Analysis on Ground Surface Deformation and Influence of Construction Parameters Caused by Two Different Shield Machines in Double-tube Tunnelling北大核心CSCD

Based on a shield-driven running tunnel project of Hangzhou Metro Line 2, this paper carries out field measuring of the ground surface deformation caused by two different shield machines in double-tube tunnelling in soft soil areas, obtains the laws of the surface deformation caused by shield-driven double-tube tunnelling and verifies the applicability of the modified Peck formula to double-tube tunnelling. The results show that in soft soil areas the impacts on ground surface deformation caused by different shield construction parameters in the previously and subsequently excavated tunnels are different, while the surface deformation changes sharply before and after the shield machine passing through the cutting face, and a rebound phenomenon occurs when the shield tail passes through the cutting face due to the influence of the grouting; The cutterhead torque of the shield machine in soft soil areas can be composed of five calculation factors, and the calculation results are in good agreement with the measured values. The larger the opening rate of the shield cutterhead is, the larger the average torque value will be, the higher the percentage of large ground loss rate will be, and the larger the maximum ground surface settlement will be; The ratio of cutterhead torque T to mucking volume per ring Q is used as the control parameter for analyzing the ground surface settlement, and a certain positive correlation between the ratio and the surface settlement value is determined, the smaller the cutterhead opening rate is, the more accurate the fitting results will be. © 2022, Editorial Office of "Modern Tunnelling Technology". All right reserved.     

Multiaxial stress creep rupture mechanisms of AZ31 magnesium alloy

The maximum principal stresses, von Mises effective stresses and principal facet stresses at the time of creep rupture were compared in uniaxial, biaxial, and triaxial stress states for AZ31 magnesium alloy. The creep rupture of this alloy was experimentally controlled by cavitation, which was the result of a low damage tolerance, λ. Creep deformation could be correlated with the von Mises effective stress parameter. The failure-mechanism control parameter governing the stress state coincided with the experimental results of the rupture of the materials under multiaxial stress states. Finally, the theoretical prediction based on constrained cavity growth and continuous nucleation agreed with the experimental rupture data to within a factor of three.     

Effect of rear slant angle on vehicle crosswind stability simulation on a simplified car model

It is important to know the effect of the aerodynamic forces and moments on driving stability because it is responsible for the excitation and influences the response of the vehicle. The purpose of this paper is to study the effect of rear slant angle of a surface vehicle on crosswind sensitivity for stability analysis. The vehicle mathematical model used to conduct a dynamic simulation was based on a simple reduced order lateral dynamics of sideslip and yaw rate motion coupled with aerodynamics model. The intention here is to compare the effect of rear slant angles response to crosswind and to rank the crosswind sensitivity ratings. The aerodynamic loads are defined as the function of the aerodynamic derivatives from the static wind tunnel tests. Result shows a 20° rear slant angle demonstrates the highest rating of crosswind sensitivity, while zero degree slant exhibits the least.     

Propagating buckles in corroded pipelines

Rigid–plastic solutions for the steady-state, quasi-static buckle propagation pressure in corroded pipelines are derived and compared to finite element predictions (ABAQUS). The corroded pipeline is modeled as an infinitely long, cylindrical shell with a section of reduced thickness that is used to describe the corrosion. A five plastic hinge mechanism is used to describe plastic collapse of the corroded pipeline. Closed-form expressions are given for the buckle propagation pressure as a function of the amount of corrosion in an X77 steel pipeline. Buckles that propagate down the pipeline are caused by either global or snap-through buckling, depending on the amount of corrosion. Global buckling occurs when the angular extent of the corrosion is greater than 90°. When the angular extent is less than 90° and the corrosion is severe, snap-through buckling takes place. The buckle propagation pressure and the corresponding collapse modes also compare well to finite element predictions.     

One city,three models: comparison of land‐use/transport policy simulation models for Dortmund

The paper reports on simulation experiments conducted by the International Study Group on Land‐Use/Transport Interaction (ISGLUTI) for the metropolitan region of Dortmund in the Federal Republic of Germany. Three land‐use/transport simulation models were applied to the Dortmund region: the DORTMUND model developed at the University of Dortmund, the LILT model being used at University College London and the MEPLAN package developed by Marcial Echenique & Partners in Cambridge. The three models are briefly characterized and their ex‐post forecasts are compared with the actual development of the region. The final section of the paper compares how the three models respond to a common set of assumptions and policies from the fields of land‐use control, traffic management and transport investment. The differences in model response give insights into the validity of the theoretical foundations and internal structure of the models.     

Damage detection in offshore structures using neural networks

This paper discusses the damage detection in offshore jacket platforms subjected to random loads using a combined method of random decrement signature and neural networks. The random decrement technique is used to extract the free decay of the structure from its online response while the structure is in service. The free decay and its time derivative are used as input for a neural network. The output of the neural network is used as an index for damage detection. It has been shown that function N is effective in damage detection in the members of an offshore structure. Experimental studies conducted on a reduced model for a real jacket structure with geometrical scale of 1:30 are used. The applied loads were random loads. Two different load spectra were used: White noise, and Pierson-Moskowitz.     

Improving pollutant emissions in diesel engines for heavy-duty transportation using retarded intake valve closing strategies

A combined theoretical and experimental study has been carried out to determine the real potential of reducing pollutant emissions in a HD diesel engine by means of retarding the intake valve closing. The effects produced by this alteration of the basic operation cycle have been examined by a preliminary modelling study, and from the obtained results, a modified camshaft was manufactured with a delayed intake valve closing of 60 crank angle degrees. Single-cylinder engine tests were carried out with this modified camshaft, and the emissions and fuel consumption were recorded. The results showed that the retarded intake valve closing can enhance the premixed combustion phase, and thus simultaneously reduce soot and NOx emissions. Moreover, the combustion process attained is extremely tolerant to exhaust gas recirculation, and by adoption of this measure, Euro-5 emissions limits can be achieved at the tested conditions without after-treatment.     

Trip distribution for limited destinations: a case study for grocery shopping trips in the Netherlands

In this paper, we introduce a new trip distribution model for destinations that are not homogeneously distributed. The model is a gravity model in which the spatial configuration of destinations is incorporated in the modeling process. The performance was tested on a survey with reported grocery shopping trips in the Dutch city of Almelo. The results show that the new model outperforms the traditional gravity model. It is also superior to the intervening opportunities model, because the distribution can be described as a function of travel costs, without increasing the computational time. In this study, the distribution was described by a simple function of Euclidean distance, which provides a good fit to the survey data. The slope of the distribution is quite steep. This shows that most trips are made to nearby supermarkets. However, a significant fraction of trips, mainly made by car, still goes to supermarkets further away. We argue that modeling of these trips by the new method will improve traffic flow predictions.