Search Results (71)

Determining the friction coefficients for uniform flows over very rough bottoms is a long-standing problem in open-channel hydraulics and river engineering. This experimental study presents measurements of the surface deformation as well as Darcy–Weisbach and Manning friction coefficients for steady, turbulent (6058 $\le \mathcal{R}e\le$ 28,502), and subcritical flows (0.14 $\le \mathcal{F}r\le$ 0.52) over large roughness elements, where $\mathcal{F}r$ and $\mathcal{R}e$ denote the Froude and Reynolds numbers, respectively. The experiments were conducted in a rectangular, inclined flume with a train of half-cylinders mounted on the bed, with radii in the range 20 mm $\le a\le$ 50 mm. These obstacles yield a relative submergence 1.45 $\le h_N/a\le$ 4.41 and a constant spacing ratio $e/a=12.8$ across all experimental runs, where $h_N$ and e denote the normal flow depth and the center-to-center spacing between cylinders, respectively. The relative amplitude of the surface profiles, ($\Delta h/a$), was analyzed and found to correlate strongly with $h_N/a$, $\mathcal{R}e$ and $\mathcal{F}r$. The results reveal very high values of the Darcy friction factor, f, which follows scaling laws of the form ${f\propto (h_N/a)}^{\widehat{n}}$, with $\widehat{n}<0$, independent of a, and ${f\propto \mathcal{R}e}^{\beta }$, where $\beta <0$ is closely linked to a. Scaling relationships for the Manning roughness coefficient, (n), were also investigated and are reported herein. Full article

This study presents a numerical investigation of fluid flow around a heated rectangular cylinder controlled by an inclined partition, aiming to suppress vortex shedding, reduce aerodynamic drag, and enhance thermal exchange. The double multiple relaxation time lattice Boltzmann method (DMRT-LBM) is employed to investigate the influence of Reynolds number variations and partition positions on the aerodynamic and thermal characteristics of the system. The results reveal the presence of three distinct thermal regimes depending on the Reynolds number. Increasing the Reynolds number intensifies thermal vortex shedding, thereby improving heat exchange efficiency. Moreover, a higher Reynolds number leads to a greater reduction in the drag coefficient, reaching $125.41\%$ for $Re=250$. Additionally, improvements in thermal performance were quantified, with Nusselt number enhancements of $29.47\%$ for $Re=100$, $55.55\%$ for $Re=150, 74.78\%$ for $Re=200$, and $82.87\%$ for $Re=250$. The influence of partition positioning g on the aerodynamic performance was also examined at $Re=150$, revealing that increasing the spacing g generally leads to a rise in the drag coefficient, thereby reducing the percentage of drag reduction. However, the optimal configuration was identified at $g=2d$, where the maximum drag coefficient reduction reached $130.97\%$. In contrast, the impact of g on the thermal performance was examined for $Re=100, 150,$ and $200$, revealing a significant heat transfer improvements on the top and bottom faces: reaching up to $99.47\%$ on the top face for $Re=200$ at $g=3d$. Nevertheless, for all Reynolds numbers and partition placements, a decrease in heat transfer was observed on the front face due to the partition shielding it from the incoming flow. These findings underscore the effectiveness of an inclined partition in enhancing both the thermal and aerodynamic performance of a rectangular component. This approach holds strong potential for various industrial applications, particularly in aeronautics, where similar control surfaces are used to minimize drag, as well as in heat exchangers and electronic cooling systems where optimizing heat dissipation is crucial for performance and energy efficiency. Full article

With ongoing technological advancements, artificial tactile systems have become a prominent area of research, aiming to replicate human tactile capabilities and enabling machines and devices to interact with their environments. Achieving effective artificial tactile sensing relies on the integration of high-performance pressure sensors, precise signal acquisition, robust transmission, and rapid data processing. In this study, we developed a sensor array system based on flexible pressure sensors designed to recognize objects of varying shapes and sizes. The system comprises a multi-channel acquisition circuit and a signal transmission circuit and employs a convolutional neural network (CNN) to classify distinct signal patterns. In a test on an individual, the test results demonstrate that the system achieves a high recognition accuracy of 99.60% across two sphere sizes, three cylinder sizes, a cone, and a rectangular prism. In a group of eight people, it can achieve a recognition accuracy of 93.75%. Furthermore, we applied this sensor array system in an experimental setting involving a ball-throwing action, and it effectively recognized four distinct stages: empty hand, holding the ball, throwing, and catching. In repeated tests by other individuals, it was also able to clearly distinguish each stage. The development of artificial tactile systems allows robots to engage with their environments in a more nuanced and precise manner, enabling complex tasks such as surgical procedures, enhancing the interactive experience of wearable devices, and increasing immersion in virtual reality (VR) and augmented reality (AR). When integrated with deep learning, artificial tactile sensing shows significant potential for creating more intelligent and efficient applications. Full article

