Aiming at the problem of low stiffness of aerostatic bearing, according to the principle of gas-solid coupling, this paper designs a kind of aerostatic thrust bearing with elastic equalizing pressure groove (EEPG) and investigates the effect of elastic equalizing pressure groove (EEPG) on the stiffness of aerostatic bearing. According to the physical model of the bearing, one deduces the deformation control equation of the elastic equalizing pressure groove and the control equation of gas lubrication, using finite difference method to derive the control equations and coupling calculation. The bearing capacity and stiffness of aerostatic bearing with EEPG in different gas film clearance are obtained. The calculation results show that the stiffness increased by 59%. The results of numerical calculation and experimental results have good consistency, proving the gas-solid coupling method can improve the bearing stiffness.
In order to solve the load-sharing characteristics of face-gear four-branching split-torque transmission system (FGFBSTTS), the static load-sharing mechanical analysis model was established. In the model, the deformation coordination conditions of torsional angle and torque balance condition were considered. By using Loaded Tooth Contact Analysis (LTCA) technology of face gear and herringbone gear, the time-varying meshing stiffness was calculated. The influences of manufacturing errors, installation errors, I-stage pinion floating, II-stage pinion spline clearance floating, and radial limit ring clearance floating on the load-sharing characteristics are analyzed. The results show that the LTCA technology is more accurate to reflect the load-sharing characteristics of each meshing position. When the I-stage pinion and the II-stage pinion floated at the same time, the best load-sharing characteristics can be obtained. The load-sharing characteristics affected by manufacturing errors showed obvious periodic change. The radial limit ring plays a better auxiliary role in load-sharing characteristics. The theoretical results were compared with the experiments to verify the correctness of the theoretical analysis. The research results can provide a theoretical basis for the optimal design of the load-sharing structure, error control, and assembly of the face gear four branch transmission system.
Physical isolation is an effective means for protecting inner network against outer network attacks,but it is harmful for the inner information systems and inner users’ routines.A Non-feedback One-way Information Transmission System is proposed for solving this problem.The system is composed of a public server,a private server and a one-way transmission tunnel.The system’s construction and working principle are explained in this paper’s forepart.And the forward error correction method,link layer design and business layer structure of the system are discussed in detail.It’s analyzed that the system’s one-way transmission error rate is 6.3×10-24,when the chain error rate is 10-5.The system is a whole set of one-way solution that transmit data from non-confidence network to confidence network.This solution is safe,reliable,efficient and convenient with broad application prospect.
The herringbone gear planetary transmission system (HGPTS) is a common component in the gearbox of wind turbines. Studying the dynamic performance of gear systems is the key to improving their stability. To reveal the influence of cracks on the dynamic characteristics of the HGPTS, using slicing method, we explore the influence of different crack factors on the time-varying meshing stiffness (TVMS) of the system. A 55-degrees of freedom bending torsion axis pendulum dynamic model was constructed using the centralized mass parameter method; in the model, factors such as TVMS of cracks as well as receding groove and errors are considered. The Runge–Kutta method was used to solve the dynamics, and the evolution diagram of the vibration and load distribution characteristics of the system under crack changes was obtained. Vibration tests were conducted on the system studied in this work. The results show that under the influence of cracks, the TVMS of the external and internal meshing pairs of the system will decrease, and as the cracks intensify, the fluctuation of the TVMS will decrease. Cracks can lead to regular impact behavior in the system. A modulation sideband centered on the meshing frequency appears in the vibration response, and the vibration trajectory of the gears will also become disordered, at the same time, under the influence of cracks, there are significant excitation factors in the load-sharing characteristics of the system. As the cracks continue to intensify, the vibration of the system becomes increasingly evident, and the load-sharing characteristics show a trend of first decreasing and then increasing. The vibration test results are in good agreement with the theoretical predictions. The correctness of the established model is verified. The research results can provide reference for the reliability research of wind turbine HGPTS.
The torsional dynamic model of double‐helical gear pair considering time‐varying meshing stiffness, constant backlash, dynamic backlash, static transmission error, and external dynamic excitation was established. The frequency response characteristics of the system under constant and dynamic backlashes were solved by the incremental harmonic balance method, and the results were further verified by the numerical integration method. At the same time, the influence of time‐varying meshing stiffness, damping, static transmission error, and external load excitation on the amplitude frequency characteristics of the system was analyzed. The results show that there is not only main harmonic response but also superharmonic response in the system. The time‐varying meshing stiffness and static transmission error can stimulate the amplitude frequency response of the system, while the damping can restrain the amplitude frequency response of the system. Changing the external load excitation has little effect on the amplitude frequency response state change of the system. Compared with the constant backlash, increasing the dynamic backlash amplitude can further control the nonlinear vibration of the gear system.
