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growing
k
D
. The most interesting point is the occurence of minimal evacua-
tion times for non-vanishing small values of the sensitivity parameter
k
D
of the
dynamic field. Therefore a small interaction with the dynamic field, which is pro-
portional to the velocity-density of the particles, is of advantage. It represents
some sort of minimal intelligence of the pedestrians. They are able to detect
regions of higher local flow and minimize their waiting times.
3.3 Friction Effects
In [22]a friction parameter
µ
has been introduced to describe clogging effects
between the pedestrians. Whenever
m>
1 pedestrians attempt to move to
the same target cell, the movement of all involved particles is denied with the
probability
µ
, i.e. all pedestrians remain at their site. This means that with
probability 1
−µ
one of the individuals moves to the desired cell. Which particle
actually moves is then determined by the rules for the resolution of conflicts
described in Sec. 2. If
µ
is high, the pedestrians handicap each other trying to
reach their desired target sites. As we will see, this local effect can have enormous
influence on macroscopic quantities like flow and evacuation time [22]. Note that
the kind of friction introduced here only influences interacting particles, not the
average velocity of a freely moving pedestrian.
Fig. 7(a) shows the influence of the friction parameter on the evacuation
time
T
for the scenario described in Sec. 3.2. As expected,
T
is monotonically
increasing with
µ
. The strongest effect can be observed in the ordered regime,
30000
15000
µ=0.0
µ=0.6
µ=0.9
disordered regime,
µ=0.0
disordered regime,
µ=0.9
ordered regime,
µ=0.0
ordered regime,
µ=0.9
20000
10000
10000
5000
0
0
0.0
0.2
0.4
0.6
0.8
1.0
0
2
4
6
8
10
ρ
ks
Fig. 7.
Dependence of evacuation times on the friction parameter
µ
(a) in the ordered
(
k
S
large,
k
D
small) and disordered regimes (
k
S
small,
k
D
large) and (b) as a function
of
k
S
for
ρ
=0
.
3.
i.e. for strong coupling
k
S
and weak coupling
k
D
. Here the evacuation time is
mainly determined by the clogging at the door. For large values of
µ
it increases
strongly due to the formation of self-supporting arches. This “arching” effect is
well-known from studies of granular materials [23].
