Meccanica最新文献

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.

The stability analysis of a linear system with the multiple delays as parameters in given intervals is not a new but hard topic in general, for which a key step is to find out all the critical stability curves/surfaces in the parameter space. In this paper, the critical stability condition is regarded as a complex equations depending nonlinearly on the delays, and it is solved in three parts: (1) The solvability of the nonlinear equation; (2) The representation of the solutions; 3) Numerical algorithms for finding the solutions. For the solvability, a necessary and sufficient condition in terms of a delay-independent inequality with clear geometrical meaning has been derived from the critical stability condition in the form of vector equation. For the representation, the critical delays in nested form are expressed explicitly in terms of a number of hypersurfaces, all the quantities have clear geometrical meaning. Based on the nested representation, two effective algorithms are proposed for finding the solutions, and illustrated with simple examples. The main results not only generalize the previous ones for systems with two delays and three delays of the nondegenerate cases, but also add new findings for the degenerated cases which have important impact on the stability of the time-delay systems.

The numerical solution of dynamic problems often results spurious oscillations. In order to eliminate them, a damping effect must be included in the numerical scheme. However, the concrete shape of the damping characteristics has a great importance in the efficiency of oscillation reduction. In this article, a novel approach has been introduced with adjustable damping character. The damping effect is exerted as viscous damping according to the formulation of Caughey damping. Using the proposed method, a wide range of damping curves can be approximated with high accuracy. The newly developed method is mainly useful for contact-impact and wave propagation problems.

The contact region is actually an ellipse during point-contact, as stated by Hertzian contact theory. The load in the contact ellipse (CE) gradually decays rather than uniformly distributes due to the varying curvature of contact surfaces. Spur-face gear drive (SFGD) is highly valued in modern machines due to its point-contact characteristics. An improved theoretical model of time-varying mesh stiffness (TVMS) for SFGD has been constructed by coupling tooth, contact and fillet-foundation stiffness. A novel thought named deformation suppression which there is a fixed effect on the CE by the area outside the CE due to the absence of force is proposed according to the local contact characteristics of point-contact. The coupling effect between the meshing teeth pairs and the fillet-foundation stiffness are both considered. The position, size and incompleteness of the CE are determined by the movement of the meshing tracks which are derived from the explicit equation and multi-state meshing regions of SFGD and the load distribution ratio (LDR) calculated based on them. The characteristics of point contact are qualitatively verified experimentally. The results show that LDR mutations of gear switching are reduced considering incomplete CE. TVMS of point-contact considering deformation suppression is improved by an order of magnitude compared to the one of line-contact which may be the cause for the high carrying capacity of point-contact. It can be the basis to investigate the characteristics of SFGD and the point-contact further. This method is applicable to the study of point-contact in other fields.