No abstract is provided for this article.
Standardised absorption measurements in reverberation rooms suffer from relatively low reproducibility, especially at low frequencies and for highly absorptive samples. In these conditions, complete sound field diffusivity cannot be achieved. However, recent research has demonstrated that the theoretical diffuse absorption emerges as the ensemble average across a wide range of rooms with different geometries, even at very low frequencies. The present study aims to investigate the influence of the room geometry, sound source positioning, and presence of panel diffusers on the sound absorption values obtained in a specific reverberation room, as well as on the difference between those values and the theoretical diffuse values. The focus is on the lowest frequency bands. A numerical simulation approach is proposed, in which the room without sample is modelled in full detail using the finite element method and coupled to the sample with a Rayleigh–Ritz approach. The measurement of diffuse sound absorption is simulated in an efficient way using a stationary power balance approach. This approach is validated against measured data and against a detailed simulation of the impulse response. From the parametric study conducted with the model, it can be concluded that, for highly absorptive samples, good agreement with the theoretical diffuse absorption values can be obtained for certain room designs. In these rooms, the measured absorption is also less sensitive to the number and positioning of sources and diffusing elements.
No abstract is provided for this article.
In order to estimate the wind loads on circular cylindrical shell structures, the pressure coefficient as a function of the Reynolds number is given for an isolated cylinder in Eurocode 1 - Part 2-4: Actions on structures - Wind actions. As cylinders are often placed in groups and the configuration of these groups largely influences the pressure distribution around the cylinders, a computation of the wind flow provides a more realistic estimation of the pressure coefficients. First, the transient 2D turbulent air flow around a single cylinder at a Reynolds number of 12.4 millions is computed using the SST turbulence model and the results are compared with the pressure coefficients in Eurocode 1 and with experimental data. The minimum pressure coefficient is underestimated, while the base pressure coefficient is slightly overestimated. Unsteady simulations are performed for the flow around a group of 2 by 2 and of 8 by 5 cylinders. Vortex shedding occurs both from the group as a whole, and from individual cylinders. The group configuration drastically changes the time-averaged pressure distribution around the cylinders. High values of suction are present at the location of the small gaps between the cylinders and upstream of the separation points of the cylinders on the side corners of the groups. The cylinders at the borders of the groups experience high drag or lift forces, while these forces are considerably lower in the middle of the group.
No abstract is provided for this article.
No abstract is provided for this article.
In this paper, a spatial dynamic analysis model for the train–bridge system under random excitations was established. The random excitations were analyzed and generated by the time series autoregressive model from the experimentally measured wheel accelerations. The whole histories of the train running on the bridges were simulated on computer. The responses of bridges were calculated and statistically studied. Based on the calculation results, the reinforcement schemes for steel girders were designed and some of them were applied to real bridges. The field-tests were carried out before and after the bridge reinforcement. The measured data from the tests proved the effectiveness of the reinforcement schemes.
No abstract is provided for this article.
No abstract is provided for this article.
In a finite element formulation for dynamic soil-structure interaction, an absorbing boundary condition is needed to model wave propagation towards infinity. When the soil is saturated, its dynamic behaviour can be modelled by means of Biot's poroelastic theory. In Part I (Degrande, G. & De Roeck, G., Soil Dynamics & Earthquake Eng., 1993, 12(7), 411-21), a local absorbing boundary condition for wave propagation in saturated poroelastic media has been developed. In the present paper, this boundary condition is implemented in an irreducible finite element formulation for a compressible pore fluid. Spurious reflections for oblique incident waves on the absorbing boundary contribute to the solution errors. Therefore, a spectral element method, based on classical analytical solution techniques, is used to assess the accuracy of the finite element formulation.
The paper aims at exploring damage assessment in masonry structures at an early stage by vibration measurements. One arch replicate of historical constructions was built as reference, undamaged, state. Afterwards, progressive damage was induced and sequential modal identification analysis was performed at each damage stage, aiming to find adequate correspondence between dynamic behaviour and internal crack growth.
