Haidong Yu

Dynamic characteristic analysis of TBM tunnelling in mixed-face conditions

Abstract In this paper, by taking into account the periodically varying mesh stiffness in multiple pinions transmission and the speed–torque characteristics of variable frequency motor drives, the dynamic model for the revolving system of tunnel boring machine (TBM) has been established. Based on the soft ground/hard rock assumption of mixed-face conditions and the analysis of cutting force on each disc cutter and each drag bit, the time-varying excavation torque on the TBM cutterhead in mixed-face tunnelling is obtained. The dynamic excavation torque and cutterhead rotation speed are discussed and compared for TBM tunnelling in several typical mixed-face conditions, which are characterized by the area percentage of soft ground on the excavation face and the uniaxial compressive strength (UCS) of rock. The results show that the excavation torque may run up to a critical value and fluctuate greatly in extremely adverse excavation environments, which may lead to an unexpected TBM stoppage and even a catastrophic failure of the drive motor. To decrease the penetration per revolution in time through applying a lower advance velocity and a higher cutterhead revolution will significantly reduce the excavation torque and effectively avoid such situations.

Dynamic model and behavior of viscoelastic beam based on the absolute nodal coordinate formulation

Viscoelastic material is widely used in mechanisms and its properties have a great influence on the dynamic behaviors of structures. In this study, a modified viscoelastic constitutive model is developed by introducing the nonlinear strain–displacement relation of materials to the classical Kelvin–Voigt model. The new model can be implemented into the finite element absolute nodal coordinate formulation directly, which can be applied to investigate the large rotation and the large deformation problem. The mass matrix and the viscoelastic stiffness matrix of a two-dimensional viscoelastic beam with shear deformation are derived with the absolute nodal coordinate formulation. The dynamic model of the beam is presented based on Newton equations. The dynamic equations are transformed from a set of differential algebraic equations to a set of first-order ordinary differential equations, which are calculated by using the fourth-order explicit Runge–Kutta method. A free falling flexible pendulum is employed to study the correlation between the dynamic behaviors of structures and the mechanical behaviors of materials. The results indicate that the modified constitutive model is able to describe the nonlinear deformation behavior of the structure, which undergoes large rotation and large deformation. The flexible deformation of the beam is related to the elastic modulus, the density and the viscosity coefficient of the material. The viscous behavior of material reduces the elastic deformation of the structure during its movement, which is beneficial to the kinematic accuracy of the multibody system.

Analysis for Dynamic Load Behavior of Shield Thrust System Considering Variable Boundary Constraints

In this paper, the load transmission model of the shield thrust system is established taking into account the variable boundary constraints between the shield skin and the surrounding strata, which is obtained based on the finite element methods. The results show that the resisting moment on the shield skin from the geologic layer has a nonlinear relationship with the bending moment loads on the cutterhead when the material behavior of the strata is modeled by an elasto-plastic Mohr-Coulomb model. The dynamic load behavior of the shield thrust system is significantly influenced by the variable shield-strata boundary constraints, which may cause incorrect load predictions of the hydraulic thrust system and consequent snake-like motions of the shield machine.

Compliant assembly variation analysis of sheet metal with shape errors based on primitive deformation patterns

In the compliant assembly of sheet metal, the performance of the product is highly related to the shape errors of surface. Therefore, variation analysis is generally required to reveal the influence principle of the components’ manufacturing variations on the surface shape errors of the product. The traditional compliant assembly variation analysis methods were used to build a variation propagation model based on characteristic points between parts and product without considering shape errors. In this paper, a new method based on primitive deformation patterns considering shape errors is proposed. The primitive deformation patterns of part can be obtained by natural mode analysis of ideal part, and the primitive deformation patterns of product can be calculated by the dynamic substructure method. The initial shape errors of part are decomposed into the individual contributions of primitive deformation patterns. Considering the force equilibrium relationship in assembly process, a variation propagation model is built based on the primitive deformation patterns between parts and product. This model reveals variation propagation in assembly process by the basic element of dimension error field (deformation patterns), which is convenient for evaluating the assembly quality. A case study on a panel parts assembly process is presented to demonstrate the proposed variation analysis method. The results show the effectiveness and accuracy of the proposed method compared with the method of finite element analysis conducted in commercial software ABAQUS.

New stiffened plate elements based on the absolute nodal coordinate formulation

In this study, several new stiffened plate element models are proposed based on the absolute nodal coordinate formulation. The stiffened plate elements with different geometrical continuity conditions and performances are developed by a full parametrized plate element and three different beam elements of absolute nodal coordinate formulation. The effect of stiffener is incorporated by internally constraining the stiffener displacement fields to the relevant plate displacement fields. The displacement compatible conditions of plate and stiffener are investigated to obtain the transformation matrix of nodal coordinates. The mass and stiffness of a stiffener is reflected at all the nodes of the plate element in which it is placed. Accordingly, the stiffener can be positioned anywhere within the plate element along lines of local coordinates and need not necessarily be placed on nodal lines, which gives a great flexibility in the choice of mesh size. The stiffened plate elements also achieve a better continuity condition with the slope constraint equations. Static, dynamic, and free vibration analyses are conducted to validate the proposed elements and to study the performance of the stiffeners. The results show that the new elements can be applied to describe mechanical behaviors of stiffened structures in both static and dynamic situations. The effects of the dimension of cross section and the number of stiffeners are also numerically investigated for both linear and nonlinear deformation problems.