In order to solve the dynamic vibration characteristics of the power-split transmission system, the system of the dynamic mechanical model is established. Firstly, according to the theoretical analysis method of the tooth contact analysis (TCA) and loaded tooth contact analysis (LTCA), the actual meshing process of each gear pair is simulated, and the time-varying mesh stiffness excitation is obtained, which can improve the numerical precision. Next, by using the lumped mass method, the bending-torsional coupling three-dimensional dynamical model of the power-split transmission is established. The identical dimensionless equations are deduced by eliminating the effect of rigid displacement and the method of dimensional normalization. Next, the frequency domain and time domain responses of this system are obtained. The dynamic load change characteristics of each gear pair are analyzed. The results show that establishment, solution, and analysis of the system dynamics model could provide a basis for the dynamic design and have an important significance for the dynamic efficiency analysis and dynamic performance optimization design of the power-split transmission. Through theoretical data compared with the experimental data, we verified the correctness of the method proposed.
Abstract A nonlinear dynamic model of Bending-Torsional-Axial-Pendular (BTAP) has been developed for a Coaxial Reverse Closed Differential Herringbone Gear Transmission System (CRCDHGTS) with consideration of gear floating. This model takes into account factors such as gear floating backlash, tooth surface friction, gyroscopic effect, Time Varying Meshing Stiffness (TVMS), meshing damping, and dynamic meshing parameters. To investigate the impact of gear floating on the nonlinear dynamic characteristics of the system, a gear floating model was developed using the concept of gear floating. The calculations included determining gear floating backlash and TVMS with consideration for gear floating. The impact of input speed, initial backlash, gear float value, and system transmission error on the nonlinear dynamic vibration characteristics is analyzed using various diagrams including bifurcation diagram, Maximum Lyapunov Exponent (MLE), time history diagram, frequency diagram, phase diagram, and Poincaré section diagram. The research reveals that gear floating diminish the chaotic motion behavior of the system under different excitation factors, improving the system's global bifurcation characteristics. The developed BTAP coupled nonlinear dynamic model provides more accurate numerical solutions compared to models with fixed meshing parameters, making it more suitable for analyzing the system's dynamic characteristics. Analysis of the gear floating value indicates an optimal range of 0-20μm and 34-43μm for generating periodic motion, with floating values around 10-20μm showing better performance in reducing the negative effects of initial backlash and transmission error.
To improve the network capacity and reduce interference, directional antenna has been used in ad hoc networks for a long time. Due to the drawbacks of random access MAC protocols with directional antennas such as inevitable collisions, a distributed TDMA-based directional MAC protocol for ad hoc networks is proposed in this paper. It takes the advantage of real-time capability of TDMA and spatial reuse potential owing to directivity. By using the binary countdown mechanism instead of CSMA/CA, collision is completely avoided in contention stages. It offers priority services as well. The network saturation throughput and average delay are analyzed theoretically. Simulation results show that this new protocol performs better than DMAC protocol, as well as IEEE802.11 DCF and TDMA-based protocol with omnidirectional antennas.
The vibration characteristics and fault diagnosis of herringbone gears are significantly affected by the time-varying meshing stiffness (TVMS), a crucial internal excitation factor. An analytical model was developed using the potential energy method to thoroughly investigate the impact of crack-pitting coupling on the TVMS of herringbone gears. This model accounted for various factors, such as different crack depths and degrees of pitting. It included 16 different crack depths and degrees of pitting, and analysed the bending stiffness, shear stiffness and axial compression stiffness of the herringbone gear pair under the influence of coupling. The problem was solved using the integral method to examine the effect of crack-pitting coupling on the TVMS of herringbone gears. The calculated TVMS results were then analysed and compared for healthy gears and those with different degrees of crack-pitting coupling faults. A finite element computational model was also established using the finite element method to assess the TVMS of herringbone gears subjected to varying degrees of crack-pitting coupling. Simulation and analysis were conducted to compare the results obtained from the model with those obtained using the analytical method. The results indicate that when the crack reaches 10%, the dominant factor influencing the coupling fault TVMS is pitting. When the crack reaches 30%–50%, the TVMS is jointly influenced by pitting and crack. At 70% crack, the dominant factor is the crack itself. The calculated results were compared to finite element calculations, with a maximum error of 2.5%, confirming the accuracy of the results. The findings of this study can furnish a theoretical foundation for analysing dynamic vibration stability and fault diagnosis in herringbone gear.
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