Computational Mechanics Research and Support for Aerodynamics ...

analysis. The basic modifications consist of creating a new rigid wall which was attached with the body
of the truck, changing the forward velocity, and applying damping and pressure load (Figure 3.18).
Damping Estimation:
In order to gain a clear understanding of the behavior of the truck, the truck was made stationary (no
forward velocity). Initially the truck was ideally modeled and to simulate the actual environmental
condition, the truck model was allowed to settle on its suspensions. The displacement graph of the ideal
truck is shown in (Figure 3.19). The graph contains displacement of three nodes from which the third
node shows a clear displacement and it was used for further analysis. The displacement graph gives the
properties of the suspension and the results of applying a global damping value to the system.
The damping estimation for LS-DYNA is calculated as follows:
(3.7)
{3.8)
Where,
T = Time period between two successive crest or troughs of the displacement graph (Figure 3.19).
D = critical damping factor.
The displacement graph gives the value as follows:
T = 0.25 seconds
This reflects,
Various damping values below the critical damping value from 20 to 45 in multiples of 5 were given to
the model. An optimum damping value was chosen in order to stabilize the truck and further application
of wind load was possible without the effect of a global damping factor. Figure 3.20 gives the
displacement obtained from various damping values.
3.2.1.5. Wind Loading
A wind pressure loading was given to the side of the trailer part of the truck. When a pressure was given
with the help of conventional way (load_segment) it was seen that the pressure remains exactly
perpendicular to the surface irrespective of the trailer position. This was contradicting with the actual
situation as the wind loading should be along the ground surface. This actual situation was simulated in
the model by developing a wind load with the help of the load_segment_nonuniform keyword
TRACC/TFHRC Y1Q3 Page 60