Meccanica最新文献

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.

The corrugation, formed by the spatial distribution of veins, is a general feature among insect wings and has drawn attention for its potential role in aerodynamic performance. In this study, a sinusoidal corrugated airfoil is proposed to enhance the design applicability of bio-inspired flapping-wing aircraft. Through fluid–structure interaction analysis, the aerodynamic characteristics of corrugated flapping airfoils with specific configurations are thoroughly studied under the Reynolds number of 900. It is found that the flexible sinusoidal corrugated airfoil outperforms the flat plate airfoil both in lift and thrust while staying lightweight and flexible, with the maximum increases of 311% and 119%, respectively. This advantage stems mainly from the positive influence of corrugations on flow field and vortex structure, coupled with a moderate reduction of the chord stiffness of airfoil. In particular, some useful rules in enhancing aerodynamics are revealed in the bionic wing design, from studying 10 sinusoidal corrugated airfoils. Lift is more sensitive to the leading-edge corrugation, and becomes optimal when the corrugation is convex with a width less than 30% of the chord length. Thrust is primarily influenced by the trailing-edge corrugation, with convex corrugation generating optimal thrust across various widths. The findings provide fundamental insights for wing section optimization in the design of bionic flapping wings.

This work presents the development of a simplified mathematical formulation for the fast evaluation of the steady state response of slender structures under parametric excitation, considering also the interaction with a still surrounding fluid. The simplified formulation is obtained from a previous solution based on the multiple scales method. However, this previous solution requires a series of cumbersome integrals to be evaluated, rendering it non-attractive for widespread use in engineering design. The objective of the simplified solution is then to render it attractive as a design aiding tool for structural engineers. Along the work, many examples are shown comparing the proposed formulation with solutions obtained with the Finite Element Method in order to address the capability of the latter to correctly predict the amplitude of response of the structure. The results presented highlight this capability, and also provide a guided approach on how the formulation can be used for parametric investigations of the structure at hand.

Soft pneu-net actuators (SPAs) are flexible structures, which are typically composed of elastomeric materials and capable of undergoing significant deformations. However, accurately characterizing and predicting their bending behavior remains challenging due to the distinct driving mechanisms of SPAs with different chamber spacing (DCS-SPAs). To address this problem, the paper presents a kinematic model for analyzing SPAs with varying spacing distances. The study focuses on the bending mechanisms of soft actuators with varying spacing distances, considering two scenarios: when the chamber sidewalls are in contact and when they are not during the bending expansion. A method for determining whether the chamber sidewalls are in contact is also introduced. The chamber-contact model is developed using finite strain membrane theory and finite hyperelastic cantilever beam theory. The non-contact chamber model is derived theoretically using the principle of virtual work. This model can predict the bending deformation of SPA with varying spacing distances in free space. The theoretical results are compared with experimental data and finite element analyses. The results indicate that the model accurately predicts the behavior of DCS-SPA. Errors for contact models range from 5 to 10%, while non-contact models range from 5 to 15%.

Direct numerical simulation is used to investigate the subcritical transition to turbulence in the counter-rotating Taylor-Couette configuration of axial aspect ratio of Γ = H/(R₂-R₁) = 4.7 and radius ratio η = R₁/R₂ = 0.9 with the end-walls attached to the inner cylinder (the narrow gap flow case, R₁, R₂ are radii of the inner and outer cylinder, H is the cylinders height). In all considered Taylor-Couette flow cases Reynolds number of the inner cylinder Re₁ = Ω₁R₁(R₂-R₁)/ν is increased along the Re₁ = Re₂ η/(Ω₂/Ω₁)  line to reach ‘featureless turbulence’ area (Ω₁, Ω₂ are angular velocities of the inner and outer cylinders, Re₂ = Ω₂R₂(R₂-R₁)/ν). Starting from this area the reduction of Re₁ is performed with the fixed Re₂ (Re₂ from − 1000 up to − 500). This leads finally to the appearance of aperiodic flow featuring interpenetrating spirals, and then to the Couette flow. For comparison, the computations are also performed for the wide gap flow case of η = 0.8 (Re₂ from − 1500 to − 500). In the (Re₂, Re₁) plane, the obtained turbulent-laminar critical line (η = 0.9) is located bellow the critical lines published in literature: bellow critical line obtained from the linear stability theory and bellow this obtained for the configuration with the end-walls attached to the outer cylinder. The results show the destabilizing influence of the end-walls attached to the inner cylinder on the flow dynamics. The radial profiles of the Reynolds stress tensor components illustrate quantitatively the changes occurring in the flow dynamics during considered processes. The Power Spectrum Density distributions are presented. The studied processes are visualized using the λ₂ method.

The post-buckling behavior of cylindrical shells was modeled using an efficient one-dimensional finite-element method. Compared to traditional three-dimensional models which require highly intricate calculations to analyze post-buckling behavior, this technique succeeded in lowering the number of degrees of freedom by 60–64% while retaining accuracy. Using higher-order Taylor expansion, the displacement function was derived. To demonstrate the ability of the model, additional geometric parameter variations were evaluated, thereby boosting its capability to simulate complex structural responses across a broader range of conditions. The nonlinear governing equations derived from the principle of virtual work were solved using the Newton–Raphson method under the arc-length constraint. Numerical results proved the effectiveness of the model, as it captured highly intricate post-buckling modes with a great extent of accuracy at a significantly reduced computational cost. The incorporation of higher-order terms and stiffener effects enables predictions to be made with even higher accuracy, especially in large deformations.

Grasping is a fundamental skill that allows humans to interact with their environment and manipulate objects effectively. Given its importance, robotics researchers have long been interested in replicating and imitating this skill in robotic systems. The field of robotic grasping has made significant progress in recent years, with a focus on designing robotic hands and control algorithms. One key aspect that can enhance the control and precision of robotic hands is the incorporation of haptic feedback. The goals of this article include implementing a control system to perform grasping functions, reproducing Cutkosky grasping classification, imitating robot hand movements from the user’s hand, and providing haptic feedback to the user’s hand. This paper presents the development and implementation of a 5-DoF robotic hand with a linkage. The robotic hand was created using 3D printing technology. To achieve control the position and force of the fingers, a Proportional-Integral-Derivative (PID) Control method is employed. Additionally, a tactile haptic interface is utilized to control the hand and provide haptic feedback to the user. In this direction, the performance of position and hybrid force/position control of the robotic hand was tested on grasping different objects. The results show that the robot hand can capture 9 Cutkosky grasping classification patterns. Furthermore, by incorporating hybrid force/position control, the robot hand was able to hold objects without damaging them and offers better grasping performance compared to position control. Finally, providing haptic feedback to the user can enhance the interaction experience.