Effect of the static compressive load on vibration propagation in multistory buildings and resulting heavyweight floor impact sounds.

Experiments were performed to identify the mechanism of heavyweight floor impact sound transmission through floors in a high-rise apartment building. Vibration and sound levels on each floor of the multistory building were measured. The vibration generated at a given floor was transferred to multiple adjacent floors with decreasing amplitudes proportional to the distance from the excited floor. This vibration transfer introduced significant sound transmissions. The structural static load varied depending on the floor location due to differences in the weight of the structure above the floor, especially for wall construction buildings. The static load at the wall of the bottom floor was the largest among the different floors. The influence of this static load on the impact sound generation was investigated through tests in the actual building and the scale model, respectively. The results were numerically analyzed using the spectral element method. With the increasing static load, the resonance frequencies of the floor increased due to the change in the vibration modes of the structure. The modulated sound generation from the floor vibrations transmitted to multiple layers with larger magnitudes due to this static load.

Flexural wave cloaking via embedded cylinders with systematically varying thicknesses.

Simulations of flexural wave cloaking from multiple scattering events that are achieved by embedded cylinders in a thin plate are performed. Minimization of refraction is performed using small surrounding cylinders with varying thickness in radial and angular directions, respectively. The thickness variations render the effective wave speed lower in the radial direction and higher in the angular direction compared to the speed in the surrounding media, which results in the cloaking effect. In order to verify the feasibility of this approach, 15 layers of cylinders are placed around the blocked area. The multiple-scattering method is used to predict wave propagations and to take the interactions between cylinders into account. The effects of the thickness variation on the cloaking performance are analyzed. The results demonstrate that minimal scattering is achieved when the area of interest is surrounded by the thickness-varying cylinders.