Assessment of the Influence of Tunnel Settlement on Operational Performance of Subway Vehicles

In the realm of subway shield tunnel operations,the impact of tunnel settlement on the operational performance of subway vehicles is a crucial concern.This study introduces an advanced analytical model to investigate rail geometric deformations caused by settlement within a vehicle-track-tunnel coupled system.The model integrates the geometric deformations of the track,attributed to settlement,as track irregularities.A novel“cyclic model”algorithm was employed to enhance computational efficiency without compromising on precision,a claim that was rigorously validated.The model’s capability extends to analyzing the time-history responses of vehicles traversing settlement-affected areas.The research primarily focuses on how settlement wavelength,amplitude,and vehicle speed influence operational performance.Key findings indicate that an increase in settlement wavelength can improve vehicle performance,whereas a rise in amplitude can degrade it.The study also establishes settlement thresholds,based on vehicle operation comfort and safety.These insights are pivotal for maintaining and enhancing the safety and efficiency of subway systems,providing a valuable framework for urban infrastructure management and long-term maintenance strategies in metropolitan transit systems.

Investigation of FRP and SFRC Technologies for Efficient Tunnel Reinforcement Using the Cohesive Zone Model

Amid urbanization and the continuous expansion of transportation networks,the necessity for tunnel construction and maintenance has become paramount.Addressing this need requires the investigation of efficient,economical,and robust tunnel reinforcement techniques.This paper explores fiber reinforced polymer(FRP)and steel fiber reinforced concrete(SFRC)technologies,which have emerged as viable solutions for enhancing tunnel structures.FRP is celebrated for its lightweight and high-strength attributes,effectively augmenting load-bearing capacity and seismic resistance,while SFRC’s notable crack resistance and longevity potentially enhance the performance of tunnel segments.Nonetheless,current research predominantly focuses on experimental analysis,lacking comprehensive theoretical models.To bridge this gap,the cohesive zone model(CZM),which utilizes cohesive elements to characterize the potential fracture surfaces of concrete/SFRC,the rebar-concrete interface,and the FRP-concrete interface,was employed.A modeling approach was subsequently proposed to construct a tunnel segment model reinforced with either SFRC or FRP.Moreover,the corresponding mixed-mode constitutive models,considering interfacial friction,were integrated into the proposed model.Experimental validation and numerical simulations corroborated the accuracy of the proposed model.Additionally,this study examined the reinforcement design of tunnel segments.Through a numerical evaluation,the effectiveness of innovative reinforcement schemes,such as substituting concrete with SFRC and externally bonding FRP sheets,was assessed utilizing a case study from the Fuzhou Metro Shield Tunnel Construction Project.

Hot-deformation kinetics analysis and extrusion parameter optimization of a dilute rare-earth free magnesium alloy

The fundamental research on thermo-mechanical conditions provides an experimental basis for high-performance Mg-Al-Ca-Mn alloys.However, there is a lack of systematical investigation for this series alloys on the hot-deformation kinetics and extrusion parameter optimization. Here, the flow behavior, constitutive model, dynamic recrystallization(DRX) kinetic model and processing map of a dilute rare-earth free Mg-1.3Al-0.4Ca-0.4Mn(AXM100, wt.%) alloy were studied under different hot-compressive conditions. In addition, the extrusion parameter optimization of this alloy was performed based on the hot-processing map. The results showed that the conventional Arrhenius-type strain-related constitutive model only worked well for the flow curves at high temperatures and low strain rates. In comparison, using the machine learning assisted model(support vector regression, SVR) could effectively improve the accuracy between the predicted and experimental values. The DRX kinetic model was established, and a typical necklace-shaped structure preferentially occurred at the original grain boundaries and the second phases. The DRX nucleation weakened the texture intensity, and the further growth caused the more scattered basal texture. The hot-processing maps at different strains were also measured and the optimal hot-processing range could be confirmed at the deformation temperatures of 600~723 K and the strain rates of 0.018~0.563 s^(-1). Based on the optimum hot-processing range, a suitable extrusion parameter was considered as 603 K and 0.1 mm/s and the as-extruded alloy in this parameter exhibited a good strength-ductility synergy(yield strength of ~ 232.1 MPa, ultimate strength of ~ 278.2 MPa and elongation-to-failure of ~ 20.1%). Finally, the strengthening-plasticizing mechanisms and the relationships between the DRXed grain size, yield strength and extrusion parameters were analyzed.

