Search Results (497)

Rheology plays an important role in the 3D concrete printing technology, because it directly governs the flowability and shape retention of the material, impacting both the printing process and the final quality of the obtained structure. Local raw materials such as Portland cement, washed sand, and tap water were used for the preparation of 3D-printed concrete mixtures. The solid-state polycarboxylate ether with an anti-foaming agent was used as superplasticizer. The Portland cement was partially replaced (by volume) with a natural zeolite additive in amounts ranging from 0% to 9% in 3D-printed concrete mixtures. A rotational rheometer with coaxial cylinders was used in this research for the determination of rheological characteristics of prepared 3D-printed concrete mixtures. The Herschel–Buckley model was used to approximate experimental flow curves and assess rheological parameters such as yield stress, plastic viscosity, and shear-thinning/thickening index. The additional experiments and calculations, such as water bleeding test and evaluation of the carbon footprint of 3D-printed concrete mixtures, were performed in this work. The replacement of Portland cement with natural zeolite additive positively influenced rheological and stability-related properties of 3D-printed concrete mixtures. Natural zeolite additive consistently reduced water bleeding, enhanced yield stress under increasing shear rates, and lowered plastic viscosity, thereby improving flowability and mixture transportation during the 3D printing process. As the shear-thinning/thickening index remained stable (indicating non-thixotropic behavior in most cases), higher amounts of natural zeolite additive introduced slight thixotropy (especially under decreased shear rates). These changes contributed to better shape retention, layer stability, and the ability to print taller and narrower structures without collapse, making natural zeolite additive suitable for use in the optimized processes of 3D concrete printing. A significant decrease in total carbon footprint (from 3% to 19%) was observed in 3D-printed concrete mixtures with an increase in the mentioned amounts of natural zeolite additive, compared to the mixture without this additive. Full article

With the increasingly stringent mandatory emission regulations for engines and the continuous growth of energy consumption, reducing energy consumption and emission pollution has become an inevitable choice for engine development. Against this backdrop, biodiesel and boot-shaped injection rates have attracted widespread attention. However, research results on the combination of boot-shaped injection and biodiesel applied to engines have not yet been reported. In order to provide direction for the optimal matching of the combustion system parameters of biodiesel engines under saddle-shaped injection conditions, this paper achieves boot-shaped injection using a dual solenoid valve control strategy for ultra-high-pressure fuel injection devices, establishes a simulation model of biodiesel engines under saddle-shaped injection conditions using software and validates the model based on experiments. Subsequently, the model is used to study the influence of nozzle numbers, swirl ratio and bore-to-stroke ratio on the performance of biodiesel engines under saddle-shaped injection conditions. The results show that under saddle-shaped injection conditions, appropriately increasing the nozzle hole can refine the fuel spray, which is beneficial for fuel–air mixing and combustion in the cylinder. However, too many nozzle holes can lead to interference between adjacent fuel sprays. When the swirl ratio is large, air flow accelerates, and the oxygen concentration in the cylinder increases, which can effectively control soot formation. When the bore-to-stroke ratio is large, the fuel spray is farther away from the combustion chamber side wall, facilitating sufficient contact between fuel and air, resulting in better fuel–air mixing and effectively reducing soot formation. However, the cylinder temperature also increases, leading to higher NOx formation. Full article

This paper focuses on power grid integration of wave energy converter (WEC) arrays that minimize added energy storage for maximizing power capture as well as smoothing the oscillatory power inputs into the grid. In particular, a linear right circular cylinder WEC array that implements complex conjugate control is compared and contrasted to a nonlinear WEC array that implements an hourglass buoy shape while both are integrated into the grid utilizing phase control (i.e., relative spacing of the WEC array) on the input powers to the grid. The Hamiltonians of the two WEC systems are derived, enabling a direct comparison of real and reactive power, with reactive power reflecting the utilization of stored energy. The control systems are simulated in MATLAB/Simulink under both regular wave conditions and irregular seas generated from a Bretschneider spectrum. For the linear right circular cylinder buoy, the proportional-derivative complex conjugate controller requires an external energy storage device to supply reactive power, whereas the nonlinear hourglass buoy inherently provides reactive power through its geometric design. This study demonstrates that: (i) The unique geometry of the hourglass buoy reduces the required energy storage size for the nonlinear system while simultaneously increasing power output. (ii) Phase control of the hexagonal hourglass array further enhances real power capture. Together, these effects substantially decrease the size and demand on the individual buoys and grid integration energy storage requirements. Full article

