Journal of Vibroengineering
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Vibration characteristics of spur gear system with non-linear damping under no lubrication condition
Get PDFGear rattle induced by backlash between meshing gears results in excessive vibration and noise in many gear systems. A dynamic model of a light-loaded spur gear pair with non-linear damping under no lubrication condition is presented in this paper. Unlike previous models, the effect of backlash on damping is considered, so the damping is not linear. In order to illustrate the effect of non-linear damping on the dynamic response, the dynamic behaviors of gear system with non-linear damping (GSND) and linear damping (GSLD) under different impact status are compared by using the numerical integration method. The results show that the behavior of gear pair with non-linear damping is different from that with linear damping, and the impact vibration of GSND is much greater than GSLD under some conditions. The influences of parameters such as load ratio, load value, meshing stiffness, and damping ratio on the dynamic responses of GSND are also discussed, and some suggestions to reduce impact vibration of gear system are proposed. The results provide a theoretical basis for the design and manufacture of gear system
Design and simulation analysis of an improved wearable power knee exoskeleton
Get PDFThe wearable lower limb power robotic exoskeleton is a device that can improve the human walking ability. In this paper, an improved exoskeleton device for knee joint is designed, including the improvement of mechanical structure and hydraulic cylinder. In order to verify the effectiveness of the improvement of the hydraulic cylinder, we have carried out the following studies. Firstly, in terms of mechanical structure, length adjusting device is added to meet the needs of different people. At the same time, a limit device is added to the knee joint to improve the safety performance and comfort. Secondly, the dynamics of the model is carried out by Lagrange, and the exoskeleton model is established for ADAMS motion simulation. The force of ADAMS simulation, the calculated by Lagrange equation and the force of the first edition of hydraulic cylinder are compared, and the force selection of hydraulic cylinder is analyzed. By comparison with the first edition, the optimization rate of the improved hydraulic cylinder reaches 8 %. Finally, in order to verify the rationality of ADAMS simulation and the effectiveness of hydraulic cylinder improvement, the wear test is carried out, the average errors of leg centroid in normal walking, wearing exoskeleton walking and ADAMS simulation data are compared. The average error rate is less than 10 %. The results show that the simulation model design is reasonable, and the effectiveness of the hydraulic cylinder improvement is verified. The exoskeleton device designed can well follow the human motion. The simulation analysis of the exoskeleton provides important parameters for the manufacture and it also provides theoretical basis for the later control theory
Collaborative model analysis on ride comfort and handling stability
Get PDFFor considering the connection and mutual influences between ride comfort and handing stability of a vehicle, a collaborative study on the two performances is carried out in the paper. Firstly based on the UniTire model and combined with filtered white noise models for front and real road excitations, 4-DOF plane model for ride comfort and 2-DOF plane model for handling stability, a collaborative model for ride comfort and handing stability is built by adopting state equations, and a collaborative simulation algorithm for them is also proposed. Then, a collaborative simulation on the ride comfort and handing stability of a vehicle under common road grade and speed conditions is conducted. The results show that the ride comfort and handling stability of a vehicle can be simulated simultaneously by using the collaborative model. The handling stability parameters simulated with the linear UniTire model are larger than those simulated with the nonlinear UniTire model, indicating that it is obviously conservative to study vehicle handling stability with the linear UniTire model
A novel faults detection method for rolling bearing based on RCMDE and ISVM
Get PDFThe rolling bearing is an essential element widely used in the rotating machinery. Bearing failures are among the main reasons for breakdown of rotating machinery. Therefore, fault detection of bearing is necessary to reduce the probability of breakdown and safety accidents. A novel fault diagnosis method for rolling bearing based on Refined Composite Multiscale Dispersion Entropy (RCMDE) and Improved Support Vector Machine (ISVM) is presented in this paper. The RCMDE is a new irregular index in biomedical signal analysis, which has lower computational cost and more stable results. Therefore, the RCMDE is introduced as fault feature to represent the bearing fault characteristics. After feature extraction, an improved support vector machine based on whale optimization algorithm (WOA) and support vector machine (SVM) is proposed as a fault classifier, which has the advantages of less training samples and good classification effect. The effectiveness of the proposed method in bearing fault diagnosis is verified by using bearing fault experimental data
Tension estimation of hangers with shock absorber in suspension bridge using finite element method
Get PDFAccurate and efficient estimation of tension in hangers is very important since hangers are the vital component of suspension bridges. But for hangers with shock absorber, the existing tension estimation methods are not suitable because they are based on a single cable model and cannot consider the effect of shock absorbers. To this end, the effect of the shock absorber is taken into account by using the degree-of-freedom condensation method, and a finite element method for tension estimation of hangers with shock absorber is proposed in this paper. Finally, the proposed method is applied in the Aizhai Bridge and Huangpu Pearl River Bridge to estimate the tension of hangers with shock absorber, the tested results show that as compared with other methods, the proposed method is a more accurate and convenient method for engineering application
