Meccanica最新文献

This study proposes a method for the design of spatial mapping profile for harmonic drives based on scaling factors, and provides an in-depth analysis of their transmission characteristics. Firstly, the tooth profile mapping equations for harmonic drive are established by using the rack approximation method and the fundamental theorem of meshing. Then, scaling factors are introduced, and planar profiles of harmonic drives with varying scaling factors are derived through the application of conjugate theory. This study investigates the effect of scaling factors on the conjugate interval. Especially, loss areas for the quadratic conjugation and two-point conjugation are analyzed. The loss areas for the quadratic conjugation and two-point conjugation increase as the scaling factor increases. According to the nonlinear deformation of the FS teeth in the axial direction, a spatial mapping profile of the harmonic drive is developed, and a finite element method is employed to analyze the Von-Mises stress and contact stress of the HD. A reasonable scaling factor is beneficial to increase the meshing interval and improve the stress distribution of the assembly stress, tooth root bending stress, and tooth surface contact stress of the harmonic drive.

This study addresses the challenge of controlling a quadrotor in the presence of external disturbances by introducing a novel optimal interval type-2 fuzzy global sliding mode controller. The proposed controller is a hybrid approach that combines the benefits of Interval Type-2 Fuzzy Logic Control (IT2FLC) and Global Sliding-Mode Control (GSMC). Initially, GSMC is utilized to guarantee that the quadrotor system's initial states begin on the sliding mode surface, thereby enhancing overall robustness. To address the chattering phenomenon commonly observed in conventional SMC approaches, the integration of IT2FLC into the control system is employed to minimize high-frequency switching components. The proposed controller utilizes the Bat Optimization Algorithm (BOA) to achieve optimum performance by simultaneously optimizing the parameters of the controller and the input Membership Functions (MFs) through BOA. The simulation results clearly demonstrate that the proposed controller surpasses a traditional PID controller in terms of tracking performance, especially when facing disturbances.

Columns and rod systems are quite common in engineering practice. For the correct design of such structures, it is necessary to have analytical expressions for critical forces for all possible load cases. The article is devoted to a theoretical study on determining critical forces in compressed-bent rod systems in the elastic stage and checking the numerical calculation methods of such rods using the displacement method. The study examines the issues of stability of rod systems, studies the effect of the rods’ own weight, final values of possible displacements of system nodes, and the direction of distributed load on the values of compressive critical forces. A differential equation for the bending of a rod is obtained taking into account the eccentricity of the application of the axial force. As a result of theoretical studies, analytical expressions were obtained for calculating the critical axial compressive force acting on a vertical rod system. The article derives and presents analytical dependencies that determine the critical forces for a rod system resting on hinged-fixed and elastically compliant supports in a transverse direction only and without semi-rigid connections in the rotational direction. The correctness of the obtained expressions is verified based on a comparison with the results of the static method for determining the critical load. The obtained expressions for determining critical forces can be used by designers when assessing the buckling resistance of rod systems.

Planet pin position error is a critical geometric quality characteristic that significantly influences key attributes of planetary systems, including power density, load sharing, and operational reliability. Its tolerance parameters are among the key design factors determining the fatigue reliability of planetary systems in large wind turbines. In order to analyze the mechanism of these errors on the fatigue reliability of wind turbine planetary systems, a fatigue reliability evaluation model is established based on an extension of the computational logic of the full probability formula. It considers the failure correlation among the gear teeth and the temporal sequencing of the gear teeth meshing. Starting from balancing the contradiction between evaluation accuracy and evaluation costs, a hybrid finite element simulation including planet pin position errors and planet carrier flexibility, and an accelerated lifetime test for tooth probabilistic lifetime transformation are employed to respectively provide load and strength input variables for the reliability model. In particular, the Monte Carlo method is incorporated in the simulation and analysis process to take into account the randomness of planet pin position errors and the coupling influence mechanism between the error individuals. Finally, a mapping relationship from the planet pin position tolerance to the fatigue reliability of the planetary system is established. Depending on the specific reliability requirements, the upper limit of the planet pin positional tolerance zone can be determined at an early stage of the design in order to achieve as much as possible a balance between the service reliability of the planetary system and the manufacturing economy.

This paper considers the frictional contact between an inflated thin-walled long hyperelastic tube and a thin rigid plate with a hole. The tube is threaded through the hole. The radius of the hole is smaller than the radius of the inflated tube. A force is applied to one end of the tube. Up to a certain value of the longitudinal force, the tube will be in equilibrium due to frictional forces. The paper studies the dependence of the ultimate force on the size of the hole, the friction coefficient and the internal pressure.

