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This study aims to research the time-varying mesh stiffness (TVMS) model for orthogonal face gear drives considering elastohydrodynamic lubrication (EHL) and provide a theoretical basis for understanding the dynamic characteristics of face gear drives.

Considering EHL, a novel model is proposed to calculate the TVMS of orthogonal face gears using the deformation compatibility condition. First, the tooth surface equations of orthogonal face gears are derived according to the tooth surface generation principle. Then, the oil film thickness on the tooth surface of face gears is obtained by solving the governing equations of EHL. Furthermore, the proposed model is used to calculate the TVMS of face gears along the mesh cycle and is verified. Finally, the effects of module, tooth number of shaper cutter and pressure angle on mesh stiffness are analyzed.

The results indicate that when the contact ratio is greater than 1 and less than or equal to 2, the TVMS of face gears exhibits a phenomenon of double-single tooth alternating meshing where sudden changes occur. As the module increases, the overall mesh stiffness of face gears increases, and the magnitude of the sudden change at the moment of single-double tooth alternating meshing gradually increases. As the tooth number of shaper cutter and pressure angle increase, so does the TVMS of face gears. When the effect of oil film is considered, the calculated TVMS of face gears slightly increases overall and the increase in average oil film thickness leads to a rise in the TVMS. This study provides a theoretical basis for understanding the dynamic characteristics of face gear drives.

This study’s originality and value lie in its comprehensive approach, which includes conducting analysis based on loaded tooth contact, considering the influence of elastohydrodynamic lubrication, proposing a novel analytical–finite–element model, calculating TVMS of face gears, verifying the proposed model and analyzing the effects of typical structural parameters and oil film thickness.

The purpose of this paper is to use a combination of numerical simulation and experiment to evaluate the performance of laser surface texturing (LST) in the field of gear lubrication, and to more accurately predict the lubrication characteristics of different surfaces.

The method used in this paper is developed on the basis of the deterministic solution of the three-dimensional (3D) mixed elasto-hydrodynamic lubrication (EHL) model and the model parameters are corrected by friction test. The film pressure, film thickness and friction coefficient of different micro-textured tooth surfaces are predicted on the basis of accurate 3D mixed EHL models.

The results demonstrate that the micro-texture structure of the tooth surface can increase the local film thickness and enhance the lubricating performance of the tooth surface without drastically reducing the contact fatigue life. The stress distribution and friction characteristics of the tooth surface can be optimized by adjusting the micro-texture arrangement and the size of the micro-textures.

A new evaluation method using a 3D hybrid EHL model and friction test to predict the lubrication characteristics of LST is proposed, which can effectively improve the processing economy and save time.

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-11-2020-0423

During the operation of a wet clutch, there are fluctuations in speed and torque, which have an impact on the stability of the clutch and the strength of the friction plate and the spline pair of the dual steel plate. The purpose of this study is to investigate the vibration characteristics of the wet clutch and the dynamic load characteristics of the spline pairs.

The spline pair model is established by the piecewise linear function method, and on this basis, dynamic equations considering the spline pair of dual steel plates and friction plates are established. Considering that the wet clutch has multiple spline pairs, an equivalent model of the number of teeth and the equivalent model of the tooth width were proposed, and the Runge-Kutta numerical method was used for the wet clutch for these two models.

The research results show that the equal tooth number model has greater meshing stiffness and smaller fluctuation than the constant tooth width model, which shows that increasing the meshing stiffness of the system is beneficial to reduce system fluctuation and improve system stability.

The friction plate has the system that multiple splines are independent of each other, which is relatively complicated. Therefore, an equivalent calculation is performed on multiple pairs of steel plates (friction plates) to simplify the calculation of the spline pairs.

This paper provides a theoretical basis for further dynamic characteristics analysis of wet clutch and reducing fluctuation of speed and torque.

Dynamic equation considering the spline pair of the dual steel plates and the friction plates is established to study the vibration characteristics of the wet clutch and the dynamic load characteristics of the spline pair, etc.

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-03-2023-0078/

This paper aims to propose a numerical method to calculate the convective heat transfer coefficient of spiral bevel gears under the condition of splash lubrication and to reveal the lubrication and temperature characteristics between the gears and the oil-air two-phase flow.