Dynamic response of long-span continuous curved box girder bridge under seismic excitation
Get PDFForm function matrix is created by introducing high order displacement interpolation function in the node. Based on the virtual work principle and dynamic finite element theory, the spatial element stiffness matrix, mass matrix and earthquake mass matrix of a thin-walled box girder having 9 freedom degrees at each node are deduced. The D’Alembert vibration equation is also established. Newmark-β method is used through MATLAB to solve the seismic response of a long-span continuous curved box girder bridge under El-centro seismic waves. Meanwhile the spatial finite element model of the whole bridge is established by ANSYS. The results indicate that the dynamic responses of pier columns exhibit spatiality. The dynamic response of a bridge structure under 2D coupling horizontal seismic excitation is much bigger than that under 1D horizontal seismic excitation. The critical angle of seismic waves is 50° for radial displacement response. Theoretical calculation results are in agreement with the finite element analysis results. The deduced element matrix not only can be used to calculate the seismic response of long-span curved beam bridge structures but also can provide significant references for the structures in vibration response caused by moving traffic
Introduction to the Special Issue: Nonlinearity and numerical simulation applications in geotechnical engineering
Get PDFTrain induced pore water pressure generation model: numerical comparison
Get PDFIn recent decades, the provisions of new challenges to railway track demanded for a better understanding of the track dynamic, especially to track geotechnical dynamics. For geotechnical problems the presence of water in the void of soils has influence on the behavior of the soil effects such as temporarily development of excess pore water pressure of the soil or even liquefaction and mud pumping can occur. To account these effects considering the soil as two-phase material would be helpful to better understand the saturated railway line failures. Hence, this paper describes the pore fluid analysis of fully saturated railway embankment response subjected to train induced vibrations using three-dimensional finite element package ABAQUS. The modelized 3D track consists of train loads, rail, pads, sleeper, sub-ballast, ballast, saturated sub-grade, saturated subsoil layer and semi-infinite bedrock. The water-saturated soil layers modeled as poroelastic and the infinite bed rock as elastic medium. To this end, the influence of relative density, hydraulic conductivity, un-drained Young’s modulus and depth of embankment on excess pore water pressure development are compressively studied. The predicated results show that hydraulic conductivity, un-drained Young’s modulus and depth of embankment have quite significant effect on the induced excess pore water pressure; while the influence of relative density is very small. The result also shows that positive excess pore water pressure mainly distributes on the soil and this will permit fine grain soils to flow out from interior to exterior region of the model. Hence, mud pumping and liquefaction is developed not in specific type of soil instead can be developed in any type of soil with low hydraulic conductivity, high depth of embankment and low un-drained Young’s modulus
Strength characteristics and failure behavior of ubiquitous-joint rock-like specimens under compressive-shear stress: experimental study and digital speckle correlation method
Get PDFIn nature, rock mass is subjected to compression-shear effect, so it is very important to study the failure mode and mechanical properties of fractured rock mass under compression-shear effect. In order to study the influence of joint inclination on strength characteristics and failure modes of rock mass under different compression-shear angles, a series of compression-shear tests were carried out. The specimens are made of a certain proportion of fine sand, cement and water. The joints are prefabricated by inserting mica sheets and the inclination angle of joints is 0°, 15°, 30°, 45°, 60°, 75°, 90°. Digital speckle correlation method is used to analyze the strain field of the specimen during the whole loading process. The specimens are speckled on the opposite side before the experiment. In the experiment, the front and back sides of the specimen are monitored by the camera, and the images are analyzed after the experiment. The result shows that: 1) The peak shear strength of specimens mainly increases with the increase of joint inclination angle; 2) The weakening degree of shear strength caused by joint inclination angle of specimens tends to increase as the compression-stress ratio increases; and 3) The failure modes can be classified into four types: coplanar shear failure mode, inclined shear failure mode, quasi-complete shear failure mode and step shear failure mode. The digital speckle strain images better prove the failure modes obtained from the experiment
Optimization calculation of stope structure parameters based on Mathews stabilization graph method
Get PDFMathews stability graphic method, based on the rock classification system, measures the stability of the ore roof area of a relatively simple calculation method and provides a theoretical basis for mine rational design stope structure size parameters. In this study, we used a large-scale tungsten mine in Jiangxi Province as the engineering background and performed on-site engineering geological surveys and indoor ore rock mechanics tests in the middle section of mine 417 to obtain multiple engineering quality indicators for the mines and surrounding rocks. The Mathews stability map method and Barton limit span theory were used. The reasonable size range of the exposed face of the stope was calculated by performing theoretical analysis on the ultimate span. Then, FLAC3D calculation and analysis software were used for the simulation of the stope structure, and the most reasonable design of the exposed surface dimension was selected and used as reference for ensuring the safe production of the mine