DAGA 2010 - Deutsche Gesellschaft für Akustik eV

Programm DAGA 2010 63
The effect of simulation parameters on computation time, room acoustic
parameters and the accuracy of echograms will be shown.
Di. 15:20 Beuth-Saal Raumakustik - Simulation und Evaluation I
Room division into convex sub-spaces and its benefits to calculation
time and diffraction simulation with ray tracing
A. Pohl und U.M. Stephenson
HafenCity Universität Hamburg
Ray- or beam tracing is frequently used in geometrical room and city
acoustics, but suffers from the deficiency of lacking diffraction simulation.
A convex sub-division (CSD) by introducing virtual, i.e. acoustic
transparent, walls is advantageous for the automatic detection of diffracting
edges as well as for a reduction of computation time (CT). This
is a part of a project to implement a Quantized Pyramidal Beam Tracing
(QPBT) where Stephenson’s sound particle diffraction module is embedded.
This module is based on the uncertainty principle and requires
the detection of sound particles passing by diffracting edges. As a first
approach, the experiments are restricted to 2D (so edges are actually
vertices). Some CSD methods (also one by Stephenson) already exist
for connected polygons, but in city acoustics the city map is perforated by
obstacles (buildings). A 2D CSD method is presented which works also
on such perforated geometries. With CSD, the CT of ray tracing depends
only on the total length of the inserted walls, but almost not on the number
of vertices. The CSD itself has a CT in the magnitude of ray tracing
with one reflection. An analytical prediction formula of that speed-up is
derived and compared with numerical experiments.
Di. 15:45 Beuth-Saal Raumakustik - Simulation und Evaluation I
Some further experiments with the beam diffraction model based
on the uncer- tainty relation - is it valid also with double diffraction?
U.M. Stephenson
HafenCity Universität Hamburg
In room and especially in city acoustics, the problem of an efficient introduction
of diffraction into ray tracing is still unsolved. The author’s energetic
approach to dif-fraction based on the uncertainty relation (UR) has
been improved in recent years in several steps. It has been extended to
themoreefficient beam tracing technique and tested for many additional
configurations, validated at the single screen and the slit as reference
cases, compared with Svensson’s exact wave-theoretical secondary edge
source model. Last year, some discrepancies occurred, mainly with
the non-fulfilling of the reciprocity principle in some cases. To overcome
this, some improved by-pass-distance- and angle-dependent diffraction
functions have been tested. Fur-ther more, the applicability of the model
to double diffraction has been investigated, a) at a slit, but now with finite
source and receiver distances, b) at two edges in cas-cade, forming a
”thick” obstacle. The aim is to apply the UR based energetic model to