In this paper, a new modelling approach is proposed for the dynamic investigation of epicyclic gear train, and the novelty of this work lies in consideration of both structural flexibility and mechanical interactions during the analysis procedure. The method is of capacity to directly present the dynamic results of the supporting structure for convenient practical engineering evaluation and reduce the dimension of the system reasonably with appropriate assumptions for better computational efficiency. Firstly, the mechanical interactions among components are discussed in detail, and the principle that the structural flexibility works is also explained at length. Secondly, taking the epicyclic gear train of the geared turbofan (GTF) engine; for example, the dynamic model of the system is then established based on the developed hybrid user-defined elements. For model validation, the governing equations of the system are also derived by the lumped mass method. Thirdly, with the same values of the parameters, the results of normal dynamic meshing force obtained by the proposed model are compared with the ones by the lumped mass model. It can be stated from the data that (1) the maximum relative error between the theoretical value and the average value calculated by the two models is 8.28%, (2) the gear mesh frequency obtained by the two models are sufficiently close to the theoretical value, and (3) the fluctuation trends of the dynamic force keep basically consistent with each other. In summary, the comparison presented clearly indicates that the proposed model is indeed reasonable, which provides a new way for dynamic investigation and structural redesign of a large epicyclic gear train. Finally, as a practical engineering application, the vibration result of the deformable supporting structure of the GTF gear train is also presented, which directly provides valuable reference for vibration monitoring, fault diagnosis and other engineering problems in practice.
<div class="section abstract"><div class="htmlview paragraph">Due to the multi-gear configuration and high integration of electric drive systems in electric vehicles, it is necessary to investigate the influence of drive motor torque fluctuation on the dynamic characteristics and load sharing performance of planetary gear transmission systems. Considering both motor torque fluctuation and internal excitations of the transmission system, a dynamic model of the electromechanical coupled system is established by combining the Maxwell motor electromagnetic model with the planetary gear dynamics model. Based on the proposed model, the dynamic characteristics, dynamic load performance and load sharing performance of the system considering motor torque fluctuation are analyzed, and the improvement of system load sharing performance due to sun gear floating is discussed. The results show that motor torque fluctuation leads to more complex dynamic response and causes the vibration displacement amplitude to more than doubled. Furthermore, the system exhibits an increased presence of high-frequency components in its vibration frequency spectrum. Under the conditions of eccentricity error only and both installation error and eccentricity error, motor torque fluctuation increases the load sharing coefficient of the planetary gear system by more than 11.5% and the dynamic load coefficient by more than 76%. The backlash float mechanism can improve the load sharing performance of the system by approximately 3% for both internal and external meshing pairs, but with limited effectiveness. Additionally, when the float amount reaches 5<i>μm</i>, the system’s load sharing performance will no longer show further improvement. This research work provides valuable insights for the optimization design of shock and noise reduction in electric-driven planetary gear systems</div></div>
Unilateral external fixators are commonly used to stabilize the fractured tibia bone. Compared with static fixation, axial dynamic motion can be used for promoting callus formation, improving bone healing at fracture sites. Moreover, non-axial motions are not conductive to promoting bone healing and remodeling. However, a fixator-bone system with 7(DOFs) can not achieve both fracture correction and axial dynamic motion. Maybe it is easy to think that this problem could be solved by adding one DOF for fixator structure. However the increased structural flexibility could not be able to meet the demands of lower cost and size, and higher stiffness. Thus, how a fixator-bone system with 7 DOFs not only can realize fracture correction, but also complete axial dynamic motion as far as possible. So far, researchers have never solved this problem. Therefore, we establish a mathematical model based on the 7 DOFs Orthofix fixators, and try to use the genetic algorithm method to reduce the tangential displacements in the process of axial dynamization after fracture correction. The results suggest that the use of genetic optimization algorithm can effectively reduce tangential displacement. This study helps facilitate appropriate and flexibility application of fixators to better control axial dynamic motion and decrease tangential displacements.
In order to analyze the influence of bolt supporting parameters on the stability of slope, based on the limit equilibrium method to establish model of slope and calculated the safety factor of slope. Research shows that: (1) As the bolt length increases, the safety factor of slope increases gradually, then the length of anchor bolt can be used as the design length when the safety factor can meet the standard requirement.(2) With the increase of the anchor Angle, the safety factor of slope present the trend of first increasing and then decreasing, when bolt spacing increased to a certain value, the safety factor of slope reduce significantly.(3)In this paper, the analysis method of slope bolting parameters on its effect to the stability is simple and strong operational, which can provide a reference for related engineering personnel.
In order to research on slope seepage field and slop stability under rainfall infiltration, this paper combines finite element with limit equilibrium theory to study. The results show that under rainfall, pore water pressure of the slope crest and slope toe in slope wash is greatly influenced by rainfall; Change in the volume moisture content is more sensitive than pore water pressure, volumetric moisture content of each location is increasing quickly at the initial stage of rain, volumetric moisture content in the lower locations is the first to reach saturated due to the continued supply and gravity of the rain; The slope stability reduces with rainfall infiltration, the greater the rainfall intensity, the more obvious decline the slope safety factor.
Due to the limitation of machining accuracy, the transmission performance uncertainty of mass gears must be evaluated quantitatively to provide the basis for its application in the whole machine. Based on the polynomial chaotic expansion (PCE) method, a dynamic uncertainty analysis method for gear systems with a specified precision was proposed in this paper. Combined with tooth surface contact analysis and load-bearing contact analysis, a dynamic model of the gear system was established to fully reflect the influence of typical manufacturing errors. Based on this, a PCE model was established to approximate the system dynamics model. The dynamic uncertainty of the gear system was quantified based on the PCE approximation model and the Monte Carlo method, respectively, and the computational accuracy and efficiency of the PCE model with different orders and numbers of sample points were compared and analyzed. Finally, Sobol′ sensitivity indices from the PCE model of the gear system to random errors were computed, and the primary and secondary relationships of influence on the dynamic performance of the gear system were determined. The results showed that the PCE method had good applicability to the quantification of dynamic uncertainty and error sensitivity analysis of gear systems, and it had both accuracy and high efficiency.
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