Search Results (698)

This paper presents the design, modeling, and experimental validation of a capacitive tactile sensor specifically conceived to sense shear-driven contact dynamics in robotic manipulation. The proposed device is a layered flexible capacitive structure, in which controlled tangential interactions are induced. The electrode design maximizes sensitivity to shear motion and promotes an isotropic response with respect to slip direction, thereby addressing two key limitations that affect the majority of existing slip-sensing technologies. An analytical model was developed to describe the essential relationship between shear-induced displacements and the electrical response, providing insight into the design parameters and supporting the selection of geometry and materials. To test the sensor in real conditions, a dedicated capacitive readout circuit based on high-frequency excitation and synchronous demodulation was developed to robustly acquire capacitance variations while rejecting static offsets and parasitic effects. Several formulations for the interposed dielectric layer material were investigated, including viscous fluids and composite mixtures with high-permittivity nanoparticles, with the aim of improving electrical sensitivity while preserving mechanical stability. Experimental results obtained under controlled loading and sliding conditions demonstrate that the sensor is highly sensitive to changes in contact state and tangential interaction dynamics. The sensor responded consistently to both load-induced shear and slip-related phenomena, enabling the reliable monitoring of contact dynamics rather than binary slip detection. A proof-of-concept integration into a robotic finger confirms the suitability of the proposed approach for grasp monitoring. Full article

This study presents a two-dimensional computational fluid dynamics analysis of a vertical-axis Savonius-type wind turbine under atmospheric conditions representative of an educational environment located in the Ecuadorian Andean region. Unlike previous studies conducted under sea-level meteorological conditions, this research is performed under high-altitude conditions (2723 m a.s.l.). The unsteady flow around the rotor was simulated using a two-dimensional approach based on the Unsteady Reynolds-Averaged Navier–Stokes (URANS) equations, discretized with the finite volume method and coupled with the k–ω Shear Stress Transport (SST) turbulence model. The rotor rotation was modeled using sliding mesh technique, employing a second-order implicit time scheme to ensure numerical stability and adequate temporal resolution. The numerical model was configured for a tip speed ratio of 0.8 and a wind speed of 3.9 m/s. The time step was defined based on a constant angular advancement of the rotor per time iteration, ensuring numerical stability and adequate temporal resolution. The aerodynamic torque was obtained by integrating the pressure and viscous forces acting on the blades, allowing the calculation of the mechanical power generated and the power coefficient. The results showed a periodic and stable torque behavior after the initial transient cycles, yielding an average torque of 0.7687 N·m and a mechanical power of 5.17 W, while the power coefficient reached a value of 0.2102. Analysis of the flow fields revealed the formation of a low-velocity wake downstream of the rotor, regions of high turbulent kinetic energy associated with periodic vortex shedding, and a significant pressure difference between the advancing and returning blades, confirming that turbine operation is dominated by drag forces. The numerical results were validated through comparison with previous studies, showing good agreement and demonstrating the reliability of the proposed Computational Fluid Dynamics (CFD) approach. This study highlights the potential of Savonius turbines for low-power applications in urban and educational environments, as well as the usefulness of CFD as a tool for evaluating and optimizing their aerodynamic performance. Full article

Time-fractional interface problems, found in heat transfer with discontinuous conductivities and fluid flows with surface tension forces, are challenging due to irregular interfaces and the history-dependent nature of fractional derivatives. This paper presents two numerical methods for simulating time-fractional double interface problems. The first method uses the Haar wavelet collocation technique, while the second relies on a meshless approach with radial basis functions. The fractional derivatives are replaced with the Caputo sense, the resulting first-order time derivatives are handled using the finite difference method, and the spatial operator is approximated using the two proposed methods. Gauss elimination is used to solve linear problems. Quasi-Newton linearization method is used for nonlinear problems. Both methods accommodate constant and variable coefficients, handling discontinuities and singularities in both solutions and coefficients. To evaluate the effectiveness of the proposed methods, numerical experiments are carried out. The accuracy of each method is quantified using the $L_{\infty }$ error norm, and a comparative analysis highlights the validity and advantages of the approaches. Moreover, the proposed schemes are rigorously analyzed to establish their stability, and the existence and uniqueness of the solutions. Full article

