Unsymmetrical load effect of geologically inclined bedding strata on tunnels of passenger dedicated lines

In order to study the unsymmetrical load effect in geological bedding strata for the Muzhailing tunnel on the Lanzhou-Chongqing passenger dedicated line in China, we investigated the deformation, mechanical response and pressure of the surrounding rock and the mechanical characteristics of bolts of the tunnel. The results suggest that open zones appear at arch and invert where joints open up, when layered stratum is horizontal, or when the dip angle of in- clined bedding is small. Open zones occur perpendicular to a joint. The failure mode is bending disjunction at the arch tain shear displacement, and lead to obvious geological bedding unsymmetrical load. The failure mode is shear damage. For the joint dip angle in the range of 75-90°, the failure mode is flexural crushing at the wall and vertical shear rup- ture above the arch. The restraining effect of two sides weakens for vertical dip. On the whole, shear failure instabilitytrend would occur and the tunnel collapses evenly. When the angle between the bolt and structure plane is greater than 23°, bolts can enhance the shearing stiffness of joint plane. Unfortunately, in the general purpose graph of tunnel for 250 km/h of passenger dedicated lines, the bolts have equal length and spacing. The rationale behind this is worthy offurther study. For inclined bedding, the surrounding rock pressure at the left wall is more than that at the right wall. In addition, lining is likely to be damaged at left shoulder and side wall. With the dip angle increasing, the unsymmetrical load gradually achieves symmetry. Asymmetry design for support is recommended to reduce the unsymmetrical load on lining disturbed by excavation.

Study on the dynamic behavior of herringbone gear structure of marine propulsion system powered by double-cylinder turbines

Propulsion systems powered by double-cylinder turbines(DCT)are widely used in large-scale ships.However,the nonlinear instability leads to hidden dangers associated with the safe operation,and there is a lack of theoretical and systematic research on this problem.Based on the gear transmission principle and non-Newtonian thermal elastohydrodynamic lubrication(EHL)theory,a torsional model of a two-stage herringbone system forced by unsymmetrical load is established.The nonlinear and time-varying factors of meshing friction,meshing stiffness,and gear pair backlash are included in the model,and multiple meshing states,including single-and double-sided impact are studied.New nonlinear phenomena of the dynamic system are explored and the effects of the unsymmetrical load on the system stability are quantified.The results indicate that the stability of the gear system is improved,and that the back-sided impact gradually disappears with the increases of load ratio between the two inputs and the input load value.Furthermore,it is found that the gear pairs on the low-load side experience more severe vibration than those on the high-load side.Finally,the stability of the gear pairs decreases along the power transmission path of the multistage gear system.The results of this research will be useful when making predictions of the stability of such systems and in the optimization of the load parameters.