A robust and elegant approach, based on the Two-Zone Moment Analysis (TZMA) method, is proposed to assess the contributions of the mobile and stationary zones, $H_{Cm}$ and $H_{Cs}$, to the C term $H_C$ in the van Deemter equation for plate height. The TZMA method yields two formulations for $H_{Cm}$ and $H_{Cs}$, both fully equivalent in terms of $H_C$, yet offering different decompositions of the contributions from the mobile and stationary zones. The first formulation proposes an expression for the term $H_{Cs}$ that has strong similarities, but also significant differences, from the well-known and widely used one proposed by Giddings. While it addresses the inherent limitation of Giddings’ approach—namely, the complete decoupling of transport phenomena in the moving and stationary zones—it introduces the drawback of a non-unique decomposition of $H_C$. Despite this, it proves highly valuable in highlighting the limitations and flaws of Giddings’ method. In contrast, the second formulation not only properly accounts for the interaction between the moving and stationary zones, but provides a unique and consistent decomposition of $H_C$ into its components. Three different geometries are investigated in detail: the 2D triangular array of cylinders (pillar array columns), the 2D array of rectangular pillars (radially elongated pillar array columns) and the 3D face-centered cubic array of spheres. It is shown that Giddings’ approach significantly underestimates the $H_{Cs}$ term, especially for porous-shell particles. Its accuracy is limited, being reliable only when intra-particle diffusivity ($D_s$) and the zone retention factor ($k^{″}$) are very low, or when axially invariant systems are considered. Full article

This study is a comprehensive review on the natural convection heat transfer in horizontal and inclined closed rectangular enclosures with internal objects (including circular, square, elliptic, rectangular, and triangular cylinders, thin plates, as well as other geometries) at various heating conditions. The review examines the influence of various pertinent governing parameters, including the Rayleigh number, Prandtl number, geometries, inclination of enclosure, concentration of nanoparticles, non-Newtonian fluids, magnetic force, porous media, etc. It also reviews various numerical simulation methods used in the previous studies. The present review shows that the presence of inner objects at different heating conditions and the inclination of enclosures significantly changes the natural convection flow and heat transfer behavior. It is found that the existing studies within the scope of the present review are essentially numerical with the assumption of laminar flow and at relatively low Rayleigh numbers, which significantly restrict the usefulness of the results for practical applications. Furthermore, the majority of the past studies focused on single and two inner objects in simple shapes (circular, square, and elliptic) and assumed identical objects and uniformly distributed placements when multiple inner objects are presented. Based on the review outcomes, some recommendations for future research on this specific topic are made. Full article

This paper investigates the forces generated by axially magnetized ring permanent magnets with trapezoidal cross-sections when placed near a soft magnetic cylinder. Utilizing the Hybrid Boundary Element Method (HBEM), this study models interactions in magnetic configurations, aiming to improve force calculation efficiency and accuracy compared to traditional finite element methods (FEMM 4.2 software program). The influence of the permanent magnet and the soft magnetic cylinder is approximated with a system of thin toroidal sources on the surfaces of the magnet and the cylinder, which significantly reduces the computation time for the force calculation. The approach is validated by comparing results with FEM solutions, revealing high precision with a much faster computation. Additionally, this study explores the influence of various parameters, including magnet size, separation distance, and magnetic permeability of the cylinder, on the magnetic force. The results demonstrate that the HBEM approach is effective for analyzing complex magnetic configurations, particularly in applications requiring efficient parametric studies. This approach can be adapted for other geometries, such as truncated cones or rectangular cross-section ring magnets. The findings contribute valuable insights into designing efficient magnetic systems and optimizing force calculations for varied magnet geometries and configurations, including the atypical ones. Full article

