations, heterogeneity, and potential biases in study results. Results: Smaller particle size (pooled r = −0.42) and lower impaction parameter (r = −0.39) were significantly associated with higher olfactory deposition. No consistent correlation was observed with breathing flow rate. Heterogeneity across studies was high (I² > 90%). Funnel plots asymmetry suggested potential publication bias in particle-related outcomes. Conclusions: Particle characteristics, especially size and inertia, are the most critical determinants of olfactory deposition in CFD simulations. These findings support design optimization of nasal delivery devices targeting the olfactory region and underscore the need for standardized reporting and validation across CFD studies. Full article

This study presents a novel approach to the development of self-compacting concrete (SCC) by partially replacing both cement and fine aggregate (sand) with waste marble sludge (WMS), a byproduct of the marble industry. The research aims to evaluate the feasibility of incorporating this industrial waste into SCC to enhance sustainability without compromising performance. To assess the fresh and hardened properties of the proposed mixtures, a comprehensive experimental program was conducted. Tests included slump flow, T₅₀, and V-funnel for evaluating workability, as well as measurements of specific gravity, compressive strength, flexural strength, Brazilian tensile strength, and water absorption at 28 days of curing. The results demonstrated that the mix containing 5% cement replacement and 20% sand replacement with marble sludge exhibited the highest mechanical performance, achieving a compressive strength of 48.2 MPa, tensile strength of 3.9 MPa, and flexural strength of 4.4 MPa. Furthermore, increasing the percentage of cement replacement led to enhanced flowability, as evidenced by an increase in slump flow diameter and a reduction in V-funnel flow time, indicating improved workability. Overall, the findings suggest that controlled incorporation of WMS can produce SCC with desirable mechanical and rheological properties, offering a promising pathway for sustainable concrete production. In addition to the technical performance, a carbon footprint analysis was conducted to examine the environmental benefits of marble sludge utilization. The mixture with 10% cement and 20% sand replacement exhibited the lowest carbon footprint, while the 7.5% replacement level provided the best balance between strength and sustainability. Full article

This research investigates the feasibility of producing eco-friendly self-compacting concrete (SCC) by partially replacing both fine and coarse natural aggregates with waste marble sludge (WMS), a byproduct of the marble industry. The objective is to evaluate whether this substitution enhances or compromises the concrete’s performance while contributing to sustainability. A comprehensive experimental program was conducted to assess fresh and hardened properties of SCC with varying WMS content. Fresh-state tests—including slump flow, T₅₀ time, and V-funnel flow time—were used to evaluate workability, flowability, and viscosity. Hardened properties were measured through compressive, flexural, and Brazilian tensile strengths, along with water absorption after 28 days of curing. The mix with 10% replacement of both sand and coarse aggregate showed the most balanced performance, achieving a slump flow of 690 mm and a V-funnel time of 6 s, alongside enhanced mechanical properties—compressive strength 48.6 MPa, tensile strength 3.9 MPa, and flexural strength 4.5 MPa—and reduced water absorption (4.9%). A complementary cost model quantified direct material cost per cubic meter and a performance-normalized efficiency metric (compressive strength per cost). The cost decreased monotonically from 99.1 $/m³ for the base mix to $90.7 $/m³ at 20% + 20% WMS (−8.4% overall), while the strength-per-cost peaked at the 10% + 10% mix (0.51 MPa/USD; +12% vs. base). Results demonstrate that WMS can simultaneously improve rheology and mechanical performance and reduce material cost, offering a practical pathway for resource conservation and circular economy concrete production. Full article

The integration of recycled materials into cementitious systems presents a sustainable path to reducing environmental impact in construction. This study investigates the mechanical and durability performance of self-compacting mortars (SCMs) incorporating finely ground mortar waste powder (MWP) as a partial cement substitute, reinforced with aluminum oxide (Al₂O₃) and iron oxide (Fe₂O₃). Eleven mixes were designed with MWP replacing cement at 0–50% by volume. Fresh-state tests showed that slump flow decreased moderately (from 259 mm to 240 mm), while V-funnel times improved (from 10.51 s to 7.01 s), indicating acceptable flowability. The optimum performance was observed in SCM2 (5% MWP + oxides), which achieved 75.62 MPa compressive and 13.74 MPa flexural strength at 28 days, outperforming the control mix. Durability under high temperature and freeze–thaw cycling revealed that oxide-reinforced mixes exhibited superior strength retention, with SCM2 maintaining over 87 MPa after 300 °C exposure and minimal degradation after 100 freeze–thaw cycles. Porosity remained low (16.1%) at optimal replacement levels but increased significantly beyond 25% MWP. The results confirm that low-level MWP replacement, when reinforced with reactive oxides, provides a viable strategy for producing durable, high-performance, and eco-efficient SCMs. Full article

This study addresses the challenge of solid pollutant collection in seawater pond recirculating aquaculture by designing a novel funnel-shaped sewage collection device and evaluating its performance through Computational Fluid Dynamics (CFD) simulations and experimental validation. The results reveal that the device forms a rotating flow field, effectively concentrating solid particles in a central low-velocity zone with a diameter of approximately 2 m when the sewage pump is inactive. The optimal bottom dip angle for efficient sewage discharge is determined to be 21 degrees, with flow velocities near the outlet ranging between 0.031 and 0.062 m per second, sufficient to mobilize particles smaller than 5 mm. Prototype testing demonstrates a solid pollutant collection efficiency of 75.7 percent, confirming the device’s practical effectiveness in improving water quality and operational performance. This research offers a validated and efficient solution for solid waste management in aquaculture systems. Full article

