Abstract:To address the poor meshing performance of helical cylindrical gears under variable center distances in high-speed rolling mills, this study establishes a finite element meshing model in Abaqus, considering gear meshing misalignment. Under typical operating conditions, simulation analyses of gear tooth contact are carried out to study the influence of center distance variation on key meshing performance parameters. Based on these results, comprehensive tooth surface modifications are proposed, including linear and crowning reliefs along the tooth lead direction and tip reliefs along the profile direction. A comparative analysis of gear meshing performance before and after modification is then performed. The results show that, prior to modification, the tooth surface exhibits significant load bias. Increases in center distance lead to a considerable decrease in contact ratio and contact area percentage, along with notable increases in maximum contact stress, maximum root bending stress, and the peak-to-peak transmission error-resulting in a substantial decline in overall meshing performance. Following surface optimization, load bias is significantly reduced, and improvements are observed across all key indicators, including reductions in maximum contact stress, bending stress and transmission error. The optimized gear surface exhibit enhanced adaptability to center distance variations, leading to a marked improvement in meshing performance.

Abstract:Under harsh service conditions and complex loading environments, gearbox cases in aero-engines are required to be both structurally robust and lightweight. A key design challenge is balancing weight reduction with control of bearing bore misalignment, which is an important performance metric. To address this issue, a topology optimization method for the gear transmission case is proposed, considering both mechanical and inertial loads. The approach is based on the solid isotropic material with penalization(SIMP) interpolation model. Inertial load effects on attached components are incorporated into the optimization model, which imposes constraints on case stress, critical bearing bore misalignment, and volume fraction of the optimized region. The objective is to minimize the weighted structural compliance of the case under multiple loading conditions. The proposed method achieves a 7.1% reduction in case weight and simultaneously decreasing maximum von Mises stress, total deformation, and critical bearing bore misalignment by 7.1%, 3.1% and 11.1%, respectively.

Abstract:As a key component of planetary transmission systems, the ring gear plays an important role in load sharing and influencing the system’s dynamic load factor. The inherent flexibility of the ring gear can significantly compensate for the transmission torque imbalance among planetary gears caused by manufacturing and assembly errors. This paper presents a detailed analysis of the structural characteristics of flexible ring gears. Comparative studies show that flexible ring gears exhibit superior adaptability compared to conventional ring gear, improving load sharing capacity and reducing dynamic load factors. However, this flexibility also introduces certain drawbacks, such as unbalanced loading, uneven stress distribution, increased amplitude of loaded transmission errors, and structural stress concentrations. The findings offer theoretical insights for optimizing flexible ring gear design and guiding structural improvements in planetary transmission systems.

Abstract:The control moment gyroscope(CMG) is a critical actuator in spacecraft attitude control systems. In the vacuum of space, heat generated by the CMG is primarily dissipated through thermal conduction and radiation, resulting in substantial temperature rises that may compromise system stability and reliability. Consequently, analyzing the CMG’s temperature field and maintaining its operating temperature within acceptable limits is essential. This study focuses on a 70 Nms single-frame CMG, for which a thermal simulation model is developed to investigate temperature distribution and assess the effects of rotational speed, applied torque, and bearing preload on thermal behavior. The model, validated against experimental data, achieves an average temperature prediction accuracy of 93.87%. Results reveal that temperature at various measurement points is highly sensitive to changes in rotational speed. The lower end of the rotor shaft exhibits a pronounced responsiveness to torque, while both ends of the rotor shaft are significantly influenced by bearing preload. The maximum observed temperature increase is 5.2 ℃ at the lower end of the rotor shaft, whereas the frame experiences the smallest increase at 1.72 ℃. The presented temperature field modeling approach offers valuable insights for optimizing the design of control moment gyroscopes and facilitating operational diagnostics of spacecraft systems.

Abstract:The transmission quality and fatigue life of electro-mechanical drive systems can be significantly affected by heavy loads and broadband excitation, which readily trigger torsional vibrations. To study the dynamic behavior of a transmission system composed of both single-planet and double-planet planetary gear sets within a power coupling mechanism, a lumped-parameter dynamic model was developed. This model incorporates the high-order dynamic characteristics of irregular structures and stepped shafts. The torsional modes of individual planetary gear sets and the overall transmission system were calculated and compared with simulation results. In addition, the effects of structural parameters on the natural frequencies of the system were investigated. The results show that the average relative error in natural frequencies between the proposed dynamic model and the simulation model is 1.4%, confirming the model's accuracy. Both individual planetary gear sets and the complete transmission system exhibit three categories of vibration modes: rigid body modes, independent torsional vibration modes of the planet gears, and overall torsional vibration modes. Furthermore, the full transmission system also exhibits localized modes associated with structural irregularities. Sensitivity analysis reveals that the structural parameters most affecting the system’s natural frequency, in descending order, are the outer diameter of the input shaft, meshing stiffness, outer diameter of the output shaft, effective meshing width of the planetary gear sets, output equivalent moment of inertia, and input equivalent moment of inertia. Notably, meshing stiffness significantly influences the independent torsional modes of the planetary gears. The methodology presented in this study offers a valuable reference for analyzing torsional vibrations in multistage planetary gear transmission systems.

