Deformation-based longitudinal equivalent stiffness beam model for shield tunnel and its application in seismic deformation method

In the longitudinal seismic deformation method for shield tunnels,one of the most commonly used is the longitudinal equivalent stiffness beam model(LES)for simulating the mechanical behavior of the lining.In this model,axial deformation and bending deformation are independent,so the equivalent stiffness is a constant value.However,the actual situation is that axial deformation and bending deformation occur simultaneously,which is not considered in LES.At present,we are not clear about the effect on the calculation results when axial deformation and bending deformation occur simultaneously.Therefore,in this paper,we improve the traditional LES by taking the relative deformation as a load and considering the coordinated deformation of axial and bending degrees of freedom.This improved model is called DNLES,and its neutral axis equations are an explicit expression.Then,we propose an iterative algorithm to solve the calculation model of the DNLES-based longitudinal seismic deformation method.Through a calculation example,we find that the internal forces based on LES are notably underestimated than those of DNLES in the compression bending zone,while are overestimated in the tension bending zone.When considering the combined effect,the maximum bending moment reached 13.7 times that of the LES model,and the axial pressure and tension were about 1.14 and 0.96 times,respectively.Further analysis reveals the coordinated deformation process in the axial and bending directions of the shield tunnel,which leads to a consequent change in equivalent stiffness.This explains why,in the longitudinal seismic deformation method,the traditional LES may result in unreasonable calculation results.

Real-time Tire Parameters Observer for Vehicle Dynamics Stability Control

The performance of the vehicle dynamics stability control system（DSC） is dominated by the accurate estimation of tire forces in real-time.The characteristics of tire forces are determined by tire dynamic states and parameters,which vary in an obviously large scope along with different working conditions.Currently,there have been many methods based on the nonlinear observer to estimate the tire force and dynamic parameters,but they were only used in off-line analysis because of the computation complexity and the dynamics differences of four tires in the steering maneuver conditions were not considered properly.This paper develops a novel algorithm to observe tire parameters in real-time controller for DSC.The algorithm is based on the sensor-fusion technology with the signals of DSC sensors,and the tire parameters are estimated during a set of maneuver courses.The calibrated tire parameters in the control cycle are treated as the elementary states for vehicle dynamics observation,in which the errors between the calculated and the measured vehicle dynamics are used as the correcting factors for the tire parameter observing process.The test process with a given acceleration following a straight line is used to validate the estimation method of the longitudinal stiffness;while the test process with a given steering angle is used to validate the estimated value of the cornering stiffness.The ground test result shows that the proposed algorithm can estimate the tire stiffness accurately with an acceptable computation cost for real-time controller only using DSC sensor signal.The proposed algorithm can be an efficient algorithm for estimating the tire dynamic parameters in vehicle dynamics stability control system,and can be used to improve the robustness of the DSC controller.

Evaluation of Myocardial Strain and Aortic Elasticity in Patients with Bicuspid Aortic Valve

This study evaluated the myocardial strain and aortic elasticity in patients with bicuspid aortic valve（BAV） and then investigated the relation between them. Thirty-nine patients（30 males; mean age 44±19 years; range 6 to 75 years） with BAV were recruited as BAV group, and 29 age- and sex-matched healthy controls（21 males; mean age 42±11 years; range 20 to 71 years） served as control group. Aortic strain, distensibility and stiffness index were derived using M-mode echocardiography. Left ventricular global myocardial strain was acquired with speckle-tracking echocardiography. Correlation between aortic elasticity and myocardial strain was also analyzed. The results showed that aortic stiffness was higher（17.5±14.0 vs. 5.3±2.7, P〈0.001）, and aortic strain（4.9±4.7 vs. 11.0±4.1, P〈0.001） and distensibility（1.8±2.1 vs. 3.7±1.6, P〈0.001） were lower significantly in BAV group than in control group. Global circumferential strain（–19.1±4.2 vs. –22.5±3.7, P〈0.001）, radial stain（29.8±14.9 vs. 38.0±8.8, P〈0.001） and longitudinal stain（–18.4±3.4 vs. –20.8±3.5, P〈0.001） were significantly lower in BAV group than in control group. There was weak association between aortic elasticity and myocardial strain. These findings indicated BAV patients manifest reduced myocardial strain which had weak relationship with aortic elastic lesion.

Analytical and numerical analysis on the torsional performance of elliptically deformed tunnels in the longitudinal direction

Segmental lining structures constructed by shields/tunnel boring machines are often subjected to uneven longitudinal cross-section torsion as a result of eccentric external loads,which is extremely adverse to tunnel safety but has not received sufficient attention for a long time.To figure out the torsional performance of segmental tunnels,it is essential to assess the longitudinal torsional stiffness and active-torsion-rejection capability of a segmented tunnel.The aim of the paper is to derive an analytical solution to the longitudinal torsional stiffness of a segmental tunnel with existing elliptical deformation.The longitudinal torsional stiffness under different internal force combinations is deduced considering the longitudinal axial force and bending moment based on the equivalent continuous model and force balance equation.The validity of the analytical solution is verified by comparing it with finite element method results.Then,a parametric analysis,using the new analytical solution,is included to investigate the effect of the key parameters on torsional behaviors,including the segment size,the bolt size and the transverse bending stiffness,etc.It is found that:(1)the longitudinal torsional stiffness efficiency(LTSE)of the segmental tunnel decreases with the rise of segment thickness to diameter ratio but increases with the ring width to diameter ratio;(2)the LTSE reduces with the increase of the effective shear length but rises with the diameter of bolts;(3)the LTSE increases rapidly with the ratio of compression-torsion or bending-torsion.Furthermore,the envelope curve of the critical load(N0,M0)for a tunnel to actively resist a certain internal torque is given.The proposed solution can be easily utilized to determine the longitudinal torsional stiffness of segmental tunnels and is an effective tool for tunnel design and maintenance.

Mechanical design of a low β superconducting elliptical cavity for CSNS-II

Background A lowβsuperconducting elliptical cavity was designed for the China Spallation Neutron Source phase II project(CSNS-II).Methods The method to improve the mechanical stability of the lowβsuperconducting elliptical cavity was introduced,and the corresponding mechanical design was given.The software COMSOL Multiphysics and ANSYS APDL were used to calculate the static Lorentz force detuning factor k_(L)(LFD)and the helium pressure sensitivity factor k_(p)(DFDP)of the bare cavity,which were−4.71 Hz(MV/m)^(−2) and−21.1 Hz/mbar,respectively.The double-ring stiffeners reinforcement scheme was adopted.Results The radii of the double-ring stiffeners were 70 and 135 mm,respectively.The structure design of the helium vessel of the cavity was given.The following is the mechanical parameters of the reinforced cavity,the tuning sensitivity is 199.8 kHz/mm,longitudinal stiffness is 4.76kN/mm,k_(L) and k_(p) were−1.39 Hz(MV/m)^(−2) and 4.67 Hz/mbar,respectively,which met the operating requirements.The tuning sensitivity and stiffness of the reinforced cavity with different wall thicknesses were optimized,and the final wall thickness was selected as 4 mm.Conclusion The mechanical design of CSNS-II 648 MHz five-cell lowβsuperconducting elliptical cavity was introduced systematically in the paper.The LFD,DFDP,and the maximum surface stress of the cavity were reduced by optimizing the cavity wall thickness and the position of the double-ring stiffeners.The reinforced cavity met operational requirements.