Model test on dynamic characteristics of invert and foundation soils of high-speed railway tunnel

A dynamic model test(CL = 4) at different velocities of train,namely different loading frequencies,is carried out to study the dynamic characteristics of a high-speed railway tunnel invert and its foundation soils.Not only are the accelerations,dynamic coefficients,dynamic stresses of the invert and foundation soils emphatically analyzed,their relationship with the velocity of the train are discussed in detail.Through laboratory testing,the attenuation of vibration propagating from up the rails is obtained and the calculation formula of the speed influence coefficient of the tunnel invert is preliminarily established.The depth of the foundation soils influenced by vibration is also determined in this study.It is shown that the responses of the tunnel invert and foundation soils to vibration are slightly increased with the velocity of the train;circumferential stresses in the bottom of the invert are tensile stresses and maximum stresses appear under the foot of the rails;the dynamic soil pressures of the foundation decrease quickly with the distance away from the tunnel invert and an exponential relationship exists between them.

Experiment about Drag Reduction of Bionic Non-smooth Surface in Low Speed Wind Tunnel

The body surface of some organisms has non-smooth structure, which is related to drag reduction in moving fluid. To imitate these structures, models with a non-smooth surface were made. In order to find a relationship between drag reduction and the non-smooth surface, an orthogonal design test was employed in a low speed wind tunnel. Six factors likely to influence drag reduction were considered, and each factor tested at three levels. The six factors were the configuration, diameter/bottom width, height/depth, distribution, the arrangement of the rough structures on the experimental model and the wind speed. It was shown that the non-smooth surface causes drag reduction and the distribution of non-smooth structures on the model, and wind speed, are the predominant factors affecting drag reduction. Using analysis of variance, the optimal combination and levels were obtained, which were a wind speed of 44 m/s, distribution of the non-smooth structure on the tail of the experimental model, the configuration of riblets, diameter/bottom width of i mm, height/depth of 0.5 mm, arranged in a rhombic formation. At the optimal combination mentioned above, the 99% confidence interval for drag reduction was 11.13% to 22.30%.

Numerical Study of Laminar-turbulent Transition on a Platein a Low-Speed Tunnel with Contoured Wall

Laminar-turbulent transition flow phenomena on a flat plate in a low-speed wind tunnel at different Reynolds numberswere studied numerically. The now calculation is based on an inviscid/boundary layer interaction method with modifiedAbu-Ghannam/Shaw (AGS ) transihon criterion. The test sechon has non- symmetric al contoured walls, and the plate islocated biased the bottom side with a height ratio of 26: 14. In test case of steady flow, a laminar-turbulent transihontakes place and a small separation bubble occurs on the upper side of the plate, when the inlet Reynolds number is assmall as 0.63lx10-6. The predicted transihon location agrees well with that of the test results, but the separation bubbleis hardly to see from the calculatod velocity profiles though the printed data of velocity in this region do show thenegahve values. The further numerical Predictions with different Reynolds numbers corresponding to the incoming flowvelocities show that when the Reynolds number is greater than 1.379xl0-6, the separahon bubble does not occur, whichis coincident with the experimental results. The influence of the side wall geomeny on the transihon on the plate is alsostudied.

IWHR HIGH SPEED WATER TUNNEL FOR CAVITATION RESEARCH

The paper concerns with the design philosophy,feasibility study,as well as some peculiar features of IWHR water tunnel for cavitation research.The highlights worth-mentioning are the maximum velocity of 35m/s and Reynolds number of 1×10~7 as well as the provision of a specially designed air resorber.