ObjectiveAiming at the insufficient research on the dynamic characteristics of the rotor system with cracked double diaphragm coupling, the cross-coupling term of coupling stiffness was considered, and the time-varying stiffness matrix of the cracked diaphragm was derived to provide a reference for the crack fault diagnosis and safe operation of such systems.MethodsFirstly, a dynamic equation of the rotor system including the cross-coupling stiffness term was established to provide model support for the analysis of crack effects. Secondly, the critical speed of the system was solved based on the finite element method, and compared with the simulation results of Ansys software to verify the correctness of the model. Then, the dynamic responses with and without cracks were solved by the Newmark-β method to obtain speed-amplitude diagrams, frequency response-speed waterfall diagrams and axis trajectories. Finally, the influence laws of crack length (5-30 mm) and position (inner and outer diameters) on the system response were systematically analyzed.ResultsThe results show that cracks introduce 2 harmonic rotational frequency components, and the inner ring of the axis trajectory rotates about 180° when the speed crosses ω1/2 (630 r/min). When the crack length at the output end increases to 20 mm, the first-order critical speed decreases from 1 270 r/min to 1 260 r/min, and the 2 harmonic component is significantly enhanced. The influence of cracks at the outer diameter is more obvious in the initial stage, and the influence at the inner diameter dominated with the increase of crack length, verifying the effectiveness of the model and analysis method.

This paper proposes a novel modeling approach for the spiral bevel gear system that incorporates the flexibility of both gears and thin-walled hollow shafts. Shell elements are employed to model the gear and shaft structures. To more accurately represent the interaction between components, a flexible connection is introduced to replace the conventional rigid beam coupling between bearing and shell elements. The gear meshing process is simulated using distributed springs rather than a single equivalent spring, and the component mode synthesis (CMS) method is applied to enhance computational efficiency. The proposed model is validated by comparing its modal and dynamic responses with those obtained from a finite element model (FEM). Using this model, the effects of interfacial coupling methods, meshing methods, gear flexibility, and rotational effects on the system's dynamic behavior are systematically analyzed. The results demonstrate that, for large diameter-to-thickness ratios, the traditional rigid coupling method introduces significant deviations in modal analysis and resonance prediction. Conventional meshing simulation methods exhibit limitations in accurately predicting critical rotational speeds. The conventional model neglects the flexibility of the gear and the radial deformation of the hollow shaft, resulting in substantial errors in resonance prediction compared to the proposed model. These findings highlight the necessity of incorporating gear and shaft flexibility. Moreover, the gyroscopic effect (GE) is identified as the dominant contributor among rotational influences and warrants particular attention.

The thin-walled spiral bevel gear system in aviation transmission systems is particularly vulnerable to resonance failure. Conventional system dynamics modeling approaches often lack the fidelity to accurately represent the dynamic behaviors arising from such thin-walled structural configurations. To address this limitation, this paper proposes a hybrid modeling method(HMM) for the dynamic characteristic analysis of thin-walled bevel gear systems which enables the characterization of traveling wave resonance (TWR), incorporates the Goodman curve and the Smith-Watson-Topper (SWT) parameter method for resonance failure identification, and validates the accuracy of the proposed modeling approach through dynamic experiment. The findings indicate that the traveling wave characteristics are manifested solely through the the gear body node. Distinct peak responses of the forward and backward traveling waves are observed at frequencies of fm-mfs and fm + mfs, respectively. Furthermore, the amplitude of axial vibration significantly exceeds that of radial vibration.The fatigue limit stress obtained via the SWT parameter method is conservative, demonstrating higher predictive efficacy for nodal diameters resonance failures dominated by bending. Dynamic experiments identify TWR speeds and corresponding frequencies with a maximum error of 5%, while the predicted vibration stress remains within a 15% deviation margin. The proposed HMM demonstrates high accuracy, providing a reliable analytical framework for resonance testing and identification in aerospace thin-walled spiral bevel gear systems.