This study evaluated the properties of two commercial filaments intended for medical and sterile applications: PLACTIVE (Copper 3D, Santiago, Chile) and CPE ANTIBAC (Fiberlogy, Brzezie, Poland). The aim of the research was to compare the dimensional accuracy, repeatability of the fused deposition modeling (FDM) 3D printing process, and the antibacterial properties of the samples using standardized procedures. Four types of samples were manufactured: geometrically differentiated specimens for metrological measurements (S1); cylinders with a diameter of 15 mm and a height of 40 mm for assessing process repeatability (S2); rectangular specimens measuring 40 × 40 × 2 mm for surface topography analysis (S3); and rectangular samples measuring 20 × 20 × 2 mm for biocidal property evaluation (S4). The results demonstrated that PLACTIVE samples exhibited higher dimensional conformity with nominal values and lower variability of diameters than CPE ANTIBAC samples, which may be associated with greater process stability. For both materials, the PSm parameter was correlated with layer height only in the 90° printing orientation. Surface topography analysis showed that increasing the layer height from 0.08 mm to 0.20 mm led to a significant rise in Rsm, Ra, and Sa values, indicating deterioration in the reproduction of micro-irregularities and increased spatial differentiation of the surface. For PLACTIVE samples, a tendency toward more convex structures with positive Rsk values and moderate kurtosis (Rku) was observed, suggesting uniform plasticization and stable interlayer bonding, particularly at the 0° orientation. In contrast, CPE ANTIBAC samples (especially those printed at 90°) were characterized by higher Ra and Sa values and negative skewness (Rsk), indicating valley-dominated, sharper surface morphology resulting from different rheological behavior and faster solidification of the material. PLACTIVE samples did not exhibit antibacterial properties against Escherichia coli (E. coli), while for Staphylococcus aureus (S. aureus), the activity was independent of printing direction and layer height. The CPE ANTIBAC material showed antibacterial effects against both tested strains in approximately 50% of the samples. The findings provide insights into the relationships between material type, printing orientation, and process parameters in shaping the dimensional and biocidal properties of FDM filaments. Full article

This study investigates the impact of eddy viscosity on equatorially trapped waves and the instability of the background shear in a simple barotropic–baroclinic model. It is the first study to include eddy viscosity in the study of tropical wave dynamics. This study also unifies the study of baroclinic and barotropic instabilities by using a coupled barotopic and baroclinic model of the tropical atmosphere. Linear wave theory is combined with a systematic Galerkin projection of the baroclinic dynamical fields onto parabolic cylinder functions. This study investigates varying shear strengths, eddy viscosities, and their combined effects. In the absence of shear, baroclinic and barotropic waves decouple. The baroclinic waves themselves separate into triads, forming the equatorially trapped wave modes known as Matsuno waves. However, when a strong eddy viscosity is included, the structure and propagation characteristics of these equatorial waves are significantly altered. Different wave types interact, leading to strong mixing in the meridional direction and coupling between meridional modes. This coupling destroys the Matsuno mode separation and offers pathways for these waves to couple and interact with one another. These results suggest that viscosity does not simply suppress growth; it may also reshape the propagation characteristics of unstable modes. In the presence of a background shear, some wave modes become unstable, and barotropic and baroclinic waves are coupled. Without eddy viscosity, instability begins with small scale and slowly propagating modes, at arbitrary small shear strengths. This instability manifests as an ultra-violet catastrophe. As the shear strength increases, the catastrophic instability at small scales expands to high-frequency waves. Meanwhile, instability peaks emerge at synoptic and planetary scales along several Rossby mode branches. When a small eddy viscosity is reintroduced, the catastrophic small-scale instabilities disappear, while the large-scale Rossby wave instabilities persist. These westward-moving modes exhibit a mixed barotropic–baroclinic structure with signature vortices straddling the equator. Some vortices are centered close to the equator, while others are far away. Some waves resemble synoptic-scale monsoon depressions and tropical easterly waves, while others operate on the planetary scale and present elongated shapes reminiscent of atmospheric-river flow patterns. Full article

