Sound rays emerging from a road in a valley under differnt meteorological conditions. Top: temperature decreasing with height during day. Bottom: Temperature inversion during night. The DLR Institut für Physik der Atmosphäre develops and operates advanced sound propagation models. In combination with meteorological mesoscale and microscale models they describe the system of atmosphere, topography and sound waves in a consistent manner. The comprehensive models are the basis of more simplified noise prediction tools. These tools can be used, for example, to define low-noise approach and departure routes at airports depending on the actual weather type and taking advantage from the natural damping properties of the atmosphere and the ground. Further applications are the planning of low-noise traffic lines as well as other noise reducing measures (e.g. noise barriers).
Two different types of sound particle models are currently in use:
(1) Linearized Euler (LE) Finite-Difference Time-Domain (FDTD) model AKU3D.
This model is based on the prognostic equations for the sound pressure and the sound velocity components. They are numerically solved in two or three dimensions using foreward differences in time and 4th order central differences in space. The model optionally considers meteorological effects (mean flow and temperature, turbulent fluctuations), orographic effects (transformed coordinates), totally or partly reflecting obstacles, and impedance ground. AKU3D is especially suited to simulate the propagation of low-frequency sound.
(2) Langrangian sound particle model AKUMET.
This model is based on sound ray theory. A large number of sound particles is released at the source. The particles travel along curved sound rays and carry sound energy into the model domain. The number of particle passages is counted in grid cells to determine the local sound level. In the case of a coherent source the wave length and phase is additionally evaluated. The model optionally considers meteorological effects (mean flow and temperature, turbulent fluctuations), orographic effects (transformed coordinates), totally or partly reflecting obstacles, and impedance ground. AKUMET is especially suited to simulate the propagation of high-frequency sound.
Contact:
Dr. Dietrich Heimann