Meccanica最新文献

To optimize the efficiency and stability of wheat pneumatic conveying systems, this study systematically analyzed the flow characteristics under varying air-to-solid ratios using the CFD-DEM (Computational Fluid Dynamics—Discrete Element Method) approach. The results demonstrate that as the gas velocity increases, the flow regime within the pipe transitions progressively from plug flow to dune flow, and ultimately to stratified flow. The standard deviation of inlet pressure fluctuations was highest under dune flow conditions, followed by plug flow, and lowest during stratified flow, while the system stability showed the inverse trend. Wheat particle velocity is highest under stratified flow conditions, followed by dune flow, and lowest during plug flow. The distribution of wheat particles transitions from a fully filled pipe state to a depositional state at the pipe bottom. Increasing the wheat feed rate reduced both the particle velocity growth rate and system stability. This study demonstrates the critical role of the air-to-solid ratio in regulating flow regimes to influence conveying stability and efficiency, providing direct guidance for optimizing air-to-solid ratio settings in wheat processing lines.

In this paper, an efficient nonlocal higher-order shear deformation beam theory is developed for bending of nanobeams based on the stress-driven model. The theory accounts for several distributions of the transverse shear strains that satisfy the zero traction boundary conditions on the surfaces of the beam. Hence, it is not necessary to use a shear correction factor. Collecting the higher-order shear deformation beam theories and the stress-driven nonlocal model, the equations of nonlocal elastic equilibrium are consistently derived. Hence, it is shown that the stress-driven model is well-posed for higher-order shear deformation theories. The accuracy of the present approach is verified by comparing the obtained results with existing solutions. It can be concluded that the present nonlocal stress-driven approach for higher-order shear deformation theory is not only accurate but also simple in predicting the bending behavior of nanobeams.

Air-core vortices occurring at intakes cause efficiency losses, vibrations, operational difficulties, and erosion at affiliated water-conveying structures. Air-core vortices are in the forms of non-air entraining vortex (air-core vortex in suspension) and air-entraining vortex. The profile of an air-core vortex is considered to be one of the main characteristics of the vortex. There are available semi-empirical formulas for the profile of a vertical non-air entraining vortex (air-core vortex in suspension) occurring at a vertically-flowing downward intake. However, there is no available developed formula relating to the profile of a vertical air-entraining vortex occurring at a vertically-flowing downward intake because the height, radii, and other physical quantities of the imaginary section of the air-entraining vortex downstream of the intake entrance are not measurable. Therefore, the profile of a vertical air-entraining vortex needs to be predicted. In the present study, by modifying the available formula relating to the profile of a non-air-entraining vortex and incorporating available test data, a practical methodology is developed for predicting the profile of a vertical air-entraining vortex. This study provides a practical formula and a chart to determine the necessary parameters to predict the profile of a vertical air-entraining vortex. The validation of the proposed methodology is examined and checked with available test data relating to the profile of a vertical air-entraining vortex occurring at a vertically-flowing downward intake. The results of the present study are in good agreement with available test data relating to the profile of vertical air-entraining vortices (the coefficient of determination is between 0.976 and 0.995).

This paper presents a dynamic continualization technique for a multi-layer beam-lattice metamaterial with an alternating chiral microstructure, where each layer is reciprocally interconnected through the insertion of pins. The study analyzes the dispersive properties of the system and its potential applications as a meta-filter, highlighting how the enhanced continualization technique introduced can capture the dispersive properties of stratified systems with chiral geometry. This approach makes it possible to derive higher-order gradient-type continuum models that yield dispersion spectra close to those obtained through a discrete Lagrangian treatment, without encountering dynamic instability effects due to thermodynamic inconsistency. These aspects are further investigated through the presentation of application examples, specifically concerning a stratified tetrachiral waveguide. A key finding of the studied examples is related to the passive/active tunability of the system, specifically in relation to the stiffness of the pin which determines significant influences on the dispersion spectra. To complete the analysis, a further example is finally proposed in which the waveguide is subjected to harmonic excitation, revealing how variations in the parameters can affect wave polarizations.

