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.

In the modeling and analysis of herringbone star gear train (HSGT), the differences in dynamic parameters and loads on both sides of the herringbone gears are usually ignored, which seriously impairs the system load-sharing performance. In this paper, the component modal synthesis method is used to solve the condensation model of the casing and the carrier. A herringbone gear meshing model with tooth surface modification and uneven meshing deformation is proposed, which accurately characterizes the dynamic load distribution of helical gears on both sides. Then, a rigid-flexible coupled dynamic model of HSGT is constructed. The effects of differentiated support stiffness on both sides and modification parameters on the offset load are analyzed, and multi-objective optimization of the dynamic performance of HSGT is carried out. A star gearbox test bench is built to test the improvement effect of differentiated modification parameters on offset load. This study provides guidance for the structural and modification design of HSGT, and improves the system load-sharing performance and vibration characteristics.

Transmission shaft systems are widely used in aviation and maritime fields, and their dynamic behaviours will be changed due to the deformed compatibility of misalignment compensation components caused by the installation platform deformation. At present, the dynamic behaviours of the transmission shaft system with deformed compatibility are still unclear. Therefore, this study focuses on the deformed compatibility of misalignment compensation components and their effect on the dynamic characteristics of the transmission shaft system. We established the parameterized mathematical model for deformed compatibility of the transmission shaft system, developed the FE (finite element) simulation models of the stiffness of the spline joint and diaphragm group, and derived the equation of motion for the transmission shaft system with deformed compatibility. We conducted a detailed evaluation of the effects of different support position deformations on the deformed compatibility angle and the stiffness changes of the spline joint and diaphragm group. Then we further analyzed the displacement response, axis trajectory, frequency spectrum, and amplitude frequency characteristics of the transmission shaft system with deformed compatibility. The experiment rig for the transmission shaft system was developed. The results of the comprehensive experiment were in excellent agreement with the theoretical calculation results, which verified the validity of the research results in this paper. The stiffness changes of the spline joint and diaphragm group, the misalignment force of diaphragm groups, gear meshing excitation force, transmission shaft imbalance excitation, and gravity are considered comprehensively in this paper. This study can provide a theoretical basis for the forward dynamic design of transmission shaft systems.

Rub-impacts and local damages of the supercritical tail drive shaft system can cause dangerous dynamic responses, thereby affecting helicopters flight safety. At present, the dynamic behaviour of this type of shaft system with rub-impacts and local damages is not known. Hence, this study is focused on modelling and experimental verification of such system. For the rub-impact caused by dry a friction damper and local damages caused by impacts, we established the dynamic model and analyzed effects of local damages. Then we proposed the local damage identification method based on vibration response analysis. The tail drive shafts with local damages were manufactured and an experimental rig to investigate the supercritical tail drive shaft systems with rub-impact and local damage was developed. Dynamics experiments of the tail drive shaft system with rub-impact and local damage verify the mathematical predictions. This paper can provide theoretical underpinning for improvement of helicopters safety.

Ballistic impact damage can cause dynamic instability of the supercritical tail drive shaft system, posing a threat to the helicopter’s safe flight. However, the effect mechanisms of ballistic impact parameters on the stability of the supercritical tail drive shaft system are unknown. Therefore, the stability characteristic equation of the supercritical tail drive shaft system with rub-impact and ballistic impact is established in this paper, which is verified by the dynamic equation through experimental verification, and then the effect laws of the rub-impact and the ballistic impact parameters on the system stability are evaluated. The research work in this paper conducts stability analysis for the first time by comprehensively considering mass loss, center of mass displacement, stiffness decrease, stiffness asymmetry, and rub-impact. Rub-impacts ensure the stable flight capability of the supercritical tail drive shaft system with hole or scratch damage, but the system becomes unstable after crack damage. The reasonable selection of rub-impact parameters is beneficial for improving the system stability, which provides a potential technical approach for the system stability control. This paper can provide new insights into the stability analysis of rotor systems at the theoretical level and assist helicopters in achieving high-reliability operation at the technical application level.

During the manufacturing of the planet carrier, the pinhole and bushing will contain eccentric errors, which will cause misalignment of the pin and unwanted system dynamic response. The phase of the eccentricity error and the form of misalignment can be adjusted by changing the assembly angle of the bushing. Appropriate misalignment can improve the system's dynamic performance. Based on the transmission principle of involute teeth, the meshing model of helical gear with misalignment is derived, where the shape of the meshing surface, the distribution of the contact line and the variable backlash along the axis under the influence of misalignment are considered. A dynamic model of herringbone star gear train (HSGT) considering different types of shaft misalignment is proposed. The validity of the model is ensured through comparison of theoretical and experimental results. Based on the influence mechanism of star gear's position error and parallelism error on dynamic characteristics, misalignment parameters that are beneficial to vibration response and load-sharing performance are found. Therefore, this study is meaningful to guide the assembly of pin bushings and the matching of misalignment errors in HSGT.

