Human biodynamic models for rotorcraft comfort assessment

This work shows how different occupant biodynamic modeling techniques are integrated in a rotorcraft design environment and discusses the resulting differences in comfort assessment. Three modeling techniques, that are used for biodynamic characterization, are considered: lumped parameter, finite element and multibody dynamics. These models are identified for the same gender, age, weight and height and then integrated into a virtual helicopter environment with a seat-cushion interface. A generic helicopter model is used to demonstrate the approach. For each of the three techniques, the vertical acceleration levels at the human-helicopter interface, as required by vibration regulations, and at the head are evaluated up to 30 Hz. At a first glance, it is observed that in terms of model set-up the lumped parameter is the easiest to implement. However, the use of lumped parameter models is limited to the population groups that they are identified from, and thus are not as flexible as the finite element and multibody ones in developing biodynamic models for individuals of an arbitrary population percentile. Furthermore, through numerical analysis it is found that the differences are not very significant in terms of accelerations at the interface. Therefore, for comfort related issues, the use of more complex models is not justified, unless complicated comfort assessments other than human interface accelerations are required. On the other hand, the spine dynamic can play a significant role when head acceleration is considered; therefore, when the head-neck health of occupants is considered, the sophisticated finite element and multibody dynamics models redeem their higher modeling cost and computation time.