Hydrogen internal combustion engines are a promising propulsion technology due to their zero-carbon emission potential and high efficiency. However, achieving stable mixture formation during direct hydrogen injection remains a key challenge affecting ignition stability and NO_x emissions. Although numerous studies address the combustion characteristics of hydrogen, only a limited number have examined the transient behavior of hydrogen/air mixing during the intake stroke, particularly its interaction with in-cylinder flow structures prior to ignition. This lack of detailed insight into early mixture stratification and jet-driven turbulence represents a significant research gap that currently limits further optimization of DI-H₂ICE systems. This study therefore deals with the numerical analysis of the process of mixing hydrogen with air in the combustion chamber of a direct hydrogen injection engine (DI-H₂ICE). A 3D CFD model of a hydrogen direct-injection engine was used to evaluate in-cylinder mixing during the intake and early compression strokes. Unlike most existing publications that focus primarily on combustion or emission formation, this work examines the mixing process from the beginning of the intake stroke and provides a new evaluation of the evolution of the hydrogen jet and its interaction with the piston-induced swirl as the crankshaft angle changes. The simulation covers the section from the exhaust top dead center (TDC) to the early compression phase, during which hydrogen is injected at a high pressure. The results show that the shape of the combustion chamber and the interaction of the hydrogen jet with the piston significantly affect the distribution of the equivalent ratio and the intensity of the swirl. Quantitative evaluation showed that the mixture remained lean overall throughout the cycle: typical hydrogen mass fractions in the cylinder ranged from 0.01 to 0.05, corresponding to equivalence ratios of φ = 0.35–1.81 (λ = 2.85–0.55). Only the core of the jet reached an instantaneous local mass fraction of 0.96, representing undiluted hydrogen and not a combustible mixture. No persistent zones with φ > 1 were detected, confirming that the chosen injection strategy prevents the formation of locally rich pockets. This study confirmed that a suitably selected injection configuration and combustion chamber geometry can significantly contribute to a uniform mixture distribution, a more stable combustion process, and lower NO_x production. The presented findings provide a methodological basis for improving mixture formation strategies in hydrogen engines and may support the development of efficient, zero-carbon powertrains in future mobility systems. Full article

In this study, we numerically investigate the influence of thermal gradients on the growth and intensification of vortices formed within a rotating cylinder subjected to inhomogeneous cooling at the top or inhomogeneous heating at the bottom. The presence of horizontal thermal inhomogeneities at the upper and lower boundaries determines whether the vortex originates near the top or the bottom of the domain. Moreover, the magnitude of both horizontal and vertical thermal gradients plays a critical role in the vortex’s intensification, vertical stretching, and overall development. The observed phenomena are interpreted through a force balance analysis. Increasing the ambient rotation rate leads to the emergence of periodic structures, such as tilted or double vortices, which also undergo intensification and stretching as thermal gradients increase. These findings highlight the importance of thermal boundary conditions in shaping vortical structures and may contribute to a deeper understanding of the genesis, morphology, and intensification mechanisms of thermoconvective vortices. Full article

This research investigates the impact of coarse aggregate (CA) type, shape, and specimen size on the compressive behavior of concrete, aiming to better understand how these factors affect its mechanical performance. Eight concrete mixtures were designed according to four different concrete mix design (CMD) codes using two types of coarse aggregates: crushed basalt and naturally rounded, both with a 15 mm size. A total of 96 concrete samples were tested to evaluate their failure mode, compressive strength (CS), energy accumulation (G_A), and post-peak fracture energy (G_F). The results show that concrete made with basalt CA offered significantly higher CS (by 7% to 40%), G_A (by 34% to 57%), and G_F (10% to 48%) compared to concrete made with natural CA across different CMD codes and specimen dimensions. Larger cylinders demonstrated higher CS than smaller cylinders, ranging from 7% to 19%. The incorporation of basalt CA enhanced the toughness and ductility of concrete, leading to superior post-peak behavior. In addition to the experimental program, four machine learning algorithms, i.e., Extreme Gradient Boosting (XGB), Gradient-Enhanced Regression Tree (GBR), Random Forest (RF), and Support Vector Regression (SVR), were employed to forecast the concrete’s CS. RF (R² = 0.93) and gradient boosting models (R² = 0.92) showed remarkable accuracy, whereas SVR underperformed. The feature importance and SHAP analysis identified cement content and CA type as the primary determinants of CS, while the water–cement ratio served as a crucial regulator. Moreover, a graphical user interface tool was developed to practically allow engineers to rapidly estimate concrete CS, bridging the gap between experimental validation and practical use. Full article

