Sound from rain drops impacting double layer structure consisted of mesh fabric.

Membrane structures and architectures such as umbrella, outdoor tents and ETFE film structures have noise problem caused by rain drops impacting. In an attempt to improve the problem, the double layer structure that is consisted of a mesh fabric as the upper layer and a membrane as the lower layer was suggested. The mesh absorbs the kinetic energy of the rain drops and scatter the rain drops. However, optimum shape of mesh fabric and distance between upper and lower layer are not clear. In order to find out the optimum mesh shape and the distance, in this paper, the sound pressure levels and the frequency characteristics of sound from rain drops impacting the double layer are measured. Four kind of grid-like meshes in different sizes are used for the acoustic experiments. In the experiments, rain drops are made by a pipette and are dropped from a height of 15 meters in a stair hall for reproducing the natural rain drops. In order to consider wet conditions of mesh fabric, two conditions those are wet and dry are adopted as an initial condition of mesh fabric. Thus, we clarified that the optimum distance is several millimeters to 20 millimeters and optimum shape of mesh fabric for double layer structures depended on the wet condition.