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The dynamic performance of railway vehicles is significantly impacted by sudden-changed aerodynamic loads. To investigate the dynamic performance of high-speed trains (HSTs) under tunnel and crosswind environments considering the car-body flexibility, an intensive study is conducted. First, a train–track interaction dynamic model with a flexible car body is established in SIMPACK for dynamic response analysis. Concurrently, an aerodynamic model for calculating the distribution of aerodynamic loads is found in FLUENT to determine forces and moments applied to each part of the car body. Then, the two models are coupled utilizing a co-simulation method developed based on the User Data Protocol (UDP). Finally, a case study is carried out, involving a train passing through tunnels subjected to crosswinds. The results reveal that the distribution of aerodynamic loads on the car-body affected by crosswind is time-variant and non-even. Interestingly, the dynamic simulation results are almost unaffected by the method used to allocate the loads on the car body. Variations in the aerodynamic loads affected by crosswinds lead to flexible first-order diamond mode vibration of the car body at around 8.5Hz when exiting the tunnel. As the crosswind speed continues to increase, vibrations at frequencies of 18.2Hz and 24.2Hz will be enhanced, corresponding to the bending mode and combined mode of the car body. However, similar flexible vibrations are insignificant when the vehicle enters the tunnel. In addition, the vertical wheel–rail interaction obtained by the dynamic model with a rigid car body is slightly greater than that with a flexible car body. [ABSTRACT FROM AUTHOR]

The support pressure on an excavation surface is a critical factor in the ground deformation and excavation stability of a submarine shield tunnel. The shield tail gap and the disturbance zone of grouting behind the tunnel wall are also important influencing factors. However, the effects of these factors on excavation stability are difficult to quantify. Consequently, a homogeneous, elastic, and annular equivalent layer is employed to simulate the thin layer behind the tunnel wall. Using COMSOL Multiphysics software, the effects of the water level depth, the thickness of the equivalent layer, the diameter of the shield tunnel, and the internal friction of soil and tunnel burial depth on the excavation deformation and ground surface subsidence of a submarine tunnel are considered with regard to the fluid–solid coupling effect. The result show that the surface subsidence of the case with respect to the fluid–solid coupling effect and the equivalent layer is larger than that without interstitial fluid and the equivalent layer, indicating that the present model can better simulate the stability of tunnel excavation. Therefore, it is important to consider the impact of the fluid–solid coupling effect and the equivalent layer on the deformation of the excavation face and ground surface subsidence. [ABSTRACT FROM AUTHOR]

The support pressure on an excavation surface is a critical factor in the ground deformation and excavation stability of a submarine shield tunnel. The shield tail gap and the disturbance zone of grouting behind the tunnel wall are also important influencing factors. However, the effects of these factors on excavation stability are difficult to quantify. Consequently, a homogeneous, elastic, and annular equivalent layer is employed to simulate the thin layer behind the tunnel wall. Using COMSOL Multiphysics software, the effects of the water level depth, the thickness of the equivalent layer, the diameter of the shield tunnel, and the internal friction of soil and tunnel burial depth on the excavation deformation and ground surface subsidence of a submarine tunnel are considered with regard to the fluid–solid coupling effect. The result show that the surface subsidence of the case with respect to the fluid–solid coupling effect and the equivalent layer is larger than that without interstitial fluid and the equivalent layer, indicating that the present model can better simulate the stability of tunnel excavation. Therefore, it is important to consider the impact of the fluid–solid coupling effect and the equivalent layer on the deformation of the excavation face and ground surface subsidence.

This paper analyses the deformation and force behavior of a wood-piled island cofferdam based on the principle of equivalent bending stiffness. The horizontal deformation and bending moments in wood piles and the axial stress in tension bars on top of piles were both analyzed by the finite difference (FD) method. Except for the analysis of the cofferdam construction process, the influence of the pile length, the dam width, the tension bar interval, and the pile interval, among the commonly adopted parameters, were detailly examined in numerical simulations. In addition, a reinforced wood-piled cofferdam model by steel pipe piles has been established to quantify the effect of reinforcement. It was found that the dewatering inside the cofferdam was detrimental to cofferdam stability. The pile deformation reached maxima (roughly 0.6% of the pile length) at solidifying stage after dewatering. The changing trend of the cofferdam structure force within a safe district was consistent with the displacement. The dam width had a vital effect on the stability of the cofferdam, especially on the horizontal deformation. The steel pipe pile reinforcement scheme performed better in further deformation control, providing a new idea for island-type cofferdams with rigorous structural deformation control. [ABSTRACT FROM AUTHOR]

Three-dimensional stability analysis of soil slopes remains a hot topic in the field of geotechnical engineering. Considering the fluid–solid coupling effect, this study performs a number of numerical analyses on the stability of a 3D excavation slope located in the Wuxi Taihu Tunnel, China. Three typical cases of the issued slope are investigated, i.e., the slope at the initial state, with the water-stop curtain, and with both the water-stop curtain and concrete-sprayed layer. The shear strength reduction method was adopted to determine the factor of safety (FOS) of the slope. The distributions of pore pressures and wetting lines, the horizontal and vertical displacements, and the critical slip surface are presented. The results indicate that the water-stop curtain can prevent the groundwater seepage effectively. The water-stop curtain and concrete-sprayed layer are effective in restraining the slope deformation, altering the critical slip surface, and improving the slope safety.

Under the action of earthquake, the dynamic interaction between the bridge pier and the surrounding water has a great impact on the dynamic response of the bridge structure. With a continuous sea-crossing beam bridge as an example, this paper studied the stochastic optimization of the parameters of nonlinear viscous damper and its damping performance under the fluid-solid coupling effect of waves and piers. In this study, a 2-degree-offreedom bridge analysis model considering the fluid-solid coupling effect was constructed, and a nonlinear viscous damper was set in the model and subject to equivalent linearization according to the equivalent energy consumption criterion. Then on this basis, with minimizing the variance of the displacement of pier top as the target, this study applied the Lyapunov method to optimize the parameters of the damper, and explored its impact on the seismic response of the bridge and the damping performance considering the fluid-solid coupling effect. The research results showed that the fluid-solid coupling effect changed the dynamic characteristics of the bridge and increased its seismic response, and the viscous damper can effectively reduce the seismic response of the sea-crossing bridge and improve its damping performance. [ABSTRACT FROM AUTHOR]

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Ice jams and ice dams in rivers will cause significant rises of water levels. Under extreme conditions, the ice flooding during winter or early spring may occur. In this paper, by considering the fluid-solid coupling effect caused by the water and the ice cover, the mechanisms of the mechanical breakup of the river ice cover are studied. A formula is obtained for determining whether or not the mechanical breakup process would happen under the hydraulic pressure of the flow. Combined with the hydraulic model under the ice covered flow, a numerical model is built and the interaction between the discharge, the hydraulic pressure under the ice cover and the date for the mechanical breakup of the river ice cover is simulated. The simulated results of the dates for the mechanical breakup of the river ice cover agree very well with the field observations of the breakups of the river ice cover in the Hequ Reach of the Yellow River. Therefore, the numerical model might serve as a good preliminary step in studying the breakup of the river ice-cover, evidencing many important parameters that affect the ice-cover process. [ABSTRACT FROM AUTHOR]