Meccanica最新文献

Aeration irrigation has garnered significant attention due to its effectiveness in enhancing crop yield and water use efficiency. Understanding the two-phase flow mechanism of water–gas in the aeration pipeline is of great significance for promoting the development of the aeration irrigation system. In this study, a formula for calculating Reynolds number of water–gas flow in aeration pipeline was established by combining theoretical analysis with experimental verification. In addition, based on the YOLO v5 image classification model, a classification and detection model of water–gas flow pattern was proposed. The results show that increasing aeration rate can increase pipeline pressure. The overall accuracy of the developed flow pattern detection software was 86.3%, which can meet the requirements of practical application. Finally, based on image classification and theoretical analysis, the formulas of the corresponding flow patterns were obtained. This study provides a solution for determining the two-phase flow pattern of water–gas in aerated irrigation system, which was of great significance for improving the hydraulic calculation of aerated irrigation system and promoting the wide application of aerated irrigation technology.

This study investigates the ditching dynamics of the ARJ21 regional airliner under both calm and wave-influenced water conditions using the Smoothed Particle Hydrodynamics (SPH) method. The DualSPHysics platform is adopted to simulate water entry events, with the modeling framework validated against experimental data from canonical wedge and cylinder impact tests. A numerical wave tank incorporating an Active Wave Absorption System (AWAS) is constructed to suppress boundary reflections and produce a stable wave environment. Comparative analyses of the aircraft's hydrodynamic responses reveal that wave conditions significantly intensify vertical acceleration and pressure loads, while amplifying the secondary rise effect. The SPH method demonstrates strong agreement with experimental results, particularly in early-stage impact behavior. These findings support the feasibility of using meshless SPH-based methods for simulating complex aircraft–wave interactions in ditching scenarios.

In self-reconfigurable structures, the mechanical design of the joints is one of the most challenging tasks. Within this context, flexural pivots are widely adopted as compliant mechanisms due to their ideal design for achieving low rotational stiffness and high off-axis stiffness. To maximize performance, they are often optimized for specific application requirements. However, designing flexural pivots for self-reconfigurable structures with an arbitrary center of rotation remains a significant challenge. To address this, we propose an approach for optimizing the topology of beam-based flexural pivots undergoing large deflections, aiming to achieve an optimal configuration with an arbitrary center of rotation. To this end, both the stiffness-based objective function and the strain energy-based objective function are introduced. For the implementation, a geometrically exact beam element is utilized to establish a dual-layer ground structure for optimization. A genetic algorithm is employed to identify optimal configurations for flexural pivots, including traditional notch hinges and cross-spring pivots. Additionally, the influence of different objective functions and their corresponding parameters on the optimized topology is examined and verified. Ultimately, this approach yields optimal topologies in three representative examples with different centers of rotation, establishing a foundation for the design of compliant mechanisms with user-defined rotational behavior.

This paper proposes a novel theoretical study on the onset of failure in finitely deformed periodic nonlinear composite materials because of microscopic instability and bifurcation mechanisms in conjunction with decohesion and contact effects at interfaces between different constituents. Original analytical investigations are firstly carried out on an introductory 2-DOF example highlighting the main features of the examined problem and using a structural mechanics approach. The theoretical setting of the problem is then developed within a finite strain continuum mechanics framework and a nonlinear homogenization formulation is adopted to drive the system along macro-deformation loading paths. The formulation includes a continuum contact mechanics model in conjunction with a class of irreversible cohesive traction–separation laws for treating both unilateral contact constraint and progressive decohesion at discontinuity interfaces. The main equations governing the equilibrium problem of the microstructure in both finite and rate forms are developed, and the relevant issues associated with loss of uniqueness in the rate equilibrium solution together with the instabilities onset are also investigated by developing an exact second-order analysis. The introductory example is then re-examined by using the proposed continuum mechanics formulation and comparisons with simplified cohesive-contact models frequently adopted in the literature are performed. The obtained results show the role played by contact and cohesive mechanisms and the significance of an appropriate modelling of their deformation sensitivity and conditionality nature to perform accurate stability and bifurcation analyses. Strategies to circumvent the complications arising both from cohesive behavior and contact mechanics nonlinearities arising at the interface are also discussed.