The bilateral teleoperation technique has garnered significant attention due to its effectiveness in performing tasks in surgical applications and simulators. The Novint Falcon robot combines affordability, haptic feedback, and versatility, making it a valuable tool for advancing haptic and teleoperation technologies. It can be used as a training simulator for otolaryngology surgery, a field that involves both hard and soft tissues, making it particularly challenging. A proper controller is essential to ensure the stability of such systems. This research proposes a robust adaptive sliding mode control approach for a one-degree-of-freedom Falcon robot. The strategy adjusts the impedance to a predefined nonlinear impedance model that approximates the properties of sino-nasal tissue. The stability of the proposed control method and the convergence of the tracking error are proven using the Lyapunov stability theorem. Simulation and experimental studies demonstrate the effectiveness of the proposed controller. Additionally, a comparison with an adaptive sliding mode controller without a robust term highlights that while both controllers achieve trajectory tracking, the proposed controller achieves significantly lower tracking errors. This error for robust adaptive control falls below 0.005 after a few seconds. However, the tracking error for adaptive control without robustness is notably larger.

In this paper we consider a saturated mixture for soils consisting of a dilatant granular medium with rigid rotating grains immersed in an incompressible fluid, under the hypothesis that the mass exchange between the phases of the mixture is non-zero, therefore it can be seen as a peculiar case of Giovine (J Solids Struct 187:3–22, 2020). For the granular constituent, we introduce two microstructural fields: the micro-spin vector and the volume fraction; the first describes the rotation of rigid grains, while the scalar models the fluctuations of voids due to the dilatancy of the granular material. For the fluid constituent, the microstructure is only scalar, represented by its volume fraction. The vectorial microstructure seems to be a novelty in these media. We choose as the system of constitutive equations the one suggested in as reported by Giovine (On adsorption and diffusion in microstructured porous media, Springer, Dordrecht, 2005), which includes diffusion and absorption phenomena. Finally, in the system of balance equations, there are four interchange terms concerning: mass, linear and micro-linear momenta and micro-angular momentum; moreover, the rules underlying the formulation of the balance laws for the mixture satisfy the three metaphysical principles of Truesdell (Rational Thermodynamics, McGraw-Hill, New York, 1969). Subsequently, we study the plane harmonic waves in the saturated granular-fluid mixture as non-trivial solutions of the system of linear differential equations, assuming that the volume microstructural wave propagates in the mixture, we obtain three longitudinal waves and three transverse waves, in both cases, two waves are mixed and one is purely microscopic: this last wave does not appear in previous model.

This study investigates the deformation and mechanical behavior of metallic hollow spheres (MHSs) under quasi-static compression. Quasi-static axial compression simulations on aluminum alloy MHSs of varying diameters and wall thicknesses were conducted using ANSYS. The effects of diameter, wall thickness, and density on deformation modes, mechanical properties, and energy absorption characteristics were analyzed. The results indicate that MHSs experience three deformation stages during quasi-static compression, exhibiting both symmetric and asymmetric indentation modes. With a constant thickness-to-diameter ratio (T/D), MHSs demonstrate consistent deformation patterns and compressive strength, with load-bearing capacity influenced by both diameter and wall thickness. For a fixed diameter, wall thickness becomes the key factor determining compressive strength. Increasing wall thickness significantly enhances shell stiffness and load-bearing capacity, while reducing the risk of sidewall instability. Notably, at a T/D value of 0.03, MHSs display enhanced structural strength due to distinctive structural transformations during compression. Additionally, at a given density, MHSs with larger diameters exhibit higher load-bearing capacity, although this improvement tends to level off when density exceeds a certain threshold. The study also reveals that the initial peak load, average compression load, and energy absorption capacity of MHSs are influenced by both diameter and wall thickness, whereas energy absorption efficiency is primarily determined by the interaction between these parameters. This research provides essential theoretical support for the design and performance optimization of MHSs and offers valuable insights for applications in energy-absorbing structural design.

In nuclear physics experiments, a typical engineering issue is the dissipation of heat from very small surfaces and volumes on which a significant amount of energy is thermally deposited by a small-sized beam of particles. This article describes a finite element method simulation methodology for heat dissipation and the subsequent design and development of the holder of a lithium-based target up to its construction. The target described in the paper is used to study the (^7)Li(p,e(^+)e(^{-}))(^8)Be process with the proton Cockcroft–Walton accelerator of the MEG experiment at the Paul Scherrer Institut (Villigen, Switzerland). The material of the target region crossed by the emitted e(^+)e(^{-}) has to be reduced as much as possible to minimally perturb the measurement of their momenta, and a thin target is required. In order to ensure the dissipation of the thermal load on the target, an in-depth thermomechanical and structural simulation was realized using ANSYS. This allowed to verify the efficiency of the dissipation mechanisms, the maximum temperatures reached, and the thermal stress on all parts to ensure a sufficiently long lifetime of the target for the physics process measurement. To realize an optimized geometry ensuring continuity of the thermal flux—essential to dissipate the incoming power—the additive manufacturing was deemed necessary. The target support has been realized in pure copper, exploiting its excellent conductive properties and the cutting-edge additive manufacturing technologies, recently developed to overcome the inherent difficulties of Laser Powder Bed Fusion (L-PBF) technology to this material.