This article focuses on the efficiency optimization and friction loss control of mechanical transmission systems, and elaborates on their significance. Analyze the factors influencing the efficiency of mechanical transmission systems, such as transmission type, design and manufacturing accuracy, lubrication and cooling, etc., and explore the sources and hazards of friction losses. Efficiency optimization strategies are proposed from aspects such as design, materials, lubrication management, operation and maintenance, and friction loss control is achieved through measures such as reasonable design, material selection, surface treatment, and operation control, aiming to provide theoretical support for improving the performance of mechanical transmission systems.

Pitch error and tooth surface error are inevitable in the machining of helical gears, which will directly impact the time-varying meshing stiffness (TVMS) and transmission error (TE), thereby altering the vibration response of the gear. However, these errors are often ignored or replaced by simplified meshing errors in previous research, which cannot accurately reflect the specific effects of different errors. In this work, the distribution of various errors on the meshing surface of helical gears is fully considered, and a nonlinear contact model for helical gears with errors is established. The influence mechanisms of different errors on meshing excitation are elucidated through quasi-static meshing analysis. By incorporating the deformation coordination relationship of the meshing unit at each time sub-step, the corresponding TVMS and TE are coupled to the gear transmission in real-time, and a dynamic model influenced by tooth surface deviation is established. Finally, the time–frequency domain and dynamic load characteristics of the system under different errors are explored and the influence of mixed modification on the dynamic response of helical gears is analyzed. The findings reveal that the modification has a notable suppression effect on load fluctuation, underscoring the generality of the model for unconventional gears.

Pitch error is inevitable in gear machining, and it will aggravate the vibration and noise of the herringbone star gear train (HSGT). Although the machining accuracy is limited, the dynamic performance of the system can be further improved by appropriately combining the error phases. In this work, according to the periodicity of the pitch error and its influence on the backlash, the different backlash formed by the meshing tooth pairs during the transmission is deduced, then the meshing state and error excitation force of each tooth pair are considered, respectively. A new dynamic model of HSGT considering multi-tooth with different backlash under the influence of pitch error is established, and the reliability of the model is verified by the vibration experiment of the gearbox. Based on the proposed model, the influence mechanism of the error phase adjustment on two-sides of the herringbone center gear on the load-sharing performance is analyzed, and the optimal error phase combination of three parallel star gears is explored. When the pitch error value is constant, this research can guide the error phases combination of each herringbone gear in the HSGT, thereby reducing the vibration and improving the load-sharing performance of the system.

Wide-faced helical gears are commonly used in ships and industrial applications, where high torque transmission is required. These gears are highly sensitive to shaft misalignment, which can alter the load distribution across a gear pair, leading to increased contact stress and tooth root stress (TRS). In this study, the finite element method is employed to analyze the relationship between load distribution on the tooth face and TRS distribution at various positions under different misalignment errors (MEs). It was ultimately determined that the TRS distribution through the tooth slot center reflects the contact state of the tooth face, and through quantitative analysis, reveals the relationship between ME and the degree of load distribution unevenness, establishing a method to identify the degree of load distribution unevenness on the tooth face by the TRS distribution through the center of the tooth slot. Finally, a new strain gauge arrangement method is proposed and experimentally validated. This method effectively captures the TRS of wide-faced helical gears with misalignment and pitch errors, thereby obtaining a more accurate TRS distribution at the center of the tooth slot.

Misalignment errors (MEs) cause uneven load distribution across the faces of the gear teeth that increase contact and tooth root stress (TRS), moving the peak TRS to the edge of the face width, seriously affecting the gear system transmission performance. This paper employs the finite element method (FEM) to calculate the TRS of helical gear pairs under different MEs. The effect of MEs on the distribution of TRS is analyzed, and the characteristics of TRS distribution under different types of MEs are determined. Subsequently, a TRS testing platform is established, and the accuracy of the finite element model is validated through strain tests by introducing misalignment errors through changes in the position of journal bearings. Finally, based on the particle swarm optimization-improved backpropagation (PSO-BP) neural network, a correlation model between MEs and the distribution characteristics of TRS along the tooth width is established. Utilizing this model, it is possible to calculate the maximum TRS at different positions of the helical gear tooth root under any MEs.

When the helical gear contains mixed modification, the backlash will vary along the tooth width and tooth profile, which will lead to uneven contact of the meshing tooth pairs and meshing impact on both sides of the gear teeth, and deeply affect the dynamic characteristics of the system. In this paper, each meshing excitation with time variation is analyzed based on the function of the meshing surface, and the quantitative calculation model of the meshing force and friction torque considering the meshing state and the contact state is developed. The nonlinear dynamic model of helical gear pair with time-varying backlash caused by mixed modification is established, and the influence mechanism of each modification amount on the bifurcation characteristics of the system is analyzed. Through optimizing the multi-modification parameters, the vibration amplitude of the chaotic motion is significantly weakened, and the obtained modification parameters are also generally applicable to the vibration suppression of other high-speed motions. Furthermore, a strong advantage of this work is that although the method is proposed for modified tooth surfaces, it is also suitable for other unconventional tooth surfaces that can be described by functions.

