Vol. 8, No. 1 (2024): Regular Issue

For cylindrical roller bearing, a dynamic model considering the degree of freedom of the rollers is established to analyze the influence of the external load and clearance on dynamic characteristics of rolling bearing. Firstly, the load distribution curve is compared with Hou's test data to verify the validity of the bearing dynamic model. Then, load distribution curves and the fixed point load sequences are calculated under different clearances. And the angular position equations of bearing components at the moment of the load mutation occurs at the fixed points on inner and outer raceways are established for analyzing the law of the load sequence variation. Finally, the load sequences of the danger points of inner raceway and outer raceway are calculated under the coupling effect of radial load and unbalanced load. The results show that the load sequence varies periodically and the period is determined by the angular position deviation of the fixed point when the first and the last contact occurs during the point rotates in one turn. Without considering the unbalanced load, the load distribution curve can completely envelop the contact load sequence at the fixed point of the inner ring raceway, and with the increase of the clearance, the span of the envelope peak of the load sequence decreases and the height increases.

Gas transmission pipeline vibration is mostly caused by gas flow fluctuation, and the disturbance of the gas flow through the tee junction pipes is one of the reasons for the large gas flow fluctuation. Large Eddy simulation (LES) method is applied to gas flow fluctuation in tee junction pipes in this paper. Firstly, the models of numerical simulation and the geometric parameters are displayed, in addition to the governing equations of compressible flow in LES. Subsequently, accuracy and applicability of LES method for compressible internal flow problem are validated and the optimal subgrid-scale (SGS) model, DSM SGS model, was selected by comparing the reference values with the values calculated of each of the SGS models. Finally, to reveal how the gas flow fluctuation in tee junction pipe (or with a blind end) vary with the influencing factors, LES method and DSM SGS model are applied to simulate the flow of compressible fluid (methane) in the tee junction pipes. The influencing factors are flow velocity and branch internal diameter, and in the case of tee junction pipes with a blind end, branch length is also taken into account.

The conformal invariance of certain statistics in the inviscid two-dimensional turbulence is derived. For this we investigate the transport equation for the two-point probability density functions of vorticity from the infinite Lundgren-Monin-Novikov hierarchy and give the conditions under which the probability measure is conformally invariant. This is an extension of our previous analyses of the one-point statistics, which also paves the way for further generalisation to arbitrary $n$-point statistics.

This paper describes a methodology for modeling a unimorph-piezoelectric portal frame based on electromechanical energy formulation of the Euler-Bernoulli beam with axial deformations, the fixed-interface component mode synthesis by Craig and Bampton, and the Rayleigh-Ritz method. An assembled model obtained from this approach is the reduced-order model in terms of generalized modal coordinates without dealing with finite-element model during modeling formulation. The operating frequency of the portal-frame energy harvester can be reduced significantly from a cantilevered-piezoelectric energy harvester. The total-voltage output of the portal frame is the sum of voltage outputs from each substructure due to in-phase voltage outputs of each substructure. The presented approach can be used systematically to study an internal resonance of the portal frame when both piezoelectric-material nonlinearity and geometric nonlinearity are included.

Aiming at the problem of low detection accuracy of small and medium targets and occluded targets in power field, a new wear detection method improved SBC_YOLOv5 is proposed. This method is based on expansion convolution, and uses multi-scale pooling operation and MHSA self attention module to improve the spatial pyramid pooling layer, so that it can obtain more abundant receptive fields. Secondly, it uses feature bridging operation and CARAFE operator to improve the Neck network, so as to improve the network's ability to extract and compensate semantic features. Finally, it uses CIoU to optimize the network's loss function and improve the regression ability of the model. The experimental results show that the wear detection method SBC established in this paper_ The average accuracy mAP(Mean Average Precision) of YOLOv5 is 82.3%, the recall rate is 81.5%, and the detection speed FPS is 44. Compared with original YOLOv5, YOLOv4, and Faster RCNN, the mAP values of YOLOv5 are increased by 1.5%, 10.27%, and 25.21%, respectively. It can effectively improve the detection accuracy of small targets and occluded targets, and meet the real-time and accuracy requirements of wear detection at power operation sites.

In this paper, nonlinear dynamics of the product-quadratic systems with self-quadratic and crossing-quadratic vector fields is presented, which is the study continuation of product-quadratic systems with two product-quadratic vector fields. With a self-quadratic field, the stability and bifurcations of product quadratic systems are discussed. The saddle-sink bifurcation for saddle and sink is discussed, and the saddle-source bifurcation for saddle and source is presented. The saddle-saddle bifurcations of the first kind are presented. The appearing bifurcation conditions for sink-source and saddle-saddle are discussed. The inflection sink (or source) bifurcations are presented for the switching bifurcations for hyperbolic flow and saddles with hyperbolic-secant flow and sink (or source). With a crossing-quadratic vector field, the dynamics and bifurcations for such a quadratic system are discussed. The saddle-center appearing bifurcations are presented through the parabola-saddle bifurcations. The center-center bifurcation and the saddle-saddle bifurcation of the second kind are discussed through the hyperbolic sink-source and circular sink-source bifurcations. The up-parabola-saddle bifurcations are for the switching of the center and hyperbolic flow with saddle and hyperbolic-secant flows. The down-parabola-saddle bifurcations are for the switching of the center and hyperbolic-secant flow with saddle and hyperbolic flows. The parabola-saddle on the infinite-equilibrium is called the switching bifurcations of saddle and center.