Search Results (136)

This paper presents an electromechanical coupling model integrating an equivalent magnetic network (EMN) model of a dual three-phase permanent magnet synchronous motor (DTP-PMSM) with the dynamic model of a helical planetary gear transmission system. Using this model, this study analyzes the dynamic characteristics of an electric drive system, specifically motor phase current, electromagnetic torque, and gear meshing force, under self-fault-tolerant control strategies. Simulation and experimental results demonstrate that the self-fault-tolerant control strategy enables rapid fault tolerance during open-phase faults, significantly reducing system fault recovery time. Meanwhile, compared to the open-phase faults conditions, the self-fault-tolerant control effectively suppresses most harmonic components within the system; only the second harmonic amplitude of the electromagnetic torque exhibited an increase. This harmonic disturbance propagates to the gear system through electromechanical coupling, synchronously amplifying the second harmonic amplitude in the gear system’s vibration response. This study demonstrates that self-fault-tolerant control strategies significantly enhance the dynamic response performance of the electric drive system under open-phase faults conditions. Furthermore, this study also investigates the electromechanical coupling mechanism through which harmonics generated by this strategy affect the gear system’s dynamic response, providing theoretical support for co-optimization electromechanical coupling design and fault-tolerant control in high-reliability electric drive transmission systems. Full article

Helical idler gear transmission systems can adapt to high-speed, heavy-load working environments and are thus widely used in aerospace, shipbuilding, and other heavy industry sectors. Root crack is one of the common fault types. Prior studies generally only considered cracks at a single working flank, lacking comparative analysis between the crack at the working flank and the non-working flank. This paper examines the dynamic response of helical idler gears with root cracks at different working flanks, comparing dynamic response differences between working and non-working flank cracks. First, a comprehensive dynamics model of the helical idler gear system is established. Second, the influence of root crack location (the working flank or the non-working flank) on time-varying meshing stiffness is considered based on potential energy method, and a flexible model is established by finite element method for the faulty gear. Finally, solution results of the rigid-flexible coupling dynamics model are analyzed. The dynamic response signal characteristics of root cracks at the working flank and the non-working flank are analyzed in time domain, frequency domain and time frequency domain, respectively. Corresponding experiments are designed based on the FZG experimental platform, and the experimental results are in good agreement with the simulation results, which verified the accuracy of the model. Full article

Topological photonic crystals have garnered significant attention due to their fascinating topological edge states. These states are robust against sharp bends and defects and exhibit the novel property of unidirectional transmission. In this study, we analyze the topological edge states of gyromagnetic topological photonic crystals in analogy with the quantum Hall effect. Through expanding and shrinking six dielectric cylinders, the optical quantum spin Hall effect is achieved. And helical edge states with pseudo-spin are demonstrated. Owing to the novel topological properties of these edge states, robust waveguides are proposed. Furthermore, integrating these two distinct types of topological states, a novel circulator with topological characteristics is designed. These topologically protected photonic devices will be beneficial for developing integrated circuits. Full article

The transmission accuracy and meshing performance of the gearbox is determined by the internal helical gears pair. Thermal deformation of internal helical gears pair is derived from sliding friction between the contacting teeth surface, resulting in shock, vibration, and misalignments. The purpose of this paper is to compare the influence of a modified gear and an unmodified gear on the temperature field and transmission characteristics of a planetary gear system under the same working conditions. This study presents an innovative temperature field model for gear pairs utilizing Surf152 elements, integrating Hertzian contact theory, tribological principles, and finite element analysis. For the first time, we quantitatively demonstrate the enhancement of thermo-mechanical performance through topological modification in helical gears. Under light-load conditions (200 rpm), the modified gear configuration exhibits a 6.38% reduction in tooth surface temperature and a 46.5% decrease in thermal deformation compared to conventional designs. Experimental validation confirms these improvements, showing an average 62.35% reduction in transmission error. These findings establish a novel methodology for high-precision gear design while providing critical theoretical foundations for planetary gear systems, ultimately leading to significant improvements in both transmission accuracy and operational lifespan. Full article

