Workpackage “Noise Modelling” Sound Propagation - new propagation models Dietrich Heimann (translated and presented by U. Isermann) DLR - Institute of Atmospheric Physics (IPA) Oberpfaffenhofen

Workpackage “Noise Modelling” emission perception transmission immission

Workpackage “Noise Modelling / Propagation” 1. Propagation effects 2. Propagation models 3. The IPA approach

Propagation effects inhomogenous, turbulent atmosphere absorption reflection refraction scattering diffraction topography, buildings, obstacles

  Propagation effects altitude lateral distance from baseline shadow for a temperature decrease temperature increase with altitude with altitude or for  wind  upward refraction downward refraction   shadow single reflection multiple reflection lateral distance from baseline

Propagation effects shadow zone due to refraction source contibutions from direct and reflected sound contributions from diffraction scatterering shadow zone due to refraction shadow zone due to topography source contributions from direct and reflected sound contributions from diffraction scattering

Magnitude of propagation effects: Spherical wave attenuation:  Lmax - 6 dB per doubling of distance Additional effects: Atmospheric absorption:  - 1 dB je 100 m (1000 Hz)  - 5 dB je 100 m (4000 Hz) Ground effects:  - 10 dB for grazing incidence Refraction:  - 25 dB for upward refraction  + 6 dB for downward refraction Scattering, diffraction  -25 dB attenuation limit in shadow zones

Workpackage “Noise Modelling / Propagation” 1. Propagation effects 2. Propagation models 3. The IPA approach

Sound propagation models 1. Standard models (z.B. ISO 9613, AIR 1845, Doc.29) Geometric term + different correction factors Atmospheric effects not accounted for (or only by simplifying approaches) 2. Numerical models (e.g. Euler model) The more effects, the more accurate the model- but with increasing modelling and calculation efforts!

Sound propagation models Euler model: Example: barrier of trees  wind field  sound propagation

Sound propagation models Euler model: Airport environment as a field of application ?

Sound propagation models Euler model: Applied for direct airport environment (1051) km3 and a frequency of 1000 Hz: Mesh-width of calculation grid: 3,4 cm Number of meshs: 1,2  1015 Numerical time step needed: 100 s Number of time steps: 300,000 Calculation time (NEC SX4) per mesh and step: 1 s

Sound propagation models Euler model: Applied for direct airport environment (1051) km3 and a frequency of 1000 Hz: Mesh-width of calculation grid: 3,4 cm Number of meshs: 1,2  1015 = 144 PByte Numerical time step needed: 100 s Number of time steps: 300,000 Calculation time (NEC SX4) per mesh and step: 1 s Total calculation time: 360 Ts = 11 million years

Sound propagation models Calculation time: 2030: 24 h ????? 2036: 15 min ???? Present: Process studies Future: Standard procedure ?

Workpackage “Noise Modelling / Propagation” 1. Propagation effects 2. Propagation models 3. The IPA approach

The IPA approach Goal: Numerical models ... ... develop them ... use them as a reference Derive simplified models to - increase the accuracy of standard procedures - but maintain their practicability and usability

The Lagrange model (sound particles) The IPA approach The Lagrange model (sound particles) 100 - 4000 Hz up to 5000 m propagation distance source altitude: 1600 m wind at 1600 m: 10 m/s ground wind wind at 1600 m

The IPA approach Realisation: Advantage: Use the principle of the standard approach: Calculate the excess attenuation LMB due to meteorological and ground effects using the Lagrange model. Store the values of LMB for a set of different propagation situations in attenuation lookup tables. Advantage: Only moderate increases in computation time are needed. This approach can also be used for standard models.

Independent parameters: The IPA approach Independent parameters: 7 classes of source altitude 8 classes of ground receiver distance 6 classes of wind speed (10 m above ground) 12 classes of angle between wind direction and direction of propagation 3 atmospheric stability classes 8 frequency classes (octave bands)  64,512 possible combinations ….

The IPA approach Example 1: source: 1600 m, wind: 10 m/s, atmosphere: neutral quieter -18 dB 0 dB +9 dB louder

The IPA approach Example 2: source: 50 m, no wind, atmosphere: unstable quieter -18 dB 0 dB +9 dB louder

The IPA approach Example 3: source: 100 m, wind: 2 m/s, inversion quieter -18 dB 0 dB +9 dB louder

Workpackage “Noise Modelling / Propagation” Summary:  Progress in the development of complex sound propagation models  Derivation of a simplified model  Definition of pre-calculated tables for meteorology- and ground-excess attenuation which can also be used for standard models

Workpackage “Noise Modelling / Propagation” Validation ... ... based on 1 year noise monitoring at Munich airport (2003)  6 aircraft types, 180 000 monitored noise values (FMG)  radar information on aircraft position (DFS)  meteorological information (DWD, Uni München, FMG) noise meteo