Meccanica最新文献

The present research presents potentials and complementary potentials used in the one-dimensional nonlocal integral formulations. The pure stress and the pure strain nonlocal formulations were considered. While the potential used in the strain driven formulation is well known, the complementary potential has not yet been presented in the literature. The same applies to the stress driven formulation. The equivalent formulations are obtained by resorting to the Legendre transformation, and their equivalence is proved. It is also shown that these results can be used to postulate a novel potential, i.e. a kind of mixed stress–strain potential, which is, however, as ill-conditioned as the pure strain-driven formulation. Finally, an example is given that practically confirms that the stress-driven formulations resulting from the potential and the complementary potential are equivalent.

Evaluating the state of historical masonry structures, particularly those built with irregular masonry, presents challenges in determining their load-bearing capacity. Most current approaches use macroscopic numerical models that treat the material as a homogeneous continuum, where defining an appropriate constitutive law is essential. To this end, homogenization has proven useful in bridging the gap between meso and macro-scales, yet using homogenized macromodels may prevent to capture specific failure modes. Alternatively, mesoscopic methodologies represent stacking modes explicitly. However, full structural analysis at this scale has mainly been applied to regular masonry due to the complexities of explicitly representing the geometry of the irregular stones. The present contribution aims to propose a method that leverages image acquisition techniques, such as orthophotos, to address these challenges. Mortar joints are lumped onto zero-thickness interfaces, determined through a distance field-based morphing procedure and medial axis principles. The load-bearing capacity is assessed using a Kinematic Limit Analysis problem, formulated and solved as a linear programming problem. A Mohr-Coulomb frictional behavior, modified with a tensile cut-off and a linearized compression cap, is assigned to the mortar joints. The blocks are considered infinitely rigid and strong. It is shown that the proposed methodology can efficiently model structures of large sizes, by illustrating its use on two 2D problems.

Cableways have been used intensively for transportation of goods and people since the early nineteenth century. Aerial cableways are primarily modelled based on a continuous representation, well-suited for traditional analytical models. However, due to the increasing complexity of these systems, cableway modeling is evolving to discretised approaches like Finite Element (FE) analysis. The Finite Element Method (FEM) is an alternative to the modal approach for studying the dynamics of nonlinear systems, and it is more suitable for the representation of large displacements needed in the view of the modeling of an entire plant; it is also flexible and computationally accurate. Dynamic models of aerial cableways based on finite element computation with significant geometry changes are currently lacking in the literature. The main purpose of this study is to fill this gap, through the development of a finite element model which is able to describe the dynamic behavior of aerial cableway, keeping into account its time-varying geometry. The system modelling is based on two cables (carrying and hauling), describing a back-and-forth aerial cableway to which a concentrated mass representing the cabin is added. After the introduction of the modelling approach, the finite element model is applied to investigate typical conditions such facilities are exposed to, i.e. overlapping between the hauling and the carrying cables or the large vibrations the hauling cable is subjected to, when the cabin is approaching the station. Versatility and ease of implementation are the main strength of the proposed model, making it suitable to further extensions.

In this study, we investigate the static and dynamic characteristics of electrostatically actuated nanobeams with elliptical cross-sections, focusing on their potential applications in nano-electromechanical systems (NEMS). Using finite element analysis (FEA) in COMSOL Multiphysics, we explore the effects of key parameters on the nanobeams’ performance. Our analysis includes a detailed examination of the static characteristic curves and natural frequencies under varying conditions. The study reveals significant insights into the behaviour of elliptical nanobeams, demonstrating how alterations in eccentricity and tilt angle influence the operational efficiency of NEMS devices. The impact of geometric variations on vibrational modes provide critical guidelines for designing robust and precise NEMS sensors and actuators.

A scissors-type bridge that applies a deployable scissors mechanism to its structural form has been researched and developed to support emergency restoration activities after disasters. The vibration characteristics of this bridge have been evaluated by eigenvalue analysis and walking experiments in past studies. However, the basic knowledge, including the design method for this bridge, was still limited. Hence, this study conducts a hammering test to obtain basic vibration characteristics and explore the change in vibration characteristics under different boundary conditions through eigenvalue analysis. Although the total weight is increased by installing the decks, it can be seen that installing the decks on the top or bottom of the scissors-type bridge significantly improves rigidity in the horizontal direction. Still, the influence in the vertical direction is less than that in the horizontal direction. Furthermore, based on the experimental and numerical results, an estimation formula for the natural frequency approximating a scissors-type bridge as a simple beam structure was proposed. It was possible to estimate the natural frequencies in the vertical primary mode with errors of less than 3(%) compared with the experimental results and errors of less than 10(%) compared with the numerical results. This finding has important implications for the developing a simple and reliable design of emergency structures that use the scissor mechanism.

The capillary imbibition phenomenon has been widely studied by establishing governing equations, some of which might be too complex to obtain accurate solutions. Moreover, the capillary rise can be influenced by the constraint of capillary edge (i.e., pinning phenomenon), which is difficult to describe by governing equations. Therefore, a new analysis method is proposed in this paper, which can predict the capillary rise with/without contact line movement considering the dynamic contact angle and entrance viscosity dissipation. Firstly, the capillary length is discretized into micro elements. Secondly, every micro fluid level rise is analyzed based on conservation of mechanical energy. Finally, the whole rise process can be predicted by the end-to-end linking of all micro-elements. The accuracy of the proposed method is verified by multiple sets of experimental data. Moreover, we discuss the pinning and depinning phenomena in detail and propose a dimensionless number to judge the occurrence of depinning phenomena.

