Meccanica最新文献

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.

This study investigates the nonlinear buckling behavior of ellipsoidal and torispherical pressure vessel heads subjected to internal pressure, employing advanced finite element analysis to evaluate structural stability under realistic loading conditions. A key novelty of the work lies in the comprehensive, parametric investigation of both global and local geometric imperfections, including eigenmode-affine shapes, localized dimples, and circular cutouts. These imperfections are systematically varied in terms of type, amplitude, location, and distribution across multiple geometries. The simulations utilize geometrically nonlinear analysis with the arc-length (Riks) method, enabling accurate tracking of the post-buckling response and capturing sudden instability phenomena. A particular emphasis is placed on the sensitivity of buckling strength to imperfection characteristics. The results demonstrate that local dimples significantly reduce the buckling capacity, especially when positioned near the apex of the head. In contrast, imperfections located in less critical zones exert a more moderate influence. Additionally, the introduction of variable wall thickness, strategically increasing local thickness in high-stress regions, proves to be an effective design strategy for enhancing buckling resistance without excessive weight penalties. The study also reveals distinct imperfection sensitivity trends between ellipsoidal and torispherical heads, highlighting the importance of geometry-specific optimization. These findings provide valuable insights for the improved design, fabrication, and inspection of thin-walled pressure components in critical engineering applications.

This study addresses the aerodynamic instability of vehicles on embankments under crosswind conditions by employing photovoltaic (PV) panels as flow control devices. Traditional wind barriers passively block airflow, which is prone to structural fatigue and serves only a single function. In contrast, the proposed PV panel system not only generates renewable energy but also regulates and redirects airflow, mitigating adverse aerodynamic loads on vehicles. A systematic investigation was conducted to analyze the effects of PV’s tilt angle, height, installation distance, and lane position on vehicle aerodynamic loads through wind tunnel experiments and computational fluid dynamics methods. Parametric analysis reveals the critical relationship between flow control mechanism of PV panels and vehicle aerodynamic performance. The results show that PV panels inhibit airflow acceleration on the embankment slope by regulating and diffusing incoming wind, thereby reducing the pressure on the vehicle surface and enhancing the vehicle’s aerodynamic stability.

This paper investigates statics and natural vibration of linear elastic cubic lattices, together with their continuum approximations. The lattice endowed with central and angular interactions, referred to as Gazis et al.’s, is considered first: since the stiffness of each lattice phase must be positive, the equivalent macroscopic Poisson’s ratio must be lower than its central limit 1/4. A volumetric interaction based on a volume-dependent internal pressure is introduced as an additional non-central interaction for a complete calibration of the equivalent Poisson’s ratio up to its incompressibility limit 1/2. This volumetric interaction can also be classified as Fuchs-type, providing a potential energy that depends on the volume variation of each cell. The mixed differential-difference equations of the associated lattice derive from Hamilton’s principle applied to the discrete energies. The algebraic properties of the stiffness matrix of the discrete cell provide information on the positive definiteness of the potential energy, for each lattice with central and non-central interactions. The convergence of this finite lattice towards a linear elastic continuous right parallelepiped is shown in several static loading schemes. The discrete Lamé problem for the free vibration of this parallelepiped is solved for all the considered lattices. It is concluded that discrete and continuum elasticity can be connected by this cubic lattice within a complete range of elasticity parameters.