To investigate the mechanisms of unexpected failures in a multi-stage gear transmission system under a relatively low load, a rigid–flexible coupled multi-body dynamics model with 10 spur gears and 12 helical gears is established. The dynamic condensation theory is applied to improve computational efficiency. The construction of this model incorporates critical nonlinear factors, ensuring high precision and reliability. Based on the proposed model, four critical dynamic parameters, including acceleration, mesh stiffness, dynamic transmission error, and vibration displacement, are analyzed. This research systematically reveals the nonlinear dynamic mechanism under the multi-gear coupling effect. The spectrum of the gears exhibits prominent low-frequency peaks at 320 Hz and 750 Hz. Notably, alternate load-dominated gears show a shift in prominent low-frequency peaks. The phenomenon of marked oscillations in mesh stiffness suggests a potential risk of localized weakening in the system’s load-carrying capacity. Critically, alternating torques induce periodic double-tooth contact regions in the gear at specific time points (0.115 s and 0.137 s), which are identified as critical factors leading to gear transmission system failures. The variation characteristics of the dynamic transmission error (DTE) demonstrate that the DTE is strongly correlated with the meshing state. The analysis of vibration displacement further indicates that the alternating external loads are the dominant excitation source of vibrations, noise, and failures in the gear transmission system. Full article

Time-varying mesh stiffness (TVMS) of the internal mesh transmission is a significant source of excitation that causes vibration and noise in planetary gear systems, and is also an important parameter in dynamics analysis. Currently, the calculation of mesh stiffness for internal gear pairs primarily relies on finite element simulation, and there still lacks a mesh stiffness analytical model that accounts for tooth surface nonlinear contact. Therefore, this paper proposes an analytical model for nonlinear contact mesh stiffness that comprehensively accounts for tooth surface modification and the flexibility of the ring gear. Firstly, a mesh stiffness calculation model for a sliced tooth pair was established using the potential energy method, which accounted for the influence of gear ring flexibility. Secondly, the tooth deviation ease-off diagram was derived from the modified tooth surface equations, which provided data support for the nonlinear contact analysis. On this basis, slicing element pairs that met the contact conditions were identified by combining elastic deformation with mesh clearance. The comprehensive mesh stiffness in nonlinear contact was calculated by integrating the deformation coordination equation with the principle of minimum potential energy. Finally, using a group of internal helical gear pairs as an example, the validity of the proposed method was verified through finite element simulation. The effects of load, modification amount, and face width on the TVMS and load transmission error (LTE) of an internal helical gear pair were investigated by the analytical model. The results show that the analytical model can provide a reference for the optimal design of internal gear transmission. Full article

Internal helical gear pairs are sensitive to manufacturing and assembly errors, loading deformation, which can result in vibration and noise. Three-dimensional topological modification of tooth surfaces is available to reduce this sensitivity. A 3D topological modification method is proposed by means of an internal helical gear form grinding method. The modified tooth surface model was constructed using spatial meshing theory and matrix transformations. Loaded tooth contact analysis (LTCA) was established to investigate the effect law of modification parameters on gear loading performance. Simulation results indicated that the contact area appeared at the middle area of the tooth surface under design loading conditions, with little edge contact existing. Transmission error decreased by up to 28.4% compared to the tooth without modification. The dynamic meshing performance of the internal helical gear pair was enhanced significantly. A transmission experiment was conducted to verify the effectiveness and validity of the simulation results. Full article

The use of supercritical carbon dioxide (SC-CO₂) coiled tubing drilling technology for developing heavy oil and other special reservoirs offers significant advantages, including non-pollution of oil layers, prevention of clay swelling, avoidance of reservoir damage, compact footprint, and enhanced oil recovery, making it a highly promising innovative drilling technology. The thermo-hydraulic coupling characteristics of SC-CO₂ in helical coiled tubes are critical to the design of SC-CO₂ coiled tubing drilling systems. However, existing models often neglect thermal conduction, variable thermophysical properties, and friction-compression coupling effects, leading to significant deviations in the prediction of temperature and pressure variations. Considering heat transmission and fluid dynamics, a coiled tube heat-transfer model which considers varying properties of both pressure and temperature has been developed based on an optimized convective heat-transfer coefficient. Then, the physical parameters of the carbon dioxide in the helical coiled tubing were researched. Results indicated that the temperature change of carbon dioxide in helical coiled tubing was small due to the low temperature difference between the carbon dioxide and the air as well as the existence of an air interlayer and low natural convective heat-transfer efficiency. The drop in pressure of the carbon dioxide increased with increasing coiled tubing length, and the pressure was half that of the conventional drilling fluid in the same condition due to its low viscosity. The density of carbon dioxide in the helical coiled tubing changed from 1078 kg/m³ to 1047 kg/m³ with increasing coiled tubing length under the conditions stated herein, and the carbon dioxide remained liquid throughout the whole process. Full article