In the present study, a novel type of nontraditional tuned mass damper (TMD), termed as a tuned mass rate-independent damper (TMRD), was proposed for structural vibration suppression. The proposed TMRD consisted of a spring element, a mass element, and a rate-independent linear damping (RILD) element, which generated damping forces independent of the excitation frequencies. Based on the fixed-point theory, analytical formula of optimally designing the characteristic parameters of the TMRD were derived. The advantages of the TMRD over TMDs in suppressing the structural vibration and damper stroke were demonstrated, when they were separately used in flexible structures subjected to harmonic and earthquake-induced ground motions. For practical applications, an approximate method was presented to passively realize the proposed TMRD. It was suggested that the proposed method can be used to physically realize the TMRD and provide a superior solution than the conventional TMD to suppressing the structural vibration and damper stroke.

To investigate the effects of axial misalignment, lead crown relief, and temperature on the meshing stiffness of gears, this study aims to derive high-precision gear stiffness values that are more aligned with practical engineering applications. Based on the thermal expansion theory, slice coupling effect, and involute profile theory, a thermal stiffness model for meshing spur gear pairs under multiple influencing factors has been established, integrating the improved potential energy method and the nonlinear contact stiffness calculation approach. A calculation method for the thermal stiffness of meshing spur gear pairs, considering the impacts of axial misalignment and lead crown relief, has been developed. Furthermore, the mechanisms by which varying temperature, modification amounts, and misalignment affect the meshing stiffness of spur gear pairs have been explored. The results indicate that both lead crown relief and axial misalignment alter the load distribution across the tooth width, leading to a relative load concentration and consequently affecting the deformation of the gears under external loading, thereby influencing their meshing stiffness. It was found that the meshing stiffness decreases with an increase in axial misalignment and lead crown relief amounts. Additionally, with the introduction of temperature effects, an increase in temperature further reduces the meshing stiffness of the gear pair. The thermal deformation induced by temperature variations results in profile errors, affecting the actual meshing positions of the gears and altering the dimensions of single and double tooth intervals along the meshing line. This research establishes a theoretical foundation for the design of gear systems and the study of gear transmission system dynamics.

In this study we evaluate the performance of different constitutive biomechanical models, focusing on their ability to reproduce the mechanical behavior of myocardial tissue under various deformation modes. Three constitutive models were analyzed assuming incompressible formulations: the invariant-based formulation of the Costa model, the Holzapfel–Ogden (HO) model, and its extended version (HOE). The study aimed to identify which model provides the best fit for different experimental data, including equibiaxial (EBx), true biaxial (TBx), simple triaxial shear (STS), and combined data sets (Equibiaxial + Shear, True biaxial + Shear). The results showed that the Costa model generally performed better when considering combined datasets, providing a good balance between fitting accuracy and parameter stability, while using the least number of parameters among the contrasted models. The HO model demonstrated reasonable fitting abilities but struggled with non-equibiaxial conditions and clearly orthotropic simple shear datasets. The extended HOE model improved the fitting performance of the standard HO formulation for more complex data, particularly in shear tests, but introduced additional complexity and a higher number of parameters. Therefore, our study highlights the importance of analyzing which validated constitutive formulation is able to adapt to the available experimental data, especially when mixed deformation modes are involved. While all the three models tested performed adequately, the Costa model proved to be the most versatile, especially when dealing with various experimental conditions, providing insights for future research on biomechanical modeling of cardiac tissue.

This paper presents a novel method for spur gear tooth profile optimization, addressing the challenge of designing gears with improved performance. Traditional gear designs often compromise between contact stress, wear, and noise. This research explores a wider design space to identify gear profiles offering a better balance. The proposed approach leverages tensor-based kinematics combined with the Reuleaux method for conjugate profile generation, creating a robust framework for exploring potential designs. This framework defines an objective function considering multiple performance criteria. Differential evolution is employed to search for novel tooth profiles minimizing this function. The performance of optimized profiles is compared against existing designs, including involute, S-gears, and cosine gears. Key performance indicators include Hertz contact and subsurface shear stresses, normal force, sliding factor, specific sliding, contact ratio, and gear mesh stiffness. Results demonstrate the method’s effectiveness in generating improved tooth profiles. Optimized solutions exhibited contact and shear stress reductions comparable to 30-degree involute and S-gears, suggesting improved pitting resistance and wear. Some designs showed substantial specific sliding reductions, indicating the potential for reduced heat generation and surface wear. While cosine gears showed reduced contact stress, they also exhibited lower contact ratios, potentially increasing dynamic loads. These optimized solutions offer a promising path towards designing high-performance gears tailored to specific applications. The method effectively explores the vast solution space and generates tooth profiles fulfilling desired optimization trade-offs, paving the way for future research incorporating additional performance criteria and exploring more complex gear geometries.