To develop a safer bone-bonding device that promotes early osseointegration with cortical bone perforation, novel subperiosteal device geometries were proposed and evaluated for their ability to facilitate surrounding bone formation and enhance bone-bonding strength. This study used animal experiments and mechanical testing to assess the performance of these designs. The experimental device consisted of two main components: a rounded rectangular plate and a centrally positioned cylinder. To promote the recruitment of bone-marrow-derived factors, slits were incorporated into the cylinder, and a center hole was created directly above it. Four device variations, differing by the presence or absence of the slits and center hole, were fabricated and then subjected to tensile tests for mechanical property evaluation. In the animal experiments, the devices were bilaterally placed on rat tibiae, and after four weeks, bone-bonding strength tests were performed. Additionally, micro-computed tomography and histological analysis of undecalcified sections were conducted. All devices demonstrated early osseointegration, and geometric design differences, specifically the presence or absence of the slits and center hole, significantly affected the mechanical properties and bone induction. However, no significant differences in bone-bonding strength were detected. These findings suggest that the newly formed bone inside the slits and center hole contributes to the reinforcement of the device. Full article

Motivated by existing techniques for implementing roughness on cylinders to control flow disturbances, we performed delayed detached eddy simulations (DDES) at Re = $6\times {10}^6$ that generated unsteady turbulent flow around a rectangular cylinder with a controlled wrinkled surface and a 1:4 aspect ratio. A systematic study of the roughness effect was carried out by implementing different configurations of equally spaced grooves and bumps on the top-surface of the cylinder. Our results suggest that groove geometries reduce energy dissipation at higher rates than the smooth reference case, whereas bumped cylinders produce relative pressures characterized by a sawtooth pattern along the middle-upper part of the cylinder. Moreover, cylinders with triangular bumps increase mean drag and lift forces by up to 8% and 0.08 units, respectively, while circular bumps increase vorticity and pressure disturbances on the wrinkled surface. All of these effects impact energy dissipation, vorticity, pressure coefficients, and flow velocity along the wrinkled surface. Both the surface-manufactured cylinders and the proposed visualization techniques could be replicated in a variety of engineering developments involving flow characterization in the presence of roughness. Full article

In order to investigate the effects of different shapes of hydrogen inlet ports on the behavioral characteristics of hydrogen in Type IV hydrogen storage cylinders under rapid refueling conditions, a mathematical model of hydrogen temperature rise and a three-dimensional numerical analysis model were developed. The rectangular, hexagonal, triangular, Reuleaux triangular, circular, elliptical and conical inlet ports were researched by using computational fluid dynamics methods. The results showed that, for the same refueling flow rate and cross-sectional area, the hydrogen temperature inside a cylinder with a rectangular inlet port is higher and the jet tilt angle is larger than for a hexagonal port, while the thermal stratification phenomenon is not obvious. The hydrogen temperature inside a cylinder with a triangular inlet port is lower than that with a Reuleaux triangle port and the jet tilt angle is larger, and neither has significant thermal stratification. The hydrogen temperature inside a cylinder with a circular inlet port is higher than that with an ellipse port, the jets are not tilted on either one, and the phenomenon of thermal stratification is prominent. Further analysis indicated that enlarging the cross-sectional area and increasing the refueling flow rate results in a higher hydrogen temperature and intensified thermal stratification and an upward-angled jet can effectively reduce or eliminate thermal stratification. Full article

The meshless displacement error-recovery parametric investigation in finite element method-based incompressible elastic analysis is presented in this study. It investigates key parameters such as interpolation schemes, patch configurations, dilation indexes, weight functions, and meshing patterns. The study evaluates error recovery effectiveness (local and global), convergence rates, and adaptive mesh improvement for triangular/quadrilateral discretization schemes. It uses meshless moving least squares (MLS) interpolation with rectangular and circular support regions and solves benchmark plate and cylinder problems. It is observed that a circular influence region, a cubic spline weight function, and regular mesh patterns yield a better performance of than an MLS-based error recovery method. The study also concludes that lower dilation index values with rectangular influence regions are preferable for regular meshes, while higher dilation index values with radial influence regions are suitable for preferable meshes to enhance MLS error recovery. Full article

This paper outlines an experimental investigation conducted at the INCAS trisonic wind tunnel, focusing on the determination of pitch damping coefficient. The model used for this investigation is the Basic Finner Model, a standard model for dynamic tests which consists in a cone-cylinder body with four rectangular fins. The study aims to evaluate the influence of various parameters—including the Mach number, angle of attack, reduced frequency, center of rotation, and roll angle—on pitch damping coefficient. The employed method for determining these coefficients is the free oscillation method which consists in measuring the model oscillation in free stream after an initial perturbation. In order to perform these dynamic tests in the wind tunnel, a dedicated rig was developed to initiate the model’s oscillation using a linear servo-actuator and to record its oscillation using a strain gauge. The results obtained from the experiments illustrate how each parameter impacts the pitch damping coefficient, highlighting the precision of the measurements. The paper’s conclusion presents that the developed rig and the method used provide accurate results, and the variation in different parameters can change the damping coefficient. Full article