Rotating machinery RUL prediction is a cornerstone of industrial prognostic and health management, where Transformer-based models have emerged as state-of-the-art approaches due to their superior long-range temporal dependency modeling capabilities. However, the inherent quadratic computational complexity of global self-attention imposes prohibitive memory and latency costs for long industrial time-series, while fixed attention architectures fail to adapt to the heterogeneous feature dynamics across equipment degradation stages. Here we present a lightweight convolutional Transformer framework that integrates a degradation-aware dynamic chunked self-attention mechanism to resolve the fundamental trade-off between prediction accuracy and computational efficiency. The dynamic chunked self-attention mechanism partitions input sequences into adaptive chunks and restricts attention computation within chunks, reducing complexity from O(n2) to linear O(nk) while preserving global dependency modeling via a lightweight cross-chunk interaction module. Uniquely, the framework employs a data-driven degradation stage perception system that dynamically adjusts chunk size and attention fusion weights based on real-time signal statistics, enabling optimal resource allocation across healthy, slow degradation, rapid degradation and severe degradation phases. Extensive validation on NASA C-MAPSS and XJTU-SY bearing datasets shows that the proposed method consistently outperforms the baseline ConvFormer, achieving substantially lower RMSE and S-score while significantly reducing model parameters and computational cost. This work establishes a high-precision, resource-efficient paradigm for industrial prognostics, enabling real-time RUL prediction on resource-constrained edge devices.

Diaphragm couplings are widely used in connecting all shaft systems because of their good axial and angular misalignment compensation ability. With the development of composite material technology, many metal parts use composite materials instead. Based on ABAQUS finite element simulation software, this paper establishes a finite element model of composite diaphragm coupling and simulates the static stiffness characteristics of it and metal diaphragm coupling to compare its compensation ability; and analyzes the influence of lay-up order and lay-up angle on the compensation ability. Finally, carbon fiber-reinforced epoxy resin prepreg is used to prepare composite diaphragm test pieces by hot pressing process, and an axial tensile test is carried out to verify the accuracy of the simulation results. The results show that under the same size conditions, the axial, angular, and radial compensation ability of composite diaphragm couplings is better than that of metal diaphragm couplings; the use of 0 °, ±45 °, 90 ° multi-angle layup can significantly improve the compensation ability, but the layup order has little effect on the compensation ability of composite materials. The results of the study are of great significance for the application of composite materials in couplings.

This study presents a novel method for determining the oil film thickness on face gear tooth surfaces during transmission. The method derives the film thickness from measured oil film resistance, based on a pre-calibrated relationship between resistance and thickness for point contact pairs. The procedure consists of two sequential experiments. First, the resistance across a controllable oil film is measured to establish a fitting function relating mean resistance to film thickness. Second, this function is applied to resistance measurements from operating face gear pairs to determine the minimum oil film thickness on their tooth surfaces. The method is validated against a thermal elastohydrodynamic lubrication (TEHL) model of face gears. Results confirm that under lubricated conditions, the measured resistance accurately represents that of the oil film. The calibration yields the function R '=38.72 h + 19.41 for mean resistance R ' (M Omega) and film thickness h (mu m) within the 0.1-1 mu m range, with a maximum fitting error of 2.95 %. The oil film thickness on face gear tooth surfaces is on the order of 10-1 mu m, increasing with rotational speed and decreasing with applied torque. The maximum error between the experimentally derived minimum oil film thickness and numerical simulation results is 4.7 %. This method also demonstrates potential for measuring oil film thickness on tooth surfaces of other gear types.

Weight is one of the critical factors limiting the performance enhancement of coaxial reverse transmission systems. Under identical operating conditions, a lighter coaxial reverse transmission system exhibits better performance. The torque-splitting transmission method, which employs one gear meshing simultaneously with multiple gears to distribute the load, is a commonly used design approach for achieving lightweight designs in coaxial reverse transmission systems. However, under the condition of lower power, the torque-splitting configuration may not significantly reduce weight. In fact, the transmission system might be lighter with a non-torque-splitting structure. To determine whether a torque-splitting design is suitable under given conditions, it is essential to explore the relationship between design power and minimum weight for both torque-splitting and non-torque-splitting structures. This study focuses on the configurations of coaxial reverse transmission system based on cylindrical gears, bevel gears, and face gears. The structural parameters of the transmission system components are treated as design variables, with strength and spatial dimensions as constraints, and weight as the objective. An optimization model for coaxial reverse transmission systems is constructed and solved using the NSGA-II algorithm to obtain the corresponding relationships between design power and minimum transmission weight for the three transmission configurations, both with and without torque-splitting structures. The results indicate that the cylindrical gear configuration is suitable for torque-splitting structures. The bevel gear configuration is suitable for non-torque-splitting structures at low design power and for torque-splitting structures at high design power. And the face gear configuration is more suitable for torque-splitting structures.