Thermal stability of different texture components in extruded Mg-3Al-1Zn alloy

Grain growth can modify the texture orientation and the fraction of different texture component.The thermal stability of two texture component in an extruded magnesium AZ31 alloy was investigated.Three types samples with different texture distribution were prepared.The results show that normal grain growth takes place in the magnesium AZ31 alloy during annealing at 300℃ and 450℃.But the grain growth does not lead to the strengthening of either texture component.Both the<0002>⊥ED texture and<0002>//ED texture components show good thermal stability,without influence of the texture volume fraction.The two different texture component possess comparable boundary migration ability,so grains of the two texture component consume indifferently the other grains,or are equally consumed during annealing.

Grain size dependence of annealing strengthening of an extruded Mg-Gd-Zn alloy subjected to pre-compression deformation

In this work, pre-strain annealing strengthening(PSAS) effect was investigated in an extruded Mg-1.0Gd-1.5 Zn(wt.%) alloy with respect to different grain sizes. The evolution of microstructures was provided by scanning electron microscopy(SEM), electron backscattered diffraction(EBSD), transmission electron microscopy(TEM) and high-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM) under the initial state, pre-compression, intermediate annealing and re-compression conditions. The obtained results showed a grain size-dependent PSAS effect in the alloy. The sample with larger grain sizes corresponded to a higher strengthening effect, which mainly resulted from a more remarkable hindrance for the growth of existing twins and a larger proportion of activation for the nucleation of new twins. This was closely associated with the increase of back stress and friction stress for twin boundary motion impeded by the larger restraint of dislocations, the higher stress field surrounding solutes and the more Zn segregation. In addition to twinning behavior, Guinier Preston(G.P.) zones on basaldislocations were found after intermediate annealing and provided an extra strengthening by inhibiting the motions of gilding pre-existing dislocations and newly formed ones, but it was independent on the grain size.

Quantitative study on the tension-compression yield asymmetry of a Mg-3Al-1Zn alloy with bimodal texture components

This study demonstrates the yield asymmetry in Mg-3Al-1Zn alloy containing both ND-texture(c-axis//ND(Normal direction))and TD-texture(c-axis//TD(Transverse direction))in a quantitative view.The results showed that the yield asymmetry is strongly dependent on the distribution of bimodal texture components,on the basis of the successful establishment of the quantified relationship between pre-deformation parameters and texture components distribution.It’s meaningful for providing key reference to texture design.Mechanical behavior of bimodal textured Mg alloy under tension and compression was tested.CYS/TYS(compressive yield stress/tensile yield stress)equal to 1 is obtained,implying that the yield asymmetry is eliminated when two textures distribute at specific fractions.The corresponding mechanism for the texture-dependence of tension-compression yield asymmetry is revealed by the analysis of slip/twinning activities and a compound use of the activation stress difference of slip/twinning(ΔStress)and geometrical compatibility factor(m′)between neighboring grains.Balanced activity of{10■2}twinning and a quite similar boundary obstacle effect against slip/twinning transfer under tension and compression accounts for such good symmetry performance.

Modelling the Effect of Initial Grain Size on Dynamic Recrystallization Using a Modified Cellular Automata and a Adaptive Response Surface Method

A modified cellular automata （CA） model of dynamic recrystallization （DRX） and a flow stress-based nucleation parameter identification method have been developed. In the method, the modified CA model, which takes the role of deformation degree on nucleation behavior into consideration, is coupled with an adaptive response surface model （ARSM） to search for the optimum nucleation parameter. The DRX behavior of an oxygen free high conductivity （OFHC） copper with different initial grain sizes has been taken as an example to validate the model. Good agreement is found between the simulated and the experimental results, which demonstrates that the new method can effectively improve the simulation accuracy.

