An improved time integration scheme is proposed for linear and nonlinear dynamics. The proposed scheme has two free parameters which control numerical dissipation and accuracy effectively. Basic properties including spectral stability, algorithmic accuracy, algorithmic damping, period elongation and overshooting behavior are investigated. The influences of algorithmic parameters on these properties are quantified. The effectiveness of the proposed scheme for linear and nonlinear dynamics is evaluated through some numerical examples. Analytical and numerical results demonstrate that the proposed scheme has the following significant characteristics: (1) desirable accuracy can be obtained for various linear and nonlinear problems, when compared with other effective schemes; (2) for nonlinear problems, new scheme also shows good performance; (3) the proposed scheme has simple formulation and good compatibility for various dynamic problems, and thus, is a promising candidate for practical analysis.
The slipstream caused by high-speed trains may harm pedestrians and workers trackside. In general, the characteristics of the slipstream are influenced mainly by the nose shape of the train. The present study explores the slipstream caused by high-speed trains with three different horizontal nose profiles based on the results of three-dimensional, improved delayed detached eddy simulation (IDDES) with an unsteady turbulence model and a set of 1/8th scaled train models. The results obtained using this numerical methodology are in good agreement with those obtained from corresponding wind tunnel tests. The trackside pressure changes around the train models are also captured and analyzed. The analysis reveals that the width of the nose can significantly influence the magnitude and arrival time of slipstream velocity and pressure peaks. The results and proposed numerical methodology can be used as guidelines for the design of high-speed train nose shapes.
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