Molten salts are essential heat transfer and storage media in high-temperature applications such as Concentrated Solar Power (CSP), owing to their high boiling points, low vapor pressures, and excellent thermal stability. The overall performance of such systems is largely governed by the convective heat transfer characteristics of molten salt fluids. This review systematically synthesizes recent advances over the past five years in enhancing the thermophysical properties and convective heat transfer of molten salts, focusing on two primary strategies: improving the intrinsic properties of molten salts through nanoparticle doping, and optimizing the structural design of heat exchangers. The enhancement of thermophysical properties is mainly achieved by preparing molten salt-based nanofluids. Dispersing low concentrations (typically 0.1–1.0 wt.%) of nanoparticles such as SiO₂, Al₂O₃, and carbon nanotubes (CNTs) can yield significant improvements—thermal conductivity increases of up to ~100% (e.g., 0.5 wt% SiO₂ in NaNO₃-KNO₃) and specific heat capacity enhancements of 20–30% (e.g., 1.0 wt% Al₂O₃ in carbonates). Multiscale simulations, particularly molecular dynamics (MD), have revealed key enhancement mechanisms, including the formation of ordered ionic layers on nanoparticle surfaces that create efficient nanoscale heat conduction pathways, and the modulation of ion–ion interactions. Concurrently, significant heat transfer enhancement can be achieved through structural optimization. Single-method technologies, such as enhanced heat transfer tubes, improve performance by disrupting the thermal boundary layer. For instance, spirally grooved tubes can increase the Nusselt number (Nu) by 19% for Re > 25,000, while twisted tape inserts can enhance laminar flow heat transfer by up to 8.6 times. Composite strategies that couple nanofluids with enhanced geometries demonstrate superior overall performance, with Performance Evaluation Criterion (PEC) values reaching up to 1.48 for converging–diverging tubes with SiO₂ nanofluids and 1.21 for trefoil-shaped U-tubes with Cu-based nanofluids. Compact heat exchangers (CHEs) offer high efficiency, achieving PEC values of 1.07–1.4 in optimized designs, but face challenges such as clogging risks in large-scale applications. Future research directions include the development of advanced composite molten salts, the application of artificial intelligence and multiscale simulations for mechanistic analysis and design optimization, the fabrication of novel heat exchanger structures via additive manufacturing, and cross-disciplinary integration for full-chain system optimization. These concerted efforts are essential for realizing efficient, cost-effective, and reliable molten salt-based energy systems. Full article

As a critical component of the hydrogen supply system for fuel cells in hydrogen-powered unmanned aerial vehicles (UAVs), the dynamic performance of the two-stage hydrogen pressure-reducing valve (PRV) directly influences the stability and safety of the fuel cell system. To address the insufficient output pressure control accuracy of existing hydrogen PRVs under a 70 MPa inlet pressure, this study designs a compact, fast-response, and high-precision two-stage hydrogen PRV. The flow coefficients of the valve orifices at each stage are obtained through Computational Fluid Dynamics (CFD) simulations, based on which a multi-physics coupled system dynamics model of the two-stage hydrogen PRV is derived. Using this multi-physics coupled dynamics model, a dynamic characteristic simulation model is established in MATLAB/Simulink. Numerical simulations performed with this model reveal the influence of different structural parameters on the dynamic characteristics of the first-stage and second-stage PRVs. The results provide theoretical and methodological references for the structural design and efficient optimization of two-stage hydrogen PRVs under high-pressure differential conditions, offering important guidance for improving the safety and stability of fuel cell hydrogen supply systems. Full article

