The purpose of this research was to investigate and improve the accuracy of the existing slab-track mat (STM) specifications in the evaluation of the vibration reduction effect. The static nonlinearity and dynamic mechanical characteristics of three types of STMs were tested, and then a modified fractional derivative Poynting–Thomson (FDPT) model was used to characterize the preload and frequency dependence. A modified vehicle–floating slab track (FST) coupled dynamic model was established to analyze the actual insertion loss. The insertion loss error evaluated by the frequency-dependent tangent stiffness increased with the increase in STM nonlinearity, and the error obtained by the third preload tangent stiffness was usually greater than that of the second preload. Compared with the secant stiffness, the second preload frequency-dependent tangent stiffness was more suitable for evaluating STMs with high-static–low-dynamics (HSLD) stiffness. In order to reflect the frequency dependence effect and facilitate engineering applications, it is recommended that second preload tangent stiffness corresponding to the natural frequency of the FST be used for evaluation. Furthermore, the insertion loss of the STMs with monotonically increased stiffness decreased as the axle load increased, and the opposite was true for the STMs with monotonically decreased stiffness. The vibration isolation efficiency of the STMs with HSLD stiffness was both stable and better than that of the STMs with monotonic stiffness.
A novel simplified numerical simulation method for bleed holes in supersonic inlets was developed to estimate the bleed mass flow rate and simulate the flowfield structure in the bleed region. First, the Prandtl–Meyer expansion theory was employed to calculate the location of the barrier shock and reconstruct the flow structure inside the bleed hole. Next, a novel discrimination algorithm was developed to distinguish the grids connected to the bleed hole in the bleed zone instead of directly modeling the hole opening and plenum chamber. Finally, the bleed mass flow rate was obtained based on the boundary-layer properties in the bleed region and the fitting scaled coefficients. This method was also evaluated by performing numerical simulations for a series of different bleeding situations. For all the examined cases, the simulation results were in good agreement with the experimental data, and the number of grid points’ requirement for modeling the bleed hole as compared with the fully resolved method was considerably reduced. Moreover, the proposed method was successfully applied to simulate porous bleed systems in a mixed-compression supersonic inlet. This illustrates that the proposed method is expected to be a useful engineering tool for designing the bleed system of the supersonic inlets.
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