Abstract:Under heavy-duty and long-stroke operating conditions, multi-strand wire ropes demonstrate excellent performance due to their complex spatial structure; however, this complexity also presents challenges in analyzing their stress distribution and wear behavior. In this study, a mathematical model of a 12× 37 WS multi-strand steel wire rope under both straight and bending state is established based on the Frenet frame. Using this model, the contact and bending stresses between strands are calculated under a tensile load of 6 t. Next, the lay lengths of the inner, middle and outer strands are treated as variables, and their influence on the contact stress is studied, providing guidance for optimizing the structural parameters of multi-strand wire ropes. A finite element model of the rope is then established in SolidWorks, and its mechanical performance is verified through simulation using ANSYS Workbench. Finally, based on theoretical calculations and finite element analysis, it is concluded that the outermost wires are more susceptible to breakage due to wear under constant tension. Additionally, stress levels increase in strands closer to the core. Therefore, a design recommendation is proposed: increasing the diameter of the core strands and reducing that of the outer strands can effectively reduce the breakage rate and enhance rope durability.

Abstract:Considering the structural characteristics and both internal and external excitations of offshore wind turbines, a rigid-flexible coupled multi-body dynamic model for large-scale turbines is established. A comprehensive performance evaluation method is proposed, integrating the interpretive structural modeling(ISM) technique with the analytic network process(ANP). A multi-dimensional performance evaluation framework is built, including five primary indicators and eleven secondary indicators. The ISM method is employed to analyze the interrelationships among evaluation indicators and to develop a multi-level hierarchical structure for comprehensive assessment. The ANP is then used to construct judgment matrices, supermatrices, and limit supermatrices, through which the weights of evaluation indicators are determined. Based on these results, the comprehensive performance of offshore wind turbines is quantitatively evaluated, and a comparative analysis of two turbine models is conducted. The results show that the most influential factors affecting overall performance include blade length, time-varying reliability of bearings, gear contact fatigue reliability, and unit megawatt weight. Additionally, the 5 MW wind turbine demonstrates superior comprehensive performance compared with the 6.2 MW model.

Abstract:To address the significant discrepancies between theoretical formulas and experimental results for axial piston pump efficiency under different working conditions, a machine learning-based efficiency calculation method is proposed. First, a nonlinear regression model for axial piston pump efficiency is established, and its validity is verified by significance testing. Subsequently, a predictive model based on a BP neural network is designed, trained and verified using experimental data. Finally, the prediction accuracies of both models are evaluated. The results show that, compared with the existing theoretical formulas under conditions of variable pressure, speed, and flow rate, both the nonlinear regression model and the BP neural network model significantly improve the prediction accuracy. Specifically, the average relative errors is reduced from 8.89% to 1.4% and 0.62%, respectively.

Abstract:To improve the flight stability of quadcopters in interference-prone environments, the under actuated strong coupling and nonlinear characteristics of the system were fully considered, and a dual closed-loop control system based on the adaptive super-twisting sliding mode method was proposed. First, the control system was structured into an outer loop for position control and an inner loop for attitude control, both designed using the super-twisting sliding mode control method, effectively reducing the chattering typically caused by conventional sliding mode control approach. Then, an adaptive disturbance compensation law was introduced to counteract unknown external disturbances, enabling the controller to maintain the stability of the closed-loop system with reduced control gain, thereby further minimizing chattering. Finally, the stability of the proposed control system was theoretically validated using Lyapunov stability theory, and its performance was verified through simulations conducted in MATLAB. The simulation results show that the designed control system offers strong robustness, high control accuracy, and effective trajectory tracking performance while significantly suppressing system chattering.

Abstract:The double pressure angle asymmetric gear is a type of involute gear characterized by different pressure angles on either side of the tooth surface. Its unique tooth profile design significantly impacts gear strength, transmission efficiency, and dynamic behavior. Unlike conventional symmetric gears, asymmetric gears enhance the load-bearing capacity at the tooth root and reduce transmission errors, making them particularly well-suited for applications involving complex dynamic loads and specialized transmission requirements. Based on gear meshing principles, this study investigates the precise design methodology for the tooth profile of double pressure angle asymmetric gears and their manufacturing using worm grinding wheels. The tooth profile equation for the asymmetric gear is derived, and the meshing relationship between the rack cutter and the gear is analyzed in detail, leading to the establishment of an accurate geometric model of the gear. In terms of worm grinding wheel tooth machining process, the study explores the profile design of the worm wheel, its truing method, and its application to asymmetric gear processing. VERICUT simulation experiments demonstrate that the gear profile obtained through asymmetric worm wheel grinding closely aligns with the theoretical design, confirming the feasibility of this approach. The findings provide a theoretical foundation for the design and manufacturing of asymmetric gears, and offer valuable insights for improving the efficiency and reliability of gear transmission systems.