The deep reservoir of the K gas field in the Xihu Depression of the East China Sea Basin has ample storage space and a vast reserve scale. However, these deep intervals remain poorly explored and developed, and their reservoir attributes and key controlling factors are not yet well constrained. Using integrated analyses of cores, cast thin sections, scanning electron microscopy, petrophysical statistics, grain-size data, high-pressure mercury intrusion, and nuclear magnetic resonance imaging, together with conventional well logs, we evaluate the roles of sedimentation, diagenesis, and overpressure in the development and distribution of high-quality reservoirs. Based on clastic grain texture and composition, authigenic minerals, diagenetic types and intensities, pore architecture, petrophysical properties, and gas saturation, two types of high-quality deep sandstone reservoirs are identified: rigid, moderately porous sandstones and strongly compacted, low-porosity sandstones. Compaction is the dominant diagenetic process controlling reservoir quality in the Eocene Pinghu Formation. Overpressure prolongs kaolinite stability and promotes precipitation within pore throats, enhancing fluid sealing and retention, yet does not significantly reduce porosity. Rigid moderately porous reservoirs mainly occur in subaqueous distributary channels, whereas strongly compacted low-porosity reservoirs are concentrated in mouth bars and sheet-sand microfacies. This distribution pattern provides guidance for exploring high-quality deep sandstone gas accumulations. Full article

The triplex reciprocating drilling pump is a critical piece of equipment in drilling platforms, and the operational condition of its core component—the valve body—directly affects the pump’s performance and the stability of the entire system. Therefore, accurate prediction of the valve body’s Remaining Useful Life (RUL) is of great significance for ensuring the safe operation of drilling pumps and enabling predictive maintenance. However, achieving this goal involves two major challenges: (1) The complex degradation process of the valve body, which involves strong impact loads, nonlinear wear, and coupling effects between fluid and mechanical systems, makes it difficult to establish a stable degradation model and achieve accurate RUL prediction. (2) There is a lack of publicly available real-world datasets for research purposes. To address these challenges, we propose CEEMDAN-BWO-optimized Bidirectional LSTM for Remaining Useful Life prediction (CB²-RUL). The method first applies Complete Ensemble Empirical Mode Decomposition with Adaptive Noise (CEEMDAN) to the raw vibration signals for decomposition and denoising, thereby improving signal stationarity and enhancing feature representation. Next, the Black Widow Optimization (BWO) algorithm is employed to automatically tune key hyperparameters of a Bidirectional Long Short-Term Memory (BiLSTM) network. Finally, the optimized BiLSTM captures the temporal evolution patterns of valve-body degradation and produces high-accuracy RUL estimates. Finally, to verify the effectiveness of the proposed approach, we constructed a real-world dataset named VB-Lifecycle, which comprises ten valve bodies from different positions within the equipment and spans the complete lifecycle from pristine condition to failure. Extensive experiments conducted on the VB-Lifecycle dataset demonstrate that the proposed method provides accurate RUL prediction for valve bodies. Full article

The objective of this study was to explore the effect of the assembly sequences of wall materials on the structure and properties of Antarctic krill peptide (AKP)-loaded ovalbumin (OVA)–chitosan (CS) nanoparticles (NPs). Two AKP-loaded NPs (CS/OVA-AKP and OVA/CS-AKP) were prepared by changing the sequences of OVA and CS. The results confirmed that CS/OVA-AKP had a smaller particle size (291 nm vs. 320 nm), lower polydispersity index (0.233 vs. 0.282), higher absolute zeta potential (34.4 mV vs. 32.1 mV), and higher encapsulation efficiency (81.6% vs. 75.4%) than OVA/CS-AKP. X-ray diffraction analysis confirmed that AKP was encapsulated in an amorphous state within the NPs. Fourier transform infrared spectroscopy and three-dimensional (3D) fluorescence spectroscopy revealed that electrostatic interactions, hydrogen bonding, and hydrophobic interactions were the primary driving forces for nanoparticle formation, with CS/OVA-AKP demonstrating a stronger OVA fluorescence quenching effect. Compared with OVA/CS-AKP, CS/OVA-AKP exhibited better redispersibility, and CS/OVA-AKP showed greater stability under various environmental factors (thermal treatment, salt concentration, pH, and storage time). During simulated gastrointestinal digestion, CS/OVA-AKP effectively protected AKP from gastric degradation and showed a higher AKP release rate in simulated intestinal fluid (61.1%) than OVA/CS-AKP (53.0%). The release followed the Korsmeyer–Peppas model, with OVA/CS-AKP exhibiting non-Fickian diffusion (n = 0.7500), and CS/OVA-AKP approached Case II transport (n = 0.9889), indicating erosion-controlled release behavior. CS/OVA-AKP also demonstrated higher hypoglycemic activity, with inhibition rates of 41.1%, 37.5%, and 36.1% for α-glucosidase, α-amylase, and DPP-IV, respectively. These findings underscore the important influence of wall-material assembly sequences on the structure and properties of AKP-loaded NPs, offering valuable insights for the development of bioactive peptide delivery systems. Full article