This paper presents a PID-based feedback control strategy for the smart spring vibration-reduction system (SSVRS), which is intended to suppress transverse vibrations in rotating machinery caused by mass imbalance. A transfer function model of the SSVRS is first established to systematically design the controller. This model allows the distinct modulation of the system's damping, stiffness, and mass characteristics by the proportional, integral, and derivative parameters to be analyzed in detail. Based on this analysis, a novel feedback control strategy is proposed which dynamically selects and combines PID components according to real-time vibration states, achieving adaptive and effective suppression. Comprehensive simulations demonstrate the performance of the strategy: the peak vibration response under swept excitation is reduced by 66.1%, while under impulse loading, displacement offset decreases by 30% and recovery time is reduced by 70%. Experimental validation on a rotating machinery test rig confirms a 51.0% reduction in the resonance peak, thus substantiating the practical effectiveness of the proposed approach and its superior vibration suppression capability.

The composite tail drive shaft of the helicopter offers the advantages of high power density, excellent vibration damping characteristics, and superior energy absorption properties. However, it is vulnerable to ballistic impact threats under operational conditions. In this study, ballistic impact tests and finite element modeling were employed to assess and analyze the ballistic impact damage of the composite tail drive shaft. To simulate the intra-laminar high-velocity impact damage behavior of composites, a dynamic damage model was developed based on continuum damage mechanics and 3D-Hashin criterion. The cohesive zone model was used to characterize the inter-laminar damage initiation and propagation of composites. Additionally, to account for the strengthening effects caused by high strain rates, the strain rate correlation coefficients were introduced to modify the constitutive model. The bullet's residual velocity, the impact process, and the damage morphology of composites obtained from numerical simulations and impact tests demonstrate a high degree of consistency, effectively validating the reliability of the simulation model. Subsequently, using the validated simulation model, the detailed impact damage process and failure characteristics under different typical impact conditions were analyzed and compared. Delamination, matrix tensile damage, and fiber tensile damage were identified as the dominant failure modes, with edge impacts causing more severe damage than central impacts. Furthermore, the effects of offset distance and incident angle on the ballistic impact damage were investigated, revealing significant non-monotonic effects on material removal volume and the bullet's residual velocity.

Projectile impact damages could chang the mass distribution and stiffness characteristics of the tail drive shaft. However, the effect mechanisms of its effect on mass distribution and stiffness characteristics are unclear. Hence, this paper conducts research on the projectile impact damage of the helicopter tail drive shaft and its effect on mass distribution and stiffness characteristics. The finite element simulation model of the projectile impact damage is established, and the stiffness simulation model is further proposed. The residual velocity, projectile impact duration, and projectile impact damage morphology have been analysed in detail. The effect of projectile impact damage on mass loss, centre of mass displacement, stiffness reduction, stiffness asymmetry, and cross stiffness is evaluated. The projectile impact experiment bench is established. The maximum error between the experimental incidence velocity and the ideal incidence velocity is 3.4%. The projectile impact damage morphology obtained from the experiment is larger than the simulated damage, with a maximum error of 26.5%, because the armour and lead sheath expand the damage area. Experimental results effectively validated the accuracy of the finite element simulation model of the projectile impact damage. This paper provides important theoretical guidance and technical support for the helicopters' survival ability.

This paper addresses the lack of proper design methods and the current status of being in the engineering imitation stage in the research of viscoelastic dampers for supporting helicopter tail drive shafting by proposing a systematic optimal design approach. First, a dynamic model of the tail drive shaft coupled with a viscoelastic damper is created using the finite element method. The influence of different viscoelastic dampers on the vibration characteristics of the tail drive shaft during the transcritical process and at supercritical stable speeds is studied, after which a test bench is constructed for verification. Next, the impact of the material and structural parameters of the viscoelastic dampers on the vibration characteristics of the tail drive shaft is investigated, and the parameters with the most significant impact are identified. Finally, a surrogate model is created using back-propagation (BP) neural network, with the key parameters of the viscoelastic damper as the input and the maximum displacement amplitude of the tail drive shaft during the transcritical process as well as the displacement amplitude at supercritical stable speeds as the output. Furthermore, the optimal design of the viscoelastic damper is conducted based on the NSGA-II genetic algorithm to minimize the displacement amplitude of the tail drive shaft. Test results show that the optimized viscoelastic damper achieves a 29.05

