Meccanica最新文献

We present analytical and numerical results on integrability and transition to chaotic motion for a generalized Ziegler pendulum, a double pendulum subject to an angular elastic potential and a follower force. Several variants of the original dynamical system, including the presence of gravity and friction, are considered, in order to analyze whether the integrable cases are preserved or not in presence of further external forces, both potential and non-potential. Particular attention is devoted to the presence of dissipative forces, that are analyzed in two different formulations. Furthermore, a study of the discrete version is performed. The analysis of periodic points, that is presented up to period 3, suggests that the discrete map associated to the dynamical system has not dense sets of periodic points, so that the map would not be chaotic in the sense of Devaney for a choice of the parameters that corresponds to a general case of chaotic motion for the original system.

Reducing relative sliding between tooth surfaces contributes to the improved reliability of gear operation. This paper presents an active design of an internal gear drive with low sliding ratio (LSR). In order to achieve a lower sliding ratio, the relationship between the sliding ratio and the contact path is established. The tooth profiles of the internal gear are determined based on a given contact path using a cubic function. Tooth interference issues arising during gear meshing and machining are systematically analyzed. Additionally, tooth profile features are illustrated through an example. The operating performance, including tooth strength and lubrication characteristics, is evaluated through a comparison with that of the traditional involute gear drive. Results indicate that the novel internal gear transmission exhibits excellent resistance to wear, bending, and lubrication performance. Finally, the rationality of the tooth profile design is validated through physical assembly.

This paper presents a numerical investigation of the film cooling performance of a new hybrid film cooling geometry. The new hybrid concept was created to enhance the film cooling performance of gas turbine blade. The scheme consists of a converging slot hole or console with a cylindrical hole featuring a branching cylindrical hole. An analysis of the cooling performance of the advanced hybrid film cooling model was carried out across blowing ratios of (B = 0.37, 0.60, and 0.87) at a density ratio of DR=1. A numerical simulation was performed using open-source CFD software OpenFOAM. The validity of the current numerical model was evaluated for the console case, revealing excellent agreement between the numerical results and the experimental data. In this study, two distinct forms, F1 and F2, are represented with the same position variation; the SST K − ({omega }) turbulence model was selected as the turbulence model for the analysis. The results show that the hybrid concepts, including auxiliary jets, enhance film cooling efficiency by effectively dispersing coolant across downstream surfaces and reducing the impact of the counter-rotating vortex pair by improving mixing with the mainstream flow. Furthermore, the supplementary jet ensures the primary coolant jet moves beside the test surface, which results in higher effectiveness, especially at high blowing ratios.

To improve the dynamic performances of nonlinear magnetorheological (MR) semi-active suspension, a hybrid damping control (HDC) based on Kalman observer of nonlinear suspension system is proposed. Firstly, the mechanical test of MR damper is carried out, and the mechanical model of MR damper and suspension system model are established. On this basis, a feedback linearization Kalman observer (FLKO) based on differential geometry theory is designed. Then, the working modes of the MR suspension system are divided according to different driving roads. HDC is proposed to achieve the dynamic control objectives under different working modes, and genetic algorithm is used to optimize the coefficients of skyhook, groundhook and distribution. The simulation results show that the estimation accuracy of FLKO is more than 85%. Compared with passive suspension, the tire dynamic load is optimized by 15.53% on A class road, improving the road holding. On B class road, the body acceleration, suspension deflection and tire dynamic load are optimized by 2.22%, 23.76% and 1.47% respectively, optimizing the dynamic performances comprehensively. On C class road, the body acceleration is optimized by 17.69%, improving the ride comfort effectively. Finally, a test bench is built, and the test results are basically consistent with simulation, which verifies the effectiveness of the designed FLKO and HDC.

Spline couplings are commonly used to transfer rotary motion in rotating structures, such as low-pressure rotor systems in dual-rotor aero-engines. The misalignment introduced by spline coupling assembly error will seriously affect the safe operation of rotor system. In this paper, a method is proposed to calculate the spline meshing stiffness under arbitrary misalignment conditions, considering the static and dynamic misalignment. The accurate meshing parameters of spline couplings under parallel and angular misalignments were determined by computing the effective meshing region of misaligned spline teeth. Furthermore, a time-varying stiffness-damping spline model is established, considering friction on the spline teeth surfaces, to derive the dynamic model of the spline-rotor system under arbitrary misalignment conditions. The Newmark-β method, in conjunction with the Newton–Raphson method, was used to solve the dynamic response of the system, and the correctness of the model was verified by experiments. Finally, the variation of spline meshing stiffness and force caused by static and dynamic misalignment is described, and the effects of parallel and angular misalignment, as well as the phase difference in unbalance, on the vibration response and self-excited vibrations are also investigated.

The paper introduces a novel three-dimensional numerical model considering hardness gradient and residual stress to predict carburized gears’ total bending fatigue life. The crack initiation life was forecasted by the strain life method, considering hardness gradient and residual stress. Linear elastic stresses and strains in the tooth root fillet were corrected by Neuber’s rule for elastic–plastic material behavior. The tooth root area of the spur gear is segmented into layers using the thin slice method, and the fatigue properties of each layer are determined using the multilayer method. The crack propagation life was predicted by the extended finite element method (XFEM), considering hardness gradient and residual stress. Fracture surface analysis with electron microscopy determines the exact location where cracks initiate. The high-speed camera records the path and life of crack propagation. Single-tooth bending fatigue life (STBF) tests are conducted to validate the proposed model. The predicted fatigue lifetimes, failure locations, and crack propagation paths agree well with the experimental results.

High-speed gear reducers are highly sensitive to vibration and noise, especially in new-energy vehicles. Hence, the current nonlinear dynamics model of gears does not fully consider the influence of tooth microstructure on backlash and friction. This study establishes a nonlinear friction dynamics model for a high-speed helical gear system, which includes time-varying dynamic backlash and friction coefficient based on the fractal characterization of tooth roughness. Furthermore, it investigates the influence of tooth surface roughness on the dynamic performance by taking into account the interaction between friction and vibration under Elastohydrodynamic Lubrication (EHL). Theoretical simulation results show that an increase in tooth roughness leads to an overall deterioration in the dynamic performance of the helical gear system; however, local optimization can also be observed. In the case of a dynamic tooth backlash, the amplitude of displacement oscillations increases, and the number of frequencies increases; in terms of frictional coefficient, the amplitude of displacement oscillations increases, but the change is small compared with that of the dynamic tooth backlash, and the number of frequencies in the spectrum decreases. The results indicate that the proposed model can provide a reference for controlling the tooth roughness of high-speed gears.