Meccanica最新文献

Quasi-static upward pull-off of a horizontal pressure-sensitive tape pulled at an internal location (double peeling) is analyzed. The finite-length tape is modeled as an inextensible elastica (beam), so that bending resistance predominates and stretching of the tape is neglected. (If bending were neglected, the tape would look like an inverted V and the process has been called V-peel.) The beam is either pulled at its center or off-center. The adhesive is modeled as a Winkler foundation, and the criterion at a peel front, based on the common fracture mechanics approach, can be written as a given critical stretching of the foundation. Displacement control is considered, and the deflections and rotations may be large. Equilibrium curves of the associated force versus vertical deflection of the pulling location are determined (typically involving at least one jump of the force), along with shapes of the beam during pulling. As the beam is pulled, the configuration changes from double peeling to single peeling. Detachment of the beam from the foundation is examined. Relevant parameters are nondimensional versions of the beam length, the pulling location, and the work of adhesion (or, equivalently, the critical stretched length of the foundation).

Piecewise linear elasticity represents the multiple states of a structure, where each state can be handled as a linear state as long as the switching does not occur. As long as each linear state is linear, the modal analysis can be used for the dynamic analysis, with the implementation of the switching between the states. Truncated modal analysis and the inelastic or plastic switching cause energy loss during the switching in discrete PL-elastic systems. This work introduces formulae for the quantitative analysis of this energy loss, allowing its substitution by a viscous damping ratio. It is shown that the energy dissipation during the switching can reach a significant ratio under specific conditions. The type of impact and the degree of modal truncation affect the magnitude of energy loss. Through simple examples, the evaluation of the possible outcomes is presented.

This paper considers the swing-up control of a three link manipulator with two joint forcing. A dynamics test of the manipulator is proposed using a controller based on inertial quasi-velocities (IQV). The benefits of describing both the control scheme known from the literature and the one designed based on the IQV are demonstrated. The presented algorithm applies dynamics equations derived from the decomposition of the manipulator’s inertia matrix. As a result, the IQV is introduced, which can be used for various purposes, namely for studying dynamics and control. This description provides some insight into the manipulator dynamics when the proposed controller is incorporated into the system. Furthermore, the use of the IQV changes the behavior of the closed-loop system due to the inclusion of couplings between the links. The proposed control scheme is not intended to improve performance but primarily to analyze the dynamics of a closed system and estimate couplings in the manipulator. Theoretical considerations are supported by simulation results on an underactuated 3 degree of freedom (DOF) manipulator.

Energy Gradient Theory has been developed in recent years for a better understanding of the flow instability and transition from laminar to turbulence in the fluid flow. In this work, we reconstruct the energy gradient theory to establish a relation between the point of inflection and Taylor-Görtler-Like (TGL) vortices in the three-dimensional (3D) rectangular lid-driven cavity flow and find out the exact location from where the TGL vortices start to be formed. Point of inflection declares whether a flow is stable or not, whereas TGL vortices are formed due to the instability or disturbances of the flow. To build the relation among them, we utilize the notion of inflectional instability for the formation of TGL vortices in the lid-driven cavity. Further, we investigate the reason for the formation of Tollmien-Schlichting or T-S waves in the cavity and how this wave plays an important role in the development of the TGL vortices. In the process, we also find the region of maximum kinetic energy, which is the birthplace of TGL vortices in the cavity. The formation of TGL vortices and their consistent relation with mushroom-shaped vortices are also discussed.

This study investigates the buckling behavior of high-density polyethylene (HDPE) pressure vessel domes—including torispherical, hemispherical, and ellipsoidal heads (aspect ratios k = 1.25, 1.5, 1.75, 2.0)—under internal pressure. Thin-walled shells are highly prone to buckling, and even small geometric imperfections can greatly reduce the critical buckling pressure (often by up to ~ 50%). Using nonlinear finite element analysis (static Riks method), we evaluate several imperfection types (eigenmode-affine shape deviations, circular cutouts, single-point load dents, and flat patches) across a range of imperfection amplitudes (e.g., dent depths from 0.01 to 10 mm). A comprehensive parametric study reveals that buckling is predominantly elastic (occurring prior to significant plastic yielding in HDPE) and that imperfection sensitivity varies strongly with dome geometry: more curved shapes (hemispherical) have higher initial buckling strength but suffer larger strength reductions due to imperfections, whereas flatter shapes are less imperfection-sensitive. Notably, adopting a variable wall thickness profile (thicker at the apex and thinner toward the equator, 11.6 mm to 8.4 mm) substantially enhances buckling resistance—by roughly 20%—in the optimal elliptical domes (k = 1.25 and 1.5) compared to constant-thickness shells. These findings underscore the importance of managing geometric imperfections and demonstrate the potential of optimized thickness designs to improve the structural stability and performance of HDPE pressure vessels.