In this paper, an analytical iterative method is presented to determine the optimal tension distribution for redundant cable-driven robots. In this method, a solution domain is defined based on the lower and upper tension limits of the cables. Then an objective function with a variable objective point is introduced. The continuous adjustment of the optimization objective point provides flexibility to increase or decrease the stiffness and energy consumption of the robot along a specified path. Furthermore, the convergence of the method to the optimal solution and the continuity of the resulting tension distribution are assured by the algorithm outlined in this study. Finally, two examples are included to compare the proposed method with some notable approaches in the literature. The first example demonstrates that other methods may fail to identify any acceptable tension distribution, while the second example illustrates the advantages of utilizing a variable objective point in the objective function.

This paper presents a one-dimensional theory for moderately thick piezoelectric beam-type structures with imperfect resistive electrodes. For practical applications, a special goal is also the finite element discretization of the electromechanically coupled partial differential equations, which combine the Telegrapher’s equations with the elastic properties of a Timoshenko beam. Unlike ideal electrodes, which satisfy the equipotential area condition, the voltage distribution in resistive electrodes is governed by the diffusion equation. For the electrical domain, Kirchhoff’s voltage and current rules are applied to derive the parabolic differential equation, which is driven by the time derivative of the axial strain. It is demonstrated that the current flow through the electrodes of the piezoelectric layer depends on the electrode resistance and the capacitance. For the mechanical domain, d’Alembert’s principle is combined with the piezoelectric constitutive equations to derive an extended version of the Timoshenko beam equations, incorporating the x-dependent voltage drop across the electrodes. A one-dimensional finite element is then formulated using Timoshenko shape functions for the deflection and the rotation angle, along with linear shape functions for the voltage drop along the beam segment. For the validation of the model a clamped-hinged piezoelectric beam is used as a benchmark example to compare the results of the one-dimensional discretization with two-dimensional finite element (FE) simulations. Various types of resistive electrodes are considered, including static deflections, dynamic vibrations, and eigenfrequency analyses. The results demonstrate that the derived piezoelectric beam model also includes the case of ideal electrodes (short- and open-circuited), when the sheet resistance is very low, and the case of a non-electroded piezoelectric beam, when the sheet resistance is very high.

To improve the aerodynamic performance and optimize the flow field structure of H-type vertical axis wind turbines (VAWTs), a split trailing-edge double-flap structure inspired by bionic fish tail fins was proposed, while maintaining the original airfoil parameters. Using 2D and 3D computational fluid dynamics (CFD), the effects of varying flap relative lengths (x/c), upper and lower flap deflection angles, and active control strategies on aerodynamic performance (C_p) were systematically investigated. First, the power coefficient and instantaneous torque of individual blades through comparative analysis to determine the optimal x/c. Second, the influence of different upper and lower flap deflection angles on the overall torque was investigated. Finally, active control strategies were applied to explore their effects on the power coefficient and tangential force. Results showed that x/c = 0.2 provided the most significant improvement. At an upper flap deflection angle of 30°, notable performance enhancements were observed across the studied tip speed ratio (TSR) range. When both deflection angles were 30°, the improvement extended to a wider TSR range. Active control increased blade surface velocity gradients, optimized velocity distributions, and enhanced blade torque.

This study examines the resonance frequency shift due to adsorption in a biomolecule-resonator sandwich nanobeam system under a temperature-induced load. The analysis incorporates shear deformation, distributed adatoms, and small-scale effects within the framework of nonlocal elasticity theory (NET). The sandwich nanobeam consists of three sections: a perforated core with a uniform square-hole pattern and two bonded functionally graded porous (FGP) layers. Adsorption-induced energy is modeled using a distribution-based approach for spike proteins and bio-receptors. The dynamic model of the nanobeam resonator integrates surface stress effects. The functional nanobeam and localized biomolecule models are used in conjunction with van der Waals (vdW) forces, employing the Lennard–Jones (6–12) and Morse potentials to assess all influencing factors. Shear force and inertia moment are explicitly derived from the nonlocal Timoshenko beam equations, with residual stress considered as an additional axial load. The Navier technique and differential quadrature method (DQM) are employed to solve the motion equations, enabling a comprehensive interpretation of the results. Numerical findings reveal that surface properties, adsorbed adatoms, perforation dimensions, hole number, thermal loads, variation in power law index, porosity parameters, and the positioning of receptors and spikes all influence the frequency shift. Results further indicate that interatomic interactions reduce system stiffness, emphasizing their significance in computational analysis. The proposed model effectively evaluates the dynamic response of biomolecule-resonators and can determine the mass and density of viruses and spikes while accounting for adatom bonding effects.