Ship limiters must not only possess high impact stiffness to withstand explosive forces but also exhibit sufficient static and dynamic stiffness and damping characteristics to resist periodic ocean loads. Based on phenomenological theory and the generalized Maxwell model, this paper establishes hyperelastic and viscoelastic constitutive models for metal-rubber and nitrile rubber composite materials. After determining material parameters, a high-precision simulation model for the vertical and transverse/longitudinal directions of the limiter was developed, accounting for its complex structure, material properties, nonlinear components, and intricate contact relationships. Using this model, the influence of geometric parameters of annular rubber components and bushings on the triaxial properties of these critical limiters was analyzed. These findings provide direct theoretical support for multi-objective co-design of limiters targeting impact resistance and vibration damping performance.

Thin-walled spiral bevel gears are critical components in the accessory transmission system of aviation engines. Due to their high rotational speeds and wide operational range, these gears frequently experience nodal diameter vibrations within the operating speed range, which pose a threat to the health and functionality of the entire transmission system. Therefore, identifying dangerous vibration modes within the operating speed range and implementing appropriate vibration reduction measures are of paramount importance. Based on the results of modal analysis and transient response analysis, the forced response model is established in order to evaluate the dangerous mode. Considering the principle of friction energy dissipation, the equivalent parameters are derived to modify the forced response model, and the response amplitude after the addition of the damping ring is obtained. A high-speed spiral bevel gear dynamic stress experiment platform is constructed to validate the accuracy and effectiveness of proposed model. This study provides a theoretical foundation for identifying dangerous vibration modes and utilizing ring damper for vibration reduction of thin-walled spiral bevel gears in the field of aviation engines.

This study addresses the severe vibration in multi-span shaft systems during acceleration beyond critical speeds, which limits overall performance. It investigates the effectiveness of a smart spring support for vibration suppression and establishes a corresponding dynamic model. First, a simulation model of the smart spring support was established based on its working principle, considering different combination states of its basic and supplementary supports. The correlation between its dynamic stiffness, damping coefficient, and main influencing factors was analyzed, leading to the development of corresponding response surface models. Subsequently, a dynamic model of the multi-span shaft system integrated with the smart spring support was built using the finite element method to reveal the vibration-damping mechanism under different support states. Finally, experimental tests were conducted to study the system's vibration characteristics. The correlation between the dynamic stiffness, damping coefficient of the smart spring support and their key influencing factors was determined, and their response surface models were successfully constructed. The vibration-damping mechanism of the system under various support combinations was elucidated. Experimental results confirmed that the established dynamic model accurately reflects the actual vibration behavior of the system. The smart spring support effectively suppresses vibration in multi-span shaft systems and enhances their operational performance when crossing critical speeds. The proposed dynamic modeling method is accurate and reliable, providing an effective tool for the analysis and design of vibration control in such systems.

Magnesium alloys ZM6 and EV31A are widely utilized in the aerospace and transportation fields. However, casting processes inevitably introduce defects such as gas pores into magnesium alloy components. In this study, the influence of gas pores on the mechanical properties of ZM6 and EV31A was systematically investigated. A novel casting method was developed to control the formation of gas pores in the castings. X-ray non-destructive testing was used to detect the gas pores in cast samples, which were then graded and screened into grades 1–3 according to ASTME155. Subsequently, the effects of gas pores on the mechanical properties were evaluated through tensile and fatigue testing, combined with fracture morphology analysis using scanning electron microscopy (SEM). The tensile strength of the magnesium alloys ZM6 and EV31A decreased from 254.34 and 303.67 MPa to 172.97 and 221.98 MPa, respectively, corresponding to maximum reduction ratios of 31.99

Dynamic performances of floating splines are directly related to the safe operation of helicopter transmission systems. The dynamic behaviour analysis of floating splines should comprehensively consider the coupling effects of O-rings, locating surfaces, and misalignment. Currently, this type of spline dynamic model is not yet available. Considering the locating surface rub-impact, misalignment, vibration displacement, this study modeled the meshing state of spline teeth and reserved clearance of locating surfaces, simplified O-rings into mechanical Voigt models, and then proposed a general floating spline dynamic model. By coupling the floating spline to the spline-rotor system, the equation of motion for the spline-rotor system is obtained, whose accuracy was verified through dynamic experiments on the spline-rotor system dynamic experimental rig. Detailed effect mechanisms of locating surfaces, O-rings, misalignment, and vibration displacement on the spline-rotor system were revealed. The floating spline dynamic model proposed in this paper can accurately determine whether locating surfaces are rub-impact or not, which can provide theoretical basis for the dynamic design of floating splines and related rotor systems.