Traditional design and shaping methods of helical gears may have difficulties in meeting the requirements of multiple performance indicators simultaneously, such as tooth surface accuracy, load-carrying capacity, and transmission efficiency. This study attempts to overcome these limitations through a multi-objective optimization method and achieve the comprehensive optimization of multiple performance indicators. This paper aims to boost gear system power transmission and cut vibration and noise. It assesses gear shaping impacts via normal load per unit length of the helical gear surface and gear vibration amplitude. Traditional gear shaping schemes were first determined using classic theories and formulas. Then, an improved genetic algorithm was applied to seek optimal helical gear shaping parameters. An eight-degree-of-freedom lumped mass model of the helical gear transmission system, considering bending–torsion–axial coupling, was developed based on Newton’s second law and solved via the fourth-order Runge–Kutta method. Comparisons showed that the traditional shaping scheme reduced the maximum normal load per unit length by 20.6% and the system’s vibration amplitude by 18.3%. In contrast, the improved genetic algorithm achieved greater reductions of 26.34% and 27.2%, respectively. Both methods effectively decreased the maximum normal load per unit length and system vibration amplitude, with the improved genetic algorithm yielding superior results. This work offers a key theoretical basis and reference for enhancing load transmission, reducing costs, and mitigating vibration and noise in gear transmission systems. Full article

This paper proposes a machine learning-based modeling and multi-objective optimization method for transcutaneous energy transfer coils to address the problem that current transcutaneous energy transfer coils with single-objective optimization design methods have difficulty achieving optimal solutions. From modeling to multi-objective optimization design, the whole transcutaneous energy transfer coil process is covered by this approach. This approach models transcutaneous energy transfer coils using the Extreme Learning Machine, and the Gray Wolf Optimization algorithm is used to tune the Extreme Learning Machine’s parameters in order to increase modeling accuracy. The Non-Dominated Sorting Whale Optimization algorithm is utilized for multi-objective optimization of the transcutaneous energy transfer coils, which is based on the established model. Using the optimization of planar helical coils applied in artificial detrusors as an example, a verification analysis was conducted, and the final optimization analysis results were demonstrated. The results indicate that the Gray Wolf Optimization algorithm significantly outperforms the comparison algorithms in tuning the parameters of the Extreme Learning Machine model, and it exhibits good convergence ability and stability. The established transcutaneous energy transfer coil prediction model outperforms the comparative prediction model in terms of evaluation metrics for predicting the three outputs (transmission efficiency, coupling coefficient, and secondary coil diameter), demonstrating excellent prediction performance. The Non-Dominated Sorting Whale Optimization algorithm performs well in the multi-objective optimization process of transcutaneous energy transfer coils, showing excellent results. The Pareto optimal solutions obtained using this algorithm have errors of 3.03%, 0.1%, and 1.7% for transmission efficiency, coupling coefficient, and secondary coil diameter, respectively, when compared to the simulation and experimental calculations. The small errors validate the correctness and effectiveness of the proposed method. Full article

A torsion sensor with directional discrimination based on a single-mode–twisted multimode–single-mode (STMS) fiber structure is demonstrated. The STMS fiber structure is fabricated by fusion-splicing a segment of multimode fiber (MMF) between two single-mode fibers (SMFs), where the MMF is simultaneously heated and twisted to form paired helical-type structures. The experimental results indicate that the resonance wavelength shifts towards shorter wavelengths as the twist rate increases in the clockwise direction, while an opposite shift occurs in the counterclockwise direction. Within a twist rate range of −5.2 rad/m~5.2 rad/m, the wavelength and transmission sensitivities are determined to be −1.38 nm/rad·m⁻¹ and 3.12 dB/rad·m⁻¹, respectively. Furthermore, the proposed twist sensor exhibits minimal temperature crosstalk of 0.0072 (rad/m)/°C, making it highly desirable for mitigating temperature-induced cross-sensitivity in torsion measurement applications. Full article

