The increased use of computational human models in evaluation of safety systems
demands greater attention to selected methods in coupling the model to its
seated environment. This study assessed the THUMS v4.0.1 in an upright driver
posture and a reclined occupant posture. Each posture was gravity settled into
an NCAC vehicle model to assess model quality and HBM to seat coupling.
HBM to seat contact friction and seat stiffness were varied across a range of
potential inputs to evaluate over a range of potential inputs. Gravity settling
was also performed with and without constraints on the pelvis to move towards
the target H-Point. These combinations resulted in 18 simulations per posture,
run for 800 ms. In addition, 5 crash pulse simulations (51.5 km/h delta V) were
run to assess the effect of settling time on driver kinematics. HBM mesh quality
and HBM to seat coupling metrics were compared at kinetically identical time
points during the simulation to an end state where kinetic energy was near
zero.
A gravity settling time of 350 ms was found to be optimal for the upright driver
posture and 290 ms for the reclined occupant posture. This suggests that
reclined passengers can be settled for less time than upright passengers,
potentially due to the increased contact area. The pelvis constrained approach
was recommended for the upright driver posture and was not recommended for the
reclined occupant posture. The recommended times were sufficient to gravity
settle both postures to match the quality metrics of the 800 ms gravity settled
time. Driver kinematics were found to be vary with gravity settling time. Future
work will include verifying that these recommendations hold for different HBMs
and test modes.