To address the lack of systematic comparison regarding rheological properties and the unclear structure–property relationships among three core fracturing fluid materials including synthetic polymers, vegetable gums, and microbial polysaccharides, this study selected acrylamide-based polymers, hydroxypropyl guar gum and xanthan gum as the representative systems. The steady-state viscosity, rheological curves, thixotropy, viscoelasticity, and temperature-shear resistance of the three samples were systematically characterized at concentrations ranging from 0.1 to 0.7 wt% using an MCR301 rotational rheometer. The outcomes indicate that the structural strength values of all three materials increase with rising concentration, but their rheological behaviors and stability differ significantly due to distinct molecular structures. The acrylamide-based copolymer forms a temporary network via weak hydrogen bonds (amide-carboxyl or amide-amide) and physical entanglements, exhibiting thixotropy and a stress pre-elastic response. The most significant effects occur at 0.7 wt%, with a thixotropic loop area of 2.874 Pa·s⁻¹ and a stress overshoot of 4.97 Pa.; hydroxypropyl guar gum has insufficient thermal stability and poor heat resistance. Its viscosity retention rate is as low as 31%, and it always exhibits a solution-type rheological property of G′ < G″; the xanthan gum exhibits elastic gel properties with tanδ < 1 due to its double-helix molecular structure. It has excellent temperature shear tolerance and the viscosity retention value can reach up to 98.6 mPa·s. Two mathematical models were established and demonstrated strong applicability: a modified Carreau model for flow curve fitting yielded a coefficient of determination (R²) greater than 0.95, enabling accurate description of fluid-type transitions; a four-parameter equation for temperature–shear resistance curves also achieved an R² above 0.95, effectively characterizing viscosity evolution with temperature. Full article

Mineral oils are increasingly being replaced by plant-based insulating liquids, known as natural esters, because of their biodegradability and high fire safety characteristic. However, their wider use in high-voltage and unsealed transformer applications is still limited due to concerns about thermo-oxidative stability and the relatively limited long-term performance data available compared to mineral oils. This study investigates improving the oxidation stability of natural esters through nanotechnology. A canola-based insulating liquid was used as the base fluid and modified with TiO₂ and SiO₂ nanoparticles of different sizes. Nanoparticle concentrations ranged from 0.05 to 0.25 wt.%, while Span 80 (sorbitan monooleate, non-ionic surfactant) served as a surfactant to ensure uniform dispersion and long-term colloidal stability. The nanofluids were subjected to accelerated aging to evaluate oxidation resistance, and key properties such as acidity, viscosity, and dissipation factor were monitored throughout the process. Dielectric performance was assessed using AC breakdown voltage testing, with results interpreted through two-parameter Weibull statistics. The TiO₂-based nanofluids demonstrated superior thermo-oxidative stability compared to both the base oil and the SiO₂-modified samples. Formulations containing smaller TiO₂ nanoparticles (5 nm) exhibited the lowest increases in viscosity, acid value, and dissipation factor, indicating strong resistance to degradation under thermal stress. In dielectric performance, SiO₂ nanofluids reached 65.8 kV, while TiO₂ nanofluids achieved a higher value of 72.4 kV, confirming their greater effectiveness. Although the nanoparticles are not biodegradable, their use at low concentrations significantly enhances the oxidative and dielectric stability of natural esters, helping extend fluid life and reduce dependence on petroleum-based insulating liquids. Full article

