Characteristics and prediction methods for tunnel deformations induced by excavations

Zheng, Gang,Du, Yiming,Cheng, Xuesong,Diao, Yu,Deng, Xu,Wang, Fanjun Techno-Press 2017 Geomechanics & engineering Vol.12 No.3

The unloading effect from excavations can cause the deformation of adjacent tunnels, which may seriously influence the operation and safety of those tunnels. However, systematic studies of the deformation characteristics of tunnels located along side excavations are limited, and simplified methods to predict the influence of excavations on tunnels are also rare. In this study, the simulation capability of a finite element method (FEM) considering the small-strain characteristics of soil was verified using a case study. Then, a large number of FEM simulations examining the influence of excavations on adjacent tunnels were conducted. Based on the simulation results, the deformation characteristics of tunnels at different positions and under four deformation modes of the retaining structure were analyzed. The results indicate that the deformation mode of the retaining structure has a significant influence on the deformation of certain tunnels. When the deformation magnitudes of the retaining structures are the same, the influence degree of the excavation on the tunnel increased in this order: from cantilever type to convex type to composite type to kick-in type. In practical projects, the deformation mode of the retaining structure should be optimized according to the tunnel position, and kick-in deformation should be avoided. Furthermore, two methods to predict the influence of excavations on adjacent tunnels are proposed. Design charts, in terms of normalized tunnel deformation contours, can be used to quantitatively estimate the tunnel deformation. The design table of the excavation influence zones can be applied to determine which influence zone the tunnel is located in.

Mesh stiffness analysis of beveloid gears for the rotating vector transmission

Yucheng Huang,Xuesong Du,Caichao Zhu,Gaoxiang Ni,Najeeb Ullah,Hao Liu 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.8

This paper investigates the meshing stiffness of beveloid gears in the beveloid rotate vector (BRV) transmission. It is a new kind of transmission evolved from rotate vector (RV) reducer. In the BRV transmission, the beveloid gear is a kind of involute gear with a bevel angle. The BRV transmission have high power density, large transmission ratio and high precision in geared coupled systems. However, there is rare systematic research conducted on the meshing stiffness analysis of the BRV transmission at present. Based on the loaded contact finite element analysis principle, a meshing stiffness analysis model for beveloid gears is established. The influence of different factors such as pitch cone angle, addendum coefficient, load and rim structure parameters of external gear on meshing stiffness are studied. The results show that the pitch cone angle and addendum coefficient have little effect on the shape of the meshing stiffness curve, but they have a significant influence on the amplitude of meshing stiffness. In contrast, the load can affect both the shape and the amplitude of the meshing stiffness curve obviously. Also, the size of scallop-hole and rim thickness have a great impact on the amplitude of the meshing stiffness. The prescribed piece of study can provide a better understanding for gear researchers in order to understand the influence of different parameters on dynamic characteristics analysis of the BRV transmission systems.

Tooth Thickness Error Analysis of Straight Beveloid Gear by Inclined Gear Shaping

Feihong Zhu,Chaosheng Song,Caichao Zhu,Xuesong Du 한국정밀공학회 2022 International Journal of Precision Engineering and Vol.23 No.4

In this paper, two approaches to calculate the tooth thickness error (TTE) of straight beveloid gear by tilt-type gear shaper were proposed. The first calculation approach of TTE was established by considering the change of pitch circle radius during the gear slotting process. The analytical tooth surface model of straight beveloid gear was derived by inclined gear shaping, and the tooth surface point set was obtained. Then, another calculation methodology of TTE was established based on the analytical straight beveloid gear model. Two approaches were employed to calculate the TTE of internal and external straight beveloid gear, respectively. And they were employed to validate each other, and the results show a good consistency. The influences of design parameters on TTE was analyzed. Results show that the internal/external straight beveloid gears have a convex/concave TTE along the tooth width direction while cutting by tilt-type gear shaper, which makes the tooth thickness of the heel and toe sides of beveloid gear thinned/thickened, respectively. The TTE of internal and external beveloid gear both increase with the increase of design cone angle, and decrease with the increase of modulus and number of teeth. For the same macro gear design parameters, the TTE of external beveloid gear is smaller than that of internal beveloid gear. The results of the two approaches show good consistency at the middle of tooth surface. The maximum difference between the results of two approaches gradually increases away from the middle of tooth surface, and it is positively correlated with the value of TTE.