Steam flow-induced vibration (FIV) of cooling tubes poses critical failure risks in nuclear power plant condensers. However, accurate FIV prediction remains challenging due to the complex three-dimensional flow structures in full-scale condensers, which are often oversimplified in existing models. To address this gap, this study develops a novel full-scale Computational Fluid Dynamics (CFD) model that uniquely integrates the low-pressure exhaust cylinder, condenser throat, and tube bundles. This approach enables a comprehensive evaluation of shell-side flow characteristics and FIV phenomena under both Valve Wide Open (VWO) and partial-load conditions (with either Modules A/C or B/D active). The results quantitatively identify peak FIV risk coefficients in specific zones—particularly at branch-shaped channel inlets and certain tube bundle corners where steam impingement is most intense—with values reaching 0.7 under VWO, 0.67 with Modules A/C active, and 0.74 with Modules B/D active. Notably, the peak FIV risk under B/D active condition is approximately 10.4% higher than under A/C active condition, indicating that partial-load operation with Modules B/D active presents the highest FIV risk among investigated scenarios. These findings provide novel insights into FIV mechanisms and establish a critical theoretical foundation for optimizing condenser design and enhancing operational safety protocols. Full article

The compressive strength is the primary parameter used for the design, control, and performance assessment of cementitious materials. However, this value is strongly influenced by specimen geometry, which has led to the introduction of shape coefficients to convert compressive strength results between different specimen types, particularly between cubes and cylinders. While this topic has been extensively investigated in concrete, very limited research has addressed the shape coefficient in soil-cement or cement-treated base materials, despite their widespread use in pavement construction. Aiming to bridge this gap, this study systematically analyzes the unconfined compressive strength (UCS) of soil-cement specimens with different geometries. Two soil-cement mixtures with distinct physical and chemical characteristics were tested at various curing ages (7, 28, and 90 days) using cylindrical specimens (150 mm diameter × 180 mm height) and cubic specimens (150 mm edge). The results show that the UCS in cylindrical specimens (UCS_cyl) was consistently higher than that of cubic specimens (UCS_cub), although the difference decreased with increasing compressive strength. By combining all datasets, a single conversion factor of 1.04 was derived, resulting in an equation, UCS_cyl = 1.04·UCS_cub, with an excellent determination coefficient (R² = 0.99), enabling reliable conversion between cubic and cylindrical UCS results for soil-cement. Full article

To mitigate the inadequate performance of traditional hydraulic systems, mechanical feedback-based digital hydraulic technology is applied to a 3-degree-of-freedom (3-DOF) crane. Digital hydraulic cylinders drive the pitch mechanism, and digital hydraulic motors power the rotary and winch mechanisms. By analyzing the working principles of digital hydraulic cylinders and motors, transfer functions of the 3-DOF actuators are derived. AMESim simulation models are established for each actuator, with model validity verified. Based on these models, simulation analysis of the digital hydraulic system is performed to examine key influencing factors: motor speed, motor subdivision, system flow rate, digital valve opening, and throttle groove shape. System characteristics are obtained, and corresponding optimization schemes are proposed. After optimization, the comprehensive performance of the digital hydraulic system is improved by 1.29%. This study provides theoretical support for the engineering application of digital hydraulic systems in cranes, clarifies their operational specifications and optimization pathways, and exhibits substantial engineering application value. Full article

Perforated cylindrical shaped metal plates are used with high efficiency in the manufacture of deflectors, components of cooling systems, wind tunnels, climatic chambers, filters, and cylindrical implants. This is particularly important for lightweight cylindrical structures, where even minor changes in stiffness can affect structural strength. One of the most important parameters determining the mechanical behavior of such structures is the effective elastic modulus of the perforated element which characterizes its resistance to deformation. The research involves plates made of stainless steel 304 alloy, where perforations were created using the laser-cutting method. The cylindrical shape of the samples with height 50 mm, thickness 1 mm, and diameter 48 mm of each specimen was obtained using metal rolling and welding techniques. To determine the effective elastic modulus, a non-destructive material property evaluation method was applied by solving an inverse problem. In this research, resonance frequencies were determined using a laser vibrometer and a full factorial experimental plan was developed. Physical samples were digitized into 3D models using 3D scanning technology. To evaluate the accuracy of the applied finite element numerical model, its convergence analysis was performed. Numerical results were approximated using the least-squares method, while the effective elastic modulus was calculated by formulating and minimizing the error functional between experimental and numerical eigenfrequencies. The results indicate that increasing the relative perforation area from 0% to 50.24% leads to a decrease in the effective elastic modulus from 184.76 GPa to 50.69 GPa, confirming that increasing the perforation area in a stainless steel 304 cylinder reduces its elastic properties. The observed reduction in resonance frequencies and elastic properties is primarily due to the stiffness decrease caused by the higher perforation volume. Full article