Transient heat conduction and mass transfer have many applications in industry such as heating, cooling, cooking, quenching of steels, freezing, and convective drying of vegetables or fruits. A novel, interactive, and fast MATLAB application, named MULTITHMT, is improved to solve multidimensional transient heat and mass transfer problems. Exact solutions are obtained for infinite rectangular bars, short cylinders, rectangular prisms, and spherical geometries. Instantaneous temperature and moisture content at any location in the objects are obtained and temperature and moisture content at the final time are displayed in two- and three-dimensional graphics. Quenching of steel for rectangle bars and cooking of cylindrical or rectangular prism-shaped meat are represented for transient heat transfer. Cooling of spherical commercial bronze and iron is also investigated. For transient mass transfer, convective drying of rectangular prunes, bananas of short cylinders, and spherical cornelian cherries with different operational conditions is calculated. Drying of cubes with the same shape and different moisture diffusivities is investigated. MULTITHMT is the only program that uses exact solutions to calculate multidimensional heat and mass transfer problems in the available literature. It is also the only application that can calculate the target time with a given temperature or moisture content for any specific location in the studied multidimensional objects. This application can be used for educational purposes in several engineering departments and industrial applications where transient heat and mass transfer processes are needed. Full article

At present, many high-temperature pipelines need to carry out non-stop detection under high-temperature conditions, and an ultrasonic guided wave is undoubtedly one of the solutions with the highest potential to solve the problem. However, there is a lack of research on the propagation characteristics of longitudinal guided wave modes in high-temperature pipelines. Based on the Green–Naghdi (GN) generalized thermoelastic theory, a theoretical model of thermoelastic guided waves in an orthotropic hollow cylinder with a temperature field is established by using the Legendre polynomial series expansion method. Firstly, based on the GN thermoelastic theory, the coupling equations expressed by displacement and temperature are established by introducing the rectangular window function. The curves of dispersion, displacement, and temperature of the guided wave are numerically solved by using this equation. Subsequently, the influence of the diameter-to-thickness ratio on the dispersion of the longitudinal thermoelastic guided wave is analyzed at the same temperature. Finally, the effect of temperature field variation on the phase velocity dispersion is discussed, which provides a theoretical basis for the study of the dispersion characteristics of hollow cylindrical pipes containing temperature fields. Full article

Diesel engine combustion is dependent mainly on the fuel injection characteristics, particularly the injection pressure and rate, which directly affect the engine efficiency and emissions. Herein, an electrically controlled supercharger is added to a traditional high-pressure common rail system to form an ultrahigh-pressure common rail system. Then, the variations in the spray, combustion, and emission characteristics of a diesel engine with a variable fuel injection rate are analyzed. Moreover, a simulation model for a diesel engine combustion chamber is built and verified by experimental results for numerical analysis. The results reveal that the injection rate can be flexibly adjusted via regulation when the solenoid valves are opened on the electrically controlled supercharger. Specifically, (1) the boot-shaped injection rate has greater potential than the traditional rectangular injection rate in terms of combustion and emission; (2) the main injection advance angle at the boot-shaped injection rate can be properly increased to improve combustion; and (3) the pilot injection quantity and advance angle are strongly coupled with the boot-shaped injection rate, potentially enhancing the mixing efficiency of fuel and air in the cylinder to achieve favorable emission results. This paper provides good guidance for the reliable design and optimization of noble-metal-based diesel engines. Full article

Free-floating and submerged wave energy converters (SWECs) are regarded as promising technologies for renewable energy production. These converters rely on a heave-motion buoy to capture the kinetic energy of ocean waves and convert it into electrical energy through power conversion systems. To better understand the impact of various factors on power generation and efficiency, the effects of different buoy shapes (rectangular, circular cylinder, and trapezoidal fin), submergence depths (0, 0.1, and 0.2 m), wave heights (0.04, 0.06, and 0.1 m), and spring stiffness (50 and 100 N/m) were investigated. A 2D numerical wave tank with a buoy was simulated, and the results were validated against experimental data. Information on vorticity, vertical displacement, power absorption, and efficiency are provided. The findings indicate that the buoy shape and wave height significantly affect power absorption and efficiency. Additionally, this study reveals that increasing submergence leads to higher power absorption and lower conversion efficiency. Full article