Co-conversion of methanol and n-hexane into aromatics using intergrown ZSM-5/ZSM-11 as a catalyst

The conversion of n-hexane and methanol into value-added aromatic compounds is a promising method for their industrially relevant utilization.In this study,intergrown ZSM-5/ZSM-11 crystals were synthesized and their resulting catalytic performance was investigated and compared to those of the isolated ZSM-5 and ZSM-1I zeolites.The physicochemical properties of ZSM-5/ZSM-l1 intergrown zeolite were analyzed using X-ray diffrac-tion,N2 isothermal adsorption-desorption,the tempera-ture-programmed desorption of ammonium,scanning clectron microscopy,Fourier transform infrared spectra of adsorbed pyridine,and nuclear magnetic resonance of 27AI,and compared with those of the ZSM-5 and ZSM-11 zeolites.The catalytic performances of the materials were evaluated during the co-feeding reaction of methanol and n-hexane under the fixed bed conditions of 400℃,0.5 MPa(N2),methanol:n-hexane=7:3(mass ratio),and weight hourly space velocity=1 h 1(methanol).Com-pared to the ZSM-5 and ZSM-11 zeolites,the ZSM-5/ZSM-11 zeolite exhibited the largest specific surface area,a unique crystal structure,moderate acidity,and suitable Brensted/Lewis acid ratio.The evaluation results showed that ZSM-5/ZSM-11 catalyst exhibited better catalytic reactivity than the ZSM-5 and ZSM-11 catalysts in terms of methanol conversion rate,n-hexane conversion rate,and aromatic selectivity.The outstanding catalytic property of the intergrown ZSM-5/ZSM-11 was attributed to the enhanced diffusion associated with its unique crystal.structure.The benefit of using zeolite intergrowth in the co-conversion of methanol and alkanes offers a novel route for future catalyst development.

Deployment and demonstration of wide area monitoring system in power system of Great Britain

The creation of a suitable wide area monitoring system(WAMS) is widely recognized as an essential aspect of delivering a power system that will be secure,efficient and sustainable for the foreseeable future. In Great Britain(GB), the deployment of the first WAMS to monitor the entire power system in real time was the responsibility of the visualization of real time system dynamics using enhanced monitoring(VISOR) project. The core scope of the VISOR project is to deploy this WAMS and demonstrate how WAMS applications can in the near term provide system operators and planners with clear, actionable information. This paper presents the wider scope of the VISOR project and the GB wide WAMS that has been deployed. Furthermore, the paper describes some of the WAMS applications that have been deployed and provides examples of the measurement device performance issues that have been encountered during the project.

Finite element modelling on microstructure evolution during multi-pass hot compression for AZ31 alloys using incremental method

Based on the principle of piecewise linearization, the incremental forms of microstructure evolution models were integrated into the thermo-mechanical coupled finite element（FE） model to simulate nonlinear microstructure evolution during multi-pass hot deformation. This is an unsteady-state deformation where dynamic recrystallization（DRX）, meta-dynamic recrystallization（MDRX）, static recrystallization（SRX） and grain growth（GG） take place during hot deformation or deformation interval. The distributions of deformation and microstructure for cylindrical AZ31 sample during single-pass and double-pass hot compressions were quantitatively calculated and compared with the metallographic observation. It is shown that both the deformation and microstructure are non-uniformly distributed due to the presence of friction between the die and the flat end of sample. The average grain size and its standard deviation under the double-pass hot compression are slightly smaller than those under single-pass compression.The simulated average grain sizes agree well with the experiments, which validates that the developed FE model on the basis of incremental forms of microstructure evolution models is reasonable.

Drag Effects of Solute and Second Phase Distributions on the Grain Growth Kinetics of Pre-Extruded Mg-6Zn Alloy

In order to control the grain size during hot forming,grain growth behavior of a pre-extruded Mg-6Zn magnesium alloy and its correlation with solute and second phase distribution were investigated.Isothermal annealing was conducted on a Gleeble-1500 thermo-mechanical simulator.The mean grain size Dg of each annealed specimen was measured by the quantitative metallography technique.The grain growth kinetics of the Mg-6Zn alloy annealed at 473-623 K was obtained as Dg^4- Dg0^4=2.25 ×10^11 exp（-95450）by the least square linear regression method.The deviation of grain growth exponent n = 4 from the theoretical value of 2 may be attributed to the presence of solute zinc and second phases which will retard the boundary migration.Microscopic observations show that the non-uniform distribution of grain size for samples pre-extruded or annealed at low temperatures is closely related to the non-uniform distribution of fine and dispersed second phases but not to the non-uniform distribution of solute zinc.This indicates that second phase pinning effect plays an important role in microstructure refinement.