This paper presents numerical and experimental investigations of acoustic agglomeration of solid particles in a chamber with three overlapping ultrasonic fields. The simultaneous generation of these fields produces an interference pattern with a greater number of pressure nodes, more evenly distributed across the chamber cross section. The chamber design is based on three piezoelectric transducers equipped with disc-shaped acoustic radiators and a cylindrical body. The transducers are evenly positioned around the cylinder’s horizontal axis of symmetry. Numerical simulations of their acoustic characteristics showed that, at a resonance frequency of 49.71 kHz and with a 125 V_p-p excitation, the system can generate up to 146 dB sound pressure level. The predicted interference field pattern indicated a high density of alternating pressure nodes across the chamber. Experimental results confirmed that, at a resonance frequency of 48.85 kHz and with the same excitation signal, the sound pressure in the chamber reached 144.8 dB. Particle agglomeration tests demonstrated effective performance: ultrafine particles in the 191–294 nm range decreased by 31.2%, while particles in the 0.75–1 µm range increased by up to 52.9%. These findings confirm the strong potential of interference acoustic fields for enhancing particle agglomeration and supporting air purification applications. Full article

The moisture content of wood components varies with changes in the external environment, which significantly affects the mechanical properties, moisture stress, decay, drying shrinkage, and cracking of wood components. Therefore, calculating the moisture content distribution of the cross-section of wood components is an important basis for in-depth research on wood components. First, a hygroscopicity test was performed on 45° sector-shaped Chinese fir thin-plate specimens. The specimens were treated to an absolutely dry state and placed in two different environments. The average moisture content and moisture content gradient on the cross-section of the specimens were measured, and the spatial distribution and temporal variation in the moisture content were studied. A theoretical model for the moisture content distribution of wood was then derived based on food drying theory. Finally, the applicability of the theoretical model was verified through experiments, and the effects of the root order μ_n of the characteristic equation of key parameters, the size of the component, and the position of the component on the moisture content distribution were discussed for the theoretical model. During the hygroscopic process, the average moisture content of wood components increased continuously, but the growth rate gradually slowed. The surface moisture content rapidly reached the level of the external moisture content first, followed by the equilibrium moisture content within a few hours. Hygroscopic hysteresis evidently occurred within the wood, which may take dozens or even hundreds of days. When calculating the average moisture content model of cylindrical components, as well as those of the models of the spatial and temporal variation in the moisture content, it is sufficient to take the first 3 orders of the root μ_n of the characteristic equation of the first Bessel function J. The rate of moisture release of cylindrical components is faster than that of laminates because the ratio of the surface area to the volume of a cylinder is greater than that of a plate, and the former is twice that of the latter. The results revealed that the theoretical model for the moisture content distribution of wood has good accuracy and applicability. Full article

A coordinated profile co-optimization strategy for the piston–liner pair was introduced to simultaneously reduce friction losses and dynamic excitation. Based on the main parameters of the engine. Lubrication theory and the finite element method, and explicitly accounting for elastic deformation of flexible bodies, a multibody dynamics simulation model of the piston–connecting rod–crankshaft–cylinder liner system was developed in AVL Excite. This model was used to evaluate the dynamic and tribological performance of five cylinder-liner pre-compensation geometries at rated operating conditions. A bottleneck-shaped liner exhibited the best tribological performance, reducing the average total piston–skirt friction loss by 20.8% and the peak asperity–contact pressure by 19.7%, while leaving piston kinematics essentially unchanged (an increase of 0.001 mm in the maximum radial displacement and 0.009° in the maximum tilt angle). Building on this liner, key piston–skirt profile parameters were optimized via response–surface methodology; with the optimized skirt, the maximum radial displacement decreased from 0.123 mm to 0.113 mm, the maximum tilt angle decreased from 0.463° to 0.462°, the third-order Fourier component of lateral acceleration decreased from 14.53 m/s² to 13.26 m/s², and the cycle-averaged total skirt friction loss decreased from 0.307 kW to 0.250 kW. Full article