The rolling soft robot usually uses circular or ellipse-like configurations but the factors influencing the robot configuration have not been sufficiently investigated. This study presents a theoretical model for investigating the morphology evolution of a thin elastic ring under gravity. The ring exhibits an ellipse-like morphology under gravity, with this morphology governed by the ratio of gravity to bending stiffness. An increase in the ratio of gravity to bending stiffness results in a flatter ellipse-like structure, accompanied by an enhanced contact length with the ground and a concomitant reduction in its gravitational moment on the slope. The ellipse-like structures calculated by the theory are in good agreement with the experiment and simulation. This study provides a theoretical basis for the material selection and geometry determination of the configuration design of required rolling soft robots.

Lattice-like cellular materials, with their unique combination of lightweight, high strength, and good deformability, are promising for engineering applications. This paper investigates the energy-absorbing properties of four truss-lattice structures with two defined volume fractions of material in static compression experiments. The mass-specific energy absorption is derived. The specimens are manufactured by SLA printing of viscoelastic polymeric material. Sustainability implies that the lattice structures can withstand multiple loads and return to their original state after some recovery. Additionally, we present finite element simulations of our experiments and show that these calculations are, in principle, able to predict the different responses of the lattices. Like in the experiments, the truncated octahedron-lattice structure proved to be the most effective for energy absorption under strong compression.

We introduce the energy-stepping Monte Carlo (ESMC) method, a Markov chain Monte Carlo (MCMC) algorithm based on the conventional dynamical interpretation of the proposal stage but employing an energy-stepping integrator. The energy-stepping integrator is quasi-explicit, symplectic, energy-conserving, and symmetry-preserving. As a result of the exact energy conservation of energy-stepping integrators, ESMC has a 100% acceptance ratio of the proposal states. Numerical tests provide empirical evidence that ESMC affords a number of additional benefits: the Markov chains it generates have weak autocorrelation, it has the ability to explore distant characteristic sets of the sampled probability distribution and it yields smaller errors than chains sampled with Hamiltonian Monte Carlo (HMC) and similar step sizes. Finally, ESMC benefits from the exact symmetry conservation properties of the energy-stepping integrator when sampling from potentials with built-in symmetries, whether explicitly known or not.

The temperature rise of the tooth surface in spiral bevel gears plays a crucial role in lubrication performance and surface failure. However, existing studies primarily investigate scuffing by analyzing tooth surface temperature through experiments and simulations, without using similarity theory to examine comparable systems. By leveraging similarity theory, researchers efficiently translate insights from controlled experiments to real-world applications, fostering innovation while conserving resources. Similarity theory is used in the study to analyze the temperature rise of the tooth surface, and it is possible to determine that gears in different systems may exhibit analogous thermal behavior under specific scaling conditions. A thermal fluid–structure coupled model is employed to conduct a precise analysis of the original system for thermal assessment and experimental validation. Similarity theory effectively predicts tooth surface temperature rise and optimizes lubrication strategies. Notably, the temperature rise is more pronounced near the tooth crest. The maximum temperature in the similarity model reaches 140.59 °C, while that in the original model is 134.5 °C. The deviation between simulation and experimental results for the original model is 6.43%, and the discrepancy between the original and similarity models remains within 4.53%. This similarity-based modeling approach accurately captures the thermal behavior of analogous systems, significantly reducing the cost of manufacturing test gears and the workload associated with tooth surface temperature experiments and simulations.

Numerous aircraft accidents involving bird flocks have occurred in aviation. Existing literature and the airworthiness certification standards are primarily focused on single bird-strike assumption. The present study addresses the possibility of bird flock incident and investigates the crashworthiness of NASA Common Research Model wing subjected to single and multiple bird strikes, using a coupled Finite Element Method and Smooth Particle Hydrodynamics approach. The numerical bird model is validated and the influence of equation of state (EOS) models, porosity and contact loads variation against the target structure’s shape, is reported. Two locations along the span i.e. towards the wing root and the wing tip, are considered for impact investigation, with emphasis on comparative penetration, energy absorption capability and potential damage to the main spar. Results revealed that the impact loads and impulse for the curved leading-edge section to reduce by more than half compared to the flat plate. The Gruneisen EOS provided a good correlation with experimental data, while adding porosity to the Polynomial EOS significantly reduced pressure peaks. Analyzing different flock orientation scenarios, the vulnerability of wing tip to multiple bird strikes was observed, leading to main spar damage. While single bird strikes may not cause critical damage, bird flocks pose a significant threat to aircraft safety, emphasizing the need for incorporating bird flock scenarios into aircraft design considerations.