Meccanica最新文献

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.

Cable-Driven Parallel Robots (CDPRs) offer several advantages over traditional parallel robots. Guiding them accurately and safely requires fast Tension Distribution Algorithms (TDAs) able to work in real-time. This paper proposes the experimental validation of our previous TDA namely, the Analytic Centre. The contribution consists of comparing the simulated results with the measured tension profiles to infer the validity of the theoretical outcome. In other words, the idea is to find evidence of the predictions made in simulations. Experiments confirm simulated results supporting the theoretical advantages of the presented Analytic Centre, proving its usefulness.

Considering the significant influence of weather conditions on heavy-duty vehicle (HDV) rollovers, this study explores a rollover warning method for HDVs subjected to crosswinds. Initially, a model to calculate the relative wind speed and direction in a crosswind environment is refined, and the formula for the lateral load-transfer ratio (LTR) is derived from vehicle rollover dynamics. Subsequently, rollover threshold boundaries for LTR are determined for 8(times)4 axle HDVs, employing histograms and quartiles to refine the sensitivity of rollover indicator alarms. The risk of vehicle rollover is then quantified by integrating the weighted Mahalanobis distance(MD) with a first-order reliability method. Lastly, a probability model is utilized to analyze the impact of various random variables on the rollover outcomes. The findings affirm that the influence of side wind conditions on vehicle stability is considerable. Enhancements in vehicle rollover warning capabilities can be achieved through the application of the weighted, and the rollover risk can be effectively assessed using the probability model.

The loaded tooth contact analysis (LTCA) is a crucial tool for examining the meshing performance of gear systems. Existing LTCA methods for face-gear drives predominantly rely on finite element method (FEM), which is computationally expensive. To overcome this limitation, a semi-analytical LTCA model is proposed. This model is developed based on deformation compatibility and force equilibrium conditions. The Influence Coefficients Method is used to establish the relationship between contact force and deformation. In this approach, the global tooth deformation compliance is calculated using the Rayleigh–Ritz method, while the local contact deformation compliance is derived from the Boussinesq solution. The semi-analytical LTCA model is solved iteratively to obtain key meshing performance characteristics, such as load distribution, contact pattern, load sharing ratio, and time-varying meshing stiffness. The proposed model is compared with FEM, demonstrating excellent agreement and high computational efficiency. Additionally, parametric analyses reveal that the number of teeth on the shaper, the parabola coefficient of profile crowning, and the output torque significantly affect the meshing performance.

Modern engineering increasingly requires materials that can meet multiple functional needs. Over the past few decades, structural optimization techniques have been used to design materials by shaping and arranging small building blocks, called representative volume elements (RVEs or unit cells), in a repeating pattern at the microscale. These unit cell designs are often complex and difficult to manufacture. However, with the development of metal additive manufacturing, producing these advanced materials has become feasible. This progress has led to increased research into methods for analyzing porous materials designed using optimization. This paper focuses on analyzing low-density porous metamaterials, where the base structure is modeled using bar or Euler–Bernoulli frame elements. While pinned bar elements are commonly used, they are only reliable for problems involving stretching forces. In real-world applications, additive manufacturing creates structures where joints transmit both moments and torque, making frame elements more suitable than bar elements. To evaluate the effective properties of these materials, asymptotic homogenization techniques are often used, particularly the NIAH variant, which allows commercial software to handle the necessary calculations. Although using rod elements in the NIAH framework is straightforward, using beam elements requires some adjustments, which are explained in this paper. Unlike many other studies, this work specifically addresses how to adapt NIAH for beam elements at the microscale while ensuring that the resulting macroscopic models only include translational movements. The paper also presents a method for defining the base cell geometry to improve accuracy. Finally, the paper compares the performance of bar and frame elements in 2D and 3D lattice periodic metamaterials.

A multi-stage contact model between fractal rough surfaces based on the actual deformation of ellipsoidal asperity is proposed. Firstly, the equations for four deformation modes based on actual deformation of asperity are deduced, and the computational expressions for the contact characteristics of asperity are established. Secondly, the contact behavior of whole surface is divided into five contact stages according to the deformation stages of asperity and the contact degree of surface. Finally, the joint distribution function of base length and eccentricity is introduced, and the multi-stage contact model of surface is established by means of integration. Accordingly, the influences of different parameters (fractal dimension D, fractal roughness G and shape parameters τ, β) on the contact area and force are analyzed. The results show that the fractal dimension has a significant influence on the contact characteristics of surface; the contact area at the same force is related to the roughness of surface; The results obtained from the contact model based on ellipsoidal asperity are smaller than those obtained from the contact model based on spherical asperity. The results of proposed model are compared with the existing models and experiment data to verify the correctness and applicability of present model.

This paper studies the dynamic response of an elastic concrete plate on a fissured poroelastic rock medium to a moving load under plane strain conditions. The plate is assumed to be thin, isotropic, and linear elastic. The fissured poroelastic rock medium is isotropic, fully saturated with water, and characterized by two types of porosity, one due to fissures separating it into blocks and one due to the pores in those blocks. The load is assumed to be uniformly distributed over a finite length and moves with constant speed. The problem, which describes a case of rigid pavement, is solved analytically/numerically by the complex Fourier series method. Thus, the load and the plate and rock medium displacements are expanded in complex Fourier series with respect to the horizontal coordinate (motion direction) and the time. Upon substitution of these expansions into the equations of motion for the plate and the half-plane rock medium, the corresponding partial differential equations are reduced to algebraic and ordinary differential equations, respectively, which can be easily solved. The resulting response solution is verified by comparison with existing solutions for special cases. Parametric studies are finally conducted for assessing the effects of problem parameters like porosities, permeabilities, thickness of the elastic plate, and vehicle load speed on the response of the plate.