Pressure transients generated when high-speed trains pass in a tunnel

An analysis is made of the pressure transients generated when two high-speed trains meet in a tunnel. Safe operation at speeds exceeding about 300 km/h usually demands that the hydraulicblockage produced by a train should be small. The problem canthen be formulated in terms of the scattering of the potentialflow near field of each train by the moving surface of theother train, and this permits the derivation of closed formrepresentations of the unsteady pressure in the special caseof ‘snub nosed’ trains in a tunnel of semicircularcross-section. This solution is used to devise a general procedurefor calculating pressure transients generated by trains ofarbitrary nose profiles in tunnels of arbitrary cross-sectionalshape in terms of a knowledge of the local incompressible potentialflow produced by each train travelling separately in the tunnel.Numerical results indicate that at train Mach numbers exceeding0.25the amplitudes of the pressure transients generated bymeeting trains will typically exceed about 25 per cent of theamplitude of the compression wave produced when a train entersor leaves the tunnel. Received 12 April, 1999. Revised 13 March, 2000.     

Einen elektrischen Widerstands-Tiegel-Ofen aus Magnesia

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Pressure and temperature dependence of the reaction of vinyl radical with ethylene

This work reports measurements of absolute rate coefficients and Rice-Ramsperger-Kassel-Marcus (RRKM) master equation simulations of the C2H3+C2H4 reaction. Direct kinetic studies were performed over a temperature range of 300-700 K and pressures of 20 and 133 mbar. Vinyl radicals (H2C=CH) were generated by laser photolysis of vinyl iodide (C2H3I) at 266 nm, and time-resolved absorption spectroscopy was used to probe vinyl radicals through absorption at 423.2 nm. Measurements at 20 mbar are in good agreement with previous determinations at higher temperature. A weighted three-parameter Arrhenius fit to the experimental rate constant at 133 mbar, with the temperature exponent fixed, gives k=(7+/-1)x10(-14) cm3 molecule(-1) s(-1) (T/298 K)2 exp[-(1430+/-70) K/T]. RRKM master equation simulations, based on G3 calculations of stationary points on the C4H7 potential energy surface, were carried out to predict rate coefficients and product branching fractions. The predicted branching to 1-methylallyl product is relatively small under the conditions of the present experiments but increases as the pressure is lowered. Analysis of end products of 248 nm photolysis of vinyl iodide/ethylene mixtures at total pressures between 27 and 933 mbar provides no direct evidence for participation of 1-methylallyl.     

The genetically optimized tunnel-entrance hood

A numerical procedure is investigated for optimizing the design of tunnel-entrance hoods used for controlling the compression wave generated when a high-speed train enters a tunnel. Long hoods are required for long tunnels and train speeds exceeding about 350 km/h. The hood must minimize the maximum pressure gradient across the compression wave-front by taking advantage of the pressure-release provided by open windows distributed along one or both of its walls. The compression wave produced by the train can be evaluated by means of a rapid computational scheme devised and validated against experiment. Optimization is achieved by representing a possible distribution of windows by a binary string. The individuals in an initial, random population of such strings are allowed to ‘mate’ and evolve by ‘natural selection’ through several generations towards an optimal configuration by application of a genetic algorithm. The genetically fittest hood is associated with the minimum possible maximum pressure gradient for prescribed values of the train speed and hood dimensions. The algorithm yields an optimal design from among a theoretically unlimited number of possibilities; it can also supply near-optimal, smoothly varying window distributions (or optimize the variation in width of a long slit-like window in the hood wall) satisfying additional constraints imposed by the designer.     

Use of plasmon spectroscopy to evaluate the mechanical properties of materials at the nanoscale.

Relationships between volume plasmon excitations and mechanical properties of various materials are considered. Based on systematic evaluation of available data, correlations between the volume plasmon energy, Ep, Young's modulus, Ym, bulk modulus, Bm, shear modulus, Gm, and microhardness, Hm, are established. The resulting correlations indicate that plasmon energies potentially can be used to predict and/or determine the local mechanical properties of technologically important materials, such as metal alloys, semiconductors, and ceramics at the nanometer level.     

On the unsteady wake-induced lift on a slotted airfoil,part II: The influence of displacement thickness fluctuations

In the preceding companion paper [1] a theoretical model for determining the influence of a slot in a thin airfoil on the unsteady lift/radiated sound caused by vortices shed into the wake was presented. The unsteady motion produces additional vorticity at the upstream edge of the slot, and it was shown that, at sufficiently low reduced frequencies based on the width of the slot, this vorticity can prevent penetration by the flow, so that the airfoil behaves as if the slot were absent. At higher frequencies, however, both the lift and the sound power were predicted to be significantly reduced relative to their respective levels for the unslotted airfoil. The analysis is extended in this paper to include the effects of displacement thickness fluctuations of the boundary layers on the “flap” downstream of the slot. These fluctuations arise as a result of the periodic ejection of vorticity from the slot. It is concluded that the earlier predictions of a reduction in the lift/sound pressure level are enhanced by the displacement thickness effects.