The traveling wave resonance (TWR) of thin-walled bevel gears in the aviation field continues to pose a significant threat to the overall system’s operational health. Despite extensive research on TWR, the method for determining critical dynamic stress for additional vibration reduction measures remains unclear, and a comprehensive method for predicting the damping effects of supplementary dampers is still lacking. This paper proposes a method for determining the allowable dynamic stress and establishes a single modal forced response (SMFR) model to predict the vibration damping effects of the ring damper. First, the allowable dynamic stress is determined by combining the gear material’s fatigue life curve with the Goodman curve. Using the SMFR model and experimental results, the modal damping ratio and resonance dynamic stress (RDS) at different points can be obtained. The frictional energy dissipation of the ring damper is analyzed to refine the SMFR model, considering the influence of structural parameters of the damper. Additionally, the damping effect is evaluated, accounting for wear between the damper and the gear, providing a solid foundation for the damper’s design. A series of tests, including continuous speed-up tests and speed hold-rise tests, are conducted to identify the TWR speed points and RDS within the working speed range. The dynamic stress reduction within the ring damper is then obtained through both the SMFR model and experimental data. The results show a maximum RDS reduction of over 60 %, with a dynamic stress prediction error of less than 13 %, thus confirming the effectiveness of the proposed model.

In high-load, highly contaminated, and maintenance-challenging harsh environments, rotary lip seals typically rely on grease lubrication. However, there is currently no suitable model for predicting the lifespan of grease-lubricated sealing systems. This study establishes a numerical simulation model to evaluate the lifespan of rotary lip seals under grease lubrication, considering rubber aging during storage and use, as well as wear. Based on experimental results from thermal aging and standardized wear testing, the evolution of reverse pumping rate and friction torque over aging and wear durations is analyzed. A performance evolution model is developed to predict the storage and service life of grease-lubricated lip seals, enabling leakage failure warnings and providing guidance for seal replacement cycles.

As critical transmission components in aero-engines, hard-tooth-surface involute helical cylindrical gears require precise control of surface morphology to ensure high-quality manufacturing with minimized subsurface damage. The complexity of form grinding processes arises from intricate wheel-workpiece spatial kinematics and heterogeneous local contact geometries, which challenge the prediction of chip formation mechanisms and resultant surface topography. This study presents a numerical calculation model to characterize surface morphology in helical gear form grinding. By analyzing localized contact conditions and geometric mapping relationships, the abrasive grain trajectories were mathematically formulated through a spatial helical motion model. The helical tooth surface was discretized to calculate undeformed chip thickness along the normal direction, enabling the reconstruction of three-dimensional surface morphology. Experimental validation using manufactured specimens confirmed the accuracy of the model, with further investigation revealing non-uniform surface distribution characteristics. Key findings demonstrate that surface roughness along the involute profile increases with rolling angle, exhibiting negative correlation with wheel speed, while positively correlating with feed rate and grinding depth. The proposed model provides a theoretical foundation for optimizing helical gear grinding parameters and enhancing in-service performance through surface integrity control.

This paper proposes a novel dynamic modeling method for spiral bevel gear (SBG) systems that incorporates rotating mesh excitation. In this approach, shell elements are employed to model the flexible web and hollow shaft, while a semi-analytical continuum model is developed for the equivalent rim. A rotating mesh unit is introduced to achieve dynamic coupling of the gear pair. The accuracy of the proposed model is validated through comparison with finite element (FE) analysis results. Based on this model, the vibration characteristics under traveling wave resonance (TWR), the excitation conditions of TWR, and the influence of different excitation modes on the dynamic response are systematically investigated. The results demonstrate that the proposed method accurately predicts and characterizes the TWR phenomenon, addressing the limitations of existing modeling approaches. Under TWR conditions, the dominant vibration frequencies are shown to be linear combinations of the meshing frequency and the rotational frequency. Furthermore, incorporating rotating mesh excitation is identified as the critical factor for capturing TWR characteristics; in contrast, conventional stationary mesh excitation fails to reflect the spatial migration of traveling waves along the circumference and cannot accurately predict the resonant speeds.