Background/Objectives: Human milk is a complex biological fluid containing not only macro- and micronutrients but also diverse bioactive molecules, including extracellular RNAs. Although RNA has been detected in milk for decades, only a subset of RNA species has been characterized in detail, and abundant families such as tRNA-, yRNA-, and rRNA-derived fragments remain underexplored. This study aimed to define the composition, fragmentation patterns, stability, and exploratory functional activity of these highly abundant RNAs in human milk. Methods: We performed small RNA sequencing on skim milk samples and analyzed the resulting profiles in comparison with publicly available milk and biofluid datasets. RNA stability assays, Northern blotting, and RT-qPCR were conducted to validate RNA abundance and degradation kinetics. Extracellular vesicles (EVs) and non-vesicular fractions were analyzed to determine the subcellular distribution of RNA species. Exploratory functional assays using synthetic RNA fragments were carried out to assess their ability to modulate cellular responses in vitro. Results: Human milk was found to be highly enriched in small RNA fragments derived from tRNA, yRNA, and rRNA, dominated by a limited set of discrete sequences. These profiles were highly reproducible across independent datasets and distinct biofluids. Orthologal validation assays confirmed their abundance and stability, with RNA levels exceeding those of serum by over two orders of magnitude. Full-length transcripts were enriched in EVs, whereas shorter fragments predominated in the non-vesicular fraction. Synthetic milk-derived exRNAs showed detectable pro-survival activity under stress conditions in vitro. Conclusions: This study reveals that human milk carries a limited set of highly abundant stable sRNA molecules, primarily derived from tRNAs, yRNAs, and rRNAs. These findings provide new insights into the RNA cargo of human milk and offer preliminary evidence that selected sRNA fragments can modulate cellular stress responses in in vitro models. Full article

In two-phase flow, the interaction between multi-scale vortex structures and interfaces (bubbles or free surfaces) triggers a range of complex physical phenomena. This study employs numerical simulations to investigate the interaction between a horizontal vortex and the interface separating two layers of immiscible fluids with different densities (e.g., water and air). The vortex is initialized as an internal motion within the heavier phase. We focus specifically on the impact of the phase density ratio and surface tension. Numerical simulations reveal that when the density ratio is near unity, interface rupture occurs only at high Weber numbers ($\mathit{We}$), where low surface tension enables the rupture of sharp interface points. Conversely, at high surface tension (low $\mathit{We}$), these sharp points stretch into thin liquid films, significantly increasing the surface area without causing breakage. As the density ratio increases, interface rupture at sharp points accelerates, even under high surface tension, leading to faster dissipation of the initial vortex. In high-$\mathit{We}$ scenarios, an increased density ratio promotes the faster formation and greater intensity of new vortex layers at the interface. However, increasing surface tension enhances the vorticity of these layers but simultaneously slows their generation rate. The findings highlight the critical interplay between surface tension and density differences in vortex–interface interactions, with surface tension stabilizing the interface and density differences driving more intense vortex shedding and deformation. These insights offer valuable guidance for understanding two-phase flow behavior and improving the design of systems involving multiphase fluids. Full article

This study investigates an inlet design for a gravitational vortex turbine (GVT), drawing inspiration from the ancient Nazca puquios. The puquios are ingenious subterranean aqueducts constructed by the Nazca culture (c. 100 BC–800 AD) in southern Peru, featuring spiral ojos de agua (water eyes) used to access groundwater and stabilize flow.The primary objective was to enhance vortex stability and overall GVT efficiency under low-head, low-flow operating conditions. A parametric Nazca-type inlet feeding a conical basin was defined by two controlling factors: the number of turns (N) and the inclination angle ($\theta$). The optimal geometry was determined through a $3^2$ full factorial design, computational fluid dynamics (CFD) simulations, and response surface methodology (RSM), with vortex circulation $(\Gamma )$ serving as the optimization metric. The best-performing inlet configuration ($N=4$, $\theta ={13}^{\circ }$) yielded $\Gamma =1.3459$ m²/s. This circulation level is comparable to that reported for optimized conventional wrap-around inlets at similar flow rates, but uniquely produced a broader and more symmetric vortex structure. Subsequently, two four-bladed runners (one with twisted blades and one with curved cross-flow blades) were evaluated numerically and experimentally using a laboratory-scale prototype operated at a consistent flow rate ($Q\approx 0.00143$ m³/s). CFD predicted maximum efficiencies of $15.37\%$ and $17.07\%$ for the twisted and curved runners, respectively, while experimental tests achieved $8.70\%$ and $11.61\%$, demonstrating similar efficiency ($\eta$) versus angular velocity ($\omega )$ characteristics. These results indicate reduced hydraulic effectiveness of the Nazca-inspired geometry for the GVT, with experimental efficiencies below those reported in the literature. Full article

