An uncertainty estimation for a higher order multi-port characterization in ducts with flow
Regular paper
KTH
Wednesday 3 june, 2015, 09:00 - 09:20
0.3 Copenhagen (49)
Abstract:
The generation and scattering behaviour of fluid machines in connected duct
or pipe systems is of great interest to minimize disturbing and harmful sound
emission, for instance of air condition systems. Such systems may be described
as networks of passive elements, which only scatter existing sound fields and
active elements, which emit noise themselves. Within the framework of the
European project “IdealVent“ the acoustic behaviour of air conditioner systems
in aircraft are investigated in detail in order to develop strategies to abate
sound emission and hence augmenting safety and comfort within the air-plane
and at the aircraft ramp. In air conditioner systems, noise is mainly emitted
by a fan combined with downstream obstacles in the form of orifices and
valves. One approach to handle such systems is to apply a linear multi-port
model that includes direction-depending transmission and reflection
coefficients for the propagating wave modes and the sound generation amplitude
per mode. Those parameters may be ascertained in two steps and either
numerically or experimentally. Once this characteristic data are determined
for all elements of interest, the sound scattering and emission behaviour of
every considerable combination of those elements can be calculated easily. In
a first step, a number of external sound fields dominating the existing sound
filed are applied, in order to terminate the system scattering. As the second
step, the reflection-free source strength can be computed. Both operations
consist of matrix inversions and wave-number assumptions, which amplify
uncertainties induced by the measurement procedure. The paper in hand shows a
method to estimate the uncertainties of a full characterization of a multi-
port of the order 6 by applying a condition number approach and a Monte-Carlo
simulation.