To address the gear interference problem in harmonic drive (HD) flexsplines (FS) during meshing transmission caused by tooth profile axial inclination after wave generator (WG) assembly under actual working conditions, this study focuses on composite cycloidal tooth profiles. Two methods, namely the linear modification(LM) method and the finite-element-method-based tooth profile modification (FEMM, defined as the construction of nonlinear axial modification along the tooth-width direction from the assembled finite-element displacement field), are employed, and MATLAB is used to simulate and analyze the pre- and post-modification motion trajectories. Finite element analyses were then conducted on HD models with linear method modification, finite element method modification, and unmodified profiles, comparing deformation and stress conditions during assembly and loaded operation. Due to the assembly-induced axial displacement being nonlinear along the tooth width and coupled with angular position (θ), linear approximation causes end-region mismatch, leading to secondary deformation and contact concentration. Accordingly, we adopt a FEMM that directly constructs nonlinear axial modification t(z) along the tooth width from the assembled 3D FE displacement field, thus eliminating the root causes of mismatch and contact concentration. Consequently, FEMM achieves lower peak stress and more uniform contact distribution under both assembly and loaded conditions. We also establish general criteria for operational stability and negligible secondary deformation, and propose a process-oriented FEMM workflow to provide transferable design guidelines across tooth profiles, tooth widths, and material parameters. For manufacturability, t(z) is parameterized as a three-station, low-degree spline with end weighting to ease machining and inspection. Compared with the linear method, FEMM only adds one assembled field extraction and one curve-fitting/verification step, resulting in limited additional computational cost.

Friction is a key nonlinear factor in pneumatic servo systems, and its accurate modeling and parameter identification directly affect control performance. The conventional LuGre model fails to describe smooth static-to-dynamic transitions, especially during low-speed startup. It also involves strong parameter coupling, which often causes traditional optimization algorithms to converge to local optima. To address these issues, an improved LuGre model and an intelligent identification method are proposed. A transition function is introduced to capture continuous friction behavior, and Lyapunov theory is used to prove model stability. Experiments show that the improved model increases friction peak prediction accuracy by 43–45%. For parameter identification, a hybrid evolutionary algorithm is developed by combining chaotic mapping and Gaussian convolution. The chaotic mapping enhances population diversity, while the Gaussian convolution improves local search capability. This dynamic combination balances global exploration and local exploitation. In experimental validation, the proposed algorithm maintains relative parameter identification errors below 2%, showing better convergence speed and accuracy than conventional methods.

Recent interest in urban and regional air mobility and the need to improve the aviation industry’s emissions has motivated research and development of novel propeller-driven vehicles. These vehicles range in configuration from conventional takeoff and landing designs to complex rotorcraft that transition between vertical and horizontal flight. These designs must be optimized to ensure optimal efficiency throughout their missions, leveraging the tightly coupled nature of propeller-wing interaction. In this work, we study the NASA tiltwing concept vehicle wing with varying numbers of propellers, ranging from no propellers to five propellers evenly spaced along the wing. Using aerodynamic shape optimization, we optimize the wing shapes for each propeller-wing configuration, minimizing the wing drag. These optimizations are carried out with DAFoam, a discrete adjoint implementation of OpenFOAM, embedded within OpenMDAO and the MPhys optimization framework. The optimizations show that the lowest drag configuration is a single propeller mounted at the wing tip. Increasing the number of propellers slightly increases drag compared to the single propeller configuration. However, aerodynamic shape optimization considering propeller-wing interaction yields a negligible benefit compared to aerodynamic optimization of an isolated wing that is subsequently trimmed to a desired flight condition in the presence of a propeller.

Dynamics of a rotating hub and clamped bimorph carrying a tip mass is studied in this paper. In the mathematical model of the structure the classical linear kinematics of the beam deformation is assumed. However, based on experimental results published in literature, the nonlinear formulation of the piezoceramic material constitutive equations is adopted by introducing second-order strain terms. The governing equations of the discussed system are formulated by means of the Hamilton’s principle of least action. The derived system of three coupled nonlinear integro-partial differential equations represents the electro-mechanical behaviour of the beam (transverse displacement and transducer output voltage) and the angular coordinate of the hub. The derived governing equations are reduced by virtue of the Galerkin method and solved numerically around the first resonance zone under periodic torque excitation supplied to the hub. The performed numerical simulations show the system performance for different scenarios of torque excitation, tip mass ratios and electrical boundary conditions.

Tracing paper made of cellulose fibres exhibit intriguing bending behaviour upon water absorption due to differential swelling across the paper layers, making them suitable candidates for water-induced actuators in paper-based microfluidic devices. However, the bending of tracing paper as a result of water absorption has not been successfully modelled. Here, a unified equation for water diffusion in cellulose papers is derived from Onsager’s principle to take into account both Fickian diffusion driven by water entropy and non-Fickian diffusion driven by osmotic strain energy of the fibres, against dissipation forces comprising friction of water transport and rheological losses of the fibre deformation. The results indicate that the bending dynamics of tracing papers with dense and uniform cellulose fibres is dominated by non-Fickian diffusion. This research advances the understanding of water transport and deformation in cellulose-based materials and provides a theoretical framework for their bending actuation driven by water diffusion.