Meccanica最新文献

An analytical efficiency expression for the 2K-V gearbox, which includes both rotational and revolutional power, is derived using virtual power analysis. The presence of a constant-speed ratio mechanism in the 2K-V gearbox results in certain components rotating revolution without self-rotation. New concept, the revolutional power, is introduced to address this aspect. The efficiency formula and power flow have been verified through several data sets and velocity iconography. Further analysis investigates the impact of specific design parameters on efficiency and power losses. Moreover, sensitivity weights for design parameters affecting total efficiency are identified using machine learning and an optimal parameter range for their optimization is established. Design recommendations aimed at enhancing efficiency are provided. The results show that the losses at the meshes are significantly lower when the ratio of the first stage gearing is set to speed-up rather than speed-down. The smaller the difference in the number of teeth in the second stage gearing, the greater the power losses at the meshes. In the majority of speed ratio scenarios, the second-stage gear pair will experience significant meshing losses as virtual power flows through it. The design parameters related to the second-stage gearing have a significant effect on the overall system efficiency.

In this paper different lumped parameters models are presented for the stability analysis of rotors supported on gas bearings. The analysis is carried out taking into account the damping and stiffness coefficients of journal bearings, calculated with the perturbation method. Lumped parameters models of different complexity are discussed for the description of the main rigid modes of the spindle. In case of symmetric systems, it is shown that the complexity of the model can be reduced by halving the number of the degrees of freedom. The analogy with the single mass approach is demonstrated. The considerations discussed in the paper are preliminary for the stability analysis of more complex systems, such as the ones with non-fixed bushes.

In this work, starting from an approach previously proposed by the Authors, we put forward an extension to the large deformation regime of the dimensionally-reduced formulation for peridynamic thin plates, including both hyperelasticity and fracture. In particular, the model, validated against numerical simulations, addresses the problem of the peeling in nonlocal thin films, which when attached to a soft substrate highlights how nonlocality of the peeled-off layer might greatly influence the whole structural response and induce some unforeseen mechanical behaviours that could be useful for engineering applications. Through a key benchmark example, we in fact demonstrate that de-localization of damage and less destructive failure modes take place, these effects suggesting the possibility of ad hoc conceiving specific networks of nonlocal interactions between material particles, corresponding to lattice-equivalent structure of the nonlocal model treated, of interest in designing new material systems and interfaces with enhanced toughness and adhesive properties.

Plasma membranes appear as deformable systems wherein molecules are free to move and diffuse giving rise to condensed microdomains (composed of ordered lipids, transmembrane proteins and cholesterol) surrounded by disordered lipid molecules. Such denser and thicker regions, namely lipid rafts, are important communication hubs for cells. Indeed, recent experiments revealed how the most of active signaling proteins co-localize on such domains, thereby intensifying the biochemical trafficking of substances. From a material standpoint, it is reasonable to assume the bilayer as a visco-elastic body accounting for both in-plane fluidity and elasticity. Consequently, lipid rafts contribute to membrane heterogeneity by typically exhibiting higher stiffness and viscosity and by locally altering the bilayer dynamics and proteins activity. A chemo-mechanical model of lipid bilayer coupled with interspecific dynamics among the resident species (typically transmembrane receptors and trasporters) has been recently formulated to explain and predict how proteins regulate the dynamic heterogeneity of membrane. However, the explicit inclusion of the membrane viscosity in the model was not considered. To this aim, the present work enriches the constitutive description of the bilayer by modeling its visco-elastic behavior. This is done through a strain-level dependent viscosity able to theoretically trace back the alteration of membrane fluidity experimentally observed in lipid phase transitions. This provides new insights into how the quasi-solid and fluid components of lipid membrane response interact with the evolution of resident proteins by affecting the activity of raft domains, with effects on cell mechano-signaling.

This paper introduces the Gibbs–Appell formalism into fluids. It devises the energy of acceleration of a perfect fluid surrounding a moving impermeable rigid body and the hydrodynamic forces acting on the body. The fluid is considered infinite, and the rigid body may have any closed tridimensional form. Therefore, the velocity field is non-divergent and irrotational; the density field is homogeneous in space and non-dependent on time, and all viscous effects are neglected. Under these assumptions, an explicit formulation for the hydrodynamic forces acting on the body is known as a-priori, and it is recovered in this text following an approach based on generalized quasi-velocities and the Gibss–Appell formalism, that may handle a vaster class of mechanical problems in comparison to Newtonian mechanics, especially non-holonomic constrained systems. The devised formulation is applied to the two-dimensional case study of a disc in unsteady rectilinear motion: the analytical form for the generalized hydrodynamic forces acting on the disc is evaluated, as well as the explicit formulae for the hydrodynamic coefficients of the body and the total energy of acceleration of the surrounding fluid.

The present study investigates thermal sensitivity of a horizontal nanofluid layer which is subjected to conductivity and viscosity variations as linear functions of volume fraction of particles. A weak heterogeneous characteristic of the fluid is considered i.e. variations freeze as the basic profile of particles in the system. Further, the study undertakes various boundary conditions on the layer to analyse the convection process such as zero particle flux, equal, top and bottom heavy distribution of volume fraction of particles. The expression of Rayleigh number for nanofluid is found to be increased significantly due to conductivity and viscosity variation effects and has negligible impact in decreasing/increasing its value due to other nanofluid variables. Thus, a substantial enhancement in the stability of the system is established except for zero flux case where overall effects due to the presence of particles become almost negligible. The properties of base fluid and particles show conflicting roles in deciding the thermal sensitivity of the layer.