The permanent magnet semi-direct drive cutting transmission system of shearer is taken as the research object, the non-linear dynamic model of the system is established and the Runge-Kutta method is used to solve it. The statistical processing is carried out to gear stress by rain-flow counting method, and an eight-stage random loading model is established. Combining the nonlinear fatigue damage theory, the dynamic reliability of gear is predicted through the modified stress-strength interference model. Finally, the influence of some parameters on gear reliability is further studied, which provides a reference for the reliability optimization of gear in shearer cutting unit.

Due to changes in the working temperature in a shearer transmission system, it is easy to cause the transmission gear to work abnormally. In this paper, the first gear pair in a cutting transmission system of a permanent magnet semi-direct drive shearer was taken as the research object. The coupling effect of time-varying meshing stiffness, meshing damping, bearing clearance and gear backlash under thermal deformation were fully considered. Then, a three degree of freedom nonlinear dynamic model of the gear pair was established, and a dimensionless analysis was performed. Finally, the Runge-Kutta method was used in the numerical calculations. The motion characteristics of the system were analysed through the gear’s bifurcation diagram of the temperature at different frequencies and the bifurcation diagram of the frequency at different temperatures. The meshing state was analysed at different frequencies and temperatures. For the chaotic motion generated in the system, a periodic resonance excitation was applied to control unstable motion. This study has revealed various specific effects of the temperature on the dynamic characteristics of the system. In addition, the periodic excitation method can effectively control the nonlinear motion in the system and realise the control of the chaos under the temperature effect.

Under the influence of electromagnetic excitation and terminal loads disturbance, the motor rotor shaft of the semi-direct cutting section of a shearer may produce electromechanical coupling resonance. Against this background, this work investigates the vibration properties of a motor rotor and the effect of electromechanical couplings. According to the electric machine theory and the Maxwell equation, the electromechanically coupled nonlinear torsional vibration model for the rotor system is first established under the influence of electromagnetic excitation and terminal load disturbance. Besides, its approximate solution is derived through the multi-scale method in the case of main parametric resonance, and the steady-state solution is determined through the numerical method. Moreover, the electromagnetic parameters including internal power factor angle, permanent magnet coefficient, number of pole pairs, and magnetic saturation coefficient and the mechanical parameters such as torsional stiffness of rotor and terminal load, which are responsible for the torsional vibration of rotor system, are studied, respectively. The results show that the stiffness failure and load mutation could cause chaotic motions, and a reasonable selection of electromagnetic and mechanical parameters for the permanent magnet synchronous motor (PMSM) could prevent the jumping and bifurcation from happening. This work is expected to benefit, both theoretically and practically, the design, optimization, and diagnosis of high-performance shearers that are operated in a complex working environment.

The nonlinear torsional vibration and instability oscillation caused by nonlinear damping in the shearer electromechanical coupling cutting transmission system in shearer driven by the permanent magnet synchronous motor (PMSM) is investigated in this paper. The electromechanical coupling transmission system in the shearer is equivalent to a concentrated mass model for the purpose of establishing the system dynamic model by the Lagrange–Maxwell equation. Then, the Routh–Hurwitz criterion is used to determine the torsional vibration critical point and stability region for the Hopf bifurcation for the cutting transmission system. According to the Routh–Hurwitz stability criterion, the Hopf bifurcation type and the effect of the supercritical Hopf bifurcation in the torsional vibration of the cutting transmission system are analyzed. Furthermore, based on the washout filter, the Hopf bifurcation controller is designed for suppressing the transmission system’s large vibration amplitude and unstable oscillation. In addition, the influences of the linear gain and nonlinear gain on the bifurcation point and the limit cycle amplitude are discussed. Finally, the numerical simulation results indicate the effectiveness of the designed controller. The research achievements can provide a theoretical basis for design or optimize the cutting transmission system of high-reliability shearer driven by PMSM.

在利用瞬变电磁勘探技术探测巷道前方的水体分布时, 由于井下条件复杂, 存在背景噪音, 从而无法准确探明巷道前方水体的分布区域.针对该问题, 本文通过对全空间条件下山西省同富新煤矿地层背景地质噪音进行模拟计算, 得到用于消除背景噪音的电压响应曲线, 并应用于同富新煤矿10201工作面辅助运输顺槽, 对原有的瞬变电磁探测数据进行校正, 结果证明采用校正后的瞬变电磁探测结果更加准确, 更能精确分析含水体分布, 可以用来指导煤矿的安全生产.

基于目前国有资源整合矿井水文地质条件复杂、老空积水危害大的问题,为研究上覆采空区积水对其下综采工作面安全回采工作的影响,以张双楼煤矿93604工作面为例,通过对其水文地质情况及上方7#煤层的采掘情况分析,采用井下全空间瞬变电磁法综合设计探测方案,对工作面上覆岩层及7#煤采空区赋水情况进行探测.通过三维处理及分析,得出工作面内及上方区域赋水情况,分析导致其呈现低阻的原因,据此针对性的制定放水设计及安全回采方案.结果表明,本方法能准确、有效的探测工作面覆岩水害分布情况,可为资源整合矿井采空区下工作面的安全回采提供理论及技术指导.