Experimental and numerical analysis on load-sharing behavior of gear set with simultaneously actuated pinions

The load-sharing behavior is important for the gear set actuated by multiple parallel pinions to avoid the excessive wear and fatigue failure. A lumped parameter dynamic model of gear set driven by three pinions simultaneously is established, in which their support stiffness and mounted positions of gear pairs are considered. A load-sharing index is defined as the ratio of the maximal and the minimal transmission loads of three gear pairs. The load-sharing behavior of gear set is numerically investigated with four distributions of three pinions. A corresponding testing device was presented. The load-sharing behavior of gear set with various mounted positions of three pinions was studied experimentally and compared with numerical results. The similar behavior denotes that the load transmission of various gear pairs has close relation with the mounted positions of pinions. Then, the load-sharing behavior of the gear set driven by three pinions is discussed in which the contact ratios and the support stiffness of pinions are considered. The results show that the increase of the contact ratios and the decrease of the support stiffness may worsen the load-sharing behavior of gear set actuated by multiple pinions. Suitable mechanical parameters of gear systems are important for the load transmission and dynamic behavior of multiple gear pairs.

Dynamical Behavior of Redundant Thrusting Mechanical System in Shield Machines with Various Grouping Strategies

The thrusting system of shield machines is consisted of multiple hydraulic cylinders which are usually divided into four groups. The dynamical behavior of shield is closely dependent on the grouping strategies. In this context, the thrusting system is equivalent as a redundant actuating parallel mechanism. Two grouping strategies are used as 4147 and 4345 for sixteen hydraulic cylinders. The dynamical model of shield was established by using Newton-Euler method. The dynamical behavior is investigated considering the two grouping methods. The results show that the fluctuations of velocities and displacements of shied are obviously different for the two grouping strategies when the fraction of soft soil on the excavating face is changed. The grouping strategies should be determined based on the complex geological structures in order to reduce the blockage accidents.

The Reconfiguration Design of Redundant Thrust of Shields Excavating in Various Geologic Conditions

The loads on the cutterhead will vary with the mechanical properties and the compositions of geologic structures on the excavation face. It is necessary that the reconfiguration design of the redundant thrust system for various geologic formations is conducted to improve the load compliance ability effectively, which is beneficial to decrease the excessive wear and the other accidents. In this paper, a 4-bar parallel manipulator is established in terms of the control characteristic of the redundant thrust system of the shield machines. The location parameters of legs on the platform and the base are used as the variables to obtain the force transmission matrix between the limbs and the platform. The force transmission behavior is studied when the shields excavate in the alignment direction. Based on the cutting principle, the total bending moment model exerted on the cutterhead is proposed. The behavior of bending moments during excavating in the various geologic formations is studied. The correlation between the bending moments and the configuration is discussed. The results show that the configurations of the thrust manipulator may be selected in terms of the geologic structures. It is useful for the compliance design of the thrust system of shields.

A new higher-order locking-free beam element based on the absolute nodal coordinate formulation

The beam elements based on the absolute nodal coordinate formulation are widely used in large deformation and large rotation problems. Some of them lead to shear and Poisson locking problems when the continuum mechanics method is employed to deduce the generalized elastic force of the element. To circumvent these locking problems, a new higher-order beam element is proposed that may capture the warping and non-uniform stretching distribution of the cross-section by introducing the trapezoidal cross-section deformation mode and increasing the order of interpolation polynomials in transverse direction. The curvature vectors are chosen as the nodal coordinates of the new element that improve the continuity condition at the element interface. Static and dynamic analyses are conducted to investigate the performance of the new element. Poisson locking phenomena may be eliminated effectively for the new element even when Poisson’s ratio is greater than zero. Meanwhile, the distortion deformation of the cross-section may be described directly. The new element has a better convergence performance compared with the spatial absolute nodal coordinate formulation beam element for that shear locking issue is eliminated. The results also show that the new element fulfills energy conservation and may be applied to the dynamics of both straight and initial curved structures with large deformation.

Compliant assembly variation analysis of thin-walled structures based on the absolute nodal coordinate formulation

Purpose Thin-walled structures inevitably always have manufacturing deviations, which affects the assembly quality of mechanical products. The assembly quality directly determines the performances, reliability and service life of the products. To achieve the automatic assembly of large-scale thin-walled structures, the sizing force of the structures with deviations should be calculated, and its assembling ability should be studied before assembly process. The purpose of this study is to establish a precise model to describe the deviations of structures and to study the variation propagation during assembly process. Design/methodology/approach Curved thin-walled structures are modeled by using the shell element via the absolute nodal coordinate formulation. Two typical deviation modes of the structure are defined. The generalized elastic force of shell elements with anisotropic materials is deduced based on a continuum mechanics approach to account for the geometric non-linearity. The quasi-static method is introduced to describe the assembly process. The effects of the deviation forms, geometrical parameters of the thin-walled structures and material properties on assembly quality are investigated numerically. Findings The geometric non-linearity of structure and anisotropy of materials strongly affect the variation propagation and the assembly quality. The transformation and accumulation effects of the deviations are apparent in the multiple assembly process. The constraints on the structures during assembly can reduce assembly deviation. Originality/value The plate element via the absolute nodal coordinate formulation is first introduced to the variation propagation analysis. Two typical shape deviation modes are defined. The elastic force of structures with anisotropic materials is deduced. The variation propagation during the assembly of structures with various geometrical and material parameters is investigated.