In developing spacecraft dust environment testing equipment, cyclone separators serve as critical particulate separation devices. To optimize cyclone performance, this study investigates the impact of inlet configurations on internal flow fields. We propose a novel helical-baffle inlet design and comparatively analyze it against volute baffle inlets and conventional single-channel inlets using Eulerian–Lagrangian multiphase simulations. Three-dimensional streamline visualization reveals internal flow patterns, while the Q-criterion identifies vortical structures. Results demonstrate that both volute and helical configurations effectively eliminate inlet gas funneling effects. The flow-splitting baffles mitigate flow field asymmetry, with the helical-baffle design exhibiting optimal performance: it maintains vortex stability, enhances fluid dynamic equilibrium, reduces pressure drop and improves separation efficiency to 95.92% for 4 μm particles. Full article

In this study, the compatibility of polycarboxylate ether-based water-reducing admixtures (PCE) with cements produced with different types and dosages of grinding aids (GA) was experimentally and statistically investigated. A total of 203 paste mixtures were prepared using seven different types of GA and one type of PCE at different dosages. The Marsh funnel flow time and mini-slump values of the mixtures were compared. A modeling study was performed using the experimental data. In this direction, Classical Regression Analysis (CRA), Multivariate Adaptive Regression Splines (MARS), and Artificial Neural Networks (AOMA-ANN) were applied. Innovative approaches, AOMA-ANN (AIP) and AOMA-ANN (ONIP), were introduced. The results showed adverse effects on flow performance with increased GA utilization, except for TEA-based GA. TEA-type GA had the lowest flow performance. AOMA-ANN (ONIP) exhibited the best performance in modeling. Marsh funnel flow-time modeling with AOMA-ANN (ONIP) considered parameters such as sieve residue at 60 microns, the number of molecules per fineness, the density of GA, the pH value of GA, and the PCE dosage. Mini-slump modeling with AOMA-ANN (ONIP) considered parameters such as sieve residue at 60 microns, the density of GA, the pH value of GA, and the PCE dosage. Full article

To enhance contact time between microalgae and nutrients in reactors, thereby improving the growth rate of microalgae and increasing pollutant removal efficiency, two funnel-shaped spoilers were added inside a traditional column photobioreactor. Compared to conventional column photobioreactors, the addition of these spoilers resulted in increased updraft, which improved horizontal flow. This change led to a greater shear force near the spoilers and a reduction in bubble diameter. As a result, the mass transfer coefficient and gas content increased by 12.17% and 7.71%, respectively, while the mixing time decreased by 30.57%. These improvements resulted in an 18.18% increase in microalgal biomass, a 13.95% increase in the CO₂ fixation rate, and increases of 4.48%, 7.5%, and 4.7% in the removal of COD, TP, and NH₄⁺-N, respectively, in the column photobioreactor with funnel-shaped spoilers. This was achieved when CO₂ was introduced at a concentration of 10%, compared to a conventional column photobioreactor. This innovative design enhances the growth efficiency of microalgae, offering a new solution for reducing carbon emissions, promoting recycling of water resources, and advancing sustainable development. Full article

Herein, a three-dimensional mathematical model was established to investigate the metallurgical behavior of liquid steel in a funnel-shaped mold equipped with single-ruler electromagnetic braking (EMBr). The effects of mold thicknesses, electromagnetic intensity, and casting speed in flow behavior were investigated. The results indicate that with EMBr, multiple pairs of induced current loops are present in the horizontal section of the magnetic pole center, distributed in pairs between the jets and broad faces. The Lorentz force acting on the main jet, which impacts the downward and upward flow at adjacent broad faces, is opposite in direction. Increasing mold thickness results in a larger jet penetration depth, leading to a higher meniscus temperature near the narrow faces accompanied by elevated velocity and turbulent kinetic energy. EMBr can lead to a decrease in shell thickness and an improvement in its uniformity at mold exit. For the thickened mold, as the magnetic flux density increases and the casting speed decreases, the penetration depth of jets and velocity near the narrow faces and meniscus decreases. The shell thickness decreases as the casting speed increases, with the lowest non-uniformity coefficient of 6.78% observed at a casting speed of 5.0 m/min. Full article

The hydrodynamic efficiency of bioreactors is contingent upon the design of the impeller, particularly the blade geometry, which influences flow symmetry. This study evaluates the impact of dimpled surfaces on the blades of a turbine impeller on mixing processes. Investigations were conducted using simulations in ANSYS (2021R2) with the k-ε turbulence model and experiments measuring vortex funnel depth and power consumption at 247 rpm in an 11-L cylindrical vessel. Results indicate that dimples disrupt the rotational symmetry of the blades, increasing the volume-averaged flow velocity from 0.312 m/s to 0.321 m/s (a 2.9% increase); the maximum shear strain rate from 161 s⁻¹ to 1442 s⁻¹; and the turbulent vortex frequency from 183 s⁻¹ to 290 s⁻¹ (a 58% increase). The volume-averaged shear strain rate rose from 44 s⁻¹ to 63 s⁻¹ (a 43% improvement), and the vortex funnel depth increased from 44 mm to 50 mm (a 14% increase), indicating enhanced homogenization. This facilitates efficient processing of sensitive biological organisms, such as mycoplasmas, and more robust structures, including fungi and mycelium. However, power consumption increased by 4.5% (from 4.9 W to 5.1 W). Thus, disrupting symmetry with dimples intensifies hydrodynamic processes, enhancing mixing efficiency, but requires optimization to reduce energy costs, offering prospects for advancing biotechnological systems. Full article