Based on computational fluid dynamics, the multiple reference frames (MRF) method was used to simulate the rotational characteristics of gears and the motions of their surrounding fluid. The lubrication and temperature characteristics of gears were studied by combining the MRF method with the volume of the fluid multiphase flow model.

The convective heat transfer coefficient can be improved by increasing the rotational speed and the oil immersion depth. Moreover, the temperature of the tooth surface having a large convective heat transfer coefficient is also found to be low. A large convection heat transfer coefficient could lead to a good cooling effect.

This method can be used to obtain the convective heat transfer coefficient values at different meshing positions, different radii and different tooth surface positions. It also can provide research methods for improving the cooling effect of gears under the condition of splash lubrication.

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-07-2020-0233/

The supercritical design of tail rotor drive shaft has attracted more attention in helicopter design due to its high power–weight ratio and low maintenance cost. However, there exists excessive vibration when the shaft passes through the critical frequency. Dry friction damper is the equipment applied to the drive shaft to suppress the excessive vibration. In order to figure out the damping mechanism of the dry friction damper and improve the damping efficiency, the dynamic model of the shaft/damper system is established based on the Jeffcott rotor model.

The typical frequency response of the system is studied through bifurcation diagrams, amplitude-frequency characteristic curves and waterfall frequency response spectrum. The typical transient responses under frequency sweeps are also obtained.

The results show that the response of the system changes from periodic no-rub motion to quasi-periodic rub-impact motion, and then to synchronous full annular rub-impact, and finally, back to periodic no-rub motion. The slip of the rub-impact ring improves the stability of the system. Besides, the effects of the system parameters including critical dry friction force, rub-impact friction coefficient, initial clearance on the stability and the vibration damping capacity are studied. It is observed that the stability changes significantly varying the three parameters respectively. The vibration damping capacity is mainly affected by the critical dry friction force and the initial clearance.

Presented results provide guidance for the design of the dry friction damper.

This paper aims to study the characteristics and evolution rules of tagging knowledge network for users with different activity levels in question-and-answer (Q&A) community represented by Zhihu.

A random sample of issue tag data generated by topics in the Zhihu network environment is selected. By defining user quality and selecting the top 20% and bottom 20% of users to focus on, i.e. top users and bot users, the authors apply time slicing for both types of data to construct label knowledge networks, use Q-Q diagrams and ARIMA models to analyze network indicators and introduce the theory and methods of network motif.

This study shows that when the power index of degree distribution is less than or equal to 3.1, the ARIMA model with rank index of label network has a higher fitting degree. With the development of the community, the correlation between tags in the tagging knowledge network is very weak.

It is not comprehensive and sufficient to classify users only according to their activity levels. And traditional statistical analysis is not applicable to large data sets. In the follow-up work, the authors will further explore the characteristics of the network at a larger scale and longer timescale and consider adding more node features, including some edge features. Then, users are statistically classified according to the attributes of nodes and edges to construct complex networks, and algorithms such as machine learning and deep learning are used to calculate large-scale data sets to deeply study the evolution of knowledge networks.

This paper uses the real data of the Zhihu community to divide users according to user activity and combines the theoretical methods of statistical testing, time series and network motifs to carry out the time series evolution of the knowledge network of the Q&A community. And these research methods provide other network problems with some new ideas. Research has found that user activity has a certain impact on the evolution of the tagging network. The tagging network followed by users with high activity level tends to be stable, and the tagging network followed by users with low activity level gradually fluctuates.

Research has found that user activity has a certain impact on the evolution of the tagging network. The tagging network followed by users with high activity level tends to be stable, and the tagging network followed by users with low activity level gradually fluctuates. For the community, understanding the formation mechanism of its network structure and key nodes in the network is conducive to improving the knowledge system of the content, finding user behavior preferences and improving user experience. Future research work will focus on identifying outbreak points from a large number of topics, predicting topical trends and conducting timely public opinion guidance and control.

In terms of data selection, the user quality is defined; the Zhihu tags are divided into two categories for time slicing; and network indicators and network motifs are compared and analyzed. In addition, statistical tests, time series analysis and network modality theory are used to analyze the tags.