Theoretical investigation of sliding ratio on oscillatory roller transmission

Chaosheng Song,Changxu Wei,Caichao Zhu,Xuesong Du,Hailan Song 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.7

The contact pairs of oscillatory roller transmission are all high pairs, so the relative sliding occurs due to the different tangential velocity of the contact points. This paper derived the mathematical model and kinematic model of oscillatory roller transmission and proposed a new sliding ratio modeling method for oscillatory roller transmission based on the velocity decomposition. The impacts of geometry design parameters on sliding ratios for oscillatory roller transmission were studied. Results suggest that sliding ratios first decrease and then increase as the rotation angle of movable rolling teeth grows. However, for parametric studies, sliding ratios increase as the radius of disk cam and transmission ratio rise, and decrease as the radius of movable rolling teeth increases. The variation of the eccentricity of disk cam has a great influence on the fluctuating values of sliding ratios. The growth of the radius of movable rolling teeth and the eccentricity of disk cam significantly increase the peakto-peak values of sliding ratios. Relatively, the radius of disk cam and transmission ratio have small impact on sliding ratios. The results provide theoretical guidance for reducing friction and improving the mechanical efficiency of oscillatory roller transmission in engineering.

Transmission accuracy–axial backlash–fatigue life-driven tolerance optimization of planetary roller screw mechanism

Liu Genshen,Wei Peitang,Liu Huaiju,Du Xuesong,Hu Rui,He Huilin,Zhou Pengliang,Tan Xiaoqing 한국CDE학회 2023 Journal of computational design and engineering Vol.10 No.6

The planetary roller screw mechanism (PRSM) is an advanced linear transmission device. The relationship between tolerance allocation and performance risk still remains elusive, which is a challenge for its future applications. This work proposes a novel transmission accuracy–axial backlash–fatigue life-driven tolerance optimization method for the screw, roller, and nut of PRSM. A computational framework for PRSM transmission accuracy, axial backlash, and fatigue life calculation is developed to work on the parametric variation of design parameters including the eccentric, pitch, nominal diameter, and flank angle. Combinations of parametric variation are obtained by the Latin hypercube sampling-based tolerance statistical model to rapidly evaluate PRSM performance risk under operation conditions and tolerance parameters. The optimal tolerance parameters with the expanded width of tolerance interval and the minimum PRSM performance risk probability are obtained using the non-dominated sorting genetic algorithm. Results reveal that PRSM performance risk probabilities change from 89.25 to 68.72% and 58.1 to 56.86%, with 29.94 and 17.38% tolerance interval width increase under the high-precision and heavy-loading operation cases studied, respectively.

Study on the relationship between machining errors and transmission accuracy of planetary roller screw mechanism using analytical calculations and machine-learning model

Wu Hanlin,Wei Peitang,Hu Rui,Liu Huaiju,Du Xuesong,Zhou Pengliang,Zhu Caichao 한국CDE학회 2023 Journal of computational design and engineering Vol.10 No.1

Correlation between machining errors and transmission accuracy of planetary roller screw mechanism (PRSM) plays an important role in tolerance design. In this study, analytical calculations, machine learning, and experimental verification are utilized for exploring the internal correlation between the machining errors and the transmission accuracy of the PRSM. A multi-roller meshing transmission error model is established, which comprehensively considers the eccentric error, nominal diameter error, flank angle error, and cumulative pitch error of the screw, roller, and nut. The importance coefficients of various machining errors on the transmission error are determined using the random forest algorithm. A genetic algorithm-back propagation neural network algorithm-based method is utilized for training the dataset generated via analytical calculations. The results show that the proposed analytical calculation model reflects the alternate meshing characteristics of rollers during the PRSM motion, providing a more accurate prediction of the transmission error than the existing prediction methods. For an actual mean travel deviation, the most significant machining error is the cumulative pitch error of the screw, whereas for the actual bandwidth of useful travel, the most significant machining errors are the eccentric errors of the screw and nut. The proposed prediction formulae for transmission error considering the essential machining errors illustrate reasonable prediction accuracy, with an average error of 10.63% for the actual mean travel deviation and 14.27% for the actual bandwidth of useful travel compared with the experiments, which can effectively support the direct design of PRSM tolerance in engineering practice.