This paper presents the results of numerical and experimental studies of forced convection of water/EG-Al₂O₃ nanofluids through a horizontal stainless steel tube (8 mm inner diameter; 2000 mm length). As a base fluid, distilled water/EG mixture of three volume ratios (90:10, 80:20, and 60:40) is used. Nanoparticle mass concentrations are 0.1%, 1%, and 5%. The tested nanofluids are prepared by use of the two-step method. No dispersant is used to stabilize the suspension. Transition and turbulent flow regimes are tested. The commercial code Ansys Fluent 19.3 is used to conduct numerical simulations. A k-ε turbulence model with an expanded boundary layer function is adopted. A homogeneous nanofluid model is assumed, with thermophysical properties depending on the mean fluid temperature and nanoparticle concentration. The nanofluids are treated as incompressible Newtonian fluids. Both experimental and numerical studies showed an increase in the average Nusselt number with the addition of Al₂O₃ nanoparticles to each of the water/EG mixtures. However, the experimental results indicated that, at the maximum mass nanoparticle concentration of 5%, the Nusselt number increased by 42%, whereas the numerical simulations showed an increase of only 16% compared with the base fluid. Both experimental studies and numerical simulations show the flow resistance of the nanofluid increases with increasing nanoparticle concentration. Similarly to heat transfer, the numerical calculations predict lower pressure drops than those observed experimentally. For the maximum nanoparticle mass concentration of 5%, the experimental results indicate an increase in nanofluid flow resistance of about 95%, while numerical simulations predict an increase of about 50%, compared to the base liquid. The generalized correlation equations are proposed to calculate the average Nusselt number and the friction factor valid for the turbulent flow of water-based nanofluids and water/EG mixtures with a volumetric water fraction above 60% and a mass concentration of nanoparticles in the range of 0.1% ≤ φ_m ≤ 5%. Full article

Enhanced oil recovery (EOR) in fractured reservoirs presents significant challenges due to fluid channeling and poor sweep efficiency. In this study, a synergistic EOR system was developed with polymer-based weak gel as the primary component and foam as the auxiliary enhancer. The system utilizes a low-concentration polymer (1000 mg·L⁻¹) that forms a weakly cross-linked three-dimensional viscoelastic gel network in the aqueous phase, inheriting the core functions of viscosity enhancement and profile control from polymer flooding. Foam acts as an auxiliary component, leveraging the high sweep efficiency and strong displacement capability of gas in fractures. These two components synergistically create a multiscale enhancement mechanism of “bulk-phase stability control and interfacial-driven displacement.” Systematic screening of seven foaming agents identified an optimal formulation of 0.5% SDS and 1000 mg·L⁻¹ polymer. Two-dimensional visual flow experiments demonstrated that the polymer-induced gel network significantly improves mobility control and sweep efficiency under various injection volumes (0.1–0.7 PV) and gravity segregation conditions. Numerical simulation in a 3D fractured network model confirmed the superiority of this enhanced system, achieving a final oil recovery rate of 75%, significantly outperforming gas flooding (65%) and water flooding (59%). These findings confirm that weakly cross-linked polymer gels serve as the principal EOR material, with foam providing complementary reinforcement, offering robust conformance control and enhanced recovery potential in fracture-dominated reservoirs. Full article