The dynamic characteristics of high-precision planetary reducers in terms of vibration response and dynamic transmission error have a significant impact on positioning accuracy and service life. However, the dynamics of high-precision two-stage helical planetary reducers have not been studied extensively enough and must be studied in depth. In this paper, the dynamic characteristics of the high-precision two-stage helical planetary reducer are investigated in combination with simulation tests, and the microscopic modification of the gears is optimized by the helix modification with drums, with the objective of reducing the vibration response and dynamic transmission error. Considering the time-varying meshing stiffness of gears and transmission errors, a translation–torsion coupled dynamics model of a two-stage helical planetary gear drive is established based on the Lagrange equations by using the centralized parameter method for analyzing the dynamic characteristics of the reducer. The differential equations of the system were derived by analyzing the relative displacement relationship between the components. On this basis, a finite element model of a certain type of high-precision reducer was established, and factors such as rotate speed and load were investigated through simulation and experimental comparison to quantify or characterize their effects on the dynamic behavior and transmission accuracy. Based on the combined modification method of helix modification with drum shape, the optimized design of this type of reducer is carried out, and the dynamic characteristics of the reducer before and after modification are compared and analyzed. The results show that the adopted modification optimization method is effective in reducing the vibration amplitude and transmission error amplitude of the reducer. The peak-to-peak value of transmission error of the reducer is reduced by 19.87%; the peak value of vibration acceleration is reduced by 14.29%; and the RMS value is reduced by 21.05% under the input speed of 500 r/min and the load of 50 N·m. The research results can provide a theoretical basis for the study of dynamic characteristics, fault diagnosis, optimization of meshing parameters, and structural optimization of planetary reducers. Full article

Tip leakage flow interacts with the mainstream, impacting the energy transmission process within the impeller of the fan and causing a significant flow loss. Understanding the flow characteristics within the impeller is a prerequisite and foundation for achieving efficient operation of the fan. Therefore, numerical simulations and experimental methods were employed to obtain the internal flow field of the mining counter-rotating axial flow fan, and the influence of flow rate on the tip leakage flow pattern was mastered. The spatial trajectory of the leakage vortex was quantified, and the distribution characteristics of the backflow were explored. The mechanism of energy loss caused by the leakage flow was revealed. The research findings indicate that when the flow rate exceeds 1.0 Q_BEP (Q_BEP is flow rate at the best efficiency point), the complex flow field near the blade tip is mainly caused by the tip leakage flow. However, the tip leakage flow and the leading edge overflow are the main factors causing disturbances in the flow field within the impeller at small flow rates. At large flow rates, the starting positions of the tip leakage vortex cores for both the front and rear impellers are located near the middle of the blade tip. As the flow rate decreases, the starting position of the vortex core gradually shifts toward the leading edge point, and the vortex structure evolves from an initial circular shape to an elliptical shape. The tip leakage flow and the leading edge overflow are the main cause of the backflow at the impeller inlet. The helical vortices caused by the tip leakage flow and the leading edge overflow, as well as the backflow in the impeller, are the key factors causing energy loss in the tip clearance flow field. Full article

The analysis of natural and artificial chiral compounds is vital wherever the nuances in the three-dimensional structure are decisive for the possibility of their further use, e.g., as pharmaceuticals or catalysts. The qualitative determination of the structure of a chiral entity requires either an anomalous scattering of X-ray radiation or chiroptical techniques, of which electronic circular dichroism (ECD) is one of the most useful. Chiroptical sensing that uses stereodynamic probes remains one of the remedies for the problem of the lack of a suitable chromophore in the molecules of the chiral compound. A covalent or non-covalent binding of an ECD-silent chiral molecule (the inducer) to the UV-active chromophoric system (chiroptical probe) led to obtaining complex ECD active at a given spectral region. The transfer of structural information from a permanently chiral inducer molecule to the structurally labile chromophoric system of the probe results in adjusting the latter’s structure to the chiral environment. This contribution focuses on some fundamental aspects of chirality sensing using conformationally labile probes. It discusses the mechanism of action of arbitrarily chosen stereodynamic chirality sensors, with particular emphasis on probes based on di- and triarylmethyl derivatives and biphenyl and its congeners. Full article

Gearboxes used in electric locomotives are a critical unit, especially in freight rolling stock. The article presents the calculation of the main parameters of the two-way oblique traction transmission of the VL-80s electric locomotive (which is operated on the railways of Uzbekistan) based on a comprehensive analysis of the diagnostic parameters obtained using the Poisson normal distribution method for the identified failures according to the Uzbekistan depot data. Also, a Pareto diagram was constructed for the chassis of 3VL-80s electric locomotives based on the data of the Locomotive Operation Department of JSC Uzbekistan Temir Yollari, and probabilistic and statistical analyses of the failures and breakdowns of the wheel pair and the large gear wheel of the traction gearbox of the VL-80s electric locomotives were carried out. An algorithm and methodology for assessing the reliability of the large gear wheel of the traction gearbox of an electric locomotive are presented. As a result of a numerical calculation of the coefficients of the empirical regression equations using approximation and spline interpolation methods, a regression equation was obtained for the dependence of the standard deviation of the wear of the tooth of the large gear wheel of the traction reducer of the VL80s electric locomotive on the mileage. Full article